JP2009035131A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of enhancing its fatigue resistance, in particular, its durability when a vehicle runs at low internal pressure while maintaining a high level of stability in steering. <P>SOLUTION: In the pneumatic tire, a carcass cord 10 is formed by aramid fiber cords 13 having a double twisting structure constituted by intertwining a plurality of primarily twisted filament bundles 10A mutually by final twisting. Fineness of each filament bundle 10A is smaller than 1,100 dtex. Twist coefficient T of the cord expressed by the expression (1) T = n×ä√(D/ρ)}×10<SP>-3</SP>(wherein, n indicates the number of twisting per 10 cm of cord length (unit: number), D indicates gross fineness of the cord (unit: dtex), and ρ indicates specific gravity of the aramid fiber) is in a scope of 2.6-3.4 when the number of filament bundles 10A is two and in a scope of 1.7-3.4 when the number is three or more. Complex modulus of elasticity E*1 of topping rubber 11 of a carcass 6 is in a scope of 3.7-12.0 Mpa. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a pneumatic tire that is suitable as a tire for a motorcycle and that matches a carcass cord with its topping rubber to improve steering stability and durability.

  Organic fiber cords such as nylon fiber, rayon fiber, and polyester fiber are widely used as carcass cords for pneumatic tires. Among them, rayon fiber cords are particularly excellent in handling because they have excellent tensile elastic properties and thermal dimensional stability. It is often used in motorcycle tires where stability is important. However, in the rayon fiber cord, waste liquid generated in the production process tends to have an adverse effect on the environment, and when the hygroscopic management of the rayon fiber cord is insufficient at the time of tire production, the adhesion between the cord and the rubber There is a problem that it is impossible to expect an improvement in the handling stability for the purpose, for example, the force decreases and the elongation at the time of loading increases.

  Therefore, in Patent Document 1 below, as a carcass cord that can exhibit the steering stability equivalent to or higher than that of the rayon fiber cord while solving the various problems of the rayon fiber cord, for example, the cord structure is 800 dtex / 2. Ultrafine aramid fiber cords of 440 dtex / 2 or 220 dtex / 2 have been proposed.

  The reason why the aramid fiber cord is used extremely finely is that it is important to balance the difficulty of elongation of the carcass cord and the restorability with respect to the steering stability of the tire. For example, a general thick fiber of 1670 dtex / 2 is used. Although the aramid fiber cord has a larger dynamic elastic modulus than the rayon fiber cord of 1840 dtex / 2 and is difficult to extend, the loss tangent is larger than that of the rayon fiber cord. Hysteresis loss at the time of removal and restoration to the original becomes large. Therefore, it is inferior in the recoverability of the code, making it difficult to improve the handling stability. On the other hand, in the proposed ultrafine aramid fiber cord, the balance between the stretchability and restorability of the cord is optimized by adjusting the twist number T to a range of 1.0 to 2.5, for example. Therefore, it is possible to exhibit excellent steering stability exceeding that of the rayon fiber cord.

JP-A-10-297211

  However, an aramid fiber cord having a twist number T in the above range is insufficient in fatigue resistance and has insufficient durability. In particular, motorcycle tires used for racing are used at a low internal pressure in order to improve grip performance. In such a case, the burden on the carcass cord becomes large, and the lack of fatigue resistance is more pronounced. It will be a thing.

  Therefore, the present invention uses an aramid fiber cord in which the fineness of the filament bundle is smaller than 1100 dtex, and regulates the twist coefficient T of the cord and the complex elastic modulus E * 1 of the topping rubber within a predetermined range. Basically, the object is to provide a pneumatic tire capable of improving fatigue resistance while maintaining steering stability at a high level, and particularly improving durability at low internal pressure traveling.

In order to achieve the above object, the invention of claim 1 of the present application is a pneumatic tire having a carcass extending from a tread portion through a sidewall portion to a bead core of a bead portion,
The carcass is composed of one or more carcass plies in which an array of carcass cords arranged at an angle of 75 to 90 ° with respect to the tire circumferential direction is covered with a topping rubber,
The carcass cord is composed of an aramid fiber cord having a double-twisted structure in which a plurality of filament bundles having a lower twist are twisted together by an upper twist, and the fineness of each filament bundle is smaller than 1100 dtex,
The twist coefficient T of the aramid fiber cord represented by the following formula (1) is in the range of 2.6 to 3.4 when the number of filament bundles is 2, and is 1.7 to 3.4 when the number of filament bundles is 3 or more. Range,
In addition, the topping rubber has a complex elastic modulus E * 1 in the range of 3.7 to 12.0 Mpa.
T = n × {√ (D / ρ)} × 10 ⁻³ −−− (1)
(However, n is the number of upper twists per 10 cm of cord length (unit: times), D is the total fineness of the cord (unit: dtex), and ρ is the specific gravity of the aramid fiber.)

  In the invention of claim 2, the aramid fiber cord is characterized in that the total fineness D of the cord is 2400 dtex or less.

  In the invention of claim 3, the aramid fiber cord is characterized in that the fineness of the filament bundle is 220 dtex, 440 dtex, or 800 dtex, and the number of filament bundles is two or three.

  According to a fourth aspect of the present invention, the topping rubber has a loss tangent (tan δ1) in the range of 0.08 to 0.17.

  In this specification, the complex elastic modulus and loss tangent of rubber are values measured using a viscoelastic spectrometer under conditions of a temperature of 70 ° C., a frequency of 10 Hz, an initial tensile strain of 10%, and a dynamic strain amplitude of ± 2%. It is.

  In the present invention, as described above, in a thin aramid fiber cord in which the thickness (fineness) of the filament bundle is smaller than 1100 dtex, the twist coefficient T when the number of filament bundles is two is 2.6 to 3.4. And the twist coefficient T (1.0 to 2.5) of Patent Document 1 are set to be larger. Due to the increase in the twist coefficient T, the fatigue resistance of the cord is increased, and the durability during traveling at a low internal pressure can be improved.

  However, the increase in the twisting factor T, on the contrary, increases the cord extensibility and lowers the tire rigidity, thereby incurring a disadvantage in handling stability. Therefore, in the present invention, by restricting the complex elastic modulus E * 1 of the carcass topping rubber to 3.7 MPa or more, a decrease in tire rigidity due to an increase in the elongation of the cord is suppressed. As a result, as a whole carcass, the balance between extensibility and restoring property is optimized, and it becomes possible to maintain steering stability at a high level. Also, in order to reduce the load and deformation on the carcass cord due to the increase in the complex elastic modulus of the topping rubber, not only the durability during normal internal pressure running but also the low resistance due to the synergistic effect with the increase in fatigue resistance of the cord itself. Durability during internal pressure running can also be greatly improved.

  Further, in the aramid fiber cord, by increasing the number of filament bundles to 3 or more, it is possible to obtain a high twist amount even when the twist coefficient T is the same as in the case of the conventional two-stranded structure. It is possible to increase the flexibility of the cord and improve the fatigue resistance. Therefore, when the number of filament bundles is three or more, the lower limit value of the twist coefficient T can be lowered from 2.6 to 1.7.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing a case where the pneumatic tire of the present invention is a motorcycle tire.

  As shown in FIG. 1, the pneumatic tire 1 of this example is a motorcycle tire and includes a carcass 6 that extends from a tread portion 2 to a sidewall portion 3 to a bead core 5 of a bead portion 4. In the present example, a band layer 7 is provided outside the carcass 6 in the radial direction and inside the tread portion 2. In this example, the tread portion 2 has a tread surface 2S that curves and extends in a convex arc shape from the tire equator C toward the tread end Te, and a tread width TW that is a distance between the tread ends Te and Te is By making the maximum tire width, it is possible to turn at a large bank angle.

  As shown conceptually in FIG. 2 (A), the carcass 6 is one or more sheets in which an array of carcass cords 10 arranged at an angle of 75 to 90 ° with respect to the tire circumferential direction is covered with a topping rubber 11. In this example, it is formed from one carcass ply 6A. The carcass ply 6 </ b> A has ply folding portions 6 b that are folded from the inner side to the outer side in the tire axial direction around the bead core 5 at both ends of the toroidal ply main body portion 6 a straddling the bead cores 5 and 5. Further, a bead apex rubber 8 for bead reinforcement extending in a tapered shape from the bead core 5 to the outer side in the tire radial direction is disposed between the ply main body portion 6a and the ply turn-up portion 6b.

  The radial height h1 of the bead apex rubber 8 from the bead base line BL is smaller than the radial height he of the tread end Te. Preferably, the lower limit is 35% or more of the height he. Is 40% or more, and the upper limit is 70% or less, further 60% or less. In this example, the case where the ply turn-up portion 6b has a high turn-up structure that terminates by being sandwiched between the ply main body portion 6a and the band layer 7 after passing through the sidewall portion 3 is illustrated. However, a structure in which the band layer 7 is terminated radially inward from the outer end of the band layer 7 may be used.

  The band layer 7 is formed by one or more, in this example, one band ply 7A in which a band cord is spirally wound at an angle of 5 ° or less with respect to the tire circumferential direction. As shown in FIG. 3, the band ply 7A includes a tape-like belt-like ply 16 in which a single band cord 14 or an aligned body of a plurality of band cords 14 is embedded in a topping rubber 15, and The angle formed between the band cord 14 and the tire circumferential direction is set to 5 ° or less. Since such a band ply 7A has a so-called jointless structure without seams, the tire ply 7A is excellent in tire uniformity and increases the restraining force on the tread portion 2 to improve the tag effect. In addition, as said band cord, organic fiber cords, such as nylon, polyester, rayon, can be used conveniently, for example.

  In the present invention, as the carcass cord 10, as illustrated in FIG. 2B, an aramid fiber cord 13 having a double twist structure in which a plurality of filament bundles 10 </ b> A twisted together is twisted together with an upper twist. Adopted. At this time, if the filament bundle 10A is too thick, even if the number of twists is increased, the flexibility is insufficient, and it is difficult to sufficiently improve the fatigue resistance. Therefore, in the present invention, a thin filament bundle having a fineness (thickness) smaller than 1100 dtex is used as the filament bundle 10A. The number of filament bundles 10A is not particularly limited, but is preferably 2 or 3 from the viewpoint of cord productivity and production cost. Accordingly, as the aramid fiber cord 13, specifically, cord structures of 220 dtex / 2, 220 dtex / 3, 440 dtex / 2, 440 dtex / 3, 800 dtex / 2, and 800 dtex / 3 are preferably employed.

  In addition, in FIG. 2 (B), the thing of the 2 twist structure which twisted together the two twisted filament bundle 10A by the upper twist is illustrated, and in this example, the number of the lower twist and the number of the upper twist The so-called balance twist type is used.

This aramid fiber cord 13 has sufficient heat resistance and thermal dimensional stability as in the case of rayon, but is inferior in fatigue resistance due to the high elastic modulus of the aramid fiber. Therefore, in order to sufficiently maintain durability at the time of running at low internal pressure while maintaining the steering stability at a high level, the twist coefficient T expressed by the following formula (1) is set to 2 filament bundles 10A. In the range of 2.6 to 3.4, and in the case of 3 or more, the range is 1.7 to 3.4, and the complex elastic modulus E * 1 of the topping rubber 11 is 3.7 to 12.0 MPa. The range is regulated. In formula (1), “n” is the number of upper twists per 10 cm of cord length (unit: times), “D” is the total fineness of the cord (unit: dtex), and ρ is a specific gravity of aramid fiber of about 1.44. It is.
T = n × {√ (D / ρ)} × 10 ⁻³ −−− (1)

  In the case of the aramid fiber cord 13 having a two-strand structure using a thin filament bundle 10A having a fineness smaller than 1100 dtex, increasing the twist coefficient T to 2.6 or more increases the fatigue resistance of the cord, and travels at a low internal pressure. Durability at the time can be improved. However, the increase in the twisting factor T, on the contrary, increases the stretchability of the cord and lowers the tire rigidity, thereby causing a disadvantage in handling stability. However, in the present invention, by limiting the complex elastic modulus E * 1 of the topping rubber 11 of the carcass 6 to 3.7 MPa or more, a decrease in tire rigidity due to an increase in cord extensibility is suppressed. As a result, as a whole carcass, the balance between extensibility and restoring property is optimized, and it becomes possible to maintain steering stability at a high level. By increasing the complex elastic modulus E * 1 of the topping rubber 11, the load on the carcass cord 10 and deformation are reduced. In addition to durability at the time, it is possible to greatly improve the durability when traveling at low internal pressure.

  In the two-strand structure, when the twist coefficient T is less than 2.6, the fatigue resistance of the cord is insufficient, and the durability during running at low internal pressure cannot be obtained sufficiently. If it exceeds .4, the elongation of the cord becomes excessive even though it is an aramid fiber, and the steering rigidity necessary for reducing the tire rigidity cannot be obtained. On the other hand, if the complex elastic modulus E * 1 is less than 3.7 MPa, a decrease in tire rigidity accompanying an increase in the twisting coefficient T cannot be sufficiently suppressed, and steering stability cannot be maintained at a high level. In addition, the load on the carcass cord 10 is increased, which is disadvantageous in improving durability. On the contrary, if the complex elastic modulus E * 1 exceeds 12.0 MPa, the tire rigidity becomes excessive and the ride comfort is impaired, and the heat generation property of the topping rubber is increased, and the productivity in the topping process is remarkably deteriorated. Incurs a disadvantage.

  From such a viewpoint, in the case of a two-strand structure, the lower limit value of the twist coefficient T is more preferably 2.7 or more, and the upper limit value is further preferably 3.2 or less. Further, the lower limit value of the complex elastic modulus E * 1 of the topping rubber 11 is more preferably 4.2 MPa or more, and the upper limit value is more preferably 10.0 MPa or less.

  On the other hand, in the aramid fiber cord 13, by increasing the number of filament bundles 10A to 3 or more, a high twist amount can be obtained even when the twist coefficient T is the same as in the case of the conventional two-stranded structure. As a result, the flexibility of the cord increases and the fatigue resistance can be improved. Therefore, in the case of three or more multi-twist structures, the lower limit value of the twist coefficient T can be lowered from 2.6 to 1.7 described above. That is, the twist coefficient T can be in the range of 1.7 to 3.4. Also in this case, as in the case of the two-strand structure, matching with the topping rubber 11 can sufficiently ensure durability particularly during low internal pressure traveling while maintaining a high level of steering stability. In the case of three or more multi-strand structures, the lower limit value of the twist coefficient T is more preferably 2.2 or more, and the upper limit value is more preferably 3.2 or less.

  Further, in this example, the loss tangent (tan δ1) of the topping rubber 11 is regulated to 0.17 or less in order to compensate for the drawback of resilience from elongation in the aramid fiber cord. Thereby, the restoring property from the elongation of the carcass 6 as a whole can be enhanced, which is advantageous for steering stability. If the loss tangent (tan δ1) is too low, less than 0.08, the tear resistance of the rubber is reduced and the durability tends to be lowered. From such a viewpoint, the lower limit value of the loss tangent (tan δ1) of the topping rubber 11 is more preferably 0.09 or more, and the upper limit value is more preferably 0.15 or less.

  As mentioned above, although especially preferable embodiment of this invention was explained in full detail, this invention is not limited to embodiment of illustration, It can deform | transform and implement in a various aspect.

  A motorcycle tire having a tire size of 190 / 50ZR17 having the structure shown in FIG. 1 was prototyped according to the specifications shown in Table 1, and the test stability, normal internal pressure durability, and low internal pressure durability of each sample tire were tested. The results are shown in Table 1. The specifications are the same except for those listed in Table 1.

  In each tire, the number of carcass plies is one and the carcass cord angle is 90 °. In addition, one band ply in which an aramid fiber cord (1670 dtex / 2) is spirally wound is used as a band layer, and the loss tangent (tan δ2) of the topping rubber is set to 0.09. Further, in the twist coefficient T, the specific gravity of rayon is 1.51, and the specific gravity of aramid is 1.44.

(1) Normal internal pressure durability;
Running on the drum under the conditions of the rim (MT 6.00 × 17), internal pressure (290 kPa), load (4.84 kN)), speed (65 km / h), the running distance until the tire is damaged, Evaluation was made with an index of Comparative Example 1 as 100. A larger index is better.

(2) Low internal pressure durability;
Running on the drum under the conditions of the rim (MT 6.00 × 17), internal pressure (100 kPa), load (4.84 kN)) and speed (65 km / h), the running distance until the tire is damaged, Evaluation was made with an index of Comparative Example 1 as 100. A larger index is better.

(3) Steering stability;
The tire is mounted on the rear wheel of a large motorcycle (1000CC) under the conditions of a rim (MT 6.00 × 17) and internal pressure (290 kPa), and the vehicle runs on a dry asphalt tire test course. Was evaluated by a five-point method in which Comparative Example 1 was set to 3 by sensory evaluation of the driver. A larger index is better.

As shown in Table 1, it can be confirmed that the tires of the examples have improved normal internal pressure durability and low internal pressure durability while maintaining steering stability at a high level.

It is sectional drawing which shows one Example of the pneumatic tire of this invention. (A) is sectional drawing which shows a carcass ply, (B) is a perspective view which expands and shows a carcass cord. It is a perspective view which shows the strip | belt-shaped ply of a band layer.

Explanation of symbols

2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 6A Carcass ply 10 Carcass cord 10A Filament bundle 11 Topping rubber 13 Aramid fiber cord

Claims (4)

A pneumatic tire having a carcass extending from a tread portion through a sidewall portion to a bead core of a bead portion,
The carcass is composed of one or more carcass plies in which an array of carcass cords arranged at an angle of 75 to 90 ° with respect to the tire circumferential direction is covered with a topping rubber,
The carcass cord is composed of an aramid fiber cord having a double-twisted structure in which a plurality of filament bundles having a lower twist are twisted together by an upper twist, and the fineness of each filament bundle is smaller than 1100 dtex,
The twist coefficient T of the aramid fiber cord represented by the following formula (1) is in the range of 2.6 to 3.4 when the number of filament bundles is 2, and is 1.7 to 3.4 when the number of filament bundles is 3 or more. Range,
In addition, the pneumatic tire is characterized in that the complex elastic modulus E * 1 of the topping rubber is in the range of 3.7 to 12.0 MPa.
T = n × {√ (D / ρ)} × 10 ⁻³ −−− (1)
(However, n is the number of upper twists per 10 cm of cord length (unit: times), D is the total fineness of the cord (unit: dtex), and ρ is the specific gravity of the aramid fiber.)   The pneumatic tire according to claim 1, wherein the aramid fiber cord has a total fineness D of 2400 dtex or less.   3. The pneumatic tire according to claim 1, wherein the aramid fiber cord has a fineness of a filament bundle of 220 dtex, 440 dtex, or 800 dtex, and the number of filament bundles is two or three.   The pneumatic tire according to any one of claims 1 to 3, wherein the topping rubber has a loss tangent (tan δ1) in a range of 0.08 to 0.17.

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