JP2003063205A - Radial tire for large vehicle and rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radial tire for heavy-duty vehicle provided with a rubber composition maintaining high elasticity and having durability by vulcanization for a long time and a belt layer made of the rubber composition and having heat resistance, durability and crack resistance. SOLUTION: This radial tire for heavy-duty vehicle has a belt layer made of a steel cord and coating rubber for the steel cord. The coating rubber is made by blending 100 pts.mass of the rubber component made of isoprene rubber and transpolybutadiene and N,N'-diphenylmethane-bis-maleimide by a specified amount. The compounding ratio of transpolybutadiene is characterized by being 25 mass% to 75 mass% of the total amount of both of N,N'-diphenylmethane-bis- maleimide and transpolybutadiene.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radial tire for large vehicles and a rubber composition, which can be suitably used for radial tires for large construction vehicles having improved durability, and belt layers of tires. The present invention relates to a rubber composition that maintains high elasticity even when it is vulcanized for a long time.

[0002]

2. Description of the Related Art Generally, in a radial tire for a large vehicle, a carcass layer embedded along a meridian direction of a ring-shaped tire body and a part of the carcass layer are overlapped with each other, that is, a tire ground contact surface. And a belt layer that is overlaid on the side. The belt layer is usually formed of a plurality of layers including a steel cord and a coating rubber of the steel cord, and imparts load resistance, traction resistance and the like to the tire. In addition, the belt layer has been devised by changing various mechanical structures or rubber component configurations, etc., to maintain heat resistance and cut separation resistance while maintaining tire load resistance, traction resistance and cut resistance. Has been proposed to increase the. For example, a tire having a structure in which the belt layer has five or more layers, is divided into a main layer and a protective layer, and uses a specific coating rubber for the protective layer to improve the heat separation resistance and the cut separation resistance of the entire tire. Proposed (JP-A-7-32)
No. 815). Further, the belt layer is composed of four layers having different widths, the sectional shape of the steel cords of the constituent layers is provided with inclination directionality, and the adjacent layers thereof are appropriately arranged according to different widths, and the steel cords are inclined in the same direction or It is proposed that the belt layer is appropriately arranged in the opposite direction to improve the separation resistance while maintaining the tire wear resistance performance, traction performance, cut resistance performance, etc. 8607, Japanese Patent Laid-Open No. 6-127213).

By the way, as described above, at least the following two points are particularly required for the coating rubber of the radial tire for a large vehicle having the belt layer composed of the steel cord and the coating rubber of the steel cord. The high elasticity required for securing the tire shape by tightening the belt due to the radial structure and the crack resistance for improving the durability of the tire. Conventionally, these two performances have been managed by controlling the degree of sulfur crosslinking of the coating rubber and the amount of carbon black added to the rubber.

[0004]

However, these days, vehicles are
In particular, with the increase in the size of construction vehicles, the tires used therein are required to be further increased in size. When the tire gets bigger,
The vulcanization time in the tire manufacturing process becomes long. In this case, particularly when the conventional sulfur crosslinking method is used, the heat resistance is insufficient, so that the performance of the coating rubber is deteriorated, and particularly the elastic modulus is lowered.

On the other hand, there is known a long-time vulcanizable rubber composition capable of suppressing a decrease in elastic modulus even when vulcanization is performed for a long time by increasing the addition amount of a filler such as carbon black. Has been. However, this rubber composition deteriorates its heat resistance, and there is a concern that tire failures may increase due to heat generation. Similarly, by increasing the amount of the vulcanization accelerator, it is possible to suppress the decrease in the elastic modulus, but there is a possibility that the crack resistance, durability, etc. of the tire may be decreased.

Therefore, in order to solve the above problems, an object of the present invention is to maintain a high elasticity even by vulcanization for a long time,
Another object of the present invention is to provide a radial tire for a large vehicle, which includes a rubber composition having durability and a belt layer made of the rubber composition, and has heat resistance, durability, and crack resistance.

[0007]

[Means for Solving the Problems] In order to solve the above problems, the inventors of the present invention have made earnest studies and, as a result, have used transpolybutadiene in combination with N, N′-diphenylmethane bismaleimide, which is a heat resistant cross-linking agent, Further, by using the heat-resistant cross-linking agent in a rubber composition in a specific ratio, excellent high elasticity is maintained even when a vulcanization step is performed for a long time, and a radial tire for large vehicles having a belt layer is applied. By using a rubber composition, it was found that the heat resistance, durability and crack resistance of the tire are extremely enhanced, and the inventions described in (1) to (10) below have been conceived.

(1) A radial tire for a large vehicle having a belt layer composed of a steel cord and a coating rubber of the steel cord, wherein the coating rubber is 100 parts by mass of a rubber component composed of isoprene rubber and trans polybutadiene, And N, N'-diphenylmethane bismaleimide are blended, and the total amount of the N, N'-diphenylmethane bismaleimide and the trans polybutadiene is 10 parts by mass or less per 100 parts by mass of the rubber component, and A radial tire for a large vehicle, wherein the compounding amount of the trans polybutadiene is 25% by mass to 75% by mass of the total amount of both the N, N'-diphenylmethane bismaleimide and the trans polybutadiene.

(2) The tire according to (1), wherein the total amount of the N, N'-diphenylmethane bismaleimide and the trans polybutadiene compounded is 5 parts by mass or less per 100 parts by mass of the rubber component. (3) The tire according to (1) or (2), wherein the N, N′-diphenylmethane bismaleimide is 0.3 to 7.5 parts by mass per 100 parts by mass of the rubber component.

(4) The coating rubber, after vulcanization,
The tensile stress at 100% elongation is 3.5 MPa (megapascal) or more, and the tan δ when measured at 25 ° C. under a strain of 2% is 0.200 or less (1) to (3) The tire according to any one of 1. (5) The trans-polybutadiene has a trans bond content of 82 to 98 mol% and a mass average molecular weight of 3 × 10 ⁴ to 20 × 10 ⁴ , and is described in any one of (1) to (4) above. Tires.

(6) 100 parts by mass of a rubber component consisting of isoprene rubber and trans polybutadiene, and N, N '
-Diphenylmethane bismaleimide is blended, and the total amount of the N, N'-diphenylmethane bismaleimide and the trans polybutadiene blended is the rubber component 10
It is 10 parts by mass or less per 0 parts by mass, and the compounding amount of the trans polybutadiene is 25% by mass to 75% by mass of the total amount of both the N, N′-diphenylmethane bismaleimide and the trans polybutadiene. A characteristic long-term vulcanizable rubber composition.

(7) The rubber composition as described in (6) above, wherein the total amount of the N, N'-diphenylmethane bismaleimide and the trans polybutadiene is 5 parts by mass or less per 100 parts by mass of the rubber component. (8) The rubber composition as described in (6) above, wherein the N, N′-diphenylmethane bismaleimide is 0.3 to 7.5 parts by mass per 100 parts by mass of the rubber component.

(9) After vulcanization, the tensile stress at 100% elongation is 3.5 MPa (megapascal) or more, and 25
Tan δ is 0.2 when measured under the condition of strain of 2% at ℃
The rubber composition according to any one of (6) to (8), which is 00 or less. (10) The trans-polybutadiene has a trans bond content of 82 to 98 mol% and a mass average molecular weight of 3 × 10 ⁴ to 20 × 10 ⁴ , and is any of the above (6) to (9). Rubber composition.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the radial tire for a large vehicle and the rubber composition used therein according to the present invention will be described in detail below. The radial tire for heavy vehicles and the rubber composition used therefor according to the present invention are not limited to the following embodiments or examples. The present invention relates to a radial tire for a large vehicle having a belt layer made of a steel cord and a coating rubber of the steel cord. The coating rubber of the radial tire for a large vehicle according to the present invention comprises 100 parts by mass of a rubber component composed of isoprene rubber and trans polybutadiene, and N, N'-diphenylmethane bismaleimide. The total amount of the'-diphenylmethane bismaleimide and the trans polybutadiene compounded is 10 parts by mass or less per 100 parts by mass of the rubber component, and the compounded amount of the trans polybutadiene is the N, N'-diphenylmethane bismaleimide and the trans compound. 25% by weight of the total amount of both polybutadiene and 7
It is 5% by mass.

Before describing such a radial tire for a large vehicle, first, a coating rubber used for such a belt layer, that is, a rubber composition according to the present invention capable of maintaining high elasticity even when a vulcanization process is carried out for a long time. Details of the item. The rubber composition of the present invention is most suitable as a coating rubber in the radial tire for large vehicles,
It is not limited to these applications, and is preferable as a rubber composition of a rubber product including a vulcanization step, particularly a step in which a vulcanization step for a long time is performed.

The rubber composition according to the present invention comprises a rubber component 100 composed of isoprene rubber and trans polybutadiene.
Parts by mass, and N, N'-diphenylmethane bismaleimide are mixed, and the total amount of the N, N'-diphenylmethane bismaleimide and the trans polybutadiene is 10 parts by mass or less per 100 parts by mass of the rubber component. And, the blending amount of the trans polybutadiene is 25 mass% to 75 mass% of the total amount of both the N, N′-diphenylmethane bismaleimide and the trans polybutadiene. Further, other rubber components, for example, styrene-butadiene rubber and other butadiene rubbers can be used in combination as long as the effects of the present invention are not impaired.

That is, the rubber composition according to the present invention comprises a rubber component and N, N'-diphenylmethane bismaleimide (hereinafter abbreviated as "BMI"). Of these, the rubber component is composed of isoprene rubber and trans polybutadiene. As the isoprene rubber used in the present invention, all of the commonly available natural rubber and synthetic isoprene can be used, but it is preferable to use natural rubber. Isoprene rubber is 90 parts by weight in 100 parts by weight of the rubber component.
To 99 parts by mass, preferably 95 to 99 parts by mass.

The trans-polybutadiene used in the present invention has a trans bond content of 82 to 98 mol%, preferably 86 to 98%. The higher the trans bond content, the higher the effect of promoting the extension crystallinity of the isoprene rubber tends to be. On the other hand, if the content is too low, the elongation crystallinity of the isoprene rubber tends to be inhibited, which is not preferable. It should be noted that the content of more than 98 mol% is out of the range because it is difficult to synthesize, but if the content of more than 98 mol% can be synthesized in the future, the range is also included in the present invention.

The mass average molecular weight of this trans polybutadiene is 3 × 10 ^{4 to} 20 × 10 ⁴ , preferably 5 × 10 ^{4 to} 15 × 10 ⁴ . When the molecular weight is within this range, the processability of the rubber composition for coating rubber before vulcanization and the physical properties during vulcanization are well balanced. On the other hand, when the molecular weight decreases, the elastic modulus tends to decrease,
When the molecular weight is high, the workability tends to decrease.

Further, the compounding amount of trans polybutadiene is 0.3 to 7.5 parts by mass, preferably 0.5 to 4 parts by mass, per 100 parts by mass of the rubber component. If the amount is less than 0.3 parts by mass, the effect of improving the heat resistance due to long-term vulcanization may not be sufficient, and the processability of the rubber composition when not vulcanized tends to deteriorate. On the other hand, when the blending amount exceeds 7.5 parts by mass, the heat resistance tends to decrease, the compatibility with the isoprene rubber may not be sufficiently obtained, and the crack resistance may deteriorate.

The trans polybutadiene used in the present invention may be a commercially available product or one obtained by synthesis. An example of the production method is a method in which a butadiene monomer is brought into contact with a quaternary catalyst of nickel boroacylate, tributylaluminum, triphenylphosphite, and trifluoroacetic acid in a solvent to perform polymerization.

The rubber composition used in the present invention comprises N, N'-diphenylmethane bismaleimide (BMI) represented by the following formula. In addition, since BMI gives a thermally stable crosslinked structure as compared with sulfur crosslinking,
It is known as a heat resistant cross-linking agent.

[0023]

[Chemical 1]

The total amount of the BMI and trans polybutadiene contained in the rubber component is 10 parts by mass or less, preferably 5 parts by mass or less, relative to 100 parts by mass of the rubber component. When the total amount of BMI with trans polybutadiene exceeds 10 parts by mass, crack resistance tends to decrease, and BMI tends to remain unreacted in the rubber composition after vulcanization. As a result, a stable cross-linked morphology, which is a characteristic of BMI, may be generated, and the effect of enhancing the heat aging resistance may be impaired.

The amount of BMI is 0.3 to 7.5 parts by weight, preferably 0.5 to 4 parts by weight, based on 100 parts by weight of the rubber component. If the amount of BMI exceeds 7.5 parts by mass, crack resistance tends to decrease, and BMI tends to remain unreacted in the rubber composition after vulcanization. As a result, BMI The characteristic stable cross-linking morphology may be generated, and the effect of enhancing the heat aging resistance may be impaired. If the amount of BMI is less than 0.3 parts by mass with respect to 100 parts by mass of the rubber component, the effect of suppressing heat resistance due to long-term vulcanization may not be sufficient.

Further, in the rubber composition of the present invention, the blending amount of the trans polybutadiene is 25 mass% to 75 mass% of the total amount of both the N, N′-diphenylmethane bismaleimide and the trans polybutadiene. It is a range. When the balance of the compounding ratio deviates from the above range, the tan δ of the tire becomes large and the hysteresis loss becomes large. Therefore, although the tensile stress at 100% elongation is high, the crack resistance is sufficiently improved. Absent.

The rubber composition used in the present invention may contain various components commonly used in the rubber industry in addition to the rubber component and BMI. For example, as various components, fillers (for example, reinforcing fillers such as carbon black and silica; and inorganic fillers such as calcium carbonate and calcium carbonate); vulcanization accelerators; antioxidants;
Examples thereof include zinc oxide; stearic acid; a softening agent; and additives such as antiozonants. As the vulcanization accelerator, M (2-mercaptobenzothiazole), DM
(Dibenzothiazyl disulfide) and CZ (N-cyclohexyl-2-benzothiazyl sulfenamide) and other thiazole vulcanization accelerators; TT (tetramethyl thiuram sulfide) and other thiuram vulcanization accelerators; and DP
Examples thereof include guanidine-based vulcanization accelerators such as G (diphenylguanidine).

The rubber composition having a rubber component composed of the isoprene rubber and trans polybutadiene preferably has the following characteristics. That is, after vulcanization, 100
The tensile stress at the time of% elongation is 3.5 MPa (megapascal) or more, and preferably 3.5 to 4.0 MPa. The tensile stress is measured according to JIS K6301-1.
It is better to measure according to 995. If the tensile stress is too small, when it is used as a coating rubber, the strain of the belt layer at the time of constant stress, which is an input to the vehicle belt rubber of the tire, increases and the crack resistance tends to decrease.

A rubber composition having a rubber component composed of isoprene rubber and trans polybutadiene is
Tan measured at a temperature of 25 ° C. and a strain of 2%
δ is 0.200 or less, preferably 0.16 to 0.2,
More preferably, it is 0.18 to 0.2. Note that tan δ is an index of hysteresis loss, and ta
The larger nδ is, the higher the hysteresis loss is, and the larger the heat generation amount is. That is, when tan δ increases, the heat resistance of the rubber composition tends to decrease. The tan δ can be measured, for example, by using a viscoelasticity measuring device (spectrometer manufactured by Toyo Seiki Co., Ltd.) under the condition of frequency: 52 Hz.

Therefore, the radial tire for large vehicles according to the present invention uses the coating rubber made of the above rubber composition, that is, the belt layer made of the coating rubber and the steel cord coated with the coating rubber. I have. The steel cord may be any steel cord that has been conventionally used in the tire industry.
The belt layer of the present invention may have another layer in addition to the steel cord and the coating rubber. The radial tire having the belt layer of the present invention is a tire used for large vehicles, particularly large construction vehicles, but may be used for other vehicles.

[0031]

The present invention will be specifically described below with reference to examples, but the present invention is not limited to the examples.

(Preparation of trans polybutadiene) A stainless reaction vessel equipped with a thermometer, a stirrer, a pressurizer, and a pouring spout was prepared, and the inside of the vessel was replaced with nitrogen gas. In this container, 4086 g of butadiene / hexane solution (23.7 mass% butadiene); 12.0 ml of hexane solution of 0.84 mol / L nickel boroacylate (hereinafter referred to as NiOB); 0.62 mol / L tributylaluminum (hereinafter, referred to as TIBAL) hexane solution 49 ml; triphenylphosphite (hereinafter TPP)
) Solution in hexane (TPP stock solution 2.64 ml)
Was dissolved in 25 ml of hexane) about 27 ml; and about 40 ml of a solution of trifluoroacetic acid (hereinafter referred to as TFA) in hexane (15.6 ml of TFA dissolved in 25 ml of hexane) were mixed, and the mixture was mixed uniformly at 80 ° C. Polymerization reaction was carried out for 6 hours. The catalyst molar ratio is Ni
OB / TIBAL / TPP / TFA = 1/3/1/20
Met.

Thereafter, excess isopropanol and aging protection were used.
Pour this solution into the container containing the stopper to stop the polymerization.
It re-sinked. Furthermore, this is filtered and vacuum dried at 50 ° C.
And crystalline trans polybutadiene (hereinafter referred to as “TR-B
R "). TR-BR obtained
S-bond content is 92%, mass average molecular weight 3.2 × 10 ^Four
Met.

(Examples 1 to 4 and Comparative Examples 1 to 10) According to the composition shown in Table 1, the components were kneaded and vulcanized at 145 ° C. for 60 minutes, and the physical properties of the vulcanizates obtained were obtained. Was evaluated. The TR-BR used was the one obtained above. Upon evaluation, the following 1) tensile stress at 100% elongation, 2) tan δ, and 3) crack resistance were measured. Next, each measurement condition etc. are described.

1) Tensile stress at 100% elongation (100% MO
D) The vulcanized product obtained as a sample was measured according to JIS K6301-19.
95.

2) tanδ The test piece of the obtained vulcanized product was measured at a temperature of 25 ° C. using a viscoelasticity measuring device (spectrometer manufactured by Toyo Seiki Co., Ltd.);
It was measured under the conditions of a strain of 2% and a frequency of 52 Hz.

3) As a crack resistance sample, its shape was dumbbell type No. 3 test piece (JI
It was cut out into S # 3). Using this sample, a constant load mode test was performed with a creep tester (manufactured by Shimadzu Corporation).
The number of breaks at that time was set to 100 as the result of Comparative Example 1,
The values of Examples 1 to 4 and Comparative Examples 2 to 10 were displayed as indices. The measurement results of the above 1) to 3) are also shown in Table 1.
Shown in.

[0038]

[Table 1]

From Table 1 above, it can be seen that the rubber compositions of Examples 1 to 4 are excellent in 100% elongation, tan δ, and crack resistance. Further, as shown in Comparative Examples 1 to 7, it is understood that the rubber composition lacking both or at least one of trans polybutadiene and N, N'-diphenylmethane bismaleimide does not satisfy all the above performances. Further, as shown in Comparative Example 10, it can be seen that when the total amount of trans polybutadiene and N, N′-diphenylmethane bismaleimide exceeds 10% by weight, the crack resistance is deteriorated. Further, it can be seen from Comparative Examples 8 and 9 that even if the trans polybutadiene content is less than 25% by weight or the total content of both is greater than 75% by weight, the crack resistance is not sufficiently improved.

[0040]

As described above, according to the present invention,
The rubber composition that is the coating rubber is a rubber component 10 comprising isoprene rubber and trans polybutadiene.
0 parts by mass and N, N'-diphenylmethane bismaleimide are compounded, and the total amount of the N, N'-diphenylmethane bismaleimide and the trans polybutadiene compounded is 10 parts by mass or less per 100 parts by mass of the rubber component. And the amount of the trans polybutadiene compounded is 25% by mass to 75% by mass of the total amount of both the N, N′-diphenylmethane bismaleimide and the trans polybutadiene. Radial tires for large vehicles, which maintain elasticity and have a belt layer made of such a rubber composition, have excellent heat resistance and crack resistance.

Claims (10)

[Claims] 1. A radial tire for a large vehicle having a belt layer composed of a steel cord and a coating rubber of the steel cord, wherein the coating rubber is 100 parts by mass of a rubber component composed of isoprene rubber and trans polybutadiene. N, N′-diphenylmethane bismaleimide is blended, and the total amount of the N, N′-diphenylmethane bismaleimide and the trans polybutadiene is 10 parts by mass or less per 100 parts by mass of the rubber component, and The compounding amount of trans polybutadiene is 25% of the total amount of both the N, N′-diphenylmethane bismaleimide and the trans polybutadiene.
A radial tire for a large vehicle, characterized in that the content is from mass% to 75 mass%. 2. The tire according to claim 1, wherein the total amount of the N, N′-diphenylmethane bismaleimide and the trans polybutadiene compounded is 5 parts by mass or less per 100 parts by mass of the rubber component. 3. The tire according to claim 1, wherein the N, N′-diphenylmethane bismaleimide is 0.3 to 7.5 parts by mass per 100 parts by mass of the rubber component. 4. The coating rubber, after vulcanization, 10
Tensile stress at 0% elongation is 3.5 MPa (megapascal)
The tire according to any one of claims 1 to 3, which has the tan δ of 0.200 or less when measured at 25 ° C under a strain of 2%. 5. The trans polybutadiene has a trans bond content of 82 to 98 mol% and a mass average molecular weight of 3 × 10 ⁴ to 20 × 10 ^4.
A tire according to claim 4. 6. A rubber component comprising 100 parts by mass of an isoprene rubber and trans polybutadiene, and N, N′-diphenylmethane bismaleimide are blended.
The total amount of N'-diphenylmethane bismaleimide and the trans polybutadiene compounded is 10 parts by mass or less per 100 parts by mass of the rubber component, and the trans polybutadiene compounded amount is the N, N'-diphenylmethane bismaleimide and the A long-term vulcanizable rubber composition, characterized in that it is 25 mass% to 75 mass% of the total amount of both trans-polybutadiene. 7. The rubber composition according to claim 6, wherein the total amount of the N, N′-diphenylmethane bismaleimide and the trans polybutadiene compounded is 5 parts by mass or less per 100 parts by mass of the rubber component. 8. The rubber composition according to claim 6, wherein the N, N′-diphenylmethane bismaleimide is 0.3 to 7.5 parts by mass per 100 parts by mass of the rubber component. 9. Tensile stress at 100% elongation after vulcanization is 3.5 MPa (megapascal) or more, and 25 ° C.
Has a tan δ of 0.20 when measured under a strain of 2%
The rubber composition according to any one of claims 6 to 8, which is 0 or less. 10. The trans-polybutadiene has a trans bond content of 82 to 98 mol% and a mass average molecular weight of 3 × 10 ⁴ to 20 × 10 ⁴ , The rubber composition according to the item.