JP4450633B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire. More specifically, the present invention relates to a pneumatic tire that has excellent durability and can travel safely even when the internal pressure is reduced.

  Cellulosic fibers (eg, Rayon) have been used as tire reinforcing cords because they are highly elastic at room temperature and have high adhesive strength. Rayon has a high Young's modulus compared to polyester (PET) at room temperature and high temperature, and a thermal shrinkage rate of 0.65% at a temperature of 173 ° C., and has high thermal dimensional stability. ing. For this reason, it has been tried to be used as a rubber reinforcing material such as a tire cord and applied to a carcass ply of a side reinforcing type run-flat tire.

When the internal pressure of the tire decreases, for example, during running during run flat (hereinafter referred to as “RF”), the internal heat generation of the tire increases. In order to improve durability at the time of RF etc., the technique of thickening the gauge of a reinforced rubber or reinforcing a shoulder part, a side part, etc. with a reinforcing member is adopted (for example, refer to patent documents 1-3). ).
Japanese translation of PCT publication No. 2002-500589 Special table 2002-500587 gazette Japanese Patent No. 3214666

  According to the study of the present inventor, with the elastic modulus of the conventional rayon, the deflection of the tire at the time of RF is large, and the rigidity of the carcass ply decreases at high temperatures [for example, 2 kgf (about 19.6 N, hereinafter, 1 kgf≈9. (Converted by 80665 N.) /% Cord elastic modulus [at a temperature of 180 ° C. and stress applied with a force of 3 kgf (about 29.4 N) per reinforcing cord] [Hereinafter, the unit of the cord elastic modulus is “N /% (180 ° C., 29.4 N) ”. ]] Further increased the deflection, and as a failure mode at the end of the RF traveling, it was found that the number of cracks in the crescent-shaped reinforcing rubber increased, and the RF durability distance was shortened.

  Further, if the rubber gauge is made thicker or the side portions and shoulder portions are reinforced, the tire weight increases and the tire vertical spring is filled when the internal air pressure is filled, that is, when the internal pressure is filled (hereinafter referred to as “INF”). The ride comfort at the time of INF is impaired.

  The subject of this invention is improving RF endurance performance, without impairing the riding comfort at the time of INF.

  The present invention relates to a pair of left and right bead portions, a carcass composed of one or more carcass plies in which a plurality of parallel reinforcing cords are embedded in a covering rubber, and a tread portion disposed on the outer side in the tire radial direction of the carcass And a left and right sidewall portion of the tread portion, and a crescent-shaped rubber reinforcing layer disposed inside the carcass and viewed in a cross-section in the tire width direction, the carcass ply reinforcement The cord is made of cellulosic fiber and has a cord elastic modulus of 50 cN / dtex or more [at a temperature of 180 ° C. and a stress applied with a force of 3 kgf (about 29.4 N) per reinforcing cord] [hereinafter this cord It relates to a pneumatic tire characterized by having a rigidity represented by “cN / dtex (180 ° C., 29.4 N)”.

  In the present invention, it is considered that the RF durability performance of the pneumatic tire can be remarkably improved by causing the reinforcing cord of the carcass ply to exhibit a predetermined rigidity at a high temperature.

  According to the pneumatic tire of the present invention, tire deflection at the time of RF is suppressed, and RF durability can be improved without changing the weight without impairing the riding comfort at the time of INF.

(1) Pneumatic tire A pair of right and left bead portions, a carcass, a tread portion disposed on the outer side in the tire radial direction of the carcass, and left and right sidewall portions of the tread portion are provided.

  The carcass can be composed of one or more carcass plies, and the carcass ply can be manufactured by embedding a plurality of parallel reinforcing cords in a covering rubber.

  A crescent-shaped rubber reinforcing layer can be disposed inside the carcass as viewed in the cross section in the tire width direction. Such tires are typically RF tires.

(2) Reinforcement cord It has a rigidity represented by a cord elastic modulus of 50 cN / dtex (180 ° C, 29.4 N) or more. When the elastic modulus at such a high temperature is less than 50 cN / dtex (180 ° C. · 29.4 N), the deflection of the tire during RF running increases, and the RF durability performance may deteriorate.

Such rigidity can be obtained using a stress-elongation curve of the reinforcing cord. FIG. 1 is a graph showing a stress (load) -elongation curve of an example reinforcing cord. As shown in FIG. 1, the force applied to each cord during filling and loading of the tire is estimated to be 3 kgf (about 29.4 N), and the stress (load) -elongation curve C at about 29. The tangent line S at the time of 4N stress is drawn, and the inclination of the tangent line S is calculated as the cord elastic modulus. The cord elastic modulus indicated by the unit “N /% (180 ° C. · 29.4 N)” and the unit “N / dtex (180 ° C. · 29.4 N)” is obtained by using the stress-elongation curve of the same reinforcing cord. For example, in the code structure of 1840 dtex / 3, about 27.6 N (2.8 kgf ) /% (180 ° C. · 29.4 N) corresponds to 50 cN / dtex (180 ° C. · 29.4 N). .

  The reinforcing cord can be produced by dipping (hereinafter referred to as “DIP”) the cord of the raw fiber. By using DIP tension for the fiber cord, that is, by performing DIP treatment in a state where a predetermined tension is applied, the fiber cord can be a reinforcing cord having a predetermined rigidity in the fiber stretching direction.

  For example, the fiber cord is applied with DIP tension, for example, is increased to a DIP tension of 0.71 cN / dtex or more, and is subjected to DIP treatment to be about 39.2 N (4 kgf) /% (180 ° C., 29.4 N). A reinforcing cord having the above cord elastic modulus can be obtained. There is no conventional rayon yarn or the like that has been DIP processed to such a DIP tension.

  By using such a high-strength reinforcing cord with high tensile and tensile rigidity for the carcass ply, the spring during normal internal pressure does not substantially change, the vertical spring during RF is raised specifically, and the amount of deflection during RF Can be suppressed. That is, the RF durability distance can be improved without impairing the ride comfort during INF.

(4) Fiber cord Cellulosic fiber can be used as a raw material. Such fiber cords can be used as reinforcement cords or for reinforcement cords. Cellulosic fibers include fibers such as rayon and lyocell.

  The lyocell fiber is, for example, a cellulosic fiber obtained from a raw material cellulose by a solvent spinning method, and is described in, for example, Japanese Patent Publication No. 60-28848 and Japanese Patent Publication No. 11-504959. In addition, a solution containing cellulose and a non-solvent such as water dissolved in an organic solvent is spun into air or a non-precipitating medium, and at this time, a speed higher than the speed at which the fiber-forming solution discharged from the spinneret is sent out. It can obtain by extending | stretching by (3) and extending | stretching by the draw ratio of 3 times or more, and processing with a nonsolvent.

The fiber cord can have a twist coefficient of 0.35 or more. If the twist coefficient is less than 0.35, the cord fatigue may be remarkably lowered.
The twist factor is

で示される。

Indicated by

  Preferably, the fiber cord is made of an organic fiber having a melting point of 300 ° C. or higher. The reason for this is to prevent the ply cord from melting because the temperature in the tire during RF running becomes very high.

The present invention will be described in detail with reference to the drawings.
FIG. 2 is a partial cross-sectional view of an example pneumatic tire of the present invention.
As shown in FIG. 2, the pneumatic tire 1 includes at least one pair of left and right bead portions 2 (one side is shown in FIG. 2) and a plurality of parallel reinforcing cords embedded in a covering rubber. The carcass 3 composed of the carcass ply, the tread portion 4 disposed on the outer side in the tire radial direction of the carcass 3, the left and right sidewall portions 5 (one side in FIG. 2), and the inside of the carcass 3 And a crescent-shaped rubber reinforcing layer 6 as viewed in the cross section in the tire width direction.

  The carcass ply reinforcing cord constituting the carcass 3 is made of cellulosic fibers such as rayon and lyocell, and has a rigidity represented by a cord elastic modulus of 50 cN / dtex (180 ° C., 29.4 N) or more.

  The bead portion 2 includes a ring-shaped bead core 2A, and bead filler rubber 2B and a carcass 3 can be disposed on the outer side in the tire radial direction. A belt 7 can be disposed outside the carcass 3 in the tire radial direction, and a tread portion 4 is disposed outside the belt 7 in the tire radial direction. A pair of sidewall portions 5 (one side in FIG. 2) are arranged on the left and right sides of the tread portion 4.

  The carcass 3 can be composed of at least one carcass ply as shown in FIG. Both ends (one side in FIG. 2) of the carcass ply can be folded around the bead core 2A to form a folded end, and the bead filler rubber 2B is positioned in the folded end of the carcass ply. be able to.

  The carcass 3 can also be composed of two or more carcass plies. In that case, as described above, the end portion of one carcass ply can be folded around the bead core 2A to form a folded end portion, and outside the folded end portion, in the sidewall portion 5, The other carcass ply can be arranged.

  The side wall portion 5 is made of side rubber on the surface side, and the inside thereof is reinforced by a crescent-shaped rubber reinforcing layer 6 as seen in the cross section in the tire width direction. As shown in FIG. 2, at least one rubber reinforcing layer 6 is typically disposed above the bead portion 2 and inside the carcass 3. The rubber reinforcing layer can be composed of a plurality of sheets. In that case, the rubber reinforcing layer is not limited to the inside of the carcass ply, and can be disposed on the outside and between them using a plurality of carcass plies. .

The present invention will be described in more detail based on examples and comparative examples with reference to the drawings.
Example 1
A pneumatic tire as shown in FIG. 2 is manufactured.
A cord of cellulose fiber (rayon) is drawn with a DIP tension of 0.71 cN / dtex and subjected to DIP treatment (temperature: 149 ° C., time: 180 seconds), and a cord of 50 cN / dtex (180 ° C., 29.4 N) or more. A reinforcing cord having rigidity represented by an elastic modulus is manufactured, and this cord is applied to a carcass ply to mold an RF tire.
Here, fiber cord type: 1840 dtex / 3, 38 × 38, DIP solution of fiber cord is F / R molar ratio: 1.98, RF / L solid mass%: 16.0, (NaOH + NH ₄ OH) / R Molar ratio: 0.80 used, Carcass ply covering rubber: 100 parts by weight of natural rubber, 50 parts by weight of HAF carbon black and 3 parts by weight of sulfur, driving carcass ply into the tire: 35 / 5cm, tire Size: 215 / 45ZR17 radial tire for passenger cars. Other conditions are also shown in Table 1.
The elastic modulus at high temperature of the reinforcing cord is calculated by using the stress-elongation curve of the cord as described above, and the force applied to each cord at the time of filling the inner pressure of the tire to the load is estimated as 3 kgf, and the stress-elongation at the time of 3 kgf stress. Draw a curve tangent and calculate (see Figure 1).

(Example 2)
As shown in Table 1, tires are manufactured in the same manner as in Example 1 except that the twist coefficient is changed from 0.57 to 0.43 in Example 1.
(Example 3)
As shown in Table 1, tires are manufactured in the same manner as in Example 1 except that the rayon of the cord material is changed to lyocell in Example 1.
Example 4
As shown in Table 1, tires are manufactured in the same manner as in Example 1 except that the rayon of the cord material is changed to lyocell in Example 2.
(Comparative Example 1)
As shown in Table 1, tires are manufactured in the same manner as in Example 1, except that the rigidity of the reinforcing cord is changed to less than 50 cN / dtex (180 ° C. · 29.4 N).

RF durability performance (drum test) of tires manufactured in Examples and Comparative Examples, and longitudinal springs at the time of INF and when the air pressure is reduced to atmospheric pressure (at the time of DEF) are measured and evaluated.
(1) RF durability performance Each tire is assembled with rims at normal pressure, air is sealed at an internal pressure of 230 kPa, and left at room temperature of 38 ° C. for 24 hours, then the valve core is removed and the internal pressure is set to atmospheric pressure. The drum running test was conducted under the conditions of about 4.17 kN (425 kgf), speed 89 km / h, and room temperature 38 ° C., and the running distance until failure occurred at this time is shown. In addition, evaluation is shown in Table 1 by the index | exponent which set the case of the comparative example 1 to 100, and RF durability performance is so favorable that a value is high.
(2) Longitudinal spring The method of evaluation test of the longitudinal spring constant of the tire is that the slope of the tangent of a certain load value on the load-deflection curve is defined as the longitudinal spring constant (kg / mm) with respect to the load, and the longitudinal spring constant index. Represents a ratio when the longitudinal spring constant of the conventional example is 100.

  As shown in Table 1, the tire of the example is improved by 45% or more in the RF durability distance as compared with the tire of the comparative example. Although not shown in Table 1, the vertical spring is INF: no change, DEF: 11% up.

  In the present invention, by applying a predetermined reinforcing cord to the carcass ply, a carcass ply exhibiting high elasticity at a high temperature can be obtained, and the RF durability performance of a pneumatic tire using the carcass ply can be improved.

It is a graph which shows the stress (load) -elongation curve of the reinforcement cord of one example. 1 is a partial cross-sectional view of a pneumatic tire according to an example of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Bead part 3 Carcass 4 Tread part 5 Side wall part 6 Rubber reinforcement layer

Claims (4)

A pair of right and left bead portions, a carcass made of one or more carcass plies in which a plurality of parallel reinforcing cords are embedded in a covering rubber, a tread portion disposed on the outer side in the tire radial direction of the carcass, and the tread A pneumatic tire comprising left and right sidewall portions of the portion, and a crescent-shaped rubber reinforcing layer disposed inside the carcass as seen in a cross section in the tire width direction,
The reinforcing cord of the carcass ply is made of cellulosic fibers, and is expressed by a cord elastic modulus of 50 cN / dtex or more (at a temperature of 180 ° C. and a stress applied with a force of 29.4 N per reinforcing cord). A pneumatic tire characterized by having rigidity.   The pneumatic tire according to claim 1, wherein the reinforcing cord has a twist coefficient of 0.35 or more.   The pneumatic tire according to claim 1 or 2, wherein the reinforcing cord is made of rayon or lyocell.   The pneumatic tire according to any one of claims 1 to 3, wherein the reinforcing cord is made of an organic fiber having a melting point of 300 ° C or higher.

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