JP3168438B2 - 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 pneumatic tire capable of reducing weight without deteriorating cut resistance and fatigue resistance of a sidewall portion.

[0002]

2. Description of the Related Art As a measure for protecting the environment of the earth against acid rain and global warming in recent years, further reduction in fuel consumption of automobiles is required. As one of the measures, reduction in weight of pneumatic tires is strongly demanded. Various methods can be considered as measures for reducing the weight of the pneumatic tire. As described in Japanese Patent Application Laid-Open No. 62-199506 proposed for the purpose of improving the weather resistance, the sidewall portion is made of foamed rubber. Doing is an effective means.

[0003] However, since foamed rubber has low cut resistance and fatigue resistance, if it is used as a sidewall rubber as it is, it is impossible to sufficiently satisfy the durability, which is the inherent characteristic required of the sidewall portion. There was a problem.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a pneumatic tire which can be reduced in weight without deteriorating cut resistance and fatigue resistance of a sidewall portion.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to form a side wall portion having a plurality of foamed rubber layers having different foaming rates from each other. This can be achieved by making it as large as possible. By forming the side wall portion from the foamed rubber layer in this manner, it is possible to reduce the weight, and furthermore, the side wall portion is formed from a plurality of foamed rubber layers, and the outer layer in which the bending strain applied to the side wall when the tire is rotated increases, the more the outer layer becomes foamed. Since the ratio is reduced, the cut resistance and fatigue resistance inherent in the sidewall portion can be secured.

In the present invention, the sidewall portion is
It refers to the "portion between the tread and the bead" specified in the JATMA automobile tire safety standard, and does not include the rim cushion portion. Hereinafter, the present invention will be specifically described with reference to the drawings. FIG. 1 shows an embodiment in which the present invention is a pneumatic radial tire. In the figure, 1 is a tread portion, 2 is a sidewall portion, 3 is a carcass layer, 5 is a bead core, and 6 is a bead filler.

The carcass layer 3 is folded at both ends so as to wrap the bead filler 6 from the inside to the outside of the tire around the left and right bead cores 5 respectively. On the outer peripheral side of the carcass layer 3 corresponding to the tread portion 1, two belt layers 7, 7 'are formed at 10 to 35 degrees with respect to the tire circumferential direction.
Are arranged so as to intersect with each other at a cord angle of.
The side wall portions 2 have different foaming rates from each other.
It is composed of three foam rubber layers 2a, 2b and 2c. These foamed rubber layers 2a, 2b, 2c
The foaming rate a of a is the smallest, and the foaming rate increases in the order of the foaming rate b of the middle layer 2b and the foaming rate c of the inner layer 2c.

In the above-described configuration, when the pneumatic tire rotates on the ground and the side wall portion 2 undergoes bending deformation, the vicinity of the center of the carcass layer 3 having a high elastic modulus becomes the bending neutral axis t. The bending strain ε at a point separated from the neutral axis t by z (the direction outside the tire from the neutral axis t is +) is expressed by the following equation. ε = ε _o + zK where ε _o : strain at the neutral axis t in bending, K: curvature change From the above equation, the bending strain ε of the sidewall portion 2 increases toward the outside of the tire. In the above-described configuration, the plurality of foamed rubber layers 2a, 2b,
2c, the foaming rate a of the foamed rubber layer 2a in which the distance z from the bending neutral axis t to the tire outer direction is the largest is minimized, and the foaming rate is sequentially increased as the inner foamed rubber layers 2b and 2c become larger. Therefore, even if the sidewall portion 2 is made of foamed rubber, its fatigue resistance can be improved, and a decrease in cut resistance can be suppressed.
Further, since the side wall portion 2 is made of foamed rubber, it is possible to contribute to weight reduction of the tire.

In such a pneumatic tire of the present invention, for example, a sidewall of a green tire is formed by stacking a plurality of unvulcanized rubber sheets having different blending amounts of a foaming agent, and the green tire is formed by a conventional method. And vulcanization at the same time as foaming. When a green tire having a sidewall is formed by vulcanization from a single unvulcanized rubber sheet containing a foaming agent, a thin film having a foaming rate of 0% is formed and the thickness from the outermost surface in contact with the mold is increased. Although the foaming rate may slightly change in the direction of the side wall, the foaming rate is not regularly increased from the outer surface of the sidewall portion toward the inside as in the present invention. And the effect of cut resistance is not satisfied.

In the present invention, in order to further improve the above-mentioned effects of fatigue resistance and cut resistance, the outer layers 2a,
Foaming rates a%, b% and c% of the middle layer 2b and the inner layer 2c
Satisfies the following relationship: 10 ≦ b ≦ 20, 0 <a <b, b <c ≦ (b + 1
0) By increasing the foaming ratio b of the intermediate layer 2b to 10% or more, the weight-reducing effect is increased, and by setting the foaming ratio b to 20% or less, the cut resistance and fatigue resistance of the sidewall portion can be more reliably maintained. Can be In addition, by setting the foaming ratio c of the inner layer 2c to which almost no bending strain is applied to be larger than the foaming ratio b of the intermediate layer 2b, the weight reduction effect can be ensured. However, even if the foaming ratio c of the inner layer 2c is excessively increased, when the wound reaches the inner layer, rapid growth is likely to occur. Therefore, it is possible to prevent the damage by setting it to (b + 10) or less.

The number of the plurality of foamed rubber layers is not particularly limited, but is preferably 3-5. The average thickness of each foamed rubber layer does not necessarily have to be the same, but the average thickness of the outer layer 2a is desirably at least 0.5 mm or more. In the present invention, as the rubber composition constituting the sidewall portion, a rubber composition containing various known foaming agents can be used, and is not particularly limited. Preferably, a urea-based auxiliary compounding less than the same amount as the compounding amount of the blowing agent is used. By adding less than the same amount of the urea-based auxiliary as the foaming agent, the vulcanization temperature of the rubber composition (usually,
The foaming agent is thermally decomposed at about 150 to 175 ° C (usually 20
0 ° C. or higher), and each rubber layer made of foamed rubber having a predetermined foaming rate can be easily formed.

[0012]

EXAMPLE The tire size was 195 / 60SR14, and the total thickness of the side wall was 3 mm. The four types of rubber compositions shown in Table 2 were used. The tires of the present invention, the conventional tires and the comparative tires having different numbers of rubber layers as shown in Table 1 were produced.

For these three types of radial tires,
The cut resistance and weight reduction were evaluated by the following methods. The results were as shown in Table 1. Cut resistance : The test tire is assembled on a rim of 14 × 6JJ, filled with air pressure of 1.8 kg / cm ² , and at its maximum width position at an angle of 45 ° with respect to the tire cross-sectional direction, a width of 5 mm and a depth of 5 mm. After inserting a 0.8 mm scalpel cut, it was mounted on a drum having a diameter of 1707 mm, a load of 310 kg was applied, and after traveling 5,000 km at a speed of 81 km / hr, the length of the scalpel cut was measured. Evaluation was made based on the difference in the length of the female cut (degree of growth).

The measurement result is based on the value of the conventional tire (10
0). The larger the index, the lower the cut resistance. Light weight property : The weight of each test tire was measured and indicated by an index using the weight of the conventional tire as a reference (100). A larger value indicates a larger tire weight.

[0015]

[0016] Note: The values in the columns of rubber components and compounding chemicals indicate parts by weight. ¹⁾ "Cellular" D (dinitrosopentamethylenetetramine) manufactured by Eiwa Kasei Kogyo Co., Ltd. ²⁾ "Cell Paste" K5 (urea compound) manufactured by Eiwa Kasei Kogyo Co., Ltd. ³⁾ Average cell area = Test from any unit cross section of foamed rubber layer A piece was cut out, flattened, and then magnified 165 times to obtain the cell area of 10 cells in the foamed rubber. The value calculated from the average = (sum of cell areas of 10 cells) / 10 ^{4 )} Bubble occupation area ratio = Percentage (%) of the area occupied by the total number of bubbles in an arbitrary unit cross section of the foamed rubber layer From Table 1, the tire of the present invention is lighter in weight than the conventional tire, and has substantially the same cut resistance. Holds sex. On the other hand, although the comparative tire is reduced in weight, the cut resistance is significantly deteriorated.

[0017]

According to the present invention, the side wall portion of the pneumatic tire is made of a foamed rubber layer to reduce the weight, and the foamed rubber layer is formed of a plurality of layers having different foaming rates from each other. Since the foaming ratio of the outer layer is made smaller and the inner layer is made larger, the cut resistance and fatigue resistance, which are the essential characteristics of the sidewall portion, can be secured.

[Brief description of the drawings]

FIG. 1 is a half sectional view showing a pneumatic tire according to an embodiment of the present invention.

[Explanation of symbols]

2 Side wall portion 2a, 2b, 2c
Foam rubber layer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-199506 (JP, A) JP-A-6-40218 (JP, A) JP-A-4-176705 (JP, A) JP-A-4-1992 133803 (JP, A) JP-A-2-162102 (JP, A) JP-A-64-83410 (JP, A) JP-A-62-184004 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B60C 13/00 B60C 1/00

Claims (1)

(57) [Claims] 1. A pneumatic tire in which a sidewall portion is composed of a plurality of foamed rubber layers having different foaming rates from each other, and the foaming rates of the plurality of foamed rubber layers are smaller in an outer layer and larger in an inner layer.