JP2731104B2 - Rubber composition for insulation and pneumatic tire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition suitable for an insulation layer of a pneumatic tire and a pneumatic tire having an insulation layer obtained therefrom.

[0002]

2. Description of the Related Art As shown in FIG. 1, a pneumatic tire has a tread portion 3, side all portions 6 extending from both ends thereof in the tire side direction, and a bead portion located at a radially inner end of the side all portion 6. Five. The tire 10 is basically formed by arranging respective rubbers outside a cord layer called a carcass. An inner liner is provided on the innermost layer of the tire for the purpose of maintaining the internal pressure of the pneumatic tire inside the carcass layer. As the rubber for the inner liner, halogenated butyl rubber is usually used. When using halogenated butyl rubber,
Since the adhesion to the carcass cord is inferior, an insulation layer having excellent adhesion to the carcass cord is provided between the inner liner layer and the carcass layer (the insulation layer is not shown in FIG. 1).

The insulation layer is usually made of natural rubber alone or a blend of natural rubber and a diene rubber such as polybutadiene rubber or styrene-butadiene rubber. This insulation layer is basically inferior in air permeability to the inner liner layer, and does not basically have the function of maintaining the internal pressure unlike the inner liner layer. On the other hand, weight reduction of tires is considered to be the most important in the future from the viewpoint of resource saving. Therefore, by maintaining the adhesiveness of the carcass cord of the insulation layer and greatly improving the air permeability, the rubber thickness of the insulation and inner liner layers can be reduced, and the tire can be reduced in weight.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to reduce the air permeability of the insulation layer, reduce the rubber thickness of the inner liner layer, and reduce the weight of the tire.

[0005]

Means for Solving the Problems That is, the rubber component 10
A rubber composition containing 2 to 4.5 parts by weight of sulfur with respect to 0 parts by weight, wherein 20 to 70% by weight of the rubber component is an epoxidized natural rubber having an epoxidation degree of 3 to 50% by mole, A rubber composition for forming an insulation layer of a pneumatic radial tire, the remainder being a diene rubber.

The present invention also provides a pneumatic tire having an insulation layer obtained from the above rubber composition for insulation.

The rubber component used in the present invention is basically a diene rubber (especially natural rubber), but epoxidized natural rubber is also used in an amount of 20 to 70% by weight.

[0008] Epoxidized natural rubber is obtained by the reaction of natural rubber latex with peracetic acid. Due to this reaction, the double bond present in the molecule of natural rubber is epoxidized, and this structure is revealed from proton nuclear magnetic resonance spectrum (NMR) and infrared absorption spectrum (IR). Further, the content of the epoxy group is measured from IR and elemental analysis. The epoxidized natural rubber used in the present invention has an epoxidation degree of 3 to 3.
It is 50 mol%, preferably 5 to 35 mol%. If the degree of epoxidation is less than 3 mol%, the effect of epoxidation will not be exhibited, and if it is more than 50 mol%, the glass transition point will be too high, and the durability at low temperature will be poor.

The epoxidized natural rubber has a lower air permeability than the natural rubber, and the air permeability tends to be greatly reduced by blending the epoxidized natural rubber. The diene rubber used in the present invention is natural rubber or synthetic rubber (butadiene rubber, isoprene rubber, styrene butadiene rubber), and natural rubber is most preferable. The rubber composition of the present invention may contain 0.1 to 0.3 parts by weight of anhydrous sodium carbonate or the like when kneading the rubber in order to adjust the scorch time of the compounded rubber.

[0010] The rubber composition of the present invention further contains sulfur. When a steel cord is used as the carcass reinforcing cord, the amount of added sulfur is 2.0 to 4.5 parts by weight. If the amount is less than 2.0 parts by weight, the adhesiveness between the rubber and the cord will be low. If the amount is more than 4.5 parts by weight, the heat aging characteristics for the adhesiveness between the rubber or the rubber and the cord will be reduced. When the reinforcing cord is a textile (organic fiber) cord, the amount of sulfur added is 1.5 to 3.5 parts by weight, preferably 2.0 to 3.0 parts.

By mixing the above components, a rubber composition for insulation can be obtained. If necessary, various additives such as carbon black, aromatic oil, zinc oxide, stearic acid, an antioxidant and the like can be mentioned.

The mixing of the above components is carried out by a usual method. For example, a rubber composition can be obtained by mixing using a Banbury mixer or a roll. The tire of the present invention can be obtained, for example, by allowing this rubber composition to be present between the inner liner and the carcass cord during tire production and vulcanizing.

In the present invention, the ratio of the thickness (D) of the insulation rubber layer to the thickness (A) of the inner liner rubber layer, that is, D / A is 0.2 to 1.2, preferably 0.3. ~ 1.0
It is necessary to be. The D / A of the conventional tire is 1 to
It was 1.7. If this ratio is less than 0.2, the inner liner layer is too thin to maintain sufficient air pressure,
If it is larger than 1.2, the thickness of the rubber under the cord becomes excessive, so that the tire weight becomes heavy.

[0014]

According to the rubber composition of the present invention, the insulation layer can be made very thin as compared with the conventional one,
In addition, a part of the function of the inner liner layer is provided to the insulation layer to improve the air permeation resistance, so that the thickness can be reduced, and the weight of the tire itself can be greatly reduced as a whole.

[0015]

EXAMPLES The present invention will be described in more detail with reference to Examples. The present invention should not be construed as being limited to these embodiments.

Example 1 A rubber composition for insulation was obtained by kneading the components shown in Table 1.

[0017]

[Table 1]

* 1 Epoxy degree 25 (manufactured by Guthrie)
Molar% epoxidized natural rubber * 2 Tokai Carbon Co., Ltd. Seast 3 * 3 Sumitomo Chemical Co., Ltd. Antioxidant FR 2,2,4 trimethyl-1,2
-Purified product of dihydroquinoline polymer * 4 Ouchi Shinko Co., Ltd. Noxeller NS N-tert-butyl-
2-Bezothiazylsenephenamide * 5 First-class commercial reagent

The following evaluation was performed using this rubber composition. (1) Adhesion to cords Arrange the cords on a 3 mm rubber sheet,
After covering with a rubber sheet of mm and vulcanizing with a plate mold at 143 ° C. for 25 minutes, the rubber was peeled off, and the state of adhesion to the cord was evaluated by a 5-point method (higher is better).

(2) Air permeable tire is prepared and mounted on a rim according to JATMA standard.
The internal pressure was filled, the change in internal pressure was measured at room temperature, and the measurement result after 3 months was indicated as an index with Comparative Example A being 100 (the smaller the better).

Embodiment 2 The carcass and the belt are made of steel cord, and the number of cords of the carcass ply is 16/50 mm. 11
The R22.5 14PR rib type tire is shown in Table 1 above as insulation rubber. Using the rubber composition, vulcanization was performed at an external temperature of 150 ° C and an internal temperature of 180 ° C for 35 minutes using a vulcanizing mold. The internal pressure of the tire manufactured in this way is 8.5k
g / cm ^{2 was} filled and the change was investigated. Comparative Example A in Table 1
For the composition of Example B, the measurement was performed by changing the ratio D / A of the thickness (A) of the inner liner of the rubber composition tire to the thickness (D) of the insulation layer. The results are shown in FIG.

The tire obtained was measured for carcass durability by the following method. Carcass durability: Running: Car 2-D.4 truck / Normal running between Tokyo and Osaka Sampling: After running 300,000 km, cut tires (8 in total)
The adhesion state of the carcass cord and rubber was compared.

When the durability is poor, the insulation / inner liner interface shows a wavy pattern as shown in FIG. If the wave height (H) exceeds 0.3 mm, rubber deformation due to air pressure increases, causing excessive shear strain between cord / rubber and breaking the cord / rubber bond. Table 2 shows the results.

[0024]

[Table 2]

Example 3 The carcass is made of 1500 d / 2 cord of polyester fiber, and the number of cords of the carcass ply is 29/5.
0 mm. Using 11R22.5 14PR tires as in Example 1, the rubber of Table 2 was used as the insulation rubber, and the tests for the adhesiveness of the cord and the air permeability of the tire were performed. The results are shown in Table 3 above.

[0026]

[Table 3]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a tire of the present invention.

FIG. 2 is a schematic cross-sectional view of a carcass cord and an inner liner in a normal state.

FIG. 3 is a graph showing measurement results of Example 2.

[Explanation of symbols]

2 ... Carcass cord, 3 ... Tread, 5 ... Bead part, 6
... sidewall part, 7 ... inner liner layer, 20 ...
Carcass cord, 21: inner liner, 22: insulation layer.

Claims (3)

(57) [Claims] 1. A rubber composition containing 1.5 to 4.5 parts by weight of sulfur with respect to 100 parts by weight of a rubber component, wherein 20 to 70% by weight of the rubber component has an epoxidation degree of 3 to 50% by mole. A rubber composition for forming an insulation layer of a pneumatic radial tire, wherein the rubber composition is an epoxidized natural rubber having a diene rubber. 2. A pneumatic tire having an insulation layer obtained from the rubber composition according to claim 1. 3. An inner liner layer (7), an insulation layer formed thereon, a carcass cord layer (2) thereon, and a tread portion (3), a sidewall portion (6) and a carcass cord layer on the carcass cord layer. Bead part (5)
Wherein the insulation layer is formed from the rubber composition according to claim 1, and a ratio D of the thickness (A) of the inner liner layer to the thickness (D) of the insulation layer. / A is 0.2 to 1.2.