Tire

Abstract

The present invention addresses the problem of providing a tire having excellent workability during manufacture and improved durability while maintaining performance on ice. The solution to this problem is a tire (1) comprising a tread rubber (10) including a cap rubber (4) and a base rubber (5) positioned on the tire-radial inner side of the cap rubber (4), the cap rubber (4) containing a rubber component, silica, and a resin, the rubber component in the cap rubber (4) containing natural rubber and butadiene rubber, the resin in the cap rubber (4) having a weight average molecular weight of 200‒3300 g / mol, the cap rubber (4) having a plurality of voids, the base rubber (5) containing a rubber component and carbon black and either containing or not containing a softener, the rubber component in the base rubber (5) containing 50 parts by mass or more of natural rubber in 100 parts by mass of the rubber component, and the softener content in the base rubber (5) being 30 parts by mass or less per 100 parts by mass of the rubber component in the base rubber (5).

Description

tire

[0001] The present invention relates to a tire.

[0002] Conventionally, studless tires with soft tread rubber have been used as tires for safe driving on ice as well as on normal road surfaces, and it is known that softening the tread rubber improves the tire's performance on ice. It is also known that applying a rubber composition containing a resin to the tire's tread rubber improves the tire's performance on ice. For example, Patent Document 1 below discloses a tire with excellent braking performance on ice, in which the tread uses a rubber composition containing 50 to 90 parts by mass of a filler containing silica per 100 parts by mass of a rubber component containing natural rubber, polybutadiene rubber, and styrene-butadiene copolymer rubber, and in which 50% by mass or more of silica is contained in the phase containing the polybutadiene rubber and the styrene-butadiene copolymer rubber. The patent document also discloses the incorporation of a resin into the rubber composition.

[0003] International Publication No. 2019 / 116701

[0004] However, rubber compositions containing conventional resins have a high adhesive property, which causes excessive adhesion to manufacturing equipment, resulting in poor workability. Furthermore, when a rubber composition with high adhesive property is used as tread rubber to manufacture a tire, the tire durability is reduced.

[0005] Therefore, an object of the present invention is to solve the above-mentioned problems of the conventional technology and to provide a tire that maintains performance on ice, has excellent workability during manufacturing, and has improved durability.

[0006] The gist of the tire of the present invention that solves the above problems is as follows.

[0007] [1] A tire having a tread rubber including a cap rubber located on the outermost surface of a tread portion and a base rubber located radially inward of the cap rubber, wherein the cap rubber includes a rubber component, a filler, and a resin, the rubber component in the cap rubber includes natural rubber and butadiene rubber, the filler in the cap rubber includes silica, the resin in the cap rubber has a weight average molecular weight of 200 to 3,300 g / mol, the cap rubber has a plurality of voids, the base rubber includes a rubber component and a filler, and may or may not include a softener, the rubber component in the base rubber includes 50 parts by mass or more of natural rubber per 100 parts by mass of the rubber component, the filler in the base rubber includes carbon black, and the content of the softener in the base rubber is 30 parts by mass or less per 100 parts by mass of the rubber component in the base rubber.

[0008] [2] The tire according to [1], wherein the content of the filler in the cap rubber is 60 to 100 parts by mass per 100 parts by mass of the rubber component in the cap rubber.

[0009] [3] The tire according to [1] or [2], wherein the filler in the cap rubber has a content ratio of the silica of 20 mass % or more.

[0010] [4] The tire according to any one of [1] to [3], wherein the content of the resin in the cap rubber is 1 to 50 parts by mass per 100 parts by mass of the rubber component in the cap rubber.

[0011] [5] The tire according to any one of [1] to [4], wherein the rubber component in the base rubber further contains styrene-butadiene rubber.

[0012] [6] The tire according to [5], wherein the rubber component in the base rubber contains 5 to 50 parts by mass of the styrene-butadiene rubber per 100 parts by mass of the rubber component.

[0013] [7] The tire according to any one of [1] to [6], wherein the content of the filler in the base rubber is 40 to 100 parts by mass per 100 parts by mass of the rubber component in the base rubber.

[0014] According to the present invention, it is possible to provide a tire that maintains performance on ice, has excellent workability during manufacturing, and has improved durability.

[0015] 1 is a cross-sectional view of an embodiment of a tire according to the present invention. 2 is a schematic diagram showing a cross section of an embodiment of a cap rubber of a tire according to the present invention.

[0016] The tire of the present invention will be described in detail below by way of example based on an embodiment thereof.

[0017] <Definitions> The compounds described herein may be derived in whole or in part from fossil resources, from biological resources such as plant resources, from recycled resources such as used tires, or from a mixture of two or more of fossil resources, biological resources, and recycled resources.

[0018] In this specification, the weight average molecular weight of a resin is measured by gel permeation chromatography (GPC) and calculated as a polystyrene equivalent value.

[0019] <Tire> Figure 1 is a cross-sectional view of one embodiment of a tire of the present invention. The tire 1 shown in Figure 1 has a pair of bead portions 2, a pair of sidewall portions 3, and a tread portion 6 connected to both sidewall portions 3 and having a cap rubber 4 and a base rubber 5, in that order from the outer side in the tire radial direction, a carcass 7 extending in a toroidal shape between the pair of bead portions 2 and reinforcing these portions 2, 3, 6, and a belt 8 disposed on the outer side in the tire radial direction of the carcass 7.

[0020] The carcass 7 of the tire shown in FIG. 1 is composed of one carcass ply made of a plurality of parallel-arranged cords covered with a coating rubber, and the carcass 7 is composed of a main body portion extending in a toroidal shape between the bead cores 9 embedded in each of the bead portions 2, and a folded-up portion wound up radially outward from the inner side toward the outer side in the tire width direction around each bead core 9, but the number of plies and the structure of the carcass 7 in the tire of the present invention are not limited to this.

[0021] 1 is composed of two belt layers, the number of belt layers constituting the belt 8 in the tire of the present invention is not limited to this, and the number of belt layers may be three or more. Here, the belt layer usually comprises a rubberized layer of reinforcing cords (preferably steel cords) extending at an angle with respect to the tire equatorial plane, and the two belt layers are laminated to constitute the belt 8 such that the reinforcing cords constituting the belt layers cross each other with the tire equatorial plane in between.

[0022] The tire of this embodiment comprises a tread rubber 10 including a cap rubber 4 located on the outermost surface of a tread portion 6 and a base rubber 5 located radially inward of the cap rubber 4, wherein the cap rubber 4 includes a rubber component, a filler, and a resin, the rubber component in the cap rubber 4 includes natural rubber and butadiene rubber, the filler in the cap rubber 4 includes silica, the resin in the cap rubber 4 has a weight average molecular weight of 200 to 3300 g / mol, the cap rubber 4 has a plurality of voids, the base rubber 5 includes a rubber component and a filler, and may or may not include a softener, the rubber component in the base rubber 5 includes 50 parts by mass or more of natural rubber per 100 parts by mass of the rubber component, the filler in the base rubber 5 includes carbon black, and the content of the softener in the base rubber 5 is 30 parts by mass or less per 100 parts by mass of the rubber component in the base rubber.

[0023] The tire of the present invention may be modified in various ways as long as it includes a tread rubber including a cap rubber located on the outermost surface of the tread portion and a base rubber located radially inward of the cap rubber. For example, a belt reinforcing layer may be provided radially outward of the belt 8 of the tire 1 shown in FIG.

[0024] In the tire 1 of this embodiment, the tread rubber 10 is divided into a cap rubber 4 located on the outermost surface of the tread portion 6 and a base rubber 5 located radially inward of the cap rubber 4. The cap rubber 4, which is involved in the tire's on-ice performance, is provided with multiple voids to ensure the tire's on-ice performance. Furthermore, a rubber composition containing a resin with a weight-average molecular weight of 3300 g / mol or less is applied to the cap rubber 4, thereby improving the tire's on-ice performance. A rubber composition containing a resin with a weight-average molecular weight of 3300 g / mol or less has lower adhesion and is less likely to adhere to manufacturing equipment than a rubber composition blended with a conventional resin with a weight-average molecular weight exceeding 3300 g / mol, thereby providing excellent workability during manufacturing. Furthermore, applying a rubber composition with low adhesion to the cap rubber 4 can also improve the durability of the cap rubber 4. Furthermore, in tire 1 of this embodiment, the durability of base rubber 5 can be improved by increasing the proportion of natural rubber in the rubber component of base rubber 5, specifically by setting the content of natural rubber to 50 parts by mass or more per 100 parts by mass of the rubber component of base rubber 5. Furthermore, the fracture properties of base rubber 5 at high temperatures can be improved by setting the content of softener in base rubber 5 to 30 parts by mass or less per 100 parts by mass of the rubber component of base rubber 5. Therefore, tire 1 of this embodiment maintains its performance on ice while improving workability during manufacturing and also improving durability.

[0025] <<Cap Rubber>> In the tire of this embodiment, the cap rubber includes a rubber component, a filler, and a resin. The cap rubber can be made from, for example, a rubber composition including the rubber component, a filler, and a resin.

[0026] (Rubber Component) The rubber component of the cap rubber includes natural rubber (NR) and butadiene rubber (BR), and may further include other rubber components. Examples of other rubber components include synthetic isoprene rubber (IR) and styrene-butadiene rubber (SBR). The butadiene rubber (BR) and / or other rubber components may be modified or unmodified. The origin of the natural rubber (NR) is not particularly limited, and examples include rubber derived from Hevea brasiliensis, guayule, and Russian dandelion. Furthermore, the natural rubber may be modified natural rubber, and examples of modified natural rubber include deproteinized natural rubber and high-purity natural rubber.

[0027] The inclusion of natural rubber in the rubber component of the cap rubber can improve the breaking strength of the cap rubber, thereby reducing the rolling resistance of the tire, improving fuel economy, and also improving the wear resistance of the tire. Here, the content of natural rubber is preferably in the range of 10 to 90 parts by mass, more preferably 20 to 80 parts by mass, more preferably 30 to 70 parts by mass, and even more preferably 40 to 60 parts by mass, per 100 parts by mass of the rubber component of the cap rubber.

[0028] Furthermore, by including butadiene rubber in the rubber component of the cap rubber, a good balance between the tire's performance on ice and its wear resistance can be achieved. The type of butadiene rubber is not particularly limited. For example, high-cis polybutadiene can be used as the butadiene rubber, and in this case, it is preferable that the cis-1,4 bond content is 90% by mass or more. The use of high-cis polybutadiene can further improve the tire's wear resistance. Here, the content of butadiene rubber is preferably in the range of 10 to 90 parts by mass, more preferably 20 to 80 parts by mass, more preferably 30 to 70 parts by mass, and even more preferably 40 to 60 parts by mass, per 100 parts by mass of the rubber component of the cap rubber.

[0029] The content of the other rubber component is preferably in the range of 0 to 30 parts by mass, more preferably 0 to 15 parts by mass, per 100 parts by mass of the rubber component of the cap rubber.

[0030] (Filler) The cap rubber contains a filler, which improves the reinforcing properties of the cap rubber.

[0031] The filler in the cap rubber contains silica. The inclusion of silica in the cap rubber can further improve the tire's performance on ice and abrasion resistance. Examples of the silica include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, and aluminum silicate. Among these, wet silica is preferred. These silicas may be used alone or in combination. Precipitated silica can be used as the wet silica. Precipitated silica is 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.

[0032] The silica is not particularly limited, but 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, the adsorption cross section per molecule of cetyltrimethylammonium bromide on the silica surface can be set to 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 can be measured in accordance with ASTM D4820-93.

[0033] The content of the silica is preferably 5 to 100 parts by mass, more preferably 10 to 50 parts by mass, and even more preferably 10 to 45 parts by mass, per 100 parts by mass of the rubber component. When the content of the silica is 5 parts by mass or more per 100 parts by mass of the rubber component, the abrasion resistance and ice performance of the cap rubber can be further improved, and by setting the content to 100 parts by mass or less, deterioration in workability during kneading of the rubber composition used for the cap rubber and deterioration in fuel economy of the tire can be suppressed.

[0034] The filler in the cap rubber preferably further contains carbon black, which can further improve the properties of the cap rubber, such as cut resistance and abrasion resistance.

[0035] Here, the type of carbon black is not particularly limited, and examples thereof include GPF, FEF, HAF, IISAF, ISAF, and SAF grade carbon black. Among these, it is preferable to use ISAF, SAF, FEF, or HAF grade carbon black from the viewpoint of further improving the abrasion resistance and cut resistance of the cap rubber. These carbon blacks may be used alone or in combination of two or more types. The carbon black has a nitrogen adsorption specific surface area (N ２ SA, measured in accordance with JIS K 6217-2:2001) is 20 to 250 m ２ It is preferable to use one having a molecular weight of 30 to 200 m / g. ２ It is more preferable to use one having a molecular weight of 30 to 150 m / g. ２ It is more preferable to use carbon black having a dibutyl phthalate (DBP) oil absorption (measured by the method described in JIS K 6217-4:2001 "Determination of DBP absorption") of 50 to 200 cm ３ It is preferable to use one having a thickness of 60 to 150 cm / 100 g. ３ It is more preferable to use one having a density of 100g / 100g.

[0036] The carbon black may be plant-derived or recycled. Examples of plant-derived carbon black include those derived from castor oil and pine oil. Examples of recycled carbon black include carbon black obtained by pyrolysis of used tires and carbon black obtained from waste oil. The grade of the carbon black is not particularly limited, and examples include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. Commercially available carbon black products can be used, including those from Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Shin-Nichika Carbon Co., Ltd., and Columbia Carbon Co., Ltd. These carbon blacks may be used alone or in combination.

[0037] The amount of carbon black is not particularly limited, but is preferably 20 to 80 parts by mass, more preferably 25 to 70 parts by mass, and even more preferably 30 to 65 parts by mass, per 100 parts by mass of the rubber component. If the amount of carbon black is 20 parts by mass or more per 100 parts by mass of the rubber component, the abrasion resistance can be further improved, and if the amount is 80 parts by mass or less, the deterioration of the fuel economy performance of the tire can be more reliably suppressed.

[0038] The filler may be, in addition to the above-mentioned silica and carbon black, a compound represented by the following general formula (1): nM.xSiO ｙ ・zH ２O ... (1) [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, an oxide or hydroxide of these metals, a hydrate thereof, or a carbonate of these metals; and n, x, y and z are integers of 1 to 5, an integer of 0 to 10, an integer of 2 to 5 and an integer of 0 to 10, respectively]. The inorganic compound of the general formula (1) may include alumina (Al) such as γ-alumina and α-alumina. ２ O ３ alumina monohydrate (Al), boehmite, diaspore, etc. ２ O ３ ・H ２ O), 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 ・H ２ O), attapulgite (5MgO.8SiO ２ ・9H ２ O), titanium white (TiO ２ ), 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 ３ 2SiO ２ ), kaolin (Al ２ O ３ 2SiO ２ ・2H ２ O), pyrophyllite (Al ２ O ３ 4SiO ２ ・H ２ O), bentonite (Al ２ O ３ 4SiO ２ ・2H ２O), 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 the charge, such as various zeolites. From the viewpoint of balancing abrasion resistance and performance on ice, the inorganic compound of general formula (1) preferably has an average particle size of 0.01 to 10 μm, and more preferably 0.05 to 5 μm.

[0039] The content of the filler in the cap rubber is preferably 60 to 100 parts by mass, more preferably 60 to 80 parts by mass, per 100 parts by mass of the rubber component in the cap rubber. When the content of the filler in the cap rubber is 60 parts by mass or more per 100 parts by mass of the rubber component, the abrasion resistance of the tire is improved, and the durability of the tire is also improved. Furthermore, when the content of the filler in the cap rubber is 100 parts by mass or less per 100 parts by mass of the rubber component, the workability in kneading the rubber composition used for the cap rubber is improved. Therefore, when the content of the filler in the cap rubber is 60 to 100 parts by mass per 100 parts by mass of the rubber component in the cap rubber, the abrasion resistance and durability of the tire are improved, and the workability during production is also good.

[0040] The silica content of the filler in the cap rubber is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, and is preferably 70% by mass or less, and more preferably 60% by mass or less. By having the silica content of the filler be 20% by mass or more, better ice performance can be obtained. Furthermore, by having the silica content of the filler be 70% by mass or less, better abrasion resistance can be obtained.

[0041] (Resin) The cap rubber contains a resin with a weight-average molecular weight (Mw) of 200 to 3300 g / mol. A rubber composition containing a resin with a weight-average molecular weight of 3300 g / mol or less has low adhesion and is less likely to adhere to manufacturing equipment, resulting in excellent workability during manufacturing. Furthermore, by using a rubber composition with low adhesion as the cap rubber, the durability of the cap rubber can be improved. Furthermore, by containing a resin with a weight-average molecular weight of 200 to 3300 g / mol in the cap rubber, the tire's performance on ice can be improved.

[0042] When the weight-average molecular weight of the resin is 200 g / mol or more, the resin is less likely to precipitate from the tire and the effects of the resin can be fully exerted, and when it is 3,300 g / mol or less, the adhesion of the rubber composition can be reduced and the resin is more likely to be compatible with the rubber component. From the viewpoint of suppressing the resin from precipitating from the tire and suppressing deterioration in the tire appearance, the weight-average molecular weight of the resin is preferably 500 g / mol or more, more preferably 550 g / mol or more, even more preferably 600 g / mol or more, even more preferably 650 g / mol or more, and still more preferably 700 g / mol or more. Furthermore, from the viewpoint of improving the compatibility of the resin with the rubber component and further enhancing the effects of the resin, the weight average molecular weight of the resin is preferably 3200 g / mol or less, more preferably 3100 g / mol or less, more preferably 3000 g / mol or less, more preferably 2900 g / mol or less, more preferably 2800 g / mol or less, more preferably 2700 g / mol or less, more preferably 2600 g / mol or less, more preferably 2500 g / mol or less, and even more preferably 2400 g / mol or less.

[0043] The resin preferably has a softening point of 80°C or higher. When the resin has a softening point of 80°C or higher, the cap rubber can be sufficiently reinforced and abrasion resistance can be sufficiently maintained. From the viewpoint of the abrasion resistance of the tire, the softening point of the resin is more preferably 85°C or higher, more preferably 90°C or higher, more preferably 95°C or higher, and even more preferably 100°C or higher. From the viewpoint of processability, the softening point of the resin is preferably 160°C or lower, more preferably 150°C or lower, more preferably 145°C or lower, more preferably 141°C or lower, even more preferably 136°C or lower, and may also be 110°C or lower. The weight average molecular weight and softening point of the resin can be determined by the method described in the examples below.

[0044] The resin is preferably at least partially hydrogenated. When the resin is at least partially hydrogenated, the compatibility of the resin with natural rubber is increased, the mobility of the rubber component is controlled, and the hysteresis loss (tan δ) in the low temperature range can be improved, thereby improving the tire's performance on ice. Note that the term "at least partially hydrogenated resin" refers to a resin obtained by reducing and hydrogenating a resin.

[0045] Here, the resin may be, for example, C ５ based resin, C ５ -C ９ based resin, C ９ Examples of the resins include terpene-based resins, dicyclopentadiene-based resins, and terpene-aromatic compound-based resins. These resins may be used alone or in combination of two or more.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] The terpene resin is a solid resin obtained by blending turpentine, which is obtained simultaneously with the extraction of rosin from pine trees, or a polymerization component separated 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. Styrene or the like may be included in the skeleton.

[0050] The dicyclopentadiene resin is, for example, AlCl ３ or BF３ This refers to a resin obtained by polymerizing dicyclopentadiene using a Friedel-Crafts catalyst such as

[0051] 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.

[0052] From the viewpoint of increasing the compatibility between the rubber component and the resin and further improving the tire's performance on ice, the resin is preferably a hydrogenated C ５ based resin, hydrogenated C ５ -C ９ It is preferable that the resin contains at least one selected from the group consisting of hydrogenated C ５ Resin and hydrogenated C ５ -C ９ It is more preferable that the resin contains at least one selected from the group consisting of hydrogenated C ５ It is more preferable that the resin contains at least a hydrogenated DCPD-based resin. It is also preferable that the resin contains at least a hydrogenated DCPD structure or a hydrogenated cyclic structure in the monomer. ５ Resin and hydrogenated C ５ -C ９ For the C-based resin, the unsaturated bonds in the molecule are partially or completely hydrogenated. ５ Resin and C ５ -C ９For example, when a resin having an aromatic ring such as a benzene ring in the main chain or side chain is hydrogenated, the aromatic ring is reduced to a saturated ring (if the aromatic ring is a benzene ring, it is reduced to a cyclohexane ring). When the unsaturated bonds in the molecule are partially or completely hydrogenated, the storage modulus (E') of the rubber composition at low temperatures decreases, and compatibility with the rubber component improves, resulting in a greater effect of increasing tan δ and enabling the realization of excellent performance on ice.

[0053] The content of the resin in the cap rubber is preferably 1 to 50 parts by mass per 100 parts by mass of the rubber component in the cap rubber. When the content of the resin in the cap rubber is 1 part by mass or more per 100 parts by mass of the rubber component, the effect of the resin is fully exhibited, and when it is 50 parts by mass or less, the resin is less likely to precipitate from the tire, allowing the effect of the resin to be fully exhibited. Therefore, when the content of the resin in the cap rubber is 1 to 50 parts by mass per 100 parts by mass of the rubber component, the effect of the resin is fully exhibited and the tire's on-ice performance can be fully improved. From the viewpoint of further improving the tire's on-ice performance, the content of the resin is more preferably 5 parts by mass or more, more preferably 7 parts by mass or more, and even more preferably 9 parts by mass or more per 100 parts by mass of the rubber component. Furthermore, from the viewpoint of suppressing resin precipitation from the tire and suppressing deterioration in the tire's appearance, the content of the resin is more preferably 45 parts by mass or less, and even more preferably 40 parts by mass or less per 100 parts by mass of the rubber component.

[0054] (Voids) As shown in Fig. 2, in the tire of this embodiment, the cap rubber 4 has a plurality of voids 11. By having the cap rubber 4 have a plurality of voids 11, the performance of the tire on ice can be improved.

[0055] The voids in the cap rubber preferably have an average diameter of about 1 to 500 μm. Here, the void diameter refers to the largest diameter of the void (if the void is not spherical, the largest distance between any two points on the inner wall of the void).

[0056] The porosity of the cap rubber is preferably 5 to 45%. By making the porosity of the cap rubber 5% or more, it is possible to more reliably improve the tire's performance on ice. From the same viewpoint, the porosity is more preferably 7% or more, and even more preferably 15% or more. Furthermore, by making the porosity of the cap rubber 45% or less, it is possible to more reliably suppress a decrease in the tire's wear resistance. From the same viewpoint, it is more preferably 40% or less, and even more preferably 37% or less. Here, the porosity refers to the ratio (volume %) of the volume of the voids in the cap rubber.

[0057] The method for providing multiple voids in the cap rubber is not particularly limited. For example, as described below, a method of providing voids in the cap rubber by compounding a void-introducing agent into the rubber composition for the cap rubber before vulcanization can be used. The void ratio can be controlled by changing the vulcanization conditions of the rubber composition or the content of the void-introducing agent. Another method for providing the voids is to compound powdered rubber into the rubber composition for the cap rubber before vulcanization, so that the powdered rubber falls off from the surface of the rubber composition after vulcanization, forming voids near the surface of the cap rubber. In this case, the size and void ratio of the voids can be adjusted by adjusting the particle size and number of the powdered rubber.

[0058] As a method for providing a plurality of voids in the cap rubber, it is preferable to compound a void-introducing agent into the rubber composition used for the cap rubber. By compounding the void-introducing agent into the rubber composition used for the cap rubber, the cap rubber has voids on the surface or inside, or on the surface and inside, so that a tire using the cap rubber has flexibility and easily adheres to an icy road surface, and water on the road surface is absorbed into the voids on the tire surface, and water is easily removed from the icy road surface, so that braking performance on ice can be improved.

[0059] Examples of the void-introducing agent include a foaming agent, a metal sulfate, a thermally expandable microcapsule, a porous cellulose particle, a lignin derivative, etc., and one of these may be used alone or two or more may be mixed together. From the viewpoint of the tire performance on ice, it is preferable to use a foaming agent as the void-introducing agent.

[0060] The content of the void-introducing agent in the rubber composition for the cap rubber 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.

[0061] - Foaming Agent - By including a foaming agent as a void-introducing agent in the rubber composition, the foaming agent generates bubbles in the vulcanized rubber during vulcanization of the rubber composition, turning the vulcanized rubber into foamed rubber. Because foamed rubber has flexibility, 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.

[0062] Examples of the foaming agent include inorganic foaming 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 foaming agents are preferably used. These foaming agents may be used alone or in combination of two or more.

[0063] The content of the foaming agent 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.

[0064] Metal Sulfate—When the rubber composition contains a metal sulfate as a void-introducing agent, the metal sulfate protrudes from the tire surface obtained by vulcanizing the rubber composition, performing a claw function without the disadvantage of being abrasive. Subsequently, the metal sulfate gradually leaves the rubber matrix, creating cavities that function as storage volumes and passageways 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, and therefore, examples of metal sulfates that improve the coefficient of friction include magnesium sulfate.

[0065] The metal sulfate preferably has micrometer-sized particles. Specifically, the average particle size and median particle size (both expressed by mass) are preferably 1 μm to 1 mm, and the median particle size is more preferably 2 μm to 800 μm. When the average particle size and median particle size are 1 μm or more, the desired technical effect (i.e., the formation of an appropriate micro-roughness) is easily achieved. Furthermore, when the average particle size and median particle size are 1 mm or less, the degradation of the tire aesthetics is suppressed (the appearance of too obvious particles on the cap rubber surface can be suppressed) and the grip performance on melting ice is less likely to be impaired. For all of these reasons, the median particle size of the metal sulfate is preferably 2 μm to 500 μm, and more preferably 5 μm to 200 μm. This particularly preferred particle size range appears to correspond to the optimal compromise between the desired surface roughness on the one hand and good contact between the cap rubber and ice on the other hand.

[0066] The amount of the metal sulfate is preferably 5 to 40 parts by mass, and more preferably 10 to 35 parts by mass, based on 100 parts by mass of the rubber component.

[0067] 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 of: 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 progressive ratio equal to 1.26); weighing the oversize particles collected on each sieve on a precision balance; estimating the percentage of oversize particles at each mesh diameter relative to the total mass of the substance from the weighing; finally, calculating the median particle size (or median diameter) or mean particle size (or mean diameter) in a known manner from a histogram of the particle size distribution.

[0068] -Thermal-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-based polymer. The thermally expandable substance encapsulated within the shell material of the microcapsules has the property of vaporizing or expanding upon heat, and is exemplified by at least one type selected from the group consisting of hydrocarbons such as isoalkanes and normal alkanes. Examples of isoalkanes include isobutane, isopentane, 2-methylpentane, 2-methylhexane, and 2,2,4-trimethylpentane. Examples of normal alkanes include n-butane, n-propane, n-hexane, n-heptane, and n-octane. These hydrocarbons may be used alone or in combination. A preferred form of the thermally expandable substance is one in which a hydrocarbon that is gaseous at room temperature is dissolved in a hydrocarbon that is liquid at room temperature. By using such a hydrocarbon mixture, sufficient expansion force can be obtained from low to high temperature ranges within the vulcanization molding temperature range (150°C to 190°C) of an unvulcanized tire.

[0069] Examples of such thermally expandable microcapsules include those manufactured by Expancel AB in 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".

[0070] The content of the thermally expandable microcapsules 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.

[0071] -Porous Cellulose Particles- When the rubber composition for the cap rubber contains porous cellulose particles as a void-introducing agent, if 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 can be 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.

[0072] 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.

[0073] 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 1,000 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. Spherical particles having a major axis / minor axis ratio of 1 to 2 are preferably used as the porous cellulose particles. The use of particles with such a spherical structure improves dispersibility in the rubber composition, contributing to improved performance on ice and the maintenance of abrasion resistance. The major axis / minor axis ratio is more preferably 1.0 to 1.5. The average particle size and major axis / minor axis ratio of the porous cellulose particles can be determined as follows. That is, porous cellulose particles are observed under a microscope to obtain an image, and this image is used to measure the long and short diameters of the particles (if the long and short diameters are the same, the length in a certain axial direction and the length in an axial direction perpendicular to it) for 100 particles, and the average particle size is obtained by calculating the average value, and the long diameter / short diameter ratio is obtained by averaging the values ​​obtained by dividing the long diameter by the short diameter.

[0074] The porous cellulose particles are commercially available from Rengo Co., Ltd. under the name "Viscopal" and are also described in JP-A Nos. 2001-323095 and 2004-115284, and can be suitably used.

[0075] The content of the porous cellulose particles is preferably 0.3 to 20 parts by mass per 100 parts by mass of the rubber component. By having the content of the porous cellulose particles at 0.3 parts by mass or more, the effect of improving performance on ice can be enhanced, and by having the content of the porous cellulose particles at 20 parts by mass or less, it is possible to prevent the rubber hardness from becoming too high and to 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.

[0076] -Lignin Derivative- When the rubber composition for the cap rubber contains a lignin derivative as a 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 of these are also acceptable.

[0077] -Foaming Aid- When the rubber composition for the cap rubber contains a foaming agent as a void-introducing agent, it is preferable that it further contains a foaming aid. Examples of the foaming aid include urea, zinc stearate, zinc benzenesulfinate, and zinc oxide. These may be used alone or in combination of two or more. By using the foaming agent and the foaming aid in combination, the foaming reaction is promoted, the degree of completion of the reaction is increased, and unnecessary deterioration over time can be suppressed.

[0078] 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. Furthermore, 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.

[0079] 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.

[0080] 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.

[0081] -Organic Acid- The rubber composition for the cap rubber may contain an organic acid, if necessary. In this case, the SP value of the organic acid is 9.15 to 16.0 (cal / cm ３ ) １／２ The organic acid has the effect of improving the foaming rate of the vulcanized rubber by balancing the rate of the decomposition / foaming reaction of the foaming agent and the rate of the vulcanization reaction of the rubber composition during vulcanization of the rubber composition. Therefore, by compounding the organic acid into the rubber composition, the workability of the rubber composition is maintained good, while the decomposition / foaming reaction of the foaming agent is promoted, and the rate of the decomposition / foaming reaction and the rate of the vulcanization reaction of the rubber composition are balanced, thereby improving the foaming rate of the vulcanized rubber. By applying this rubber composition to a tire, the tire's performance on ice can be improved. The SP value of the organic acid is 9.15 (cal / cm ３ ) １／２If the SP value of the organic acid is less than 16.0 (cal / cm), the decomposition of the foaming agent may not be sufficiently promoted. ３ ) １／２ If the content exceeds this range, the adhesiveness of the rubber composition containing the organic acid will be high, and the rubber composition may adhere to manufacturing equipment such as rolls during production of the rubber composition, which may deteriorate the workability of the rubber composition.

[0082] From the same viewpoint, the SP value of the organic acid is 10.5 to 14.3 (cal / cm ３ ) １／２ The SP value of the organic acid is preferably 10.5 (cal / cm ３ ) １／２ When the SP value of the organic acid is 14.3 (cal / cm or more), the effect of promoting the decomposition of the foaming agent is further increased. ３ ) １／２ When the SP value is 9.12 (cal / cm), the adhesiveness of the rubber composition containing the organic acid can be further reduced, and the workability of the rubber composition can be further improved. ３ ) １／２ In this specification, the SP value (solubility parameter) of an organic acid is calculated according to the Fedors method.

[0083] The organic acid may be any of monocarboxylic acid, dicarboxylic acid, tricarboxylic acid, etc., and may be aliphatic or aromatic. Furthermore, it may have a functional group other than a carboxyl group, such as a hydroxyl group, a ketone group, or an ethylenically unsaturated group. The organic acid preferably has an aromatic ring (aromatic), and more preferably a monocarboxylic acid. When the organic acid has an aromatic ring, the adhesion of the rubber composition can be further reduced, the workability of the rubber composition is further improved, and the rubber composition is less likely to adhere to manufacturing equipment such as rolls.

[0084] Examples of the aliphatic monocarboxylic acid include palmitic acid. Examples of the aliphatic dicarboxylic acid include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid. Examples of the aromatic monocarboxylic acid include benzoic acid and salicylic acid. Examples of the aromatic dicarboxylic acid include phthalic acid. Examples of organic acids having a functional group other than a carboxyl group include tartaric acid, malic acid, maleic acid, glycolic acid, and α-ketoglutaric acid. The organic acids may be used alone or in combination of two or more.

[0085] It is particularly preferable to use benzoic acid as the organic acid. When benzoic acid is compounded into the rubber composition, the adhesion of the rubber composition can be further reduced, the workability of the rubber composition is further improved, and the rubber composition becomes even less likely to adhere to manufacturing equipment such as rolls.

[0086] From the viewpoints of workability of the rubber composition, the foaming rate of the vulcanized rubber, and the tire's performance on ice, the content of the organic acid is preferably 0.1 to 7 parts by mass, more preferably 1.5 to 7 parts by mass, and even more preferably 3 to 7 parts by mass, per 100 parts by mass of the rubber component. Furthermore, from the viewpoints of the foaming rate of the vulcanized rubber and the tire's performance on ice, the total content of the foaming agent and the organic acid is preferably 3 parts by mass or more and less than 15 parts by mass, more preferably 5 parts by mass or more and less than 15 parts by mass, and even more preferably 7 parts by mass or more and less than 15 parts by mass, per 100 parts by mass of the rubber component. Furthermore, from the viewpoints of the foaming rate of the vulcanized rubber and the tire's performance on ice, the mass ratio of the foaming agent to the organic acid (foaming agent:organic acid) is preferably in the range of 1:0.5 to 1:1.5, and more preferably 1:0.7 to 1:1.3.

[0087] - Composite Fiber - The rubber composition for the cap rubber also preferably contains composite fiber. By containing the composite fiber, it is possible to ensure sufficient affinity with water, and to impart excellent drainage properties and performance on ice to the tire. The composite fiber is preferably made of a hydrophilic resin having a coating layer formed on its surface. This is because providing a coating layer on the surface of the composite fiber improves the dispersibility of the composite fiber in the rubber composition. The hydrophilic resin is preferably insoluble in water, and by using a water-insoluble hydrophilic resin, 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).

[0088] 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. Specifically, it is preferably a resin that contains an oxygen atom, a nitrogen atom, or a sulfur atom, such as —OH, —C(═O)OH, —OC(═O)R (R is an alkyl group), —NH ２ , —NCO, and —SH. Among these groups, the most preferred are resins containing at least one group selected from the group consisting of —OH, —C(═O)OH, —OC(═O)R, —NH ２ , —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, and cellulose-based resins. 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.

[0089] 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 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, the coating layer is preferably formed so as to occupy at least 50% of the total surface area of ​​the hydrophilic resin.

[0090] 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.

[0091] 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.

[0092] To produce a composite fiber made of a hydrophilic resin with a coating layer made of the low-melting-point resin, the resins can be blended using a mixing mill, melt-spun to form an undrawn yarn, and then hot-drawn the undrawn yarn to form a fiber. Alternatively, the resins can be blended using two twin-screw extruders equipped with dies and then similarly shaped into a fiber. In this case, the hydrophilic resin and the low-melting-point resin are simultaneously extruded from the two die outlets, forming an undrawn yarn. The amount of resins added to the mixing mill or hopper varies depending on the length and diameter of the resulting composite (fiber), but is preferably 5 to 300 parts by mass, more preferably 10 to 150 parts by mass, of the low-melting-point resin per 100 parts by mass of the hydrophilic resin. Adding these resins in amounts within the above ranges effectively forms a coating layer that can exert the desired effects on the surface of the hydrophilic resin composite (fiber) obtained after the drawing process.

[0093] 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.

[0094] 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. Furthermore, 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, the on-ice performance is further improved. Note that, as long as A / B is greater than 1, the cross-sectional shape is not particularly limited and may be any of elliptical, rectangular, polygonal, irregular, etc.

[0095] 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.

[0096] (Other Components) In addition to the above-mentioned components, the rubber composition used for the cap rubber may contain compounding agents commonly used in the rubber industry as other components. As for other components, for example, silane coupling agents, vulcanizing agents, vulcanization accelerators, polyethylene glycol, softeners, antioxidants, zinc oxide (zinc white), etc. may be appropriately selected and contained within a range that does not impair the object of the present invention. As these compounding agents, commercially available products can be suitably used.

[0097] When the rubber composition used for the cap rubber contains silica as the filler, it is preferable that the rubber composition further contains a silane coupling agent. By containing the silane coupling agent, the effects of the silica on cut resistance, reinforcement, and low loss can be further improved. In addition, known silane coupling agents can be used as appropriate. 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.

[0098] 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.

[0099] 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.

[0100] The rubber composition used for the cap rubber may contain a softener other than the resin described above, in order to increase the flexibility of the rubber and achieve better performance on ice. The softener may be any conventionally known softener, and is not particularly limited. Examples of such softeners 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 alone, these softeners may be used alone or in combination of two or more. 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, among the softeners described above, such as petroleum-based softeners such as aroma oil, paraffin oil, and naphthenic oil.

[0101] The method for producing the rubber composition used for the cap rubber is not particularly limited, and can be obtained, for example, by blending and kneading the above-mentioned rubber component, filler containing at least silica, resin, and other optional components by a known method.

[0102] <<Base Rubber>> In the tire of this embodiment, the base rubber includes a rubber component and a filler, and may or may not include a softener. The base rubber can be made from, for example, a rubber composition including a rubber component and a filler, and optionally including a softener.

[0103] (Rubber Component) The rubber component of the base rubber contains natural rubber (NR) and may further contain other rubber components. The origin of the natural rubber (NR) is not particularly limited, and examples include rubber derived from Hevea brasiliensis, guayule, and Russian dandelion. The natural rubber may also be modified natural rubber, and examples of modified natural rubber include deproteinized natural rubber and high-purity natural rubber. By including natural rubber in the rubber component of the base rubber, the breaking strength of the base rubber can be increased, and as a result, the durability of the tire can be improved. Here, the content of natural rubber is 50 parts by mass or more per 100 parts by mass of the rubber component of the base rubber. By including 50 parts by mass or more of natural rubber per 100 parts by mass of the rubber component of the base rubber, the durability of the base rubber can be improved, and therefore the durability of the tire can be improved. The amount of natural rubber is preferably 60 parts by mass or more, more preferably 70 parts by mass or more, more preferably 80 parts by mass or more, even more preferably 90 parts by mass or more, and may be 100 parts by mass, per 100 parts by mass of the rubber component of the base rubber. When other rubber components are used in combination, the amount of natural rubber is preferably 95 parts by mass or less, more preferably 90 parts by mass or less, per 100 parts by mass of the rubber component of the base rubber.

[0104] The rubber component in the base rubber preferably further contains styrene-butadiene rubber (SBR). When the rubber component in the base rubber contains styrene-butadiene rubber in addition to natural rubber, the wet performance of the tire is improved. The styrene-butadiene rubber is not particularly limited, and examples include solution-polymerized styrene-butadiene rubber (S-SBR) and emulsion-polymerized styrene-butadiene rubber (E-SBR). Of these, emulsion-polymerized styrene-butadiene rubber (E-SBR) is preferred. The styrene-butadiene rubber may be modified or unmodified. The rubber component in the base rubber preferably contains 5 to 50 parts by mass of the styrene-butadiene rubber per 100 parts by mass of the rubber component. By setting the content of styrene-butadiene rubber to 5 parts by mass or more per 100 parts by mass of the rubber component of the base rubber, the wet performance of the tire can be further improved.

[0105] The rubber component in the base rubber may contain other rubber components such as synthetic isoprene rubber (IR) and butadiene rubber (BR) in addition to the natural rubber and styrene-butadiene rubber described above. These other rubber components may be modified or unmodified. The content of the other rubber components is preferably in the range of 0 to 30 parts by mass, more preferably 0 to 15 parts by mass, per 100 parts by mass of the rubber component of the base rubber.

[0106] (Filler) The base rubber contains a filler, which improves the reinforcing properties of the base rubber.

[0107] The filler in the base rubber includes carbon black, and may further include other fillers. When the base rubber includes carbon black, the breaking strength of the base rubber can be improved, and as a result, the durability of the tire can be improved.

[0108] Here, the type of carbon black is not particularly limited, and examples thereof include GPF, FEF, HAF, IISAF, ISAF, and SAF grade carbon black. Among these, it is preferable to use ISAF, SAF, FEF, or HAF grade carbon black from the viewpoint of further improving the breaking strength of the base rubber. These carbon blacks may be used alone or in combination of two or more types. The carbon black is preferably selected from those having a nitrogen adsorption specific surface area (N ２ SA, measured in accordance with JIS K 6217-2:2001) is 20 to 250 m ２ It is preferable to use one having a molecular weight of 30 to 200 m / g. ２ It is more preferable to use one having a molecular weight of 30 to 150 m / g. ２ It is more preferable to use carbon black having a dibutyl phthalate (DBP) oil absorption (measured by the method described in JIS K 6217-4:2001 "Determination of DBP absorption") of 50 to 200 cm ３ It is preferable to use one having a thickness of 60 to 150 cm / 100 g. ３ It is more preferable to use one having a density of 100g / 100g.

[0109] The carbon black may be plant-derived or recycled. Examples of plant-derived carbon black include those derived from castor oil and pine oil. Examples of recycled carbon black include carbon black obtained by pyrolysis of used tires and carbon black obtained from waste oil. The grade of the carbon black is not particularly limited, and examples include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. Commercially available carbon black products can be used, including those from Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Shin-Nichika Carbon Co., Ltd., and Columbia Carbon Co., Ltd. These carbon blacks may be used alone or in combination.

[0110] The amount of carbon black is not particularly limited, but is preferably 40 to 100 parts by mass, more preferably 25 to 70 parts by mass, and even more preferably 30 to 65 parts by mass, per 100 parts by mass of the rubber component in the base rubber. When the amount of carbon black is 40 parts by mass or more per 100 parts by mass of the rubber component, the reinforcing properties of the base rubber are further improved, and when the amount is 100 parts by mass or less, workability in kneading the rubber composition used for the base rubber is improved, and the fuel economy performance of the tire is also improved.

[0111] The filler may contain, in addition to the above-mentioned carbon black, inorganic fillers such as silica, clay, talc, calcium carbonate, and aluminum hydroxide.

[0112] The content of the filler in the base rubber is preferably 40 to 100 parts by mass per 100 parts by mass of the rubber component in the base rubber. When the content of the filler in the base rubber is 40 parts by mass or more per 100 parts by mass of the rubber component, the reinforcement of the base rubber is improved, and the durability of the tire is improved. Furthermore, when the content of the filler in the base rubber is 100 parts by mass or less per 100 parts by mass of the rubber component, the workability in kneading the rubber composition used for the base rubber is improved, and the fuel economy performance of the tire is also improved. Therefore, when the content of the filler in the base rubber is 40 to 100 parts by mass per 100 parts by mass of the rubber component, the durability and fuel economy of the tire are improved, and the workability during production is also good.

[0113] (Softener) The base rubber may or may not contain a softener, i.e., the softener is an optional component in the base rubber. When the base rubber contains a softener, the kneading of the rubber composition used for the base rubber becomes easier, and the grip performance, such as the wet performance, of the tire can be improved.

[0114] The content of the softener in the base rubber is 30 parts by mass or less per 100 parts by mass of the rubber component of the base rubber. By setting the content of the softener in the base rubber to 30 parts by mass or less per 100 parts by mass of the rubber component of the base rubber, the fracture properties of the base rubber at high temperatures can be improved. The content of the softener is preferably 28 parts by mass or less per 100 parts by mass of the rubber component of the base rubber, more preferably 26 parts by mass or less, more preferably 24 parts by mass or less, even more preferably 22 parts by mass or less, and may be 0 parts by mass.

[0115] The softener has the effect of softening the rubber composition, and examples of the softener include oil and resin.

[0116] The oil is a general term for liquid oils added as compounding ingredients to rubber compositions [more specifically, liquid at 25°C (room temperature)] and extender oils contained in rubber components, and includes petroleum-based softeners such as aromatic oils, paraffinic oils, naphthenic oils, etc.; and vegetable-based softeners such as palm oil, castor oil, cottonseed oil, soybean oil, etc. Among these, petroleum-based softeners such as aromatic oils, paraffinic oils, naphthenic oils, etc. are preferred as oils.

[0117] The resin may be C ５ based resin, C ５ -C ９ based resin, C ９ These resins may be used alone or in combination of two or more.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] The terpene resin is a solid resin obtained by blending turpentine, which is obtained simultaneously with the extraction of rosin from pine trees, or a polymerization component separated 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. Styrene or the like may be included in the skeleton.

[0122] The dicyclopentadiene resin is, for example, AlCl ３ or BF３ This refers to a resin obtained by polymerizing dicyclopentadiene using a Friedel-Crafts catalyst such as

[0123] The resin may be at least partially hydrogenated, which further enhances compatibility with natural rubber, controls the mobility of the rubber component, and further improves the wet performance of the tire.

[0124] The rubber composition used for the base rubber may contain, in addition to the rubber components, fillers, and softeners described above, various components commonly used in the rubber industry, such as silane coupling agents, antioxidants, waxes, processing aids, stearic acid, zinc oxide (zinc white), vulcanization accelerators, vulcanizing agents, etc., selected appropriately as needed within the scope of the present invention. Commercially available products can be suitably used as these compounding ingredients.

[0125] The method for producing the rubber composition used for the base rubber is not particularly limited, and can be obtained, for example, by blending and kneading the above-mentioned rubber component, the filler containing at least carbon black, and other optional components, etc., by a known method.

[0126] <Tire Manufacturing Method> Depending on the type of tire to be applied, the tire of this embodiment may be obtained by molding and vulcanizing an unvulcanized rubber composition (a rubber composition for each component, including a rubber composition for the cap rubber and a rubber composition for the base rubber) and a reinforcing material, or by molding and then vulcanizing a semi-vulcanized rubber that has undergone a pre-vulcanization process or the like instead of an unvulcanized rubber composition. The components of the tire of this embodiment other than the cap rubber and base rubber are not particularly limited, and known components can be used. The tire of this embodiment is preferably a pneumatic tire, and the gas to be filled into the pneumatic tire can be normal air or air with an adjusted oxygen partial pressure, or an inert gas such as nitrogen, argon, or helium.

[0127] 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.

[0128] <Method of Analyzing Resin> The weight average molecular weight and softening point of the resin were measured by the following methods.

[0129] (1) Weight-average molecular weight The average molecular weight of the resin was measured by gel permeation chromatography (GPC) under the following conditions, and the weight-average molecular weight in terms of polystyrene was calculated: Column temperature: 40°C Injection volume: 50 μL Carrier and flow rate: tetrahydrofuran 0.6 mL / min Sample preparation: Approximately 2.5 mg of resin was dissolved in 10 mL of tetrahydrofuran.

[0130] (2) Softening Point The softening point of the resin was measured in accordance with JIS-K2207-1996 (ring and ball method).

[0131] <Preparation of Rubber Composition for Capped Rubber> A rubber composition for cap rubber was prepared by blending and kneading each component according to the formulation shown in Table 1. The obtained rubber composition for cap rubber was evaluated for adhesion, storage modulus (E'), and loss tangent (tan δ) by the following methods.

[0132] The rubber composition for the cap rubber contained predetermined amounts of sulfur, a vulcanization accelerator, a foaming agent, etc. in addition to the components shown in Table 1. It was also confirmed that a plurality of voids were formed in the obtained rubber composition after vulcanization.

[0133] (3) Adhesion After preparation, a circular metal piece having a diameter of 10 mm was pressed against a rubber composition that had been left for one day at 10 N for 10 seconds, and the load required for the separation was measured. The value was expressed as an index, with the separation load for Comparative Example 1 being set at 100. A smaller index value indicates a smaller separation load and better adhesion (lower adhesion).

[0134] (4) Storage Modulus (E') and Loss Tangent (tan δ) The obtained rubber composition was vulcanized at 145°C for 33 minutes to obtain a vulcanized rubber test piece. The storage modulus (E') at -20°C and the loss tangent (tan δ) at 40°C of the obtained vulcanized rubber test piece were measured using a viscoelasticity measuring device (manufactured by Rheometrics) under conditions of 1% strain and 52 Hz frequency, and each was expressed as an index, with Comparative Example 1 being set at 100. For the storage modulus (E') at -20°C, a smaller index value indicates better on-ice performance. For the loss tangent (tan δ) at 40°C, a smaller index value indicates better fuel economy performance.

[0135] <Preparation of Rubber Composition for Base Rubber> A rubber composition for the base rubber was prepared by blending and kneading each component according to the formulation shown in Table 2. The fracture properties and loss tangent (tan δ) of the obtained rubber composition for the base rubber were evaluated by the following methods.

[0136] In addition to the components shown in Table 2, the rubber composition for the base rubber contained predetermined amounts of sulfur, vulcanization accelerator, etc.

[0137] (5) Fracture Properties The resulting rubber composition was vulcanized at 145°C for 33 minutes to obtain vulcanized rubber test pieces. Tensile tests were performed on the resulting vulcanized rubber test pieces at room temperature (23°C) and 100°C in accordance with JIS K 6251 to measure elongation at break (EB), tensile strength (TB), and toughness (TF), and the values ​​were expressed as indices, with Comparative Example 2 being set at 100. A higher index value indicates better fracture properties.

[0138] (6) Loss Tangent (tan δ) The obtained rubber composition was vulcanized at 145°C for 33 minutes to obtain a vulcanized rubber test piece. The loss tangent (tan δ) at 40°C of the obtained vulcanized rubber test piece was measured using a viscoelasticity measuring device (manufactured by Rheometrics Co., Ltd.) under conditions of 1% strain and 52 Hz frequency, and expressed as an index with Comparative Example 2 being 100. For the loss tangent (tan δ) at 40°C, a smaller index value indicates better fuel economy performance.

[0139]

[0140]

[0141] *1 NR: Natural rubber, TSR20 *2 BR: Butadiene rubber, manufactured by ENEOS Materials Corporation, trade name "BR54" *3 Carbon black 1: SAF grade carbon black, manufactured by CABOT Corporation, trade name "VULCAN10H" *4 Silica: Manufactured by Tosoh Silica Corporation, trade name "Nipsil AQ" *5 C ５ System resin 1: Manufactured by ENEOS, trade name “T-REZ RA100”, weight average molecular weight (Mw) = 3319 g / mol, softening point = 100°C *6 C ５ System resin 2: Manufactured by Mitsui Chemicals, trade name “Hiretz T500X”, weight average molecular weight (Mw) = 2357 g / mol, softening point = 96°C *7 Hydrogenated C ５ Resin: Synthomer Adhesive Technology LLC, trade name "Impera™ E1780 Hydrocarbon Resin", weight average molecular weight (Mw) = 661 g / mol, softening point = 133 ° C. * 8 Oil: ENEOS Corporation, trade name "Super Oil Y22" * 9 S-SBR: Solution polymerization styrene-butadiene rubber, Asahi Kasei Corporation, trade name "TUFDEN3835" * 10 E-SBR: Emulsion polymerization styrene-butadiene rubber, ENEOS Materials Corporation, trade name "ESBR0122" * 11 Carbon black 2: HAF grade carbon black, Tokai Carbon Co., Ltd., trade name "Seat KHA" * 12 Carbon black 3: SAF grade carbon black, manufactured by Tokai Carbon Co., Ltd., product name "Seat 7HM"

[0142] Table 1 shows that the rubber compositions for the cap rubber of the Examples have low adhesion and are able to maintain sufficient performance on ice. Table 2 shows that the rubber compositions for the base rubber of the Examples have excellent fracture properties and improved durability. Therefore, the results of Tables 1 and 2 show that by combining the rubber compositions for the cap rubber of the Examples with the rubber compositions for the base rubber of the Examples, it is possible to produce tires that maintain performance on ice, have excellent workability during manufacturing, and have improved durability.

[0143] 1: Tire 2: Bead portion 3: Sidewall portion 4: Cap rubber 5: Base rubber 6: Tread portion 7: Carcass 8: Belt 9: Bead core 10: Tread rubber 11: Gap

Claims

1. A tire having a tread rubber including a cap rubber located on the outermost surface of the tread portion and a base rubber located radially inward of the cap rubber, wherein the cap rubber includes a rubber component, a filler, and a resin, the rubber component in the cap rubber includes natural rubber and butadiene rubber, the filler in the cap rubber includes silica, the resin in the cap rubber has a weight average molecular weight of 200 to 3,300 g / mol, the cap rubber has a plurality of voids, the base rubber includes a rubber component and a filler, and may or may not include a softener, the rubber component in the base rubber includes 50 parts by mass or more of natural rubber per 100 parts by mass of the rubber component, the filler in the base rubber includes carbon black, and the content of the softener in the base rubber is 30 parts by mass or less per 100 parts by mass of the rubber component in the base rubber.

2. The tire according to claim 1, wherein the content of the filler in the cap rubber is 60 to 100 parts by mass per 100 parts by mass of the rubber component in the cap rubber.

3. The tire according to claim 1, wherein the filler in the cap rubber contains silica in an amount of 20 mass % or more.

4. The tire according to claim 1, wherein the content of the resin in the cap rubber is 1 to 50 parts by mass per 100 parts by mass of the rubber component in the cap rubber.

5. The tire according to claim 1, wherein the rubber component in the base rubber further contains styrene-butadiene rubber.

6. The tire according to claim 5, wherein the rubber component in the base rubber contains 5 to 50 parts by mass of the styrene-butadiene rubber per 100 parts by mass of the rubber component.

7. The tire according to claim 1, wherein the content of the filler in the base rubber is 40 to 100 parts by mass per 100 parts by mass of the rubber component in the base rubber.

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