Vulcanized rubber composition for tires, and tire

Abstract

Provided is a vulcanized rubber composition for tires, which has excellent on-ice performance.　The present invention is characterized by being obtained by vulcanizing a rubber composition comprising a rubber component that contains a modified conjugated diene-based polymer having a (meth)acrylic acid ester in the molecule, and a filler that contains at least silica. The present invention is characterized in that the content of silica in the rubber composition is 30-70 parts by mass with respect to 100 parts by mass of the rubber component, and the proportion of the silica in the filler is 55 mass% or more. The present invention is further characterized by having a plurality of voids.

Description

Vulcanized rubber composition for tires and tires

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

[0002] When tires are driven on snowy and icy roads, a film of water forms between the road surface and the tire, causing the tire to slip and reducing braking performance. Therefore, there is a demand for studless tires to have improved performance on ice, such as gripping effectively on snowy and icy roads and making it easier to brake the vehicle.

[0003] Known methods for improving performance on ice include increasing the surface roughness (surface irregularities) of the tread rubber and improving its flexibility (flexibility and adhesion) at low temperatures. It is believed that increasing the surface roughness of the tread rubber allows the recessed portions to capture the water film on the ice and the protruding portions to come into contact with the ice surface, thereby increasing the contact area with the ice surface compared to tread rubber with a smooth surface. A common method for increasing the surface roughness of tread rubber is to incorporate a foaming agent or thermally expandable microcapsules into the rubber composition (see, for example, Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2020-19862

[0005] However, with the method exemplified in Patent Document 1, while the greater the surface roughness, the more water film can be absorbed, the smaller the area that can come into contact with the ice surface. For this reason, it can be said that there is a limit to the effectiveness of surface roughness in improving performance on ice.

[0006] Therefore, an object of the present invention is to provide a vulcanized rubber composition for tires having excellent performance on ice. Another object of the present invention is to provide a tire having excellent performance on ice.

[0007] The present inventors have conducted extensive research to further improve on-ice performance, and have found that by incorporating a modified conjugated diene polymer having a (meth)acrylic acid ester in the molecule into a vulcanized rubber composition for tires and by forming multiple voids, it is possible to significantly improve on-ice performance, and further by optimizing the silica content in the rubber composition and the silica content ratio in the filler, it is possible to increase the contact area with the road surface when the rubber composition is applied to a tire, thereby achieving even better on-ice performance.

[0008] That is, the vulcanized rubber composition for tires of the present invention is obtained by vulcanizing a rubber composition including a rubber component containing a modified conjugated diene polymer having a (meth)acrylic acid ester in the molecule and a filler containing at least silica, wherein the content of silica in the rubber composition is 30 to 70 parts by mass per 100 parts by mass of the rubber component, and the proportion of silica in the filler is 55% by mass or more, and the rubber composition has a plurality of voids. By having the above configuration, excellent performance on ice can be achieved.

[0009] In the vulcanized rubber composition for tires of the present invention, the content of the (meth)acrylic acid ester in the modified conjugated diene polymer is preferably 0.5 to 10 mol %, because this allows for achieving better performance on ice without deteriorating performance such as abrasion resistance.

[0010] Additionally, in the vulcanized rubber composition for tires of the present invention, the (meth)acrylic acid ester is preferably an alkoxyalkyl (meth)acrylic acid ester, since this allows for better performance on ice to be achieved.

[0011] Furthermore, in the vulcanized rubber composition for tires of the present invention, the glass transition temperature of the modified conjugated diene polymer is preferably −100 to −50° C. This is because better performance on ice can be achieved without deteriorating performance such as abrasion resistance.

[0012] Furthermore, in the vulcanized rubber composition for tires of the present invention, it is preferable that the modified conjugated diene polymer contains 1,3-butadiene units, and the vinyl bond content of the 1,3-butadiene units is 10 to 20 mol %, because this allows for achieving better performance on ice without deteriorating performance such as abrasion resistance.

[0013] Furthermore, in the vulcanized rubber composition for tires of the present invention, the content ratio of the modified conjugated diene polymer in the rubber component is preferably 5 to 40% by mass, because this allows for achieving better performance on ice without deteriorating performance such as abrasion resistance.

[0014] In the vulcanized rubber composition for tires of the present invention, the rubber component preferably further contains an unmodified conjugated diene polymer having a bound styrene content of less than 10% and a vinyl bond content of 20% or more in the conjugated diene units, because this allows for excellent on-ice performance to be achieved without deteriorating other performances.

[0015] Furthermore, in the vulcanized rubber composition for tires of the present invention, the vinyl bond content of the conjugated diene units of the unmodified conjugated diene polymer is preferably 70% or less, because this allows for excellent on-ice performance to be achieved without deteriorating other performances.

[0016] In the vulcanized rubber composition for tires of the present invention, the vinyl bond content of the conjugated diene units of the unmodified conjugated diene polymer is preferably 45% or more and 55% or less, because this allows for excellent on-ice performance to be achieved without deteriorating other performances.

[0017] Furthermore, in the vulcanized rubber composition for tires of the present invention, the unmodified conjugated diene polymer is preferably unmodified polybutadiene, because this allows for excellent performance on ice to be achieved without deteriorating other performances.

[0018] Furthermore, in the vulcanized rubber composition for tires of the present invention, the content ratio of the unmodified conjugated diene polymer is preferably 1 to 40 mass %, because this allows for the realization of excellent on-ice performance without deteriorating other performances.

[0019] In the vulcanized rubber composition for tires of the present invention, the mass ratio of the content of the modified conjugated diene polymer to the content of the unmodified conjugated diene polymer (content of modified conjugated diene polymer / content of liquid polymer) is preferably 0.5 to 5. This is because better on-ice performance can be achieved without deteriorating other performances.

[0020] In addition, in the vulcanized rubber composition for a tire of the present invention, the rubber composition preferably further contains a void-introducing agent, and more preferably the void-introducing agent is at least one selected from the group consisting of a foaming agent, a metal sulfate, a thermally expandable microcapsule, porous cellulose, and a lignin derivative, because this allows for better on-ice performance to be achieved.

[0021] Furthermore, in the vulcanized rubber composition for tires of the present invention, it is preferable that the rubber composition further contains bicomponent fibers, because this allows for achieving better performance on ice.

[0022] Furthermore, in the vulcanized rubber composition for tires of the present invention, the void ratio of the vulcanized rubber composition for tires is preferably 5 to 45%, because this allows for better performance on ice to be achieved.

[0023] In the vulcanized rubber composition for tires of the present invention, the rubber component more preferably contains natural rubber and butadiene rubber or styrene-butadiene rubber, because this allows for achieving better performance on ice while maintaining good performance such as abrasion resistance and low heat buildup.

[0024] Furthermore, in the vulcanized rubber composition for tires of the present invention, the content ratio of the natural rubber in the rubber component is preferably 30 to 70% by mass, because this allows for achieving better performance on ice while maintaining good performance such as abrasion resistance and low heat buildup.

[0025] Furthermore, in the vulcanized rubber composition for tires of the present invention, the content ratio of the butadiene rubber or the styrene-butadiene rubber in the rubber component is preferably 15 to 45% by mass, because this allows for achieving better performance on ice without deteriorating performance such as abrasion resistance.

[0026] In the vulcanized rubber composition for tires of the present invention, the rubber composition preferably contains a fatty acid amide, and more preferably contains 0.1 to 10 parts by mass of the fatty acid amide per 100 parts by mass of the rubber component, because this allows for better performance on ice to be achieved without deteriorating performance such as abrasion resistance.

[0027] Furthermore, in the vulcanized rubber composition for tires of the present invention, the fatty acid amide is preferably a fatty acid bisamide, and more preferably an ethylene bis fatty acid amide, because this allows for better performance on ice to be achieved.

[0028] The tire of the present invention is characterized in that the above-mentioned vulcanized rubber composition for a tire is used in the tread portion. By having the above-mentioned constitution, excellent performance on ice can be achieved.

[0029] In addition, in the tire of the present invention, the tread surface of the tread portion is partitioned into a plurality of blocks by a plurality of circumferential main grooves extending in the tire circumferential direction and a plurality of widthwise grooves extending in the tire width direction, and a plurality of sipes and a plurality of shallow grooves are provided on the surface of each block so as to extend in opposite directions in the tire width direction relative to one direction in the tire circumferential direction, and the depth of the shallow grooves is smaller than the depth of the sipes, the inclination angle θ1 of the sipes with respect to the tire circumferential direction is greater than 0° and less than 90°, and the inclination angle θ2 of the shallow grooves with respect to the tire circumferential direction is greater than 0° and less than 90°, and the magnitude of the difference between the inclination angle θ1 and the inclination angle θ2 is preferably 30° or less, because this allows for better on-ice performance to be achieved without compromising performance such as wear resistance.

[0030] According to the present invention, it is possible to provide a vulcanized rubber composition for a tire having excellent performance on ice, and also to provide a tire having excellent performance on ice.

[0031] FIG. 1 is a diagram schematically showing a plurality of voids present in a vulcanized rubber composition for a tire according to one embodiment of the present invention. FIG. 2 is a diagram schematically showing a cross section of a void present in a vulcanized rubber composition for a tire according to one embodiment of the present invention. FIG. 3 is a development diagram schematically showing a tread pattern of a pneumatic tire according to one embodiment of the present invention. FIG. 4 is a diagram schematically showing water flow when θ1 = 60° and θ2 = 15°. FIG. 5 is a diagram schematically showing water flow when θ1 = θ2 = 60°.

[0032]

[0023] Hereinafter, embodiments of the present invention will be described with reference to the drawings as necessary. <Vulcanized rubber composition for tire> The vulcanized rubber composition for tire of the present invention is a vulcanized rubber composition for tire obtained by vulcanizing a rubber composition including a rubber component containing a modified conjugated diene-based polymer having a (meth)acrylic acid ester in the molecule, and is characterized in that the vulcanized rubber composition for tire 10 has a plurality of voids 20, as shown in Figure 1.

[0033] In the vulcanized rubber composition for tires of the present invention, a modified conjugated diene polymer having a (meth)acrylic acid ester in the molecule, which will be described later, is contained in the rubber composition. In addition, the vulcanized rubber composition for tires 10 of the present invention has a plurality of voids 20 as shown in FIG. 1 , which can greatly improve the performance on ice when applied to tires.

[0034] Here, the voids in the vulcanized rubber composition for 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 tires, as shown in FIG. 1 . The void diameter refers to the largest diameter D of the voids 20 (if the voids are not spherical, the largest distance D between any two points on the inner wall of the voids), 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 tires of the present invention. In the present invention, the cross section of the vulcanized rubber composition for 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 × 2.5 mm) is used. Since the shape and size of the voids do not vary significantly within a single vulcanized rubber composition for tires, the average value of the voids in one field of view can be used as the average void diameter.

[0035] Furthermore, the porosity of the vulcanized rubber composition for tires of the present invention is preferably 5 to 45%. By setting the lower limit of the porosity to 5%, it is possible to more reliably improve performance on ice. 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%, it is possible to more reliably suppress deterioration in abrasion resistance 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 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.).

[0036] Here, the vulcanized rubber composition for tires of the present invention has a plurality of voids, but the method for providing 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 tires. For example, as described below, a method for providing voids in the vulcanized rubber composition for tires can be exemplified 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.

[0037] The vulcanized rubber composition for 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 performed under any conditions depending on the required performance.

[0038] The unvulcanized rubber composition (hereinafter simply referred to as "rubber composition") that is the base material for the vulcanized rubber composition for tires of the present invention will be described below. The rubber composition includes a rubber component containing a modified conjugated diene-based polymer having a (meth)acrylic acid ester in the molecule.

[0039] (Rubber Component) The rubber component contained in the rubber composition is required to contain a modified conjugated diene polymer having a (meth)acrylic acid ester in the molecule (hereinafter, sometimes referred to as a "(meth)acrylic acid ester-modified polymer"). Because the (meth)acrylic acid ester is hydrophilic, using a polymer having a (meth)acrylic acid ester incorporated in the molecule as a rubber component can hydrophilize the rubber surface, thereby significantly improving performance on ice. Additionally, since the (meth)acrylic acid ester-modified polymer has a (meth)acrylic acid ester moiety in the molecule, it can also suppress deterioration in performance such as abrasion resistance compared to when a hydrophilic material such as a resin is added to the rubber composition. The term "(meth)acrylic acid ester" refers to an acrylic acid ester and / or a methacrylic acid ester, and "having a (meth)acrylic acid ester in the molecule" means that the (meth)acrylic acid ester is incorporated in the molecule as a functional group (e.g., an acryloyl group, a methacryloyl group), and does not include mixtures. Among these, the (meth)acrylic acid ester is preferably an alkoxyalkyl (meth)acrylic acid ester.

[0040] The (meth)acrylic acid ester-modified polymer is not particularly limited as long as it contains a (meth)acrylic acid ester in the molecule, but the (meth)acrylic acid ester content in the (meth)acrylic acid ester-modified polymer is preferably 0.5 to 10 mol%. When the (meth)acrylic acid ester content in the (meth)acrylic acid-modified polymer is 1 mol% or more, sufficient hydrophilicity is obtained, resulting in better performance on ice. When the (meth)acrylic acid ester content in the (meth)acrylic acid ester-modified polymer is 10 mol% or less, deterioration in performance such as abrasion resistance can be suppressed. From the same perspective, the (meth)acrylic acid ester content in the (meth)acrylic acid ester-modified polymer is preferably 2 to 7 mol%, and more preferably 3 to 6 mol%. The (meth)acrylic acid ester content in the (meth)acrylic acid-modified polymer can be measured by NMR.

[0041] From the viewpoint of realizing better performance on ice, the glass transition temperature of the (meth)acrylic acid-modified polymer is preferably −100 to −50° C., and more preferably −90 to −70° C. The glass transition temperature of the (meth)acrylic acid-modified polymer can be measured using a differential scanning calorimeter (for example, DSC, manufactured by TA Instruments Japan, Ltd., “DSCQ2000”) in accordance with JIS K 7121-1987.

[0042] Here, the conjugated diene polymer constituting the (meth)acrylic acid ester-modified polymer is not particularly limited, but is preferably a homopolymer of a conjugated diene unit or a copolymer having an aromatic vinyl unit and a conjugated diene unit. Examples of the conjugated diene compound as the monomer include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethylbutadiene, 2-phenyl-1,3-butadiene, and 1,3-hexadiene. Among these, 1,3-butadiene and isoprene are preferred. On the other hand, examples of the aromatic vinyl compound as the monomer include styrene, p-methylstyrene, m-methylstyrene, p-tert-butylstyrene, α-methylstyrene, chloromethylstyrene, and vinyltoluene.

[0043] Furthermore, the conjugated diene polymer constituting the (meth)acrylic acid ester-modified polymer preferably has a vinyl bond content of the 1,3-butadiene units of 10 to 20 mol%, more preferably 13 to 18 mol%. By making the vinyl bond content of the 1,3-butadiene units less than 18 mol%, it is possible to prevent an increase in rubber hardness and deterioration of performance on ice. Furthermore, by making the vinyl bond content of the 1,3-butadiene units 13% or more, it is possible to increase the strength of the (meth)acrylic acid-modified polymer.

[0044] The diene polymer rubber of the present invention can be produced by copolymerizing a diene monomer and a (meth)acrylic acid ester monomer, although the method for producing the diene polymer rubber is not particularly limited. The polymerization method is not particularly limited, and known emulsion polymerization or solution polymerization methods may be used. However, from the viewpoint of industrial productivity, emulsion polymerization is preferred. That is, a method in which a monomer mixture containing a diene monomer and a (meth)acrylic acid ester monomer is polymerized in an aqueous medium in the presence of an emulsifier is preferred. In emulsion polymerization, in addition to the emulsifier, a polymerization initiator and a molecular weight modifier may be used, and in addition to these, commonly used polymerization auxiliary materials may also be used.

[0045] The emulsifier is not particularly limited, but a carboxylic acid-based emulsifier can be suitably used. Examples of carboxylic acid-based emulsifiers include fatty acid soaps and rosin acid soaps. Examples of fatty acid soaps include sodium or potassium salts of long-chain aliphatic carboxylic acids having 12 to 18 carbon atoms, such as lauric acid, myristic acid, palmitic acid, stearic acid, and oleic acid, as well as mixed aliphatic carboxylic acids. Examples of rosin acid soaps include sodium or potassium salts of disproportionated or hydrogenated natural rosins, such as gum rosin, wood rosin, and tall oil rosin. Examples of natural rosins include those containing abietic acid, levopimaric acid, palustric acid, dehydroabietic acid, tetrahydroabietic acid, and neoabietic acid as main components. The amount of emulsifier used is preferably 0.05 to 10 parts by weight, more preferably 0.5 to 5 parts by weight, per 100 parts by weight of the monomers used in the polymerization.

[0046] The polymerization initiator is not particularly limited as long as it is a radical initiator, but examples thereof include inorganic peroxides such as potassium persulfate, sodium persulfate, ammonium persulfate, potassium perphosphate, and hydrogen peroxide; organic peroxides such as t-butyl peroxide, cumene hydroperoxide, p-menthane hydroperoxide, t-butylcumyl peroxide, acetyl peroxide, isobutyryl peroxide, octanoyl peroxide, dibenzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, t-butylperoxyisobutyrate, and diisopropylbenzene hydroperoxide; and azo compounds such as azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, azobiscyclohexanecarbonitrile, and methyl azobisisobutyrate. These polymerization initiators can be used alone or in combination of two or more. Inorganic or organic peroxides are preferred as the polymerization initiator. When a peroxide is used as the polymerization initiator, it can also be used in combination with a reducing agent as a redox polymerization initiator. The reducing agent is not particularly limited, but examples thereof include compounds containing reduced metal ions such as ferrous sulfate and cuprous naphthenate; sulfinates such as sodium hydroxymethanesulfinate; sulfites such as sodium sulfite, potassium sulfite, sodium hydrogen sulfite, aldehyde sodium hydrogen sulfite, and potassium hydrogen sulfite; etc. The amount of the polymerization initiator to be added is preferably 0.01 to 2 parts by weight based on 100 parts by weight of the monomers used in the polymerization.

[0047] The molecular weight modifier is not particularly limited, but examples thereof include α-methylstyrene dimer; mercaptans such as t-dodecyl mercaptan, n-dodecyl mercaptan, and octyl mercaptan; halogenated hydrocarbons such as carbon tetrachloride, methylene chloride, and methylene bromide; and sulfur-containing compounds such as tetraethylthiuram disulfide, dipentamethylenethiuram disulfide, and diisopropylxanthogen disulfide. Among these, mercaptans are preferred, and t-dodecyl mercaptan is more preferred. These molecular weight modifiers may be used alone or in combination of two or more. The amount of molecular weight modifier used varies depending on the type, but is preferably 0.1 to 1.5 parts by weight, more preferably 0.2 to 1.0 part by weight, per 100 parts by weight of the monomers used in the polymerization.

[0048] As the medium for emulsion polymerization, an aqueous medium such as water is usually used. The amount of the aqueous medium is preferably 80 to 500 parts by weight, more preferably 80 to 300 parts by weight, per 100 parts by weight of the monomers used in the polymerization.

[0049] In emulsion polymerization, if necessary, it is possible to use additional polymerization auxiliary materials such as stabilizers, dispersants, pH adjusters, oxygen scavengers, particle size adjusters, etc. When these are used, the types and amounts used are not particularly limited.

[0050] Examples of methods for adding the monomers include adding the monomers to be used all at once to the reaction vessel, adding them continuously or intermittently as the polymerization progresses, and adding a portion of the monomers and reacting them to a specific conversion rate, followed by adding the remaining monomers continuously or intermittently to polymerize them. Any of these methods may be used. When the monomers are mixed and added continuously or intermittently, the composition of the mixture may be constant or may be varied. Furthermore, the various monomers to be used may be mixed in advance and then added to the reaction vessel, or each may be added separately to the reaction vessel.

[0051] The polymerization temperature during emulsion polymerization is not particularly limited, but is usually 0 to 95° C., and preferably 5 to 70° C. The polymerization time is not particularly limited, but is usually about 5 to 40 hours.

[0052] The polymerization terminator is not particularly limited as long as it is one that is typically used in emulsion polymerization, and specific examples include hydroxylamine compounds such as hydroxylamine, hydroxyamine sulfate, diethylhydroxyamine, hydroxyamine sulfonic acid, and alkali metal salts thereof; sodium dimethyldithiocarbamate; hydroquinone derivatives; catechol derivatives; aromatic hydroxydithiocarboxylic acids such as hydroxydimethylbenzenethiocarboxylic acid, hydroxydiethylbenzenedithiocarboxylic acid, and hydroxydibutylbenzenedithiocarboxylic acid, and aromatic hydroxydithiocarboxylic acid compounds such as alkali metal salts thereof; etc. The amount of the polymerization terminator used is not particularly limited, and is typically 0.05 to 2 parts by weight per 100 parts by weight of the monomers used in the polymerization.

[0053] The diene polymer rubber of the present invention can be obtained by adding an antioxidant, such as a phenolic stabilizer, a phosphorus-based stabilizer, or a sulfur-based stabilizer, to the copolymer latex obtained by emulsion polymerization, if desired, followed by salting out or coagulation with alcohol, filtration, drying, etc. In this case, the filtration and drying steps following coagulation can each be carried out by a known method. The amount of antioxidant to be added is preferably 0.05 to 2 parts by weight per 100 parts by weight of the diene polymer rubber or 100 parts by weight of the monomers used in the polymerization.

[0054] The rubber component may contain any rubber other than the (meth)acrylic acid ester-modified polymer. For example, the rubber component preferably contains a diene rubber, which can provide excellent cut resistance and abrasion resistance.

[0055] Examples of the diene rubber include natural rubber, synthetic polyisoprene (IR), styrene-butadiene copolymer rubber (SBR), and polybutadiene rubber (BR). The diene synthetic rubber in the rubber component may be contained alone or as a blend of two or more. The rubber component may also contain a non-diene synthetic rubber depending on the required performance.

[0056] Among the diene rubbers mentioned above, the rubber component preferably contains natural rubber, butadiene rubber, or styrene-butadiene rubber. By including these rubbers, it is possible to maintain good cut resistance and abrasion resistance while also improving performance on ice. Note that the butadiene rubber and styrene-butadiene rubber do not include the (meth)acrylic acid ester-modified polymer mentioned above.

[0057] The content of the modified conjugated diene polymer in the rubber component is not particularly limited, but is preferably 5 to 50% by mass, and more preferably 10 to 45% by mass. By setting the content of the modified conjugated diene polymer in the rubber component to 5% by mass or more, it is possible to more reliably improve performance on ice, and by setting it to 50% by mass or less, it is possible to more reliably prevent deterioration of performance such as abrasion resistance.

[0058] Furthermore, the content of natural rubber in the rubber component is not particularly limited, but from the viewpoint of further improving abrasion resistance and performance on ice, the content of natural rubber is preferably 30% by mass or more of the rubber component. By using a rubber component containing a certain amount of natural rubber together with a fatty acid amide, etc., as described below, the on-ice performance of the vulcanized rubber composition for tires can be more reliably improved. From the same viewpoint, the content of natural rubber in the rubber component is preferably 35% by mass or more, more preferably 40% by mass or more. The upper limit is preferably 90% by mass or less, more preferably 80% by mass or less. Furthermore, the content of butadiene rubber or styrene-butadiene rubber in the rubber component is not particularly limited, but from the viewpoint of further improving abrasion resistance and performance on ice, it is preferably 15 to 45% by mass, more preferably 20 to 40% by mass.

[0059] (Fatty Acid Amide) The vulcanized rubber composition for tires of the present invention preferably contains a fatty acid amide in the rubber composition. The fatty acid amide can promote hydrophilicity of the rubber surface and increase viscous resistance, thereby further improving the on-ice performance of the vulcanized rubber composition for tires.

[0060] Here, the content of the fatty acid amide is preferably 0.1 to 10 parts by mass per 100 parts by mass of the rubber component. When the content of the fatty acid amide is 0.1 part by mass or more per 100 parts by mass of the rubber component, a sufficient effect of improving performance on ice can be obtained. On the other hand, when the content of the fatty acid amide is 10 parts by mass or less per 100 parts by mass of the rubber component, deterioration of performance such as abrasion resistance and reinforcement of the rubber composition can be suppressed. From the same viewpoint, the content of the fatty acid amide is preferably 0.1 to 8 parts by mass, more preferably 0.3 to 5 parts by mass per 100 parts by mass of the rubber component.

[0061] The type of fatty acid amide is not particularly limited as long as it can promote the hydrophilicity of the rubber surface, and examples thereof include caproic acid amide, lauric acid amide, myristic acid amide, palmitic acid amide, stearic acid amide, oleic acid amide, erucic acid amide, methylene bisstearic acid amide, and ethylene bisstearic acid amide.

[0062] Furthermore, from the viewpoint of realizing better performance on ice, the fatty acid amide is preferably a fatty acid bisamide, and more preferably an ethylene bis fatty acid amide, such as ethylene bis stearic acid amide or ethylene bis oleic acid amide.

[0063] (Liquid Polymer) In addition to the rubber component and fatty acid amide described above, the rubber composition preferably further contains a liquid polymer having a bound styrene content of less than 10% and a vinyl bond content of 20% or more in conjugated diene units. By containing the liquid polymer, flexibility of the rubber composition as a whole can be ensured, and further, by using the liquid polymer together with a cyclic polyol compound and a filler described below, both performance on ice and abrasion resistance can be achieved at a high level.

[0064] From the viewpoint of obtaining better on-ice performance, the vinyl bond content of the conjugated diene compound portion of the liquid polymer is preferably 30% or more, more preferably 40% or more, and even more preferably 45% or more. From the viewpoint of suppressing an increase in rubber hardness, the vinyl bond content of the conjugated diene compound portion of the liquid polymer is preferably 70% or less, more preferably 65% ​​or less, and even more preferably 55% or less.

[0065] The liquid polymer may be any liquid polymer having a bound styrene content of less than 10% and a vinyl bond content of 20% or more in the conjugated diene units, but is preferably an unmodified conjugated diene polymer, which allows the liquid polymer to be more easily distributed in the natural rubber phase of the rubber component, thereby achieving better on-ice performance.

[0066] Furthermore, when the liquid polymer is an unmodified conjugated diene polymer, if the amount of bound styrene in the conjugated diene compound portion is less than 10%, the flexibility of the rubber composition can be sufficiently ensured, and the on-ice performance of the vulcanized rubber obtained from the rubber composition and the tire equipped with the tread portion can be further improved. From the same viewpoint, the amount of bound styrene in the conjugated diene compound portion of the liquid polymer is more preferably 5% or less, even more preferably 3% or less, and particularly preferably 0%.

[0067] The liquid polymer has a low molecular weight so as not to form a crosslinked structure with the rubber component when the rubber composition is vulcanized. Specifically, the weight average molecular weight (hereinafter sometimes simply referred to as "weight average molecular weight") in terms of polystyrene as measured by gel permeation chromatography is preferably 5,000 or more and less than 40,000. If the weight average molecular weight of the liquid polymer is less than 5,000, the vulcanized rubber obtained from the rubber composition and the tire tread may become excessively flexible, potentially impairing wear resistance. If the weight average molecular weight of the liquid polymer is 40,000 or more, flexibility may be lost, potentially impairing the ice performance of the vulcanized rubber obtained from the rubber composition and the tire equipped with a tread using the rubber composition. Furthermore, from the same viewpoint, the weight average molecular weight of the liquid polymer is more preferably 5,500 to 30,000, even more preferably 6,000 to 25,000, and particularly preferably 6,500 to 20,000.

[0068] Furthermore, the content of the liquid polymer is preferably 1 to 40 parts by mass per 100 parts by mass of the rubber component. This is because it imparts flexibility to the rubber composition, and can improve the on-ice performance of a tire equipped with a vulcanized rubber and a tread portion obtained from the rubber composition, while suppressing a decrease in abrasion resistance. From the same viewpoint, the content of the liquid polymer is more preferably 3 to 30 parts by mass, even more preferably 5 to 25 parts by mass, and particularly preferably 7 to 20 parts by mass per 100 parts by mass of the rubber component.

[0069] Furthermore, from the viewpoint of achieving both high levels of on-ice performance and abrasion resistance, it is preferable that the mass ratio of the content of the modified conjugated diene polymer to the content of the liquid polymer (content of modified conjugated diene polymer / content of liquid polymer) is 0.5 to 5. By setting this mass ratio to 0.5 or more, the effect of the modified conjugated diene polymer in improving on-ice performance can be fully exerted, and by setting this mass ratio to 5 or less, the effect of the liquid polymer in improving flexibility can be fully exerted.

[0070] Here, when the liquid polymer is an unmodified conjugated diene polymer, the type of conjugated diene polymer is not particularly limited as long as it has a specific weight-average molecular weight, a bound styrene content in the conjugated diene compound moiety that is kept below a certain value, and a specific vinyl bond content. However, a homopolymer of a conjugated diene compound or a copolymer of an aromatic vinyl compound and a conjugated diene compound is preferred. Examples of the conjugated diene compound as a monomer include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethylbutadiene, 2-phenyl-1,3-butadiene, and 1,3-hexadiene. Among these, 1,3-butadiene and isoprene are preferred. On the other hand, examples of the aromatic vinyl compound as a monomer include styrene, p-methylstyrene, m-methylstyrene, p-tert-butylstyrene, α-methylstyrene, chloromethylstyrene, and vinyltoluene. The liquid polymer is preferably either or both of polybutadiene and polyisoprene, with polybutadiene being more preferred. These monomers may be used alone or in combination of two or more.

[0071] Furthermore, when the liquid polymer is an aromatic vinyl compound-conjugated diene compound copolymer, the amount of the aromatic vinyl compound bonded is preferably less than 5% by mass. By keeping the amount of the aromatic vinyl compound bonded to less than 5% by mass, it is possible to prevent an increase in rubber hardness and deterioration of performance on ice.

[0072] (Filler) The rubber composition further contains a filler containing at least silica in addition to the above-mentioned rubber component, fatty acid amide, and liquid polymer as preferred components. By including silica as a filler, the contact area with the road surface can be increased when the vulcanized rubber composition for tires is applied to a tire, and performance on ice can be significantly improved.

[0073] Examples of the silica include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, and aluminum silicate. Of these, wet silica is preferred. These silicas may be used alone or in combination of two or more. Precipitated silica can be used as the wet silica. Precipitated silica is silica obtained by growing primary silica particles in a reaction solution at a relatively high temperature in a neutral to alkaline pH range in the early stages of production, and then agglomerating the primary particles by controlling the pH to the acidic side.

[0074] The silica is not particularly limited, but may be, for example, a silica having a CTAB specific surface area (cetyltrimethylammonium bromide adsorption specific surface area) of 70 m ２ / g or more, 250m ２ The CTAB specific surface area is a value measured in accordance with ASTM D3765-92. However, when the adsorption cross section per molecule of cetyltrimethylammonium bromide on the silica surface is 0.35 nm ２ and the specific surface area (m ２ / g) is the CTAB specific surface area. The BET specific surface area of ​​the silica is 100 m ２ / g or more, 250m ２ The BET specific surface area is a specific surface area determined by the BET method, and in the present invention, can be measured in accordance with ASTM D4820-93.

[0075] The content of the silica is 30 to 70 parts by mass per 100 parts by mass of the rubber component, and the proportion of the silica in the filler is 55% by mass or more. When the content of the silica is 30 parts by mass or more per 100 parts by mass of the rubber component and the proportion of the silica in the filler is 55% by mass or more, the contact area with the road surface when the vulcanized rubber composition for tires is applied to a tire increases, thereby further improving ice performance. On the other hand, when the content of the silica is 70 parts by mass or less per 100 parts by mass of the rubber component, deterioration of the processability of the rubber composition and deterioration of abrasion resistance due to a reduction in carbon black can be suppressed. Note that the upper limit of the proportion of the silica in the filler is not limited, but from the viewpoint of suppressing deterioration of the processability of the rubber composition and deterioration of abrasion resistance due to a reduction in carbon black, it is preferable that the content be 80% by mass or less. From the same viewpoint, the content of the silica is preferably 35 to 65 parts by mass and more preferably 40 to 60 parts by mass relative to 100 parts by mass of the rubber component, and the proportion of the silica in the filler is preferably 55 to 80% by mass and more preferably 60 to 75% by mass or more.

[0076] Furthermore, the filler preferably further contains carbon black in addition to the silica. 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. Here, examples of plant-derived carbon black include those derived from castor oil and pine oil. Recycled carbon black will be described in detail below.

[0077] From the viewpoint of further improving the abrasion resistance of the rubber composition and a tire using the same, the content of the 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 the 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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).

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] Furthermore, the total content of the silica and the carbon black is preferably 40 to 90 parts by mass, and more preferably 50 to 80 parts by mass, per 100 parts by mass of the rubber component, because this allows the properties of the vulcanized rubber composition for tires, such as abrasion resistance and performance on ice, to be further improved while maintaining good performance such as low heat buildup and processability.

[0104] The filler may be, in addition to the above-mentioned silica and carbon black, a filler represented by the following general formula (XX): nM.xSiO ｙ ・zH ２ O ... (XX) [wherein M is at least one selected from the group consisting of a metal selected from the group consisting of aluminum, magnesium, titanium, calcium and zirconium, oxides or hydroxides of these metals, hydrates thereof, or carbonates of these metals; and n, x, y and z are integers of 1 to 5, integers of 0 to 10, integers of 2 to 5 and integers of 0 to 10, respectively]. The inorganic compound of general formula (XX) may include alumina (Al) such as γ-alumina and α-alumina. ２ O ３ alumina monohydrate (Al), boehmite, diaspore, etc. ２ O ３ HO), aluminum hydroxides such as gibbsite and bayerite [Al(OH) ３ ], aluminum carbonate [Al ２ (CO ３ ) ３ ], magnesium hydroxide [Mg(OH) ２ ], magnesium oxide (MgO), magnesium carbonate (MgCO ３ ), talc (3MgO.4SiO ２ ・HO), attapulgite (5MgO ・8SiO ２ ・9H ２ O), titanium white (TiO2), titanium black (TiO ２ｎ－１ ), calcium oxide (CaO), calcium hydroxide [Ca(OH) ２ ], magnesium aluminum oxide (MgO.Al ２ O ３ ), clay (Al ２ O ３2SiO ２ ), kaolin (Al ２ O ３ 2SiO ２ ・2H ２ O), pyrophyllite (Al ２ O ３ 4SiO ２ ・H2O), bentonite (Al ２ O ３ 4SiO ２ ・2H ２ O), aluminum silicate (Al ２ SiO ５ , Al ４ 3SiO ４ ・5H ２ O, etc.), magnesium silicate (Mg ２ SiO ４ , MgSiO ３ etc.), calcium silicate (Ca ２ SiO ４ etc.), calcium aluminum silicate (Al ２ O ３ CaO 2SiO ２ etc.), magnesium calcium silicate (CaMgSiO ４ ), calcium carbonate (CaCO ３ ), zirconium oxide (ZrO ２ ), zirconium hydroxide [ZrO(OH) ２ ・nH ２ O], zirconium carbonate [Zr(CO ３ ) ２ and crystalline aluminosilicates containing hydrogen, alkali metals or alkaline earth metals that compensate for charge, such as various zeolites. From the viewpoint of the balance between wear resistance and wet performance, the inorganic compound of general formula (XX) preferably has an average particle size of 0.01 to 10 μm, and more preferably 0.05 to 5 μm.

[0105] (Void-introducing agent) The rubber composition preferably further contains a void-introducing agent in addition to the above-mentioned rubber component, filler, and fatty acid amide and liquid polymer as suitable components. 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. This makes a tire using the vulcanized rubber flexible and more easily adheres to icy road surfaces. In addition, water on the road surface is absorbed into the voids on the tire surface, making it easier to remove water from icy and snowy road surfaces, thereby improving braking performance on ice.

[0106] 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.

[0107] 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.

[0108] 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 blowing agents include inorganic blowing agents such as azodicarbonamide (ADCA), dinitrosopentamethylenetetramine (DPT), dinitrosopentastyrenetetramine, benzenesulfonylhydrazide derivatives, p,p'-oxybisbenzenesulfonylhydrazide (OBSH), carbonates such as ammonium carbonate, sodium carbonate, and potassium carbonate, and bicarbonates (hydrogencarbonates) 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, azodicarbonamide (ADCA), dinitrosopentamethylenetetramine (DPT), and inorganic blowing agents are preferably used. These blowing agents may be used alone or in combination of two or more.

[0109] 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.

[0110] 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 the 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 ice is no longer lubricated, thus improving the coefficient of friction. Examples of metal sulfates include magnesium sulfate.

[0111] The metal sulfate is preferably in the form of 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.

[0112] For all these reasons, the median particle size of the metal sulfate is preferably 2 μm to 500 μm, more preferably 5 to 200 μm. This particularly preferred particle size range appears to represent an optimum compromise between the desired surface roughness on the one hand and good contact between the rubber composition and ice on the other hand.

[0113] Furthermore, for the same reason as above, the content of the metal sulfate in the rubber composition is preferably 5 to 40 parts by mass, and more preferably 10 to 35 parts by mass, per 100 parts by mass of the rubber component.

[0114] 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.

[0115] 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 microcapsule shell material 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.

[0116] 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 Seiyaku Co., Ltd. under the trade names "Matsumoto Microsphere F-85D" or "Matsumoto Microsphere F-100D."

[0117] 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.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] (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.

[0126] 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.

[0127] 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.

[0128] From the viewpoints of the foaming rate of the vulcanized rubber and the on-ice 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.

[0129] (Composite Fiber) The rubber composition preferably further contains a composite fiber in addition to the above-described rubber component and filler, and the preferred components of fatty acid amide, liquid polymer, void-introducing agent, and foaming aid. By including the composite fiber, sufficient affinity with water can be ensured, and excellent drainage and ice performance can be imparted, particularly when used in tire applications. Furthermore, the composite fiber is preferably made of a hydrophilic resin having a coating layer formed on its surface. 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 water-insoluble. By using a water-insoluble hydrophilic resin, dissolution of the composite fiber can be suppressed even when the composite fiber is exposed on the surface of a product (e.g., a tire).

[0130] 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.

[0131] The surface of the hydrophilic resin fiber 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 voids within the composite fiber. This ensures good dispersion of the composite fiber in the rubber component, fully demonstrating the drainage effect of the hydrophilic resin, while also fully demonstrating the on-ice performance improvement effect of the voids present within the composite fiber. Furthermore, the low-melting-point resin melts during vulcanization, forming a fluid coating layer that contributes to adhesion between the rubber component and the composite fiber, thereby imparting good on-ice 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.

[0132] 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.

[0133] 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.

[0134] To produce a composite fiber made of a hydrophilic resin with a coating layer made of the low-melting-point resin, a method can be used in which the resins are 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 these 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.

[0135] 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.

[0136] Furthermore, 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 keeping the ratio within the above range, on-ice performance is further improved. 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.

[0137] 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, it is possible to form cavities within 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 performance on ice, 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.

[0138] (Hydrogenated Resin) The rubber composition preferably further contains a hydrogenated resin in addition to the above-described rubber component and filler, and the preferred components of fatty acid amide, filler, liquid polymer, foaming aid, and composite fiber. The hydrogenated resin is highly compatible with the rubber component, and can therefore provide the tire with the flexibility necessary for grip performance on wet and icy and snowy surfaces, thereby improving grip performance on icy and snowy surfaces, i.e., performance on ice.

[0139] Here, the hydrogenated resin is a resin obtained by reducing and hydrogenating a resin. ５ based resin, C ５ -C ９ based resin, C ９ These resins may be used alone or in combination of two or more.

[0140] 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. ５ The 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. ５ Commercially available resins can be used.

[0141] 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. ３More 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 above components are contained in an amount of less than 50% by mass, preferably 40% by mass or less. ５ -C ９ Commercially available resins can be used.

[0142] 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.

[0143] The terpene resin is a solid resin obtained by blending turpentine, which is obtained simultaneously when rosin is obtained from pine trees, or a polymerization component separated from the blend, and polymerizing the blend using a Friedel-Crafts catalyst. Examples of such resins include β-pinene resin and α-pinene resin. Furthermore, a representative example of a terpene-aromatic compound resin is terpene-phenol resin. This terpene-phenol resin can be obtained by reacting terpenes with various phenols using a Friedel-Crafts catalyst, or by further condensing the terpene with formalin. There are no particular limitations on the terpenes used as raw materials; monoterpene hydrocarbons such as α-pinene and limonene are preferred, with those containing α-pinene being more preferred, and α-pinene being particularly preferred.

[0144] The dicyclopentadiene resin is, for example, AlCl ３ or BF ３This refers to a resin obtained by polymerizing dicyclopentadiene using a Friedel-Crafts catalyst such as

[0145] The resin used as the raw material for the hydrogenated resin is, for example, C ５ A resin (C) copolymerized with the fraction and dicyclopentadiene (DCPD) ５ -DCPD-based resin). When the dicyclopentadiene-derived component is 50% by mass or more in the total amount of the resin, C ５ - DCPD-based resins are included in dicyclopentadiene-based resins. When the dicyclopentadiene-derived component is less than 50% by mass in the total amount of resin, C ５ -DCPD resin is C ５ The same applies to cases where a small amount of a third component is contained.

[0146] From the viewpoint of increasing the compatibility between the rubber component and the hydrogenated resin and further improving the tire's performance on snow, the hydrogenated resin is ５ based resin, hydrogenated C ５ -C ９ and hydrogenated dicyclopentadiene resins (hydrogenated DCPD resins), and ５ Resin and hydrogenated C ５ -C ９ It is more preferable that the resin is at least one selected from the group consisting of hydrogenated C ５ Furthermore, it is preferable that the resin has at least a hydrogenated DCPD structure or a hydrogenated cyclic structure in the monomer.

[0147] The softening point of the hydrogenated resin is preferably higher than 110°C. This is because, when the softening point of the hydrogenated resin exceeds 110°C, the rolling resistance of the tire can be sufficiently reduced. From the viewpoint of further reducing the rolling resistance of the tire, the softening point of the hydrogenated resin is preferably 115°C or higher, more preferably 118°C or higher, more preferably 123°C or higher, and even more preferably 125°C or higher. In addition, from the viewpoint of further improving the wet grip performance and on-snow performance of the tire, the softening point of the hydrogenated resin is preferably 145°C or lower, more preferably 138°C or lower, and even more preferably 133°C or lower.

[0148] The polystyrene-equivalent weight average molecular weight of the hydrogenated resin is preferably 200 to 1200 g / mol. This is because when the polystyrene-equivalent weight average molecular weight of the hydrogenated resin is 200 g / mol or more, precipitation of the hydrogenated resin from the tire can be suppressed, and when it is 1200 g / mol or less, the hydrogenated resin can be reliably compatible with the rubber component. From the viewpoint of suppressing precipitation of the hydrogenated resin from the tire and suppressing deterioration of the tire appearance, the polystyrene-equivalent weight average molecular weight of the hydrogenated resin is preferably 500 g / mol or more, more preferably 550 g / mol or more, more preferably 620 g / mol or more, more preferably 670 g / mol or more, more preferably 720 g / mol or more, more preferably 750 g / mol or more, and even more preferably 780 g / mol or more. Furthermore, from the viewpoint of increasing the compatibility of the hydrogenated resin with the rubber component and further enhancing the effects of the hydrogenated resin, the polystyrene-equivalent weight average molecular weight of the hydrogenated resin is preferably 1300 g / mol or less, preferably 1100 g / mol or less, preferably 1050 g / mol or less, preferably 950 g / mol or less, preferably 900 g / mol or less, and more preferably 850 g / mol or less.

[0149] Furthermore, the weight average molecular weight (Mw ＨＲ ) (unit: g / mol) of the hydrogenated resin to the softening point (Ts ＨＲ) (unit: ° C.) is preferably 0.15 or more [0.15≦(Ts ＨＲ / Mw ＨＲ ) ]. ＨＲ / Mw ＨＲ From the viewpoint of further improving the wet grip performance and snow performance of the tire, (Ts) is more preferably 0.155 or more, more preferably 0.158 or more, even more preferably 0.160 or more, and still more preferably 0.162 or more. ＨＲ / Mw ＨＲ ) is preferably 0.2 or less, more preferably 0.185 or less, more preferably 0.178 or less, more preferably 0.172 or less, more preferably 0.168 or less, and even more preferably 0.163 or less, from the viewpoint of suppressing deterioration in tire performance.

[0150] The content of the hydrogenated resin in the rubber composition is preferably 5 to 50 parts by mass per 100 parts by mass of the rubber component. When the content of the hydrogenated resin is 5 parts by mass or more per 100 parts by mass of the rubber component, the effects of the hydrogenated resin can be fully exhibited, while when the content of the hydrogenated resin is 50 parts by mass or less per 100 parts by mass of the rubber component, precipitation of the hydrogenated resin from the tire can be suppressed. Furthermore, from the viewpoint of further enhancing the effects of the hydrogenated resin, the content of the hydrogenated resin in the rubber composition is preferably 7 parts by mass or more, and more preferably 9 parts by mass or more, per 100 parts by mass of the rubber component. Additionally, from the viewpoint of suppressing precipitation of the hydrogenated resin from the tire and suppressing deterioration of the tire appearance, the content of the hydrogenated resin in the rubber composition is preferably 40 parts by mass or less, more preferably 30 parts by mass or less, more preferably 25 parts by mass or less, and even more preferably 20 parts by mass or less, per 100 parts by mass of the rubber component.

[0151] (Cyclic Polyol Compound Having Hydrocarbyl Group) Furthermore, the rubber composition preferably further contains a cyclic polyol compound having a hydrocarbyl group in addition to the above-mentioned rubber component and filler, and the preferred components of fatty acid amide, liquid polymer, void-introducing agent, foaming aid, composite fiber, and hydrogenated resin. The cyclic polyol compound having a hydrocarbyl group contained in the rubber composition can significantly improve the abrasion resistance and cut resistance of the vulcanized rubber composition for tires of the present invention. Furthermore, by enhancing the interaction between the rubber molecules of the rubber component and the agent described below, the physical properties of the rubber after crosslinking can be homogenized, thereby improving reinforcement properties. It has also been revealed that the voided rubber composition of the present invention further improves abrasion resistance and cut resistance. Furthermore, since the cyclic polyol compound having a hydrocarbyl group has fewer hydrophilic moieties than compounds such as sorbitol, self-aggregation in the rubber composition can be suppressed, thereby maintaining good elongation fatigue properties of the vulcanized rubber composition for tires.

[0152] The amount of the hydrocarbyl group-containing cyclic polyol compound is preferably 0.1 to 5 parts by mass per 100 parts by mass of the natural rubber. When the amount of the hydrocarbyl group-containing cyclic polyol compound is 0.1 part by mass or more per 100 parts by mass of the natural rubber, a sufficient improvement in abrasion resistance is achieved. On the other hand, when the amount of the hydrocarbyl group-containing cyclic polyol compound is 5 parts by mass or less per 100 parts by mass of the natural rubber, self-aggregation in the rubber composition is reliably suppressed, resulting in further improvement in elongation fatigue properties. From the same perspective, the amount of the hydrocarbyl group-containing cyclic polyol compound is preferably 0.1 to 3 parts by mass, more preferably 0.3 to 2.5 parts by mass, per 100 parts by mass of the natural rubber.

[0153] From the viewpoint of improving abrasion resistance and cut resistance, the hydrocarbyl group-containing cyclic polyol compound is preferably dispersed in the rubber component, and more preferably dispersed in the natural rubber. The hydrocarbyl group-containing cyclic polyol compound does not act as a surfactant for other compounding ingredients, but rather disperses in the rubber to improve abrasion resistance and cut resistance, and is therefore distinguished from surfactants.

[0154] Here, the cyclic polyol compound having a hydrocarbyl group preferably has two or more hydroxyl groups, and more preferably has three or more hydroxyl groups. This is because having many hydroxyl groups allows for stronger interaction between the rubber component and the additives, resulting in better abrasion resistance and cut resistance. On the other hand, from the viewpoint of suppressing self-aggregation in the rubber due to an increased number of hydrophilic sites, it is preferable for the compound to have five or less hydroxyl groups, and more preferably four or less hydroxyl groups.

[0155] Furthermore, the cyclic polyol compound having a hydrocarbyl group is preferably a cyclic polyol compound having a hydrocarbyl ester group, since this allows for achieving better abrasion resistance and cut resistance.

[0156] Furthermore, in order to realize better abrasion resistance and cut resistance, the cyclic polyol compound having a hydrocarbyl group is selected from the group consisting of cyclic polyols represented by the following formula (1): It is more preferable that the compound is represented by the following formula:

[0157] In the above formula (1), A is a hydrocarbyl ester group having 6 to 30 carbon atoms or a hydrocarbyl ether group having 6 to 30 carbon atoms, and the number of carbon atoms in the hydrocarbyl group portion of A is preferably 12 to 24. When the number of carbon atoms in the hydrocarbyl group portion of A in formula (1) is in the range of 12 to 24, good elongation fatigue properties are maintained while the abrasion resistance and cut resistance are further improved. It is preferable that A in formula (1) is an oxygen atom at the first atom from the ring portion (i.e., the atom bonded to the ring) or the second atom from the ring portion. Examples of A in which the first atom from the ring portion is an oxygen atom include groups represented by -O-A' and -O-CO-A'', and examples of A in which the second atom from the ring portion is an oxygen atom include, for example, -CH ２ -O-A'', -CH ２ Examples include groups represented by -O-CO-A''', where A' is preferably a hydrocarbyl group having 6 to 30 carbon atoms, A'' is preferably a hydrocarbyl group having 5 to 29 carbon atoms, and A''' is preferably a hydrocarbyl group having 4 to 28 carbon atoms, and more preferably A', A'' and A''' are each a hydrocarbyl group having 12 to 24 carbon atoms.

[0158] In addition, in the above formula (1), X １ , X ２ , X ３ and X ４ are each independently —OH or —R (wherein —R is —H or —CH ２ OH), with the proviso that X １ , X ２ , X ３ and X ４ At least two of X are —OH. １ , X ２ , X ３ and X ４ Preferably, two or more of １ , X ２ , X ３ and X ４ When three or more of the above are —OH, the abrasion resistance and cut resistance of the rubber composition are further improved.

[0159] Furthermore, among the compounds represented by the above formula (1), compounds represented by the following formula (2) or formula (3): Compounds represented by the formula (2) are more preferred, and compounds represented by the formula (2) are particularly preferred. In formulas (2) and (3), n is a natural number, preferably in the range of 11 to 23. By blending a compound represented by the formula (2) or (3) as the modified cyclic polyol compound, it is possible to further improve abrasion resistance.

[0160] The cyclic polyol compound having a hydrocarbyl group is not particularly limited, but can be obtained, for example, by reacting a polyol compound such as sorbitol, sorbitan, glucose, or fructose with an aliphatic alcohol such as octanol, decanol, dodecanol, tetradecanol, or hexadecanol, or an aliphatic carboxylic acid such as lauric acid, myristic acid, palmitic acid, stearic acid, or oleic acid.

[0161] Specific examples of the cyclic polyol compound having a hydrocarbyl group include ester compounds such as sorbitan monolaurate, sorbitan monomyristate, sorbitan monopalmitate, sorbitan monostearate, and sorbitan monooleate, and ether compounds such as octyl-β-D-glucopyranoside, decyl-β-D-glucopyranoside, dodecyl-β-D-glucopyranoside, tetradecyl-β-D-glucopyranoside, and hexadecyl-β-D-glucopyranoside. These compounds may be used alone or in combination of two or more. Among these compounds, sorbitan monostearate (sorbitan monoester) is preferred as the cyclic polyol compound having a hydrocarbyl group, from the viewpoint of achieving both higher levels of elongation fatigue resistance and cut resistance.

[0162] Furthermore, the melting point of the cyclic polyol compound having a hydrocarbyl group is preferably 40 to 100° C., and more preferably 45 to 90° C. When the melting point of the cyclic polyol compound having a hydrocarbyl group is 100° C. or lower, the solubility during kneading and vulcanization reaction can be improved, and when the melting point is 40° C. or higher, the cut resistance at high temperatures can be improved.

[0163] (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. The other components may include, for example, a silane coupling agent, a vulcanizing agent, a vulcanization accelerator, polyethylene glycol, a softener, an antioxidant, zinc oxide, etc., selected appropriately within the scope of the present invention. Commercially available products may be suitably used as these compounding agents.

[0164] In addition, when silica is contained as the above-mentioned filler, it is preferable to further contain a silane coupling agent. This is because the effects of silica on cut resistance, reinforcing properties, and low loss properties can be further improved. In addition, known silane coupling agents can be used appropriately. Examples of the silane coupling agent include bis(3-triethoxysilylpropyl) polysulfide, 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-mercaptopropyl trimethoxysilane, 3-mercaptopropyl triethoxysilane, 2-mercaptoethyl trimethoxysilane, 2-mercaptoethyl triethoxysilane, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, Examples of the silane coupling agent include triethoxysilylpropyl-N,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. These silane coupling agents may be used alone or in combination of two or more.

[0165] The content of the silane coupling agent varies depending on the type of silane coupling agent, but is preferably 0.2 or less, more preferably 0.1 or less, and even more preferably 0.09 or less, in mass ratio relative to the silica content. This is because by reducing the content of the silane coupling agent to 0.2 or less, in mass ratio relative to the silica content, the cut resistance of the rubber composition can be further improved.

[0166] The vulcanization accelerator may be any known one and is not particularly limited, but examples thereof include sulfenamide vulcanization accelerators such as CBS (N-cyclohexyl-2-benzothiazylsulfenamide), TBBS (N-t-butyl-2-benzothiazylsulfenamide), and TBSI (N-t-butyl-2-benzothiazylsulfenimide); guanidine vulcanization accelerators such as DPG (diphenylguanidine); thiuram vulcanization accelerators such as tetraoctylthiuram disulfide and tetrabenzylthiuram disulfide; and zinc dialkyldithiophosphate. The content thereof is preferably less than the sulfur content, and more preferably about 1 to 10 parts by mass per 100 parts by mass of the rubber component.

[0167] Furthermore, the rubber composition may contain a softener to enhance the flexibility of the rubber and achieve better wet and icy performance. The softener may be any conventionally known softener, and is not particularly limited. Examples include petroleum-based softeners such as aroma oil, paraffin oil, and naphthenic oil, and plant-based softeners such as palm oil, castor oil, cottonseed oil, and soybean oil. When used, one or more of these may be selected and used individually or in combination. The softener does not include the fatty acid amides described above. When the softener is contained, from the viewpoint of ease of handling, it is preferable to use a softener that is liquid at room temperature, such as 25°C, such as petroleum-based softeners such as aroma oil, paraffin oil, and naphthenic oil.

[0168] The method for producing the rubber composition is not particularly limited, and can be obtained, for example, by blending and kneading the above-mentioned components by a known method.

[0169] <Tire> The tire of the present invention is characterized in that the vulcanized rubber composition for tires of the present invention described above is used in the tread portion. By applying the rubber composition to the tread portion, excellent performance on ice can be achieved. Here, the tire of the present invention can be used, for example, as a tire for construction vehicles, a tire for trucks and buses, a tire for aircraft, or a tire for passenger cars, and is particularly preferably a tire for passenger cars or a tire for trucks and buses. This is because the vulcanized rubber composition for tires used as a material for the tread portion has excellent performance on ice and abrasion resistance, and is therefore highly advantageous when used as a tire for passenger cars or a tire for trucks and buses.

[0170] When the vulcanized rubber composition for a tire of the present invention is used in a tread portion, the tread structure can have a tread pattern such as that shown in Fig. 3. Fig. 3 is a development view schematically showing the tread pattern of a tire according to one embodiment of the present invention (hereinafter also simply referred to as a tire). The internal structure of the tire is not particularly limited, but according to convention, the tire can have a pair of bead portions, a pair of sidewalls connected to the bead portions, and a tread portion connected to the sidewall portions. Furthermore, the tire can have a carcass toroidally spanning the pair of bead portions, and a reinforcing layer such as a belt on the radially outer side of the crown portion of the carcass.

[0171] As shown in FIG. 3 , this tire has a plurality of circumferential main grooves 2 extending in the circumferential direction of the tire on the tread surface 1 of the tread portion, and a plurality of land portions 3 are defined between the circumferential main grooves 2 or by the circumferential main grooves 2 and the tread edge TE.

[0172] In the illustrated example, three circumferential main grooves 2 are formed, with the circumferential main groove 2a located in one half of the tire width direction bounded by the tire equatorial plane CL, the circumferential main groove 2b extending on the tire equatorial plane CL, and the circumferential main groove 2c located in the other half of the tire width direction bounded by the tire equatorial plane CL. Meanwhile, the number of circumferential main grooves 2 is not limited to three, but may be any number. In the illustrated example, all circumferential main grooves 2 extend straight in the tire circumferential direction, but they may also extend in a zigzag, bent, or curved manner. In the illustrated example, the circumferential main grooves 2 extend in the tire circumferential direction (without inclination), but they may also extend at an inclination angle of 5° or less relative to the tire circumferential direction. The groove width (opening width) of the circumferential main groove 2 may be, for example, 2 mm to 12 mm. The groove depth (maximum depth) of the circumferential main groove 2 may be, for example, 5 mm to 12 mm.

[0173] In the illustrated example, four land portions 3 are formed, with land portions 3a and 3b located in one half in the tire width direction bounded by the tire equatorial plane CL, and land portions 3c and 3d located in the other half in the tire width direction bounded by the tire equatorial plane CL. Meanwhile, the number of land portions 3 corresponds to the number of circumferential main grooves 2, and may be three or more. Also, any of the land portions 3 may be located on the tire equatorial plane CL.

[0174] Each land portion 3 is provided with a plurality of widthwise grooves 4 extending in the tire width direction. In the illustrated example, in each land portion 3, the plurality of widthwise grooves 4 are arranged at approximately equal intervals in the tire circumferential direction, thereby dividing the land portion 3 into a plurality of blocks 5 (of approximately the same shape). In the illustrated example, all widthwise grooves 4 extend straight, but they may also extend in a zigzag, bent, or curved shape. Furthermore, the widthwise grooves 4 may extend in the tire width direction, or may extend at an inclination angle of 60° or less (or 45° or less, or 30° or less) with respect to the tire width direction. The groove width (opening width) of the widthwise grooves 4 may be, for example, 2 mm to 12 mm. The groove depth (maximum depth) of the widthwise grooves 4 may be, for example, 5 mm to 12 mm. In the illustrated example, the widthwise grooves 4 that define land portion 3a and the widthwise grooves 4 that define land portion 3b are positioned on a straight line, and the widthwise grooves 4 that define land portion 3c and the widthwise grooves 4 that define land portion 3d are positioned on a straight line. This configuration can further improve drainage. On the other hand, the widthwise grooves 4 that define land portion 3a and the widthwise grooves 4 that define land portion 3b do not have to be positioned on a straight line (their virtual extension lines may be offset from each other in the tire circumferential direction), and the widthwise grooves 4 that define land portion 3c and the widthwise grooves 4 that define land portion 3d do not have to be positioned on a straight line (their virtual extension lines may be offset from each other in the tire circumferential direction). In addition, in the illustrated example, the widthwise grooves 4 located in one half of the tire width direction bounded by the tire equatorial plane CL and the widthwise grooves 4 located in the other half of the tire width direction are inclined in opposite directions in the tire circumferential direction relative to the tire width direction, but they may also be inclined in the same direction in the tire circumferential direction relative to the tire width direction.

[0175] In this way, a plurality of blocks 5 are defined by a plurality of circumferential main grooves 2 extending in the tire circumferential direction and a plurality of widthwise grooves 4 extending in the tire width direction. In the illustrated example, the blocks 5 have a substantially parallelogram shape in a plan view, but are not limited to this shape.

[0176] 3, a plurality of sipes 6 and a plurality of shallow grooves 7 are provided on the surface of the block 5 so as to extend in opposite directions in the tire width direction with respect to one direction in the tire circumferential direction. The sipes 6 and the shallow grooves 7 intersect with each other.

[0177] In the illustrated example, four sipes 6 are arranged in each block 5. The number of sipes 6 may be any number greater than one and is not limited to four. In the illustrated example, the four sipes 6 are arranged at equal intervals in the tire circumferential direction so that the block pieces separated by the sipes 6 are approximately the same size. On the other hand, the sipes 6 do not necessarily have to be arranged at equal intervals in the tire circumferential direction. In the illustrated example, the sipes 6 are flat sipes that extend linearly in a plan view, but they may also extend in a zigzag pattern. The sipes 6 may also be so-called three-dimensional sipes, in which the inner wall surface of the sipe is uneven along the sipe depth direction. In this example, both ends of the sipe 6 open to the circumferential main groove 2, but either one or both ends may terminate within the block 5.

[0178] In this embodiment, the inclination angle θ1 of the sipes 6 with respect to the tire circumferential direction is greater than 0° and less than 90°. The inclination angle θ1 is preferably 45° or greater, more preferably 60° or greater, and even more preferably 75° or greater. In this example, the sipes 6 have the same inclination angle with respect to the tire circumferential direction as the widthwise grooves 4, but the inclination angles may be different.

[0179] In this example, the sipe depth (maximum depth) of the sipe 6 can be set to, for example, 5 to 8 mm.

[0180] In the illustrated example, 15 shallow grooves 7 are arranged in each block 5. The number of shallow grooves 7 may be any number greater than one and is not limited to 15. In addition, in the illustrated example, the 15 shallow grooves 7 are arranged at equal intervals in the tire circumferential direction so that the block pieces partitioned by the shallow grooves 7 are approximately the same size. The circumferential pitch interval of the shallow grooves 7 may be, for example, 1.0 to 3.0 mm. On the other hand, the shallow grooves 7 do not necessarily have to be arranged at equal intervals in the tire circumferential direction. In the illustrated example, the shallow grooves 7 extend linearly in a plan view, but may extend in a zigzag pattern. In this example, both ends of the shallow groove 7 open to the circumferential main groove 2, but either one or both ends may terminate within the block 5.

[0181] In this embodiment, the inclination angle θ2 of the shallow groove 7 with respect to the tire circumferential direction is greater than 0° and less than 90°. The inclination angle θ2 is preferably 45° or greater, more preferably 60° or greater, and even more preferably 75° or greater.

[0182] The groove width (opening width) of the shallow groove 7 is preferably 0.75 to 1.0 times the sipe width (opening width) of the sipe 6. Although not particularly limited, the groove width (opening width) of the shallow groove 7 can be, for example, 0.3 to 0.4 mm. The groove depth (maximum depth) of the shallow groove 7 is smaller than the depth (maximum depth) of the sipe 6. The groove depth (maximum depth) of the shallow groove 7 can be, for example, 0.1 to 0.3 mm.

[0183] In this embodiment, the difference between the inclination angle θ1 and the inclination angle θ2 is 30° or less (the absolute value of θ1-θ2 is 30° or less). It is also preferable that the difference between the inclination angle θ1 and the inclination angle θ2 is 15° or less. The effects of the pneumatic tire of this embodiment will be described below.

[0184] In order to solve the above-mentioned problems, the inventors of the present invention studied the behavior of water on ice in tires having sipes and shallow grooves in the blocks, focusing on the inclination angles of the sipes and shallow grooves with respect to the tire circumferential direction. Fig. 4A is a diagram schematically showing the flow of water when θ1 = 60° and θ2 = 15°. Fig. 4B is a diagram schematically showing the flow of water when θ1 = θ2 = 60°. As shown schematically in Figs. 4A and 4B, when the difference in the inclination angles with respect to the tire circumferential direction between the sipes and the shallow grooves is large (Fig. 4A), as shown schematically by the difference in the thickness of the arrows, it was found that more water flows toward the groove with a smaller inclination angle with respect to the tire circumferential direction (the shallow groove in Fig. 4A). As a result, the flow becomes uneven and water overflows easily occur. In contrast, when the difference in the inclination angle between the sipes and the shallow grooves relative to the tire circumferential direction is small (including when it is 0) (Figure 4B), water flows evenly between the sipes and the shallow grooves, making it less likely for water to overflow, and it was found that the drainage function is improved.

[0185] The pneumatic tire of this embodiment has a plurality of sipes 6 and a plurality of shallow grooves 7 on the surface of each block 5. Therefore, both the sipes 6 and the shallow grooves 7 can remove water film, improving grip performance on ice, especially when the tire is new. The sipes 6 and the shallow grooves 7 are arranged to extend in opposite directions in the tire width direction relative to one direction in the tire circumferential direction, and the difference between the inclination angle θ1 and the inclination angle θ2 is 30° or less. As a result, as schematically illustrated in FIG. 4B , water flows uniformly through the sipes 6 and the shallow grooves 7, reducing the likelihood of water overflow. This improves drainage and further improves grip performance on ice. If the inclination angle θ1 is 0°, the edge component in the tire width direction (edge ​​component relative to the tire circumferential direction) of the sipes 6 is reduced. If the inclination angle θ1 is 90°, the edge component in the tire circumferential direction (edge ​​component relative to the tire width direction) of the sipes 6 is reduced. Similarly, if the inclination angle θ2 is 0°, the edge component in the tire width direction (edge ​​component in the tire circumferential direction) due to the shallow grooves 7 will be reduced. Also, if the inclination angle θ2 is 90°, the edge component in the tire circumferential direction (edge ​​component in the tire width direction) due to the shallow grooves 7 will be reduced. The depth of the shallow grooves 7 is smaller than the depth of the sipes 6, and the shallow grooves 7 can be removed early, for example, by running in. As described above, the pneumatic tire of this embodiment can improve grip performance on ice.

[0186] Here, the inclination angle θ1 is preferably 45° or more, more preferably 60° or more, and even more preferably 75° or more, because by increasing the edge component of the sipe 6 in the tire width direction (edge ​​component relative to the tire circumferential direction) and improving the function of wiping water in the tire circumferential direction, grip performance on ice can be further improved.

[0187] The inclination angle θ2 is preferably 45° or more, more preferably 60° or more, and even more preferably 75° or more. This is because the edge component in the tire width direction (edge ​​component in the tire circumferential direction) of the shallow groove 7 is increased to improve the function of wiping water in the tire circumferential direction, thereby further improving grip performance on ice.

[0188] As described above, from the viewpoint of allowing water to flow uniformly between the sipes 6 and the shallow grooves 7 and further improving grip performance on ice, the magnitude of the difference between the inclination angle θ1 and the inclination angle θ2 is more preferably 15° or less, even more preferably 10° or less, particularly preferably 5° or less, and most preferably 0°. Note that even when the magnitude of the difference between the inclination angle θ1 and the inclination angle θ2 is greater than 15° and less than 30°, this may be preferable from the viewpoint of ensuring the rigidity of the land portion and improving ground contact by preventing the block pieces defined by the sipes 6 and the shallow grooves 7 from having portions with too small an acute angle.

[0189] The groove width (opening width) of the shallow groove 7 is preferably 0.75 to 1.0 times the sipe width (opening width) of the sipe 6. This is because when the widths of the sipe 6 and the shallow groove 7 are nearly equal as in the above range, water flows more evenly and grip performance on ice can be further improved when the magnitude of the difference between the inclination angle θ1 and the inclination angle θ2 is within each of the above ranges.

[0190] The compounds described herein may be derived partially or entirely from fossil resources, from biological resources such as plant resources, or from recycled resources such as used tires, or may be derived from a mixture of two or more of fossil resources, biological resources, and recycled resources.

[0191] 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.

[0192] (Production of Acrylate Ester-Modified Butadiene Rubber) An acrylate ester-modified polymer, acrylate ester-modified butadiene rubber (BR-2), was prepared as follows. A reactor was charged with 200 parts of ion-exchanged water, 4.5 parts of disproportionated potassium rosinate / sodium fatty acid salt, 0.1 parts of potassium chloride, 10 parts of methoxyethyl acrylate, and 0.3 parts of t-dodecyl mercaptan (molecular weight modifier), in this order. The internal gas was purged with nitrogen three times, and then 90 parts of 1,3-butadiene was charged. The reactor was then maintained at 10°C, and 0.1 parts of diisopropylbenzene hydroperoxide (polymerization initiator), a reducing agent, and an appropriate amount of a chelating agent were charged. The polymerization reaction was initiated with stirring. The polymerization reaction was continued with stirring, and when the polymerization conversion rate reached 75%, 0.2 parts of diethylhydroxylamine (polymerization terminator) was added to terminate the polymerization reaction. After terminating the polymerization reaction, residual monomers were removed under reduced pressure at a water temperature of 60°C, followed by the addition of 0.5 parts of an alkylated phenol as an antioxidant. The resulting polymer latex was then added to an aqueous calcium chloride solution to coagulate, yielding a crumb-like polymer. The resulting crumb-like polymer was then removed, washed with water, and dried at 60°C under reduced pressure to yield a diene polymer (A-1). The resulting acrylate-modified butadiene rubber (BR-2) had a 1,3-butadiene unit content of 91% by weight (96.0 mol%), a methoxyethyl acrylate unit content of 9% by weight (4.0 mol%), a vinyl bond content in the 1,3-butadiene units of 16 mol%, a Mooney viscosity (ML1+4) of 55, and a glass transition temperature (Tg) of -76°C.

[0193] <Samples 1 to 7> Rubber composition samples were prepared by compounding and kneading in a conventional manner according to the formulations shown in Table 1. Each of the obtained samples was subjected to a vulcanization treatment to prepare a sample of vulcanized rubber composition for a tire, and then the following evaluation (1) was carried out.

[0194] <Evaluation> (1) Performance of vulcanized rubber on ice Each sample of the vulcanized rubber composition for tires was molded into a test piece with a diameter of 50 mm and a thickness of 10 mm, and then pressed against fixed ice and rotated. The frictional force generated when the test piece was rotated was detected with a load cell, and the dynamic friction coefficient μ was calculated. The measurement temperature was -2°C and the surface pressure was 12 kgf / cm. ２ The sample rotation peripheral speed was 20 cm / sec. In Table 1, the evaluation is shown as an index when the dynamic friction coefficient μ of Comparative Example 1 is set to 100. The larger the index value, the larger the dynamic friction coefficient μ and the better the performance on ice.

[0195]

[0196] *1 BR-1: Manufactured by Ube Industries, Ltd., product name "UBEPOL BR150L" *2 BR-2: Acrylate ester-modified butadiene rubber produced under the conditions described above *3 SBR: Modified styrene-butadiene rubber produced by the following method (Method for producing modified styrene-butadiene rubber) A cyclohexane solution of 1,3-butadiene and a cyclohexane solution of styrene were added to a dried, nitrogen-substituted 800 mL pressure-resistant glass vessel so that the total amount was 67.5 g of 1,3-butadiene and 7.5 g of styrene, and then 0.6 mmol of 2,2-ditetrahydrofurylpropane and 0.8 mmol of n-butyllithium were added, followed by polymerization at 50°C for 1.5 hours. To the polymerization reaction system, where the polymerization conversion rate was nearly 100%, 0.72 mmol of N,N-bis(trimethylsilyl)-3-[diethoxy(methyl)silyl]propylamine was added as a modifier, and the modification reaction was carried out at 50°C for 30 minutes. Thereafter, 2 mL of a 5 mass % solution of 2,6-di-t-butyl-p-cresol (BHT) in isopropanol was added to terminate the reaction, and the mixture was dried in a conventional manner to obtain modified SBR. Measurement of the microstructure of the obtained modified SBR revealed that the bound styrene content was 10 mass % and the vinyl bond content in the butadiene moiety was 40%. * 4 Carbon black: SAF grade carbon black * 5 Silica: "Nipsil AQ" manufactured by Tosoh Silica Industry Co., Ltd. * 6 Silane coupling agent: "ABC-856" manufactured by Shin-Etsu Chemical Co., Ltd. * 7 Resin: "Quinton (registered trademark) M100" manufactured by Nippon Zeon Co., Ltd. * 8 Vulcanization accelerator: Vulcanization accelerator containing "Noccela CZ-G" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. * 9 Vulcanizing agent: "Sulfax 5" manufactured by Tsurumi Chemical Industry Co., Ltd. * 10 Antiaging agent: "Antigen 6C" manufactured by Sumitomo Chemical Co., Ltd. * 11 Foaming agent: Dinitrosopentamethylenetetramine, "Cellular Z-K" manufactured by Eiwa Chemical Industry Co., Ltd. In addition to the listed ingredients, in Table 1, oil, stearic acid, and zinc oxide are contained in the same amounts in each example and comparative example.

[0197] The results in Table 1 show that the vulcanized rubber compositions for tires of the Examples have superior performance on ice compared to the vulcanized rubber compositions for tires of the Comparative Examples.

[0198] According to the present invention, it is possible to provide a vulcanized rubber composition for a tire having excellent performance on ice, and also to provide a tire having excellent performance on ice.

[0199] REFERENCE SIGNS LIST 10 Vulcanized rubber composition for tire 20 Void 1 Tread surface 2 Circumferential main groove 3 Land portion 4 Width direction groove 5 Block 6 Sipe 7 Shallow groove 100 Communication device, CL Tire equatorial plane TE Tread edge

Claims

1. A vulcanized rubber composition for tires, which is obtained by vulcanizing a rubber composition comprising a rubber component containing a modified conjugated diene polymer having a (meth)acrylic acid ester in the molecule and a filler containing at least silica, wherein the content of silica in the rubber composition is 30 to 70 parts by mass per 100 parts by mass of the rubber component, and the proportion of silica in the filler is 55% by mass or more, and the vulcanized rubber composition has a plurality of voids.

2. The vulcanized rubber composition for tires according to claim 1, wherein the content of the (meth)acrylic acid ester in the modified conjugated diene polymer is 0.5 to 10 mol %.

3. The vulcanized rubber composition for tires according to claim 1 or 2, wherein the (meth)acrylic acid ester is an alkoxyalkyl (meth)acrylic acid ester.

4. The vulcanized rubber composition for tires according to claim 1 or 2, wherein the glass transition temperature of the modified conjugated diene polymer is -100 to -50°C.

5. The vulcanized rubber composition for tires according to claim 1 or 2, characterized in that the modified conjugated diene polymer has 1,3-butadiene units, and the vinyl bond amount of the 1,3-butadiene units is 13 to 18 mol %.

6. The vulcanized rubber composition for tires according to claim 1 or 2, characterized in that the content of the modified conjugated diene polymer in the rubber component is 5 to 50 mass %.

7. The vulcanized rubber composition for tires according to claim 1 or 2, further comprising a liquid polymer having a bound styrene content of less than 10% and a vinyl bond content of conjugated diene units of 20% or more, and having a weight average molecular weight in terms of polystyrene of less than 40,000 as measured by gel permeation chromatography.

8. The vulcanized rubber composition for tires according to claim 7, wherein the vinyl bond content of the conjugated diene units of the liquid polymer is 45% or more and 55% or less.

9. The vulcanized rubber composition for tires according to claim 7, characterized in that the liquid polymer is unmodified polybutadiene.

10. The vulcanized rubber composition for tires according to claim 7, characterized in that the content of the liquid polymer is 1 to 40 mass %.

11. The vulcanized rubber composition for tires according to claim 7, characterized in that the mass ratio of the content of the modified conjugated diene polymer to the content of the liquid polymer (content of modified conjugated diene polymer / content of liquid polymer) is 0.5 to 5.

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

13. The vulcanized rubber composition for tires according to claim 1 or 2, characterized in that the rubber composition further contains bicomponent fibers.

14. The vulcanized rubber composition for tires according to claim 1 or 2, characterized in that the void ratio of the vulcanized rubber composition for tires is 5 to 45%.

15. A vulcanized rubber composition for tires according to claim 1 or 2, characterized in that the rubber component contains natural rubber, and either an unmodified butadiene rubber having a weight average molecular weight of 40,000 or more as measured by gel permeation chromatography relative to polystyrene standards, or an unmodified styrene-butadiene rubber having a weight average molecular weight of 40,000 or more as measured by gel permeation chromatography relative to polystyrene standards.

16. The vulcanized rubber composition for tires according to claim 15, characterized in that the content of said natural rubber in said rubber component is 30 to 70 mass %.

17. The vulcanized rubber composition for tires according to claim 15, characterized in that the content of the unmodified butadiene rubber or the unmodified styrene-butadiene rubber in the rubber component is 15 to 45 mass %.

18. The vulcanized rubber composition for tires according to claim 1 or 2, characterized in that the rubber composition further contains a fatty acid amide.

19. The vulcanized rubber composition for tires according to claim 18, characterized in that the rubber composition contains 0.1 to 10 parts by mass of the fatty acid amide per 100 parts by mass of the rubber component.

20. The vulcanized rubber composition for tires according to claim 19, characterized in that the fatty acid amide is a fatty acid bisamide.

21. The vulcanized rubber composition for tires according to claim 20, characterized in that the fatty acid bisamide is ethylene bis fatty acid amide.

22. A tire, characterized in that the vulcanized rubber composition for tires according to claim 1 or 2 is used in the tread.

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