Vulcanized rubber composition for studless tire and studless tire

Abstract

Provided is a vulcanized rubber composition for a studless tire excellent in wet performance and on-ice performance, wherein workability and sustainable rate are also improved.　In order to solve the above problem, the present invention is a vulcanized rubber composition for a studless tire, the vulcanized rubber composition being obtained by vulcanizing a rubber composition comprising a rubber component, a resin component, and a liquid plasticizer. The vulcanized rubber composition is characterized in that the resin component is at least one selected from the group consisting of terpene-based resins and rosin-based resins, the content of the resin component is 15 parts by mass or more based on 100 parts by mass of the rubber component, the content of the liquid plasticizer is 30 parts by mass or less based on 100 parts by mass of the rubber component, and the vulcanized rubber composition has a plurality of voids.

Description

Vulcanized rubber composition for studless tires and studless tires

[0001] The present invention relates to a vulcanized rubber composition for studless tires and a studless tire.

[0002] Natural rubber is generally known for its excellent mechanical properties and abrasion resistance. Natural rubber is extracted as natural rubber latex and obtained through the following processes: coagulation, aging as needed, washing, dehydration, drying, and packing. The desired rubber product is produced by masticating this natural rubber, blending it with compounding ingredients, molding, and vulcanizing it. Natural rubber latex contains approximately 25-35% w / v (weight / volume) rubber content as well as non-rubber components such as proteins, lipids, carbohydrates, and inorganic substances. Natural rubber obtained by coagulating it with formic acid or the like contains approximately 6% by mass of non-rubber components. While these non-rubber components have anti-aging and vulcanization-accelerating effects, highly polar compounds such as proteins have been found to impair the processability and heat generation of vulcanized rubber.

[0003] For example, Patent Document 1 discloses a method for producing natural rubber in which proteins contained in non-rubber components of natural rubber latex are partially deproteinized using only mechanical separation means such as centrifugation to reduce the total nitrogen content in the solid components of the natural rubber latex to more than 0.1% by mass but not more than 0.4% by mass, followed by coagulation and drying, in order to improve low heat buildup without impairing aging resistance. Patent Document 2 also discloses a natural rubber having a phosphorus content of 200 ppm or less, and a method for producing the same, in consideration of the processability of natural rubber and the fact that it is preferable that natural rubber be substantially free of phospholipids, by saponifying natural rubber latex with an alkali, washing the coagulated rubber after saponification, and then drying it. However, both the natural rubbers obtained by the techniques of Patent Documents 1 and 2 left room for further improvement in terms of processability and workability during production (hereinafter simply referred to as "workability").

[0004] Research has been conducted, particularly on tire treads, to improve the braking and driving performance of tires on wet roads and icy and snowy roads (hereinafter referred to as wet performance and ice performance, respectively). Because the water film generated on wet roads and icy and snowy roads reduces the coefficient of friction between the tire and the road surface, improving the wet and snowy and snowy performance of tires requires improving the tire tread's water film removal ability, edge effect, and spike effect. For example, it is known that providing a tire tread with water film removal ability involves providing micro-drainage grooves in the tire's road surface, which remove the water film and increase the tire's coefficient of friction on icy and snowy roads. However, while providing micro-drainage grooves in the tire's road surface can improve the tire's ice performance in the early stages of use, there are problems with reduced tire wear resistance and difficulty in maintaining ice performance, and further improvements are desired.

[0005] As a technology for improving the balance of other performances in addition to the above-mentioned wet performance and icy performance, for example, Patent Document 1 discloses a rubber composition for treads that contains a rubber component including an isoprene-based rubber and a butadiene rubber, a filler, a specific terpene-based resin, and water-soluble microparticles and / or a foaming agent. However, with regard to the technology of Patent Document 1, further improvement in wet performance and icy performance is desired. Furthermore, with regard to the technology of Patent Document 1, when the content of the terpene-based resin increases, the viscosity of the rubber composition increases, and improvement is also needed from the viewpoint of workability, etc.

[0006] In addition, from the perspective of social sustainability, there has been a recent demand for the use of so-called sustainable materials, such as materials derived from biological resources (biomass resources) and materials derived from recycled resources, for the various components used in tires, and there is a need to develop technologies to increase the usage rate of sustainable materials (hereinafter referred to as the "sustainability rate").

[0007] Japanese Patent Application Laid-Open No. 2019-206653

[0008] Therefore, an object of the present invention is to provide a vulcanized rubber composition for studless tires that has excellent wet performance and ice performance, and also has improved workability and sustainability.Another object of the present invention is to provide a studless tire that has excellent wet performance and ice performance, and also has improved workability and sustainability.

[0009] The present inventors conducted extensive research to further improve the wet and icy performance and sustainability rate of vulcanized rubber compositions for studless tires. They discovered that by incorporating specific amounts of at least one resin selected from the group consisting of a terpene resin and a rosin resin, and a liquid plasticizer, high workability can be achieved in rubber compositions even when currently used fossil-derived materials are replaced with sustainable materials, and that by providing multiple voids in the vulcanized rubber composition, wet and icy performance can also be improved.

[0010] That is, the gist of the present invention is as follows: A vulcanized rubber composition for studless tires, obtained by vulcanizing a rubber composition containing a rubber component, a resin component, and a liquid plasticizer, wherein the resin component is at least one selected from the group consisting of terpene resins and rosin resins, the content of the resin component is 15 parts by mass or more per 100 parts by mass of the rubber component, the content of the liquid plasticizer is 30 parts by mass or less per 100 parts by mass of the rubber component, and the vulcanized rubber composition has a plurality of voids. The vulcanized rubber composition for studless tires of the present invention has excellent wet performance and performance on ice, and can also improve workability and sustainability.

[0011] A studless tire comprising the vulcanized rubber composition for studless tires of the present invention. The studless tire of the present invention has excellent wet performance and ice performance, and is high in workability and sustainability.

[0012] According to the present invention, it is possible to provide a vulcanized rubber composition for studless tires that is excellent in wet performance and ice performance, and also has improved workability and sustainability. Furthermore, according to the present invention, it is also possible to provide a studless tire that is excellent in wet performance and ice performance, and also has improved workability and sustainability.

[0013] 1 is a diagram showing a cross section of a plurality of voids present in a vulcanized rubber composition according to one embodiment of the present invention, and FIG.

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings as necessary. The compounds described in this specification may be derived in part or entirely from fossil resources, from biological resources such as plant resources, or from recycled resources such as used tires. They may also be derived from a mixture of two or more of fossil resources, biological resources, and recycled resources.

[0015] In addition, in this specification, the term "sustainability rate" refers to the total mass ratio of components derived from biological resources (biomass resources) and components derived from recycled resources (recycled resources) in a target material.

[0016] In this specification, the term "biological resources (biomass resources)" refers to carbon-neutral organic resources derived from living organisms, and includes, for example, materials 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 is a resource excluding fossil resources (petroleum, coal, natural gas, etc.). The biological resources may be edible or non-edible, but are preferably non-edible in order not to compete with food and from the viewpoint of effective resource utilization.

[0017] 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 excrement, 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 oil, etc.), and the like. Examples of biological resources include: corn oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, tung oil, coconut oil, etc.), carbohydrate crops (corn, wheat, rice, rice husks, rice bran, old rice, potatoes, buckwheat, cassava, sago palm, sugarcane, etc.), bagasse (i.e., the residue left after sugarcane juicing), soybeans, soybean pulp refuse, essential oils (pine oil, orange oil, eucalyptus oil, etc.), pulp black liquor, and algae. The biological resources may also be processed (i.e., biological resource-derived substances). Examples of processing methods include biological processing methods utilizing the activity of microorganisms, plants, animals, and their tissue cultures; chemical processing methods utilizing acids, alkalis, catalysts, thermal energy, light energy, etc.; and physical processing methods such as pulverization, compression, microwave treatment, and electromagnetic wave treatment. The biological resources may also be extracted and purified from the biological resources or biological resources that have undergone the above-described processing (i.e., biological resource-derived substances). For example, sugars, proteins, amino acids, fatty acids, fatty acid esters, etc., purified from the above-mentioned biological resources can also 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, with valine, leucine, isoleucine, arginine, and phenylalanine being preferred.The amino acids may be either L-amino acids or D-amino acids, but L-amino acids are preferred from the viewpoints of abundance in nature and ease of availability. Examples of the fatty acids include butyric acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, etc., which are derived from biological resources. Examples of the fatty acid esters include modified products of vegetable oils, animal oils, and fats and oils derived from biological resources. These biological resources may contain various materials and impurities.

[0018] 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.

[0019] <Vulcanized rubber composition for studless tires> The vulcanized rubber composition for studless tires of the present invention is a vulcanized rubber composition for studless tires obtained by vulcanizing a rubber composition containing a rubber component, a resin component, and a liquid plasticizer, wherein the resin component is at least one selected from the group consisting of terpene resins and rosin resins, the content of the resin component is 15 parts by mass or more per 100 parts by mass of the rubber component, the content of the liquid plasticizer is 30 parts by mass or less per 100 parts by mass of the rubber component, and the vulcanized rubber composition has a plurality of voids.

[0020] In the vulcanized rubber composition for studless tires of the present invention, the compatibility of the resin component with the rubber component can be improved by containing at least one resin selected from the group consisting of terpene-based resins and rosin-based resins, and a specific amount of liquid plasticizer. Therefore, even when the fossil resource-derived material (synthetic rubber) currently used in the rubber composition is replaced with a sustainable material (natural rubber), high processability and workability can be achieved.

[0021] In addition, the vulcanized rubber composition 10 for studless tires of the present invention has a plurality of voids 20 as shown in FIG. 1, thereby improving wet performance when applied to a tire.

[0022] Here, the voids in the vulcanized rubber composition for studless tires of the present invention refer to holes with an average diameter of approximately 1 to 500 μm formed in the vulcanized rubber composition for studless tires, as shown in FIG. 1. Here, the void diameter refers to the largest diameter D of the void 20 (if the void is not spherical, the longest distance D between any two points on the inner wall of the void) as shown in FIG. 2. The average void diameter is the average value of the diameters D of the voids 20 present in the vulcanized rubber composition for studless tires of the present invention. In the present invention, the cross section of the vulcanized rubber composition for studless tires is observed using a digital microscope ("VHX-100" manufactured by Keyence Corporation), and the average value of the diameters of all voids present in one field of view (2.5 mm x 2.5 mm) is used. Note that in the vulcanized rubber composition for studless tires of the present invention, the shape and size of the voids do not vary significantly within a single vulcanized rubber composition for studless tires, so the average value of the voids in one field of view can be used as the average void diameter.

[0023] Furthermore, the porosity of the vulcanized rubber composition for studless tires of the present invention is preferably 5 to 45%. By setting the lower limit of the porosity to 5%, wet performance can be more reliably improved. From the same perspective, the porosity is preferably 7% or more, and more preferably 15% or more. On the other hand, by setting the upper limit of the porosity to 45%, deterioration of abrasion resistance can be more reliably suppressed even when multiple voids are present. From the same perspective, the porosity is preferably 40% or less, and more preferably 37% or less. The porosity refers to the volume ratio (volume %) of the voids in the vulcanized rubber composition for studless tires of the present invention. The method for measuring the porosity is not particularly limited, and can be measured using, for example, a hydrometer (ViBRA hydrometer "DMA-220" manufactured by Shinko Denshi Co., Ltd.).

[0024] Here, the vulcanized rubber composition for studless tires of the present invention has a plurality of voids, but the method for forming the voids is not particularly limited. The voids can be formed using known techniques depending on the void conditions and the equipment used to produce the vulcanized rubber composition for studless tires. For example, as described below, voids can be formed in the vulcanized rubber composition for studless tires by blending a foaming agent, a foaming aid, composite fibers, etc. into the rubber composition before vulcanization. The void ratio can be controlled by changing the vulcanization conditions or by adjusting the content of void-introducing agents such as foaming agents and composite fibers. Another method for forming the voids is to blend powdered rubber into the rubber composition before vulcanization, causing the powdered rubber to detach from the surface of the rubber composition after vulcanization, forming voids near the surface of the vulcanized rubber composition for studless tires. In this case, the size and void ratio of the voids can be adjusted by adjusting the particle size and number of the powdered rubber.

[0025] The vulcanized rubber composition for studless tires is a vulcanized rubber obtained by vulcanizing an unvulcanized rubber composition. The vulcanization conditions (temperature, time) are not particularly limited, and the vulcanization treatment can be carried out under any conditions depending on the required performance.

[0026] The unvulcanized rubber composition (hereinafter simply referred to as "rubber composition") that is the base material for the vulcanized rubber composition for studless tires of the present invention will be described below. The rubber composition contains at least natural rubber. Each component constituting the rubber composition will be described below.

[0027] (Rubber Component) The rubber composition contains a rubber component that provides rubber elasticity to the composition. The rubber component preferably has a sustainability rate of 30% by mass or more, more preferably 40% by mass or more, more preferably 50% by mass or more, 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.

[0028] The rubber component is preferably the rubber derived from biological resources and the rubber derived from recycled resources. Here, the proportion of the monomer component 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, even more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may be 100 mol%. Furthermore, the proportion of the monomer component derived from recycled resources in 100 mol% of the 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, even more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may be 100 mol%.

[0029] The rubber component is a component that contributes to crosslinking, and typically 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 is 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 can be determined in terms of standard polystyrene based on measurements obtained using, for example, a gel permeation chromatograph (GPC) (GPC-8000 series, manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M, manufactured by Tosoh Corporation).

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

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

[0032] The isoprene-based rubber preferably has a sustainability ratio of 30% by mass or more, more preferably 40% by mass or more, more preferably 50% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass. To achieve a sustainability ratio 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 recycled 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 recycled resources, a copolymer of a monomer derived from biological resources and a monomer derived from recycled resources, or a copolymer of a monomer derived from biological resources and / or a monomer derived from recycled resources and a monomer derived from fossil resources (petroleum, etc.).

[0033] Examples of the butadiene-based 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-based rubber, is preferably derived from biological resources or recycled resources.

[0034] Examples of the butadiene rubber (BR) include high-cis butadiene rubber, low-cis butadiene rubber, and butadiene rubber containing syndiotactic polybutadiene crystals. Commercially available butadiene rubbers 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 Corporation, and Zeon Corporation. These butadiene rubbers may be used alone or in combination of two or more.

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

[0036] The butadiene-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, 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. To achieve a sustainability rate within the above range, for example, a polymer synthesized using a bioresource-derived butadiene, a recycled resource-derived butadiene, a bioresource-derived aromatic vinyl compound (e.g., bioresource-derived styrene), or a recycled resource-derived aromatic vinyl compound (e.g., recycled resource-derived styrene) as a monomer component may be used. In this case, the synthesized polymer may be a homopolymer of a bioresource-derived monomer, a homopolymer of a recycled resource-derived monomer, a copolymer of a bioresource-derived monomer and a recycled resource-derived monomer, or a copolymer of a bioresource-derived monomer and / or a recycled resource-derived monomer and a fossil resource (e.g., petroleum)-derived monomer. Note that the butadiene rubber (B-BR) derived from biological resources (biomass resources) and aromatic vinyl compound-butadiene copolymer rubber derived from biological resources (for example, styrene-butadiene rubber (B-SBR) derived from biological resources (biomass resources)) include not only rubber obtained by polymerizing butadiene or the like according to conventional methods, but also rubber obtained by reactions involving microorganisms, plants, animals, and tissue cultures thereof (hereinafter also referred to as "microorganisms, etc.") or enzymatic reactions.

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

[0038] Generally, the production of rubber composition materials for tires (e.g., rubber and its monomers, fillers, resins, etc.) requires large-scale production equipment, and therefore is typically produced in large factories in specific regions, requiring significant energy for the storage and transportation of raw materials and products. In contrast, materials derived from biological resources (biomass resources) are derived from local agricultural products, forests, etc., and can be produced on a small scale through microbial fermentation and catalytic reactions. Therefore, by utilizing local products and waste, the energy required for transporting and storing raw materials can be reduced, and furthermore, the energy required for transporting and storing the produced materials to tire factories can also be reduced, making them environmentally friendly. Materials derived from recycled resources can be obtained, for example, by dismantling and pyrolyzing used tires to extract the tire-constituting materials, 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 raw materials for tire rubber compositions can be obtained from various waste products and used items. In this way, the use of sustainable materials (materials derived from biological resources or materials derived from recycled resources) can reduce the overall environmental impact of 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 incurred over the entire life cycle (LCC), and reducing the use of fossil resources.

[0039] Furthermore, when producing the rubber composition, the ratios of monomer components derived from biological resources, monomer components derived from recycled resources, and monomer components derived from fossil resources can be appropriately selected depending on 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). By polymerizing the monomer components derived from biological resources, monomer components derived from recycled resources, and monomer components derived from fossil resources, rubber derived from sustainable materials (materials derived from biological resources or materials derived from recycled resources) can be obtained that has performance equivalent to that of conventional synthetic rubber. When using monomer components derived from recycled resources, it may be difficult to separate them from monomer components derived from fossil resources due to the manufacturing process of the monomers. In such cases, the environmental impact can be evaluated by adopting the mass balance approach.

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

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

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

[0043] The functional group can be introduced, for example, by reacting a compound (modifier) ​​having the functional group with the rubber component. The functional group is a modified functional group that has interactivity with fillers such as silica and carbon black, and examples thereof include nitrogen-containing functional groups, silicon-containing functional groups, and oxygen-containing functional groups. Examples of compounds (modifiers) having nitrogen-containing functional groups include amino group-containing compounds, and examples of compounds (modifiers) having silicon-containing functional groups include silicon halides and hydrocarbyloxysilane compounds. Examples of compounds (modifiers) having oxygen-containing functional groups include alkoxy group-containing compounds, alkylene oxide group-containing compounds, and trialkylsilyloxy group-containing compounds. More specifically, examples of the compounds described in WO 2016 / 194316 and WO 2019 / 117256 include the compounds described in WO 2016 / 194316 and WO 2019 / 117256. These modifiers may be used alone or in combination of two or more.

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

[0045] Regarding the method for preparing bioresource-derived rubber from the above-mentioned bioresources, for example, the method described in JP 2022-179158 A can be used. For example, by using butadiene obtained from a bioresource as the monomer component, it is possible to obtain a bioresource (biomass resource)-derived butadiene rubber (B-BR). Furthermore, by using styrene obtained from a bioresource and butadiene obtained from a bioresource as the monomer components, it is possible to obtain a bioresource (biomass resource)-derived styrene-butadiene rubber (B-SBR). Here, methods for obtaining B-BR and B-SBR from bioresources include artificial polymerization methods, in vivo polymerization methods, and polymerization methods using 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 depending on the desired tire performance.

[0046] Suitable butadienes obtained from biological resources include butadienes derived from alkyl alcohols (preferably ethanol and butanol, more preferably butanol), butadienes derived from alkenes (preferably ethylene), and butadienes derived from unsaturated carboxylic acids (preferably tiglic acid). Two or more of these butadienes may be used in combination. Suitable styrenes obtained from biological resources include styrenes obtained from plants (preferably plants belonging to the Hamamelidaceae, Styraxaceae, and Apocynaceae families, more preferably plants belonging to the Liquidambar, Styrax, and Catharanthus roseus, and even more preferably sweetgum, Styrax rostrata, and Catharanthus roseus), and styrenes obtained from microorganisms (preferably microorganisms belonging to the Penicillium and Escherichia genera, more preferably P. citrinum, and transformed E. coli). Suitable styrenes may be used in combination.

[0047] Recently, biomass industrial complexes centered on bioethanol, bioethylene, and the like have been planned. However, bioethanol and bioethylene are produced primarily using sugars and / or cellulose as biological resources, and do not effectively utilize other biological resources such as proteins, lipids, and amino acids. Furthermore, sugars compete with food, and excessive use of cellulose leads to deforestation. Therefore, depending on the supply status of various biological resources, the supply status of renewable resources, the supply status of fossil resources, and market demands (e.g., demand for biomass resources as food), it is preferable to use multiple types of biological resource-derived monomer components as the biological resource-derived monomer components, or to use a combination of biological resource-derived monomer components, renewable resource-derived monomer components, and fossil resource-derived monomer components, and further adjust the ratios of these monomer components appropriately. This allows for the effective utilization of a wide range of biological resources, such as sugars, proteins, and lipids, as well as renewable resources, without relying on a single type of biological resource. It also allows for a stable supply of rubber derived from sustainable materials and further contributes to environmental considerations depending on the production conditions. When multiple types of monomer components derived from biological resources are used, 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 butadienes derived from multiple types of biological resources with different origins as the biological resource-derived butadiene, and / or to use a mixture of styrenes derived from multiple types of biological resources with different origins as the biological resource-derived styrene. This allows for effective use of multiple types of biological resources.

[0048] (Resin) The rubber composition further contains a resin in addition to the rubber component. By including a resin, the processability and productivity of the rubber composition can be improved, and wet and icy performance can be enhanced when applied to a tire. The resin is at least one selected from the group consisting of terpene resins and rosin resins. As described above, the inclusion of a terpene resin and / or a rosin resin improves compatibility with the rubber component, thereby achieving excellent wet and icy performance even with a small amount. It also reduces stickiness and other issues caused by the resin component and improves productivity. Furthermore, since terpene resins and rosin resins are naturally derived, blending a terpene resin and / or a rosin resin into a rubber composition can improve the sustainability of studless tires incorporating the rubber composition and further reduce the environmental impact.

[0049] The resin may be hydrogenated, i.e., may be a hydrogenated resin (hydrogenated resin). Furthermore, the resin may be modified to introduce a functional group that interacts with fillers such as carbon black and silica. Examples of such functional groups include amino groups, amide groups, isocyanate groups, imino groups, imidazole groups, urea groups, ammonium groups, imide groups, hydrazo groups, azo groups, diazo groups, carboxyl groups, nitrile groups, pyridyl groups, alkoxy groups, hydroxyl groups, oxy groups, epoxy groups, ether groups, carbonyl groups, oxycarbonyl groups, silyl groups, alkoxysilyl groups, mercapto groups, sulfide groups, disulfide groups, sulfonyl groups, sulfinyl groups, and thiocarbonyl groups.

[0050] The terpene resin is a solid resin obtained by blending turpentine, which is obtained simultaneously with the extraction of rosin from pine trees, or a polymerization component separated therefrom, and polymerizing the blend using a Friedel-Crafts catalyst. Examples of such resins include β-pinene resin and α-pinene resin. Terpene resins also include terpene-aromatic compound resins, representative examples of which include terpene-phenol resin and styrene-terpene resin. Terpene-phenol resins can be obtained by reacting terpenes with various phenols using a Friedel-Crafts catalyst, or by further condensing the terpene with formalin. The styrene-terpene resin can be obtained by reacting styrene with terpenes using a Friedel-Crafts catalyst. The terpenes used as raw materials are not particularly limited; monoterpene hydrocarbons such as α-pinene and limonene are preferred, with those containing α-pinene being more preferred, and α-pinene being particularly preferred.

[0051] 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, and examples of modified rosins, rosin derivatives, and modified rosin derivatives include polymerized rosin and partially hydrogenated rosin thereof; glycerin ester rosin and partially hydrogenated rosin thereof; pentaerythritol ester rosin and partially hydrogenated rosin thereof; and pentaerythritol ester rosin and partially hydrogenated rosin thereof; etc. From the viewpoint of further improving the wet performance, ice performance, and productivity of the rubber composition, it is preferable that the resin component contains at least a rosin-based resin.

[0052] The resin preferably has 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. In this specification, the softening point of the resin is the temperature at which the ball drops when the softening point as defined in JIS K 6220-1:2015 (ISO 28641:2010) is measured using a ring and ball softening point tester.

[0053] Commercially available resins can be used as the resins. Examples of commercially available resins include products from Arakawa Chemical Industries, Ltd., Clayton Corporation, Yasuhara Chemical Co., Ltd., Arizona Chemical Company, and the like.

[0054] The content of the resin in the rubber composition is not particularly limited and can be adjusted appropriately depending on, for example, the tire category to which the composition is applied, tire components, target performance, etc. For example, the content of the resin is preferably in the range of 5 to 100 parts by mass, more preferably in the range of 10 to 60 parts by mass, per 100 parts by mass of the rubber component.

[0055] When the rubber component contains an isoprene skeleton rubber, the resin component has an SP value that is different from the isoprene skeleton rubber by 0.6 (cal / cm ３ ) １／２ It is preferable that the value is 0.58 (cal / cm ３ ) １／２ When 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 rubber composition for a tire case member described below has excellent fracture resistance due to high compatibility between the rubber component and the resin component.

[0056] The content of the resin component must be 15 parts by mass or more per 100 parts by mass of the rubber component, and is preferably 15 to 50 parts by mass. When the content of the resin component is 15 parts by mass or more per 100 parts by mass of the rubber component, the workability of the rubber composition is improved, and when the content of the resin component is 50 parts by mass or less per 100 parts by mass of the rubber component (A), deterioration of the abrasion resistance of the rubber composition can be suppressed.

[0057] The rubber composition may also contain resin components other than the terpene resin and rosin resin described above. Examples of the other resin components include C ５ based resin, C ５ -C ９ based resin, C ９ Examples of the other resin components include cyclopentadiene-based resins, aromatic resins, coumarone resins, indene resins, coumarone-indene-based resins, olefin-based resins, polyurethane resins, and acrylic resins. These other resin components may be used alone or in combination of two or more.

[0058] The other resin components may be hydrogenated, i.e., may be hydrogenated resins (hydrogenated resins). Furthermore, functional groups that interact with fillers such as carbon black and silica may be introduced into the resins by modification. Examples of such functional groups include amino groups, amide groups, isocyanate groups, imino groups, imidazole groups, urea groups, ammonium groups, imide groups, hydrazo groups, azo groups, diazo groups, carboxyl groups, nitrile groups, pyridyl groups, alkoxy groups, hydroxyl groups, oxy groups, epoxy groups, ether groups, carbonyl groups, oxycarbonyl groups, silyl groups, alkoxysilyl groups, mercapto groups, sulfide groups, disulfide groups, sulfonyl groups, sulfinyl groups, and thiocarbonyl groups.

[0059] Said C ５ As a resin based on C, there is C obtained by thermal decomposition of naphtha in the petrochemical industry. ５ and aliphatic petroleum resins obtained by (co)polymerizing the distillate. ５The fraction usually contains 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.

[0060] Said C ５ -C ９ The C-based resin is ５ -C ９ It refers to synthetic petroleum resin, ５ -C ９ Examples of the resin include petroleum-derived C ５ -C １１ The fraction was treated with AlCl ３ , B.F. ３ More specifically, copolymers containing styrene, vinyltoluene, α-methylstyrene, indene, etc. as the main component may be mentioned. ５ -C ９ As the resin, ９ Resins containing less of the above components are preferred from the viewpoint of compatibility with the rubber component. ９ "Low amount of the above components" means that the C ９ This means that the content of the above components is less than 50% by mass, preferably 40% by mass or less.

[0061] Said C ９ The C-based resin is ９ This refers to synthetic petroleum resins, such as AlCl ３ or BF ３ Using a Friedel-Crafts type catalyst such as C ９ It refers to a solid polymer obtained by polymerizing the fraction. ９ Examples of the resin include copolymers containing indene, α-methylstyrene, vinyltoluene, etc. as main components.

[0062] The cyclopentadiene-based resin refers to a resin containing a unit derived from a cyclopentadiene-based monomer as a monomer unit. Examples of the cyclopentadiene-based resin include a homopolymer of a cyclopentadiene-based monomer, a copolymer of two or more cyclopentadiene-based monomers, and a copolymer of a cyclopentadiene-based monomer and another monomer. Here, examples of the cyclopentadiene-based monomer include cyclopentadiene, dicyclopentadiene, and tricyclopentadiene. Among these, dicyclopentadiene is preferred. That is, the cyclopentadiene-based resin is preferably a dicyclopentadiene-based resin. The dicyclopentadiene-based resin is, for example, a copolymer of AlCl ３ or BF ３ The term "dicyclopentadiene-based resin" refers to a resin obtained by polymerizing dicyclopentadiene using a Friedel-Crafts catalyst such as Benzene, etc. Dicyclopentadiene-based resins include homopolymers of dicyclopentadiene, copolymers of dicyclopentadiene and aromatic monomers, copolymers of dicyclopentadiene and C ９ Examples include copolymers with distillates (vinyl toluene, indene, etc.).

[0063] The aromatic resin refers to a resin containing units derived from aromatic monomers as monomer units. Examples of the aromatic resin include homopolymers of aromatic monomers, copolymers of two or more aromatic monomers, and copolymers of aromatic monomers with other monomers. Examples of the aromatic monomer include styrene-based monomers such as styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-methoxystyrene, p-tert-butylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, and p-phenylstyrene; phenol-based monomers such as phenol, alkylphenol, and alkoxyphenol; and naphthol-based monomers such as naphthol, alkylnaphthol, and alkoxynaphthol.

[0064] The softening point of the other resin component is preferably 30° C. or higher, more preferably 60° C. or higher, more preferably 80° C. or higher, more preferably higher than 110° C., more preferably 116° C. or higher, more preferably 120° C. or higher, more preferably 123° C. or higher, and even more preferably 127° C. or higher. From the viewpoint of processability, the softening point of the resin is preferably 160° C. or lower, more preferably 150° C. or lower, more preferably 145° C. or lower, more preferably 141° C. or lower, and even more preferably 136° C. or lower.

[0065] Commercially available products can be used as the other resin components. Examples of commercially available resin products include those from ENEOS Corporation, Arakawa Chemical Industries, Ltd., ExxonMobil Corporation, Clayton Corporation, Yasuhara Chemical Co., Ltd., Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical Company, Nitto Chemical Co., Ltd., Nippon Shokubai Co., Ltd., and Taoka Chemical Co., Ltd.

[0066] The content of the other resin component is not particularly limited and can be adjusted appropriately 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 component 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, per 100 parts by mass of the rubber component.

[0067] (Reinforcing Filler) The rubber composition preferably further contains a reinforcing filler. This is because the vulcanized rubber composition of the present invention can have improved properties such as strength, abrasion resistance, low heat buildup, and wet performance. The reinforcing filler may be any reinforcing filler commonly used in the rubber field, and examples thereof include carbon black, silica, talc, clay, aluminum hydroxide, and titanium oxide.

[0068] Silica: Examples of the silica include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, and aluminum silicate. Among these, wet silica is preferred because it contains a large number of silanol groups. These silicas may be used alone or in combination of two or more. Commercially available silicas can be used, and examples of commercially available silicas include products from Tosoh Silica Co., Ltd., Degussa, Rhodia, Solvay Japan Co., Ltd., and Tokuyama Corporation.

[0069] From the viewpoint of reducing environmental impact, silica derived from siliceous plants is preferred as the silica. Examples of siliceous plants include mosses, ferns, horsetails, Cucurbitaceae, Urticaceae, and Gramineae plants. Among these plants, grasses are preferred. Examples of grasses include rice, bamboo, and sugarcane, with rice being preferred. Rice is widely cultivated for food and therefore can be procured locally over a wide area. Furthermore, rice husks are generated in large quantities as industrial waste, making it easy to secure a sufficient supply. Therefore, from the viewpoint of availability, silica derived from rice husks (hereinafter also referred to as "rice husk silica") is particularly preferred as silica. The use of rice husk silica allows for the effective use of rice husks, which are industrial waste, and also allows for the local procurement of raw materials near tire manufacturing plants, thereby reducing the energy and costs involved in transportation and storage, 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 process 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. The method for producing the rice husk charcoal is not particularly limited, and various known methods can be used. For example, rice husk charcoal can be obtained by pyrolyzing rice husks by steaming them in a kiln. The rice husk charcoal obtained in this manner can be pulverized using a known pulverizer (e.g., 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, for example.

[0070] The silica has a nitrogen adsorption specific surface area (N ２ SA) is 50m ２ / g or more, and ２ / g or more is more preferable, and 150m ２ / g or more, and ２ / g or less, and ２ / g or less is more preferable, and 230m ２ / g or less is more preferable, and 200m ２ / g or less. In this specification, the nitrogen adsorption specific surface area (N ２ SA) is a value measured by the BET method in accordance with ASTM D3037-93.

[0071] The content of the silica can be adjusted appropriately depending on, for example, the tire category to which the rubber composition is applied, the tire components, the target performance, etc. For example, the content of silica is, relative to 100 parts by mass of the rubber component, 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 preferably 300 parts by mass or less, more preferably 200 parts by mass or less, still more preferably 180 parts by mass or less, and particularly preferably 150 parts by mass or less.

[0072] Carbon Black: The carbon black reinforces the rubber composition and can improve the abrasion resistance of the rubber composition. As the carbon black, plant-derived carbon black and recycled carbon black (also called "recycled carbon black") are preferred. Examples of plant-derived carbon black include those derived from castor oil and pine oil. Recycled carbon black will be described in detail below.

[0073] From the viewpoint of further improving the abrasion resistance of the rubber composition and a tire using the same, the content of carbon black (total of recycled carbon black and carbon black other than recycled carbon black) in the rubber composition 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. Also, from the viewpoint of workability of the rubber composition, the content of carbon black in the rubber composition is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, and even more preferably 70 parts by mass or less, per 100 parts by mass of the rubber component.

[0074] As used herein, "recycled carbon black" refers to carbon black recovered from recycled waste materials. Examples of such waste include waste rubber, used tires, and waste oil. Waste rubber refers to all discarded rubber, including not only waste generated from rubber products but also unwanted scraps generated during the production or repair of rubber products. Examples of scraps include buffing powder and peeled rubber. Buffing powder is fine rubber generated during the buffing process of scraping the tread portion remaining on the base tire during tire retreading, for example. Peeled rubber is a long piece of rubber, e.g., 1 to 2 cm wide, peeled from the surface of a rubber product such as a tire. Peeled rubber is generated by scraping the surface of a rubber product such as a tire using a U- or V-shaped knife like a peeler. Furthermore, waste rubber is not limited to crosslinked rubber but also includes unvulcanized rubber. Rubber products include, for example, final products such as tires and rubber hoses, as well as rubber parts or components during the manufacturing process of final products. Used tires may be tires to be retreaded, or may be tires discarded for some reason, such as tires generated during tire replacement or scrapping, or ELTs (End-of-Life Tires) that have reached the end of their service life. Waste oils are not limited to those generated during the decomposition of plastics and rubber, but also include used oils discharged from industry, such as animal and vegetable oils, lubricating oils, insulating oils, and cutting oils. Among these, waste oils that contain no non-organic components, such as those derived from silicone rubber or polyvinyl chloride, are desirable. Furthermore, waste oils containing carbon black or rubber containing carbon black are desirable. "Recycled carbon black" differs from carbon black produced directly from hydrocarbons such as petroleum, natural gas, and coal, i.e., non-recycled carbon black. Note that "used" here refers not only to waste oils discarded after actual use, but also to waste oils that were produced but discarded without actually being used.

[0075] The recycled carbon black is preferably obtained by pyrolysis of a vulcanized rubber product containing carbon black. Recycled carbon black obtained by pyrolysis of a vulcanized rubber product containing carbon black is readily available because vulcanized rubber products containing carbon black are readily available and can be easily obtained by pyrolysis. Furthermore, the recycled carbon black is preferably obtained from the solid residue produced by the pyrolysis of the vulcanized rubber product containing carbon black. When a rubber product containing carbon black is pyrolyzed, a solid residue and a volatile component (oil) are obtained, and recycled carbon black can be recovered from either of them. When recovering carbon black from the volatile component, the oil component with a specific gravity suitable for producing carbon black can be recovered and used to produce carbon black using existing carbon black production methods (e.g., JP 2015-520259 A). Unlike carbon black recovered from solid residues, this method offers advantages such as no impurities and no mixed grades. In addition, in the production of environmentally friendly carbon black, various options are available, including oils obtained by recovering volatile components from rubber pyrolysis, as described above, as well as vegetable oils and oils derived from waste plastics. However, edible resources such as vegetable oils are needed for other uses, such as food, and there are challenges in securing sufficient quantities, as well as the environmental impact of expanding cultivated land. Furthermore, oils derived from waste plastics are also used for other purposes, such as horizontal plastic recycling, so supply issues are also a concern. On the other hand, using volatile components (oils) produced by the pyrolysis of vulcanized rubber products, particularly tires, allows for the continued use of existing materials due to the tire industry's ongoing system of using existing materials, thereby reducing the consumption of new materials in new tire production and contributing to a reduction in the industry's environmental impact. The grade of carbon black is not particularly limited, and examples include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762.

[0076] Solid residues obtained by pyrolysis of waste materials such as used rubber and used tires contain ash in addition to carbon black. The ash is derived from non-volatile components contained in the rubber and tires. Therefore, recycled carbon black obtained from the solid residues has a relatively low carbon black content. On the other hand, considering the various physical properties required for tires manufactured using recycled carbon black, the higher the carbon content of the recycled carbon black, the better. The carbon content of the recycled carbon black is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 87% by mass or more, and particularly preferably 89% by mass or more. Furthermore, the carbon content of the recycled carbon black is preferably 97% by mass or less. Note that the carbon content does not include adsorbed moisture.

[0077] Specific examples of the ash include zinc oxide, zinc sulfide, silica, iron compounds (iron oxide), calcium oxide, aluminum oxide, and magnesium oxide. In the case of recycled carbon black produced from solid residue obtained by pyrolysis of waste, a certain amount of ash remains even after various processes for removing the ash. In this embodiment, the recycled carbon black is allowed to contain ash. In one embodiment, the lower limit of the ash content of the recycled carbon black may be 0.5% by mass.

[0078] The recycled carbon black can also be obtained from a pyrolysis process of used pneumatic tires. For example, European Patent Application Publication No. 3,427,975, citing "Rubber Chemistry and Technology," Vol. 85, No. 3, pp. 408-449 (2012), particularly pp. 438, 440, and 442, describes that recycled carbon black can be obtained by pyrolysis of organic materials at 550-800°C in the absence of oxygen, or by vacuum pyrolysis at relatively low temperatures (paragraph

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

[0004] of Japanese Patent Publication No. 6,856,781 (Comparison of the Surface Morphology and Chemistry of Pyrolytic Carbon Black and Commercially Available Carbon Black, Powder Technology 160 (2005) pp. 190-193).

[0079] The recycled carbon black may lack functional groups on its surface, or may be treated to include functional groups on its surface. The treatment to include functional groups on the surface of recycled carbon black can be carried out by conventional methods. For example, in European Patent Application Publication No. 3,173,251, carbon black obtained by a pyrolysis process is treated with potassium permanganate under acidic conditions to obtain carbon black containing hydroxyl and / or carboxyl groups on its surface. Furthermore, in Japanese Patent Publication No. 6,856,781, carbon black obtained by a pyrolysis process is treated with an amino acid compound containing at least one thiol or disulfide group to obtain surface-activated carbon black. The recycled carbon black according to this embodiment also includes carbon blacks treated to include functional groups on their surfaces.

[0080] Furthermore, examples of thermal decomposition of crosslinked rubber products (vulcanized rubber products) such as used tires include thermal decomposition methods at temperatures of 650° C. or higher.

[0081] The crosslinked rubber products used for the decomposition may be grouped by the type of rubber component previously compounded, and then the decomposition step may be performed for each group. Alternatively, the crosslinked rubber products may be grouped by the type of filler previously compounded (e.g., type of carbon black, type of silica, 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 by both type of rubber component and 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 can be obtained, and when the recycled carbon black is compounded again into a rubber component, a rubber composition with better performance can be obtained.

[0082] Furthermore, when the crosslinked rubber product used in the degradation is derived from tires, the tires may be grouped in advance by type (e.g., for passenger cars, for trucks and buses, for large vehicles such as off-road vehicles, for aircraft, for agricultural vehicles, etc.), and the degradation step may be carried out for each group. Alternatively, the tires may be grouped in advance by tire component (e.g., tread rubber, sidewall rubber, bead rubber, steel cord-coated rubber, organic fiber-coated rubber, pad rubber, cushion rubber, etc.), and the degradation step may be carried out for each group. Furthermore, the tires may be grouped both by type and by tire component, and the degradation step may be carried out for each group. When the degradation step is carried out for each group in this way, recycled carbon black with more uniform physical properties can be obtained, and therefore, when the recycled carbon black is blended again into a rubber component, a rubber composition with better performance can be obtained.

[0083] The recycled carbon black has a nitrogen adsorption specific surface area of ​​40 to 100 m as measured by the BET method. ２ / g, and 50 to 90m ２ / g, and more preferably 55 to 75m ２ In this specification, the nitrogen adsorption specific surface area of ​​recycled carbon black measured by the BET method is a statistical thickness specific surface area (STSA) determined in accordance with ASTM D6556.

[0084] The pH of the recycled carbon black is preferably 4 to 12, more preferably 5 to 11, and particularly preferably 6 to 10. In this specification, the pH of the recycled carbon black is determined in accordance with ASTM D1512.

[0085] The recycled carbon black preferably has a toluene color transmittance of 60% or more, more preferably 70% or more, and particularly preferably 80% or more. Herein, the toluene color transmittance of recycled carbon black is determined in accordance with ASTM D1618.

[0086] The recycled carbon black preferably has a heat loss of 3% by mass or less, more preferably 2.5% by mass or less, and particularly preferably 2% by mass or less at 125°C. Herein, the heat loss of recycled carbon black at 125°C is determined in accordance with ASTM D1509.

[0087] The recycled carbon black preferably has a sulfur content of 5% by mass or less, more preferably 3.5% by mass or less, and particularly preferably 3% by mass or less.

[0088] The recycled carbon black preferably has a 35 mesh sieve residue of 20 mass ppm or less, more preferably 15 mass ppm or less, and particularly preferably 10 mass ppm or less. Herein, the 35 mesh sieve residue of recycled carbon black is determined in accordance with ASTM D1514.

[0089] The recycled carbon black preferably has a 325 mesh (44 μm) sieve residue of 1000 mass ppm or less, more preferably 700 mass ppm or less, and particularly preferably 300 mass ppm or less. Herein, the 325 mesh (44 μm) sieve residue of the recycled carbon black is determined in accordance with ASTM D1514.

[0090] The recycled carbon black preferably has a pellet hardness of 100 cN or less, more preferably 90 cN or less, and particularly preferably 80 cN or less. Herein, the pellet hardness of recycled carbon black is determined in accordance with ASTM D5230.

[0091] The recycled carbon black preferably has a pellet fine powder content of 10% by mass or less, more preferably 7% by mass or less, and particularly preferably 5% by mass or less. Herein, the pellet fine powder content of recycled carbon black is determined in accordance with ASTM D1508.

[0092] The particle size (D97) of the recycled carbon black is preferably 25 μm or less, more preferably 15 μm or less, and particularly preferably 10 μm or less. Here, in this specification, the particle size (D97) of the recycled carbon black is determined using a laser diffraction particle size distribution analyzer, assuming a refractive index of 1.33 for water and a refractive index of 1.75 for the filler.

[0093] The recycled carbon black preferably contains particles of 5 μm or less in a proportion of 50% by volume or more, more preferably 70% by volume or more, and particularly preferably 80% by volume or more.

[0094] The recycled carbon black preferably has an ash content of 25% by mass or less, more preferably 20% by mass or less, and particularly preferably 15% by mass or less. When the ash content of the recycled carbon black is 25% by mass or less, the physical properties of the rubber product to which the rubber composition is applied can be improved. Herein, the ash content of the recycled carbon black is determined in accordance with ASTM D8474 and D1506.

[0095] The recycled carbon black preferably has a dibutyl phthalate (DBP) absorption of 70 to 120 mL / 100 g, more preferably 75 to 110 mL / 100 g, and particularly preferably 80 to 100 mL / 100 g. Herein, the DBP absorption of recycled carbon black is determined in accordance with ASTM D2414.

[0096] The recycled carbon black preferably has a compressed dibutyl phthalate (24M4DBP) absorption capacity of 50 to 110 mL / 100 g, more preferably 60 to 100 mL / 100 g, and particularly preferably 70 to 90 mL / 100 g. Herein, the 24M4DBP absorption capacity of the recycled carbon black is determined in accordance with ASTM D3493.

[0097] Commercially available recycled carbon black can be used. For example, Enrestec's product name "PB365" can be mentioned as such a commercially available product. PB365 is a recycled carbon black produced through the thermal decomposition of used tires, and has a nitrogen adsorption specific surface area of ​​73.6 m2 as measured by the BET method. ２ / g and contains about 17% by mass of ash.

[0098] The amount of recycled carbon black is preferably 1 to 100 parts by mass, more preferably 5 to 80 parts by mass, even more preferably 5 to 50 parts by mass, still more preferably 5 to 30 parts by mass, and particularly preferably 5 to 20 parts by mass, per 100 parts by mass of the rubber component. When the amount of recycled carbon black is 5 parts by mass or more per 100 parts by mass of the rubber component, the effect of improving the proportion of sustainable materials in rubber products to which the rubber composition is applied is significant, and when the amount is 50 parts by mass or less, the fracture resistance of the rubber composition can be more reliably maintained.

[0099] 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 tire components, the target performance, etc. For example, in the case of tread rubber for passenger car tires, 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. Furthermore, 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.

[0100] (Silane Coupling Agent) When the rubber composition contains silica, it is preferable that the rubber composition contains a silane coupling agent in order to improve the effect of the silica. Examples of the silane coupling agent include bis(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide, 3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide, 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. Commercially available silane coupling agents can be used, and examples of commercially available silane coupling agents that can be used include products from Degussa, Momentive, Shin-Etsu Silicones Co., Ltd., Dow Corning Toray Co., Ltd., Tokyo Chemical Industry Co., Ltd., and AZMAX Corporation. These silane coupling agents may be used alone or in combination of two or more.

[0101] The content of the silane coupling agent can be adjusted appropriately depending on, for example, the tire category to which it is applied, the tire component, 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.

[0102] (Liquid Plasticizer) The rubber composition further contains a liquid plasticizer. Here, the "liquid plasticizer" 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 plasticizers may be used alone or in combination of two or more.

[0103] The oil is a general term for extender oils contained in rubber components and liquid oils added as compounding agents to rubber compositions. Examples include vegetable oils, process oils, oils obtained by recycling vegetable oils or process oils, and mixtures thereof. From the perspective of reducing environmental impact, vegetable oils and recycled oils are preferred. Examples of vegetable oils include palm oil, castor oil, cottonseed oil, soybean oil, linseed oil, rapeseed oil, coconut oil, pine oil, pine tar, tall oil, corn oil, rice oil, safflower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, tung oil, and coconut oil. Examples of process oils include paraffin-based process oils, aromatic process oils, and naphthenic process oils. Commercially available oils can be used as the oil, and examples of commercially available oils that can be used include products from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., Japan Energy Co., Ltd., Oriso Co., Ltd., H&R Corporation, Toyokuni Oil Mills Co., Ltd., Showa Shell Sekiyu K.K., Nisshin Oillio Group Co., Ltd., and Fuji Kosan Co., Ltd. These oils may be used alone or in combination of two or more.

[0104] The liquid polymer is preferably a liquid diene-based polymer. Examples of the liquid diene-based 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 their 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.

[0105] The content of the liquid plasticizer is 30 parts by mass or less per 100 parts by mass of the rubber component. This makes it possible to obtain good snow and ice performance and wet grip performance while suppressing deterioration of abrasion resistance and handling stability. From the same viewpoint, the content of the liquid plasticizer is preferably 28 parts by mass or less, and more preferably 25 parts by mass or less, per 100 parts by mass of the rubber component. Furthermore, from the viewpoint of obtaining good snow and ice performance and wet grip performance, the content of the rubber composition is preferably 5 parts by mass or more, and more preferably 10 parts by mass or more, per 100 parts by mass of the rubber component.

[0106] (Rubber Crumb) The rubber composition preferably contains rubber crumb. The rubber crumb may be obtained by pulverizing used rubber products such as used tires and, if desired, removing reinforcing materials such as steel and fibers, dust, glass, sand, stones, etc., or by preparing a new vulcanized rubber composition for producing rubber crumb and pulverizing the pulverized rubber. For example, rubber crumb can be obtained from vulcanized rubber by the method described in "Rubber Chemistry and Technology." The process of pulverizing vulcanized rubber to obtain rubber crumb may involve mechanical treatment or low-temperature treatment. For example, in mechanical treatment, various crushing devices such as a cracker mill or a granulator can be used to mechanically crush the vulcanized rubber into fine particles. In low-temperature treatment, the finely chopped vulcanized rubber is frozen at a cryogenic temperature and then crushed into fine particles. A magnetic separator or the like can be used to remove steel, and an air separator or the like can be used to remove fibers. The rubber powder may be a commercially available product, such as those from Global Corporation or Nantong Huili Rubber Corporation. From the viewpoint of reducing the environmental impact, it is preferable to use rubber powder obtained by crushing used rubber products such as used tires. The rubber powder may be used alone or in combination of two or more types.

[0107] The composition of the rubber crumb is not particularly limited and depends on the composition of the vulcanized rubber from used rubber products (used tires) or the like that serve as the raw material. In one embodiment, the rubber crumb contains a rubber component, carbon black, silica, etc. The rubber component, carbon black, silica, etc. contained in the rubber crumb may be the same as or different from the rubber component, carbon black, silica, etc. contained in the rubber composition of this embodiment described above.

[0108] The rubber powder preferably has a volume average particle size of 1000 μm or less, more preferably 500 μm or less, even more preferably 200 μm or less, and even more preferably 100 μm or less. 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 with a laser diffraction particle size distribution analyzer, for example, a "CAPA500" manufactured by Horiba, Ltd.

[0109] The rubber powder preferably has a 60-mesh sieve residue of less than 1% by mass, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less, with no particular lower limit. The rubber powder preferably has an 80-mesh sieve residue of less than 10% by mass, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less, with no particular lower limit. In this specification, the sieve residue is measured in accordance with ASTM D5644-01.

[0110] The rubber crumb 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 extractable content in the rubber crumb refers to the acetone extractable content (%) determined by the acetone extraction method in accordance with JIS K6350.

[0111] The content of rubber crumb in the rubber component is not particularly limited, and can be adjusted appropriately depending on, for example, the tire category to which the rubber component is applied, the tire components, the target performance, etc. For example, the content of rubber crumb 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, still 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, per 100 parts by mass of the rubber component.

[0112] (Antiaging Agent) The rubber composition may further contain an antioxidant. Examples of the antioxidant include 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. Commercially available products can be used as the antioxidant, and examples of commercially available antioxidants that can be used include products from Ouchi Shinko Chemical Industry Co., Ltd., Sumitomo Chemical Co., Ltd., Seiko Chemical Co., Ltd., Flexis Co., Ltd., etc. These antioxidants may be used alone or in combination of two or more.

[0113] The content of the antioxidant is not particularly limited and can be adjusted appropriately depending on, for example, the tire category to which the antioxidant is applied, the tire components, the target performance, etc. For example, the content of the antioxidant 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, per 100 parts by mass of the rubber component.

[0114] (Wax) The rubber composition may also contain a wax. Examples of such waxes include natural waxes such as vegetable waxes and animal waxes; petroleum waxes such as paraffin wax and microcrystalline wax; and synthetic waxes such as ethylene polymers and propylene polymers. Commercially available waxes can be used, and examples of commercially available waxes include products from Seiko Chemical Co., Ltd., Nippon Seiro Co., Ltd., Ouchi Shinko Chemical Industry Co., Ltd., and the like. These waxes may be used alone or in combination of two or more.

[0115] The content of the wax is not particularly limited and can be adjusted appropriately depending on, for example, the tire category to which the rubber composition is applied, the tire components, 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, per 100 parts by mass of the rubber component.

[0116] (Stearic Acid) The rubber composition may contain stearic acid. Commercially available stearic acids are available, including those from NOF Corporation, Kao Corporation, Fujifilm Wako Pure Chemical Industries, Ltd., Chiba Fatty Acid Co., Ltd., and the like. These commercially available stearic acids may be used alone or in combination of two or more.

[0117] The content of stearic acid is not particularly limited and can be adjusted appropriately depending on, for example, the tire category to which the rubber composition is applied, the tire components, the target performance, etc. For example, the content of 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, per 100 parts by mass of the rubber component.

[0118] (Zinc Oxide) The rubber composition may also contain zinc oxide (zinc white). The zinc oxide is preferably zinc oxide obtained by recycling. Commercially available zinc oxide products can be used, including those available from Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., Mitsui Mining & Smelting Co., Ltd., and Toho Zinc Co., Ltd. These commercially available zinc oxide products may be used alone or in combination of two or more.

[0119] The content of the zinc oxide is not particularly limited and can be adjusted appropriately depending on, for example, the tire category to which the rubber composition is applied, the tire components, 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.

[0120] (Sulfur) The rubber composition preferably contains sulfur. The sulfur may be derived from fossil resources, recycled resources, or materials derived from the processing of biological resources. From the perspective of reducing environmental impact, sulfur obtained from waste derived from biological resources is particularly preferred. Examples of methods for obtaining sulfur from waste derived from biological resources include the method described in the aforementioned Japanese Patent Application No. 2022-140390. The sulfur may also be powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, soluble sulfur, and the like, which are commonly used as crosslinking agents in the rubber industry. Commercially available sulfur products are available from Tsurumi Chemical Industry Co., Ltd., Hosoi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Chemical Industry Co., Ltd., Flexis Corporation, Nippon Kanzuri Kogyo Co., Ltd., and the like. These sulfurs may be used alone or in combination of two or more.

[0121] 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 tire components, 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, more preferably 5 parts by mass or less, per 100 parts by mass of the rubber component.

[0122] (Void-introducing agent) The rubber composition preferably further contains a void-introducing agent. When the rubber composition contains the void-introducing agent, the vulcanized rubber has voids on the surface or inside, or on the surface and inside, so that a tire using the vulcanized rubber has flexibility and can easily adhere to icy road surfaces, and water on the road surface is absorbed into the voids on the tire surface, making it easy to remove water from the road surface, thereby improving braking performance on wet or icy road surfaces.

[0123] Examples of the void-introducing agent include foaming agents, metal sulfates, thermally expandable microcapsules, porous cellulose particles, lignin derivatives, etc., and one of these may be used alone or two or more may be mixed together. Furthermore, from the viewpoint of performance on ice, it is preferable to use the foaming agents.

[0124] The content of the void-introducing agent in the rubber composition is not particularly limited, but from the viewpoint of obtaining a desired void ratio and maintaining abrasion resistance, etc., it is preferably 0.1 to 20 parts by mass, more preferably 0.3 to 10 parts by mass, and even more preferably 0.5 to 5 parts by mass, per 100 parts by mass of the rubber component.

[0125] Foaming Agent: By including a foaming agent as the void-introducing agent in the rubber composition, bubbles are generated in the vulcanized rubber by the foaming agent during vulcanization of the rubber composition, thereby converting the vulcanized rubber into foamed rubber. Because foamed rubber is flexible, the surface of a tire using vulcanized rubber can easily adhere to icy road surfaces. In addition, the bubbles create holes (foam pores) on the surface of the vulcanized rubber and the tire surface, which function as water channels for draining water. Specific examples of foaming agents include inorganic foaming agents such as azodicarbonamide (ADCA), dinitrosopentamethylenetetramine (DPT), dinitrosopentastyrenetetramine, benzenesulfonyl hydrazide derivatives, p,p'-oxybisbenzenesulfonylhydrazide (OBSH), carbonates such as ammonium carbonate, sodium carbonate, and potassium carbonate, bicarbonates (hydrogen carbonates) such as ammonium bicarbonate, sodium bicarbonate, and potassium bicarbonate, nitrogen-generating nitrososulfonylazo compounds, N,N'-dimethyl-N,N'-dinitrosophthalamide, toluenesulfonylhydrazide, p-toluenesulfonylsemicarbazide, and p,p'-oxybisbenzenesulfonylsemicarbazide. Among these, from the viewpoint of manufacturing processability, it is preferable to use azodicarbonamide (ADCA), dinitrosopentamethylenetetramine (DPT), or an inorganic foaming agent, and it is more preferable to include at least sodium bicarbonate. These foaming agents may be used alone or in combination of two or more.

[0126] The content of the foaming agent in the rubber composition is not particularly limited, but is preferably 1 to 10 parts by mass, and more preferably 2 to 8 parts by mass, per 100 parts by mass of the rubber component. The rubber composition may further contain a foaming aid such as urea, zinc stearate, zinc benzenesulfinate, or zinc oxide. These may be used alone or in combination of two or more. The use of a foaming aid in combination can promote the foaming reaction, increase the degree of completion of the reaction, and suppress unnecessary deterioration over time.

[0127] Metal sulfate: When the rubber composition contains a metal sulfate as the void-introducing agent, the metal sulfate protrudes from the tire surface obtained by vulcanizing the rubber composition, performing a claw function without the disadvantage of being abrasive. Subsequently, the metal sulfate gradually leaves the rubber matrix, creating cavities that function as storage volumes and passages for draining the water film on the ice surface. Under these conditions, contact between the tire surface (e.g., the tread surface) and the ice is no longer lubricated, and therefore, examples of metal sulfates that improve the coefficient of friction include magnesium sulfate.

[0128] The metal sulfate preferably has micrometer-sized particles. Specifically, the average particle size and median particle size (both expressed by mass) are preferably 1 μm to 1 mm, and the median particle size is more preferably 2 μm to 800 μm. When the average particle size and median particle size are 1 μm or more, the desired technical effect (i.e., the formation of an appropriate micro-roughness) is easily achieved. Furthermore, when the rubber composition is used as a tread, when the average particle size and median particle size are 1 mm or less, deterioration in aesthetics is suppressed (the appearance of too obvious particles on the tread surface can be suppressed) and grip performance on melting ice is less likely to be impaired.

[0129] For all of these reasons, the median particle size of the metal sulfate is preferably 2 μm to 500 μm, and more preferably 5 μm to 200 μm. This particularly preferred particle size range appears to correspond to an optimal compromise between the desired surface roughness on the one hand and good contact between the rubber composition and the road surface on the other hand. Furthermore, for the same reasons as above, the content of the metal sulfate in the rubber composition is preferably 5 to 40 parts by mass, more preferably 10 to 35 parts by mass, per 100 parts by mass of the rubber component.

[0130] Various known methods for analyzing particle size and calculating the median particle size of microparticles (or the average diameter of microparticles assuming a substantially spherical shape), for example by laser diffraction, are applicable (see, for example, standard ISO-8130-13 or standard JIS K5600-9-3). Particle size analysis by mechanical sieving can also be used simply and preferably; the procedure consists in sieving a defined amount of sample (for example, 200 g) for 30 minutes on a vibrating table through various sieve diameters (for example, through meshes of 1000, 800, 630, 500, 400, ... 100, 80 and 63 μm, according to a progression ratio equal to 1.26); the oversize particles collected on each sieve are weighed on a precision balance; the percentage of the oversize particles at each mesh diameter relative to the total mass of the substance is estimated from the weighing; finally, the median particle size (or median diameter) or average particle size (or average diameter) is calculated in a known manner from a histogram of the particle size distribution.

[0131] Thermally Expandable Microcapsules: The thermally expandable microcapsules are configured by encapsulating a thermally expandable substance within a shell material made of a thermoplastic resin. The shell material of the thermally expandable microcapsules can be formed from a nitrile polymer. The thermally expandable substance encapsulated within the shell material of the microcapsules has the property of vaporizing or expanding upon heat, and is exemplified by at least one type selected from the group consisting of hydrocarbons such as isoalkanes and normal alkanes. Examples of isoalkanes include isobutane, isopentane, 2-methylpentane, 2-methylhexane, and 2,2,4-trimethylpentane. Examples of normal alkanes include n-butane, n-propane, n-hexane, n-heptane, and n-octane. These hydrocarbons may be used alone or in combination. A preferred form of the thermally expandable substance is one in which a hydrocarbon that is gaseous at room temperature is dissolved in a hydrocarbon that is liquid at room temperature. By using such a hydrocarbon mixture, sufficient expansion force can be obtained from low to high temperature ranges within the vulcanization molding temperature range (150°C to 190°C) of an unvulcanized tire.

[0132] Examples of such thermally expandable microcapsules include those manufactured by Expancel AB of Sweden under the trade names "EXPANCEL 091DU-80" or "EXPANCEL 092DU-120" and those manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd. under the trade names "Matsumoto Microsphere F-85D" or "Matsumoto Microsphere F-100D."

[0133] The content of the thermally expandable microcapsules in the rubber composition is preferably 0.1 to 10 parts by mass, and more preferably 0.5 to 5 parts by mass, per 100 parts by mass of the rubber component.

[0134] Porous Cellulose Particles When the rubber composition contains porous cellulose particles as the void-introducing agent, and the porous cellulose particles are exposed on the surface of a tire obtained by vulcanizing the rubber composition, water on the icy or snowy road surface is absorbed by the porous cellulose particles, thereby removing water from between the tire and the road surface. Furthermore, the presence of cellulose, which is a polysaccharide, causes an interaction between the tire and water on the icy or snowy road surface, which can further enhance the interaction between the tire and water by the modified polyoxyalkylene glycol.

[0135] The porous cellulose particles have a porous structure with a porosity of 75 to 95%, and when incorporated into a rubber composition, they can significantly improve performance on ice. A porosity of 75% or more in the porous cellulose particles provides excellent performance improvement on ice, while a porosity of 95% or less enhances particle strength. The porosity is more preferably 80 to 90%. The porosity of the porous cellulose particles can be calculated by measuring the volume of a given mass of sample (i.e., porous cellulose particles) with a measuring cylinder, determining the bulk density, and then using the following formula: Porosity [%] = {1 - (bulk density of sample [g / ml]) / (true specific gravity of sample [g / ml])} × 100, where the true specific gravity of cellulose is 1.5.

[0136] The particle size of the porous cellulose particles is not particularly limited, but from the viewpoint of abrasion resistance, particles having an average particle size of 1000 μm or less are preferably used. The lower limit of the average particle size is not particularly limited, but it is preferably 5 μm or more. The average particle size is more preferably 100 to 800 μm, and even more preferably 200 to 800 μm.

[0137] The porous cellulose particles are preferably spherical particles having a major axis / minor axis ratio of 1 to 2. The use of particles with such a spherical structure improves dispersibility in the rubber composition, contributing to improved performance on ice and maintenance of abrasion resistance, etc. The major axis / minor axis ratio is more preferably 1.0 to 1.5.

[0138] The average particle size and the major axis / minor axis ratio of porous cellulose particles can be determined as follows: the porous cellulose particles are observed under a microscope to obtain an image, and the major axis and minor axis (if the major axis and minor axis are the same, the length in a certain axis direction and the length in an axis direction perpendicular to the major axis) of 100 particles are measured using this image, and the average particle size is obtained by calculating the average value, and the major axis / minor axis ratio is obtained by averaging the values ​​obtained by dividing the major axis by the minor axis.

[0139] Such porous cellulose particles are commercially available from Rengo Co., Ltd. under the name "Viscopal" and are described in JP-A-2001-323095, JP-A-2004-115284, etc., and these can be suitably used. The content of the porous cellulose particles in the rubber composition is preferably 0.3 to 20 parts by mass per 100 parts by mass of the rubber component. A content of 0.3 parts by mass or more can enhance the effect of improving performance on ice, and a content of 20 parts by mass or less can prevent the rubber hardness from becoming too high and suppress a decrease in abrasion resistance. The content of the porous cellulose particles is more preferably 1 to 15 parts by weight, and even more preferably 3 to 15 parts by mass.

[0140] Lignin Derivative: When the rubber composition contains a lignin derivative as the void-introducing agent, the effect of improving performance on ice can be enhanced. Here, lignin sulfonates are preferably used as the lignin derivative. Examples of lignin sulfonates include alkali metal salts, alkaline earth metal salts, ammonium salts, and alcoholamine salts of lignin sulfonic acid, and at least one of these can be used. Preferred are alkali metal salts and / or alkaline earth metal salts of lignin sulfonic acid, such as potassium salt, sodium salt, calcium salt, magnesium salt, lithium salt, and barium salt, and mixed salts thereof are also acceptable.

[0141] (Foaming Aid) Furthermore, when the rubber composition contains a foaming agent as the void-introducing agent, it is preferable that the rubber composition further contains a foaming aid. Examples of the foaming aid include urea, zinc stearate, zinc benzenesulfinate, zinc oxide, etc. These may be used alone or in combination of two or more. By using the foaming aid in combination, it is possible to promote the foaming reaction, increase the degree of completion of the reaction, and suppress unnecessary deterioration over time.

[0142] Furthermore, the total content of the foaming agent and the foaming aid is preferably 1 to 30 parts by mass per 100 parts by mass of the rubber component. When the total content of the foaming agent and the foaming aid is 1 part by mass or more, the rubber composition can be sufficiently foamed during vulcanization, and the foaming rate of the vulcanized rubber can be maintained high. On the other hand, even when the total content of the foaming agent and the foaming aid is 30 parts by mass or less, a decrease in the foaming rate can be suppressed. From the viewpoint of suppressing a decrease in the foaming rate as described above, the total content of the foaming agent and the foaming aid is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, per 100 parts by mass of the rubber component. From the viewpoint of suppressing a decrease in the foaming rate as described above, the total content of the foaming agent and the foaming aid is preferably 25 parts by mass or less, more preferably 20 parts by mass or less, per 100 parts by mass of the rubber component.

[0143] In addition, in the rubber composition, the mass ratio of the foaming agent to the foaming aid (foaming agent:foaming aid) is preferably 1:1.1 to 1:3.3. If the mass ratio (foaming agent:foaming aid) is less than 1:1.1, the rubber composition may not foam sufficiently during vulcanization, which may result in a decrease in the foaming rate of the vulcanized rubber. On the other hand, if the mass ratio (foaming agent:foaming aid) exceeds 1:3.3, the foaming rate may also decrease. From the viewpoint of suppressing the decrease in the foaming rate as described above, the mass ratio of the foaming agent to the foaming aid (foaming agent:foaming aid) is preferably 1:1.2 or more, and more preferably 1:1.3 or more. From the viewpoint of suppressing a decrease in the foaming rate as described above, the mass ratio of the foaming agent to the foaming aid (foaming agent:foaming aid) is preferably 1:3.2 or less, more preferably 1:3.1 or less, even more preferably 1:2.9 or less, still more preferably 1:2.7 or less, still more preferably 1:2.5 or less, and particularly preferably 1:2.3 or less.

[0144] From the viewpoints of the foaming rate of the vulcanized rubber and the wet performance of the tire, the content of the foaming aid is preferably in the range of 4 to 14 parts by mass, and more preferably in the range of 6 to 14 parts by mass, per 100 parts by mass of the rubber component.

[0145] (Organic Acid) The rubber composition may contain an organic acid, if necessary. In this case, the SP value of the organic acid is 9.15 to 16.0 (cal / cm ３ ) １／２ The organic acid has the effect of improving the foaming rate of the vulcanized rubber by balancing the rate of the decomposition / foaming reaction of the foaming agent and the rate of the vulcanization reaction of the rubber composition during vulcanization of the rubber composition. Therefore, by compounding the organic acid into the rubber composition, the workability of the rubber composition is maintained good, while the decomposition / foaming reaction of the foaming agent is promoted, and the rate of the decomposition / foaming reaction and the rate of the vulcanization reaction of the rubber composition are balanced, thereby improving the foaming rate of the vulcanized rubber. By applying this rubber composition to a tire, the wet performance of the tire can be improved. The SP value of the organic acid is 9.15 (cal / cm ３ ) １／２If the SP value of the organic acid is less than 16.0 (cal / cm), the decomposition of the foaming agent may not be sufficiently promoted. ３ ) １／２ If the content exceeds this range, the adhesiveness of the rubber composition containing the organic acid will be high, and the rubber composition may adhere to manufacturing equipment such as rolls during production of the rubber composition, which may deteriorate the workability of the rubber composition.

[0146] From the same viewpoint, the SP value of the organic acid is 10.5 to 14.3 (cal / cm ３ ) １／２ The SP value of the organic acid is preferably 10.5 (cal / cm ３ ) １／２ When the SP value of the organic acid is 14.3 (cal / cm or more), the effect of promoting the decomposition of the foaming agent is further increased. ３ ) １／２ When the SP value is 9.12 (cal / cm), the adhesiveness of the rubber composition containing the organic acid can be further reduced, and the workability of the rubber composition can be further improved. ３ ) １／２ In this specification, the SP value (solubility parameter) of an organic acid is calculated according to the Fedors method.

[0147] The organic acid may be any of monocarboxylic acid, dicarboxylic acid, tricarboxylic acid, etc., and may be aliphatic or aromatic. Furthermore, it may have a functional group other than a carboxyl group, such as a hydroxyl group, a ketone group, or an ethylenically unsaturated group. The organic acid preferably has an aromatic ring (aromatic), and more preferably a monocarboxylic acid. When the organic acid has an aromatic ring, the adhesion of the rubber composition can be further reduced, the workability of the rubber composition is further improved, and the rubber composition is less likely to adhere to manufacturing equipment such as rolls.

[0148] Examples of the aliphatic monocarboxylic acid include palmitic acid. Examples of the aliphatic dicarboxylic acid include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid. Examples of the aromatic monocarboxylic acid include benzoic acid and salicylic acid. Examples of the aromatic dicarboxylic acid include phthalic acid. Examples of organic acids having a functional group other than a carboxyl group include tartaric acid, malic acid, maleic acid, glycolic acid, and α-ketoglutaric acid. The organic acids may be used alone or in combination of two or more.

[0149] It is particularly preferable to use benzoic acid as the organic acid. When benzoic acid is compounded into the rubber composition, the adhesion of the rubber composition can be further reduced, the workability of the rubber composition is further improved, and the rubber composition becomes even less likely to adhere to manufacturing equipment such as rolls.

[0150] From the viewpoints of workability of the rubber composition, the foaming rate of the vulcanized rubber, and the wet performance of the tire, the content of the organic acid is preferably 0.1 to 7 parts by mass, more preferably 1.5 to 7 parts by mass, and even more preferably 3 to 7 parts by mass, per 100 parts by mass of the rubber component. Furthermore, from the viewpoints of the foaming rate of the vulcanized rubber and the wet performance of the tire, the total content of the foaming agent and the organic acid is preferably 3 parts by mass or more and less than 15 parts by mass, more preferably 5 parts by mass or more and less than 15 parts by mass, and even more preferably 7 parts by mass or more and less than 15 parts by mass, per 100 parts by mass of the rubber component. Furthermore, from the viewpoints of the foaming rate of the vulcanized rubber and the wet performance of the tire, the mass ratio of the foaming agent to the organic acid (foaming agent:organic acid) is preferably in the range of 1:0.5 to 1:1.5, and more preferably 1:0.7 to 1:1.3.

[0151] (Composite Fiber) The rubber composition preferably further contains a composite fiber. By containing the composite fiber, it is possible to ensure sufficient affinity with water, and to impart excellent drainage and wet performance, particularly when used in tire applications. Furthermore, it is preferable that the composite fiber is made of a hydrophilic resin having a coating layer formed on the surface. This is because providing a coating layer on the surface of the composite fiber improves the dispersibility of the composite fiber in the rubber composition. The hydrophilic resin is preferably insoluble in water, and by using a water-insoluble hydrophilic resin, it is possible to suppress dissolution of the composite fiber even when it is exposed on the surface of a product (e.g., a tire).

[0152] The hydrophilic resin is not particularly limited as long as it is a resin that can exhibit affinity with water, that is, a resin that has a hydrophilic group in the molecule, but specifically, a resin containing an oxygen atom, a nitrogen atom, or a sulfur atom is preferred, and examples thereof include resins containing at least one group selected from the group consisting of -OH, -C(=O)OH, -OC(=O)R (R is an alkyl group), -NH2, -NCO, and -SH. Among these groups, -OH, -C(=O)OH, -OC(=O)R, -NH2, and -NCO are preferred. More specific examples of the hydrophilic resin include ethylene-vinyl alcohol copolymers, vinyl alcohol homopolymers, poly(meth)acrylic acid resins or ester resins thereof (hereinafter, copolymers containing structural units derived from (meth)acrylic acid and (co)polymers containing structural units derived from (meth)acrylic acid esters are collectively referred to as (meth)acrylic resins), polyamide resins, polyethylene glycol resins, carboxyvinyl copolymers, styrene-maleic acid copolymers, polyvinylpyrrolidone resins, vinylpyrrolidone-vinyl acetate copolymers, polyester resins, cellulose-based resins, etc. Among these, ethylene-vinyl alcohol copolymers, vinyl alcohol homopolymers, poly(meth)acrylic acid resins, polyamide resins, aliphatic polyamide-based resins, aromatic polyamide-based resins, polyester resins, polyvinyl alcohol-based resins, cellulose-based resins, and (meth)acrylic resins are preferred, with ethylene-vinyl alcohol copolymers being more preferred.

[0153] The surface of the fiber made of the hydrophilic resin is preferably coated with a low-melting-point resin (hereinafter also referred to as "low-melting-point resin") that has affinity for the rubber component and preferably has a melting point lower than the maximum vulcanization temperature. Forming such a coating layer effectively maintains the hydrophilic resin's inherent affinity for water while exhibiting good affinity with the rubber component near the composite fiber. It also captures the hydrophilic resin, which is difficult to melt during vulcanization (foaming), and promotes the formation of cavities within the composite fiber. That is, it ensures good dispersion of the composite fiber in the rubber component, fully exhibiting the drainage effect due to the hydrophilic resin, while also fully exhibiting the wet performance improvement effect due to the voids present within the composite fiber. Furthermore, the low-melting-point resin melts during vulcanization to form a fluid coating layer, contributing to improved adhesion between the rubber component and the composite fiber, thereby imparting good wet performance and abrasion resistance. The thickness of the coating layer may vary depending on the amount of the hydrophilic resin blended, the average diameter of the composite fiber, and other factors, but is preferably 0.001 to 10 μm, and more preferably 0.001 to 5 μm. By forming the coating layer with a thickness within the above range, the desired effects of the present invention can be fully achieved. The coating layer may be formed over the entire surface of the hydrophilic resin, or may be formed on only a portion of the surface of the hydrophilic resin. Specifically, it is preferable that the coating layer be formed so as to occupy at least 50% of the total surface area of ​​the hydrophilic resin.

[0154] Specifically, the low-melting-point resin used in the coating layer is preferably a resin in which the polar component is 50% by mass or less of the total components, and more preferably a polyolefin resin. Resins with polar components within the above range have an appropriate difference in SP value with the rubber component and a melting point that is appropriately lower than the maximum vulcanization temperature. This allows for easy melting during vulcanization and promotes foaming of the vulcanized rubber while ensuring sufficient affinity with the rubber component. This allows for more reliably improved dispersion of the hydrophilic resin fiber in the rubber composition and reliably forming cavities within the composite fiber.

[0155] The polyolefin-based resin may be branched, linear, or the like. It may also be an ionomer resin in which ethylene-methacrylic acid copolymer molecules are crosslinked with metal ions. Specific examples of the polyolefin-based resin include polyethylene, polypropylene, polybutene, polystyrene, ethylene-propylene copolymer, ethylene-methacrylic acid copolymer, ethylene-ethyl acrylate copolymer, ethylene-propylene-diene terpolymer, ethylene-vinyl acetate copolymer, and ionomer resins thereof. These may be used alone or in combination of two or more. Among these, polyethylene-based resins, polypropylene-based resins, polyolefin ionomers, and maleic anhydride-modified α-polyolefins are preferred as the polyolefin-based resin. When polyolefin ionomers or maleic anhydride-modified α-polyolefins are used, they also adhere to the hydroxyl groups of hydrophilic resins, thereby further improving rubber strength.

[0156] To produce a composite fiber made of a hydrophilic resin with a coating layer made of the low-melting-point resin, the resins can be blended using a mixing mill, melt-spun to form an undrawn yarn, and then hot-drawn the undrawn yarn to form a fiber. Alternatively, the resins can be blended using two twin-screw extruders equipped with dies and then similarly shaped into a fiber. In this case, the hydrophilic resin and the low-melting-point resin are simultaneously extruded from the two die outlets, forming an undrawn yarn. The amount of resins added to the mixing mill or hopper varies depending on the length and diameter of the resulting composite (fiber), but is preferably 5 to 300 parts by mass, more preferably 10 to 150 parts by mass, of the low-melting-point resin per 100 parts by mass of the hydrophilic resin. Adding these resins in amounts within the above ranges effectively forms a coating layer that can exert the desired effects on the surface of the hydrophilic resin composite (fiber) obtained after the drawing process.

[0157] The average length of the resulting composite fiber is preferably 0.1 to 500 mm, more preferably 0.1 to 7 mm, and the average diameter is preferably 0.001 to 2 mm, more preferably 0.005 to 0.5 mm. When the average length and average diameter are within the above ranges, there is no risk of the composite fibers becoming entangled more than necessary, and there is no risk of impairing good dispersibility. The aspect ratio is preferably 10 to 4,000, more preferably 50 to 2,000. The aspect ratio refers to the ratio of the major axis to the minor axis of the composite fiber.

[0158] Furthermore, with regard to the obtained conjugated fiber, the ratio (A / B) of the length A of the cross section in the major axis direction in a cross section perpendicular to the major axis direction to the length B of the cross section in the minor axis direction perpendicular to the major axis direction is preferably greater than 1, more preferably 1.5 or more, even more preferably 1.8 or more, and particularly preferably 2.0 or more. The ratio A / B is preferably 20 or less, even more preferably 15 or less, and particularly preferably 10 or less. By setting it in the above range, the wet performance is further improved. Note that, as long as A / B is greater than 1, the cross-sectional shape is not particularly limited and may be any of elliptical, rectangular, polygonal, irregular, etc.

[0159] The blending amount of the composite fiber made of a hydrophilic resin having a coating layer formed thereon is preferably 0.1 to 100 parts by mass, more preferably 0.3 to 30 parts by mass, even more preferably 0.5 to 10 parts by mass, and even more preferably 1 to 6 parts by mass, per 100 parts by mass of the rubber component. When the blending amount of the composite fiber made of a hydrophilic resin having a coating layer formed thereon is within the above range, cavities are formed inside the composite fiber, thereby exhibiting good drainage properties and maintaining sufficient durability. Furthermore, the content ratio of the composite fiber and the void-introducing agent is not particularly limited, but from the viewpoint of achieving and improving both abrasion resistance and wet performance, the mass ratio of the composite fiber to the void-introducing agent (void-introducing agent / composite fiber) is preferably 0.5 to 10, more preferably 1 to 8, even more preferably 1.5 to 7, and particularly preferably 2 to 6.

[0160] (Other Components) In addition to the above-mentioned components, the rubber composition may contain compounding agents commonly used in the rubber industry as other components. Examples of other components include fillers other than the above-mentioned reinforcing fillers; organic peroxides; etc. The content of these additives is not particularly limited and can be adjusted appropriately depending on, for example, the tire category to which the composition is applied, the tire components, the target performance, etc. For example, the content is preferably in the range of 0.1 to 200 parts by mass per 100 parts by mass of the rubber component.

[0161] (Method for producing vulcanized rubber composition for studless tires) The method for producing the vulcanized rubber composition for studless tires of the present invention is not particularly limited, but for example, the rubber composition can be produced by blending various components appropriately selected as necessary with the rubber component, and kneading, heating, extruding, etc. The obtained rubber composition can then be vulcanized to produce a vulcanized rubber.

[0162] 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 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.

[0163] The conditions for the heat-in are not particularly limited, and various conditions such as the heat-in temperature, heat-in time, and heat-in device can be appropriately selected depending on the purpose. Examples of the heat-in device include a heat-in roll mill typically used for heat-in of rubber compositions.

[0164] 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 typically used for extruding rubber compositions. The extrusion temperature can be appropriately determined.

[0165] The vulcanization apparatus, method, conditions, etc. are not particularly limited and can be appropriately selected depending on the purpose. Examples of apparatuses for vulcanization include molding vulcanizers using molds used for vulcanizing rubber compositions. The vulcanization temperature is, for example, about 100 to 190°C.

[0166] <Studless Tire> The studless tire of the present invention is characterized by including the vulcanized studless rubber composition of the present invention described above. Use of this rubber composition results in excellent wet performance and ice performance, and also improves workability and sustainability. Here, the studless tire of the present invention can be used, for example, as a tire for a construction vehicle, a tire for a truck or a bus, a tire for an aircraft, or a tire for a passenger car, and is particularly preferably a tire for a passenger car or a tire for a truck or a bus. This is because the vulcanized studless rubber composition used as a material for the tread portion has excellent wet performance and abrasion resistance, and is therefore a great advantage when used as a tire for a passenger car or a tire for a truck or a bus.

[0167] When the vulcanized rubber composition for studless tires of the present invention is used, for example, an unvulcanized rubber composition may be molded and then vulcanized, or a semi-vulcanized rubber that has been subjected to a pre-vulcanization step or the like may be molded and then further vulcanized. The tire of this embodiment is preferably a pneumatic tire, and the gas to be filled into 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.

[0168] 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.

[0169] [Example 1, Comparative Example 1] Rubber composition samples are prepared by compounding and kneading in the usual manner according to the formulations shown in Table 1. In Table 1, the rubber component, silica, carbon black, resin component, and liquid softener component are expressed as integers. Others are expressed to one decimal place. For the obtained rubber composition, 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.

[0170]

[0171] The components used in Table 1 above are as follows: Natural rubber: TSR20 Modified BR: cis-1,4-polybutadiene rubber, trade name "UBEPOL 150L" manufactured by UBE Elastomers Co., Ltd. Modified SBR: modified styrene-butadiene copolymer rubber produced by the following method Silica: NIPSIL AQ manufactured by Tosoh Silica Co., Ltd., trade name, CTAB specific surface area = 150 m ２ / g, nitrogen adsorption specific surface area (N ２ SA) = 200m ２ / g Carbon black: Asahi Carbon Co., Ltd., trade name "Carbon N134", N2SA = 146 m ２ / g Silane coupling agent: Evonic Corporation, trade name "Si69" Naphthenic process oil, Idemitsu Kosan Co., Ltd., trade name "Diana Process Oil NS-24", pour point = -30°C C5 resin: Tonen Chemical Co., Ltd., trade name "Escorez 1102" Terpene resin: Kraton Corporation, trade name "SYLVATRAXX8125" Void-introducing agent: foaming agent, dinitrosopentamethylenetetramine (DPT) Hydrophilic short fibers: hydrophilic short fibers prepared by the following method Stearic acid: New Japan Chemical Co., Ltd., trade name "Stearic Acid 50S" Zinc oxide: Hakusui Tech Co., Ltd., trade name "Zinc Oxide No. 3" Vulcanization accelerator: Ouchi Shinko Chemical Industry Co., Ltd., trade name "Noccela DM", di-2-benzothiazolyl disulfide Vulcanizing agent: Tsurumi Chemical Co., Ltd., trade name "Powdered sulfur" Antioxidant: N-isopropyl-N'-phenyl-p-phenylenediamine

[0172] (Method for Producing Modified SBR) A cyclohexane solution of 1,3-butadiene and a cyclohexane solution of styrene were added to a dried, nitrogen-purged 800 mL pressure-resistant glass vessel so that the total weight of the mixture was 67.5 g of 1,3-butadiene and 7.5 g of styrene. 0.6 mmol of 2,2-ditetrahydrofurylpropane and 0.8 mmol of n-butyllithium were then added. Polymerization was then carried out at 50°C for 1.5 hours. To the polymerization reaction system, which had reached a polymerization conversion rate of nearly 100%, 0.72 mmol of N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane was added as a modifier, and the modification reaction was carried out at 50°C for 30 minutes. The reaction was then terminated by adding 2 mL of a 5% by weight solution of 2,6-di-t-butyl-p-cresol (BHT) in isopropanol, and the mixture was dried in the usual manner to obtain modified SBR.

[0173] (Method for producing hydrophilic staple fibers) According to Production Example 3 disclosed in JP 2012-219245 A, two twin-screw extruders were 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.] were charged into the hoppers. Each was simultaneously extruded from the die outlet, and the resulting fibers were cut to a length of 2 mm according to a conventional method to produce hydrophilic staple fibers having a polyethylene coating layer formed thereon.

[0174] The results in Table 1 also show that the rubber compositions of the examples are excellent in sustainability.

[0175] According to the present invention, it is possible to provide a vulcanized rubber composition for studless tires that is excellent in wet performance and ice performance, and also has improved workability and sustainability. Furthermore, according to the present invention, it is also possible to provide a studless tire that is excellent in wet performance and ice performance, and also has improved workability and sustainability.

[0176] 10 Vulcanized rubber composition for studless tires 20 Void

Claims

1. A vulcanized rubber composition for studless tires, obtained by vulcanizing a rubber composition containing a rubber component, a resin component, and a liquid plasticizer, wherein the resin component is at least one type selected from the group consisting of terpene-based resins and rosin-based resins, the content of the resin component is 15 parts by mass or more per 100 parts by mass of the rubber component, the content of the liquid plasticizer is 30 parts by mass or less per 100 parts by mass of the rubber component, and the vulcanized rubber composition has a plurality of voids.

2. The vulcanized rubber composition for studless tires according to claim 1, wherein the resin component contains at least a rosin-based resin.

3. The vulcanized rubber composition for studless tires according to claim 1 or 2, characterized in that the rubber composition further contains a void-introducing agent.

4. The vulcanized rubber composition for studless tires according to claim 1 or 2, characterized in that the rubber composition further contains a foaming agent and a foaming assistant.

5. A studless tire comprising the vulcanized rubber composition for studless tires according to claim 1 or 2.

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