JPS61119411A - Pneumatic tire with durability improved - Google Patents

Abstract

PURPOSE:To control changes in rubber at a time of vulcanization so as to improve durability by employing a reinforcing rubber layer which is made of a composition of rubber with short fibers that have the stated dimension and are mixed with the stated ratio, in a place among a bead wire, a stiffner around the bead wire, and a carcass ply. CONSTITUTION:A pneumatic tire 1 includes a carcass ply which is composed of rubber coated cords, both ends 5a of which are turned up at bead toes 2 and then fixed on bead wires 3, and stiffners 6 arranged on the outer surfaces of the bead wires 3 to the radial direction. In this case, a reinforcing rubber layer 7 is arranged in a place between the bead wire 3 and the stiffner 6 around the bead wire, and in a place between the bead wire 3 an the carcass ply 5. The reinforcing rubber 7 is made of a composition of rubber with short fibers of more than 8pts.wt. Here, the short fibers have an average diameter of smaller than 1mum, and a ratio L/D of more than 8 where L represents an average length of the short fibers while D represents their average diameter. And the above mentioned short fibers are arranged in the same direction as the bead wire 3 are arranged.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a pneumatic tire, for example, a pneumatic tire with improved durability in which bead wires are covered with a rubber sheet to reduce bead deformation.

(Prior art) The area around the bead of a conventional pneumatic tire is only covered with a thin rubber sheet, and during vulcanization, the bead portion is pushed by a bladder, and due to deformation of the unvulcanized tire. It is also dragged from the carcass ply. For this reason, the bead of the vulcanized tire is significantly deformed from the shape of the unvulcanized bead, and the position of the bead deviates from the design target. As a result, even when the tire is assembled on a rim, it may not fit well with the rim, it may cause abnormal friction and wear on the outer periphery of the bead, and sometimes it may cause air leaks in the case of tubeless tires. There is a problem.

As a conventional pneumatic tire, there is one shown in FIG. 3, for example. In FIG. 3, reference numeral 31 indicates a conventional pneumatic tire, and the pneumatic tire 31 includes a bead portion 33 having a bead wire 32, and a carcass ply 35 that is folded back at the bead portion 33 and secured to the bead wire 32.
and a belt 36 located on the outer periphery of the carcass ply 35.
and a tread 37 located on the outer periphery of the belt 36. The bead wire 32 of the bead portion 33 has a hexagonal shape when unvulcanized, but there is a problem in that the hexagonal shape is greatly deformed due to pressure and heating during vulcanization.

(Objective of the Invention) Therefore, in order to improve the above-mentioned drawbacks, the present invention aims to sufficiently orient a short fiber reinforced rubber composition containing micro short fibers,
Furthermore, the area around the bead is coated with rubber that has short fibers oriented in the direction of orientation, suppressing the flow of the rubber during vulcanization as much as possible, and ensuring that the shape and position of the bead are as designed after vulcanization. The purpose of the present invention is to provide a pneumatic tire with improved durability.

(Structure of the Invention) A pneumatic tire with improved durability according to the present invention consists of a bead wire located in a bead portion and a rubberized cord layer in which a large number of cords are arranged in parallel, and both ends are made of vinyl. In a pneumatic tire having a carcass ply folded back and locked to the bead wire and a stiffener disposed on the outer surface of the bead wire in the radial direction, an average diameter of 1 μm is provided between the bead wire and the stiffener and carcass ply located around the bead wire. The following features include a rubber reinforcing layer made of a rubber composition containing 5 parts by weight or more of short fibers having an average length to average diameter ratio (L/D) of 8 or more. Further, it is preferable that the orientation direction of the short fibers of the rubber reinforcing layer and the arrangement direction of the bead wires are the same. Further, it is preferable that the short fibers of the rubber reinforcing layer are made of a thermoplastic polymer having an amide group, and are grafted to the rubber portion via a phenol-formalde or do-based condensate.

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 depends on the shape of the short fibers, and naturally the smaller the short fibers, the smaller the strain applied to both ends of the short fibers, so the shear stress also decreases. becomes smaller.

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 short fiber reinforcing effect, which is the object of the present invention, cannot be expected. In the present invention, as described later, by orienting the short fibers as much as possible and making the orientation direction the same as the direction of the bead wire, it is possible to obtain a tire with less rubber flow.

In the present invention, it is preferable that the direction in which the bead wires are arranged is the same as the direction in which the short fibers in the short fiber reinforced rubber are oriented, because the effect of short fiber reinforcement can be maximized if they are the same. be.

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 the elastic modulus M2 under strain (M 1 /M 2 ) is 2.5 or more, but this indicates the degree of orientation of the short fibers, and the short fibers oriented to this degree are The greatest effect is produced when the short fiber-reinforced rubber composition contained in the rubber composition is arranged in the same direction as the bead wires and the short fibers in the short fiber-reinforced rubber.

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 tactical polypropylene.

Examples will be described in more detail below.

(Example 1) 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 rotational speed of the rotor was adjusted to 1100 rpm. Inside the OC Banbury mixer (manufactured by Kobe Steel),
1400g of natural rubber with a Mooney viscosity of 4 at 100℃
, and 14 g of N-(3methacryloyloxy-2-hydroxypropyl)-N'-phenyl-P-phenylenediamine [TSKURAK G-1, manufactured by Shinko Ohmukai] were added and masticated for 1 minute. Next, 6-nylon (product name: 1
030B, manufactured by Ube Industries ■, melting point 221°C, molecular weight 3°0
00) 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 material was mixed with a nozzle having an inner diameter of 2 ml and 1 liter.
Using a 30III1φ 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 at a die temperature of 235°C, and the extrudate was cooled to 0°C. It was cooled and solidified with water, and then wound up on a bobbin through a guide roll at a draft ratio of 9 and a speed of 35 m/min. After vacuum-drying this roll at room temperature for one day and night to remove adhering water,
Approximately 500 of these rolls are bundled into a sheet (2 mm thick).
, medium 150 mm), 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 reinforcing layer The reinforced rubber composition described above was blended with the ingredients and blending ratios shown in Table 1, at a temperature of 70°C and a rotor rotation speed of 7 Or, p, m.
OCC Banbury mixer (Kobe Steel 11) articulated with
A rubber composition 1 made of short fiber reinforced rubber was prepared by kneading the mixture.

Further, for comparison, Rubber Composition 2 and Rubber Composition 3 were created using the same blending ingredients and blending ratios that did not include the reinforced rubber composition, but using the same manufacturing method. Further, these Rubber Compositions 1 to 3 were formed into rubber reinforcing layers made of rubber sheets having a predetermined thickness using an ordinary rubber roll.

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

(Hereinafter, the margin of this page) Table 1 (a) Liquid IR is LIR manufactured by Clarei Soprene Chemical.
-50.

(b) The novolac-type phenol resin modified with walnut oil is a novolak-type phenolic resin modified with 40 parts by weight of walnut 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 Iriuchi 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.

FIG. 1 and FIG. 2 are diagrams showing a pneumatic tire of the present invention.

First, to explain the structure, the pneumatic tire 1 according to the present invention consists of a bead wire 3 located in the bead portion 2 and a rubberized cord layer in which a large number of cords are arranged in parallel, as shown in FIG. A carcass ply 5 whose portion 5a is folded back at the bead portion 2 and is locked to the bead wire 3, and a stiffener 6 disposed on the outer surface of the bead wire 3 in the radial direction.
and has. A rubber reinforcing layer 7 is provided between the bead wire 3 and a stiffener 6 around the bead wire 3 and between the bead wire 3 and the carcass ply 5.

The rubber reinforcing layer 7 is made of a rubber composition containing 8 parts by weight or more of short fibers having an average diameter of 1 pn or less and a ratio of average length to average diameter (L/D) of 8 or more.

The orientation direction of the short fibers of the rubber reinforcing layer and the arrangement direction of the bead wires (ie, the circumferential direction) are the same. Further, the short fibers of the rubber reinforcing layer are made of a thermoplastic polymer having an amide group, and are grafted to the rubber portion via a phenol formaldehyde condensate.

(4) Tire Manufacture and Performance Test Results (Function) The tire was manufactured by the usual method, that is, the unvulcanized parts were made of a wire 3, a stiffener 6, and a rubberized cord layer (carcass). Ply 5), 4 belt layers,
A rubber reinforcing layer consisting of a rubber sheet containing a tread, sidewalls, and short fibers and oriented in a predetermined amount and having a thickness of, for example, 0.2 to 3.0 mm is prepared. Next, the rubber reinforcing layer was a bead having a circular rubber reinforcing layer with a diameter of 20 mm that was attached around the bead wire 3 at a predetermined thickness over the entire circumference of the bead wire 3.

Next, these prepared members are pasted together in a predetermined order using a predetermined tire molding machine to manufacture a so-called green case. Next, a product tire (Example 1) is manufactured by pressurizing and heating in a vulcanizer to vulcanize the tire.

At this time, the green case is pressurized and heated in the vulcanizer, but the outer diameter of the green case is slightly smaller than the outer diameter of the tire mold, and the green case is pressurized from the radial inside of the tire. Heated by the high temperature inside the tire and the tire mold. This softens the rubber of the green case and deforms the green case so that its outer diameter becomes larger. At this time, at the bead part, -
The carcass ply 5 around the bead wire 3 moves slightly from the outside to the inside of the tire, and a force is applied to deform the bead wire.

However, a rubber reinforcing layer in which the short fibers of the present invention are oriented in the arrangement direction of the bead wire is provided around the bead wire to a predetermined thickness.

Therefore, the stress that tends to deform the bead wire is alleviated by the rubber inside and in the vicinity of the anisotropic rubber reinforcing layer, and the shear strain thereof is also alleviated. Therefore, the deformation of the bead wire and the deformation of the vicinity are extremely small, and a pneumatic tire having the bead shape as designed is produced. Tire size is 295/75R22,
5 tubeless radial tires.

Further, a tire of a comparative example is manufactured in the same manner as in Example 1 using a rubber sheet layer that does not contain short fibers.

The tires of these Examples and Comparative Examples were subjected to a bead durability test (shown as bead durability test in Table 2) and an anatomical test (shown as shape disturbance in Table 2) using a predetermined method. (Hereinafter, these two tests will simply be referred to as performance tests).

In the bead durability test, a normal drum testing machine is used to run on the drum under the conditions of an internal pressure of 10 kg/ad and a JIS 180% load, and the test is performed until a failure occurs in the bead section and the tire is destroyed. The evaluation was based on the number of distance traveled. Further, in the dissection test, the specimen was dissected using a predetermined method, and it was tested whether the shape of the bead having the rubber reinforcing layer and its vicinity was as designed. The test results are shown in Table 2. In Table 2, "Yes" indicates that the bead is deformed, and (large) and (medium) mean that the deformation of and -do is large and medium, respectively.

In Table 2, Example 1 has no disorder in shape, and
The bead durability test was 29.700 km, showing a result that was significantly superior to Comparative Example 1.2.

From the above explanation, the pneumatic tire according to the present invention has a smaller shear strain of the rubber around the bead than a conventional tire, and changes in the bead shape and bead placement position are small, and the durability of the bead portion is improved. It can be seen that this has been significantly improved.

Table 2 (Examples 2 to 4) In Examples 2 to 4, the short fibers used in the present invention had an average diameter of 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 Heat (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 dissolved in a mixed solvent of phenol and orthodichlorobenzene at a ratio of 1:3 (weight ratio), and the molecules were analyzed using nuclear magnetic resonance spectroscopy (NMR) using hydrogen nuclei H (internal standard: tetramethylsilane), and the NMR chart was 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 were cut. The graft ratio was calculated by determining the molar ratio of 6-nylon and natural rubber by the 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 has short fibers with an average diameter of 1.1
The diameter exceeds the average diameter limit of 1 μm according to the present invention. In addition, the reinforced rubber composition obtained according to Table 4 (Sample 2
~6), rubber compositions 4~
No. 8 was 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 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, the tires of Examples 2 to 4 and Comparative Examples 5 and 6 were manufactured using the reinforcing layers of the rubber compositions 4 to 8 described above (Example 1). were manufactured in accordance with the above and then performance tests were conducted. Performance test results are shown in Table 6.

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

On the other hand, the tire of Comparative Example 3 uses Rubber Composition 5 in which the average diameter of short fibers exceeds 1.0 μm, and the performance test results show that the mileage is low and the shape is irregular. The effect of fiber reinforced rubber is small. 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 4, 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 stimulant effect of Comparative Example 4 in Table 6 is not sufficient. From this, the aspect ratio of short fibers (L/D)
must be 8 or more.

(Hereinafter, this page margin) Table 8 In addition, 1s disclosed in Japanese Patent Application Laid-open No. 10632/1983
It is fully possible to arrange the o-polypropylene staple fibers so that they exhibit high anisotropy, which is an essential requirement of the present invention.
S'yn-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; It can be used for radial tires using am fiber as belts, bias tires with belts (belted bias tires), bias tires, etc., and can be used not only for passenger car tires but also 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 short fibers are oriented around the bead wire so that the orientation direction of the short fibers is the same as the arrangement direction of the bead wire. and the stiffener and carcass ply.

A rubber reinforcing layer made of this short fiber reinforced rubber composition is arranged. This makes it possible to minimize changes in the rubber during vulcanization and to maintain the bead shape and bead placement position as designed after vulcanization. In addition, by combining this short fiber reinforced rubber with regular coating rubber, there is a synergistic effect that reduces changes in the area around the bead wire, and these effects make it possible to create pneumatic tires with significantly improved tire durability. can be provided.

[Brief explanation of drawings]

1.2 shows an embodiment of a pneumatic tire 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. FIG. 3 is a sectional view of a conventional pneumatic tire. 1. --- Pneumatic tire, 2. --- Bead portion, 3. --- Bead wire, 5. --- Carcass ply, 5a --- One both ends, 6. --- Stiffener 1 7 --- Rubber reinforcing layer.

Claims (3)

[Claims] (1) A bead wire located at the bead part, a carcass ply consisting of a rubberized cord layer in which many cords are arranged in parallel, both ends of which are folded back at the bead part and locked to the bead wire, and an outer surface in the radial direction of the bead wire. In a pneumatic tire having a stiffener arranged in A pneumatic tire with improved durability, comprising a rubber reinforcing layer made of a rubber composition containing 5 parts by weight or more of short fibers having a molecular weight of 8 or more. (2) A pneumatic tire with improved durability according to claim 1, wherein the orientation direction of the short fibers of the rubber reinforcing layer and the arrangement direction of the bead wires are the same. (3) The short fibers of the rubber reinforcing layer are made of a thermoplastic polymer having an amide group, and are grafted to the rubber portion via a phenol formaldehyde condensate. A pneumatic tire with improved durability according to item 1.