JPS61122010A - Pneumatic tire with improved durability - Google Patents

Abstract

PURPOSE:To improve the durability of a pneumatic tire with an organic fiber carcass ply by providing a short fiber containing rubber reinforcing layer inside the carcass ply that is adjacent to a stiffner. CONSTITUTION:A rubber reinforcing layer 13 containing the five parts or more by weight of the short fiber made of thermoplastic polymer with 0.2-1.0mm thicknesses, less than 1mum average diameter, and the ratio of the average length L to the average diameter D exceeding 8 or more is arranged between the adjacent cord layers 5a-5c of the inside section 6b of a carcass ply 6 that is adjacent to a stiffner 10. The short fiber orientation direction of this rubber reinforcing layer 113 is set to 0-10 deg. for the cord orientation direction of the carcass play 6. Besides, the 50% distortion modulus of elasticity when the reinforcing rubber is pulled in the short fiber orientation direction is set to 2.5 times or more the vertical modulus of elasticity and 1.5 times or more the modulus of elasticity of ply coating rubber. As a result of this structure, the durability of a pneumatic tire can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention provides a pneumatic tire with improved durability, for example:
This invention relates to a pneumatic tire with improved durability by arranging a rubber reinforcing layer in which short fibers are oriented as much as possible between the cord layers of the carcass ply at the bead portion.

(Conventional technology) Recently, tires with excellent durability have greatly improved with the advent of radial tires, but with the development of expressways and improvements in the performance of automobiles, long-term driving at high speeds and high loads has further increased. ing. Therefore, there is a demand for tires that can withstand long-term high-speed running, and that have significantly improved performance and durability. An example of a conventional pneumatic tire with excellent durability is the one shown in FIG. In FIG. 3, reference numeral 31 denotes a conventional pneumatic tire with excellent durability. A carcass ply 36 consists of a rubberized hood layer 35 (shown as a single line in FIG. 3) of three layers of 6-6 nylon cord folded from the inside to the outside around the bead wires 32 and 34. , a belt 37 located on the outer peripheral surface of the carcass ply 36, a tread 38 located on the outer peripheral surface of the belt 5, and a pair of sides that cover both sides of the pneumatic tire 31 from the tread 38 to the bead portion 33. It has wall rubber 40. The three cord layers 35 of the carcass ply 36 are arranged in the direction from the inner surface to the outer surface of the tire.
G is arranged, and both ends 41 of these cord layers 35 are located outside the bead portion 33. Recently, the position of the end portion 41 has been provided to be located radially inward.

A pneumatic tire (for example, for a trunk) 31 is normally filled with air at a pressure of 6 to 7 volts/-, so a large tension is applied to the cord layer of the carcass ply 36 in the direction of the cord. There is. Furthermore, when a load W (indicated by arrow W) is applied, the shape of the pneumatic tire 31 perpendicularly below the rotational axis of the tire is defined by the outline of the solid line (indicated by arrow T) in FIG. It bends from the three-dot chain line Ta (indicated by the arrow Ta) to the contour line (only a portion is shown).

Due to this change in shape, shear strain occurs between the eyebrows of the cord layer 35 of the carcass ply 36. This shear strain occurs every revolution of the pneumatic tire, and this shear strain is particularly large at the inner bead portion of the pneumatic tire. Furthermore, in a pneumatic tire for a large truck, the number of cord layers 35 increases, and the greater the number of layers, the greater the shear strain. Furthermore, the greater the load, the greater the tire deflection, and the greater the shear strain between the layers of the bead portion 33.

In recent pneumatic tires for large trunks that run continuously for long periods of time, there is a problem in that separation failure occurs between the layers of the cord layer 35 of the bead portion 33. It is possible to reduce the thickness of the rubberized cord layer 35, but in this case, there is a problem that the overall rigidity of the bead portion 33 decreases, deformation due to load increases, and shear strain increases.

(Objective of the Invention) Therefore, in the present invention, in a pneumatic tire having a carcass ply made of organic fibers, the above-mentioned problems are eliminated, and failures that occur at the bead portion and the inner side of the carcass ply in the vicinity of the bead portion, such as peeling. It solves troubles, cord breakage, etc. without significantly changing the shape of the bead or the rigidity of the bead, and without significantly increasing the weight of the tire. It also enables continuous high-speed running and improves durability. The purpose is to provide an improved pneumatic tire with excellent durability.

(Structure of the Invention) The pneumatic tire with improved durability according to the present invention has a bead wire located at the tire and a cord layer in which a large number of organic fiber cords are arranged in parallel and rubberized with ply coating rubber. a carcass ply, which has both ends folded back at the bead part and locked to the bead wire, and has an outer part located on the outer side in the axial direction of the bead wire with the bead wire as a boundary, and an inner part located on the inner side in the axial direction of the bead wire; In a pneumatic tire having a stiffener disposed radially outward, and sidewall rubber covering the outside of a part of the carcass ply from the bead to the sidewall, the carcass ply adjacent to the stiffener may be It is characterized in that a rubber reinforcing layer containing short fibers with a thickness of 0.2 to 1.0 mm is provided between adjacent cord layers on the inner side. Further, it is preferable that the short fibers of the rubber reinforcing layer have an average diameter of 1 μm or less and a ratio of average length to average diameter (L/D) of 8 or more.

Further, it is preferable that the rubber reinforcing layer contains at least 5 parts by weight of short fibers. Moreover, it is preferable that the orientation direction of the short fibers of the rubber reinforcing layer is 0 degrees to 10 degrees with respect to the orientation direction of the cords of the carcass ply. In addition, in the short fiber reinforced rubber 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 M2 at 50% strain when pulled in the direction perpendicular to the direction in which the short fibers are arranged. Ratio M 1
/M2 is preferably 2.5 or more.

Further, it is preferable that the elastic modulus of the rubber reinforcing layer after vulcanization at 50% strain when pulled in the orientation direction of the short fibers is 1.5 times or more the elastic modulus of the briny coating rubber at 50% strain. Further, the short fibers of the rubber reinforcing layer have amide groups.
It is preferable that the rubber part is grafted via a condensate of 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 short fibers are subjected to strain (stress), 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 cuff resistance and torsional properties, which are the objectives of short fiber reinforcement, and high anisotropy, which is utilized in the present invention.

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, as will be described later, by orienting the short fibers as much as possible and controlling the angular difference between the orientation direction and the cord direction, it is possible to obtain a tire as designed.

In the present invention, the reason why the thickness of the rubber sheet of the short fiber-reinforced rubber composition containing short fibers is limited to 0.2 to 1.0 mm is that a rubber sheet thinner than 0.2 mm can be industrially produced. This is because it is difficult to do so, and at this thinness, sufficient effects cannot be expected. On the other hand, if it exceeds 1.0 mm, the overall thickness of the tire will become too thick, the shape of the bead and the rigidity of the bead will change significantly, and the weight of the tire will increase significantly. Not realistic.

In the present invention, the angle θ between the arrangement direction of the cords of the carcass ply and the orientation direction of the short fibers in the short fiber reinforced rubber is preferably 0 degrees to 10 degrees. This is because the effect can be maximized. The angle θ between the arrangement direction of the cords of the carcass ply 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 at 50% strain when pulled in the direction in which the short fibers are arranged, and the elastic modulus M1 at 50% strain when stretched in the direction perpendicular to the direction in which the short fibers are arranged. 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 arrangement direction of the cords of the carcass ply and the arrangement direction of the short fibers in the short fiber reinforced rubber is 0 degrees to 10 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 the polymer having an amide group is 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, and 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 3) Example 1 shows that the pneumatic tire of the present invention has significantly improved durability performance compared to conventional tires.

(1) Process for manufacturing reinforced rubber composition In an OOC Banbury mixer (manufactured by Kobe Steel), the temperature was adjusted to 150°C and the rotation speed of the rotor was adjusted to 1100 rpm.
1400g of natural rubber with a Mooney viscosity of 4 at 100℃
, and 14 g of N-(3methacryloyloxy-2-hydroxypropyl)-N'-phuninyluP~phenylenediamine [Tsukrank G-1, manufactured by Shinko Ohmukai],
The wire was stranded for 1 minute. Next, 6-nylon (trade name 210
30B, manufactured by Ube Industries, melting point 221℃, molecular weight 3000
0) 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 first XJI condensate (manufactured by Meisho Kasei@, trade name 550PL) was added, and after kneading for 7 minutes, 3 g of hexamethylenetetramine was added,
After kneading for 2.5 minutes (during which time the temperature of the bump 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 material has a nozzle inner diameter of 2 ff1
Using a 30 mmφ extruder (manufactured by Ikegai Co., Ltd.) having a circular die with a length to inner diameter ratio (L/D) of 2, the extrudate was extruded into a string shape at a set temperature of 235°C. It was cooled and solidified with cooling water at a temperature of .degree. C., and then wound onto a bobbin through a guide roll at a draft ratio of 9 and a speed of m/min. After vacuum drying this roll at room temperature for one day to remove adhering water, approximately 500 rolls were bundled into a sheet (2 mm thick,
150 m+n), this sheet-like material was rolled by a pair of rolling rolls with a roll gap of 0.2 mm and a temperature of 60°C.
A reinforced rubber composition (sample 1) reinforced with short fibers was obtained by roll rolling to a size of 0.

(2) Manufacturing method of short fiber reinforced rubber and rubber sheet layer (rubber reinforced layer) The reinforced rubber composition described above was blended with the ingredients and blending ratios shown in Table 1, and heated at a temperature of 70''C and a rotor rotation speed of 7O.
The mixture was kneaded using an OCC Banbury mixer (manufactured by Kobe Steel, Ltd.) with eight cycles of r, p, and m, to prepare a rubber composition 1 consisting of short fiber reinforced rubber.

Further, for comparison, Rubber Composition 2 and Rubber Composition 3 were prepared using the blending components and blending ratios that did not include the reinforced rubber composition, and using the other methods. Furthermore, these Rubber Compositions 1 to 3 were made into rubber reinforcing layers consisting of rubber sheet layers having a predetermined thickness using an ordinary rubber roll.

Further, for comparison, as shown in Table 1, Rubber Composition 2 and Rubber Composition 3 were created using the same formulation components and blending ratios that did not include the reinforced rubber composition, but using the same manufacturing method. Furthermore, these rubber compositions 1 to 3 are usually used to prepare a rubber sheet layer of a predetermined thickness (a rubber sheet having a thickness of 0.4 mm in Example 1) using nine rubber rolls. Since the rubber composition 1 contains a predetermined amount of short fibers, it becomes the rubber sheet layer of the present invention in which the short fibers are oriented in the drawing direction of the rubber roll (that is, the longitudinal direction L).

Next, this rubber sheet layer is used as a carcass layer.
A nylon blind cord was pasted at a predetermined position on the carcass layer with a predetermined width (60 mm in Example 1, and 80 mm depending on the tire size) and with a predetermined thickness of 0.4 mm in Example 1. ) A carcass layer with a rubber reinforcing layer is formed.

(Hereinafter, the margin of this page) Table 1 (a) Liquid IR is LI manufactured by Clarei Sobren Chemical ■
R-Father.

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

(c) Anti-aging agent is Tsurank 8 manufactured by Iriuchi Shinko Chemical Industry ■
10-NA.

(d) Nobs are Tsukusera MS manufactured by Daien Shinko Chemical Industry ■
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.

Figures 1 and 2 show an embodiment of a pneumatic radial tire with improved durability according to the present invention. be.

First, the configuration will be explained. 1 and 2, reference numeral 1 indicates a pneumatic tire with improved durability according to the present invention, and the pneumatic tire 1 has a bead wire 3 located in a bead portion 2, and a large number (three layers in Example 1). ) organic fiber cords (6-6 nylon cords in Example 1) are arranged in parallel and have a carcass ply 6 consisting of a cord layer 5 rubberized with ply coating rubber.

Each cord layer 5 of the carcass ply 6 constitutes three cord layers 5a, 5b, 5c in the direction from the inner surface to the outer surface of the tire, and both ends are folded back at the bead portion 2 and locked to the bead wire 3. 3 as a boundary, an outer part 6a located on the outer side of the bead wire 3 in the tire axial direction A, and an inner part 6 located on the inner side of the wire wire 3 in the axial direction A.
It has b. The pneumatic tire 1 also includes a belt 7 located on the outer peripheral surface of the carcass ply 6, a trend 8 located on the outer peripheral surface of the belt 7, and a stiffener 10 located outside in the radial direction B of the bead wire 3. Todo part 2
The sidewall rubber 12 covers the outer trend 8 of the carcass ply 6 of the sidewall 11. The rubber reinforcing layer 13 (indicated by a dotted line in the figure) is attached to the inner side 6b of the carcass ply 6 adjacent to the stiffener 10.
Provided between adjacent cord layers of 0.2 to 1.0 m
m thickness (0.4 mn+ in Example 1) and contains short fibers. Further, the short fibers of the rubber reinforcing layer 13 have an average diameter of 1 μm or less and a ratio L/D of average length to average diameter of 8 or more. Further, the amount of short fibers in the rubber reinforcing layer 13 is 5 parts by weight or more. Further, the orientation direction of the short fibers of the rubber reinforcing layer 13 is 0 degrees to
It is 10 degrees. In the rubber reinforcing layer 13 after vulcanization, the ratio of the elastic modulus M1 at 50% strain when pulled in the orientation direction of the short fibers to the elastic modulus M2 at 50% strain when pulled in the direction perpendicular to the orientation direction of the short fibers. M 1 /M 2 is 2.5 or more. In the rubber reinforcing layer 11 after vulcanization, the elastic modulus at 50% strain when pulled in the orientation direction of the short fibers is 5 of that of the ply coating rubber.
The elastic modulus is 1.5 times or more than the elastic modulus at 0% strain. Rubber reinforcement layer 1
The short fibers in No. 3 are made of a thermoplastic polymer having an amide group, and are grafted via a rubber part and a condensate of phenol-formaldehyde resin. (meaning the same thing in the present invention).

(4) Tire manufacturing and performance test results (effects) Tire manufacturing was carried out by the usual method (tire size was 1.
0 R20 and is a radial tire) In other words, it contains as unvulcanized members a dwarf wire 3, a stiffener 10, a belt 7, a trend 8, a sidewall rubber 12 and short fibers, and has a thickness in which a predetermined amount is distributed. A rubber reinforcing layer 13 with a diameter of 0.4 mm is placed at a position on the inner side 6b of the cord layer 5 with a predetermined width (60 mm in Example 1), and the rubber reinforcing layer 13
Three cord layers 5 are prepared such that the orientation direction of the short fibers is at an angle of 0 degrees with respect to the orientation direction of the cords of the carcass ply 6. Here, the ply coating rubber 12 used for the carcass ply 6 was made using the rubber composition N13 shown in Table 1.Next, these prepared members were pasted in a predetermined order using a predetermined tire molding machine to form a so-called green material. Manufacture cases (unvulcanized tires). Next, the tire is pressurized and heated in a vulcanizer to produce a product tire (Example 1). Further, a tire of a comparative example is manufactured in the same manner as in Example 1 using a rubber composition that does not contain short fibers.

The tires of these Examples and Comparative Examples were filled with air to a predetermined air pressure and subjected to a durability drum test. The durability drum test (hereinafter simply referred to as durability test) was conducted in the order described below.

First, a test tire was made by removing the tread of the tire of Example 1 by puffing it with a grinder. Next, the test tire was set to an air pressure of 10 kg/cat, and the JIS
A drum test was conducted under the test conditions of applying a load of 110% and running at a predetermined speed while applying a slip angle of 3.5 degrees alternately on the left and right sides.

Evaluation was made based on the number of times (number of cycles) added to the slip angle until failure occurred in the bead portion. The results of the durability test are shown at the bottom of Table 2. This durability test is an accelerated test.
Pneumatic tires are installed on long-distance trucks,
This is a durability test of the bead portion 2 which corresponds to the case of continuous running for a long period of time. In the pneumatic tire, the cord layer 5 may peel off between the eyebrows at the bead portion 2 and in the vicinity of the bead portion 2 during long-term driving.

The durability test is a durability test that has a high correlation with actual driving by creating the same shear strain between the eyebrows of the test tire as that which occurs during long-term driving, so that the same peeling failure will occur in a short period of time. .

Next, the effect will be explained. The tread of the tire of Example 1 was removed by puffing, and the tire was mounted on the drum of a durability drum tester, and a running test was conducted under the above-mentioned test conditions. The air pressure of a pneumatic tire is 10 kg/cr&, which is much higher than the normal air pressure of about 7 kg/10 d.
An extremely large tension is acting on the 6-6 nylon cord of the cord layer 5 of the carcass ply 6. In addition, since the drum gives the tire a lateral slip angle of 3.5 degrees with each rotation, there is an extremely large amount of space between the eyebrows of the cord layer 5 and between the cord layer 5 and the stiffener 10 at the inner side 6b of the carcass ply 6. Causes large glabellar shear strain. However, in the tire of Example 1, each cord layer 5a, 5b, 5c
A rubber reinforcing layer 13 having short fibers is provided between the glabella and between the cord layer 5a and the stiffener 10.

Therefore, these strain distributions with high peaks of large shear strain are weakened to a distribution of very low shear strain, the fatigue due to this shear strain is reduced, and the life is increased very significantly. Therefore, in the durability test, Table 2
As shown in Example 1, 845 times, Comparative Examples 1 to 3, 652 times, 612 times, and 53 times, respectively.
6 times, and it can be seen that the durability of the bead portion 2 of Example 1, in which the rubber reinforcing layer 13 having the short fibers of the present invention was provided, was extremely excellent.

As this durability test was an accelerated test as mentioned above, a failure occurred in the bead part, but since the tire of Example 1 has a rubber reinforcing layer 13, it was actually installed in a large trunk for a long period of time. When running, there were no peeling failures at the bead part. In other words, this is a pneumatic tire in which the durability of the bead portion 2 has been significantly improved.

As explained above, the rubber reinforcing layer 13 having short fibers is arranged between the cord layers 5 on the inner side 6b of the carcass ply 6 of the bead portion and between the cord layer 5c and the stiffener 10 (as described above). This greatly improved the durability of the bead. A pneumatic tire with improved durability can be provided.

Further, Examples 1 to 3 show that the orientation direction of the short fibers of the rubber reinforcing layer preferably has an angle of 0 to 10 drums with respect to the arrangement direction of the carcass plies.

As shown in Examples 1 to 3 in Table 2, the orientation direction of the short fibers of the rubber reinforcing layer is at an angle of 0 degrees, 10 degrees, and 20 degrees with respect to the arrangement direction of the cords of the carcass ply 6, respectively.
Durability test results are shown for the case (hereinafter simply referred to as rubber reinforcement angle). From this result, the rubber reinforcement angle is 10
It can be seen that when the angle exceeds 100 degrees, the durability test results deteriorate. From this, it can be seen that the rubber reinforcement angle is preferably 0 degrees to 10 degrees. Here, the tires of Examples 2 and 3 were manufactured in the same manner as in Example 1, except that the rubber reinforcement angles were 10 degrees and 20 degrees, respectively, and a durability test was conducted.

(Hereinafter, this page margin) (Examples 4 to 6) In Examples 4 to 6, 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 ml 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 nylon fiber was mixed with phenol and orthodichlorobenzene in a ratio of 1:3 (ffi ratio).
It was dissolved in a mixed solvent of and analyzed by nuclear magnetic resonance spectroscopy (NMR) using hydrogen nuclei H (internal standard: tetramethylsilane), and from the NMR chart, methyl groups and methylene groups originating from natural rubber, and 6-nylon originating. co
For each peak of the methylene group adjacent to the group, the methylene group adjacent to the NH group, and the other three methylene groups, the molar ratio of 6-nylon to natural rubber is determined by the cut area method, and the grafting ratio is calculated. did. 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 has short fibers with an average diameter of 1
．． The average diameter of 1 μm exceeds the average diameter limit of 1 μm according to the present invention. Further, using the reinforced rubber compositions (samples 2 to 6) obtained according to Table 4, rubber composition 4 was prepared according to the manufacturing method of (2) short fiber reinforced rubber and rubber sheet layer in (Examples 1 to 5). - 8 were manufactured, and furthermore, each reinforcing layer was manufactured using each rubber composition. Here, the compounding components of rubber compositions 4 to 8 are shown in Table 5, and rubber composition 5 is the same as sample 3.
It is a rubber composition in which the average diameter of short fibers exceeds 1.0 μm.

Next, as shown in Table 6, using the rubber reinforcing layers of the aforementioned rubber compositions 4 to 8, the tires of Examples 4 to 6 and Comparative Examples 4.6 had a thickness of the rubber reinforcing layer of 0.451. ?1I11 was manufactured according to the tire of Example 1 described above,
Next, a durability test was conducted. The results of the durability test are shown in Table 6.
is shown. The tire size is 11 R22.5, and it is a tubeless tire.

In Table 6, Examples 4 to 6 both have short fibers with an average diameter of 1 μm.
Sample 2, Sample 4, and Sample 6 in Table 4 below are used, and the durability test results for these tires are 8.
It shows good results of 62 times, 795 times, and 788 times.

. On the other hand, the tire of Comparative Example 5 uses a rubber composition vIJ5 in which the average diameter of short fibers exceeds 1.0 μm,
The durability test result was 645 times, which is low.

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 6, and the average diameter of the short fibers was 0.2 μm, which was less than 1 μm, but the aspect ratio was 7.8. ing. In this case, the reinforcing effect of Comparative Example 6 in Table 6 is not sufficient. From this, the aspect ratio of short fibers (L/D)
must be 8 or more.

(Examples 7 to 11) Examples 7 to 11 show that the thickness of the short fiber reinforced rubber layer of the rubber reinforcing layer 13 is preferably 0.2 mm to 1.0 mrn.

As shown in Table 7, using rubber composition 1, the tires of Examples 7 to 11 were different from each other except that the thickness of the rubber reinforcing layer of each example was changed from 0.2 mm to 1.1 ms+. was manufactured according to the manufacturing method of Example 1. Next, a durability test was conducted in the same manner as in Example 1. As can be seen from the results of the durability test in Table 7, the thickness of the rubber reinforcing layer was 0.
If the thickness is less than 2 mm, a rubber sheet cannot be manufactured industrially.

Also, if it exceeds 1.0 mm, the number of durability tests will be 700.
It will be as low as 3 times or less. From this, the thickness of the short fiber reinforced rubber layer is preferably 0.2 to 1.0 mm.

(Example 12.13) Example 12.13 shows that the amount of short fibers in the short fiber reinforced rubber is preferably 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
．． 10 were manufactured. The amount (parts by weight) of short fibers was 3 parts by weight in rubber composition 9 and 5 parts by weight in rubber composition 10. Using these rubber compositions, a rubber reinforcing layer with a thickness of 0.511111 mm was manufactured in the same manner as in Example 1. Using this rubber reinforcing layer, the tire of Example 12.13 in Table 9 (tubeless tire with tire size 11R22.5) was produced in the same manner as in Example 1 except that the thickness of the rubber reinforcing layer was 0.5 mm. was manufactured and subjected to durability tests. The test results are shown in Table 9. In Table 9, Example 12 shows a lower number of times than Example 13.

This shows that the amount of short fibers is preferably 5 parts by weight or more.

(Hereinafter, the margin of this page) Table 8 (a) MO is the elastic modulus of the braai coating rubber at % strain.

Table 9 (Examples 14 to 17) In Examples 14 to 17, the degree of orientation of the short fibers in the rubber composition No. 1 was changed, and the preferable range was [short fibers in the short fiber reinforced rubber of vulcanized rubber]. 50V6 pulled in the orientation direction of
The ratio (Ml/M2) of the elastic modulus under strain M1 to the elastic modulus under 50% strain M2 when pulled in a direction perpendicular to the direction of orientation of the short fibers is 2.
5 or more.

In Table 10, rubber reinforcement J used in Examples 14 to 17
Rubber sheets with different degrees of orientation of ii13 were created as follows.

For non-oriented materials, unvulcanized rubber is sheeted using a press.
Using this, a tire of an example was made. In this case, M
l-M2. The degree of orientation was determined by changing the gap between the rolls, and the thickness of the rubber reinforcing layer was subsequently adjusted by stacking two rubber sheets or by using a press.

The tires of Examples 14 to 17 in Table 10 (tire size 1°R20) were manufactured in the same manner as in Example 1, except that rubber reinforcing layers with different degrees of orientation were used, and were subjected to a durability test. carried out. The test results are shown in the lower part of Table 10.

In Table 10, the degree of orientation of short fibers, that is, M 1
The tires of Examples 16 and 17 with a /M 2 ratio of 2.5 had durability test results of 849 and 899 times, respectively, showing superior durability than Examples 14 and 15.

From this, M 1 /M, which indicates the degree of orientation of short fibers,
It can be seen that it is preferable to use a rubber reinforcing layer in which 2 is 2.5 or more.

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 sy n-l52-polybutadiene short fibers disclosed in Japanese Patent Publication No. 530 and Japanese Patent Publication No. 57-30662 can also be used in the same manner. 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 short fiber reinforced rubber composition containing micro short fibers is sufficiently oriented, and the orientation direction of the short fibers is 0 to 10% relative to the orientation direction of the cords of the carcass ply.
By arranging the rubber reinforcing layer of the short fiber reinforced rubber composition between the cord layers of the carcass ply and between the carcass ply and the stiffener at an angle of The magnitude of shear strain is reduced by removing the peak of shear strain that occurs near the area. As a result, fatigue caused by shear strain is reduced, the life span is greatly improved, and a pneumatic tire with improved durability and improved durability of the bead portion can be provided.

In addition, by combining this short fiber reinforced rubber with regular coating rubber, there is a synergistic effect that reduces the flow of regular coating rubber, and these effects result in a pneumatic tire with significantly improved tire durability. can be provided.

[Brief explanation of the drawing]

Fig. 1.2 shows an embodiment of a pneumatic tire with improved durability according to the present invention, Fig. 1 is a sectional view thereof, and Fig. 2 is a partially enlarged sectional view of a bead portion. be. FIG. 3 is a sectional view of a conventional pneumatic tire. 1--Pneumatic tire, 2--Bead portion, 3--Bead wire, 5--Cord layer, 6--Carcass ply, 10-- --Stiffener-1 12.--Side wall rubber, 13.--Rubber reinforcing layer.

Claims (7)

[Claims] (1) It consists of a bead wire located at the bead part and a cord layer in which a large number of organic fiber cords are arranged in parallel and rubberized with ply coating rubber, and both ends are folded back at the bead part and locked to the bead wire. A carcass ply having an outer part located on the axially outer side of the bead wire and an inner part located on the axially inner side of the bead wire as a boundary, a stiffener arranged radially outward of the bead wire, and a carcass ply from the bead part to the sidewall part. A pneumatic tire having a sidewall rubber covering the outside of a part of the ply, in which short fibers having a thickness of 0.2 to 1.0 mm are interposed between adjacent cord layers on the inside of the carcass ply adjacent to the stiffener. A pneumatic tire with improved durability characterized by having a reinforced layer containing rubber. (2) The short fibers of the rubber reinforcing layer 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. Pneumatic tires with improved durability. (3) The pneumatic tire with improved durability according to claim 1, wherein the rubber reinforcing layer contains at least 5 parts by weight of short fibers. (4) Durability according to claim 1, wherein the orientation direction of the short fibers of the rubber reinforcing layer forms an angle of 0 degrees to 10 degrees with respect to the arrangement direction of the cords of the carcass ply. improved pneumatic tires. (5) Elastic modulus M1 of the short fiber reinforced rubber after vulcanization at 50% strain when pulled in the direction in which the short fibers are arranged, and elasticity at 50% strain when pulled in the direction perpendicular to the direction in which the short fibers are arranged. A pneumatic tire with improved durability according to claim 1, characterized in that the ratio M1/M2 of the ratio M2 is 2.5 or more. (6) The elastic modulus of the rubber reinforcing layer after vulcanization at 50% strain when pulled in the orientation direction of short fibers is 1.5 times or more the elastic modulus of the ply coating rubber at 50% strain. A pneumatic tire with improved durability according to claim 1. (7) Claim 1, characterized in that the short fibers are made of a thermoplastic polymer having an amide group, and are grafted via a condensate of a rubber part and a phenol formaldehyde resin. Pneumatic tires with improved durability as described.