JPS61119408A - Pneumatic tire with durability improved - Google Patents

Abstract

PURPOSE:To decrease both shear stress and shear strain of a belt by allowing coating rubber used for coating belt cords that compose a belt, and end rubber used for coating the both sides of the above mentioned coating rubber, to be made of a composition of rubber with short fibers that have the stated dimension and are mixed with the stated ratio. CONSTITUTION:A pneumatic tire 1 includes a carcass ply 5 which is composed of a rubber coated cord layer, a belt 10 which has numbers of layers with belt cords 6 located on the outer circumference of the carcass, and a tread 11 located on the outer circumference of the belt. The belt cords 6 are coated with coating rubber 7, the both sides 7a of which (7) are coated with end rubber 8. In this case, two adjacent ones, at least, of the above mentioned rubber 7 and 8 are made of a composition of rubber with short fibers of more than 5pts.wt. Here, the short fibers have an average diameter of smaller than 1mum, and a ration L/D of more than 8 where L represents an average length of the short fibers while D represents their average diameter. And the short fibers which are included in each of the rubber 7 and 8, are arranged so as to form the angles of from 0-30 deg., and from 45-90 deg. respectively to the direction of the belt cord 6.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to pneumatic tires with improved durability, such as belt coating rubber constituting a belt or belt end rubber covering the end of the belt. This invention relates to a pneumatic tire whose durability is significantly improved by using rubber containing fibers.

(Prior art) The durability of tires has been greatly improved by changing from bias structure tires to radial structure tires, but due to the performance of automobiles and the expansion of highways, the high-speed performance, especially durability, of tires has improved. We need to raise that level.

An example of a conventional pneumatic radial tire with excellent durability is the one shown in FIG.

In FIG. 3, 31 is a conventional pneumatic radial tire, and the pneumatic radial tire 31 has a bead portion 32,
It has a carcass ply 33, a belt 34 and a trend 35.

The highly durable radial tire 31 has been made with various improvements; for example, the belt cord 36 of the belt 34 has been changed from a textile cord such as nylon or polyester to a steel cord, and also from a steel cord to a Kevlar cord aimed at reducing weight. It is changing to Also, in terms of structure, the belt layers 34a and 34b constituting the bell 1-34 are
, 34c.

Efforts have been made to reduce the glabellar shear strain that occurs between the 34 and d. This glabellar shear strain occurs at the end 34 of the belt 34.
It becomes large at f, causing a peeling failure.

This is the belt cord 36 at the end 34f of the belt 34.
This is because the Young's modulus of the belt rubber 37 is greatly different from that of the belt rubber 37, and this shear strain causes a large stress concentration, and peeling failure occurs from this end 34f. Therefore, in order to relieve the shear stress, the belt layers 34a, 34b, 3 of the end portion 34f, as indicated by the number 3 in FIG.
Measures have been taken such as increasing the distance between 4c and 34d.

However, even if such measures are taken, the durability is not sufficient, and in the presently advanced tires, the end 34f of the belt 34 has a small angle (for example, 5 degrees) with respect to the circumferential direction. A reinforcing layer 39 arranged in the following manner is arranged to provide this high-speed durability.

However, in this case, the elastic modulus in the direction of arrangement of the cords is too high, which not only greatly reduces the vibration riding comfort performance, but also
There is also a problem in that the steering stability during low-speed driving also deteriorates.

(Object of the Invention) Therefore, the present invention reduces the shear stress and shear strain that occurs inside the belt of a tire and near the belt end due to tire air pressure, heavy load loading, and long-term high-speed running, and in particular, To provide a pneumatic tire with improved durability by minimizing in-plane shear strain occurring between the eyebrows of the belt layer and improving the durability of the belt without changing the rigidity of the belt as a hoop. purpose.

(Structure of the Invention) A pneumatic tire with improved durability according to the present invention consists of a bead wire located at a bead portion and a rubberized cord layer in which a large number of cords are arranged in parallel, and both ends are folded back at the bead portion. A carcass ply is secured to a bead wire, and a belt cord is located on the outer peripheral surface of the carcass ply and consists of multiple layers, each layer being arranged at a predetermined angle, and this belt cord is covered with belt coating rubber. In a pneumatic tire comprising a belt in which both ends of the belt coating rubber in the axial direction are covered with belt end rubber, and a tread located on the outer peripheral surface of the belt, the belt meets all of the following items A to A. It is characterized by satisfying the following.

A. At least two adjacent belt coating rubbers and at least two adjacent belt end rubbers have an average diameter of 1 μm or less, and the ratio of average length to average diameter (L/D)
It consists of a rubber composition containing 5 parts by weight or more of short fibers having a value of 8 or more.

B. The angle between the orientation direction of short fibers in the belt coating rubber and the belt cord is 0 to 30 degrees.

The angle between the orientation direction of short fibers in the C0 belt end rubber and the belt cord is 45 to 90 degrees.

D. The angle between the orientation direction of the short fibers in the belt end rubber and the orientation direction of the short fibers in the belt coating rubber adjacent to the belt end rubber is 6 to (equal) degrees.

In addition, in the reinforcing layer of short fibers after vulcanization, the elastic modulus M1 at 50% strain when pulled in the direction in which the short fibers are arranged, and the elastic modulus M1 at 50% strain when pulled in the direction perpendicular to the direction in which the short fibers are arranged. It is preferable that the ratio of elastic modulus M2 (M 1 /M2) is 2.5 or more. Further, it is preferable that the short fibers are made of a thermoplastic polymer having an amide group, and are grafted via a condensate of a rubber portion and a phenol formaldehyde resin.

In the present invention, the average diameter of the short fibers is limited to 1 μm or less for the following reason.

Originally, when strain (stress) is applied to short fibers, large shearing stress is applied to both ends of the short fibers, and due to the shear stress, cracks occur and grow from both ends of the short fibers, resulting in a short fiber reinforced rubber composition. There was a strong tendency to produce large leaps characteristic of . It is known that the shear stress greatly depends on the shape of the short fibers, and naturally, the smaller the short fibers are, the smaller the strain applied to both ends of the short fibers, and the smaller the shear stress. .

As the short fibers become smaller, the reinforcing effect per short fiber becomes smaller, but since the number of short fibers increases, overall, the inclusion of short fibers increases fatigue resistance, especially creep after repeated strain. can be prevented. Furthermore, it is possible to exhibit high elastic modulus, excellent cut resistance, and high anisotropy utilized in the present invention, which are the objectives of short fiber reinforcement.

In order to bring out the merits of the short fiber reinforcement mentioned above, it is necessary that the aspect ratio (L/D) is 8 or more,
In order to maintain this aspect ratio at 8 or more and reduce the shear stress applied to both ends of the short fibers to a level that does not pose a problem,
The average diameter of short fibers must be 1 μm or less.

In the present invention, the reason why the amount of short fibers is limited to 5 parts by weight or more is that if it is less than 5 parts by weight, the effect of reinforcing short fibers, which is the object of the present invention, cannot be expected. (In the present invention, short fiber orientation and short fiber arrangement mean the same thing).

In the present invention, it is preferable that the angle between the orientation direction of short fibers in the belt coating rubber and the belt cord is 0 to 30 degrees. Further, it is preferable that the angle between the orientation direction of the short fibers in the belt end rubber and the orientation direction of the short fibers in the belt coating rubber adjacent to the belt end rubber is 45 to 90 degrees. This is because the effect of fiber reinforcement can be maximized. The angle θ between the arrangement direction of the belt cord and the orientation direction of the short fibers in the short fiber reinforced rubber is measured at an "acute angle".

In the present invention, in the short fiber reinforced rubber after vulcanization, the elastic modulus M1 when pulled in the direction of arrangement of the short fibers is
and 50% pulled in the direction perpendicular to the short fiber arrangement direction.
It is preferable that the ratio of elastic modulus M2 under strain (Ml/M2) is 2.5 or more, which indicates the degree of orientation of the short fibers, and contains short fibers oriented to this degree. As mentioned above, the short fiber reinforced rubber composition produces the greatest effect when the angle θ between the belt cord direction and the short fiber arrangement direction in the belt end rubber is set to 45 degrees to 90 degrees.

In the present invention, it is preferable to use a thermoplastic polymer having an amide group as the material for the short fibers.
This is because the short fibers have excellent fatigue resistance because polymers having amide groups are easy to crystallize, and orientation of crystals is relatively easy, making it difficult to form spherulites. Further, the crystal melting point of a polymer having an amide group is usually 200° C. or higher, and there is no problem in terms of heat resistance.

In the present invention, it is preferable that the short fibers and the rubber portion are grafted via a condensate of phenol formaldehyde resin. This is because the fatigue resistance of rubber can be improved.

However, the material of the short fibers is not limited to this example;
It may also be a thermoplastic polymer such as polybutadiene or isotactic polypropylene.

Examples will be described in more detail below.

(Examples 1 to 5) Example 1 shows that the pneumatic tire of the present invention has significantly improved durability performance compared to conventional tires.

(1) Manufacturing method of reinforced rubber composition The temperature was 150° C., and the rotor rotation speed was 1100 rpm. Inside the OC Banbury mixer (manufactured by Kobe Steel),
Natural rubber 140 with a Mooney viscosity of 25 at 100°C
0 g and 14 g of N-(3methacryloyloxy-2-hydroxypropyl)-N'-phenyl-P-phenylenediamine [Tsukrank G-1, manufactured by Ohmukai Shinko Co., Ltd.] were added, and the wire was heated for 1 minute. Next, 6-nylon (product name:
1030B, manufactured by Ube Industries, melting point 221°C, molecular weight 30
000) and kneaded for 7 minutes.

During this time, the temperature inside the Banbury mixer rose to 232°C, and the 6-nylon melted. Next, 30 g of novolak-type phenol formaldehyde initial condensate (manufactured by Meisho Kasei ■, trade name 550PL) was added, and after kneading for 7 minutes, 3 g of hexamethylenetetramine was added, and 2.5 g of hexamethylenetetramine was added.
After kneading for a minute (during which time the temperature of the batter of the Banbury mixer was 230° C.) to cause a graft reaction, the mixture was dropped to the bottom of the Banbury mixer and taken out.

Next, the obtained kneaded product was prepared using a 30 m circular die with a nozzle inner diameter of 21 and a length to inner diameter ratio (L/D) of 2.
Using a mφ extruder (manufactured by Ikegai Co., Ltd.), set the temperature at 235
The extrudate was extruded into a string at 0.degree. C., cooled and solidified with cooling water at 0.degree. C., and then wound onto a bobbin via a guide roll at a draft ratio of 9 at a speed of 35 m/min. After vacuum drying this roll for a day and night at room temperature to remove adhering water, approximately 500 rolls were bundled into a sheet (2 mm thick, medium 15 mm).
0 mm), and roll this sheet material with a roll gap of 0.2
A reinforced rubber composition (sample 1) reinforced with short fibers was obtained by rolling the rubber composition about 10 times with a pair of rolling rolls at a temperature of 60°C.

(2) Short fiber reinforced rubber and rubber sheet layer F (reinforcement layer)
The above-mentioned reinforced rubber composition was blended with the ingredients and blending ratios shown in Table 1, at a temperature of 70°C and a rotor rotation speed of 7Or.
, p, and m were mixed in an OCc Banbury mixer (manufactured by Kobe Steel) to prepare a rubber composition 1 made of short fiber-reinforced rubber.

For comparison, Rubber Composition 2 and Rubber Composition 3 were created using the same blending components and blending ratios that did not include the reinforced rubber composition, but with the same manufacturing process. Furthermore, these Rubber Compositions 1 to 3 were formed into reinforcing layers consisting of rubber sheet layers having a predetermined thickness using an ordinary rubber roll.

Since the rubber composition 1 contains a predetermined amount of short fibers, it becomes the rubber sheet layer F of the present invention in which the short fibers are oriented in the direction in which the rubber roll is pulled out.

Table 1 (a) Liquid IR is LIR manufactured by Clarei Sobrene Chemical ■
-50.

(b) Novolac-type cashew-modified phenolic resin is a novolak-type phenolic resin modified with 40 parts by weight of cashew oil per 100 parts by weight of phenol.

(C) Anti-aging agent is Tsukurak 8 manufactured by Daien Shinko Chemical Industry Co., Ltd.
10-NA.

(d) Nobs are Tsukusera MS manufactured by Ohmukai Shinka Kasa Kogyo ■
It is A-G.

(e) Amount of short fibers (parts by weight) indicates the amount of short fibers in Sample 1 as the amount of short fibers contained per 100 parts by weight of rubber in the rubber composition.

(3) Tire structure Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows a pneumatic tire with improved durability according to the present invention.

First, the configuration will be explained. As shown in FIG. 1, the pneumatic tire 1 according to the present invention consists of a bead wire 3 located in a bead portion 2 and a rubberized cord j-5a in which a large number of cords are arranged in parallel, and both ends 5b are connected to the bead. Part 2
a carcass ply 5 which is folded back and secured to the bead wire 3; and a belt cord 6 which is located on the outer peripheral surface of the carcass ply 5 and is composed of a plurality of layers (four layers in the embodiment), each layer being arranged at a predetermined angle. (for example, a steel cord), the belt cord 6 is covered with a belt coating rubber 7, and both axial ends 7a of the belt coating rubber 7 are covered with belt end rubber 8, and an outer peripheral surface of the belt 10. and a tread 11 located at. The belt 10 consists of four belt layers, and each belt layer includes a first belt layer 10a, a second belt layer 10b, a third belt layer 10C, and a fourth belt layer 10d radially outward from the outer peripheral surface side of the carcass ply 5. They are provided in this order. The belt coating rubber 7 and the belt end rubber 8 have an average length of 1 μm or less, and a ratio of average length to average diameter (L
A rubber sheet layer F made of a rubber composition containing 5 parts by weight or more of short fibers having /D) of 8 or more is used. The angle between the orientation direction of the short fibers in the belt coating rubber 7 and the belt cord 6 is 0 to 30 degrees, and the angle between the orientation direction of the short fibers in the belt end rubber 8 and the belt cord 6 is 45 degrees. The angle between the orientation direction of the short fibers in the belt end rubber 8 and the orientation direction of the short fibers in the belt coating rubber 7 adjacent to the belt end rubber 8 is 45 to 90 degrees.

In addition, the elastic modulus M1 at 50% strain when stretched in the direction of arrangement of short fibers in the reinforcing layer of short fibers after vulcanization (i.e., rubber sheet layer F), and the modulus of elasticity M1 at 50% strain when pulled in the direction of arrangement of short fibers, The elastic modulus M2 (Ml/M2) at 50% strain under tension is 2.5 or more.

Further, the short fibers are made of a thermoplastic polymer having an amide group, and are grafted to the rubber portion via a condensate of a phenol formaldehyde resin.

(4) Tire Manufacture and Performance Test Results (Function) When manufacturing a tubeless radial tire using the above-mentioned rubber sheet layer F, first, the components are the bead wire 3, stiffener, rubberized cord layer 5a, and belt cord. 6. Prepare belt coating rubber 7, belt end rubber 8, rubber for tread 11, and sidewalls. Here, belt coating rubber 7 and belt end rubber 8
is the belt 1 shown in the first example of Table 2-1 and Table 2-2.
Set the configuration to 0. Next, using the rubber sheet layer F of the rubber composition containing the aforementioned short fibers, the short fibers are made to have a predetermined orientation. Next, the oriented belt coating rubber 7 is applied to both sides of the belt cords 6 arranged in parallel using a roll, and the angle between the orientation direction of the short fibers and the belt cords 6 is 0 to 30 degrees. Build layers. Next, belt layers IQa, 10b, 1 are formed by attaching oriented belt end rubber 8 of a predetermined width to the exposed portions of the belt cord 6 at both ends of the belt layer.
Create 0c and 10d. At this time, the angle between the orientation direction of the short fibers and the arrangement direction of the belt cords 6 is set to be 45 to 90 degrees. Next, the above-mentioned members are attached in a predetermined order using a predetermined tire molding machine to manufacture a so-called green case. Here, when pasting, belt layers 10a, 10b, 10c using the belt coating rubber 7 and belt end rubber 8 containing the aforementioned short fibers are formed.
, 10d is a first belt layer 10a, a second belt layer 10b, a third belt layer 10c, and a fourth belt layer 10d in the order radially outward from the outer peripheral surface of the carcass ply 5, and
The belt is attached so that the orientation direction of the short fibers in the belt end rubber 8 forms an angle of 45 to 90 degrees with the orientation direction of the short fibers in the adjacent belt coating rubber 7. Next, the green case is heated under pressure in a vulcanizer to produce a product tire.

In addition, a rubber sheet layer that does not contain short fibers is used to
Tires of Examples and Comparative Examples are manufactured in the same manner as in the Examples.

The tires of these examples and comparative examples were filled with air at a predetermined pneumatic pressure, a predetermined load was applied, and then subjected to a long-term continuous running test (slip angle durability drum test,
A crack test (hereinafter simply referred to as a crack test) after running on a rough road (hereinafter simply referred to as a crack test) is performed on the road surface. (Hereinafter, the above-mentioned two tests will be simply referred to as a performance test) The results of these tests are shown in Tables 2-1, 2-2, 3-1, and 3-2.

When the tire is filled with air to a predetermined pressure (approximately 7 kg/cd), a large tension is applied to the steel cord 6 within the belt 10, and the angle of the steel cord 6 changes. The angle change of the steel cord 6 differs in the direction and amount of change depending on the belt layers IQ a - d. Therefore, the belt layer IQ constituting the belt 10
Shear stress and strain occur within a-d and between these glabella. FIG. 2 is a partially enlarged sectional view of the second and third belt layers of the belt 10, and shows the distribution of the magnitude of shear strain occurring inside the layer in the horizontal axis direction (R) in relation to the position within the layer.
This is shown in .

Shear stress and shear strain inside the belt 10 also occur due to the load applied to the tires, and also occur during high-speed running as described above. However, in the pneumatic tire of the present invention, as shown in FIG. 2, the belt coating rubber 7 and the belt end rubber 8 are provided with a rubber sheet layer F containing short fibers. Therefore, the magnitude of the shear strain occurring between belt layers IQ a - d is maximum So (indicated by arrow B), compared to SL in the case of a conventional pneumatic tire (Fig. 5). The shear strain distribution between the belt layers is extremely small, and the distribution of shear strain between the belt layers becomes small in the form of a valley at the boundary between two adjacent belt coatings. This shows that the effect of alleviating the in-plane shear strain of the belt coating rubber layer containing short fibers is extremely large.

Further, FIG. 3 shows the distribution of the magnitude of shear strain between the belt end rubber 8 and the belt coating rubber 7 and in the vicinity of the belt end rubber 8, similarly to FIG. 2.

As shown in Figure 3, the rubber sheet layer F containing short fibers
A belt 10 having a belt end rubber 8 made using
In this case, the shear strain near the belt end rubber 8 is extremely small.

As explained using FIGS. 2 and 3, in the tire of Example 1, the shear strain in the vicinity of the belt coating rubber 7 and the belt end rubber 8 is extremely small. Compared to the comparative example, the performance was significantly improved, and it can be seen that the effect of the rubber sheet NF, which incorporates short fibers, is extremely large.

In Tables 2-1, 2-2, 3-1, and 3-2, performance tests were conducted on the tires of Examples 1 to 4 and Comparative Examples 1 to 8. Performance test results are shown at the bottom of each table. The larger the numerical value of the durability test is, the better it is, and the smaller the numerical value of the crack test result is, the better.

The results of Example 1 are the same as those of Comparative Example 1 which does not use rubber sheet layer F.
．． This is extremely superior to the performance test results for No. 2. Also,
Example 2 also shows similar excellent results.

From the above results, the following can be said. By using the short fiber reinforced rubber of the present invention (i.e., rubber sheet layer F), shear stress and intralayer shear strain inside the belt 10 can be alleviated, and shear strain can also be alleviated in the vicinity of the belt 10. There is. Furthermore, it can be seen that when the rubber sheet layer F is used for the belt coating rubber 7 and the belt end rubber 8 at the same time, there is a synergistic effect that the shear strain is significantly lower than when it is used only for one side, and the performance is extremely improved. .

(This page, the following margins) (a) In All, A indicates the coating rubber, 1 indicates the first belt, and 1 indicates the angle between the short fiber orientation direction and the cord arrangement direction.

(b) In A12, A indicates the coating rubber, 1 indicates the first belt, and 2 indicates the angle of the short fiber orientation direction with respect to the circumferential direction.

(c) In B33, B indicates the end rubber, 3 indicates the third belt, and 3 indicates the angle between the end rubber and the orientation direction of short fibers in the coating rubber of the second belt.

(d) In B43, B indicates the end rubber, 4 indicates the fourth belt, and 3 indicates the angle between the end rubber and the orientation direction of short fibers in the coating rubber of the third belt.

(e) Numerical values for Example 5 are not shown.

(Examples 6 to 8) In Examples 6 to 8, the average diameter of the short fibers used in the present invention was 1
Indicates that it is limited to micrometers or less.

Reinforced rubber compositions (Samples 2 to 6) were manufactured by changing the average particle size of the nylon resin powder used in accordance with the manufacturing method of the aforementioned reinforced rubber composition (Sample 1). Table 4 shows the average diameter and physical properties of the short fibers of Samples 1 to 6.

Table 4 (a) Grafting ratio was measured and calculated as follows.

2 g of the reinforced rubber composition obtained in Example 1 was mixed with 20 g of benzene.
0 mJ at room temperature to dissolve the rubber component in the reinforced rubber composition, and the resulting slurry was centrifuged at room temperature to separate into a solution portion and a precipitate portion. After repeating the above operation seven times on the precipitated portion, the precipitated portion was dried to obtain nylon fibers. This ≠Iron fiber was dissolved in a mixed solvent of phenol and orthodichlorobenzene at a ratio of 1:3 (weight ratio), and analyzed by nuclear magnetic resonance spectroscopy (NMR) using hydrogen nuclei H (internal standard: tetramethylsilane). From the chart, the peaks of the methyl group and methylene group originating from natural rubber, the methylene group adjacent to the CO group originating from 6-nylon, the methylene group adjacent to the NH group, and the other three methylene groups, The graft ratio was calculated by determining the molar ratio of 6-nylon and natural rubber by the cut area method. Further, the shape of about 200 fibers was measured using a scanning electron microscope at a magnification of 10,000 times. The fibers were extremely thin short fibers with a circular cross section. Sample 3 had an average diameter of short fibers of 1.1 μm, which exceeded the limit of the average diameter of 1 μm according to the present invention. Also,
Using the reinforced rubber compositions (samples 2 to 6) obtained according to Table 4, rubber compositions 4 to 8 were prepared according to the manufacturing method of (2) short fiber reinforced rubber and rubber sheet layer in (Examples 1 to 4). were manufactured, and furthermore, each reinforcing layer was manufactured using each rubber composition. Here, the ingredients of rubber compositions 4 to 8 are shown in Table 5.
Rubber Composition 5 uses Sample 3 and is a rubber composition in which the average diameter of short fibers exceeds 1°0 μm.

Next, as shown in Table 6, using the reinforcing layers of the rubber compositions 4 to 8, the tires of Examples 6 to 8 and Comparative Examples 9 and 10 were manufactured as described above (Example 1). It was manufactured according to the performance test and then the performance test was conducted. Performance test results are shown in Table 6.

In Table 6, Examples 6 to 8 both have short fibers with an average diameter of 1 μm.
Sample 2, Sample 4, and Sample 6 in Table 4 below mn+ are used, and the performance test results of this tire show good results.

On the other hand, the tire of Comparative Example 9 uses Rubber Composition 5 in which the average diameter of short fibers exceeds 1.0 μI, and the performance test results are poor. That is, when the average diameter of the short fibers exceeds 1 μm, the rubber reinforcing effect is small. From the above explanation, the average diameter of the short fibers is limited to 1 μm or less.

In addition, sample 5 in Table 4 was used in the tire of Comparative Example 10, and the average diameter of the short fibers was 0.2 μm and 1 μm.
Although it is shown below, an aspect ratio of 7.8 is used. In this case, the reinforcing effect is not sufficient. From this, it is necessary that the aspect ratio (L/D) of the short fibers is 8 or more.

(This page, hereafter in the margin) (Example 9.10) Examples 9 to 10 show that the amount of short fibers in the short fiber reinforced rubber is limited to 5 parts by weight or more.

A rubber composition was prepared in the same manner as in Example 1 using the aforementioned reinforced rubber composition (Sample 1) and using the compounding components in Table 8 so that the amount of short fibers in the short fiber reinforced rubber was 5 parts by weight or more. 9
~11 were produced. The amount (parts by weight) of short fibers was 3 in rubber composition 9 and 5.10 parts by weight in rubber compositions 10 and 11, respectively. Using these rubber compositions, a rubber sheet layer F having a thickness of 0.6 nm was manufactured in the same manner as in Example 1. Using this rubber sheet layer F, Table 9
The tires of Examples 9 and 10 and Comparative Example 11 of Example 1
was manufactured in the same way. The tire of Comparative Example 11 has significantly lower performance test results. This shows that the amount of short fibers is required to be 5 parts by weight or more.

Table 8 Table 9 (Examples 11 to 13) Examples 11 to 13 show that M 1 /M 2 is preferably 2.5 or more. Rubber composition sample 1 was prepared by varying the degree of orientation.

Non-oriented sheets were pressed to have plane orientation. Therefore, Ml/
M2=O.

Table 10 In addition, 1s disclosed in Japanese Patent Application Laid-Open No. 57-10632
It is fully possible to arrange the o-polypropylene short fibers so as to exhibit "high anisotropy" which is an essential requirement of the present invention. Also, Special Publication No. 57-4527, Special Publication No. 57-4
The 5yn-1,2-polybutadiene short fibers disclosed in Japanese Patent Publication No. 530 and Japanese Patent Publication No. 57-30662 can also be used. However, most preferred are the nylon short fibers used in the present invention.

Furthermore, the present invention is not limited to the above-mentioned embodiments, and can be used in radial tires using organic fibers as belts, bias tires with belts (belted bias tires), bias tires, etc., and can also be used in tires for passenger cars. In addition, it can also be used for large tires.

(Effects of the Invention) As explained above, the shear stress and shear strain that occur inside the tire belt and near the end of the belt due to the tire air pressure, heavy load, and long-term running are
By using a rubber sheet layer containing micro short fibers for belt coating rubber and belt end rubber,
It is possible to significantly reduce the increase in belt thickness and weight without changing the belt stiffness, and to minimize the increase in belt thickness and weight.This greatly improves tire durability. I can do it.

[Brief explanation of the drawing]

1 to 3 are diagrams showing an embodiment of a pneumatic tire with improved durability according to the present invention. FIG. 1 is a cross-sectional view thereof, and FIG. Fig. 3 is an enlarged sectional view of the main part explaining the shear strain occurring at the end of the belt in Fig. 1; Figs. 4 and 5- show a conventional pneumatic tire. FIG. 4 is a sectional view thereof, and FIG. 5 is an enlarged sectional view of a main part showing shear strain of the belt shown in FIG. 4. 1-------Pneumatic tire, 2------Bead part, 3--------Bead wire, 5-------Carcass ply, 6--------Belt cord, 7・----Belt coating rubber, 8----
-Belt end rubber, 10-----Belt.

Claims (3)

[Claims] (1) A bead wire located at the bead part, a carcass ply consisting of a rubberized cord layer with many cords arranged in parallel, both ends of which are folded back at the bead part and locked to the bead wire, and a carcass ply on the outer peripheral surface of the carcass ply. The belt cord consists of multiple layers, each layer has a belt cord arranged at a predetermined angle, this belt cord is covered with belt coating rubber, and both axial ends of the belt coating rubber are covered with belt end rubber. A pneumatic tire with improved durability, characterized in that the belt satisfies all of the following items A to D. tire. A. 5 short fibers in which at least two adjacent belt coating rubbers and at least two adjacent belt end rubbers have an average diameter of 1 μm or less and a ratio of average length L to average diameter D (L/D) of 8 or more. It consists of a rubber composition containing at least part by weight. B. The angle between the orientation direction of short fibers in the belt coating rubber and the belt cord is 0 to 30 degrees. C. The angle between the orientation direction of short fibers in the belt end rubber and the belt cord is 45 to 90 degrees. D. The angle between the orientation direction of the short fibers in the belt end rubber and the orientation direction of the short fibers in the belt coating rubber adjacent to the belt end rubber is 45 to 90 degrees. (2) Elastic modulus M1 at 50% strain when pulled in the direction of short fiber arrangement in the reinforcing layer of short fibers after vulcanization, and at 50% strain when pulled in the direction perpendicular to the short fiber arrangement direction Elastic modulus M
2. The pneumatic tire with improved durability according to claim 1, wherein the ratio of M1/M2 is 2.5 or more. (3) The short fibers are made of a thermoplastic polymer having an amide group, and are grafted via a condensate of a rubber portion and a phenol formaldehyde resin. Pneumatic tires with improved durability.