tire

Abstract

To provide a tire improved in low heat build-up while maintaining good elongation at break and cut resistance, excellent in dimensional stability of unvulcanized side rubber, and having small electric resistance.SOLUTION: The tire of the embodiment includes a side rubber and a tie rubber. The side rubber contains 18 to 50 parts by mass of carbon black having a CTAB adsorption specific surface area of 20 to 60m2 / g and 3 to 25 parts by mass of silica having a CTAB adsorption specific surface area of 60 to 120m2 / g. The tie rubber contains 5 to 40 parts by mass of the carbon black (A) having a CTAB adsorption specific surface area of 25 to 50m2 / g and 20 to 80 parts by mass of the carbon black (B) having a CTAB adsorption specific surface area of 70 to 130m2 / g, and the total content of the carbon blacks (A) and (B) is 35 parts by mass or more. The product of the CTAB adsorption specific surface area [m2 / g] and the mass fraction of each of the carbon blacks (A) and (B) in the tie rubber is 20 to 40.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a tire having a side rubber in a sidewall portion. [Background technology]

[0002] In pneumatic tires, there is a demand for improving fuel economy during driving in order to reduce environmental impact. To this end, efforts have been made to suppress heat generation in rubber compositions constituting various parts of pneumatic tires. In recent years, in order to further improve fuel economy, for example, studies have been made on suppressing heat generation in side rubber of pneumatic tires.

[0003] Tan δ at 60°C (hereinafter referred to as tan δ(60°C)) measured by dynamic viscoelasticity measurement is generally used as an index of heat buildup of a rubber composition, and the smaller the tan δ(60°C) of a rubber composition, the smaller the heat buildup. One method for reducing the tan δ(60°C) of a rubber composition is to reduce the amount of filler such as carbon black. However, such a method may not necessarily provide the elongation at break and cut resistance required for side rubber. Therefore, there is a need for further measures to improve low heat buildup (low tan δ(60°C)) while maintaining good elongation at break and cut resistance in side rubber.

[0004] On the other hand, depending on the amount and particle size of the filler in the rubber composition, the dimensions of the unvulcanized rubber rolled into a sheet may not be stable after rolling, and in subsequent processes, it may not be possible to accurately bond the rubber composition to other parts of the tire.

[0005] On the other hand, as the amount of carbon black used in tires decreases in line with the trend toward lower heat generation, the problem of increased tire electrical resistance arises. High tire electrical resistance makes it difficult for static electricity accumulated in a vehicle to be discharged to the road surface, which can cause problems such as noise in the car radio (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-237337 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a tire which has improved low heat buildup while maintaining good breaking elongation and cut resistance, excellent dimensional stability of the unvulcanized side rubber, and low electrical resistance. [Means for solving the problem]

[0008] The present disclosure encompasses the following aspects. Aspect [1] A tire, a pair of annular bead cores; a carcass that is bridged between the bead cores to form a toroidal shape; a tie rubber disposed on an inner side of the tire with respect to the carcass and extending along the carcass between the bead cores; a side rubber disposed on an outer side of the tire with respect to the carcass and positioned on a surface of a sidewall portion of the tire, The side rubber has a CTAB adsorption specific surface area of ​​20 to 60 m per 100 parts by mass of a rubber component contained in the side rubber. 2 18 to 50 parts by mass of carbon black having a specific surface area of ​​60 to 120 m / g and 2 and 3 to 25 parts by mass of silica having a molecular weight of 1 / g, The Thai rubber has a CTAB adsorption specific surface area of ​​25 to 50 m per 100 parts by mass of the rubber component contained in the Thai rubber. 2 5 to 40 parts by mass of carbon black (A) having a specific surface area of ​​70 to 130 m / g and 2and 20 to 80 parts by mass of carbon black (B) having a carbon black content of 100 parts by mass of the rubber component, wherein the total content of the carbon black (A) and the carbon black (B) is 35 parts by mass or more per 100 parts by mass of the rubber component, The CTAB adsorption specific surface area [m 2 / g) and the mass fraction of the carbon black (A) and the carbon black (B) in the rubber composition, that is, a specific surface area×mass fraction (TR) of 20 to 40.

[0009] Aspect [2] The side rubber contains, per 100 parts by mass of the rubber component of the side rubber, 30 to 60 parts by mass of an isoprene-based rubber and 40 to 70 parts by mass of a butadiene rubber synthesized using a neodymium-based catalyst or a cobalt-based catalyst and having a vinyl content of 2.0% by mass or less, The tire according to aspect [1], wherein the tie rubber contains 50 to 95 parts by mass of an isoprene-based rubber and 5 to 50 parts by mass of a styrene-butadiene rubber, based on 100 parts by mass of the rubber component of the tie rubber.

[0010] Aspect [3] The tire according to aspect [1] or [2], wherein the maximum thickness of the side rubber at the tire radial position where the thickness of the side rubber is greatest is 5.0 mm or less.

[0011] Aspects [4] The tire according to any one of aspects [1] to [3], wherein the content of the carbon black (B) is greater than the content of the carbon black (A). [Effects of the Invention]

[0012] According to the tire of the above embodiment, the low heat buildup property is improved while maintaining good breaking elongation and cut resistance, and the unvulcanized side rubber has excellent dimensional stability and low electrical resistance. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a diagram showing a meridian cross section of a tire according to an embodiment; DETAILED DESCRIPTION OF THE INVENTION

[0014] The tire of the embodiment will be described in detail below. The tire of the present invention is preferably an internally inflatable tire such as a pneumatic tire, and the tire of this embodiment is a pneumatic tire. The cavity region surrounded by the rim and the internally inflatable tire mounted on the rim can be filled with air, an inert gas such as nitrogen, or other gases.

[0015] Fig. 1 is a diagram showing a meridian cross section of a tire according to this embodiment. The tire according to this embodiment includes a tread portion 1 extending in the tire circumferential direction to form an annular shape, a pair of sidewall portions 2 arranged on both sides of the tread portion 1 in the tire width direction, and a pair of bead portions 3 arranged on the tire radially inward side of the sidewall portions 2. In Fig. 1, CL indicates a tire centerline. The following description using Fig. 1 will basically be based on the meridian cross section shape, but each portion of the tire extends in the tire circumferential direction to form an annular shape.

[0016] Each bead portion 3 has an annular bead core 5, which is formed by winding a steel wire coated with rubber a plurality of times in the circumferential direction of the tire, for example.

[0017] The carcass 4 is fitted over a pair of bead cores 5 to form a toroidal shape, extends between the pair of bead cores 5, and is folded back around each of the bead cores 5 from the inner side to the outer side in the tire width direction. The carcass 4 is made of a plurality of reinforcing cords that are aligned so as to extend in the tire radial direction and are covered with rubber. The reinforcing cords are made of organic fibers such as PET fibers.

[0018] A bead filler 6 is disposed on the outer side of the bead core 5 in the tire radial direction. The bead filler 6 is wrapped by the portion of the carcass 4 folded around the bead core 5.

[0019] In the tread portion 1, a belt 7 made up of multiple layers (two layers in the example shown in FIG. 1) is embedded on the tire radial outer side of the carcass 4. The belt 7 includes multiple reinforcing cords (e.g., steel cords) inclined with respect to the tire circumferential direction, and is arranged so that the inclination directions of the reinforcing cords with respect to the tire circumferential direction intersect with each other between layers. The inclination angle of the reinforcing cords of each belt 7 with respect to the tire circumferential direction is, for example, 10° to 40°.

[0020] A belt cover 8 is provided on the outer side in the tire radial direction of the top layer belt 7. In the example shown in Fig. 1, two layers of belt covers 8 are provided, a lower layer belt cover 8 (inner side in the tire radial direction) that covers the entire area of ​​the top layer belt 7 in the tire width direction, and a pair of upper layer belt covers 8 (outer side in the tire radial direction) that cover both end portions in the tire width direction of the lower layer belt cover 8. The belt cover 8 includes organic fiber cords oriented in the tire circumferential direction. The inclination angle of the organic fiber cords of the belt cover 8 with respect to the tire circumferential direction is, for example, 0° to 5°.

[0021] An inner liner 9 is provided on the surface of the tire facing the hollow region between the tire and rim (inside the tire). The inner liner 9 is a rubber that is arranged on the tire inside of the carcass 4 and extends along the carcass 4 between a pair of bead cores 5. The inner liner 9 is made of a rubber composition mainly containing butyl rubber (IIR). As shown in FIG. 1, the end of the inner liner 9 on the bead core 5 side preferably contacts a rim cushion rubber 30, which will be described later.

[0022] A tie rubber 10 is disposed between the carcass 4 and the inner liner 9. The tie rubber 10 is a rubber sandwiched between the carcass 4 and the inner liner 9 and extending along the carcass 4 between a pair of bead cores 5. When a conductive rubber (described later) is provided in the tread portion 1, the tie rubber 10 preferably extends from the bead core 5 side to a position that passes through at least a straight line passing through the tire radially inner end of the conductive rubber and extending in the tire radial direction. With this type of tie rubber 10, a path for electricity to flow between the rim and the road surface is easily secured even if the electrical resistance of the side rubber 20 is high. The tie rubber 10 is preferably a single piece of rubber that passes through the tire center line CL and whose both ends on the bead core 5 side each contact the rim cushion rubber 30. In the example shown in FIG. 1 , the bead core 5 side ends of the inner liner 9 and the tie rubber 10 are sandwiched between the carcass 4 and the rim cushion rubber 30 on the tire radially inner side of the bead core 5.

[0023] In the tread portion 1, a tread rubber 11 is arranged on the radially outer side of the carcass 4. The tread rubber 11 in the example shown in Fig. 1 has a cap tread rubber 12 having a contact surface that comes into contact with the road surface, and an undertread rubber 13 arranged on the radially inner side of the cap tread rubber 12. The undertread rubber 13 is in contact with the cap tread rubber 12 and the belt cover 8.

[0024] It is preferable that conductive rubber (also called earth tread rubber), not shown, is embedded in the tread rubber 11. The conductive rubber is in contact with the belt 7, or in the example shown in FIG. 1, in contact with the belt cover 8, and penetrates the tread rubber 11 in the tire radial direction to be exposed at the ground contact surface. For example, the conductive rubber extends around the tire circumferential direction on the tire center line CL, and has a length in the tire width direction of, for example, 1 to 20 mm. The conductive rubber is made of a rubber composition containing carbon black, and contains, for example, 40 to 80 parts by mass of carbon black per 100 parts by mass of the rubber component contained in the rubber composition.

[0025] Each sidewall portion 2 is provided with a side rubber 20, which is disposed on the outer side of the tire (outside in the tire width direction) relative to the carcass 4 and is located on the tire outer surface of the sidewall portion 2. The side rubber 20 is required to have excellent breaking elongation (flexural fatigue resistance) because it is the part of the tire that experiences the greatest flexing during running. In addition, it is required to have excellent cut resistance because it tends to be frequently subjected to external damage.

[0026] In the bead portion 3, a rim cushion rubber 30 that comes into contact with the rim is arranged around the carcass 4.

[0027] The side rubber 20 has a CTAB (n-hexadecyltrimethylammonium bromide) adsorption specific surface area of ​​20 to 60 m per 100 parts by mass of the rubber component contained in the side rubber 20. 2 18 to 50 parts by mass of carbon black having a specific surface area of ​​60 to 120 m / g and 2 The rubber composition includes 3 to 25 parts by mass of silica having a specific surface area of ​​1 / g. In this specification, the CTAB adsorption specific surface area of ​​carbon black is a value measured in accordance with JIS K6217-3. Depending on the type of rubber contained in the rubber component of the side rubber (for example, when a butadiene rubber polymerized using a neodymium-based catalyst or a cobalt-based catalyst, as described below, is used), the breaking elongation and cut resistance of the side rubber may be reduced. However, according to this embodiment, the side rubber 20 contains large-particle silica as described above, thereby suppressing these performance degradations. On the other hand, the use of large-particle silica may cause a deterioration in tan δ (60°C). However, since the compounding amounts of large-particle silica and carbon black are set as described above, the tan δ (60°C) can be maintained at a good level. These effects can improve low heat buildup (low tan δ (60°C)) while maintaining good breaking elongation and cut resistance, thereby enabling the side rubber to exhibit good physical properties. Specifically, the rubber component of the side rubber 20 is a diene-based rubber.

[0028] Furthermore, by including silica in the side rubber 20 in the above-described blending amounts and particle sizes in addition to carbon black, the unvulcanized rubber rolled into a sheet is easily stress-relieved, shrinking occurs quickly, and the dimensions after rolling are stable. This reduces the impact on dimensions of the unvulcanized side rubber due to the length of storage time, and allows it to be precisely bonded to unvulcanized rubbers such as the inner liner 9 and tie rubber 10 during the molding process. In other words, the dimensional stability of the unvulcanized side rubber is excellent.

[0029] As the silica, for example, silica usually used in rubber compositions for tires, such as wet process silica, dry process silica, or surface-treated silica, can be used. However, the silica should not have a CTAB adsorption specific surface area (in accordance with JIS K6430:2008) of 60 m 2 / g~120m 2 / g, preferably 70m 2 / g~90m 2 / g, more preferably 75m 2 / g~85m 2 The silica with a CTAB adsorption specific surface area of ​​60m is used. By using silica with a large particle size, it is possible to suppress the decrease in breaking elongation caused by using Nd-BR or Co-BR, which will be described later. 2 If the CTAB adsorption specific surface area of ​​silica is less than 120 m 2 If the silica content exceeds 1 / g, the dimensional stability of the unvulcanized side rubber will deteriorate, and the cut resistance and abrasion resistance will decrease. Any silica that satisfies the above conditions may be appropriately selected from commercially available silicas, and silica obtained by a conventional manufacturing method may also be used.

[0030] The compounding amount Ms of silica is 3 to 25 parts by mass, preferably 3 to 20 parts by mass, and more preferably 5 to 15 parts by mass, per 100 parts by mass of the rubber component of the side rubber 20. By compounding an appropriate amount of silica in this way, it is possible to improve the breaking elongation, low heat buildup, and cut resistance in a well-balanced manner. On the other hand, the compounding amount Ms of silica is preferably 15 to 25 parts by mass, more preferably 20 to 25 parts by mass, per 100 parts by mass of the rubber component of the side rubber 20. By compounding silica in this way, the unvulcanized rubber of the side rubber 20 rolled into a sheet quickly shrinks, improving dimensional stability. If the compounding amount of silica is less than 3 parts by mass, the breaking elongation and cut resistance tend to decrease. If the compounding amount of silica exceeds 25 parts by mass, the low heat buildup property and cut resistance tend to deteriorate. Furthermore, if the compounding amount of silica is less than 3 parts by mass, the dimensional stability of the unvulcanized side rubber deteriorates.

[0031] The carbon black used is one that is commonly used in tire rubber compositions and has a CTAB adsorption specific surface area of ​​20 m 2 / g~60m 2 / g, preferably 30m 2 / g~50m 2 / g, more preferably 35m 2 / g~45m 2 The carbon black used has a specific surface area of ​​35 m / g. The use of such carbon black improves the breaking elongation, low heat buildup, and cut resistance in a well-balanced manner, and is advantageous in improving the dimensional stability of the unvulcanized side rubber. On the other hand, the specific surface area of ​​35 m / g is preferably 35 m / g. 2 / g~60m 2 / g, more preferably 40m 2 / g~60m 2 / g, more preferably 45m 2 / g~60m 2 Carbon black with a CTAB adsorption specific surface area of ​​20 m / g is also preferably used. When an appropriate amount of such carbon black is blended, it contributes to reducing the electrical resistance of the tire. 2If the CTAB adsorption specific surface area of ​​the carbon black is less than 60 m / g, the abrasion resistance will decrease. 2 If the carbon black content exceeds 1 / g, the heat buildup property decreases. Examples of carbon black include GPF and FEF grades.

[0032] The blending amount Mc of carbon black is preferably 20 to 50 parts by mass, more preferably 35 to 50 parts by mass, and even more preferably 45 to 50 parts by mass, per 100 parts by mass of the rubber component of the side rubber 20. By blending such an amount of carbon black, the unvulcanized rubber of the side rubber 20 rolled into a sheet shrinks quickly, improving dimensional stability. In this case, if the CTAB specific surface area of ​​the carbon black is large, the effect of stabilizing the dimensions of the unvulcanized rubber of the side rubber 20 after rolling is further improved. The CTAB specific surface area of ​​such carbon black is preferably 30 m 2 / g~60m 2 / g, more preferably 40m 2 / g~50m 2 / g. When the CTAB specific surface area of ​​carbon black is large and the compounding amount Mc is high, the side rubber 20, together with the tie rubber 10, functions as a parallel path for electricity to flow between the rim and the road surface, contributing to lowering the tire's electrical resistance. If the compounding amount of carbon black is less than 18 parts by mass per 100 parts by mass of the rubber component of the side rubber 20, the dimensional stability of the unvulcanized side rubber 20 deteriorates, and cut resistance deteriorates. If the compounding amount of carbon black exceeds 50 parts by mass per 100 parts by mass of the rubber component of the side rubber 20, low heat buildup deteriorates.

[0033] The total amount of silica and carbon black in the side rubber 20 is 55 parts by mass or less, preferably 25 to 40 parts by mass, and more preferably 20 to 30 parts by mass, per 100 parts by mass of the rubber component. By blending silica and carbon black in appropriate amounts, it is possible to improve the elongation at break, cut resistance, and abrasion resistance in a balanced manner, and improve the dimensional stability of the unvulcanized side rubber. If the total amount of silica and carbon black exceeds 55 parts by mass, heat buildup decreases. The amount of carbon black alone is not particularly limited, but is preferably 15 to 30 parts by mass.

[0034] The ratio Ms / Mc, where Ms is the amount of silica to Mc is 0.8 or less, preferably 0.1 to 0.75, and more preferably 0.25 to 0.7. By incorporating appropriate amounts of silica and carbon black, and particularly by keeping the amount of silica in the filler low, it is possible to suppress the deterioration of tan δ(60°C) caused by incorporating large-particle silica, and to achieve a balanced improvement in elongation at break, low heat buildup, and cut resistance. If the ratio Ms / Mc exceeds 0.8, it is not possible to maintain a good tan δ(60°C), and low heat buildup deteriorates.

[0035] Thai Rubber 10 has a CTAB adsorption specific surface area of ​​25 to 50 m for 100 parts by mass of the rubber component contained in Thai Rubber 10. 2 5 to 40 parts by mass of carbon black (A) having a specific surface area of ​​70 to 130 m / g and 2The rubber composition includes 20 to 80 parts by mass of carbon black (B) having a particle size of 1 / g, and the total content of carbon black (A) and carbon black (B) is 35 parts by mass or more per 100 parts by mass of the rubber component. When tie rubber 10 contains large particle size carbon black (A) and small particle size carbon black (B) in the above-mentioned blending amounts, it is easy to obtain the effect of suppressing heat generation in tie rubber 10 while reducing the electrical resistance of the tire. Examples of carbon black (A) include GPF and FEF grades. Examples of carbon black (B) include HAF and ISAF grades. The total content of carbon black (A) and carbon black (B) is preferably 40 parts by mass or more, and more preferably 65 parts by mass or less, per 100 parts by mass of the rubber component contained in the rubber composition of tie rubber 10. Specifically, the rubber component of tie rubber 10 is a diene rubber.

[0036] CTAB adsorption specific surface area [m 2 / g] and the mass fraction of the carbon black (A) and the carbon black (B) in the rubber composition [parts by mass / parts by mass], that is, specific surface area×mass fraction (TR) is 20 to 40.

[0037] According to the inventors' investigations, the susceptibility to heat generation and the magnitude of electrical resistance in each part of a tire are strongly correlated with the magnitude of the product of the CTAB adsorption specific surface area of ​​the carbon black contained in each part of the tire and the mass fraction of the carbon black in the rubber composition; a larger product leads to a higher likelihood of heat generation, while a smaller product leads to an increase in electrical resistance. According to this finding, even if the amount of carbon black compounded in each part of the tire is small, if the particle size of the carbon black is too small, the value of this product increases, and heat generation cannot be sufficiently suppressed. Conversely, even if the amount of carbon black compounded in each part of the tire is large, if the particle size of the carbon black is too large, the value of this product decreases, and electrical resistance cannot be sufficiently reduced. It is believed that a larger particle size of carbon black results in a wider spacing between particles, resulting in an increase in electrical resistance, compared to a case where the particle size of the carbon black is small and the value of this product is the same. In the tire of this embodiment, the ratio of specific surface area to mass fraction (TR) is 20 to 40, so that the tie rubber 10 functions as a conductive path between the tire and the rim, contributing to reducing the tire's electrical resistance. This, along with the aforementioned effect of the side rubber 20 improving low heat buildup (tan δ at 60°C), also contributes to suppressing heat buildup in the tire. If the ratio of specific surface area to mass fraction (TR) is too small, it is difficult to alleviate stress generated by rolling in the unvulcanized rubber sheet that becomes the tie rubber 10, making it difficult to stabilize the dimensions. Depending on the dimensional stability of the side rubber, shrinkage of both the side rubber and the tie rubber may hinder the production of an unvulcanized tire.

[0038] Therefore, according to this embodiment, a tire can be obtained that has improved low heat buildup, excellent dimensional stability of the unvulcanized side rubber, and low electrical resistance while maintaining good breaking elongation and cut resistance. In particular, in a tire that includes the side rubber 20 containing silica and with a limited amount of carbon black, a conductive path can be ensured and electrical resistance can be effectively reduced.

[0039] The specific surface area x mass fraction (TR) is preferably 25-35.

[0040] The specific surface area x mass fraction of a rubber composition containing two types of carbon black (A) and (B) is calculated using the following formula: {(CTAB adsorption specific surface area of ​​carbon black (A) [m 2 / g) × (carbon black (A) content [parts by mass] + (CTAB adsorption specific surface area of ​​carbon black (B) [m 2 / g) × (carbon black (B) content [parts by mass] / Mass of rubber composition [parts by mass] It is calculated according to

[0041] The content of carbon black (A) is preferably 5 to 35 parts by mass, more preferably 10 to 25 parts by mass, based on 100 parts by mass of the rubber component contained in the tie rubber 10. The content of carbon black (B) is preferably 25 to 70 parts by mass, more preferably 30 to 60 parts by mass, based on 100 parts by mass of the rubber component contained in the tie rubber 10. The content of carbon black (B) is preferably higher than the content of carbon black (A). Such blending amounts of carbon black (A) and carbon black (B) improve the low heat buildup property, improve the dimensional stability of the unvulcanized tie rubber, and contribute to lowering the electrical resistance of the tire.

[0042] The side rubber 20 preferably contains 30 to 60 parts by mass of isoprene-based rubber and 40 to 70 parts by mass of butadiene rubber per 100 parts by mass of the rubber component of the side rubber 20. Using an isoprene-based rubber and a butadiene rubber in the side rubber 20 in this way is advantageous for improving low heat buildup while maintaining good elongation at break and cut resistance.

[0043] Examples of isoprene-based rubbers include various natural rubbers, epoxidized natural rubbers, and various synthetic polyisoprene rubbers. Among these isoprene-based rubbers, natural rubber is particularly suitable. The amount of isoprene-based rubber blended is 30% to 60% by mass, preferably 35% to 60% by mass, and more preferably 40% to 55% by mass, based on 100% by mass of diene-based rubber. Blending such an amount of isoprene-based rubber can improve elongation at break, low heat buildup, and abrasion resistance in a well-balanced manner. If the amount of isoprene-based rubber blended is less than 30% by mass, elongation at break decreases. If the amount of isoprene-based rubber blended exceeds 60% by mass, cut resistance deteriorates.

[0044] Examples of butadiene rubber include butadiene rubber (Nd-BR or Co-BR) polymerized using a neodymium-based catalyst or a cobalt-based catalyst. Nd-BR is a known material and is butadiene rubber polymerized using a neodymium-based catalyst (a catalyst containing neodymium), such as neodymium alone, compounds of neodymium with other metals, or organic neodymium compounds. Co-BR is a known material and is butadiene rubber polymerized using a cobalt-based catalyst (a catalyst containing cobalt), such as cobalt alone, compounds of cobalt with other metals, or organic cobalt compounds. Butadiene rubber synthesized using these neodymium-based or cobalt-based catalysts has the characteristics of a high molecular weight and a narrow molecular weight distribution. Commercially available Nd-BRs are available, such as Buna CB22 and Buna CB24 manufactured by Arlanxeo. Commercially available Co-BRs are available, such as UBEPOL BR360L manufactured by UBE Elastomers.

[0045] The butadiene rubber contained in the side rubber 20 preferably has a vinyl content of 0.5% to 2.0% by mass, more preferably 0.8% to 1.7% by mass, and even more preferably 0.9% to 1.5% by mass. Such a low vinyl content is advantageous for improving heat buildup. If the vinyl content in the butadiene rubber is less than 0.5% by mass, processability may be reduced. If the vinyl content in the butadiene rubber exceeds 2.0% by mass, heat buildup decreases. The vinyl content is measured by infrared spectroscopy (Hampton method). The vinyl content in the butadiene rubber can be appropriately adjusted (increased or decreased) by conventional methods, such as by changing the specific type of catalyst or the solvent used in polymerization. Thus, when the butadiene rubber is polymerized using a neodymium-based catalyst or a cobalt-based catalyst and the vinyl content is 0.5% to 2.0% by mass, low heat buildup can be improved. The butadiene rubber polymerized using a neodymium-based catalyst or a cobalt-based catalyst mainly contains cis-1,4-bonds and also contains trans-1,4-bonds and vinyl bonds, and the total content of these three bonds is 100% by mass.

[0046] The amount of butadiene rubber blended is 40% to 70% by mass, preferably 45% to 65% by mass, and more preferably 50% to 60% by mass, based on 100% by mass of diene rubber. Blending an appropriate amount of butadiene rubber in this manner is advantageous for achieving a balanced improvement in elongation at break, low heat buildup, and abrasion resistance. If the amount of butadiene rubber blended is less than 35% by mass, cut resistance deteriorates. If the amount of butadiene rubber blended is more than 65% by mass, elongation at break decreases.

[0047] The rubber composition of the side rubber 20 may contain other diene rubbers in addition to isoprene rubber and butadiene rubber. The other diene rubbers may be rubbers that are generally used in tire rubber compositions. For example, styrene-butadiene rubber may be used. These other diene rubbers may be used alone or in any blend.

[0048] The rubber composition of the tie rubber 10 preferably contains 50 to 95 parts by mass of isoprene-based rubber and 5 to 50 parts by mass of styrene-butadiene rubber per 100 parts by mass of the rubber component. When the amount of isoprene-based rubber is 50 parts by mass or more per 100 parts by mass of the rubber component, the breaking elongation of the tie rubber 10 is likely to be improved, and the durability of the tire is likely to be improved. Furthermore, when the amount of isoprene-based rubber is 95 parts by mass or less per 100 parts by mass of the rubber component, the occurrence of defects such as holes in the rolled unvulcanized rubber sheet of the tie rubber 10 is likely to be suppressed. It is more preferable that the tie rubber 10 contains 60 to 95 parts by mass of isoprene-based rubber per 100 parts by mass of the rubber component.

[0049] Examples of isoprene-based rubbers include various natural rubbers, epoxidized natural rubbers, and various synthetic polyisoprene rubbers. Among these isoprene-based rubbers, natural rubber is particularly suitable. The amount of isoprene-based rubber blended is 50% to 95% by mass, preferably 60% to 90% by mass, and more preferably 70% to 85% by mass, based on 100% by mass of diene-based rubber.

[0050] The blending amount of the styrene butadiene rubber is 5% by mass to 50% by mass, preferably 10% by mass to 40% by mass, and more preferably 15% by mass to 30% by mass, based on 100% by mass of the diene rubber.

[0051] The rubber composition of the tie rubber 10 may contain other diene rubbers in addition to the isoprene rubber and styrene-butadiene rubber. The other diene rubbers may be rubbers that are generally used in tire rubber compositions. Examples include butadiene rubber. These other diene rubbers may be used alone or in any blend.

[0052] The rubber composition of the side rubber 20 may contain fillers other than silica and carbon black. The rubber composition of the tie rubber 10 may contain fillers other than carbon black. Examples of other fillers include materials commonly used in rubber compositions for tires, such as clay, talc, calcium carbonate, mica, and aluminum hydroxide.

[0053] When compounding the silica into the rubber composition of the side rubber 20, a sulfur-containing silane coupling agent is compounded. Compounding the sulfur-containing silane coupling agent can improve the dispersibility of silica in diene rubber. Examples of sulfur-containing silane coupling agents include bis-(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)disulfide, 3-trimethoxysilylpropylbenzothiazoletetrasulfide, γ-mercaptopropyltriethoxysilane, and 3-octanoylthiopropyltriethoxysilane. Among these, those having a tetrasulfide bond in the molecule are particularly suitable. The compounding amount of the silane coupling agent is preferably less than 10% by mass, more preferably 3% to 9% by mass, relative to the compounding amount of silica. If the compounding amount of the silane coupling agent is 10% by mass or more of the compounding amount of silica, the silane coupling agents condense with each other, making it impossible to obtain the desired hardness and strength of the rubber composition.

[0054] It is preferable that sulfur and a vulcanization accelerator are further compounded into the rubber composition of the side rubber 20. When sulfur and a vulcanization accelerator are compounded, the total compounding amount is preferably 2.5 parts by mass or more, more preferably 2.5 to 3.0 parts by mass, per 100 parts by mass of the rubber component. By compounding sufficient amounts of sulfur and vulcanization accelerator in this way, low heat buildup can be improved. If the total compounding amount of sulfur and vulcanization accelerator is less than 2.5 parts by mass, heat buildup decreases. Note that the individual compounding amounts of sulfur and vulcanization accelerator are not particularly limited, but the sulfur is preferably 1.0 to 2.0 parts by mass, more preferably 1.5 to 2.0 parts by mass, and the vulcanization accelerator is preferably 0.5 to 1.5 parts by mass, more preferably 0.5 to 1.0 part by mass.

[0055] It is preferable to further compound sulfur and a vulcanization accelerator into the rubber composition of the tie rubber 10. The amount of sulfur is preferably 2.0 to 3.0 parts by mass, more preferably 2.5 to 3.0 parts by mass, and the amount of vulcanization accelerator is preferably 0.5 to 1.5 parts by mass, more preferably 0.5 to 1.0 part by mass.

[0056] The vulcanization accelerator may be one generally used in rubber compositions for tires, such as a sulfenamide vulcanization accelerator, a guanidine vulcanization accelerator, or a thiuram vulcanization accelerator. Examples of sulfenamide vulcanization accelerators include N,N-dicyclohexyl-1,3-benzothiazole-2-sulfenamide (DZ), N-cyclohexyl-2-benzothiazole sulfenamide (CZ), N-oxydiethylene-2-benzothiazole sulfenamide (OBS), and N-(tert-butyl)benzothiazole-2-sulfenamide (NS). Examples of guanidine vulcanization accelerators include diphenylguanidine and di-orthotolylguanidine. Examples of thiuram vulcanization accelerators include tetramethylthiuram monosulfide and tetramethylthiuram disulfide.

[0057] Other compounding agents than those mentioned above can be added to the rubber compositions of the side rubber 20 and the tie rubber 10. Examples of other compounding agents include various compounding agents commonly used in rubber compositions for tires, such as vulcanizing or crosslinking agents other than sulfur, antioxidants, and liquid polymers. The compounding amounts of these compounding agents can be conventional amounts as long as they do not deviate from the objectives of the present invention. Furthermore, as the kneading machine, a conventional rubber kneading machine, such as a Banbury mixer, kneader, or roll, can be used. On the other hand, it is preferable that the rubber composition of the tie rubber 10 does not contain a surfactant such as a nonionic surfactant. If a surfactant is contained, the viscosity of the unvulcanized rubber composition decreases, which makes mixing time longer. Furthermore, the decrease in viscosity may cause the rubber composition to adhere to the mixing equipment.

[0058] The rubber compositions of the side rubber 20 and the tie rubber 10 can be kneaded using a conventional method. However, to more effectively reduce heat buildup, it is preferable to knead the isoprene-based rubber, neodymium-catalyzed butadiene rubber, carbon black, and silica in a step prior to mixing the vulcanization compounding ingredients (sulfur, vulcanization accelerator, etc.). In particular, this step may involve first kneading the entire isoprene-based rubber with carbon black and silica in a first kneading step, and then adding and kneading the neodymium-catalyzed butadiene rubber to the mixture obtained in the first kneading step in a second kneading step. By kneading in this order, including the first and second kneading steps, the neodymium-catalyzed butadiene rubber is added and kneaded after the isoprene-based rubber, carbon black, and silica. This allows for control so that the carbon black is preferentially incorporated into the isoprene-based rubber, which was added first. This allows for improved cut resistance while achieving low heat buildup.

[0059] The maximum thickness of the side rubber 20 at the radial position of the tire where the thickness of the side rubber 20 is greatest is preferably 5.0 mm or less. This contributes to reducing the tire weight and is advantageous for improving low heat generation.

[0060] The thickness of the tie rubber 10 is preferably thinner than that of the side rubber 20, and is preferably 0.1 to 2 mm. Such a thickness of the tie rubber 10 contributes to suppressing heat generation in the tie rubber 10 while ensuring a conductive path between the rim and the tire, and does not hinder the side rubber 20 from exhibiting good physical properties. Furthermore, such a thickness of the tie rubber 10 has less impact on heat generation throughout the tire than the side rubber 20.

[0061] (Examples, Comparative Examples, and Reference Examples) In order to confirm the effects of the tire of this embodiment, the specifications of the rubber compositions of the side rubber and tie rubber were changed in various ways, and rubber compositions and vulcanized test tires were produced (reference example, comparative example, example), and the breaking elongation, tan δ (60°C), dimensional stability, ease of lamination with the tie rubber, cut resistance, and electrical resistance of the tire of the side rubber were evaluated.

[0062] In preparing the rubber compositions, the compounding ingredients except for the vulcanization accelerator and sulfur were weighed and mixed in a 1.8 L internal Banbury mixer for 5 minutes, and the master batch was discharged and cooled at room temperature. Then, this master batch was fed to a 1.8 L internal Banbury mixer, and the vulcanization accelerator and sulfur were added and mixed for 2 minutes to obtain each rubber composition.

[0063] Of the rubber compositions of the side rubbers shown in Tables 3 to 5, the blends of raw materials excluding the rubber component and filler are all as shown in the following Table 1. The values ​​in the table represent parts by mass relative to 100 parts by mass of the rubber component.

[0064] [Table 1]

[0065] The raw materials of the side rubbers shown in Tables 1 and 3 to 5 are as follows. NR: Natural rubber, NUSIRA BR1: butadiene rubber synthesized using a neodymium catalyst, Buna CB22 manufactured by ARLANXEO (cis-1,4-bond content: 98 mol% (vinyl content: 0.5% to less than 2% by mass), glass transition temperature Tg = -106°C, weight average molecular weight Mw = 7.5 × 10 5 ) BR2: butadiene rubber synthesized using a cobalt catalyst, UBEPOL BR360L manufactured by UBE Elastomers (cis-1,4-bond content: 98 mol% (vinyl content: 1 mass%), glass transition temperature Tg = -106°C, weight average molecular weight Mw = 4.8 × 10 5 ) CB1: Carbon black, Nitelon #55S (CTAB adsorption specific surface area: 32 m) manufactured by Nippon Steel Carbon Co., Ltd. 2 / g) CB2: Carbon black, manufactured by Cabot Japan, STERLING SO(CTAB) Adsorption specific surface area: 45 m 2 / g) CB3: Carbon black, manufactured by Cabot Japan Co., Ltd. VULCAN M (CTAB adsorption specific surface area: 90 m 2 / g) Silica 1: Zeosil 1085GR (CTAB adsorption specific surface area: 80 m 2 / g, BET specific surface area: 90m 2 / g) ·Silica 2: ULTRASIL VN3GR manufactured by Evonik (CTAB adsorption specific surface area: 160m 2 / g, nitrogen adsorption specific surface area N2SA: 220m 2 / g) Silane coupling agent: Shin-Etsu Chemical KBE-846 Zinc oxide: Zinc oxide manufactured by ZM Silesia Stearic acid: Kao Corporation Lunac S-25 Sulfur: Bigensha MIDAS-105 Vulcanization accelerator: Bayer Vulkacit NZ / EG

[0066] Of the rubber compositions of Thai Rubber shown in Tables 3 to 5, the blending of raw materials excluding the rubber component and filler is as shown in the following Table 2. The values ​​in the table represent parts by mass relative to 100 parts by mass of the rubber component.

[0067] [Table 2]

[0068] The raw materials for Thai rubber shown in Tables 2 to 5 are as follows: NR: Natural rubber, TSR20 SBR: Styrene butadiene rubber, SBR1502 manufactured by Nippon Zeon Co., Ltd. CB1: Carbon black, OCI Company Ltd. DASHBLACK N660 (CTAB adsorption specific surface area: 32 m 2 / g) CB4: Carbon black, Nitelon #300 (CTAB adsorption specific surface area: 115 m) manufactured by Nippon Steel Carbon Co., Ltd. 2 / g) Oil: Idemitsu Kosan Diana Process NH-70S Anti-aging agent: Nocrac 6C manufactured by Ouchi Shinko Chemical Co., Ltd. Stearic acid: Stearic acid 50S manufactured by Nisshin Rika Co., Ltd. Zinc oxide: Three types of zinc oxide manufactured by Seido Chemical Industry Co., Ltd. Sulfur: Myucron OT-20 manufactured by Shikoku Chemicals Corporation Vulcanization accelerator: Sancerer NS-G manufactured by Sanshin Chemical Industry Co., Ltd.

[0069] The numerical values ​​for the raw materials in Tables 1 to 5 represent parts by mass relative to 100 parts by mass of the rubber component. Tables 3 to 5 show only the rubber components and fillers among the raw materials of the rubber compositions of the side rubber and tie rubber. The specific surface area x mass fraction of the rubber composition of the tie rubber was calculated according to the above formula. As a result, the specific surface area x mass fraction of the reference example was 20 (m 2 / g)·(mass part / mass part), and the specific surface area × mass fraction of both the comparative examples and examples is 20 to 40 (m 2 / g)·(parts by mass / parts by mass).

[0070] For each test tire, the maximum thickness of the side rubber was 4 mm, and the thickness of the tie rubber was 0.5 mm. The rubber composition of each part of the tire, excluding the side rubber and tie rubber, was a composition typically used for fuel-efficient tires. In the tread, conductive rubber was provided along the tire center line CL.

[0071] The breaking elongation of the side rubber, cut resistance, ease of lamination with the tie rubber, tan δ (60°C) of the side rubber and tie rubber, dimensional stability, and electrical resistance of the tire were evaluated as follows.

[0072] (Elongation at break) The rubber composition of each side rubber was vulcanized in a mold of a predetermined shape at 170°C for 10 minutes to prepare vulcanized rubber test pieces. These vulcanized rubber test pieces were used to cut out JIS No. 3 dumbbell-shaped test pieces in accordance with JIS K6251, and tensile tests were conducted at room temperature (20°C) at a pulling rate of 500 mm / min. The tensile elongation at break (%) at break was measured and shown in the "Elongation at break" column in Tables 3 to 5. A larger value indicates a larger tensile elongation at break.

[0073] (tanδ(60℃)) The rubber compositions for each side rubber and tie rubber were vulcanized in a mold of a predetermined shape at 170°C for 10 minutes to prepare vulcanized rubber test specimens. These vulcanized rubber test specimens were measured for tan δ at 60°C using a viscoelasticity spectrometer manufactured by Toyo Seiki Seisakusho, Ltd., under the following conditions: initial strain 10%, amplitude ±2%, frequency 20 Hz, and temperature 60°C. The measured values ​​are shown in the "tan δ (60°C)" column in Tables 3 to 5. The smaller this value, the better the low heat buildup property.

[0074] (Cut resistance) Test tires (tire size: 245 / 45R19) were produced with side rubbers made from each rubber composition and having the basic structure shown in Figure 1. Each test tire was mounted on a 19-inch rim wheel, inflated to 270 kPa, and mounted on a test vehicle. The tire was driven over a 110 mm high curb at a 30° angle at a speed of 10 km / h, and the extent of damage (pinch cut) (length and depth of damage) to the sidewall (side rubber) when the tire went over the curb was evaluated. The evaluation results were expressed as an index using the reciprocal of the measured value, with the reference example value being 100. A higher index value indicates smaller length and depth of damage and better cut resistance.

[0075] (Dimensional stability) The unvulcanized rubber composition of each side rubber and tie rubber was rolled into a sheet and wound up on a roll. Immediately after rolling, the sheet was pulled out from the roll, cut into a 70 cm long section in the longitudinal direction (the direction it was pulled out), placed on a table, and a 50 cm long mark was made in the longitudinal direction to start measuring time. Every 10 minutes, the ratio of the shrinkage of the marking to the 50 cm length at the start of measurement was calculated as the shrinkage rate, and the time until the rate of change in the shrinkage rate fell within 5% was measured. The evaluation results were expressed as an index, with the reference example value being 100. A smaller index value indicates better dimensional stability.

[0076] (Ease of lamination) A laminate was prepared by sandwiching an unvulcanized carcass between a rolled sheet of the unvulcanized rubber composition of each side rubber and a laminated sheet of the unvulcanized rubber composition sheets of the inner liner and tie rubber, which were stacked on top of each other. After one hour, if wrinkles occurred in the sheets of the other rubber compositions due to shrinkage of the side rubber, the laminate was evaluated as "unacceptable," and if no wrinkles occurred, the laminate was evaluated as "good."

[0077] (electrical resistance) In an environment with a temperature of 23°C and humidity of 50%, a test tire was mounted on a 19x8J rim wheel, and a voltage of 1000V was applied to the wheel under conditions of an air pressure of 200kPa and a load of 5.26kN. Five minutes later, the electrical resistance value [Ω] between the tread surface and the rim was measured. Measurements were taken at three points around the circumference of the tire, and the average value was calculated. The value 10 to the power of n (n is a natural number) is shown in the table as the electrical resistance value [Ω] as "10^n." The smaller the n, the lower the tire's electrical resistance, and the better its discharge and static electricity suppression performance.

[0078] As a result of the above, the electrical resistance value in the table is 10 11 Those with a breaking elongation lower than Ω, a breaking elongation greater than 480%, a tan δ (60°C) of less than 0.13 for the side rubber and less than 0.18 for the tie rubber, a dimensional stability index value of less than 100, ease of lamination with the tie rubber being "good", and a cut resistance index value of 100 or more were evaluated as having improved low heat buildup while maintaining good breaking elongation and cut resistance, excellent dimensional stability of the unvulcanized side rubber, and low electrical resistance.

[0079] [Table 3]

[0080] [Table 4]

[0081] [Table 5]

[0082] Comparison of the Examples with the Reference Example and Comparative Example reveals that the tires of the above-described embodiments have improved low heat buildup while maintaining good breaking elongation and cut resistance, and have excellent dimensional stability of the unvulcanized side rubber and low electrical resistance. The breaking elongation of the tie rubber compositions of Examples 14 and 1 was measured in the same manner as for the rubber compositions of the side rubbers. The breaking elongation of the tie rubber of Example 14 was smaller than that of Example 1.

[0083] Although the tire of the present invention has been described in detail above, the tire of the present invention is not limited to the above-described embodiments or examples, and it goes without saying that various improvements and modifications may be made within the scope of the gist of the present invention. [Explanation of symbols]

[0084] 1 Tread section 2 Sidewall 3 Bead section 4. Carcass 5 bead core 6 Bead filler 7 Belt 8 Belt cover 9 Inner liner 10 Thai Rubber 11 Tread rubber 12 Cap tread rubber 13 Undertread rubber 20 Side rubber 30 Rim cushion rubber

Claims

1. A tire, a pair of annular bead cores; a carcass that is bridged between the bead cores to form a toroidal shape; a tie rubber disposed on an inner side of the tire with respect to the carcass and extending along the carcass between the bead cores; a side rubber disposed on an outer side of the tire with respect to the carcass and positioned on a surface of a sidewall portion of the tire, The side rubber has a CTAB adsorption specific surface area of ​​20 to 60 m per 100 parts by mass of a rubber component contained in the side rubber. 2 18 to 50 parts by mass of carbon black having a CTAB adsorption specific surface area of ​​60 to 120 m 2 and 3 to 25 parts by mass of silica having a viscosity of 1000 MPa or less, The Thai rubber has a CTAB adsorption specific surface area of ​​25 to 50 m per 100 parts by mass of a rubber component contained in the Thai rubber. 2 5 to 40 parts by mass of carbon black (A) having a CTAB adsorption specific surface area of ​​70 to 130 m 2 and 20 to 80 parts by mass of carbon black (B) having a viscosity of 1000 MPa or less, wherein the total content of the carbon black (A) and the carbon black (B) is 35 parts by mass or more per 100 parts by mass of the rubber component, The CTAB adsorption specific surface area [m 2 / g] and the mass fraction of the carbon black (A) and the carbon black (B) in the rubber composition, that is, a specific surface area × mass fraction (TR) is 20 to 40.

2. The side rubber contains, per 100 parts by mass of the rubber component of the side rubber, 30 to 60 parts by mass of an isoprene-based rubber and 40 to 70 parts by mass of a butadiene rubber synthesized using a neodymium-based catalyst or a cobalt-based catalyst and having a vinyl content of 2.0% by mass or less, The tire according to claim 1, wherein the tie rubber contains 50 to 95 parts by mass of an isoprene-based rubber and 5 to 50 parts by mass of a styrene-butadiene rubber, based on 100 parts by mass of the rubber component of the tie rubber.

3. The tire according to claim 1 or 2, wherein a maximum thickness of the side rubber at a position in the tire radial direction where the thickness of the side rubber is greatest is 5.0 mm or less.

4. The tire according to claim 1 or 2, wherein the content of the carbon black (B) is greater than the content of the carbon black (A).

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