JP2001213113A - Pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic radial tire having improved belt durability and a lighter weight in spite of using steel cords in a simple structure for a belt layer reinforcing material. SOLUTION: This pneumatic radial tire comprises a carcass layer extending from a tread portion through sidewall portions to bead portions where it is turned around bead cores and a steel cord belt layer for reinforcement between the carcass layer and a tread portion belt layer. Steel cords constituting the belt layers are 1×N structured steel cords consisting of three or four filaments having sizes of 0.25 mm to 0.31 mm. The cross section of the steel cords in the belt layer is oblate with a minor diameter in the tire radial direction. A value for P/d is 52-82 where d is the diameter of the filament and P is a twist pitch.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a carcass layer that is folded from a tread portion via a sidewall portion to a bead core of a bead portion, a steel cord belt layer for reinforcing between the carcass layer and the tread rubber layer. The present invention relates to a pneumatic radial tire for a passenger car, which has an excellent belt durability and a light weight tire by improving a constituent steel cord.

[0002]

2. Description of the Related Art Conventionally, steel cords having a 1 × N structure (mainly N = 4 or 5) have been widely used for belt reinforcement layers of radial tires for passenger cars due to their high productivity and low cost. Was. The 1 × N structural steel cord was twisted with a twist pitch of 40 to 48 times the filament diameter to ensure fatigue resistance. However, in a normal twisted structure, a void is formed in the center of the cord shown in FIG. Since (5) is present and the rubber has poor penetration into the gap, there is a problem that when the tread is damaged, moisture enters the gap, and the durability of the belt portion due to corrosion is greatly deteriorated.

In order to improve the corrosion resistance, a twist structure has been proposed in which rubber enters the cord. For example, loose open 1 × N to provide space between filaments
In the structure, a tension is applied to the cord during rubber coating or vulcanization of the tire, and it is difficult to manufacture the tire while securing the space uniformly. In addition, there is a drawback that a portion where the twist is expanded and a portion where the twist is tightened are easily generated alternately, and a filament is easily broken due to buckling in the changed portion.

Further, an N + N, M + N structure (N, M = 2,
3) has good rubber penetration and improved corrosion resistance and fatigue resistance, but requires a special twisting machine at the time of cord production, which leads to high cord production costs, and requires a large cord diameter and a thick coating rubber. There was a disadvantage in reducing the tire weight.

[0005] In recent years, not only the above-mentioned problems in tire performance, but also reduction in cost has become an important issue due to economic conditions.

[0006]

Therefore, in recent years, the filament diameter has been increased and the number of filaments has been reduced to 1 × 2.
A steel cord with a simplified structure such as 1x3 has high strength and belt stiffness can be easily obtained, so it can contribute to a reduction in the amount of cord used. It has come to be used for tire belt cords.

[0007] However, steel cords have a large filament diameter and a low fatigue resistance.
The × 2 structure has a problem in fatigue resistance under severe conditions, and 1 × 3
In the structure, the gap in the cord was small, but there was still concern about the corrosion resistance. Furthermore, as the filament diameter is increased, the rigidity of the cord becomes too high, the belt layer becomes hard, and the riding comfort tends to deteriorate, and there is a problem that it is unsuitable for passenger car tires.

The present invention solves the above-mentioned problem by improving the twisted structure of a steel cord used for a belt reinforcing layer. Even if a thick filament is used, the fatigue resistance of the cord does not decrease. Provided is a pneumatic radial tire using a steel cord for a belt reinforcing layer, which has excellent corrosion resistance, can maintain a comfortable ride, and can reduce the cost while reducing the cost. The purpose is to:

[0009]

SUMMARY OF THE INVENTION The present invention comprises a carcass layer which is turned from a tread portion to a bead core of a bead portion through a sidewall portion and a steel cord belt layer which reinforces a portion between the carcass layer and the tread portion rubber layer. In the pneumatic radial tire, the steel cord forming the belt layer has a filament diameter of 0.25 mm to 0.31.
1 × N steel cord composed of 3 or 4 filaments of 1 mm in diameter. The cross section of the steel cord in the belt layer has a flat shape having a minor diameter in the tire radial direction. When the pitch is P,
A pneumatic radial tire characterized in that the value of P / d is in the range of 52 to 82.

A pneumatic radial tire in which the steel cord in the belt layer has a short diameter in the tire radial direction and a flattened cross-section having a flatness of 1.15 to 1.50.

Further, the steel cord before vulcanizing the tire is a pneumatic radial tire in which the load at the time of elongation by 0.5% is 39 N to 147 N.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 5 is a half sectional view of a pneumatic radial tire to which the present invention is applied. The tire (T) of the present invention comprises a carcass layer (15), a carcass layer, and a tread rubber layer (16) which are turned from the tread portion (11) through the sidewall portion (12) at the bead core (14) of the bead portion (13). This is a pneumatic radial tire having a general internal structure, provided with two intersecting belt layers (17) made of a steel cord for reinforcing a space between the belts.

The steel cord forming the belt layer (17) has a filament diameter of 0.25 mm to 0.31 m.
It is a 1 × N structure composed of 3 or 4 filaments of m. The filament diameter not only determines the basic properties of the steel cord, such as cord strength, fatigue resistance, and cord rigidity, but also greatly affects wire drawing workability, that is, productivity.

If the filament diameter is less than 0.25 mm, the strength of the belt cord is insufficient, the rigidity is reduced, and the steering stability is reduced. Further, as the diameter becomes smaller, the efficiency of wire drawing during the production of filaments becomes worse and the productivity becomes lower, so that the cost increases as a general-purpose belt cord, which is not preferable. Conversely, if the filament diameter exceeds 0.31 mm, the fatigue resistance is rapidly reduced and cord breakage is apt to occur, and the belt breaks due to the adhesive failure that causes the non-plated portion of the steel cord end at the end of the belt layer to initiate. Edge separation failure is apt to occur, which is not preferable. Further, the cord rigidity is too high, and the ride comfort is deteriorated, which is not preferable particularly for tires for passenger cars.

[0015] The number of filaments is less than 3, that is, 2
In the case of a book, two filaments are arranged in parallel and an asymmetric cross section appears alternately in one pitch. Especially when a thick filament is used, the fatigue resistance under severe conditions such as running on rough roads and running sharply is difficult. Inferior, the cord may be broken. If the number of filaments is 5 or more, the strength and rigidity of the cord become too high, which is not suitable for passenger car tires.
In addition, the cord diameter becomes too large, and the belt layer becomes thick, so that the belt weight increases, which is not preferable.

The steel cord having the 1 × N structure can be produced at a high speed by using an in-out type, out-in type buncher-type stranded wire machine or a large tubular stranded wire machine. Although advantageous, the conventional ordinary twisted 1 × N structure has the disadvantage that the rubber penetration into the cord center is poor and the corrosion resistance is significantly poor as described above.

Therefore, according to the present invention, the steel cord (2) taken out of the belt layer has a diameter of the filament (1) of d,
When the twist pitch is P, a twist configuration in which the value of P / d is in the range of 52 to 82 is proposed.

If the value of P / d is less than 52, the productivity of the cord is poor and the cost is disadvantageous, and the cord weight per cord strength is undesirably large. When P / d exceeds 82, the twist pitch becomes too long, the fatigue resistance is rapidly reduced, and the cord may be broken under severe conditions such as running on a rough road or running sharply.

The steel cord of the present invention can be implemented by twisting with an over-preform having a filament molding rate of 100% or more, but the molding rate must be set to an optimum value depending on the filament diameter and the number of filaments. Here, the preform ratio is a normal tight twisted cord diameter Dc shown in FIG.
In contrast, the ratio is expressed as a percentage of the ratio (De / Dc) of the filament spiral diameter De of the loosely twisted cord in FIG.

The steel cords (FIG. 3) twisted by the over-preform are arranged in parallel at a predetermined interval, covered with rubber by a calender, cut into a predetermined angle and width, and then formed into a tire belt layer as a tire belt layer. Green (unvulcanized) tires. In the next vulcanization step, while the rubber is in a fluidized state by heating, the steel cord of the belt layer is crushed by the vulcanization pressure, and the substantially circular cross section changes to a flat shape (FIG. 1). As shown in the figure, the major axis direction flat in the tire width direction is buried in parallel in the belt layer.

When the ratio (Da / Db) of the major axis Da to the minor axis Db of the circumscribed ellipse of the cord is in the range of 1.15 to 1.50, the number of cords for normal tire strength is reduced. Within this range, steel cords with a flat cross section can be arranged along the width direction of the tire, and the belt layer can be made thinner, leading to a reduction in weight. Can also be maintained. If it is less than 1.15, the cross section of the cord is still close to a circle, and the above-mentioned effect of weight reduction cannot be obtained. To obtain a flat shape exceeding 1.50, a loose cord having a large original cord diameter is required. It is necessary to increase the thickness of the rubber, which increases the weight of the belt layer. Also, adjacent cords that are flattened and arranged side by side by the vulcanization pressure are in contact with each other or the cord interval (FIG. 2, C) is too narrow, and the adhesive strength between the belt layers is low. Edge separation easily occurs.

As a method of manufacturing a steel cord having a flat cross-sectional shape, generally, a steel cord after a stranded wire is rolled through a roll or the like and plastically deformed to adjust the cross-sectional shape. According to this, the loose open cord can be used as it is, and the above-mentioned processing becomes unnecessary, and the cord manufacturing process can be rationalized. In addition, there is no fear of damage to the cord due to the rolling process, for example, peeling of the plating, and the quality is preferable.

The steel cord is rubber-coated in parallel at predetermined intervals by a calender facility and processed into a tire member. If the load at the time of 0.5% elongation of the steel cord before tire vulcanization (hereinafter referred to as 0.5% LASE) is less than 39N, the cord is too loosely twisted, so that an excessive over-preform in the twisting wire process is performed. In other words, it is difficult to manufacture, and it is difficult to obtain uniform cord characteristics, and it is also difficult to control cord tension in a calendering operation at the time of rubber coating, and the quality of the sheet after rubber coating is deteriorated. Also, 14
If it exceeds 7N, the residual stress remaining in the filament will increase, and the cord of the cut portion will be twisted by cutting the sheet after rubber coating, so-called a warping phenomenon will occur, and problems will occur in the workability of cutting, joints and the like. . The above range is an appropriate range in which the cord is crushed by the vulcanization pressure in the vulcanizing step after embedding the rubber, the cross section becomes the flat shape, and the workability in the tire manufacturing process is not hindered, and the twist pitch is And 0.5% LASE adjustment.

(Example) A steel filament (1) having a diameter of 0.28 mm was prepared by using SWRS specified in JIS G3502.
Using 82A material, apply brass plating after primary drawing,
It was manufactured by ordinary wet wire drawing. Three of these were used with an out-in type buncher-type twisting machine, and at a twist pitch shown in Table 1, 0.5% LASE had the values shown in Table 1.
A loose open steel cord (3) having a substantially circular cross section as shown in FIG.

Each of the above steel cords has a width of 4 cm per 5 cm.
Using a usual calendering equipment with the number of three pieces to be driven, rubber coating was performed with a compounding rubber for belt to obtain a steel cord-rubber composite sheet. The sheet is cut and jointed at a predetermined angle and width to obtain a belt material, and has a two-layer belt structure (17) as shown in FIG. 5, having a size of 185 / 70R1.
The radial tire No. 4 was experimentally manufactured for the example and comparative examples 1 to 5.

The belt layer steel cord is flattened in cross section during tire vulcanization as shown in FIG. 1 by the vulcanization pressure, and buried in the belt layer so that the cord major axes are parallel in the belt layer as shown in FIG. You. The oblateness ratio (Da / Db) was obtained by measuring the major axis (Da) and minor axis (Db) of the cross section of 20 steel cords taken out from each tire, and calculating the average value.

The carcass (15) is 1670 dte
One layer of x / 2 polyester cord is used, and other members other than the belt layer and the tire structure are common to the tires of the example and the comparative example.

For each tire, high-speed durability, cord breaking resistance under severe running conditions, rust separation resistance,
The following methods were used to evaluate edge separation resistance and processing / workability. (Hereinafter, separation is abbreviated as separation.) The results are shown in Table 1.

High-speed durability: The result of the pass / fail judgment based on the indoor drum durability test standard conforming to the FMVSS109 standard.

Cord breaking resistance under severe running conditions: 2000 cc domestic tires with air pressure adjusted to 180 KPa
After being mounted on the front wheel of a passenger car and traveling 500 laps at a speed of 20 km / h on a figure 8 with a 20 m diameter circular road in parallel,
An X-ray photograph of the belt layer portion was taken, and the film was observed under magnification to measure the number of creases in the cord.
It was indicated by an index of 0. The smaller the value, the better.

Rust-resistant separation resistance: The tires of the example and the comparative tires each having three drilled holes of 5 mm in diameter reaching the belt layer from the outside of the tread are mounted on the front and rear wheels of a domestic 2000 cc passenger car, respectively. Adjust the air pressure to 180KPa, rough road test course (apply 3cm crushed stone on average,
After running 5,000km on a 4km-peripheral track-like circuit with 2 pools of 5cm in depth and 10m in length containing 5% saline, the tread rubber is disassembled and drilled. The total area of rust separation occurring in the belt layer around the hole was indicated by an index with Comparative Example 1 being 100. The smaller the value, the better.

Edge Separation Resistance: The belt edge portion of the same tire for which the above rust separation resistance was evaluated was dismantled and visually observed.
The degree of separation was compared with the tire of Comparative Example 1 as a reference. Compared to Comparative Example 1, ○ indicates that rust separation was small, and X indicates that rust separation was large.

Workability and workability: The processability such as the rate of scrap generation during the processing of twisted steel cord, the occurrence of trouble during the calendar work, and the presence or absence of warpage during sheet cutting was evaluated in comparison with Comparative Example 1.比較: equivalent to Comparative Example 1, ×:
Inferior with problems.

[0034]

[Table 1] Comparative Example 1 is a steel cord having an ordinary twisted tight structure as shown in FIG. 4 and having a void at the center of the cord.
The tires of the examples and the comparative examples pass the high-speed durability test and have no problem in normal running.

As compared with Comparative Example 1, the embodiment reduces the cord breakage by half under severe running conditions, has excellent rust separation resistance due to the effect of rubber penetration, and has the same edge separation resistance, workability and workability.

In Comparative Example 2, the flatness is large, the cord spacing in the belt layer is small, the occurrence of edge separation is large, and the cord breakage tends to increase due to bending fatigue in the tire radial direction.
In Comparative Example 3, the twist pitch was long, the fatigue resistance was inferior, the cord was frequently broken, and rust separation was observed at the broken part of the cord. In Comparative Example 4, the twist was too loose and 0.5% LASE was used.
And the cord diameter is large, the edge separation resistance is inferior, and trouble occurs in the stranded wire process and the calender process.
In Comparative Example 5, the flattening of the cross section of the cord in the belt layer was small, voids were left in the cord, the rust-resistant separation property was poor, and the sheet was warped due to twisting in the cutting process, and the belt joint was defective. Occurred frequently.

On the other hand, in comparison with a tire of the same size and the same specification in which a conventional 1 × 5 × 0.25 mm steel cord is used for the belt layer, the tire of the present embodiment can realize about 1% reduction in tire weight on average. Was.

[0038]

As described above, the pneumatic radial tire according to the present invention reinforces the carcass layer which is turned from the tread portion to the bead core at the bead portion via the sidewall portion, and between the carcass layer and the tread portion rubber layer. In a pneumatic radial tire having a steel cord belt layer, a steel cord constituting the belt layer has a 1 × N structure including three or four filaments having a filament diameter of 0.25 mm to 0.31 mm. The steel cord section in the layer has a flat shape having a minor axis in the tire radial direction, and the filament diameter is d and the twist pitch is P, and the value of P / d is in the range of 52 to 82. Despite using a simple steel cord structure as the belt layer reinforcement, the belt has excellent durability and contributes to weight reduction. It could be obtained a pneumatic radial tire capable. It is also possible to rationalize the processing steps of steel cord production.

[Brief description of the drawings]

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

FIG. 2 is an enlarged sectional view of a belt layer of the pneumatic radial tire according to the embodiment of the present invention.

FIG. 3 is a cross-sectional view of a steel cord according to an embodiment of the present invention after a stranded wire.

FIG. 4 is a sectional view of a conventional 1 × 3 steel cord.

FIG. 5 is a half sectional view of the pneumatic radial tire of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Filament 2 ... Example steel cord 3 ... Loose open steel cord 4 ... Conventional tight twisted 1x3 structure steel cord 5 ... Void at the center of cord 6 ... Belt layer C ... Within belt layer Cord interval Da: major diameter of the example cord Db: minor diameter of the example cord Dc: cord diameter of the comparative example De: cord diameter of loose open after twisted wire of the example steel cord d: filament diameter T …… Pneumatic radial tire 17 …… Belt layer

Claims (3)

[Claims] 1. A pneumatic radial tire comprising: a carcass layer that is turned from a tread portion to a bead core of a bead portion via a sidewall portion via a sidewall portion; and a steel cord belt layer that reinforces a space between the carcass layer and the tread portion rubber layer. The steel cord constituting the layer is a steel cord having a 1 × N structure composed of three or four filaments having a filament diameter of 0.25 mm to 0.31 mm, and the cross section of the steel cord in the belt layer is in the tire radial direction. Is a flat shape having a short diameter, and the filament diameter is d,
A pneumatic radial tire wherein the value of P / d is in the range of 52 to 82, where P is the twist pitch. 2. The steel cord in the belt layer,
The flatness of the cross-sectional flat shape having the minor axis in the tire radial direction is 1.
2. The method according to claim 1, wherein the range is from 15 to 1.50.
The pneumatic radial tire according to 1. 3. The steel cord before tire vulcanization,
The pneumatic radial tire according to claim 1 or 2, wherein a load at the time of 0.5% extension is 39N to 147N.