JPS63255105A - Pneumatic radial tire for heavy load application - Google Patents

Abstract

PURPOSE:To prevent any separation at the carcass layer end from occurring by setting up a chafer layer at the carcass layer outside of a bead part, and forming the chafer layer adjacent to the carcass layer with a steel cord, while specifying an elastic modulus of the cord covering rubber. CONSTITUTION:In an internal between a symmetrical pair of bead part 1, there is provided with a carcass layer. And, an edge 2' of this carcass layer 2 is turned op to the outside from the inside of a tire in the circumference of a bead core 4 being annularly set up in the tire circumferential direction at these bead parts 1. In this structure, more than one layer, for example, two chafer layers 31 and 32 are set up at the outside of the carcass layer 2 in these bead parts 1. In addition, the chafer layer 31 adjacent to the carcass layer 2 is formed by a steel cord. And, coar rubber of the chafer layer 31 adjacent to the carcass layer 2 makes its elastic modulus measured under the specified condition higher than that of the carcass layer 2, while it is set to be within the range of 10 MPa-15MPa.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a heavy-duty pneumatic radial tire with improved bead durability.

[Prior Art] Conventionally, improving the durability of the bead part depends on how to reduce the movement (distortion) of the turn-amp edge of the carcass layer that is folded and rolled up from the inside of the tire to the outside around the bead core. For this purpose, while keeping the cord coating rubber of the carcass layer (hereinafter referred to as coat rubber) and the coat rubber of the chafer layer adjacent to the carcass layer the same, the height of the turn-up edge of the carcass layer and the height of the chafer layer are In addition, the durability of the bead portion is improved by appropriately considering bead filler gauges, etc.

However, these measures do not fundamentally reduce the movement (distortion) of the turn-up edge of the carcass layer.

[Purpose of the invention]

The present invention is an air pump for heavy loads that reduces the movement around the bead core of the carcass layer and the movement of the turn-up edge of the carcass layer, prevents separation of the turn-up edge of the carcass layer, and improves the durability of the bead part. The purpose is to provide radial tires.

[Structure of the invention]

Therefore, the present invention provides a pneumatic radial tire in which a carcass layer is installed between a pair of left and right bead portions, and the end portion of the carcass layer is folded back and rolled up from the inside of the tire to the outside around a bead core. One or more chafer layers are arranged outside the carcass layer of the carcass layer, and the chafer layer adjacent to the carcass layer is made of steel cord, and the elastic modulus of the cord-coated rubber of the chafer layer is set to be the same as that of the cord-coated rubber of the carcass layer. higher than the elastic modulus of and 10
The gist of the present invention is a pneumatic radial tire for heavy loads characterized by a pressure of ~15 MPa.

Hereinafter, the configuration of the present invention will be explained in detail with reference to the drawings.

FIG. 1 is an explanatory cross-sectional view showing a bead portion of an example of a heavy-load pneumatic radial tire of the present invention.

In FIG. 1, a carcass layer 2 is mounted on a pair of left and right bead portions 1°1. This carcass layer 2 is made of cords such as steel cords and aromatic polyamide fiber cords, and may have two or more layers instead of one layer. Carcass N
2 is folded back and rolled up from the inside of the tire to the outside at the bead portion 1 around a bead core 4 that is annularly arranged in the circumferential direction of the tire. Above the bead core 4 is a lower bead rubber stock 5. Two bead rubber stocks are provided: and an upper bead rubber stock 5□. Furthermore, two chafer layers 36, 3□ are arranged outside the carcass N2 in the bead portion 1. One or more chafer layers may be arranged.

ho is the height of the turn-up edge 2 of the carcass layer 2 from the bead heel 6, hl is the height of the outside of the tire from the bead heel 6 of the chafer layer 31 adjacent to the carcass layer N2, and h4 is the height of the chafer layer 31 adjacent to the carcass layer 2. h2 represents the height of the chafer layer 3I on the inside of the tire from the bead heel 6, and h2 represents the height of the chafer layer 3□ disposed outside the chafer layer 31 from the bead heel 6, respectively.

In the present invention, the chafer layer 3 adjacent to the carcass layer 2. consists of steel cord. This is to enhance the reinforcing effect on the carcass layer 2 as a chafer layer.

The coated rubber of the chafer layer 3° adjacent to the carcass layer 2 was measured using a viscoelastic spectrometer at a temperature of 20°C, a strain of 10% ± 2%, and an elastic modulus M1 of 2011Z. Elastic modulus Mz
(Measured under the same conditions as the coated rubber of the chafer layer 31) higher than (M+ >Mz) and 10MP
It is necessary to set the pressure to not less than a and not more than 15 MPa.

When the elastic modulus Ml of the coated rubber of Chafer-N3I is lower than the elastic modulus M2 of the coated rubber of carcass layer 2, that is, when it is less than 10 MPa, the movement of the end portion of carcass layer 2 increases, causing distortion in the end portion of carcass N2. is concentrated, and the occurrence of separation from the end portion of the carcass N2 is unavoidable.
must be higher than that. On the other hand, the modulus of elasticity M1 of the coated rubber of the first layer of the chipper at 3° is the modulus of elasticity M of the coated rubber of the carcass layer 2! If it becomes extremely high than 15 MPa, carcass layer 2 and chafer layer 3. Separation tends to occur between coated rubber layers.

As described above, the elastic modulus M1 of the coat rubber of the chafer layer 31 is higher than the elastic modulus M2 of the coat rubber of the carcass layer 2, and is set to 10 MPa to 15 MPa.

Further, the coat rubber of the chafer layer 31 preferably contains a cobalt metal salt such as cobalt naphthenate in order to improve adhesion to the steel cord. In this case, the content of the cobalt metal salt is 0.1 parts by weight to 0.4 parts by weight per 100 parts by weight of the raw rubber as the cobalt element content.
Parts by weight.

As a result, the rubber attachment to the steel cords constituting the chafer layer 3I was 90% or more. (evaluated by rubber coverage rate (%)),
Chafer layer 3. This prevents separation from occurring from the end portion of the bead, making it possible to significantly improve the durability of the bead portion.

If the coat rubber of the chafer layer 3I does not contain a cobalt metal salt, or if the cobalt element content is less than 0.1 parts by weight, the chafer layer 3. The rubber adhesion to the steel cord constituting the steel cord is less than 90%, and no improvement in the durability of the bead portion can be expected. On the other hand, if the cobalt element content exceeds 0.4 parts by weight, the temperature should be 160°C x 12°C during overvulcanization.
The rubber adhesion to the 0 minute steel cord is less than 80%, and no significant improvement in the durability of the bead portion can be expected. Therefore, the coated rubber of the chafer layer 31 preferably contains a cobalt metal salt as a cobalt element content of 0.1 to Q.4 parts by weight based on 100 parts by weight of the raw material rubber.

Next, tires having specifications A- shown in Table 1 below were produced, and the results of evaluating the bead portion durability of each tire are shown below. Here, the tire size is 1000 B20, has the bead structure shown in Fig. 1, and ho = 70 mm %
h+ = 60 mm, h2 = 88 mm. In addition, in the conventional tire, the elastic modulus M of the coat rubber of the chafer layer 31 is the same as the elastic modulus M2 of the coat rubber of the carcass layer 2, and does not contain cobalt metal salt (
Specifications A).

To evaluate the bead durability, an indoor drum test was conducted under the following conditions, and the bead durability was determined by the distance traveled until a crank of 5 mm or more was visible on the tire bead surface. Table 1 shows the mileage of conventional tires as an index, with the distance traveled as 100. The higher the number, the better.

Air pressure 9.0 kgf/cIa rim
700 T x 20 load
200% of JIS standard load Speed: 50 km/h Room temperature: 30±2°C Drum diameter: 1700 a+a+ Figure 2 shows the relationship between the modulus of elasticity of the coated rubber of the chafer layer, the presence or absence of cobalt metal salt, and the durability of the bead portion. Further, FIG. 3 shows the relationship between the cobalt element content and the amount of rubberized material. In FIG. 3, a shows the case where the chafer layer was vulcanized at 160° C. for 20 minutes, and b shows the case where the chafer layer was vulcanized at 160° C. for 120 minutes.

Table 1 From these results, it can be seen that if the coating rubber of the chafer layer 31 is as follows, the durability of the bead portion of the tire is improved by 130% or more compared to the conventional tire even under heavy load conditions.

If the elastic modulus M+ (measured by a viscoelastic spectrometer) of the coated rubber of the chafer layer 3I is smaller than the elastic modulus M, (measured by a viscoelastic spectrometer) of the coated rubber of the carcass layer 2, the turn-up edge of the carcass layer 2 The strain concentrated at the end portion of 2' is not sufficiently alleviated, resulting in insufficient durability of the bead portion.

Therefore, the elastic modulus M of the coat rubber of the chafer layer 31 needs to be higher than the elastic modulus M2 of the coat rubber of the carcass layer 2 (Table 1, FIG. 2).

When the coat rubber of the chafer layer 31 does not contain cobalt metal salt, the bead portion durability is poor (Table 1).

The coated rubber of the chafer layer 31 does not contain cobalt metal salt, even if the elastic modulus M of the coated rubber of the chafer layer 3 is higher than the elastic modulus M2 of the coated rubber of the carcass layer 2, it contains a cobalt metal salt. The durability of the bead portion is inferior compared to that of the above (Table 1, Fig. 2).

Even if the coat rubber of the chafer layer 31 contains cobalt metal salt, if the modulus of elasticity M1 of the coat rubber of the chafer layer 3I is smaller than the modulus of elasticity M2 of the coat rubber of the carcass layer 2, the bead portion durability will be insufficient. be.

Chafer layer 3. Even if the coated rubber contains cobalt metal salt, if the cobalt metal salt content causes the amount of rubber adhesion to be 90% or less during overvulcanization, the durability of the bead portion will be poor (Fig. 3, Fig. 2, Table 1).

The elastic modulus M of the coated rubber of Chafer layer 3I measured by a viscoelastic spectrometer is 10 MPa to 15 MP
a and is higher than the elastic modulus M2 measured by a viscoelastic spectrometer of the coating rubber of the carcass layer 2, more preferably the chafer layer 3. The coating rubber is coated with cobalt metal salt and the raw rubber has a cobalt element content of 10%.
When it is contained in an amount of 0.1 to 0.4 parts by weight relative to 0 parts by weight, it is possible to significantly improve the bead part durability by 130% or more compared to a tire having a conventional bead part structure.

〔Effect of the invention〕

As explained above, according to the present invention, the following effects can be achieved.

■ Since the chafer layer adjacent to the carcass layer reliably suppresses the movement of the turn-up edge of the carcass layer, the fatigue of the turn-up edge of the carcass layer is reduced and the separation of the turn-up edge can be suppressed. The durability (especially under heavy loads) is improved (130%).
improvement).

■ Since the movement of the turn-up edge of the carcass layer is reduced, rolling resistance is reduced (3% reduction).

■ Movement around the bead core in the carcass layer is reduced, improving steering stability.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional explanatory diagram showing the bead portion of an example of a heavy-duty pneumatic radial tire of the present invention, and FIG. 2 is a graph showing the relationship between the elastic modulus of the coated rubber of the chafer layer, the presence or absence of cobalt metal salt content, and the bead portion durability. FIG. 3 is a diagram showing the relationship between the cobalt element content and the rubberized amount. 1...Bead part, 2...Carcass layer, 2"...
Turn-up edge, 31, 3□... Chafer layer, 4... Bead core, 5I... Lower bead rubber stock, 5□... Upper bead rubber stock, 6...
・Bead heels.

Claims (1)

[Scope of Claims] A pneumatic radial tire in which a carcass layer is installed between a pair of left and right bead parts, and the end part of the carcass layer is folded around a bead core from the inside to the outside of the tire and rolled up. One or more chafer layers are arranged outside the carcass layer, and the chafer layer adjacent to the carcass layer is made of steel cord, and the elastic modulus of the cord-coated rubber of the chafer layer is set to Higher than elastic modulus and 10-15M
A pneumatic radial tire for heavy loads characterized by Pa.