JPH07266813A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To improve durability of bead to ply end exfoliation so as to prevent lack of a bead toe part by specifying a range of modulus value in 100% extension and break extension value of chafer rubber which covers a surface part from the inside to the outside in the axial direction of a tire bead part. CONSTITUTION:Specification of characteristic values of two kinds of chafers can improve exfoliation performance of ply ends and prevent defects of a bead toe part 4 without spoiling rim abrasion resistance. In a pair of tire bead parts in which both ends of a carcass ply composed of a plurality of codes, which are arranged parallel in the approximately perpendicular direction to the tire meridian direction, are wound around bead wire bunches positioned in left/right sides of the tire axial direction respectively, modulus M100 in 100% extension of chafer rubber 2 and break extension Eb after thermal aging are selected in the range of 40kg/cm<=M100, 230%<=Eb respectively and at the same time sulfur content added to the chafer rubber is set within 1.0wt. or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement in durability of a bead portion of a radial tire for heavy loads such as trucks and buses.

[0002]

2. Description of the Related Art Unlike tires for small and lightweight vehicles such as general passenger cars, radial tires used for trucks, buses, etc. are often filled with a high internal pressure and are subjected to heavy loads. Further, since the running distance until the groove of the tire tread portion is worn is long, it is also generalized that a new tread rubber is attached again after the wear and reused as a retreaded tire several times. For this reason, in the case of radial tires, many improvements in durability performance have been proposed in the past in the bead portion, which is one of the places where stress and strain are significantly concentrated during tire running. For example, in Japanese Patent Laid-Open No. 59-216710, abrasion of rubber on the back side of the bead portion (referred to as rim rubbing) due to friction with a wheel rim flange is prevented, and the inner end of the bead portion in the axial direction of the tire is prevented. There has been proposed a means for preventing a portion (referred to as a bead toe portion) from being damaged and missing when the tire is detached from the wheel or remounted. According to the description of the publication, the chafer rubber is divided into an inner portion and an outer portion in the tire axial direction, and different chafer rubbers are used according to the function emphasized in each portion. . That is, a rubber-made chafer having a characteristic specialized for preventing chipping of the bead toe portion is provided on the inner side in the axial direction of the tire, and a chamfer for preventing rim friction damage is provided on the outer side in the axial direction of the tire. Attach a rubber chafer with the specified characteristics.

[0003]

SUMMARY OF THE INVENTION However, as pointed out by various experiments and analyzes by the inventor, the chafer rubber of the outer side portion in the tire axial direction by repeated pressure contact with the wheel rim flange due to long-distance running under heavy load. Cause fatigue and settling, and as a result, the position of the bead wire bundle is moved and deformed to increase the stress strain of the carcass plycode terminal wound around it and so-called ply end peeling failure is induced. No new and important problem regarding the above-mentioned problem is described in the above-mentioned Japanese Patent Laid-Open No. 59-216710.
Further, when two types of chafer rubber are used as in the above publication, there is a problem that the number of tire assembly members increases and productivity at the time of tire production is lowered, and further, the boundary between the two types of chafer rubber is further increased. There is a problem that it is not possible to fully enjoy the intended effect because it is difficult to make it so that the position is exactly at the set place.

On the other hand, with respect to the problem that the chafer rubber of the tire axially outer portion fatigues and induces a ply end peeling failure, the tire axially outer portion is provided as a countermeasure against this problem. 100 pieces of chafer rubber
It has already been found that increasing the modulus value at 100% elongation M ₁₀₀ reduces the ply edge peeling failure. However, increasing the modulus value at 100% elongation makes it possible to increase the elongation at break E _b after heat aging. Since there is a two-pronged tendency that makes it difficult to increase the value, it is disadvantageous to the toe chipping, and no technique has been established for simultaneously increasing the rubber characteristic values of both M ₁₀₀ and E _b with one type of rubber chafer. It was the current situation.

Therefore, an object of the present invention is to establish a rubber compounding method for simultaneously increasing both the characteristic values M ₁₀₀ and E _b of the rubber chafer rubber, and to optimize the rubber characteristic values M ₁₀₀ and E _b . To provide a pneumatic radial tire capable of improving the peeling resistance of the ply end and preventing damage to the bead toe portion without damaging the rim friction resistance.

[0006]

In order to achieve the above object, in claim 1, the characteristic values of the two types of rubber chafers are limited so that the rim friction resistance is not impaired.
Means for improving peeling resistance of the ply end and preventing damage to the bead toe portion, and as described in the above claims, a plurality of means arranged in a direction substantially perpendicular to the meridian direction of the tire. In a pair of tire bead portions, each end of a carcass ply layer made of the cord is wound around a bead wire bundle located on the left and right in the tire axial direction. The modulus M ₁₀₀ at 100% elongation of the chafer rubber covering the surface portion from the inside to the outside and the elongation at break E _b after heat aging are 40 kg / cm ² ≦ M ₁₀₀ and 230% ≦ E _b , respectively. The pneumatic radial tire is characterized in that the amount of sulfur added to the chafer rubber is set to 1.0 part by weight or more at the same time as being selected to a value in the range.

According to the second aspect of the invention, the chafer rubber for simultaneously increasing the modulus value M ₁₀₀ at 100% elongation of the chafer rubber and the elongation at break E _b after heat aging is simultaneously increased. The pneumatic radial according to claim 1, wherein a styrene-butadiene type resin (referred to as SPB), a VC-BR (trade name) polymer, or a phenol type resin is mixed alone or in combination as a rubber reinforcing chemical. Tires.

[0008] Incidentally, Choi - fa - Modjurasu value M ₁₀₀ at 100% elongation of the rubber is Taiyabi after vulcanization - Choi from de unit - fa - Rubber Shi finishing cutting buff 1mm thick cut to a predetermined size A sample punched with a German standard DIN type die blade is attached to an Instron type tensile testing machine, a tensile test is performed at a pulling speed of 100 mm / min, and a modulus value at 100% elongation is calculated. Further, the breaking elongation E _b after heat aging is the same as the above, after the DIN type sample is left in a gear oven kept at a temperature of 100 ° C. for 24 hours to be heat aged. It is calculated by measuring the elongation when the sample is cut.

[0009]

The inventor of the present invention has caused a large number of running tires for trucks and buses due to distortion of the ply end under internal pressure and load and deformation of the bead member due to running fatigue after dissecting those tires. The amount of displacement of the bead wire-bundle in the bead was measured and compared, and it was found that the larger the amount of displacement of the bead wire-bundle before and after running was, the greater the distortion of the ply end was. . Separately 1 of chafer rubber
Several types of tires with different modulus values when stretched by 00% were made as prototypes and run for a long time under a predetermined internal pressure load.
From an experiment in which the amount of displacement of the position of the wire bundle within the bead was measured, it was found that the tire having a larger modulus value at 100% extension has a smaller movement amount of the wire bundle. The change in the position of the bead wire bundle within the bead before and after running is due to running fatigue of the chafer rubber sandwiched between the highly rigid bead wire bundle and the wheel rim flange. In order to reduce the wall thickness, the bundle of bead wires moves toward the wheel rim flange and is generated. Therefore, the shift amount of the bead wire bundle is determined by the chain outside the tire axial direction.
It is obtained by measuring the distance from the outer surface of the far rubber to the bundle of bead wires before and after running the tire.

Based on such knowledge, 1 of chafer rubber
A bead endurance drum test was conducted on several tires having different modulus values at the time of 00% elongation, and the results shown in FIG. 2 were obtained. As can be seen from Fig. 2, the chafer rubber 100
If the modulus value at the time of% extension is less than 40 kgf / cm ^{2, the} bead durability is drastically reduced. This test is conducted by using the bead durability test method and conditions described later until the peeling failure occurs at the ply end.

Next, the values of the elongation at break of the chafer rubber of the tire toe were measured for the many truck and bus tires described above, and the tires were assembled and removed on the wheel rim. Then, the amount (number and size) of the missing beads in the bead toe portion was confirmed. As a result, as the running distance of the tire becomes longer, the chafer rubber is thermally deteriorated due to the heat history during running, the elongation value at break becomes gradually smaller, and especially the elongation value at break becomes 200%. It was found that the dropout amount in the bead toe part increased sharply when the amount became below.

Based on the results of the above-described examinations, the pneumatic radial tire of the present invention has a chafer rubber 10
Since the modulus value at 0% elongation and the elongation value at break are limited to the ranges described in claim 1, the bead durability against peeling of the ply end is significantly improved and the lack of the bead toe part is almost completely eliminated. Can be prevented.

Here, a rubber composition for producing a chafer rubber in which the modulus value at 100% elongation of the chafer rubber and the elongation value at break are within the range described in claim 1 at the same time. Can be achieved by simply decreasing the amount of sulfur and increasing the amount of carbon, but when the amount of sulfur is less than 1.0 parts by weight, it is adjacent to the rubber chafer in the usual bead structure. There is a risk of delamination between the fabric reinforcing layers, such as the wire chafer layer and the chafer rubber, which are arranged in parallel. In consideration of this point, in claim 1, the amount of sulfur mixed in the chafer rubber is 1.0 part by weight or more. According to the present invention described in claim 2, styrene butadiene-based resin (SPB), VC-B is used as a reinforcing chemical for chafer rubber.
R, phenol resin, alone or in combination, is used as a chafer.
By mixing in the rubber, the modulus value at 100% elongation and the elongation at break can be within a desired range without adversely affecting other members of the bead portion or deteriorating other performances of the chafer rubber. Can be easily set.

From the viewpoint of prevention of rim friction failure due to contact friction with the wheel flange, the basic composition of the chafer rubber is a blend of a polymer NR (natural rubber) and BR (butadiene rubber) according to conventional studies. It is said that the most suitable carbon as the reinforcing material is HAF grade. However, according to the inventor's experimental experience, the reinforcing chemicals SPB, VC-BR and phenol resin are added to this basic composition. When mixed with SPB, SPB = 3 to 20 parts by weight, VC-BR = 5
It is preferable to select the number of parts by weight of each reinforcing chemical in the range of ˜50 parts by weight and phenolic resin = 1˜10 parts by weight. In the case of SPB and VC-BR, if the above upper limit value is exceeded, the kneading workability at the time of production will decrease, while if it is below the lower limit value, the effect will be insufficient. Further, in the case of a phenol resin, from the viewpoint of material cost, it is suppressed to 10 parts by weight or less, while if it is 1.0 parts by weight or less, the effect becomes insufficient.

[0015]

EXAMPLE Example 1 using tires having a tire size of 11R22.5 and 14PR and using chafer rubber 2 made by various formulations shown in Table 1 in the tire having a bead structure 1 shown in FIG. Eight types of tires, 2, 3, and 4 and Comparative Examples 1, 2, 3, and 4, were prototyped in predetermined numbers. Further, the modulus value at 100% elongation and the elongation value at break after heat aging of the tires of these various Examples and Comparative Examples were described above using the samples cut out from the tire bead portion after vulcanization and before running. The combinations shown in Table 1 were measured by the method. In addition, in setting the mixture, in order to prevent so-called rim friction wear due to repeated contact and separation with the wheel rim flange 3 that is received during tire running, as a main compounding material, a basic polymer is blended with NR / BR and carbon is used. HAF.

Next, a bead durability test and a peeling test were carried out in order to evaluate the various kinds of tires manufactured as described above. The test condition of the bead endurance test is that the tire tread surface has a residual groove depth of 0.5 mm in order to cause a failure in the bead part.
A tire that has been buffed up to this point is run by pressing the internal pressure load on the circumference of a steel drum as a regular condition of JIS standard.
It is a measure of the durability of a vehicle in terms of the number of kilometers it takes before a failure occurs. Moreover, after the tire finished due to the bead failure was removed from the tester, the tire was mounted on the wheel rim again, and after removal, it was confirmed in detail whether the bead toe portion 4 was cracked or rubber was missing. Incidentally, the unmarked values in the table are tires finished due to peeling failure at the ply end 5,
Those marked with * indicate tires which have ended due to peeling between the chafer rubber and the fabric reinforcing layer disposed inside thereof, for example, the wire chafer layer 6. Next, the peeling test was carried out on each product tire before running.
After the chafer rubber and the fabric reinforcing layer are cut out integrally from the cord portion and a knife cut is inserted at the boundary between both members, the ends of both members are gripped and peeled off, and the force at that time is measured. Incidentally, the numerical values of the test results in the tables in both tests are indexed with the value of the tire of Comparative Example 4 which is a conventional standard product being 100, and the larger the index, the better.

[0017]

[Table 1]

Looking at the test results in detail, in Comparative Example 1, 1
Since the modulus value M ₁₀₀ at the time of ₁₀₀ % elongation is out of the range of the present invention, the bead durability is inferior, and in the tires of Comparative Examples 3 and 4, the breaking elongation E _b after heat aging is small and the drum test is conducted. After the completion, there were several missing parts in the toe part of the tire.
Further, in Comparative Example 2, the compounding amount of sulfur is out of the range of the present invention, but the peel strength is low and the result of the bead endurance drum test is also inferior. On the other hand, the tires of the examples maintained good levels in bead durability drum test and peeling strength, and no toe chipping was observed. In particular, in the tires of Examples 3 and 4, the reinforcing chemicals SPB and VC-BR were appropriately blended, and the bead durability and toe loss resistance were excellent. Moreover, the BR and the amount of carbon were manufactured from the viewpoint of blending. It is reasonably workable and highly practical.

[0019]

With the pneumatic radial tire to which the chafer rubber according to the present invention is applied, the chafer can be used even when traveling for a long period of time under severe load conditions.
It is possible to prevent the peeling failure of the bead member typified by the peeling of the ply end and to prevent the damage to the bead toe portion due to running fatigue without causing the rubber rim rubbing wear damage.

[Brief description of drawings]

FIG. 1 is a diagram showing a bead structure according to the present invention.

FIG. 2 is a graph showing the relationship between the modulus value and the bead durability at 100% elongation.

[Explanation of symbols]

 1 bead structure 2 chafer rubber 3 wheel rim flange 4 bead toe part 5 ply end 6 wire chafer layer

Claims (2)

[Claims] 1. A carcass ply layer comprising a plurality of cords juxtaposed in a direction substantially perpendicular to the meridian direction of a tire, both ends of which are respectively wound around a bundle of bead wires located on the left and right in the tire axial direction. In the pair of tire beads that are
The modulus M ₁₀₀ at 100% elongation of the chafer rubber covering the surface portion of the tire bead portion from the inner side to the outer side in the axial direction of the tire and the breaking elongation E _b after heat aging are respectively 40 kg / cm ² ≦ M Pneumatic radials characterized in that the amount of sulfur added to the chafer rubber is set to 1.0 part by weight or more at the same time as being selected to a value in the range of ₁₀₀ , 230% ≦ E _b. tire. 2. A styrene-butadiene type resin or a VC-BR (trade name) polymer as a reinforcing chemical for chafer rubber, and further a phenol type resin, alone or in combination, according to claim 1. Pneumatic radial tire.