Rubber composition for studless tire tread, tread rubber, and studless tire

Abstract

To provide a rubber composition for a studless tire tread which can improve the ratio of sustainable materials while improving on-ice performance of a studless tire.SOLUTION: The rubber composition for a studless tire tread contains a rubber component (A), at least one resin component (B) selected from the group consisting of terpene-based resins and rosin-based resins, and an acrylic resin (C) having a weight average molecular weight (Mw) of 1,000 or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a rubber composition for a tread of a studless tire, a tread rubber, and a studless tire. [Background technology]

[0002] In general, high performance on ice is required for the rubber composition for the tread of a studless tire. For example, by using a rubber composition with high hysteresis loss (tan δ) containing a resin component such as a petroleum resin as the tread rubber of a studless tire, the performance on ice of the studless tire can be improved.

[0003] Meanwhile, in recent years, from the perspective of social sustainability, there has been a demand to use sustainable materials, such as materials derived from biological resources (biomass resources) and materials derived from renewable resources (recycled resources), for the various components used in studless tires, and there is also a demand to increase the proportion of sustainable materials in the rubber compositions for the treads of the above-mentioned studless tires. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-206653 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, simply replacing the fossil resource-derived materials currently used in the rubber composition for the tread of studless tires with sustainable materials in order to increase the proportion of sustainable materials in studless tires would reduce hysteresis loss and could result in a decline in the performance of the studless tires on ice.

[0006] Therefore, an object of the present invention is to provide a rubber composition for the tread of a studless tire that can improve the performance on ice of the studless tire while increasing the proportion of sustainable materials, and a tread rubber using such a rubber composition. Another object of the present invention is to provide a studless tire that has improved performance on ice and a high ratio of sustainable materials. [Means for solving the problem]

[0007] The rubber composition for a tread of a studless tire, the tread rubber, and the studless tire of the present invention, which solve the above problems, are outlined as follows.

[0008] [1] A rubber component (A), At least one resin component (B) selected from the group consisting of terpene-based resins and rosin-based resins; and an acrylic resin (C) having a weight average molecular weight (Mw) of 1,000 or more. The rubber composition for treads of studless tires of the present invention described in [1] above can improve the performance of studless tires on ice while increasing the proportion of sustainable materials.

[0009] [2] The rubber composition for studless tire treads according to [1], wherein the content of the resin component (B) is 0.5 to 30 parts by mass per 100 parts by mass of the rubber component (A). The rubber composition for treads of studless tires described in [2] above can improve the performance on ice, fracture resistance, abrasion resistance, etc. of studless tires.

[0010] [3] The rubber composition for studless tire treads according to [1] or [2], wherein the rubber component (A) contains an isoprene skeleton rubber. The rubber composition for treads of studless tires described in [3] above can increase the breaking strength of the tread rubber of studless tires.

[0011] [4] The resin component (B) has an SP value difference from the isoprene skeleton rubber of 0.6 (cal / cm 3 ) 1 / 2 The rubber composition for a tread of a studless tire according to [3] below. The rubber composition for treads of studless tires described in [4] above has excellent fracture resistance.

[0012] [5] A tread rubber comprising the rubber composition for a tread of a studless tire according to any one of [1] to [4]. The tread rubber of the present invention described in [5] above can improve the performance of studless tires on ice while increasing the proportion of sustainable materials.

[0013] [6] A studless tire comprising the tread rubber described in [5]. The studless tire of the present invention described in [6] above has improved performance on ice and a higher proportion of sustainable materials. Effect of the Invention

[0014] According to the present invention, it is possible to provide a rubber composition for the tread of a studless tire that can improve the performance on ice of the studless tire while increasing the proportion of sustainable materials, and a tread rubber using such a rubber composition. Furthermore, according to the present invention, it is possible to provide a studless tire that has improved performance on ice and a high ratio of sustainable materials. [Brief description of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view of one embodiment of a tire of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The rubber composition for treads of studless tires, the tread rubber, and the studless tires of the present invention will be illustrated in detail below based on the embodiments.

[0017] <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.

[0018] In this specification, the "proportion of sustainable materials" refers to the total mass ratio of materials derived from biological resources (biomass resources) and materials derived from renewable resources (recycled resources) in the rubber composition for the tread of the target studless tire, the tread rubber, and the studless tire.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] <Rubber composition for tread of studless tires> The rubber composition for studless tire treads of this embodiment is characterized by including a rubber component (A), at least one resin component (B) selected from the group consisting of terpene resins and rosin resins, and an acrylic resin (C) having a weight average molecular weight (Mw) of 1,000 or more.

[0023] Conventionally, a rubber composition for tread rubber of a studless tire may contain a resin component such as a petroleum resin in order to improve hysteresis loss (tan δ). In contrast, in the rubber composition for tread rubber of a studless tire of this embodiment, at least one resin component (B) selected from the group consisting of terpene resins and rosin resins is compounded in order to improve hysteresis loss (tan δ). In the rubber composition for tread rubber of a studless tire of this embodiment, since the terpene resin and the rosin resin are materials derived from biological resources (biomass resources), by compounding at least one resin component (B) selected from the group consisting of terpene resins and rosin resins in the rubber composition for tread rubber of a studless tire, the ratio of sustainable materials in the tread rubber and the studless tire to which the rubber composition is applied can be increased. The rubber composition for studless tire tread of this embodiment contains at least one resin component (B) selected from the group consisting of terpene resins and rosin resins, and also contains an acrylic resin (C) having a weight average molecular weight (Mw) of 1,000 or more. Terpene resins and rosin resins have polar groups, and therefore are more compatible with the acrylic resin (C) than commonly used petroleum resins. The high compatibility between the resin component (B) selected from the terpene resins and rosin resins and the acrylic resin (C) further increases the hysteresis loss (tan δ) of the rubber composition, and the application of the rubber composition to the tread rubber of a studless tire improves the performance on ice of the studless tire. The high compatibility between the resin component (B) selected from the terpene resins and rosin resins and the acrylic resin (C) can suppress changes in the physical properties of the rubber composition, and the effect of improving the performance on ice of a studless tire to which the rubber composition is applied to the tread rubber can be maintained for a long period of time. Therefore, according to the rubber composition for treads of studless tires of this embodiment, it is possible to improve the performance on ice of studless tires while increasing the proportion of sustainable materials.

[0024] (Rubber component (A)) The rubber composition for studless tire tread of this 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. Here, the "sustainability rate" of the rubber component (A) refers to the total mass ratio of components derived from biological resources (biomass resources) and components derived from recycled resources (recycled resources) in the rubber component (A).

[0025] As the rubber component (A), the rubber derived from biological resources and the rubber derived from recycled resources are preferred. 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%.

[0026] 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).

[0027] 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.

[0028] 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.

[0029] 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.).

[0030] The rubber component (A) preferably contains an isoprene skeleton rubber. The isoprene skeleton rubber is a rubber whose main skeleton is an isoprene unit, and specific examples thereof include the above-mentioned natural rubber (NR), synthetic isoprene rubber (IR), modified natural rubber (modified NR), modified natural rubber (modified NR), and modified synthetic isoprene rubber (modified IR). When the rubber component (A) contains an isoprene skeleton rubber, the breaking strength of the tread rubber of a studless tire can be increased. As a result, the breaking resistance of a studless tire having the tread rubber can be improved.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.").

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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. 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 unit derived from butadiene can also be adjusted appropriately. 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.

[0039] 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.

[0040] The rubber component (A) 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 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.

[0041] 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, 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] (Resin component (B)) The rubber composition for studless tire tread of this embodiment contains at least one resin component (B) selected from the group consisting of terpene resins and rosin resins. As described above, by blending the terpene resin and / or rosin resin into the rubber composition for studless tire tread, the hysteresis loss (tan δ) of the rubber composition can be improved, and by combining with the acrylic resin (C), the hysteresis loss (tan δ) of the rubber composition becomes even larger, and by applying the rubber composition to the tread rubber of a studless tire, the performance on ice of the studless tire is improved. In addition, since the terpene resin and the rosin resin are naturally derived sustainable resins, by blending the terpene resin and / or rosin resin into the rubber composition for studless tire tread, the ratio of sustainable materials in the tread rubber and studless tire to which the rubber composition is applied can be improved, and the environmental load can be further reduced.

[0047] The resin component (B) may be hydrogenated, i.e., may be a hydrogenated resin (hydrogenated resin). In addition, the resin component (B) 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.

[0048] 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.

[0049] 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.

[0050] The softening point of the resin component (B) 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 component (B) 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 component 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.

[0051] As the resin component (B), commercially available products can be used. Examples of commercially available products of the resin component (B) that can be used include products from Arakawa Chemical Industries, Ltd., Clayton Corporation, Yasuhara Chemical Co., Ltd., Arizona Chemical Company, etc.

[0052] When the rubber component (A) contains an isoprene skeleton rubber, the resin component (B) has an SP value difference from the isoprene skeleton rubber of 0.6 (cal / cm 3 ) 1 / 2 It is preferable that the calorie content is 0.58 (cal / cm 3 ) 1 / 2 In the case where the rubber component (A) contains an isoprene skeleton rubber, the difference in SP value between the rubber component (A) and the isoprene skeleton rubber of the resin component (B) is 0.6 (cal / cm 3 ) 1 / 2 The following rubber composition for treads of studless tires has excellent fracture resistance due to high compatibility between the rubber component (A) and the resin component (B).

[0053] The content of the resin component (B) is preferably 0.5 to 30 parts by mass, more preferably 5 to 25 parts by mass, per 100 parts by mass of the rubber component (A). When the content of the resin component (B) is 0.5 parts by mass or more per 100 parts by mass of the rubber component (A), the hysteresis loss of the rubber composition becomes larger, and the performance on ice of a studless tire in which the rubber composition is applied to the tread rubber is further improved. When the content of the resin component (B) is 30 parts by mass or less per 100 parts by mass of the rubber component (A), the fracture resistance, abrasion resistance, etc. of the studless tire in which the rubber composition is applied are improved. Therefore, the rubber composition for the tread of a studless tire in which the content of the resin component (B) is 0.5 to 30 parts by mass per 100 parts by mass of the rubber component (A) can improve the performance on ice, fracture resistance, abrasion resistance, etc. of the studless tire.

[0054] (Acrylic resin (C)) The rubber composition for studless tire tread of this embodiment contains an acrylic resin (C) having a weight-average molecular weight (Mw) of 1,000 or more. The acrylic resin (C) having a weight-average molecular weight (Mw) of 1,000 or more has good compatibility with the above-mentioned terpene-based resin and rosin-based resin, and therefore can improve the hysteresis loss (tan δ) of the rubber composition, and also contributes to improving the on-ice performance of a studless tire in which the rubber composition is used as a tread rubber.

[0055] The acrylic resin (C) is a resin obtained by polymerization of an acrylic monomer such as acrylic acid, methacrylic acid, or a derivative thereof (acrylic acid ester, methacrylic acid ester, etc.). The main chain of the acrylic resin (C) may be an all-acrylic type main chain obtained by polymerization of an acrylic monomer such as acrylic acid, methacrylic acid, or a derivative thereof, or a styrene-acrylic type main chain obtained by copolymerization of an acrylic monomer with a styrene monomer such as styrene, α-methylstyrene, p-methylstyrene, or vinyltoluene. In one embodiment, the main chain of the acrylic resin (C) is an all-acrylic type main chain.

[0056] The acrylic resin (C) may be an unmodified acrylic resin (an acrylic resin containing no functional group) or a modified acrylic resin (an acrylic resin containing a functional group).

[0057] Examples of the functional group contained in the modified acrylic resin include a hydroxyl group, a carboxyl group, an epoxy group, a long-chain alkyl group, an alkoxysilyl group, and combinations thereof. Examples of the long-chain alkyl group include an alkyl group having 8 to 30 carbon atoms. Examples of the alkoxy of the alkoxysilyl group include methoxy and ethoxy. The alkoxysilyl group may be any one of a trialkoxysilyl group, a dialkoxysilyl group, and a monoalkoxysilyl group.

[0058] The weight average molecular weight (Mw) of the acrylic resin (C) may be 1,000 or more, and is, for example, 2,000 or more, 3,000 or more, 4,000 or more, 5,000 or more, 6,000 or more, 7,000 or more, 8,000 or more, 9,000 or more, or 10,000 or more. The weight average molecular weight (Mw) of the acrylic resin (C) is, for example, 30,000 or less, 20,000 or less, 15,000 or less, 10,000 or less, 9,000 or less, 8,000 or less, 7,000 or less, 6,000 or less, 5,000 or less, 4,000 or less, or 3,000 or less. In this specification, the weight average molecular weight (Mw) of the acrylic resin (C) can be determined, for example, by converting the weight average molecular weight (Mw) into standard polystyrene based on a measurement value obtained using a gel permeation chromatograph (GPC) (GPC-8000 series, manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M, manufactured by Tosoh Corporation).

[0059] The form of the acrylic resin (C) is not particularly limited, and may be, for example, any of liquid, solid, powder, flake, etc. In one embodiment, the acrylic resin (C) is a liquid polymer.

[0060] The acrylic resin (C) may be a commercially available product. Examples of commercially available acrylic resins (C) include ARUFON (registered trademark) series, such as non-functional acrylic polymer "UP-1000" series, hydroxyl group-containing acrylic polymer "UH-2000" series, carboxyl group-containing acrylic polymer "UC-3000" series, epoxy group-containing acrylic polymer "UG-4000" series, long-chain alkyl group-containing acrylic polymer "UF-5000" series, and alkoxysilyl group-containing acrylic polymer "US-6000" series, all of which are manufactured by Toagosei Co., Ltd. The acrylic resin (C) may be used alone or in combination of two or more kinds.

[0061] The content of the acrylic resin (C) may be appropriately adjusted and may be, for example, 1 part by mass or more, 2 parts by mass or more, 5 parts by mass or more, 10 parts by mass or more, 15 parts by mass or more, 20 parts by mass or more, 30 parts by mass or more, 40 parts by mass or more, or 50 parts by mass or more, relative to 100 parts by mass of the rubber component (A). Also, for example, the content of the acrylic resin (C) may be 60 parts by mass or less, 50 parts by mass or less, 40 parts by mass or less, 30 parts by mass or less, 20 parts by mass or less, 10 parts by mass or less, 5 parts by mass or less, or 1 part by mass or less, relative to 100 parts by mass of the rubber component (A).

[0062] (Other resin components) The rubber composition for tread of studless tires of this embodiment may contain resin components other than the above-mentioned terpene resin, rosin resin, and acrylic resin. Examples of the other resin components include C5 resin, C5-C9 resin, C9 resin, cyclopentadiene resin, aromatic resin, coumarone resin, indene resin, coumarone-indene resin, olefin resin, polyurethane resin, etc. These other resin components may be used alone or in combination of two or more.

[0063] The other resin components may be hydrogenated, i.e., may be hydrogenated resins (hydrogenated resins). In addition, functional groups that interact with fillers such as carbon black and silica may be introduced into the resins by modification. Examples of the functional groups include amino groups, amide groups, isocyanate groups, imino groups, imidazole groups, urea groups, ammonium groups, imide groups, hydrazo groups, azo groups, diazo groups, carboxyl groups, nitrile groups, pyridyl groups, alkoxy groups, hydroxyl groups, oxy groups, epoxy groups, ether groups, carbonyl groups, oxycarbonyl groups, silyl groups, alkoxysilyl groups, mercapto groups, sulfide groups, disulfide groups, sulfonyl groups, sulfinyl groups, and thiocarbonyl groups.

[0064] 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.

[0065] The C5-C9 resin refers to a C5-C9 synthetic petroleum resin. Examples of the C5-C9 resin include petroleum-derived C5-C 11 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.

[0066] 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.

[0067] 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.).

[0068] 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.

[0069] The other resin components preferably have a softening point of 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 resin preferably has a softening point of 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.

[0070] As the other resin components, commercially available products can be used. 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.

[0071] The content of the other resin components is not particularly limited, and can be appropriately adjusted depending on, for example, the tire category to which the rubber composition is applied, the target performance, etc. For example, the content of the other resin components is preferably in the range of 5 to 100 parts by mass, and more preferably in the range of 10 to 60 parts by mass, relative to 100 parts by mass of the rubber component (A).

[0072] (silica) The rubber composition for tread of studless tires of this embodiment may contain silica. 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, commercially available products may be used, and examples of the commercially available silica products include products from Tosoh Silica Corporation, Evonik, Solvay, Solvay Japan, Tokuyama Corporation, etc.

[0073] 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. From the viewpoint of reducing the environmental load, it is also preferable to use, as the silica, silica obtained by extracting silicic acid components from scraps of silicon wafers, which are the raw material for semiconductors, glass bottles, etc., and recycling the extracted silica for use in the production.

[0074] 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, and 2 / 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.

[0075] The content of the silica can be appropriately adjusted depending on, for example, the tire category to which the rubber composition is applied, the target performance, etc. For example, the content of the silica is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, more preferably 30 parts by mass or more, more preferably 50 parts by mass or more, more preferably 70 parts by mass or more, even more preferably 80 parts by mass or more, still more preferably 100 parts by mass or more, particularly preferably 110 parts by mass or more, and is preferably 300 parts by mass or less, more preferably 200 parts by mass or less, even more preferably 180 parts by mass or less, and particularly preferably 150 parts by mass or less, relative to 100 parts by mass of the rubber component.

[0076] (Silane coupling agent) When the rubber composition for tread of the studless tire of the present embodiment contains silica, in order to improve the effect of the silica, the rubber composition preferably contains a silane coupling agent. The silane coupling agent is 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.

[0077] Bioethanol can also be used as a raw material for the silane coupling agent. Bioethanol is produced mainly 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 ethanol (bioethanol) derived from biological resources as the raw material for the silane coupling agent, or to use ethanol (bioethanol) derived from biological resources, ethanol derived from renewable resources, and ethanol derived from fossil resources in combination, depending on the supply status of various biological resources, the supply status of renewable resources, the supply status of fossil resources, and market demands (for example, the demand for biomass resources as food). 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 also to consider the environment depending on the situation at the time of production.

[0078] The content of the silane coupling agent can be appropriately adjusted depending on, for example, the tire category to which it is applied, the target performance, etc. 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.

[0079] (Carbon Black) The rubber composition for tread of the studless tire of this embodiment preferably contains carbon black. As the carbon black, carbon black derived from plants and carbon black obtained by recycling (i.e., recycled carbon black) are particularly preferable. Examples of carbon black derived from plants include those derived from castor oil and rosin oil. Examples of recycled carbon black include carbon black obtained by decomposition (particularly thermal decomposition) of crosslinked rubber products such as used tires, and carbon black obtained from waste oil.

[0080] 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 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 recycled carbon black is blended again with the rubber component, a rubber composition with better performance is obtained.

[0081] In addition, when the crosslinked rubber product used for the decomposition is derived from a tire, the tire 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 step may be performed for each group. In addition, the tire 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 step may be performed for each group. Furthermore, the tire may be grouped by type and by tire components, 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, so that when it is blended again into the rubber component, a rubber composition with better performance is obtained.

[0082] The grade of the carbon black is not particularly limited, and examples thereof include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. Commercially available carbon blacks can be used, and examples of the commercially available carbon blacks 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., and Birla Carbon Co., Ltd. These carbon blacks may be used alone or in combination of two or more.

[0083] The nitrogen adsorption specific surface area (N2SA) of the carbon black is not particularly limited and can be appropriately adjusted depending on, for example, the tire category to which it is applied, the target performance, etc. For example, the nitrogen adsorption specific surface area (N2SA) of carbon black is 20 m 2 / g or more is preferable, and 50m 2 / g or more is more preferable, and 70m 2 / g or more is more preferable, and 90m 2 / g or more is more preferable, and 200m 2 / g or less is preferable, and 150m 2 / g or less is more preferable, and 130m 2 / g or less is more preferable. 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).

[0084] The content of the carbon black is not particularly limited, and can be appropriately adjusted depending on, for example, the tire category to which the rubber is applied, the target performance, etc. For example, the content of the carbon black is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the rubber component.

[0085] The proportion of silica in the total content of silica and carbon black is not particularly limited, and can be appropriately adjusted depending on, for example, the tire category to which it is applied, the target performance, etc. For example, in the case of tread rubber of studless tires for passenger cars, the proportion of silica in the total content of silica and carbon black is preferably 50% 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 95% by mass or more. In addition, the proportion of silica in the total content of silica and carbon black may be 100% by mass, but is preferably 98% by mass or less.

[0086] (rubber powder) The rubber composition for the tread of the studless tire of this 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.

[0087] 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. that may be contained in the rubber composition for tread of the studless tire of the present embodiment described above.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] The content of the rubber powder is not particularly limited, and can be appropriately adjusted depending on, for example, the tire category to which the rubber component (A) is applied, the target performance, etc. For example, the content of the rubber powder is preferably 1 part by mass or more, more preferably 2 parts by mass or more, 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).

[0092] (liquid softener) The rubber composition for studless tire tread of this 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 preferred. These liquid softeners may be used alone or in combination of two or more.

[0093] 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 Corporation, 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.

[0094] 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.

[0095] The content of the liquid softener is not particularly limited, and can be appropriately adjusted depending on, for example, the tire category to which the softener is applied, the target performance, etc. 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).

[0096] (Anti-aging agent) The rubber composition for tread of the studless tire 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.

[0097] The content of the antiaging agent is not particularly limited, and can be appropriately adjusted depending on, for example, the tire category to which the antiaging agent is applied, the target performance, etc. 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).

[0098] (wax) The rubber composition for tread of the studless tire of this embodiment may contain 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 products can be used as the wax, and examples of the commercially available wax products 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.

[0099] The content of the wax is not particularly limited, and can be appropriately adjusted depending on, for example, the tire category to which the rubber composition is applied, the target performance, etc. 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, relative to 100 parts by mass of the rubber component (A).

[0100] (Stearic acid) The rubber composition for studless tire tread of the present embodiment may contain stearic acid. As the stearic acid, a commercially available product can be used, and as the commercially available stearic acid, products of NOF Corp., Kao Corp., Fujifilm Wako Pure Chemical Corp., Chiba Fatty Acid Corp., etc. can be used. These commercially available stearic acid products may be used alone or in combination of two or more.

[0101] The content of the stearic acid is not particularly limited, and can be appropriately adjusted depending on, for example, the tire category to which the rubber composition is applied, the target performance, 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).

[0102] (Zinc Oxide) The rubber composition for tread of studless tires of this embodiment may contain zinc oxide (zinc white). As the zinc oxide, not only zinc metal but also zinc oxide obtained from recycled zinc or zinc dross (i.e., obtained by recycling) is preferable. As the zinc oxide, commercially available products can 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., etc. These commercially available zinc oxide products may be used alone or in combination of two or more.

[0103] The content of the zinc oxide is not particularly limited, and can be appropriately adjusted depending on, for example, the tire category to which the rubber composition is applied, the target performance, 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, per 100 parts by mass of the rubber component (A).

[0104] (sulfur) The rubber composition for the tread of the studless tire of this 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.

[0105] The sulfur content is not particularly limited, and can be appropriately adjusted depending on, for example, the tire category to which the rubber composition is applied, the target performance, etc. 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).

[0106] (Vulcanization accelerator) The rubber composition for tread of the studless tire 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, for example, by the method disclosed in 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.

[0107] The content of the vulcanization accelerator is not particularly limited, and can be appropriately adjusted depending on, for example, the tire category to which the rubber is applied, the target performance, etc. 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).

[0108] (Cellulose nanofiber) The rubber composition for studless tire tread of this 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.

[0109] 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.

[0110] The content of the cellulose nanofibers is not particularly limited, and can be appropriately adjusted depending on, for example, the tire category to which the rubber composition is applied, the target performance, 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).

[0111] (Porous cellulose particles) The rubber composition for studless tire treads of this embodiment may contain porous cellulose particles. The porous cellulose particles are preferably cellulose particles having a porous structure with a porosity of 75 to 95%, and by compounding them with a rubber composition, performance on ice can be improved. 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 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.

[0112] 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.

[0113] 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.

[0114] The content of the porous cellulose particles is not particularly limited, and can be appropriately adjusted depending on, for example, the tire category to which the rubber composition is applied, the target performance, etc. For example, 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 weight, and even more preferably in the range of 3 to 15 parts by mass, relative to 100 parts by mass of the rubber component (A).

[0115] (solid fine particles) The rubber composition for tread of studless tires of this 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, or 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.

[0116] The content of the solid fine particles is not particularly limited, and can be appropriately adjusted depending on, for example, the tire category to which the rubber composition is applied, the target performance, etc. 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).

[0117] (others) In addition to the above-mentioned components, the rubber composition for studless tire tread of this embodiment may further contain various additives commonly used in the tire industry, such as fillers such as calcium carbonate, talc, alumina, clay, aluminum hydroxide, mica, etc.; void-introducing agents such as foaming agents; organic peroxides; etc. The content of these additives is not particularly limited and can be appropriately adjusted depending on, for example, the tire category to which the composition is applied, the target performance, etc., and is preferably in the range of 0.1 to 200 parts by mass with respect to 100 parts by mass of the rubber component (A).

[0118] (Method of manufacturing rubber composition) The method for producing the rubber composition for studless tire treads of this embodiment is not particularly limited, but for example, the rubber composition can be produced by blending at least one resin component (B) selected from the group consisting of terpene resins and rosin resins, an acrylic resin (C) having a weight average molecular weight (Mw) of 1,000 or more, and various other components appropriately selected as necessary with the rubber component (A), followed by kneading, heating, extrusion, etc. The obtained rubber composition can be vulcanized to produce a vulcanized rubber.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] <Tread rubber> The tread rubber of this embodiment is characterized by being made of the above-mentioned rubber composition for treads of studless tires. Since the tread rubber of this embodiment is made of the above-mentioned rubber composition for studless tire treads, by applying it to studless tires, it is possible to improve the performance of the studless tires on ice while increasing the proportion of sustainable materials. The tread rubber of the present embodiment may be applied to a new tire or a retread tire.

[0124] <Studless tires> The studless tire of this embodiment is characterized by including the above-mentioned tread rubber. The studless tire of this embodiment includes the above-mentioned tread rubber, and therefore has improved performance on ice and a higher proportion of sustainable materials.

[0125] Next, one embodiment of a studless tire of the present invention will be described in detail with reference to the drawings. Fig. 1 is a cross-sectional view of one embodiment of a studless tire of the present invention. The studless tire 1 of this embodiment shown in Fig. 1 has a pair of bead portions 2, a pair of sidewall portions 3, and a tread portion 4 connected to both sidewall portions 3, and is equipped with a carcass 5 that extends in a toroidal shape between the pair of bead portions 2 and reinforces these portions 2, 3, 4, and a belt 6 that is disposed on the outer side of the crown portion of the carcass 5 in the tire radial direction.

[0126] The carcass 5 of the studless tire 1 shown in FIG. 1 is composed of one carcass ply made of a plurality of parallel-arranged cords covered with a coating rubber, and the carcass 5 is composed of a main body portion extending in a toroidal shape between the bead cores 7 respectively embedded in the bead portion 2, and a folded-up portion wound up radially outward around each bead core 7 from the inner side toward the outer side in the tire width direction; however, in the studless tire of the present invention, the number of plies and the structure of the carcass 5 are not limited to this.

[0127] 1 is composed of two belt layers 6A, 6B, but in the studless tire of the present invention, the number of belt layers constituting the belt 6 is not limited to this, and the number of belt layers may be three or more. Here, the belt layers 6A, 6B are usually composed of rubberized layers of cords (preferably steel cords) extending at an angle to the tire equatorial plane, and the two belt layers 6A, 6B are laminated to constitute the belt 6 such that the cords constituting the belt layers 6A, 6B cross each other with the tire equatorial plane in between.

[0128] The studless tire 1 of this embodiment has tread rubber 8 on the outermost surface of the tread portion 4, and the above-mentioned rubber composition for the tread of the studless tire of this embodiment is used for the tread rubber 8. Therefore, the studless tire 1 of this embodiment has improved performance on ice and a ratio of sustainable materials.

[0129] The studless tire of the present invention may have the tread rubber of the above-mentioned embodiment, and may be modified in various ways. For example, it is possible to provide a belt reinforcing layer on the radially outer side of the belt 6 of the studless tire 1 shown in Fig. 1, or to divide the tread rubber 8 into a cap rubber located on the outermost side and a base rubber located on the radially inner side of the cap rubber.

[0130] The studless tire of this embodiment can be manufactured by a normal method using the above-mentioned rubber composition as the tread rubber. For example, the studless 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. The studless 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. EXAMPLES

[0131] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples in any way.

[0132] <Preparation and Evaluation of Rubber Composition> Rubber compositions of the examples and comparative examples are prepared according to the compounding recipes shown in Table 1. For the obtained rubber compositions, the total mass ratio of materials derived from biological resources (biomass resources) and materials derived from recycled resources (recycled resources) is calculated to calculate the sustainable material ratio. The results are shown in Table 1.

[0133] [Table 1]

[0134] *1 Natural rubber: TSR20 *2 BR: UBE Elastomers Co., Ltd., product name "UBEPOL 150L", cis-1,4-polybutadiene rubber *3 Modified SBR: Modified styrene-butadiene copolymer rubber produced by the following method *4 Silica: Manufactured by Tosoh Silica Co., Ltd., product name "NIPSIL AQ", CTAB specific surface area = 150m 2 / g, nitrogen adsorption specific surface area (N2SA)=200m 2 / g *5 Carbon black: Asahi Carbon Co., Ltd., product name "Carbon N134", N2SA=146m 2 / g *6 Silane coupling agent: Evonic, product name "Si69" *7 Oil: naphthenic process oil, manufactured by Idemitsu Kosan Co., Ltd., product name "Diana Process Oil NS-24", pour point = -30℃ *8 C5 resin: Tonen Chemical Co., Ltd., product name "Escorez 1102" *9 Terpene resin: Kraton Corporation, product name "SYLVATRAXX8125" *10 Acrylic resin: Toa Gosei Co., Ltd., product name "ARUFON UG-4010" *11 Foaming agent: void-introducing agent, dinitrosopentamethylenetetramine (DPT) *12 Hydrophilic short fibers: Hydrophilic short fibers produced by the following method *13 Stearic acid: New Japan Chemical Co., Ltd., product name "Stearic acid 50S" *14 Zinc oxide: Manufactured by Hakusui Tech Co., Ltd., product name "No. 3 zinc oxide" *15 Vulcanization accelerator: Ouchi Shinko Chemical Industry Co., Ltd., product name "Noccela DM", di-2-benzothiazolyl disulfide *16 Vulcanizing agent: Tsurumi Chemical Co., Ltd., product name "Powdered sulfur" *17 Anti-aging agent: N-isopropyl-N'-phenyl-p-phenylenediamine

[0135] [Manufacturing method of modified SBR(*3)] A cyclohexane solution of 1,3-butadiene and a cyclohexane solution of styrene are added to a dried, nitrogen-purged 800 mL pressure-resistant glass container so that the resulting mixture is 67.5 g of 1,3-butadiene and 7.5 g of styrene. Furthermore, 0.6 mmol of 2,2-ditetrahydrofurylpropane and 0.8 mmol of n-butyllithium are added. Polymerization is then carried out at 50°C for 1.5 hours. At this time, 0.72 mmol of N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane is added as a modifier to the polymerization reaction system, which has reached a polymerization conversion rate of almost 100%, and the modification reaction is carried out at 50°C for 30 minutes. Then, 2 mL of a 5% by mass solution of 2,6-di-t-butyl-p-cresol (BHT) in isopropanol is added to stop the reaction, and the modified SBR is obtained by drying according to a conventional method.

[0136] [Method of manufacturing hydrophilic short fibers (*12)] According to Production Example 3 disclosed in JP 2012-219245 A, two twin-screw extruders are used, and 40 parts by mass of polyethylene [Novatec HJ360 (MFR 5.5, melting point 132°C) manufactured by Japan Polyethylene Co., Ltd.] and 40 parts by mass of an ethylene-vinyl alcohol copolymer [Eval F104B (MFR 4.4, melting point 183°C) manufactured by Kuraray Co., Ltd.] are charged into the hopper. They are simultaneously extruded from the die outlet, and the resulting fibers are cut to a length of 2 mm according to a conventional method to produce hydrophilic short fibers having a coating layer made of polyethylene.

[0137] From Table 1, it can be seen that the rubber compositions of the examples according to the present invention have an improved ratio of sustainable materials.

[0138] [Contribution to the United Nations-led Sustainable Development Goals (SDGs)] The SDGs have been proposed to realize a sustainable society. One embodiment of the present invention is considered to be a technology that can contribute to "No. 12_Responsible Consumption and Production" and "No. 13_Concrete measures against climate change." [Explanation of symbols]

[0139] 1: Studless tires 2: Bead section 3: Sidewall 4: Tread section 5: Carcass 6: Belt 6A, 6B: Belt layer 7: Bead core 8: Tread rubber

Claims

1. A rubber component (A); At least one resin component (B) selected from the group consisting of terpene-based resins and rosin-based resins; and an acrylic resin (C) having a weight average molecular weight (Mw) of 1,000 or more.

2. The rubber composition for studless tire treads according to claim 1, wherein the content of the resin component (B) is 0.5 to 30 parts by mass per 100 parts by mass of the rubber component (A).

3. The rubber composition for a tread of a studless tire according to claim 1 , wherein the rubber component (A) contains an isoprene skeleton rubber.

4. The resin component (B) has an SP value difference of 0.6 (cal / cm) from the isoprene skeleton rubber. ３ ) １／２ The rubber composition for a tread of a studless tire according to claim 3, wherein:

5. A tread rubber comprising the rubber composition for treads of studless tires according to claim 1.

6. A studless tire comprising the tread rubber according to claim 5.

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