JPH0692108A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To substantially improve durability of a tire itself by suppressing generation and growth of separation in a belt end part of a pneumatic radial tire. CONSTITUTION:A pneumatic radial tire has a carcass 2 of striding a bead part and at least two adjacent crossing belt main layers 4 of hooping a crown part of this carcass fastened to bury a metal cord. A rubber member, dispersedly compounding 5 to 40 pts.wt. syndiotactic-1,2-polybutadiene of 130 to 170 deg.C melting point with 100mum or less grain size relating to 100 pts.wt. diene rubber, is arranged as a belt undercushion rubber 3 between the carcass 2 and a free end of the innermost belt layer adjacent to the carcass 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic radial tire having improved durability, and more particularly to a heavy duty pneumatic radial tire for large construction vehicles, trucks and buses.

[0002]

2. Description of the Related Art Pneumatic radial tires used for running on rough roads are often subjected to excessive strain input such as riding over bumps, and the belt that reinforces the crown portion of the tire is usually a plurality of cross belts in which metal cords are embedded. It is composed of stacked main layers.

However, it is important for avoiding a failure due to the belt separation which is generated from the end portion of the cross belt main layer and grows, and it is important to improve the tire durability, and various measures have been tried so far.

For example, as shown in Japanese Patent Laid-Open No. 52-133604, the end portion of the belt portion is reinforced by a cross belt layer, and a cord layer having different bending rigidity is arranged to cause shear strain at the belt end portion. Is suppressed by suppressing the movement of the belt to improve the belt durability.

In Japanese Patent Laid-Open No. 63-38007, there is one in which a shear belt ply having a modulus lower than that of the belt ply is arranged to reduce the shear strain at the end portion of the belt layer having the maximum width.

However, in any case, as the hardness of the belt coating rubber, a high hardness rubber is used in order to increase the rigidity of the belt. In this way, when the coating of the belt layer is composed of uniform high hardness rubber,
Although it has the effect of increasing the rigidity of the belt as a whole, strain concentration occurs at the boundary with the rubber of other low hardness parts adjacent to the belt coating rubber, such as the rubber that constitutes the belt end shoulder part, and the belt part becomes rigid. Even if an attempt is made to stop the generation of strain by the means for changing the load, a large strain stress may be generated by an external input under the condition of a heavy load on a bad road.

To solve these problems, for example, in JP-A-62-244702, a belt end is reinforced, and as shown in JP-A-49-132705, a rubber hardness lower than that of a belt coating rubber. There is an idea to insert a cushion rubber having a difference between the belt layers so that the rubber having low hardness absorbs the shear strain.

Further, as in Japanese Patent Laid-Open No. 63-38007, a reinforcing portion for reinforcing the outer side of the large diameter cord with a cord having a smaller diameter is provided for the large diameter cord constituting the belt portion. In some cases, the durability of the belt is improved by reducing the shear strain stress generated at the belt end portion.

[0009]

However, when a belt end is reinforced as disclosed in Japanese Patent Laid-Open No. 62-244702, a large tire used for traveling on a rough road receives a projection input from the road surface. Since the side force input at the time of a curve or curve is large, there is a risk that even greater distortion will be applied to the belt end and separation will eventually occur at the belt end.

When a cushion rubber is inserted between the belt layers as disclosed in JP-A-49-132705, the belt layer gauge becomes thicker, so that the cross-sectional shape of the belt is kept constant during filling with internal pressure. And the heat generation temperature of the running tire is increased, which causes a failure.

Further, in the means for providing the reinforcing portion on the outside of the belt portion as disclosed in the above-mentioned Japanese Patent Laid-Open No. 63-38007, the reinforcing belt depends on the rigidity of the coating rubber used and the cord diameter. There has been a problem that separation occurs at the end of the layer and it is difficult to obtain sufficient durability.

In the case of heavy-duty pneumatic tires for large vehicles and the like, it has been a great problem how to increase the belt rigidity and suppress the generated belt edge distortion. The reality is that these problems cannot be solved sufficiently.

Therefore, an object of the present invention is to provide a pneumatic tire in which the occurrence and growth of separation at the belt end portion of the pneumatic radial tire is suppressed and the durability is greatly improved.

[0014]

SUMMARY OF THE INVENTION In order to solve the above problems, the present inventors have proposed a large tire for heavy load, which is used for traveling on a rough road, when a projection input during traveling on an unpaved road or during a sharp curve traveling. By receiving the side force input, strain concentration occurs in a portion where the belt ends of the laminated cross belt layers are not constrained by other belt layers, that is, the belt layer end portions forming the free ends, and the ends thereof are concentrated. The belt undercushion sandwiched between the carcass and the free end of the innermost belt layer adjacent to the carcass, whereas the belt coating rubber and the carcass coating rubber have high hardness because of the separation from the portion. Since rubber (hereinafter abbreviated as “BUC”) has a lower hardness than the above-mentioned coated rubber, the belt-coated rubber and the BUC, and the carcass-coated rubber and the BUC are Stiffness level difference occurs in the rubber interface,
This causes strain concentration at such an interface,
Therefore, the separation generated from the belt end portion progresses to the belt-covered rubber / BUC interface and further from inside the BUC to the BUC / carcass-covered rubber interface. As a result of intensive studies focusing on a series of mechanisms in which the generation and growth of the belt, the belt layer end portion that forms such a free end has the following structure that can withstand the strain, so that the generation and growth of the separation can be prevented. Found that it can suppress and improve the durability of the belt end,
The present invention has been completed.

That is, according to the present invention, the carcass straddling the bead portion and at least two of the crown portions thereof are squeezed.
In a pneumatic radial tire having a layer and an adjacent cross belt main layer in which a metal cord is embedded, a melting point of 130 to 170 ° C. and a particle size are provided between the carcass and the free end of the innermost belt layer adjacent to the carcass. Syndiotactic-1,2-polybutadiene having a size of 100 μm or less (hereinafter referred to as “syn-1,2PB”) is a diene rubber 10
The present invention relates to a pneumatic radial tire in which a rubber member in which 5 to 40 parts by weight is mixed and mixed with 0 parts by weight is arranged as a BUC.

In the present invention, the diene rubber which constitutes BUC is a natural rubber, a synthetic polyisoprene rubber, a styrene-butadiene copolymer rubber, a polybutadiene rubber or another diene rubber, or a mixture thereof, which is required. Depending on the amount, carbon black, inorganic filler such as silica, aroma oil, softening agent such as spindle oil, antioxidant, vulcanizing agent, vulcanization accelerator, vulcanization accelerating aid, etc. It goes without saying that the compounding agent can be appropriately mixed.

Syn-1,2P used in the present invention
The polymerization catalyst of B comprises soluble cobalt such as cobalt octoate, cobalt 1-naphthate, cobalt benzoate and the like, an organoaluminum compound such as trimethylaluminum, triethylaluminum, tributylaluminum, triphenylaluminum and the like, and carbon dioxide. A catalyst system etc. can be mentioned. As specific polymerization methods, the methods described in JP-B-53-39917, JP-B-54-5436 and JP-B-56-18005 can be used, but syn-1,2PB used in the present invention can be used. The polymerization method of is not particularly limited to the methods described in these.

Further, in the present invention, such syn-
1,2PB is dispersed in the BUC rubber matrix with a particle size of 100 μm or less, preferably 50 μm or less after vulcanization, but the mixing method of the rubber composition is not particularly limited, and even in the wet blending method in a solvent, Alternatively, the same effect can be obtained by a dry blend method using a Banbury mixer or the like.

Next, an example pneumatic tire of the present invention will be described with reference to the drawings. In a radial tire (ORR) 1 for a large construction vehicle of a pneumatic tire shown in FIG. 1, the BUC 3 extends below the free end of the innermost belt layer of the belt trunk layer 4 to the carcass ply end on the carcass 2. Exists In the figure, 5 is a belt protective layer.

In another example of the pneumatic tire, a radial tire for trucks and buses (TBR) 11, the BUC 13 is mainly on the carcass 12 below the free end of the innermost belt layer of the belt main trunk layer 14. It is located on the shoulder. In the figure, 15 is a belt protective layer as in FIG.

[0021]

The inventors of the present invention have conducted various studies to make the end portion of the belt layer forming the free end a structure capable of withstanding strain,
It has been found to be effective to make the hardness of BUC close to that of the belt-coated rubber or the carcass-coated rubber.

However, in the case of a large-sized pneumatic tire that is used for running on a rough road due to heavy load, due to the severe operating conditions, it is possible to obtain an irregular input simply by arranging a high-hardness rubber BUC. As a result, a crack is generated at the belt end. Therefore, what is important here is how to suppress the progress and growth of cracks generated from the belt end portion under a large deformation input. For this purpose, the present inventors have made clear that the following is important.

That is, how to improve the fracture resistance of BUC rubber, and at the same time how to suppress the temperature rise due to self-heating during running of the belt end portion, that is, BU
How to improve the low heat generation characteristics of C rubber. In the present invention, by using the BUC rubber having the above-described structure, the hardness of the BUC rubber itself is increased, and at the same time, the BUC rubber has a low heat generation property, whereby the durability of the belt end portion can be significantly improved. It has become.

If the BUC rubber is simply made to have a high hardness, there are some methods that can be considered based on the prior art. For example, the following method is used. (1) Reinforcement by high filling of an inorganic filler such as carbon black or silica (2) Reinforcement to restrain the rubber molecular chain by forming a mesh in the rubber molecular chain (3) Thermosetting resin such as phenol resin Reinforcement to be used (4) Reinforcement of rubber matrix by addition of short fibers such as nylon

In the present invention, it goes without saying that these techniques can be used together if necessary. However, it is impossible to achieve the object of the present invention only by the above methods, no matter how they are combined.

That is, the reinforcement of the inorganic filler such as carbon black or silica by high filling surely increases the hardness of the rubber, but has a drawback that the low heat generation property is deteriorated, and the specific gravity of the filler itself is high. Since it is high, it also has a drawback that the specific gravity of the rubber composition of BUC itself becomes large.

Further, in the reinforcement for forming a mesh in the rubber molecular chain, an increase in the mesh to some extent increases the strength of the rubber,
Although the low heat generation property is also improved, when the density is higher than the mesh density which is generally used at present, the hardness of the rubber is further increased, but the breaking strength and the elongation at break are significantly reduced.

Further, when a thermosetting resin such as a phenol resin is used to reinforce the rubber matrix, the hardness of the rubber is greatly increased, but the low heat-generating property is remarkably deteriorated, and the resin-like property is exhibited due to the property. It becomes like this.

On the other hand, when reinforced with short fibers such as nylon, the hardness of the rubber along the orientation direction of the fibers is extremely high, but the hardness of the rubber is relatively low in the direction of 90 degrees with respect to the orientation direction, and the rubber physical properties are low. Large anisotropy exists, BUC
It was unsuitable as a material.

The BUC rubber material according to the present invention does not have the above-mentioned problems, and it is possible to improve the fracture resistance of the vulcanized rubber by increasing the hardness of the rubber, and further improve the low heat generation property. It is a rubber composition having little anisotropy.

However, the syn- used in the present invention
It is necessary that 1 and 2PB satisfy the above conditions.
That is, when the melting point measured by a differential thermal analyzer (DSC) is less than 130 ° C., sufficient hardness of rubber cannot be obtained.
If the temperature exceeds 70 ° C, sufficient rubber hardness can be obtained,
The fracture resistance is reduced. Similarly, syn-
If the compounding amount of 1,2PB is less than 5 parts by weight relative to 100 parts by weight of the diene rubber, sufficient rubber hardness cannot be obtained. On the other hand, if it exceeds 40 parts by weight, sufficient rubber hardness can be obtained and fracture resistance. The characteristics deteriorate. Further, the particle size of the syn-1,2PB particles in the rubber matrix after vulcanization is 10
When it exceeds 0 μm, the particles themselves become fracture nuclei and microscopic stress concentration occurs, so that sufficient fracture resistance cannot be obtained.

[0032]

EXAMPLES Next, the present invention will be specifically described with reference to Examples and Comparative Examples. First, various syn-
1,2PB resin was prepared. Dehydrated benzene 760 was placed in an autoclave with a volume of 2 liters in which air was replaced with nitrogen gas.
cc was added and 74 g of 1,3-butadiene was dissolved. Cobalt octoate 1mmol (concentration 1mmol / cc
Was used) and 1 minute later, 2 mmol of triethylaluminum (benzene solution having a concentration of 1 mmol / cc) was added and stirred, and 1 minute later, the amount of acetone shown in Table 1 below was added. 1 minute later carbon disulfide 0.6 m
mol (a benzene solution having a concentration of 0.3 mmol / cc) was added, and the mixture was stirred at 10 ° C. for 60 minutes to polymerize 1,3-butadiene.

0.75 g of 2,4-ditertiary-butyl-p-cresol was added to the resulting syn-1,2PB resin production liquid. Next, the syn-1,2PB resin production liquid was added to 1000 cc of methanol to produce syn-
The 1,2PB resin was precipitated. This syn-1,2
PB was further washed with methanol, filtered to remove methanol, and then dried in vacuum. The melting points of the obtained syn-1 and 2PB are also shown in Table 1 below.

[0034]

[Table 1]

A rubber composition for BUC was prepared by using the above-mentioned various syn-1,2PB and the formulation shown in Table 2 below.

[0036]

[Table 2] 1) N- (1,3-dimethylbutyl) -N'-phenyl-P-phenylenediamine 2) N-tert-butyl-2-benzothiazolylsulfenamide

Various rubber compositions shown in Table 2 were added at 150 ° C. × 3.
Various test pieces were prepared by vulcanization under the condition of 0 minutes. Also,
Such a rubber composition was used as BUC of a tire, and FIG.
Radial tire (size 21.00)
Various prototypes of R35) were produced. In this example, various measurements were performed according to the following methods.

1) Melting point Using a differential thermal analyzer (DSC200) manufactured by Seiko Co., Ltd., a nitrogen flow rate of 20 ml / min and a temperature of 20 ° C. to 10 ° C.
It was measured at a temperature rising rate of / min.

2) Hardness (Hd) Measured at 25 ° C. according to JIS spring type hardness (A type).

3) Resilience and elongation at break (%) The resilience was measured according to JIS K6301.

4) Belt-end separation resistance (index) Various trial tires were put on a drum tester, and the time until belt-end separation occurred at 100% load was measured. Compared. The larger the number, the better the result. The results obtained are shown in Table 3 below.

[0042]

[Table 3]

From the test results shown in Table 1, it was confirmed that in the tires of the present invention shown in Examples 1 to 3, the durability of the belt end portion was significantly improved as compared with the tires of Comparative Examples.

Similarly, a radial tire (size 1000R20) having the structure shown in FIG. 2, which was experimentally produced using the rubber composition of Example 2 as the BUC rubber, also gave good results.

[0045]

As described above, in the pneumatic tire of the present invention, between the carcass and the free end of the innermost belt layer adjacent to the carcass, a specific syn-1,
By arranging the BUC rubber in which a predetermined amount of 2PB is mixed and dispersed, it is possible to obtain an effect that the durability of the belt end portion is significantly improved, and thus the durability of the tire itself is significantly improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a radial tire for a large construction vehicle, which is an example of the present invention.

FIG. 2 is a cross-sectional view of another example radial tire for trucks and buses of the present invention.

[Explanation of sign]

 1 Radial tires for large construction vehicles 11 Radial tires for trucks and buses 2,12 Carcass 3,13 BUC 4,14 Belt main layer 5,15 Belt protective layer

Claims (2)

[Claims] 1. A pneumatic radial tire having a carcass straddling a bead portion and at least two layers of adjacent cross belt main layers in which a metal cord is buried, which is to be tightened at its crown portion, wherein the carcass and the carcass are adjacent to each other. Between the innermost layer and the free end of the belt layer, the melting point is 130 to 170 ° C. and the particle size is 10
Pneumatic radials characterized in that a rubber member in which 5 to 40 parts by weight of syndiotactic-1,2-polybutadiene having a size of 0 μm or less is dispersed and mixed with 100 parts by weight of diene rubber is arranged as a belt under cushion rubber. tire. 2. The pneumatic radial tire according to claim 1, wherein the rubber member extends to the end of the carcass ply.