JPH11321247A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain weight reduction while maintaining required bead core strength, air retentivity and corrosion resistance and improve rim assembling performance by using monofilament formed of a synthetic resin regulated in a fusing point, a thermal shrinkage percentage and a moisture percentage, as a core in a cable bead structure. SOLUTION: A bead core 2 comprises a core 9 using monofilament 9A, and a sheath 10 with one to five layers formed by spirally winding a sheath wire 10A around the core 9. The monofilament 9A is formed of synthetic resin material with a diameter K1 of 1.5-8.0 mm, a fusing point of 200 deg.C or higher, a thermal shrinkage percentage being 2% or less and a moisture percentage being less than 5%. The sheath wire 10A is formed of hard steel wire material with a diameter K2 of 0.8-2.6 mm and the carbon content of 0.65-0.88%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire having a bead core which is excellent in rim assembling performance and has a reduced weight without deteriorating air retention and corrosion resistance.

[0002]

2. Description of the Related Art An annular strong bead core is provided at a bead portion of a tire in order to fix an end of a carcass and to maintain a fitting with a rim to keep a filling internal pressure airtight.

Conventionally, as this bead core a, FIG.
As shown in (A) and (B), a so-called tape bead structure a1 in which a plurality of layers of hard steel wires b are arranged side by side in a belt-like strand c, or a single hard steel wire b is used. In addition to the so-called single-wind structure a2 continuously wound in a spiral shape, FIG.
As shown in (C), around the core made of the hard steel wire b1,
A so-called cable bead structure a3 in which a plurality of small-diameter hard steel wires b2 are spirally wound is known.

[0004] On the other hand, in order to reduce the weight of tires due to recent fuel savings, etc., it is strongly desired to reduce the weight of the bead core a. Therefore, instead of the hard steel wire b,
It has been proposed to use an aromatic polyamide fiber cord having a high tensile elasticity comparable to the hard steel wire b.

[0005]

However, the aromatic polyamide fiber cord is advantageous in terms of weight reduction because of its low specific gravity, but has a large elongation under a low load compared to hard steel wire and has a high breaking strength. Is characterized by a low elongation. Therefore, when the hard steel wire is replaced with an aromatic polyamide fiber cord, a sudden force applied to the bead core cannot be borne by the entire cord, resulting in a large decrease in the bead core strength.

Therefore, the present inventor has made a study focusing on the cable bead structure a3. As a result, a part of the plurality of hard steel wires b used for the bead core is replaced with a synthetic resin.
Specifically, by forming a core with a low contribution rate as a strength member from monofilament of synthetic resin, the weight is reduced while maintaining the same strength and air retention as a conventional bead core formed of hard steel wire. And improved rim assembly performance.

That is, the present invention is based on the use of a synthetic resin monofilament whose melting point, heat shrinkage and moisture content are regulated as the core in the cable bead structure, and based on the required bead core strength, air retention, corrosion resistance and the like. It is an object of the present invention to provide a pneumatic tire that can achieve a reduction in weight while maintaining rim and can improve rim assembly performance.

[0008]

To achieve the above object, the present invention provides a pneumatic tire having a carcass extending from a tread portion to a sidewall portion to a bead core at a bead portion. , A core using a monofilament, and a sheath of 1 to 5 layers formed by spirally winding a sheath wire around the core, and the sheath wire has a diameter of 0.8 to 2.6 mm. And having a carbon content of 0.65 to 0.88%, and the monofilament has a carbon content of 1.5 to
It is made of a synthetic resin material having a diameter of 8.0 mm, a melting point of 200 ° C. or more, a heat shrinkage of 2% or less, and a water content of less than 5%.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, a pneumatic tire 1 is a tire for a passenger car in this example, and has bead portions 3 on both sides through which a bead core 2 passes, and a sidewall portion 4 extending outward from each bead portion 3 in the tire radial direction. And a tread portion 5 connecting between the upper ends thereof. A carcass 6 is bridged between the bead portions 3, and a belt layer 7 is wound around the outside of the carcass 6 and inside the tread portion 5 in the circumferential direction.

The carcass 6 is formed of one or more carcass plies in which carcass cords are arranged at an angle of 70 to 90 ° with respect to the tire equator C. Then, the bead portion 3 is turned around from the inside to the outside around the bead core 2 and locked. As the carcass cord, a synthetic resin cord made of nylon, polyester, rayon, aromatic polyamide, and the like, and a metal fiber cord such as steel can be used, but a synthetic resin cord is preferable from the viewpoint of weight reduction.

The belt layer 7 includes a plurality of belt plies, in this example, a belt cord with respect to the tire equator C.
Two belt plies 7 arranged at an angle of 10 to 30 °
A and 7B. The belt cords are superposed with different inclination directions so that the belt cords intersect between the plies.

Next, the bead core 2 has a cable bead structure, and as shown in an enlarged view in FIG. 2, a core 9 using a monofilament 9A and a sheath wire 10A wound around the core 9 in a spiral shape. 1 formed by attaching
And 5 layers of the sheath 10. In this example, a case having one sheath 10 is illustrated.

The bead core 2 needs to have a certain degree of hardness in order to keep the tire 1 in close contact with the rim and maintain the internal pressure.
It is formed from a thick synthetic resin material having a diameter K1 of 1.5 to 8.0 mm. The monofilament 9A mainly functions as a core material for spirally winding the sheath wire 10A and as a core material for maintaining the shape of the sheath wire 10A wound at the time of vulcanization molding. That is, the strength as the bead core 2 does not need to bear almost any strength on the monofilament 9A, such as mainly covered by the sheath wire 10A. Various synthetic resin materials having a low modulus of not more than mm ² can be used.

However, the monofilament 9A needs to be able to maintain the shapes and dimensions of the bead core 2 and the bead portion 3 without being softened and deformed by heating and pressure during the vulcanization molding process. Accordingly, the synthetic resin material of the monofilament 9A has a melting point of 200 ° C. or more and a heat shrinkage of 2%.
The following are adopted. Also, since a hard steel wire is used as the sheath wire 10A, if the moisture content in the synthetic resin material is too large,
Corrosion damage such as rust easily occurs on the sheath wire 10A.
Therefore, it is necessary to regulate the moisture content of the synthetic resin material to less than 5%.

Here, the "heat shrinkage rate" means a heat shrinkage Ly of the monofilament 9A when the monofilament 9A is left unloaded at a temperature of 180 ° C. for 20 minutes, and a length Lx of the monofilament 9A before leaving. Is calculated using the following equation. Heat shrinkage = Ly / Lx The “moisture percentage” is the mass Mx of the monofilament 9A,
It is calculated from the absolute dry mass My after drying using the following equation.・ Moisture percentage = (Mx−My) / My

If the melting point is less than 200 ° C., the bead core 2 is deformed by the heat of vulcanization, causing poor fitting with the rim, deterioration of the air holding property and rim assembling property, and impairing the bead strength. Create a problem. If the heat shrinkage exceeds 2.0%, the bead diameter becomes small due to the shrinkage of the bead core due to the heat of vulcanization, and the rim assembling property is remarkably impaired. When the moisture content is 5% or more, rust is generated on the sheath wire 10A due to moisture contained in the core 9, and durability is impaired.

When the diameter K1 of the monofilament 9A is less than 1.5 mm, the bending rigidity of the bead core 2 is excessively reduced, for example, the second moment of area of the annular body composed of the sheath 10 is reduced, and the strength and bead strength of the bead core 2 are reduced. This leads to a decrease in rigidity. On the other hand, if the thickness exceeds 8.0 mm, the bead core 2 becomes unnecessarily large, and the tire design is supported, and the merit of weight reduction cannot be expected.

As the sheath wire 10A, the sheath wire having the same configuration as the sheath wire (current product) used for the bead core of the conventional cable bead structure a3 can be suitably used.
In the present application, a hard steel wire having a diameter K2 of 0.8 to 2.6 mm and a carbon content of 0.65 to 0.88% is employed.

As described above, the bead core 2 has an annular structure in which the sheath wire 10A, which is a substantial strength member, surrounds the layer in a layered manner, and each sheath wire 10A repositions the core 9 in a helical manner. Therefore, the stress is not concentrated, the strength of each sheath wire 10A can be effectively exhibited, and the strength of the bead core 2 and the bead tightening force can be effectively improved. In addition, since the cross-sectional shape of the bead core 2 is circular along the carcass cord, the bead tightening force can be further improved.

However, when the strength per one of the sheath wires 10A is too small, the effect of impairing the improvement effect is brought about, and the total number of the sheath wires 10A and the sheath 1
The number of 0 layers increases, and the shape and dimensions of the bead core 2 increase, thereby supporting tire design and manufacture. Therefore, as described above, the sheath wire 10A has the diameter K2 of 0.8 to 2..
It is necessary that the carbon content be 6 mm and the carbon content be 0.65 to 0.88%. If the carbon content is larger than 0.88% and the diameter is larger than 2.6 mm, not only the quality becomes excessive, but also the rigidity is increased and the rim assemblability is impaired.
Bead core 2 that makes it difficult to mold and bend when winding
Production efficiency decreases.

In this example, the sheath 10 has a single layer, but it can be set appropriately in the range of 1 to 5 layers according to the required tire performance. Each sheath wire 10A
Although it is preferable to use the same structure, the diameter of the sheath wire or the carbon content can be different for each sheath (each layer).

The tire of the present invention is not limited to a tire for a passenger car, and can be formed as various tires such as a tire for a heavy load, a tire for a small truck, a tire for a motorcycle, and a tire for an aircraft.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Tire size 195/8 having the structure of FIG.
A 0R15 passenger car tire was prototyped using the bead core described in the specifications in Table 1, and the bead core weight, rim assembly performance, air retention, and sheath wire corrosion state of the prototype tire were tested. No. 1.

(1) Bead core weight: The weight of the bead core alone was measured. The value in parentheses is an index with Comparative Example 1 being 100, and the smaller the value, the lighter the weight. (2) Rim assembling performance: The workability when assembling the test tire to the standard rim (5.5JJ × 15) specified by JATMA is evaluated as “good”, “normal”, or “bad” according to the operator's feeling. "In three stages. (3) Air retention: An internal pressure P1 (240 kpa) is filled in the tire assembled with the standard rim, and the internal pressure P2 of the tire after being left at room temperature (20 to 30 ° C.) for 2 months.
Was measured and evaluated by the pressure ratio P2 / P1. The larger the value, the higher the air retention and the better. (4) Corrosion state of the sheath wire: 300 ml of water was put into the tire assembled with the standard rim and the internal pressure was 240
After filling with kpa, it was left in an oven at 80 ° C. for 2 months. During the standing, 300 ml of water is sequentially added every week so that the water does not evaporate. Also after leaving
The bead core was taken out from the tire, two of the sheath wires in contact with the core were peeled off, and the contact portion was observed with a magnifying glass to check for the occurrence of rust.

[0025]

[Table 1]

In Comparative Example 2, since the core diameter was too small, the bending stiffness and strength of the bead core were reduced, and the tire burst during internal pressure filling, making it difficult to test air retention and corrosion resistance. Was. In Comparative Example 3, since the heat shrinkage of the core was excessive, the bead core shrunk by heating during vulcanization molding, and the bead diameter was reduced, making it difficult to assemble the rim. In Comparative Example 4, since the moisture content of the core is excessive, rust is generated on the sheath wire due to moisture contained in the core, and the durability is impaired. In Comparative Example 5, since the melting point of the core was too low, the bead core and the bead portion were deformed by heating and pressurizing during vulcanization molding, so that the rim assembling property, air holding property and corrosion resistance test could not be performed. .

[0027]

As described above, according to the present invention, in the cable bead structure, a monofilament made of a synthetic resin having a regulated melting point, heat shrinkage and moisture content is used as the core.
It is possible to achieve weight reduction while maintaining necessary bead core strength, air retention, corrosion resistance, and the like, and improve rim assembly performance.

[Brief description of the drawings]

FIG. 1 is a sectional view of a tire according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view showing a bead core.

FIGS. 3A, 3B, and 3C are cross-sectional views illustrating a conventional bead core.

[Explanation of symbols]

 2 Bead core 3 Bead section 4 Side wall section 5 Tread section 6 Carcass 9 Core 9A Monofilament 10 Sheath 10A Sheath wire

Claims (1)

[Claims] 1. A pneumatic tire comprising a carcass extending from a tread portion to a bead core of a bead portion through a sidewall portion, wherein the bead core includes a core using a monofilament,
It comprises a sheath of 1 to 5 layers formed by spirally winding a sheath wire around the core, wherein the sheath wire has a diameter of 0.8 to 2.6 mm and a carbon content of The monofilament has a diameter of 1.5 to 8.0 mm, a melting point of 200 ° C. or more, a thermal shrinkage of 2% or less, and 0.65 to 0.88% of a hard steel wire. A pneumatic tire comprising a synthetic resin material having a water content of less than 5%.