JPH04191103A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To enhance weather resistance and cut resistance as well as to make a tire light in weight by letting those such as rupture strength, rupture elongation, counts and side wall gauge be specifically related with one another, letting each carcass cord be composed of a mono-filament organic fiber cord in a flat shape in cross section where each minor axis and minor axis/major axis are specified, and thereby specifying the rubber constituents of side rubber. CONSTITUTION:A radial tire is made up of the layer of a carcass ply where fiber cords are arranged so as to be 90 deg. to 75 deg. to the circumferential direction. In this case, the relation ship indicated by formulas I and II shall be satisfied by the fiber cords characterized by those such as rupture strength Tb(kg), rupture elongation(%), the count N of a crown section and the total gauge S(mm) of a side wall at its thinnest section. And each fiber cord shall be composed of a mono-filament in a flat shape in cross section where a minor axis D1 is 0.2 to 0.5mm, major axis D2/minor axis D1 is 2.0 to 5.0. And side rubber shall contain 15 to 45 parts of ter polymers by weight in a ethylen.propyne.dien series. And the side wall total gauge S shall be less than 4.0mm.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a pneumatic radial tire, and more specifically, the present invention relates to a pneumatic radial tire. The present invention relates to a pneumatic radial tire that achieves weight reduction without impairing weather resistance and excellent side appearance.

(Conventional technology) In recent years, efforts have been made to reduce vehicle displacement, reduce exhaust gas, and improve energy efficiency in order to address the problem of global warming due to an increase in carbon dioxide in the atmosphere and to prepare for the depletion of fossil fuels in the future. being shouted at. Therefore, with regard to tires used in vehicles, it is desired to reduce the rolling resistance during running and to reduce the amount of fuel used by reducing the weight of the tires.

However, current radial tires generally have a tread reinforced with an extremely rigid belt ply layer along the tire circumferential direction, and a carcass fly reinforced with a carcass fly arranged in a direction substantially perpendicular to the tire circumferential direction. Therefore, to reduce the weight of the tire, reducing the amount of rubber in the sidewall and making the side gauge thinner will certainly make the tire lighter, but it will also reduce collisions with curbs while driving. It has become clear that the essential problem is that the side surface of the tire is easily damaged by running over the tire or by being damaged by sharp stones or the like when driving on rough roads, resulting in poor side cut resistance.

In addition, due to the decrease in the side rubber gauge, another problem occurred in that the deformation strain of the side rubber increased during transfer, and the ozone crank resistance of the side rubber surface during actual driving also deteriorated.

On the other hand, multifilament twisted fiber cords are common for polyester fiber cords, rayon fiber cords, and nylon fiber cords, which are commonly used for the carcass fly of many tires. It is a cord made by twisting together. Each filament is extremely thin, typically 10 to 30 microns in diameter, and is flexible and flexible against bending. Further, the cross-sectional shape of such a cord is generally approximately circular.

In addition, diene rubbers such as natural rubber and polybutadiene rubber have traditionally been used as side rubber compounding polymers, and in order to impart ozone resistance, crack resistance, and heat aging resistance to these rubber components, p-phenylenediamine It was common to add amine anti-aging agents and waxes.

(Problem to be solved by the invention) However, in the conventional method of simply increasing the strength of polyester fiber cords, etc. to improve side cut resistance, the cord diameter naturally becomes large and the side gauge S is made thinner. There was a problem in that the original purpose of reducing the weight of tires could not be achieved.

Further, even if an anti-aging agent is added, thinning the side gauge lowers the side rigidity and increases the amount of deformation (distortion) of the side portion, resulting in deterioration of ozone resistance.

Furthermore, if a large amount of an amine anti-aging agent is blended in order to improve ozone resistance, the discoloration property will deteriorate and the tire appearance will be significantly impaired.

Therefore, an object of the present invention is to reduce the weight of a pneumatic radial tire without impairing the cut resistance of the sidewall part of the tire from road curbs or when driving on rough roads, the weather resistance against ozone cracks, and the side appearance. Our goal is to provide technology that can achieve this goal.

(Means for Solving the Problems) As a result of intensive research to solve the above problems, the present inventors have determined the fiber material of the carcass fly cord to be used, the ratio of the short axis to the long axis of the cross-sectional shape of the cord, By setting a certain relationship between the strength and elongation physical property value, the number of strokes, and the side thickness, and the cord diameter range under specific conditions,
The inventors have discovered that the above object can be achieved and have completed the present invention.

That is, the present invention provides a radial tire in which the fiber cords are formed at an angle of 90'' to 75 degrees with respect to the tire circumferential direction and have one carcass fly layer, in which the fiber cords have a flat cross-sectional shape made of organic fibers. The cord taken out from the tire has the following formula: A > 3990-2503 (where Tb is the breaking strength (kg) and Eb is the breaking elongation (%).
), N is the number of strokes at the crown center (number of strokes/
5 cm), S indicates the sidewall total gauge at the thinnest part of the tire sidewall), and the short axis of the cord diameter is within the range of 0.2 to 0.5 g. Yes, and the aspect ratio of the short axis D1 and the long axis D2 (Dz
/DI) is within the range of 2.0 to 5.0, and the ethylene-propylene-diene terpolymer is used as the rubber component of the side rubber constituting the surface layer of the tire sidewall part. The present invention relates to a pneumatic radial tire that uses a rubber component containing 15 to 45 parts by weight per part of the tire, and has a sidewall total gauge S of 4.0 fins or less at the thinnest part of the tire sidewall.

The sidewall total gauge S at the thinnest part of the tire sidewall is preferably 2.0 to 3.5 a
It is m.

Also, the oblateness ratio (D) between the short axis D+ and the long axis D1.

/D, ) is preferably in the range of 2.5 to 5.0, more preferably 3.0 to 5.0.

(Function) Currently, radial tires generally use a carcass fly having a multifilament fiber twisted cord made of polyester, rayon, nylon, or the like. If the carcass of the polyester multifilament fiber twisted cord, which has been commonly used in the past, is used as it is as a carcass fly material constituting a lightweight tire with a thin side gauge as the object of the present invention, as described above,
The side cut resistance performance decreases, and in order to improve this side cut resistance performance, if a high strength twisted thick yarn cord is used as a polyester multifilament fiber,
The cord diameter increases, making it difficult to manufacture tires with a thin side gauge, which is the original objective.

In contrast, the monofilament cord used in the present invention, which has a flat cross-sectional shape and is made of organic fibers, allows the cord gauge to be made thin while maintaining high strength, and its bending rigidity is higher than that of multifilament fibers. Because it is extremely high compared to the cord, it was confirmed that even if the tire side gauge was thinned, side deformation such as when running over a curb was suppressed, and the cut and burst resistance was good.

Furthermore, even when the above-mentioned flat monofilament cord is used for the carcass fly, the breaking strength Tb of the cord of the tire is
If the toughness per width A (= 1/2 x Tb x Eb x N) determined from the cutting elongation Eb and the number of driving strokes N is below a certain limit value, the side cut resistance is still insufficient, and this limit value is It has been empirically found that it changes depending on the thickness of the side gauge S. This is because the ease of bending of the tire side part changes depending on the side gauge S, and the smaller S is, the easier the side part is to bend when deformed by colliding with a curb, etc., so the rim flange and the curb or rock etc. It is interpreted that this is because the side part becomes more likely to get caught between the two and the side cut resistance changes.

Furthermore, the short diameter of the cord needs to be in the range of 0.2 to 0.5M in order to achieve the objective of the present invention, which is tire weight reduction. If the minor diameter D1 is 0.5 m, the tire side gauge cannot be made sufficiently thin, and if it is less than 0.2IlI11, the bending rigidity of the cord will not be sufficiently high.

Furthermore, the cross-sectional shape of such a cord must be an ellipse, a rectangle with rounded corners, or a flat shape such as a rectangle as shown in FIGS. 1(a) and (b), and the minor axis D+ of this cord is The aspect ratio (Dt/D,) with the major axis Dt is 2
．． It is necessary to be within the range of 0 to 5.0. Dt
/ D + is less than 2.0, the aspect ratio is too small, and the cord thickness is not sufficient when D is made small.
On the other hand, if the cord strength exceeds 5.0, the cord bending rigidity will decrease, and since the cord width is too wide, peeling between the cord and the rubber will easily occur during tire molding, which is not preferable.

As the material of the flat monofilament cord according to the present invention, melt-spun polyamides and polyesters can be used, and their heat resistance stability, deterioration resistance in rubber,
From the viewpoint of fatigue resistance, 6.6-nylon, 6-nylon, polyethylene terephthalate, polyethylene naphthalate, etc. can be suitably used.

In order to achieve the target weight reduction in the present invention, that is, thinner gauge of the side part, it is preferable that the total gauge of the sidewall at the thinnest part of the sidewall is 3.5 W+ or less as described above. but,
For relatively large tires with heavy regular loads and tires that require high side cut resistance such as Jeep tires and rally tires, the side gauge is 411II.
Even if it is more than II, a sufficient weight reduction effect can be obtained compared to the conventional one.

By the way, the thinner the side gauge, the better for weight reduction, but the minimum thickness of each of the innermost inner liner layer, carcass fly layer, and surface side rubber layer to prevent leakage of the air filled in the tire. The practical lower limit of the possible range based on current manufacturing technology is 2.0.

Next, the polymer constituting the rubber exposed on the side surface of the tire of the present invention will be explained.

When using conventional compounded rubber based on polymers such as natural rubber and polybutadiene rubber, if the tire side part is made thinner, it will be stretched due to internal pressure filling and the side surface will be damaged due to increased bending deformation during traveling. Since the distortion is larger than that of conventional tires, the occurrence and propagation of ozone cracks from the side portions to the upper part of the rim flange is promoted, resulting in a poor appearance.

However, in the present invention, a predetermined amount of ethylene-propylene-diene terpolymer (EPDM), which is a polymer with excellent ozone resistance, is used as the rubber component of the side rubber that constitutes the surface layer of the tire sidewall. As a result, the objectives of improving ozone resistance and reducing weight (thinner gauge) can be better achieved, and the amount of amine anti-aging agent and wax used can also be reduced, resulting in an even better side appearance. .

In other words, when a rubber compound made of the weather-resistant polymer EPDM, which does not contain C=C double bond gel in the polymer, is placed on the side surface layer, the occurrence and progression of ozone cracks can be suppressed, and anti-aging agents and waxes can be prevented. Since only a small amount is required, there is no discoloration caused by these factors, and it is possible to maintain a good side appearance. In such a case, the side rubber may have a single layer structure using EPDM, or the surface may be a rubber using EPDM, and a conventional diene polymer rubber such as natural rubber or polybutadiene rubber may be placed inside. It can also have a two-layer structure or the like.

In addition, in order to improve side cut resistance, by adding a so-called protect line, which is a thick annular raised part of the side part in the circumferential direction of the tire, bending deformation of the side part is suppressed and side cut resistance is improved. It can also increase credibility.

Furthermore, in the present invention, as shown in FIG. 2, the height H from the tip of the bead filler rubber to just above the bead wire in the cross section of the tire, and the tire height from the inner surface of the crown center to just above the bead wire are determined by the following formula: 0 It is necessary to satisfy the relationship: .5≧H/L≧0.2. If the value of H/L exceeds 0.5, the bead filler rubber area is too large.
The effect of thinning the side gauge, which is the objective of the present invention, is not fully utilized, and weight reduction cannot be achieved. on the other hand,
If the value of H/L is less than 0.2, the side bending point becomes low, the side part becomes easily deflected, the side cut resistance decreases, and the tire lateral rigidity decreases, resulting in insufficient handling stability. Undesirable.

(Example) Next, the present invention will be explained by examples.

Side rubber was compounded according to the compounding recipe (parts by weight) shown in Table 1 below, and various test tires of size 145SR13 were produced. The carcass fly cords for these tires are made by the usual method.The multifilament fiber cords are made by first twisting and final twisting the fiber yarns and then being twisted together, while the monofilament cords are made by applying adhesive and heat treatment without heating. It was made into a deep code.

The monofilament cord used in this example was obtained according to the usual monofilament melt spinning method,
It is obtained by extruding a molten polymer through a predetermined die, cooling it through an air gap and a water bath, and then stretching it.

The cross-sectional shape used was rectangular with rounded corners as shown in FIG.

The ratio of the major axis D2 to the minor axis D1 was adjusted to a certain degree by changing the spinneret.

Further, as shown in FIG. 3, the cord is topped and top-bottomed with brie coating rubber so that each gauge on the top and bottom of the cord is 1/2 of the dip cord gauge D.
A rubberized sheet was created.

Here, the flat monofilament cords were arranged in parallel in the longitudinal direction as shown in FIG. still,
One piece of such carcass fly cord was used for each tire production.

The side rubber of the test tires was adjusted to various thicknesses using the formulations shown in Table 1.

Table 1: O-Tolylguanidine The various properties in this example were measured as follows.

After removing as much rubber from the surface of the carcass fly cord taken out from a rattan Y tire with scissors as possible without damaging the fibers, the strength and elongation measurement method of JTS L 1017 was performed. According to
The breaking strength Tb (
kg) and elongation at break Eb (%) were determined.

Such a code sample has a diameter of 25 mm centered around the tire side part.
The sample length was cm, the tensile speed was 3001IIllZ, and the average value of 10 measurements was used.

Cleanly cut the center part of the tire crown along the circumferential direction of the tire, then place a ruler on the cut surface of the cut sample.51! The number of codes existing within the IIn width is set to 0.
．． It was calculated in units of five. Do this for three locations around the tire circumference, average the three values, and calculate N (lines/5 cm
).

Originally, the number of implants should be compared using the number of implants on the side part, but as the number of implants per unit width becomes denser from the side part to the bead part, it is difficult to specify the numerical value, so as an alternative value, Measurements were taken at the center of the tire crown, where it is easy to

In addition, the diameter D (D, ) of the cord cross section at the cut surface in the side thickness direction and, for flat monofilament cords, the major axis in the cord arrangement direction (see Figure 3) were also measured to the nearest 0.01 mm using calipers. did. code 1
The values obtained by measuring 0 lines are averaged, and D, D, , Dt(
Cabinet).

Cut the tire side part in the radial direction and measure the gauge at the thinnest part of the tire sidewall as shown in Figure 2 to 0.1 am.
Measured to the nearest unit. Calculation measurements were taken at three locations around the tire circumference, and the three values were averaged to determine S.

4. Attach the side cut test tire to the vehicle and set it to a height of 120 mm as shown in Figure 4.
The vehicle ran over a vertically steep curb with a corner curvature of 20 mmR at a speed of 15 b/hour from an angle of approach of 15 degrees with the curb. The internal pressure of the same test tire is 3
kg/Cll1! The internal pressure P (kg/cm") at which the cut burst occurred at the side portion was determined.

When the internal pressure is below P, the side parts are easily deflected and all cut bursts occur, so the lower P is, the better the side cut resistance is, and conversely, the higher P is, the more side cuts are likely to occur, and the side cut resistance is judged to be worse. did. The P value of the control tire is Po, and the P value of the test tire is P with respect to this Po.

- When the paper is closed, the side cut resistance index C is expressed by the following formula, P.

It can be expressed as This test was conducted on three identical tires, and the index C was determined based on the average P value of the three tires.

5. Ozone Cooling: Each test tire was subjected to an ozone spray drum test, and ozone cracks on the sides were visually compared.
Comparative rankings were made using a four-level evaluation system: medium, small, and very small.

Side discoloration of the tires that had completed the ozone spray drum test described in item (5) above was visually compared for large, medium, and small tires.

The results obtained are shown in Table 2 below.

Incidentally, various test tires of size 185/70SR14 were similarly manufactured and various tests were conducted as described above.

These results are also shown in Table 2 below.

The following was confirmed from Table 2.

The tire of Conventional Example 1 uses the same multi-polyester fiber cord as the carcass material as the commercially available structure, and has a thick side gauge of 4.8 ff1m.

On the other hand, the structure of the carcass fly material is the same as in Conventional Example 1, and only the side gauge S is simply 1.5 mm < L.

In Comparative Example 1 where the thickness was 3.3 mm, the side cut resistance index C was 57, which was significantly inferior, as described above.

In this tire, while using polyester fiber as the cord material of the carcass fly, we produced a prototype with a high strength cord, and produced a trial tire with side cut resistance comparable to Conventional Example 1. 2/2
Comparative Example 2 using a thick yarn cord (2 1500 d raw yarns are twisted together in the first twist, and the two yarns are twisted together in the final twist) finally has a side cut resistance index C equal to that of the conventional example 1. I found out that it was more than that. However, in this case, the cord diameter is as thick as 0.94-, and the side total gauge is 4.
．． 2M, and it was not possible to obtain a lightweight tire with thin side walls, which is the objective of the present invention.

On the other hand, in Example 1 using the flat monofilament cord of 6,6-nylon fiber according to the present invention, a side cut resistance index of 102 could be obtained. At this time, the short diameter D1 of the cord was as thin as 0.42 mm, and the side total gauge could be made significantly thinner as 2.6 mm. still,
In this case, the toughness A per width is 3382kg・%
/ 5 cm.

Furthermore, in Comparative Example 3, the same flat monofilament cord as in Example 1 was used, but when the number of implants N was decreased, the side cut resistance index decreased to 94. On this occasion,
Toughness A per width was 1649. That is,
It has been found that even if a flat monofilament cord is used, sufficient side cut resistance cannot be ensured if the toughness A value per width is below a certain limit.

On the other hand, as in Example 2, when the denier configuration of the same type of flat monofilament cord as in Example 1 is changed, the side total gauge S is 2. Even when it is made extremely thin to I Im, the side cut resistance index C is 104,
It was found that side cut resistance could be ensured.

By the way, regarding the ozone crack resistance after subjecting the tires of Examples 1 to 3 to an ozone spray drum test, these Examples showed that the composition A shown in Table 1 was compared with the composition system A containing EPDM as a rubber component. Since the ozone crank resistance level and discoloration resistance are substantially replaced by conventional example 1,
It turns out that it can be improved to a significantly better level than the previous one.

In Comparative Example 4, in which the breaking strength of the cord was reduced, the side cut resistance was 91 because the toughness per radius was not sufficient.
The results were inferior to the control of Conventional Example 1.

Next, the results of various tests conducted on various test tires of size 185/705R14 will be discussed.

The tire of Conventional Example 2 uses a carcass fly made of multifilament polyester fiber cord, which is the same as the commercially available structure, and the side rubber gauge is as thick as 5.8.

On the other hand, in Example 4, in which the flat monofilament cord according to the present invention was used instead of the cord in Conventional Example 2, and an appropriate number of strokes was selected, even if the side gauge S was significantly thinned to 3.5 m, We were able to secure side cut resistance equal to or better than that of the control. The short diameter D1 of the cord at this time was 0.37 mm. Also, in Example 5, in which polyethylene terephthalate was used as the cord material of the carcass fly material, the side cut resistance was similarly good, being 100.

By the way, the composition of the side rubber in Examples 4 to 6 is as follows:
Unlike Conventional Example 2, which used the conventional compounding system containing only diene polymers in compounding system A, side rubber compounding system B was used, so as in Examples 1 to 3, ozone crank resistance and discoloration resistance were significantly improved. improved.

However, as in Comparative Example 5, when the breaking strength of the cord of Example 7 was lowered, the toughness per width was insufficient, so the side cut resistance index C was 91.

By the way, for the nine cases of Examples 1 to 6 and Comparative Examples 3 to 5,
The fifth graph plots the relationship between side cut resistance index C and side rubber gauge S and toughness per width A.
It is a diagram. In the figure, the subscript number of each point is the side cut resistance index C. From these data, even in the carcass fly using the flat monofilament cord according to the present invention, A is S.
It was confirmed that sufficient side cut resistance can be ensured only when the relationship A>3990-25O3 of the present invention is satisfied.

(Effects of the Invention) As explained above, in the pneumatic radial tire of the present invention, the fiber material of the carcass fly cord used, the ratio of the short axis to the long axis of the cross-sectional shape of the cord, the strength and elongation physical property values of the cord, etc. By setting a certain relationship between the number of strokes, side thickness, and cord diameter range under specific conditions, the tire sidewall is lightweight and resistant to road curbs and when driving on rough roads. It has excellent cutability, and by specifying the main component polymer of the rubber exposed on the tire side surface, it has the effect of maintaining good side appearance without impairing weather resistance against ozone cracks etc. can get.

[Brief explanation of drawings]

Figures 1 (a) and (b) are cross-sectional views of a flat monofilament cord, Figure 2 is a partial radial cross-sectional view of a pneumatic radial tire, and Figure 3 is a cross-sectional view of the crown center portion of a pneumatic radial tire. Figure 4 is a cross-sectional view of the curb stone used in the side cut resistance test; Figure 5 is a graph showing the relationship between the side cut resistance index C and the side gauge S and the toughness per width A. It is. Figure 1 (a) (b) Figure 3 f 2 3456 Said F゛ gauge S (m)

Claims (1)

[Claims] 1. A radial tire having one carcass fly layer in which the fiber cords form an angle of 90° to 75° with respect to the tire circumferential direction, wherein the fiber cords are made of organic fibers and have a flat cross-sectional shape. The cord taken out from the tire has the following formula: A=(Tb×Eb)/2×NA A>3990-250S (where Tb is the breaking strength (kg) and Eb is the breaking elongation ( %
), N is the number of strokes in the crown center area (drives/5
cm), S indicates the sidewall total gauge (mm) at the thinnest part of the tire sidewall), and the short axis D_1 of the cord diameter of the cord is 0.2 to 0.
5 mm, and the aspect ratio (D_2/D_1) of the short axis D_1 and the long axis D_2 is within the range of 2.0 to 5.0, and the rubber of the side rubber forming the surface layer of the tire sidewall part. A rubber component containing 15 to 45 parts by weight of an ethylene-propylene-diene terpolymer based on 100 parts by weight of the total rubber component is used, and the sidewall total gauge S at the thinnest part of the tire sidewall is 4.0 mm. A pneumatic radial tire characterized by: 2. Height H of the bead filler rubber in the tire cross section
The pneumatic radial tire according to claim 1, wherein the pneumatic radial tire satisfies the following relationship with respect to the height L of the tire: 0.5≧H/L≧0.2. 3. The pneumatic radial tire according to claim 1 or 2, wherein the sidewall total gauge S at the thinnest part of the tire sidewall is 2.0 to 3.5 mm.