Tread rubber and tire

Abstract

To provide a tread rubber that can contribute to improved sustainability.SOLUTION: The present invention provides a tread rubber comprising a rubber composition that contains a rubber component (A) and carbon black (B), wherein the carbon black (B) includes recycled carbon black and has a plurality of voids formed.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a tread rubber and a tire. [Background technology]

[0002] 2. Description of the Related Art As a technique for improving the performance of tires on ice, various studies have been conducted on materials (tread rubber) used in producing tire treads (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2017 / 069273 Summary of the Invention [Problem to be solved by the invention]

[0004] Recently, from the perspective of social sustainability, there has been a demand for businesses and products to use so-called sustainable materials, such as materials derived from biological resources (biomass resources) and materials derived from recycled resources, and there is also a demand to increase the usage rate of sustainable materials (hereinafter sometimes referred to as the "sustainability rate") for various components used in tires.

[0005] However, no attention or consideration has been given to the contribution of the above-mentioned tread rubber to sustainability.

[0006] Therefore, an object of the present invention is to provide a tread rubber that can contribute to improving sustainability. Another object of the present invention is to provide a tire that uses such tread rubber and can contribute to improving sustainability. [Means for solving the problem]

[0007] That is, the essential configurations of the tread rubber and tire of the present invention that solve the above problems are as follows.

[0008] [1] A tread rubber using a rubber composition containing a rubber component (A) and carbon black (B), The carbon black (B) comprises recycled carbon black, A tread rubber having a plurality of voids formed therein. Such a tread rubber of the present invention can contribute to improving sustainability.

[0009] [2] The tread rubber according to [1], wherein the rubber composition further contains a void-introducing agent (C). In this case, a plurality of voids can be formed on the surface and / or inside of the tread rubber.

[0010] [3] The tread rubber according to [2], wherein the void-introducing agent (C) is a foaming agent. In this case, the performance on ice can be effectively improved.

[0011] [4] The tread rubber according to [3], wherein the foaming agent is sodium bicarbonate. In this case, in addition to improving the performance on ice, manufacturing processability can be improved.

[0012] [5] The tread rubber according to any one of [1] to [4], wherein the recycled carbon black is obtained by thermal decomposition of a vulcanized rubber product containing carbon black. In this case, used rubber products can be effectively utilized, which can further contribute to reducing the environmental load.

[0013] [6] The tread rubber according to any one of [1] to [5], wherein the recycled carbon black has an ash content of 20 mass% or less. In this case, various physical properties of a rubber product to which the tread rubber is applied can be improved.

[0014] [7] The tread rubber according to any one of [1] to [6], wherein the proportion of the recycled carbon black in the carbon black (B) is 50 mass % or more. In this case, it can further contribute to improving sustainability.

[0015] [8] A tire, characterized in that the tread rubber according to any one of [1] to [7] is used in a tread portion. Such a tire of the present invention can contribute to improving sustainability. Effect of the Invention

[0016] According to the present invention, it is possible to provide a tread rubber that can contribute to improving sustainability. Furthermore, according to the present invention, it is possible to provide a tire that uses such a tread rubber and that can contribute to improving sustainability. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The tread rubber and tire of the present invention will be illustrated in detail below based on embodiments thereof.

[0018] <Definition> The compounds described herein may be derived in whole or in part from fossil sources, from biological sources such as plant sources, from recycled sources such as used tires, or from a mixture of two or more of fossil sources, biological sources, and / or renewable sources.

[0019] In this specification, the "sustainability rate" refers to the total mass ratio of components derived from biological resources (biomass resources) and components derived from renewable resources (recycled resources) in a target material.

[0020] In this specification, the biological resources (biomass resources) refer to carbon-neutral organic resources derived from living organisms, and include, for example, those stored in the form of starch or cellulose, the bodies of animals that grow by eating plants, and products obtained by processing plants or animals, and are resources other than fossil resources (petroleum, coal, natural gas, etc.). The biological resources may be edible or non-edible, but are preferably non-edible from the viewpoint of not competing with food and of effective resource utilization.

[0021] Specific examples of the biological resources include cellulosic crops (pulp, kenaf, wheat straw, rice straw, waste paper, papermaking residues, etc.), wood, charcoal, compost, food waste, vegetable oil residues, fishery residues, livestock waste, food waste, wastewater sludge, natural rubber, cotton, oils and fats (palm oil, castor oil, cottonseed oil, soybean oil, linseed oil, rapeseed oil, coconut oil, peanut oil, tall oil, corn oil, rice oil, safflower oil, sesame oil, olive ... Examples of the biological resources include crops (corn, wheat, rice, rice husks, rice bran, old rice, potatoes, buckwheat, cassava, sago palm, sugarcane, etc.), bagasse (i.e., the residue after squeezing juice from sugarcane), soybeans, soybean pulp, essential oils (pine oil, orange oil, eucalyptus oil, etc.), pulp black liquor, algae, etc. The biological resources may be processed (i.e., biological resource-derived substances). Examples of the processing methods include biological processing methods that utilize the functions of microorganisms, plants, animals, and tissue cultures thereof; chemical processing methods that utilize acids, alkalis, catalysts, thermal energy, light energy, etc.; physical processing methods such as micronization, compression, microwave processing, and electromagnetic wave processing; and the like. The biological resources may also be extracted and refined from the biological resources or biological resources that have been processed (i.e., biological resource-derived substances). For example, sugars, proteins, amino acids, fatty acids, fatty acid esters, etc., purified from the biological resources can be used. Examples of the sugars include sucrose, glucose, trehalose, fructose, lactose, galactose, xylose, allose, talose, gulose, altrose, mannose, idose, arabinose, apiose, maltose, cellulose, starch, chitin, etc., derived from biological resources. Examples of the proteins include compounds derived from biological resources and formed by linking amino acids (preferably L-amino acids), including oligopeptides such as dipeptides. Examples of the amino acids include valine, leucine, isoleucine, arginine, lysine, asparagine, glutamine, phenylalanine, etc., derived from biological resources, and among these, valine, leucine, isoleucine, arginine, and phenylalanine are preferred.The amino acid may be either an L-amino acid or a D-amino acid, but L-amino acids are preferred from the viewpoints of abundance in nature and ease of availability. The fatty acids include butyric acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, etc., which are derived from biological resources. The fatty acid esters include modified products of vegetable oils, animal oils, and fats and oils derived from biological resources. These biological resources may be contaminated with various materials and impurities.

[0022] In this specification, the term "recycled resources" refers to resources obtained by regenerating (recycling) products that have been used once, or that have been collected without being used, or that have been discarded. For example, recycled resources include resources obtained by regenerating (recycling) used rubber products such as used tires.

[0023] <Tread rubber> The tread rubber of one embodiment of the present invention (hereinafter, sometimes referred to as "the tread rubber of this embodiment") is a tread rubber using a rubber composition containing a rubber component (A) and carbon black (B) (hereinafter, sometimes referred to as "the rubber composition of this embodiment"). In other words, the tread rubber of this embodiment contains the rubber component (A) and the carbon black (B). Furthermore, a plurality of voids are formed in the tread rubber of this embodiment. In other words, the tread rubber of this embodiment has a plurality of voids. Furthermore, the tread rubber of this embodiment is characterized in that the carbon black (B) contains recycled carbon black. In this way, by using carbon black (B) containing at least recycled carbon black, the tread rubber can contribute to improving sustainability.

[0024] The tread rubber of this embodiment has a plurality of voids, and therefore, when applied to a tire, the performance on ice can be improved. In this specification, the voids in the tread rubber refer to holes having an average diameter of about 1 to 500 μm formed in the tread rubber. In the case where the voids are not spherical, the diameter of the voids refers to the maximum distance between any two points on the inner wall of the voids. The average diameter of the voids can be obtained by observing the cross section of the tread rubber with a digital microscope ("VHX-100" manufactured by Keyence Corporation) and averaging the diameters of all the voids present in one field of view (2.5 mm x 2.5 mm). In the tread rubber of this embodiment, the shape and size of the voids do not change significantly within one tread rubber, so the average value of the diameters of the voids in one field of view can be used as the average diameter of the voids.

[0025] The void ratio in the tread rubber of this embodiment is preferably 5 to 45%. If the void ratio is 5% or more, the performance on ice can be improved more reliably. From the same viewpoint, the void ratio is preferably 7% or more, and more preferably 15% or more. On the other hand, if the void ratio is 45% or less, even if there are multiple voids, the decrease in abrasion resistance can be suppressed. From the same viewpoint, the void ratio is preferably 40% or less, and more preferably 37% or less. In this specification, the void ratio refers to the ratio (volume %) of the volume of voids in the tread rubber. The method for measuring the void ratio is not particularly limited, and the void ratio can be measured, for example, using a specific gravity meter (ViBRA specific gravity meter "DMA-220" manufactured by Shinko Denshi Co., Ltd.).

[0026] Hereinafter, each component constituting the tread rubber of this embodiment (and further, the rubber composition of this embodiment) will be described.

[0027] (Rubber component (A)) The rubber composition of the present embodiment contains a rubber component (A), which provides rubber elasticity to the composition. The rubber component (A) has a sustainability rate of 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.

[0028] The rubber component (A) is preferably a rubber derived from biological resources or a rubber derived from recycled resources. Here, the proportion of the monomer components derived from biological resources in 100 mol% of the monomer components constituting the rubber derived from biological resources is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, still more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may be 100 mol%. The proportion of monomer components derived from recycled resources in 100 mol% of monomer components constituting the rubber derived from recycled resources is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, still more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may be 100 mol%.

[0029] The rubber component (A) is a component that contributes to crosslinking, and usually has a weight average molecular weight (Mw) of 10,000 or more, preferably 50,000 or more, more preferably 150,000 or more, and even more preferably 200,000 or more, and preferably 5,000,000 or less, more preferably 2,000,000 or less, more preferably 1,500,000 or less, and even more preferably 1,300,000 or less. In this specification, the weight average molecular weight (Mw) of the rubber component (A) can be determined, for example, by converting the weight average molecular weight (Mw) into standard polystyrene based on a measurement value obtained by gel permeation chromatography (GPC) (GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M manufactured by Tosoh Corporation).

[0030] The rubber component (A) is preferably a diene rubber, and the diene rubber is preferably an isoprene rubber or a butadiene rubber, where the isoprene rubber refers to a rubber containing a unit derived from isoprene as a monomer unit, and the butadiene rubber refers to a rubber containing a unit derived from butadiene as a monomer unit.

[0031] Examples of the isoprene-based rubber include natural rubber (NR), synthetic isoprene rubber (IR), modified natural rubber (modified NR), modified natural rubber (modified NR), and modified synthetic isoprene rubber (modified IR). Examples of the natural rubber (NR) that can be used include those commonly used in the tire industry, such as RSS#3 and TSR20 (e.g., SIR20 and STR20). The origin of the natural rubber (NR) is not particularly limited, and examples of the natural rubber include those derived from Hevea brasiliensis, guayule, and Russian dandelion. Examples of the synthetic isoprene rubber (IR) are not particularly limited, and examples of the synthetic isoprene rubber that can be used include those commonly used in the tire industry, such as IR2200. Examples of the modified NR include deproteinized natural rubber (DPNR) and highly purified natural rubber (UPNR). Examples of the modified NR include epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber. The modified IR includes epoxidized synthetic isoprene rubber, hydrogenated synthetic isoprene rubber, grafted synthetic isoprene rubber, etc. These isoprene-based rubbers may be used alone or in combination of two or more. Among these, NR is preferred as the isoprene-based rubber.

[0032] The isoprene-based rubber preferably has a sustainability rate of 30% by mass or more, more preferably 40% by mass or more, more preferably 50% by mass or more, still more preferably 60% by mass or more, still more preferably 70% by mass or more, even more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 100% by mass. In order to set the sustainability rate of the isoprene-based rubber within the above range, it is preferable to use natural rubber (NR) or a polymer synthesized using isoprene derived from biological resources or isoprene derived from renewable resources as a monomer component. In this case, the synthesized polymer may be a homopolymer of a monomer derived from biological resources, a homopolymer of a monomer derived from renewable resources, a copolymer of a monomer derived from biological resources and a monomer derived from renewable resources, or a copolymer of a monomer derived from biological resources and / or a monomer derived from renewable resources and a monomer derived from a fossil resource (petroleum, etc.).

[0033] Examples of the butadiene rubber include butadiene rubber (BR), aromatic vinyl compound-butadiene copolymer rubber (for example, styrene-butadiene rubber (SBR)), etc. Here, butadiene, which is a raw material for butadiene rubber, is preferably derived from biological resources or recycled resources.

[0034] Examples of the butadiene rubber (BR) include high cis content butadiene rubber, low cis content butadiene rubber, and butadiene rubber containing syndiotactic polybutadiene crystals. Commercially available products can be used as the butadiene rubber (BR), and examples of commercially available butadiene rubbers include products from UBE Elastomers Co., Ltd., ENEOS Materials Corporation, Asahi Kasei Co., Ltd., and Zeon Corporation. These butadiene rubbers may be used alone or in combination of two or more.

[0035] Examples of the aromatic vinyl compound-butadiene copolymer rubber (e.g., SBR) include emulsion-polymerized aromatic vinyl compound-butadiene copolymer rubber (e.g., emulsion-polymerized styrene-butadiene rubber (E-SBR)), solution-polymerized aromatic vinyl compound-butadiene copolymer rubber (e.g., solution-polymerized styrene-butadiene rubber (S-SBR)), and the like. In the aromatic vinyl compound-butadiene copolymer rubber, examples of the aromatic vinyl compound (aromatic vinyl monomer) include styrene, vinylnaphthalene, divinylnaphthalene, and the like. These aromatic vinyl compounds may be used alone or in combination of two or more. Among these, styrene is preferred, and styrene derived from biological resources and styrene derived from recycled resources are particularly preferred. That is, the aromatic vinyl compound-butadiene copolymer rubber is preferably SBR. The styrene may have a substituent. As the aromatic vinyl compound-butadiene copolymer rubber, commercially available products can be used, and examples of the commercially available products include products from Asahi Kasei Corporation, ENEOS Materials Corporation, Nippon Zeon Corporation, Sumitomo Chemical Co., Ltd., and the like. These aromatic vinyl compound-butadiene copolymer rubbers may be used alone or in combination of two or more.

[0036] The butadiene-based rubber has a sustainability rate of preferably 30% by mass or more, more preferably 40% by mass or more, more preferably 50% by mass or more, still more preferably 60% by mass or more, still more preferably 70% by mass or more, even more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 100% by mass. In order to make the sustainability rate of the butadiene-based rubber fall within the above range, for example, a polymer synthesized using butadiene derived from biological resources, butadiene derived from renewable resources, aromatic vinyl compounds derived from biological resources (e.g., styrene derived from biological resources), and aromatic vinyl compounds derived from renewable resources (e.g., styrene derived from renewable resources) as monomer components may be used. In this case, the synthesized polymer may be a homopolymer of a monomer derived from biological resources, a homopolymer of a monomer derived from renewable resources, a copolymer of a monomer derived from biological resources and a monomer derived from renewable resources, or a copolymer of a monomer derived from biological resources and / or a monomer derived from renewable resources and a monomer derived from a fossil resource (petroleum, etc.). In addition, the butadiene rubber (B-BR) derived from biological resources (biomass resources) and aromatic vinyl compound-butadiene copolymer rubber derived from biological resources (e.g., styrene-butadiene rubber (B-SBR) derived from biological resources (biomass resources)) include not only rubber obtained by polymerizing butadiene, etc. according to a conventional method, but also rubber obtained by reactions or enzyme reactions caused by microorganisms, plants, animals, and tissue cultures thereof (hereinafter also referred to as "microorganisms, etc.").

[0037] In order to set the sustainability rate of the entire rubber component (A) within the above range, it is preferable to use natural rubber (NR) as the rubber component (A) or a polymer synthesized using monomer components derived from biological resources or monomer components derived from recycled resources as monomer components.

[0038] Generally, materials for rubber compositions for tires (rubber and its monomers, fillers, resins, etc.) require large-scale manufacturing equipment for their production, and are therefore usually produced in large factories in specific regions, and a lot of energy is required for the storage and transportation of raw materials and products. In contrast, materials derived from biological resources (biomass resources) are derived from agricultural products, forests, etc. in each region, and can be produced on a small scale by fermentation of microorganisms and catalytic reactions, so by utilizing products and waste from each region, the energy required for the transportation and storage of raw materials can be reduced, and further the energy required for the transportation and storage of the produced materials to tire factories can also be reduced, which is environmentally friendly. In addition, materials derived from regenerated resources (recycled resources) can be obtained, for example, by dismantling and pyrolyzing used tires to extract materials that constitute tires, such as rubber, fillers, and steel cords. In addition, sulfur can be obtained from biological resources or processed products of biological resources by a method including a desulfurization step of desulfurizing biological resources or processed products of biological resources to remove sulfur-containing substances from the biological resources or processed products of biological resources, a recovery step of recovering sulfur from the desulfurization residue generated in the desulfurization step, and a processing step of processing the recovered sulfur into sulfur for vulcanization (for example, the method described in Japanese Patent Application No. 2022-140390), and materials for rubber compositions for tires can be obtained from various wastes and used items. In this way, by using sustainable materials (materials derived from biological resources or materials derived from recycled resources), it is possible to reduce the overall environmental load in tire manufacturing, such as reducing carbon dioxide emissions (LCCO2) over the entire life cycle, reducing energy consumption (LCE) over the entire life cycle, reducing costs (LCC) incurred over the entire life cycle, and reducing the amount of fossil resources used.

[0039] In addition, when producing the rubber composition, the ratio of the monomer components derived from biological resources, the monomer components derived from renewable resources, and the monomer components derived from fossil resources can be appropriately selected according to the supply situation of biological resources, recycled resources, and fossil resources (e.g., monomer components derived from fossil resources) and / or market demand (e.g., demand for biological resources as food), and the monomer components derived from biological resources, the monomer components derived from renewable resources, and the monomer components derived from fossil resources can be polymerized to obtain rubber derived from sustainable materials (materials derived from biological resources or materials derived from renewable resources) having performance equivalent to that of conventional synthetic rubber. When using monomer components derived from renewable resources, it may be difficult to separate them from monomer components derived from fossil resources due to the manufacturing process of the monomer. In that case, the impact on the environment can be evaluated by adopting the concept of mass balance.

[0040] The ratio of each monomer unit (e.g., unit derived from isoprene, unit derived from butadiene, unit derived from aromatic vinyl compound) in the entire rubber component (A) can be adjusted appropriately depending on the component to which the rubber component (A) is applied. The ratio of each monomer unit in the entire rubber component (A) can be adjusted, for example, by appropriately combining the above-mentioned isoprene-based rubber and butadiene-based rubber. In addition, the ratio of cis-bond units in the butadiene-based units can also be adjusted appropriately depending on the component to which the rubber component (A) is applied. In this specification, the term "monomer unit" refers to a structural unit of a polymer, the term "unit derived from isoprene" refers to a structural unit in a polymer constituted based on the monomer isoprene (including the isoprene unit in natural rubber), the term "unit derived from butadiene" refers to a structural unit in a polymer constituted based on the monomer butadiene, and the term "unit derived from an aromatic vinyl compound" refers to a structural unit in a polymer constituted based on the monomer aromatic vinyl compound. In this specification, the ratio of each monomer unit is measured by NMR.

[0041] The rubber component (A) may contain diene rubbers such as acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), styrene-isoprene-butadiene copolymer rubber (SIBR), etc., in addition to the above-mentioned isoprene-based rubber, butadiene rubber (BR), and aromatic vinyl compound-butadiene copolymer rubber (e.g., SBR). These rubber components may be used alone or in combination of two or more.

[0042] The rubber component (A) may be modified to introduce a functional group that interacts with a filler such as carbon black (B) or silica. Examples of the functional group include amino, amide, isocyanate, imino, imidazole, urea, ammonium, imide, hydrazo, azo, diazo, carboxyl, nitrile, pyridyl, alkoxy, hydroxyl, oxy, epoxy, ether, carbonyl, oxycarbonyl, silyl, alkoxysilyl, mercapto, sulfide, disulfide, sulfonyl, sulfinyl, and thiocarbonyl groups, and these functional groups may have a substituent. These functional groups may be introduced into the rubber component alone or in combination of two or more. Among these, an amino group, an alkoxy group, and an alkoxysilyl group are preferred, and a substituted amino group in which a hydrogen atom of an amino group is substituted with an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, and an alkoxysilyl group having 1 to 6 carbon atoms are more preferred.

[0043] The functional group can be introduced, for example, by reacting a compound (modifier) ​​having the functional group with the rubber component. The functional group is a modified functional group having an interactive property with a filler such as silica or carbon black (B), and examples thereof include a nitrogen-containing functional group, a silicon-containing functional group, and an oxygen-containing functional group. Examples of compounds (modifiers) having a nitrogen-containing functional group include amino group-containing compounds, and examples of compounds (modifiers) having a silicon-containing functional group include silicon halides and hydrocarbyloxysilane compounds. Examples of compounds (modifiers) having an oxygen-containing functional group include alkoxy group-containing compounds, alkylene oxide group-containing compounds, and trialkylsilyloxy group-containing compounds. More specifically, examples of the compounds include those described in International Publication No. 2016 / 194316 and International Publication No. 2019 / 117256. These modifiers may be used alone or in combination of two or more.

[0044] The rubber derived from sustainable materials (materials derived from biological resources or materials derived from renewable resources) can be produced in the same manner as conventional synthetic rubber derived from fossil resources, for example, by using monomer components derived from biological resources or monomer components derived from renewable resources, and, if necessary, monomer components derived from fossil resources. The rubber derived from sustainable materials (particularly rubber derived from biological resources) can also be obtained by reactions with microorganisms or enzyme reactions.

[0045] Regarding the method for preparing rubber derived from biological resources from the above-mentioned biological resources, for example, the method described in JP 2022-179158 A can be used. For example, by using butadiene obtained from biological resources as a monomer component, it is possible to obtain butadiene rubber (B-BR) derived from biological resources (biomass resources), and by using styrene obtained from biological resources and butadiene obtained from biological resources as monomer components, it is possible to obtain styrene-butadiene rubber (B-SBR) derived from biological resources (biomass resources). Here, methods for obtaining B-BR and B-SBR from biological resources include, in addition to artificial polymerization methods, methods of polymerization in vivo, and methods of polymerization with biological enzymes. The molecular weight, branching, microstructure, etc. of the obtained B-BR and B-SBR can be appropriately adjusted by changing the polymerization conditions according to known methods according to the target tire performance.

[0046] As the butadiene obtained from the 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 tiglic acid) can be suitably used. Two or more of these butadienes may be used in combination. As the styrene obtained from the biological resources, styrene obtained from a plant (preferably a plant belonging to the family Hamamelidaceae, Styraxaceae, or Apocynaceae, more preferably a plant belonging to the genera Liquidamus, Styrax, or Catharanthus, and even more preferably Sweetgum, Styrax rosa, or Catharanthus roseus) or a microorganism (preferably a microorganism belonging to the genera Penicillium or Escherichia, more preferably P. citrinum or transformed E. coli) can be suitably used. Two or more of these styrenes may be used in combination.

[0047] Recently, biomass combinat mainly using bioethanol, bioethylene, etc. are planned, but bioethanol and bioethylene are mainly produced using sugars and / or cellulose as biological resources, and other biological resources such as proteins, lipids, and amino acids cannot be effectively utilized. Furthermore, sugars compete with food, and excessive use of cellulose leads to deforestation. Therefore, it is preferable to use multiple types of monomer components derived from biological resources as the monomer components derived from the biological resources, or to use monomer components derived from biological resources, monomer components derived from renewable resources, and monomer components derived from fossil resources in combination, and further to appropriately adjust the ratio of these monomer components. This makes it possible to effectively utilize a wide range of biological resources and renewable resources such as sugars, proteins, and lipids without relying on one type of biological resource, and to stably supply rubber derived from sustainable materials, and further to consider the environment depending on the situation at the time of production. In addition, when using multiple types of monomer components derived from biological resources, it is preferable to use monomer components derived from different biological resources, i.e., monomer components obtained from different biological resources. Specifically, it is preferable to use a mixture of butadiene derived from multiple types of biological resources with different origins as the butadiene derived from biological resources, and / or to use a mixture of styrene derived from multiple types of biological resources with different origins as the styrene derived from biological resources. This allows multiple types of biological resources to be effectively utilized.

[0048] In the rubber composition of the present embodiment, the rubber component (A) preferably contains the above-mentioned isoprene-based rubber and the above-mentioned butadiene-based rubber. The butadiene-based rubber is preferably at least one selected from butadiene rubber (BR) and styrene-butadiene rubber (SBR). In this case, abrasion resistance, reinforcement, and low heat generation can be improved.

[0049] In the rubber composition of the present embodiment, the use of an isoprene-based rubber can increase the breaking strength of the rubber composition, which can reduce the rolling resistance of a tire using the rubber composition, improve fuel economy, and improve the wear resistance of the tire.

[0050] The proportion of the isoprene-based rubber in the rubber component (A) is preferably 1 to 80% by mass. In this case, the wear resistance and ice performance of a tire to which the rubber composition is applied can be improved. From the same viewpoint, the proportion of the isoprene-based rubber in the rubber component (A) is more preferably 10% by mass or more and more preferably 55% by mass or less.

[0051] The proportion of the butadiene rubber in the rubber component (A) is preferably 20 to 99% by mass. In this case, a tire using the rubber composition can have a good balance between performance on ice and wear resistance. From the same viewpoint, the proportion of the butadiene rubber in the rubber component (A) is more preferably 50% by mass or more, further preferably 60% by mass or more, and more preferably 90% by mass or less.

[0052] In the rubber composition of the present embodiment, by using a butadiene rubber (BR), which is one of the butadiene-based rubbers, it is possible to achieve a good balance between the performance on ice and the abrasion resistance of the rubber composition.

[0053] The butadiene rubber (BR) preferably has a cis-1,4 bond content of 90% by mass or more, which can further improve the wear resistance of a tire to which the rubber composition is applied.

[0054] In the rubber composition of the present embodiment, by using styrene-butadiene rubber (SBR), which is one of the butadiene rubbers, the performance on ice of the rubber composition can be improved.

[0055] The glass transition temperature of the styrene-butadiene rubber is preferably less than -40°C, more preferably less than -45°C, and even more preferably less than -50°C. The glass transition temperature of the styrene-butadiene rubber is preferably higher than -90°C, and even more preferably higher than -75°C. When the glass transition temperature of the styrene-butadiene rubber is less than -40°C, the fuel economy and wear resistance of the tire to which the rubber composition is applied can be maintained well. When the glass transition temperature of the styrene-butadiene rubber is higher than -90°C, the performance on ice can be improved.

[0056] The bound styrene content of the styrene-butadiene rubber is preferably 15% by mass or less. The bound styrene content of the styrene-butadiene rubber means the ratio of styrene units contained in the styrene-butadiene rubber. When the bound styrene content of the styrene-butadiene rubber is 15% by mass or less, the glass transition temperature is likely to be low, and the performance on ice can be further improved. From the same viewpoint, the bound styrene content of the styrene-butadiene rubber is more preferably 14% by mass or less, further preferably 13% by mass or less, and even more preferably 12% by mass or less. From the viewpoint of the wear resistance performance of a tire to which the rubber composition is applied, the bound styrene content of the styrene-butadiene rubber is preferably 5% by mass or more, more preferably 7% by mass or more, and even more preferably 8% by mass or more. The bound styrene content of the styrene-butadiene rubber can be adjusted by the amount of monomer used in polymerization of the styrene-butadiene rubber, the degree of polymerization, and the like.

[0057] The butadiene rubber preferably has a functional group introduced therein. In this case, the dispersibility of the filler such as carbon black (B) can be improved, so that the balance of the performance on ice, the fuel efficiency, and the wear resistance of the tire to which the rubber composition is applied can be improved. Examples of the functional group include functional groups having at least one element selected from nitrogen, silicon, oxygen, and tin, and more specifically, examples of the functional group include amino groups, imino groups, amide groups, isocyanate groups, silyl groups, alkoxy groups, alkoxysilyl groups, epoxy groups, glycidyl groups, and carbonyl groups.

[0058] (Carbon Black (B)) The rubber composition of the present embodiment contains carbon black (B) as a filler, and the carbon black (B) must contain recycled carbon black. By including carbon black (B) together with the rubber component (A), the cut resistance, abrasion resistance, and other properties of the tread rubber can be further improved.

[0059] The grade of the carbon black (B) is not particularly limited, and examples thereof include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. As the carbon black (B), a commercially available product can be used, and examples of the commercially available carbon black (B) include products from Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Nippon Steel Carbon Co., Ltd., Birla Carbon Co., Ltd., and the like. These carbon blacks (B) may be used alone or in combination of two or more.

[0060] The nitrogen adsorption specific surface area of ​​the carbon black (B) is 20 m 2 / g or more, and 2 / g or more is more preferable, and 250m 2 / g or less, and 2 / g or less is more preferable, and 150m2 It is more preferable that the molecular weight is not more than 1 / g. In this specification, the nitrogen adsorption specific surface area (N2SA) of carbon black is determined in accordance with JIS K 6217-2:2017 (ISO 4652:2012).

[0061] The carbon black (B) has an oil absorption of 50 cm 3 / 100g or more is preferable, 60cm 3 / 100g or more is more preferable, and 200cm 3 / 100g or less is preferable, and 150cm 3 It is more preferable that the weight ratio is 1 / 100g or less. In this specification, the dibutyl phthalate (DBP) oil absorption of carbon black is measured by the method described in JIS K 6217-4:2001 "Determination of DBP absorption."

[0062] The content of the carbon black (B) is preferably 20 parts by mass or more and 80 parts by mass or less relative to 100 parts by mass of the rubber component (A). When the content of the carbon black (B) is 20 parts by mass or more relative to 100 parts by mass of the rubber component (A), the abrasion resistance can be improved, and when the content is 80 parts by mass or less, the deterioration of the low heat generation property can be suppressed. From the same viewpoint, the content of the carbon black (B) relative to 100 parts by mass of the rubber component (A) is more preferably 25 parts by mass or more, even more preferably 30 parts by mass or more, and more preferably 70 parts by mass or less, and even more preferably 65 parts by mass or less.

[0063] -Recycled carbon black- In the rubber composition of the present embodiment, the carbon black (B) must contain recycled carbon black. In this specification, "recycled carbon black" refers to carbon black obtained by recovering from raw materials that are waste materials that have been recycled. Examples of the waste materials that have been recycled include rubber products (particularly vulcanized rubber products) that contain carbon black, such as used rubber and used tires, and waste oil. "Recycled carbon black" is different from carbon black that is produced directly from raw materials such as hydrocarbons, such as petroleum and natural gas, that is, carbon black that is not recycled. Note that "used" here includes not only carbon black that has been actually used and then discarded, but also carbon black that has been produced but not actually used and then discarded.

[0064] The proportion of the recycled carbon black in the carbon black (B) is preferably 50% by mass or more. In this case, it can further contribute to improving sustainability. From the same viewpoint, the proportion of the recycled carbon black in the carbon black (B) is more preferably 70% by mass or more, further preferably 90% by mass or more, and particularly preferably 100% by mass (i.e., carbon black (B) is composed only of recycled carbon black).

[0065] In addition, the recycled carbon black used in this embodiment is preferably obtained by pyrolysis of a vulcanized rubber product containing carbon black. In this case, used rubber products can be effectively utilized, which can further contribute to reducing the environmental load. Furthermore, the recycled carbon black used in this embodiment is preferably obtained from a solid residue generated by pyrolysis of the vulcanized rubber product containing carbon black. When a rubber product containing carbon black is pyrolyzed, a solid residue and a volatile component (oil) are obtained, and the recycled carbon black can be recovered from either of them. However, the recycled carbon black used in this embodiment preferably does not include carbon black recovered from oil.

[0066] The solid residue obtained by pyrolysis of wastes such as used rubber and used tires contains ash in addition to carbon black. Ash is derived from non-volatile components contained in rubber and tires. Therefore, the recycled carbon black obtained from the solid residue has a relatively low carbon black content. On the other hand, in consideration of the various physical properties required for tires manufactured using recycled carbon black, the higher the carbon content in the recycled carbon black, the better. In the recycled carbon black used in this embodiment, the carbon content is preferably 80% by mass or more, more preferably 85% by mass or more, more preferably 87% by mass or more, and even more preferably 89% by mass or more. In the recycled carbon black used in this embodiment, the carbon content is preferably 97% by mass or less. The carbon content is a value that does not include adsorbed moisture.

[0067] Specific examples of ash include 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 pyrolysis of waste, a certain amount of ash remains even after various processes for removing the ash. In this embodiment, the recycled carbon black is allowed to contain ash. The lower limit of the ash content of the recycled carbon black used in this embodiment may be 0.5% by mass. On the other hand, in consideration of the various physical properties required for tires and the quality of the recycled carbon black, the ash content of the recycled carbon black is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 5.0% by mass or less. When the ash content of the recycled carbon black (B) is 20% by mass or less, the various physical properties of a rubber product to which the tread rubber is applied can be improved. In this specification, the ash content of carbon black is calculated from the mass of unburned components (ash content) obtained by burning carbon black at 550° C.±25° C. to convert it to incineration.

[0068] Reclaimed carbon black can also be obtained from the pyrolysis process of used pneumatic tires. For example, European Patent Application Publication No. 3427975, referring to "Rubber Chemistry and Technology", Vol. 85, No. 3, pp. 408-449 (2012), in particular pp. 438, 440, and 442, describes that it can be obtained by pyrolysis of organic materials at 550-800°C with the exclusion of oxygen, or by vacuum pyrolysis at relatively low temperatures (

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

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

[0069] The regenerated carbon black may lack functional groups on its surface, or may be treated to include functional groups on its surface. The treatment to include functional groups on the surface of the regenerated carbon black can be carried out by a conventional method. For example, in European Patent Application Publication No. 3173251, carbon black obtained from a pyrolysis process is treated with potassium permanganate under acidic conditions to obtain carbon black having hydroxyl and / or carboxyl groups on its surface. In Japanese Patent No. 6856781, carbon black obtained from a pyrolysis 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 regenerated carbon black according to the present embodiment also includes carbon black that has been treated to include functional groups on its surface.

[0070] Moreover, examples of the thermal decomposition of crosslinked rubber products (vulcanized rubber products) such as used tires include thermal decomposition methods at temperatures of 650° C. or higher.

[0071] The crosslinked rubber products used for the decomposition may be grouped according to the type of rubber component previously blended, and then the decomposition step may be performed for each group. Alternatively, the crosslinked rubber products may be grouped according to the type of filler previously blended (e.g., the type of carbon black, the type of silica, the mixing ratio of carbon black and silica, etc.), and then the decomposition step may be performed for each group. Furthermore, the crosslinked rubber products may be grouped according to both the type of rubber component and the type of filler, and then the decomposition step may be performed for each group. When the decomposition step is performed for each group in this way, recycled carbon black with more uniform physical properties is obtained, and therefore, when the carbon black is blended again with the rubber component, a rubber composition with better performance is obtained.

[0072] In addition, when the crosslinked rubber product used for the decomposition is derived from tires, the tires may be grouped in advance by type (for example, for passenger cars, for trucks and buses, for large vehicles such as off-road vehicles, for aircraft, for agricultural vehicles, etc.), and then the decomposition process may be performed for each group. In addition, the tires may be grouped in advance by tire components (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 performed for each group. Furthermore, the tires may be grouped both by type and by tire components, and then the decomposition process may be performed for each group. When the decomposition process is performed for each group in this way, recycled carbon black with more uniform physical properties is obtained, so that when it is blended again into the rubber component, a rubber composition with better performance can be obtained.

[0073] The recycled carbon black used in this embodiment has a nitrogen adsorption specific surface area NSA of 20 to 150 m 2 / g, and the DBP oil absorption is preferably 50 to 150 ml / 100 g. Note that, as the recycled carbon black in this embodiment, a commercially available product can be used, and an example of such a commercially available product is "PB365" manufactured by Enrestec. PB365 is a recycled carbon black produced by pyrolysis of used tires, and has an N2SA of 73.6 m 2 / g. PB365 also contains about 17% by mass of ash.

[0074] -Carbon black other than recycled carbon black- The rubber composition of the present embodiment may further contain, as the carbon black (B), a carbon black other than the recycled carbon black (virgin carbon black) in addition to the above-mentioned recycled carbon black. Examples of the carbon black other than the recycled carbon black include carbon black derived from plants, and examples of the plant-derived carbon black include those derived from castor oil and pine oil.

[0075] The carbon black other than the regenerated carbon black preferably has a dibutyl phthalate (DBP) oil absorption of 50 to 150 mL / 100 g. The carbon black other than the regenerated carbon black preferably has a dibutyl phthalate (DBP) oil absorption of 50 to 150 mL / 100 g and a nitrogen adsorption specific surface area (N2SA) of 20 to 130 m 2 / g, and more preferably, the dibutyl phthalate (DBP) oil absorption is 80 to 130 mL / 100 g and the nitrogen adsorption specific surface area (N2SA) is 20 to 60 m 2 By combining such carbon black (carbon black other than recycled carbon black) with the recycled carbon black (B), the fracture resistance of the rubber composition can be maintained more reliably.

[0076] The content of the carbon black other than the recycled carbon black is not particularly limited, and can be appropriately adjusted depending on, for example, the target performance of the tire to which the rubber composition is applied. For example, the content of the carbon black other than the recycled carbon black is preferably 1 part by mass or more, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, and is preferably 100 parts by mass or less, based on 100 parts by mass of the rubber component (A).

[0077] (silica) The rubber composition of the present embodiment preferably further contains silica as a filler together with the carbon black (B). By using silica, the performance on ice and the abrasion resistance can be improved when the rubber composition is applied to a tire. Examples of the silica include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, etc., and among these, wet silica is preferred because it has a large number of silanol groups. These silicas may be used alone or in combination of two or more. As the silica, a commercially available product can be used, and examples of the commercially available silica include products from Tosoh Silica Co., Ltd., Evonik, Solvay, Solvay Japan Co., Ltd., Tokuyama Corporation, etc.

[0078] As the silica, silica derived from silicic acid plants is preferred from the viewpoint of reducing environmental load. The silicic acid plants are present, for example, in mosses, ferns, horsetails, Cucurbitaceae, Urticaceae, and Gramineae plants. Among these plants, Gramineae plants are preferred. In addition, the Gramineae plants include rice, bamboo grass, sugarcane, and the like, among which rice is preferred. Since rice is widely cultivated for food, it can be procured locally in a wide area, and since rice husks are generated in large quantities as industrial waste, it is easy to secure the amount. Therefore, from the viewpoint of easy availability, silica derived from rice husks (hereinafter also referred to as "rice husk silica") is particularly preferred as silica. By using the rice husk silica, rice husks that become industrial waste can be effectively utilized, and since the raw material can be procured locally near the tire manufacturing plant, the energy and cost of transportation and storage can be reduced, which is environmentally preferable from various viewpoints. The rice husk silica may be a powder of rice husk charcoal obtained by carbonizing rice husks by heating, or may be precipitated silica produced by a wet method using an alkali silicate aqueous solution, which is prepared by extracting rice husk ash generated when rice husks are burned as fuel in a biomass boiler with an alkali and extracting the rice husk ash with an alkali silicate aqueous solution. The method for producing the rice husk charcoal is not particularly limited, and various known methods can be used. For example, rice husks can be pyrolyzed by steaming them in a kiln to obtain rice husk charcoal. The rice husk charcoal thus obtained is pulverized using a known pulverizer (for example, a ball mill), and then sorted and classified into a predetermined particle size range to obtain rice husk charcoal powder. The rice husk-derived precipitated silica can be produced by the method described in JP 2019-38728 A. Further examples of the silica include silica produced by recycling silicon components from scraps of silicon wafers, which are raw materials for semiconductors, glass bottles, etc.

[0079] The silica has a nitrogen adsorption specific surface area (N2SA) of 50 m 2 / g or more, and 2 / g or more is more preferable, and 150m 2 / g or more is more preferable, and 2 / g or less, and2 / g or less is more preferable, 2 / g or less is more preferable, 2 It is even more preferable that the molecular weight is not more than 1 / g. In this specification, the nitrogen adsorption specific surface area (N2SA) of silica is a value measured by the BET method in accordance with ASTM D3037-93.

[0080] The content of the silica is preferably 5 parts by mass or more and 100 parts by mass or less relative to 100 parts by mass of the rubber component (A). When the content of the silica is 5 parts by mass or more relative to 100 parts by mass of the rubber component (A), the abrasion resistance and performance on ice can be improved, and when the content is 100 parts by mass or less, deterioration of the processability and the rolling resistance of the rubber composition can be suppressed. From the same viewpoint, the content of the silica relative to 100 parts by mass of the rubber component (A) is more preferably 10 parts by mass or more, more preferably 50 parts by mass or less, and further preferably 45 parts by mass or less.

[0081] The proportion of silica in the total content of the silica and carbon black (B) is preferably 20% by mass or more and 70% by mass or less. If the proportion of silica is 20% by mass or more, the performance on ice can be improved, and if it is 70% by mass or less, the abrasion resistance can be improved. From the same viewpoint, the proportion of silica in the total content of the silica and carbon black (B) is more preferably 30% by mass or more, even more preferably 40% by mass or more, and more preferably 60% by mass or less.

[0082] (Fillers other than carbon black and silica) In the rubber composition of the present embodiment, in addition to the above-described carbon black (B) and silica, a rubber compound represented by the following general formula (XX): nM xSiO y zH2O (XX) [wherein M is at least one selected from the group consisting of metals selected from the group consisting of aluminum, magnesium, titanium, calcium, and zirconium, oxides or hydroxides of these metals, and hydrates thereof, or carbonates of these metals; and n, x, y, and z are integers of 1 to 5, integers of 0 to 10, integers of 2 to 5, and integers of 0 to 10, respectively]. Examples of the inorganic compound represented by the general formula (XX) include alumina (Al2O3) such as γ-alumina and α-alumina, alumina monohydrate (Al2O3·H2O) such as boehmite and diaspore, aluminum hydroxide [Al(OH)3] such as gibbsite and bayerite, aluminum carbonate [Al2(CO3)3], magnesium hydroxide [Mg(OH)2], magnesium oxide (MgO), magnesium carbonate (MgCO3), talc (3MgO·4SiO2·H2O), attapulgite (5MgO·8SiO2·9H2O), titanium white (TiO2), titanium black (TiO 2n-1 ), calcium oxide (CaO), calcium hydroxide [Ca(OH)2], magnesium aluminum oxide (MgO·Al2O3), clay (Al2O3·2SiO2), kaolin (Al2O3·2SiO2·2H2O), pyrophyllite (Al2O3·4SiO2·H2O), bentonite (Al2O3·4SiO2·2H2O), aluminum silicate (Al2SiO5, Al4·3SiO4·5H2O, etc.), magnesium silicate (Mg2SiO4, MgSiO3, etc.), ke Examples of such inorganic silicates include calcium aluminate (Ca2SiO4, etc.), calcium aluminium silicate (Al2O3·CaO·2SiO2, etc.), calcium magnesium silicate (CaMgSiO4), calcium carbonate (CaCO3), zirconium oxide (ZrO2), zirconium hydroxide [ZrO(OH)2·nH2O], zirconium carbonate [Zr(CO3)2], and crystalline aluminosilicates that contain hydrogen, alkali metals, or alkaline earth metals to compensate for the charge, such as various zeolites. From the viewpoint of the balance between abrasion resistance and performance on ice, the inorganic compound represented by the general formula (XX) preferably has an average particle size of 0.01 to 10 μm, and more preferably 0.05 to 5 μm.

[0083] (Silane coupling agent) When the rubber composition of the present embodiment contains silica, in order to improve the effect of the silica, the rubber composition preferably contains a silane coupling agent. 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-N, Examples of the silane coupling agent include N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropyl benzothiazolyl tetrasulfide, 3-triethoxysilylpropyl benzothiazolyl tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, bis(3-diethoxymethylsilylpropyl)tetrasulfide, 3-mercaptopropyldimethoxymethylsilane, dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, dimethoxymethylsilylpropyl benzothiazolyl tetrasulfide, etc. As the silane coupling agent, a commercially available product can be used, and examples of the commercially available silane coupling agent include products from Evonik, Momentive, Shin-Etsu Silicone Co., Ltd., Dow Corning Toray Co., Ltd., Tokyo Chemical Industry Co., Ltd., and Azumax Co., Ltd. These silane coupling agents may be used alone or in combination of two or more.

[0084] The content of the silane coupling agent can be appropriately adjusted depending on, for example, the target performance of the tire to which the silane coupling agent is applied. For example, the content of the silane coupling agent is preferably 1 part by mass or more, more preferably 6 parts by mass or more, and even more preferably 8 parts by mass or more, and is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, even more preferably 12 parts by mass or less, and even more preferably 10 parts by mass or less, relative to 100 parts by mass of the silica.

[0085] (Porosity Inducing Agent (C)) The rubber composition of the present embodiment preferably further contains a void-introducing agent (C). By containing the void-introducing agent (C) in the rubber composition, a plurality of voids can be formed on the surface and / or inside of the tread rubber. A tire using the tread rubber has flexibility and easily adheres to an icy road surface, and water on the road surface is absorbed into the voids on the tire surface, making it easier to remove water from the icy and snowy road surface, thereby improving braking performance on ice.

[0086] Examples of the void-introducing agent (C) include foaming agents, metal sulfates, thermally expandable microcapsules, porous cellulose particles, lignin derivatives, etc. These void-introducing agents (C) may be used alone or in combination of two or more. In particular, among the above-mentioned, from the viewpoint of effectively improving performance on ice, it is preferable that the void-introducing agent (C) is a foaming agent.

[0087] -Foaming agent- When the rubber composition contains a foaming agent as the void-introducing agent (C), the foaming agent generates bubbles in the vulcanized rubber during vulcanization of the rubber composition, and the vulcanized rubber can be made into a foamed rubber. Since the foamed rubber has flexibility, the surface of a tire using the vulcanized rubber as the tread rubber can easily adhere to an icy road surface. In this case, holes (foam holes) resulting from the bubbles are generated in the vulcanized rubber (tread rubber) and the surface of the tire, and these holes function as water channels to drain water, improving performance on ice.

[0088] Examples of the foaming agent include inorganic foaming agents such as carbonates such as ammonium carbonate, sodium carbonate, and potassium carbonate, and bicarbonates (hydrogen carbonates) such as ammonium bicarbonate, sodium bicarbonate, and potassium bicarbonate; and organic foaming agents such as azodicarbonamide (ADCA), dinitrosopentamethylenetetramine (DPT), dinitrosopentastyrenetetramine, benzenesulfonyl hydrazide derivatives, p,p'-oxybisbenzenesulfonyl hydrazide (OBSH), nitrogen-generating nitrososulfonyl azo compounds, N,N'-dimethyl-N,N'-dinitrosophthalamide, toluenesulfonyl hydrazide, p-toluenesulfonyl semicarbazide, and p,p'-oxybisbenzenesulfonyl semicarbazide. These foaming agents may be used alone or in combination of two or more. Among these, from the viewpoints of manufacturing processability as well as performance on ice, inorganic foaming agents, azodicarbonamide (ADCA), and dinitrosopentamethylenetetramine (DPT) are preferred, and sodium bicarbonate is more preferred.

[0089] The content of the foaming agent is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, based on 100 parts by mass of the rubber component (A).

[0090] -Metal sulfate- When the rubber composition contains a metal sulfate as the void-introducing agent (C), the metal sulfate protrudes from the surface of the tread rubber obtained by vulcanizing the rubber composition, and performs a claw function without the disadvantage of being abrasive. Then, the metal sulfate gradually leaves the rubber matrix, creating cavities, which function as storage volumes and passages for discharging the water film on the ice surface. From the viewpoint of improving the friction coefficient, magnesium sulfate can be used as the metal sulfate.

[0091] The metal sulfate preferably has a particle shape of micrometer size. Specifically, the metal sulfate preferably has an average particle size and a median particle size (both of which are expressed by mass) of 1 μm to 1 mm, and more preferably has a median particle size of 2 μm to 800 μm. When the average particle size and the median particle size are 1 μm or more, it is easy to obtain an appropriate micro-roughness. In addition, when the average particle size and the median particle size are 1 mm or less, it is difficult to impair the grip performance on melting ice while suppressing a decrease in the aesthetics of the tread rubber (suppressing the appearance of too obvious particles on the tread surface). From the same viewpoint, the median particle size of the metal sulfate is preferably 2 μm to 500 μm, and more preferably 5 μm to 200 μm. In addition, various known methods, for example by laser diffraction, can be applied to analyze particle size and calculate the median particle size of the microparticles (or the average diameter of the microparticles assuming that they are substantially spherical) (see, for example, standard ISO-8130-13 or standard JIS K5600-9-3).

[0092] The content of the metal sulfate is preferably 5 parts by mass or more, and more preferably 10 parts by mass or more, and is preferably 40 parts by mass or less, and more preferably 35 parts by mass or less, based on 100 parts by mass of the rubber component (A).

[0093] -Thermal expansion microcapsules- The thermally expandable microcapsules may be configured to contain a thermally expandable substance in a shell material formed of a thermoplastic resin. The shell material may be formed of a nitrile-based polymer. The thermally expandable substance may be, for example, a hydrocarbon such as isoalkane or normal alkane, which has a property of vaporizing or expanding by heat. Examples of the isoalkane include isobutane, isopentane, 2-methylpentane, 2-methylhexane, and 2,2,4-trimethylpentane. Examples of the normal alkane include n-butane, n-propane, n-hexane, n-heptane, and n-octane. These hydrocarbons may be used alone or in combination of two or more. A preferred form of the thermally expandable substance is one in which a hydrocarbon that is gaseous at room temperature is dissolved in a hydrocarbon that is liquid at room temperature. By using such a mixture of hydrocarbons, sufficient expansion force can be obtained from a low temperature region to a high temperature region in the vulcanization molding temperature range (150°C to 190°C) of an unvulcanized tire.

[0094] Examples of the thermally expandable microcapsules include those manufactured by Expancel of Sweden under the trade names "EXPANCEL 091DU-80" and "EXPANCEL 092DU-120" and those manufactured by Matsumoto Yushi Seiyaku Co., Ltd. under the trade names "Matsumoto Microsphere F-85D" and "Matsumoto Microsphere F-100D".

[0095] The content of the thermally expandable microcapsules is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, based on 100 parts by mass of the rubber component (A).

[0096] -Porous cellulose particles- When the rubber composition contains porous cellulose particles as the void-introducing agent (C), when the porous cellulose particles are exposed on the surface of the tread rubber obtained by vulcanizing the rubber composition, water on the snowy and icy road surface is absorbed by the porous cellulose particles, and the water between the tire and the road surface can be removed. In addition, the presence of cellulose, which is a polysaccharide, causes an interaction between the tire and water on the snowy and icy road surface, so that the interaction between the tire and water can be further enhanced. In other words, by blending the porous cellulose particles in the rubber composition, the performance on ice can be improved.

[0097] The porosity of the porous cellulose particles is preferably 75 to 95%. When the porosity of the porous cellulose particles is 75% or more, the effect of improving performance on ice is excellent, and when the porosity is 95% or less, the strength of the particles can be increased. The porosity is more preferably 80 to 90%. The porosity of the porous cellulose particles can be calculated by measuring the volume of a certain mass of a sample (i.e., the porous cellulose particles) with a measuring cylinder, calculating the bulk density, and using the following formula. Porosity (%) = {1-[bulk specific gravity of sample (g / mL)] / [true specific gravity of sample (g / mL)]} x 100 Here, the true specific gravity of cellulose is 1.5.

[0098] The particle size of the porous cellulose particles is not particularly limited, but from the viewpoint of abrasion resistance, the average particle size is preferably 1000 μm or less. The lower limit of the average particle size is not particularly limited, but is preferably 5 μm or more. The average particle size is more preferably 100 to 800 μm, and further preferably 200 to 800 μm. The porous cellulose particles are preferably spherical particles having a major axis / minor axis ratio of 1 to 2. By using particles having such a spherical structure, the dispersibility in the rubber composition is improved, which contributes to improving performance on ice and maintaining abrasion resistance, etc. The major axis / minor axis ratio is more preferably 1.0 to 1.5. The average particle size and the long axis / short axis ratio of the porous cellulose particles are obtained as follows: That is, the porous cellulose particles are observed under a microscope to obtain an image, and the long axis and short axis of the particles (when the long axis and short axis are the same, the length in a certain axis direction and the length in an axis direction perpendicular to the long axis) are measured for 100 particles using the image, and the average particle size is obtained by calculating the average value, and the long axis / short axis ratio is obtained by averaging the values ​​obtained by dividing the long axis by the short axis.

[0099] The porous cellulose particles are commercially available from Rengo Co., Ltd. under the name "Viscopearl" and are described in JP-A-2001-323095, JP-A-2004-115284, etc., and these can be suitably used.

[0100] The content of the porous cellulose particles is preferably in the range of 0.3 to 20 parts by mass, more preferably in the range of 1 to 15 parts by mass, and further preferably in the range of 3 to 15 parts by mass, based on 100 parts by mass of the rubber component (A).

[0101] -Lignin derivatives- When the rubber composition contains a lignin derivative as the void-introducing agent (C), the effect of improving the performance on ice can be enhanced. The lignin derivative is preferably a lignin sulfonate. The lignin sulfonate may be an alkali metal salt, an alkaline earth metal salt, an ammonium salt, or an alcoholamine salt of lignin sulfonic acid. These lignin derivatives may be used alone or in combination of two or more. In particular, the lignin derivative is preferably an alkali metal salt and / or an alkaline earth metal salt of lignin sulfonic acid, more specifically, a potassium salt, a sodium salt, a calcium salt, a magnesium salt, a lithium salt, a barium salt, or a mixed salt thereof.

[0102] (foaming aid) When the rubber composition of the present embodiment contains a foaming agent as the void-introducing agent (C), it is preferable that the rubber composition further contains a foaming assistant. By using the foaming assistant together with the foaming agent, it is possible to promote the foaming reaction, increase the degree of completion of the reaction, and suppress unnecessary deterioration over time. Examples of the foaming assistant include urea, zinc stearate, zinc benzenesulfinate, zinc oxide, etc. These foaming assistants may be used alone or in combination of two or more.

[0103] The total content of the foaming agent and the foaming assistant is preferably 1 to 30 parts by mass relative to 100 parts by mass of the rubber component (A). When the total content of the foaming agent and the foaming assistant is 1 part by mass or more, the rubber composition can be sufficiently foamed during vulcanization, and the foaming rate of the vulcanized rubber can be maintained high. On the other hand, even when the total content of the foaming agent and the foaming assistant is 30 parts by mass or less, the decrease in the foaming rate can be suppressed. From the same viewpoint, the total content of the foaming agent and the foaming assistant relative to 100 parts by mass of the rubber component (A) is more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, and more preferably 25 parts by mass or less, and even more preferably 20 parts by mass or less.

[0104] In the rubber composition of the present embodiment, the mass ratio of the foaming agent to the foaming assistant (foaming agent:foaming assistant) is preferably 1:1.1 to 1:3.3. If the mass ratio (foaming agent:foaming assistant) is less than 1:1.1, the rubber composition may not be sufficiently foamed during vulcanization, and the foaming rate of the vulcanized rubber may decrease. On the other hand, if the mass ratio (foaming agent:foaming assistant) exceeds 1:3.3, the foaming rate may also decrease. From the same viewpoint, the mass ratio of the foaming agent to the foaming assistant (foaming agent:foaming assistant) is more preferably 1:1.2 or more, even more preferably 1:1.3 or more, more preferably 1:3.2 or less, even more preferably 1:3.1 or less, even more preferably 1:2.9 or less, even more preferably 1:2.7 or less, even more preferably 1:2.5 or less, and particularly preferably 1:2.3 or less.

[0105] From the viewpoints of the foaming rate of the vulcanized rubber and the performance of the tire on ice, the content of the foaming aid is preferably in the range of 4 to 14 parts by mass, and more preferably in the range of 6 to 14 parts by mass, per 100 parts by mass of the rubber component (A).

[0106] (resin) The rubber composition of the present embodiment preferably further contains a resin. Examples of the resin include terpene resin, rosin resin, C5 resin, C5-C9 resin, C9 resin, cyclopentadiene resin, aromatic resin, coumarone resin, indene resin, coumarone-indene resin, olefin resin, polyurethane resin, acrylic resin, and the like. These resins may be used alone or in combination of two or more. Among these resins, terpene resin, rosin resin, C5 resin, C5-C9 resin, C9 resin, cyclopentadiene resin, and aromatic resin are preferred, and terpene resin and rosin resin are particularly preferred. Terpene resin and rosin resin are naturally derived sustainable resins, so that they can further reduce the environmental load and can further improve tire performance, such as grip performance on various road surface conditions such as dry road surface, wet road surface, snowy road surface, and frozen road surface. In addition, C5 resin, C9 resin, C5-C9 resin, and cyclopentadiene resin can improve wear resistance and fuel economy in a well-balanced manner, while aromatic resin can improve grip performance, wear resistance, and rubber strength in a well-balanced manner.

[0107] The terpene resin is a solid resin obtained by blending turpentine obtained at the same time when rosin is obtained from pine trees, or a polymerization component separated therefrom, and polymerizing it using a Friedel-Crafts catalyst, and examples of the terpene resin include β-pinene resin and α-pinene resin. The terpene resin also includes terpene-aromatic compound resin, and representative examples of the terpene-aromatic compound resin include terpene-phenol resin and styrene-terpene resin. The terpene-phenol resin can be obtained by reacting terpenes with various phenols using a Friedel-Crafts catalyst, or by further condensing with formalin. The styrene-terpene resin can be obtained by reacting styrene with terpenes using a Friedel-Crafts catalyst. The terpenes as the raw material are not particularly limited, and are preferably monoterpene hydrocarbons such as α-pinene and limonene, more preferably those containing α-pinene, and particularly preferably α-pinene.

[0108] Examples of the rosin-based resin include natural resin rosins such as gum rosin, tall oil rosin, and wood rosin contained in raw pine resin and tall oil. Examples of modified rosin, rosin derivatives, and modified rosin derivatives include polymerized rosin, partially hydrogenated rosin thereof, glycerin ester rosin, partially hydrogenated rosin thereof, and fully hydrogenated rosin thereof, pentaerythritol ester rosin, partially hydrogenated rosin thereof, and polymerized rosin, etc.

[0109] The C5 resins include aliphatic petroleum resins obtained by (co)polymerizing C5 fractions obtained by thermal cracking of naphtha in the petrochemical industry. C5 fractions usually include olefinic hydrocarbons such as 1-pentene, 2-pentene, 2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene, and diolefinic hydrocarbons such as 2-methyl-1,3-butadiene, 1,2-pentadiene, 1,3-pentadiene, and 3-methyl-1,2-butadiene.

[0110] The C5-C9 resin refers to a C5-C9 synthetic petroleum resin. Examples of the C5-C9 resin include petroleum-derived C5-C11 Examples of the solid polymers include those obtained by polymerizing the fraction using a Friedel-Crafts catalyst such as AlCl3 or BF3, and more specifically, copolymers mainly composed of styrene, vinyltoluene, α-methylstyrene, indene, etc. As the C5-C9 resin, a resin with a small amount of C9 or more components is preferred from the viewpoint of compatibility with the rubber component. Here, "a small amount of C9 or more components" means that the amount of C9 or more components in the total amount of the resin is less than 50 mass%, preferably 40 mass% or less.

[0111] The C9 resin refers to a C9 synthetic petroleum resin, for example, a solid polymer obtained by polymerizing a C9 fraction using a Friedel-Crafts catalyst such as AlCl3 or BF3. Examples of the C9 resin include copolymers mainly composed of indene, α-methylstyrene, vinyltoluene, etc.

[0112] The cyclopentadiene resin refers to a resin containing a unit derived from a cyclopentadiene monomer as a monomer unit. Examples of the cyclopentadiene resin include a homopolymer of a cyclopentadiene monomer, a copolymer of two or more cyclopentadiene monomers, and a copolymer of a cyclopentadiene monomer and another monomer. Here, examples of the cyclopentadiene monomer include cyclopentadiene, dicyclopentadiene, and tricyclopentadiene, and among these, dicyclopentadiene is preferred, that is, the cyclopentadiene resin is preferably a dicyclopentadiene resin. The dicyclopentadiene resin refers to a resin obtained by polymerizing dicyclopentadiene using a Friedel-Crafts catalyst such as AlCl3 or BF3. Examples of dicyclopentadiene resins include homopolymers of dicyclopentadiene, copolymers of dicyclopentadiene and aromatic monomers, and copolymers of dicyclopentadiene and C9 fractions (vinyl toluene, indene, etc.).

[0113] The aromatic resin refers to a resin containing a unit derived from an aromatic monomer as a monomer unit. Examples of the aromatic resin include a homopolymer of an aromatic monomer, a copolymer of two or more aromatic monomers, and a copolymer of an aromatic monomer and another monomer. Examples of the aromatic monomer include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-methoxystyrene, p-tert-butylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, and p-phenylstyrene; phenolic monomers such as phenol, alkylphenol, and alkoxyphenol; and naphthol monomers such as naphthol, alkylnaphthol, and alkoxynaphthol.

[0114] The resin may be hydrogenated, i.e., may be a hydrogenated resin (hydrogenated resin). In addition, the resin may be modified to introduce a functional group that interacts with a filler such as carbon black or silica. Examples of the functional group include an amino group, an amide group, an isocyanate group, an imino group, an imidazole group, a urea group, an ammonium group, an imide group, a hydrazo group, an azo group, a diazo group, a carboxyl group, a nitrile group, a pyridyl group, an alkoxy group, a hydroxyl group, an oxy group, an epoxy group, an ether group, a carbonyl group, an oxycarbonyl group, a silyl group, an alkoxysilyl group, a mercapto group, a sulfide group, a disulfide group, a sulfonyl group, a sulfinyl group, and a thiocarbonyl group.

[0115] From the viewpoint of increasing compatibility with the rubber component (A) and improving the on-ice performance of a tire to which the rubber composition is applied, the resin is preferably a hydrogenated resin, and among these, it is more preferable that the resin is at least one selected from hydrogenated terpene resins, hydrogenated C5 resins, hydrogenated C5-C9 resins, and hydrogenated cyclopentadiene resins, even more preferable that the resin is at least one selected from hydrogenated C5 resins and hydrogenated C5-C9 resins, and even more preferable that the resin is a hydrogenated C5 resin. The hydrogenated C5 resin and hydrogenated C5-C9 resin refer to C5 resin and C5-C9 resin in which the unsaturated bonds in the molecule have been partially or completely hydrogenated.

[0116] The softening point of the resin is preferably 30° C. or higher, more preferably 60° C. or higher, more preferably 80° C. or higher, more preferably higher than 110° C., more preferably 116° C. or higher, more preferably 120° C. or higher, more preferably 123° C. or higher, and even more preferably 127° C. or higher. From the viewpoint of processability, the softening point of the resin is preferably 160° C. or lower, more preferably 150° C. or lower, more preferably 145° C. or lower, more preferably 141° C. or lower, and even more preferably 136° C. or lower. In this specification, the softening point of the resin is the temperature at which the ball drops when the softening point defined in JIS K 6220-1:2015 (ISO 28641:2010) is measured using a ring and ball softening point tester.

[0117] The resin preferably has a weight average molecular weight in terms of polystyrene of 200 g / mol or more and 1600 g / mol or less. When the weight average molecular weight of the resin is 200 g / mol or more, the resin is less likely to precipitate from the tire, and the effect of the resin can be fully exhibited. When the weight average molecular weight of the resin is 1600 g / mol or less, the resin is easily compatible with the rubber component (A). From the viewpoint of suppressing the resin from precipitating from the tire and suppressing deterioration of the tire appearance, the weight average molecular weight in terms of polystyrene of the resin is more preferably 500 g / mol or more, even more preferably 550 g / mol or more, even more preferably 600 g / mol or more, even more preferably 650 g / mol or more, and particularly preferably 700 g / mol or more. In addition, from the viewpoint of improving the compatibility of the resin with the rubber component (A) and further enhancing the effect of the resin, the weight average molecular weight of the resin in terms of polystyrene is more preferably 1570 g / mol or less, more preferably 1530 g / mol or less, more preferably 1500 g / mol or less, more preferably 1470 g / mol or less, more preferably 1430 g / mol or less, more preferably 1400 g / mol or less, more preferably 1370 g / mol or less, more preferably 1330 g / mol or less, more preferably 1300 g / mol or less, more preferably 1200 g / mol or less, more preferably 1100 g / mol or less, more preferably 1000 g / mol or less, and even more preferably 950 g / mol or less. The weight average molecular weight of the resin can be determined by gel permeation chromatography (GPC) in terms of polystyrene.

[0118] The weight average molecular weight (Mw HR ) (unit: g / mol) vs. the softening point of the resin (Ts HR ) (unit: °C) ratio (Ts HR / Mw HR) is preferably 0.07 or more, more preferably 0.083 or more, more preferably 0.095 or more, more preferably 0.104 or more, more preferably 0.14 or more, and even more preferably 0.141 or more. HR / Mw HR ) is preferably 0.25 or less, and more preferably 0.23 or less.

[0119] As the resin, commercially available products can be used, and examples of commercially available resin products that can be used include products from ENEOS Corporation, Arakawa Chemical Industries, Ltd., ExxonMobil Corporation, Clayton, Yasuhara Chemical Co., Ltd., Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Clayton Polymers, Nippon Paint Chemical Co., Ltd., Nippon Shokubai Co., Ltd., and Taoka Chemical Co., Ltd.

[0120] The content of the resin is preferably 1 part by mass or more and 50 parts by mass or less relative to 100 parts by mass of the rubber component (A). When the content of the resin is 1 part by mass or more relative to 100 parts by mass of the rubber component (A), the effect of the resin is fully exhibited, and when it is 50 parts by mass or less, the resin is less likely to precipitate from the tire, and the effect of the resin can be fully exhibited. From the same viewpoint, the content of the resin relative to 100 parts by mass of the rubber component (A) is more preferably 5 parts by mass or more, even more preferably 7 parts by mass or more, even more preferably 9 parts by mass or more, and more preferably 45 parts by mass or less, and even more preferably 40 parts by mass or less.

[0121] (organic acid) The rubber composition of this embodiment may further contain an organic acid, particularly when the foaming agent is contained. The organic acid has the effect of improving the foaming rate of the vulcanized rubber by balancing the rate of the decomposition and foaming reaction of the foaming agent and the rate of the vulcanization reaction of the rubber composition during vulcanization of the rubber composition. Therefore, by blending the organic acid into the rubber composition, the workability of the rubber composition can be maintained good, while the decomposition and foaming reaction of the foaming agent can be promoted, and the rate of the decomposition and foaming reaction and the rate of the vulcanization reaction of the rubber composition can be balanced to improve the foaming rate of the vulcanized rubber. Then, by applying such a rubber composition to the tread of a tire, the performance on ice of the tire can be improved.

[0122] The organic acid may be a monocarboxylic acid, a dicarboxylic acid, a tricarboxylic acid, or the like, and may be aliphatic or aromatic. The organic acid may have a functional group other than a carboxyl group, such as a hydroxyl group, a ketone group, or an ethylenically unsaturated group. In particular, the organic acid is preferably one having an aromatic ring (aromatic), and is preferably a monocarboxylic acid. When the organic acid has an aromatic ring, the adhesion of the rubber composition can be further reduced, the workability of the rubber composition is further improved, and the rubber composition is further less likely to adhere to manufacturing equipment such as rolls. Benzoic acid is particularly preferred as such an organic acid.

[0123] The content of the organic acid is preferably 0.1 to 7 parts by mass per 100 parts by mass of the rubber component (A) from the viewpoints of workability of the rubber composition, foaming rate of the vulcanized rubber, and performance on ice of the tire. From the same viewpoints, the content of the organic acid is more preferably 1.5 parts by mass or more, and further preferably 3 parts by mass or more, per 100 parts by mass of the rubber component (A).

[0124] (Composite Fiber) The rubber composition of the present embodiment may further contain composite fibers. By containing the composite fibers, affinity with water can be sufficiently ensured, and drainage properties and performance on ice can be further improved.

[0125] The composite fiber is preferably made of a hydrophilic resin having a coating layer formed on the surface thereof. More specifically, examples of the hydrophilic resin include an ethylene-vinyl alcohol copolymer, a vinyl alcohol homopolymer, a poly(meth)acrylic acid resin or an ester resin thereof, a polyamide resin, a polyethylene glycol resin, a carboxyvinyl copolymer, a styrene-maleic acid copolymer, a polyvinylpyrrolidone resin, a vinylpyrrolidone-vinyl acetate copolymer, a polyester resin, and a cellulose-based resin.

[0126] The average length of the composite fibers is preferably 0.1 to 500 mm, more preferably 0.1 to 7 mm, and the average diameter is preferably 0.001 to 2 mm, more preferably 0.005 to 0.5 mm. When the average length and average diameter are within the above ranges, there is no risk of the composite fibers being unnecessarily entangled with each other, and there is no risk of impairing good dispersibility. The aspect ratio of the composite fibers is preferably 10 to 4,000, more preferably 50 to 2,000. The aspect ratio means the ratio of the major axis to the minor axis of the composite fiber.

[0127] The content of the composite fiber is preferably 0.1 to 100 parts by mass, more preferably 0.3 to 30 parts by mass, further preferably 0.5 to 10 parts by mass, and even more preferably 1 to 6 parts by mass, based on 100 parts by mass of the rubber component (A). When the content of the composite fiber is within the above range, cavities are formed inside the composite fiber, thereby exhibiting good drainage properties and maintaining sufficient durability.

[0128] (rubber powder) The rubber composition of the present embodiment may contain rubber powder. The rubber powder may be obtained by crushing used rubber products such as used tires, and removing reinforcing materials such as steel materials and fibers, dust, glass, sand, stones, etc., as desired, or by preparing a new vulcanized rubber composition to produce 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 the mechanical treatment, various crushing devices such as a cracker mill and a granulator can be used to mechanically crush the vulcanized rubber into fine particles. In the low-temperature treatment, the finely chopped vulcanized rubber is frozen at a very low temperature and then crushed into fine particles. In addition, a magnetic separator or the like can be used to remove steel materials, and an air separator or the like can be used to remove fibers. As the rubber powder, a commercially available product can be used, and examples of the commercially available rubber powder include products from Global Corporation or Nantong Huili Rubber Corporation. From the viewpoint of reducing the environmental load, 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 kinds.

[0129] The composition of the rubber powder is not particularly limited, and depends on the composition of vulcanized rubber such as used rubber products (used tires) that serve as a raw material. In one embodiment, the rubber powder contains a rubber component, carbon black, silica, etc. The rubber component, carbon black, silica, etc. contained in the rubber powder may be the same as or different from the rubber component, carbon black, silica, etc. contained in the rubber composition of the present embodiment described above.

[0130] The rubber powder has a volume average particle size of preferably 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. The smaller the volume average particle size of the rubber powder, the better, and there is no particular lower limit. In this specification, the volume average particle size is measured by a laser diffraction particle size distribution measuring device, for example, "CAPA500" manufactured by Horiba, Ltd.

[0131] The rubber powder has a 60 mesh sieve residue of preferably less than 1 mass%, more preferably 0.5 mass% or less, and even more preferably 0.1 mass% or less, with no particular lower limit. Also, the rubber powder has an 80 mesh sieve residue of preferably less than 10 mass%, more preferably 1 mass% or less, and even more preferably 0.5 mass% or less, with no particular lower limit. In this specification, the sieve residue is measured in accordance with ASTM D5644-01.

[0132] The rubber powder has an acetone extractable content of preferably 12% by mass or less, more preferably 11% by mass or less, and 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 extractables in the rubber powder refer to the acetone extractables (%) determined by the acetone extraction method in accordance with JIS K6350.

[0133] The content of the rubber powder is not particularly limited, and can be appropriately adjusted depending on, for example, the target performance of the tire to which the rubber powder is applied. For example, the content of the rubber powder is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and even more preferably 3 parts by mass or more, and is 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, relative to 100 parts by mass of the rubber component (A).

[0134] (liquid softener) The rubber composition of the present embodiment may contain a liquid softener. Here, the "liquid softener" is a compounding agent that is liquid at 25°C (room temperature) and has the effect of softening the rubber composition. The liquid softener is not particularly limited, and examples thereof include oil and liquid polymer, among which oil is preferable. These liquid softeners may be used alone or in combination of two or more.

[0135] The oil is a general term for the extender oil contained in the rubber component and the liquid oil added as a compounding agent of the rubber composition, and examples thereof include vegetable oil, process oil, oil obtained by recycling vegetable oil or process oil, or a mixture thereof. From the viewpoint of reducing the environmental load, the oil is preferably vegetable oil or oil obtained by recycling. Examples of the vegetable oil 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, coconut oil, etc. Examples of the process oil include paraffin-based process oil, aromatic process oil, naphthene-based process oil, etc. The oil may be a commercially available product, and examples of the commercially available oil include products from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., ENEOS Corp., Orisoi Co., Ltd., H&R Corporation, Toyokuni Oil Mills Co., Ltd., and Nisshin Oillio Group Co., Ltd. These oils may be used alone or in combination of two or more.

[0136] The liquid polymer is preferably a liquid diene polymer. Examples of the liquid diene polymer include liquid styrene-butadiene copolymer (liquid SBR), liquid polybutadiene (liquid BR), liquid polyisoprene (liquid IR), liquid styrene-isoprene copolymer (liquid SIR), liquid styrene-butadiene-styrene block copolymer (liquid SBS block polymer), liquid styrene-isoprene-styrene block copolymer (liquid SIS block polymer), liquid polyfarnesene, and liquid farnesene-butadiene copolymer. These liquid polymers may be hydrogenated, or the terminals or main chains may be modified with functional groups (polar groups). These liquid polymers may be used alone or in combination of two or more.

[0137] The content of the liquid softener is not particularly limited, and can be appropriately adjusted depending on, for example, the target performance of the tire to which the liquid softener is applied. For example, the content of the liquid softener is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and is preferably 100 parts by mass or less, more preferably 70 parts by mass or less, even more preferably 50 parts by mass or less, and even more preferably 30 parts by mass or less, relative to 100 parts by mass of the rubber component (A).

[0138] (Anti-aging agent) The rubber composition of the present embodiment may contain an antioxidant, such as N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine (77PD), N,N'-diphenyl-p-phenylenediamine (DPPD), N,N'-bis(1-ethyl-3-methylpentyl)-p-phenylenediamine, 2,2,4-trimethyl-1,2-dihydroquinoline polymer (TMDQ), 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline (AW), and 6-anilino-2,2,4-trimethyl-1,2-dihydroquinoline. As the antiaging agent, commercially available products can be used, and examples of the commercially available antiaging agent include products from Ouchi Shinko Chemical Industry Co., Ltd., Sumitomo Chemical Co., Ltd., Seiko Chemical Co., Ltd., Flexis Co., Ltd., etc. These antiaging agents may be used alone or in combination of two or more.

[0139] The content of the antiaging agent is not particularly limited, and can be appropriately adjusted depending on, for example, the target performance of the tire to which the antiaging agent is applied. For example, the content of the antiaging agent is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, and even more preferably 2 parts by mass or more, and is preferably 12 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 8 parts by mass or less, relative to 100 parts by mass of the rubber component (A).

[0140] (wax) The rubber composition of the present embodiment may contain a wax. Examples of the wax include natural waxes such as vegetable wax and animal wax; petroleum waxes such as paraffin wax and microcrystalline wax; and synthetic waxes such as ethylene polymers and propylene polymers. Commercially available waxes can be used, and examples of the commercially available waxes include products from Seiko Chemical Co., Ltd., Nippon Seiro Co., Ltd., Ouchi Shinko Chemical Co., Ltd., and the like. These waxes may be used alone or in combination of two or more.

[0141] The content of the wax is not particularly limited and can be appropriately adjusted depending on, for example, the target performance of the tire to which the rubber component (A) is applied. For example, the content of the wax is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and is preferably 10 parts by mass or less, more preferably 6 parts by mass or less, based on 100 parts by mass of the rubber component (A).

[0142] (Stearic acid) The rubber composition of the present embodiment may contain stearic acid. Commercially available stearic acid may be used, and examples of the commercially available stearic acid include products from NOF Corp., Kao Corp., Fujifilm Wako Pure Chemical Corp., Chiba Fatty Acid Corp., etc. These commercially available stearic acid products may be used alone or in combination of two or more.

[0143] The content of the stearic acid is not particularly limited and can be appropriately adjusted depending on, for example, the target performance of the tire to which the composition is applied, etc. For example, the content of the stearic acid is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 6 parts by mass or less, relative to 100 parts by mass of the rubber component (A).

[0144] (Zinc Oxide) The rubber composition of the present embodiment may contain zinc oxide (zinc white). The zinc oxide is preferably zinc oxide obtained by recycling. Commercially available zinc oxide may be used, and examples of the commercially available zinc oxide include products from Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., and the like. These commercially available zinc oxide products may be used alone or in combination of two or more. The zinc used for the zinc oxide may be not only zinc bullion, but also zinc obtained from recycled zinc or zinc dross.

[0145] The content of the zinc oxide is not particularly limited, and can be appropriately adjusted depending on, for example, the target performance of the tire to which the composition is applied, etc. For example, the content of the zinc oxide is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 6 parts by mass or less, relative to 100 parts by mass of the rubber component (A).

[0146] (sulfur) The rubber composition of the present embodiment preferably contains sulfur. The sulfur may be derived from fossil resources, recycled resources, or materials derived from biological resources. From the viewpoint of reducing the environmental load, it is particularly preferable to use sulfur obtained from waste derived from biological resources. Examples of a method for obtaining sulfur from waste derived from biological resources include the method described in the above-mentioned Japanese Patent Application No. 2022-140390. In addition, the sulfur may be powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, soluble sulfur, etc., which are generally used as crosslinking agents in the rubber industry. As the sulfur, commercially available products can be used, and examples of commercially available sulfur products include products from Tsurumi Chemical Industry Co., Ltd., Hosoi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Chemical Industry Co., Ltd., Flexis Co., Ltd., etc. These sulfurs may be used alone or in combination of two or more types.

[0147] The sulfur content is not particularly limited, and can be appropriately adjusted depending on, for example, the target performance of the tire to which the rubber component (A) is applied. For example, the sulfur content is preferably 0.3 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 0.8 parts by mass or more, and is preferably 8 parts by mass or less, and more preferably 5 parts by mass or less, relative to 100 parts by mass of the rubber component (A).

[0148] (Vulcanization accelerator) The rubber composition of the present embodiment preferably contains a vulcanization accelerator. The vulcanization accelerator may be derived from fossil resources, recycled resources, or biological resources, but is preferably derived from biological resources from the viewpoint of reducing environmental load. The vulcanization accelerator derived from biological resources can be obtained by the method disclosed in, for example, JP-A-2005-139239. Examples of the vulcanization accelerator include sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N,N-dicyclohexyl-2-benzothiazolylsulfenamide, N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-oxyethylene-2-benzothiazolesulfenamide, and N,N'-diisopropyl-2-benzothiazolesulfenamide; 1,3-diphenylguanidine (DPG), 1,3-diphenylguanidine (DPG), and 1,3-diphenylguanidine (DPG). Examples of the vulcanization accelerator include guanidine-based vulcanization accelerators such as o-tolylguanidine and o-tolylbiguanidine; thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole (M) and di-2-benzothiazolyl disulfide (MBTS, DM); and thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide (TMTD), tetrastearylthiuram disulfide, tetrabenzylthiuram disulfide (TBzTD), and tetrakis(2-ethylhexyl)thiuram disulfide (TOT-N). Commercially available products can be used as the vulcanization accelerator, and examples of the commercially available vulcanization accelerators include products from Ouchi Shinko Chemical Industry Co., Ltd. and Sumitomo Chemical Co., Ltd. These vulcanization accelerators may be used alone or in combination of two or more.

[0149] The content of the vulcanization accelerator is not particularly limited, and can be appropriately adjusted depending on, for example, the target performance of the tire to which the vulcanization accelerator is applied. For example, the content of the vulcanization accelerator is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and even more preferably 3 parts by mass or more, and is preferably 8 parts by mass or less, more preferably 6 parts by mass or less, and even more preferably 5.5 parts by mass or less, relative to 100 parts by mass of the rubber component (A).

[0150] (Cellulose nanofiber) The rubber composition of the present embodiment may contain cellulose nanofibers (CNF). The cellulose nanofibers can reinforce the rubber composition by blending them with the rubber composition. The cellulose nanofibers are preferably modified cellulose nanofibers, which are fine fibers made from modified cellulose. The fiber diameter of the cellulose nanofibers is not particularly limited, but is about 3 to 500 nm. The average fiber diameter and average fiber length of the cellulose nanofibers can be obtained by averaging the fiber diameters and fiber lengths obtained from the results of observing each fiber using a scanning electron microscope (SEM), an atomic force microscope (AFM), or a transmission electron microscope (TEM). The cellulose nanofibers can be obtained by defibrating cellulose. The average fiber length and average fiber diameter of the fine fibers can be adjusted by oxidation treatment and defibration treatment.

[0151] The raw material for the cellulose nanofibers is not particularly limited as long as it contains cellulose, and examples thereof include plants (e.g., wood, bamboo, hemp, jute, kenaf, agricultural waste, cloth, pulp (softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), hardwood bleached kraft pulp (LBKP), bleached kraft pulp (BKP), softwood unbleached sulfite pulp (NUSP), softwood bleached sulfite pulp (NBSP), thermomechanical pulp (TMP), recycled pulp, waste paper, etc.), animals (e.g., ascidians), algae, microorganisms (e.g., acetic acid bacteria (Acetobacter)), microbial products, etc. These cellulose raw materials may be used alone or in combination of two or more.

[0152] The content of the cellulose nanofibers is not particularly limited and can be appropriately adjusted depending on, for example, the target performance of the tire to which the cellulose nanofibers are applied, etc. For example, the content of the cellulose nanofibers is preferably in the range of 1 to 100 parts by mass, more preferably in the range of 5 to 70 parts by weight, and even more preferably in the range of 10 to 40 parts by mass, relative to 100 parts by mass of the rubber component (A).

[0153] (solid fine particles) The rubber composition of the present embodiment may contain solid fine particles. The solid fine particles can improve the performance on ice by blending them with the rubber composition. The solid fine particles preferably have an average particle diameter of 1 μm or more, and more preferably 1000 μm or less, and more preferably 300 μm or less. Examples of the solid fine particles include powders derived from plants such as rice husks, walnut powder, and walnut shells; powders derived from animals such as eggshells (eggshell powder) and bone powder; powders derived from natural minerals such as whitebait; inorganic fine particles such as graphite and zinc oxide whiskers; water-soluble metal salt fine particles such as magnesium sulfate and metal salts of lignin sulfonate; non-metallic fibers such as glass fibers; and the like. Among these, rice husks, walnut shells, eggshells, and whitebait are preferred.

[0154] The content of the solid fine particles is not particularly limited, and can be appropriately adjusted depending on, for example, the target performance of the tire to which the rubber component (A) is applied. For example, the content of the solid fine particles is preferably in the range of 0.3 to 20 parts by mass, more preferably in the range of 1 to 15 parts by weight, and further preferably in the range of 3 to 15 parts by mass, relative to 100 parts by mass of the rubber component (A).

[0155] (others) In addition to the above-mentioned components, the rubber composition of the present embodiment may further contain various additives commonly used in the tire industry, such as organic peroxides, etc. The content of these additives is not particularly limited and can be appropriately adjusted depending on, for example, the target performance of the tire to which the composition is applied, and is preferably in the range of 0.1 to 200 parts by mass per 100 parts by mass of the rubber component.

[0156] (Method of producing rubber composition (tread rubber)) The method for producing the rubber composition of the present embodiment is not particularly limited, but for example, the rubber composition can be produced by blending the rubber component (A) with the carbon black (B) and various other components appropriately selected as necessary, and kneading, heating, extruding, etc. The obtained rubber composition can be vulcanized to produce a vulcanized rubber.

[0157] The conditions for the kneading are not particularly limited, and various conditions such as the input volume of the kneading device, the rotation speed of the rotor, the ram pressure, the kneading temperature, the kneading time, the type of the kneading device, etc. can be appropriately selected depending on the purpose. Examples of the kneading device include a Banbury mixer, an intermix, a kneader, a roll, etc. that are usually used for kneading rubber compositions.

[0158] The conditions of the heat-in are not particularly limited, and various conditions such as the heat-in temperature, heat-in time, heat-in equipment, etc. can be appropriately selected depending on the purpose. Examples of the heat-in equipment include a heat-in roller machine usually used for heat-in of a rubber composition.

[0159] The extrusion conditions are not particularly limited, and various conditions such as extrusion time, extrusion speed, extrusion device, and extrusion temperature can be appropriately selected depending on the purpose. Examples of the extrusion device include an extruder that is usually used for extruding a rubber composition. The extrusion temperature can be appropriately determined.

[0160] The vulcanization apparatus, method, conditions, etc. are not particularly limited and can be appropriately selected according to the purpose. As the vulcanization apparatus, a molding vulcanizer using a mold used for vulcanizing a rubber composition can be mentioned. As the vulcanization condition, the temperature is, for example, about 100 to 190°C.

[0161] The method of providing voids in the tread rubber is not particularly limited. The voids can be formed using known techniques depending on the conditions of the voids and the equipment for producing the tread rubber or rubber composition. For example, a method of providing voids in the vulcanized rubber composition (tread rubber) by blending a void-introducing agent (C) such as the foaming agent in the rubber composition before vulcanization can be mentioned. The void ratio can be controlled by changing the vulcanization conditions, or by changing the content of the void-introducing agent (C) such as the foaming agent and the foaming assistant. Furthermore, as a method of providing the voids, a technique can be used in which a solid material such as the metal sulfate, rubber powder, solid fine particles, etc. described above is blended in the rubber composition before vulcanization, so that the solid material falls off from the surface of the rubber composition after vulcanization, forming voids in the vicinity of the surface of the rubber composition (tread rubber). In this case, the size of the voids, the void ratio, etc. can be controlled by adjusting the particle size and number of the solid material.

[0162] <Tires> A tire according to one embodiment of the present invention (hereinafter, sometimes referred to as "the tire according to the present embodiment") is characterized in that the tread rubber according to the present embodiment described above is used in the tread portion. In other words, the tire according to the present embodiment is characterized in that the tread portion is provided with the tread rubber according to the present embodiment described above. By using the tread rubber according to the present embodiment, the tire obtained is excellent in performance on ice and can contribute to improving sustainability.

[0163] The tire of this embodiment can be manufactured by a normal method by applying the above-mentioned rubber composition to the tread portion. For example, the tire of this embodiment may be obtained by molding an unvulcanized rubber composition and then vulcanizing it, or by molding a semi-vulcanized rubber that has been subjected to a pre-vulcanization process or the like and then further vulcanizing it, depending on the type of tire to be applied. The tire of this embodiment is preferably a pneumatic tire, and the gas to be filled in the pneumatic tire may be normal air or air with an adjusted oxygen partial pressure, or an inert gas such as nitrogen, argon, or helium.

[0164] The tire of the present embodiment can be used, for example, as a construction vehicle tire, a truck / bus tire, an aircraft tire, or a passenger car tire, and is preferably a passenger car tire or a truck / bus tire in view of the advantage of excellent performance on ice. EXAMPLES

[0165] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples and can be modified as appropriate without departing from the gist of the present invention.

[0166] A rubber composition is prepared by compounding and kneading in the usual manner according to the composition shown in Table 1. In Table 1, the rubber component, silica, carbon black, resin component, and liquid softener component are expressed as integers, and the others are expressed to one decimal place. Each rubber composition obtained is subjected to a vulcanization treatment to prepare a rubber sample corresponding to the tread rubber. Note that multiple voids are formed in each rubber sample. The sustainability rate is evaluated by calculating the total mass ratio of the components derived from biological resources (biomass resources) and the components derived from recycled resources (recycled resources) for the prepared rubber samples. The results are shown in Table 1.

[0167] [Table 1]

[0168] *1 Butadiene rubber: "UBEPOL BR150L" manufactured by Ube Industries, Ltd. *2 Styrene-butadiene rubber: Solution polymerization SBR, manufactured by JSR Corporation, "JSR HPR540" *3 Virgin carbon black: SAF-class carbon black, manufactured by Showa Cabot Corporation, "Show Black N134" *4 Recycled carbon black: Enrestec, product name "PB365", ash content = 17% by mass *5 Silica: Tosoh Silica Industries Co., Ltd., product name "Nipsil AQ" *6 Liquid softener: Contains at least an oil component *7 Resin: Hydrogenated C5 resin, manufactured by Eastman Co., Ltd., trade name "Registered trademark Impera E1780", softening point = 130°C, weight average molecular weight (Mw) = 909g / mol, SP value = 8.35 (cal / cm 3 ) 1 / 2 *8 Silane coupling agent: Bis(3-triethoxysilylpropyl) polysulfide, manufactured by Shin-Etsu Chemical Co., Ltd. *9 Anti-aging agent: Product name "Nocrac 6C" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. *10 Foaming chemicals: total content of sodium bicarbonate and urea *11 Vulcanization accelerator: The total amount of CZ-based vulcanization accelerators and DM-based vulcanization accelerators *12 Other chemicals: Additives other than those listed in the table

[0169] From Table 1, it can be seen that the rubber sample of Example 1 has a higher sustainability rate than the rubber sample of Comparative Example 1, and can contribute to improving sustainability. [Industrial Applicability]

[0170] According to the present invention, it is possible to provide a tread rubber that can contribute to improving sustainability. Furthermore, according to the present invention, it is possible to provide a tire that uses such a tread rubber and that can contribute to improving sustainability.

Claims

1. A tread rubber using a rubber composition containing a rubber component (A) and carbon black (B), The carbon black (B) comprises recycled carbon black, A tread rubber having a plurality of voids formed therein.

2. The tread rubber according to claim 1 , wherein the rubber composition further contains a void-introducing agent (C).

3. The tread rubber according to claim 2, wherein the void-introducing agent (C) is a foaming agent.

4. 4. The tread rubber of claim 3, wherein said foaming agent is sodium bicarbonate.

5. The tread rubber according to any one of claims 1 to 4, wherein the recycled carbon black is obtained by pyrolysis of a vulcanized rubber product containing carbon black.

6. The tread rubber according to any one of claims 1 to 4, wherein the recycled carbon black has an ash content of 20 mass% or less.

7. The tread rubber according to any one of claims 1 to 4, wherein the proportion of the recycled carbon black in the carbon black (B) is 50 mass% or more.

8. A tire, comprising a tread rubber according to any one of claims 1 to 4 in a tread portion.

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