JP4605691B2 - Pneumatic tire - Google Patents

Description

The present invention relates to a pneumatic tire having the features pneumatic tire particularly on the structure of the sipe.

For the purpose of maintaining drainage performance while ensuring steering stability of the tire, etc., the block is formed by a plurality of sipes extending in the tire width direction in blocks formed by the main groove in the tire circumferential direction and the lug groove in the tire width direction. A tread pattern having formed sub-blocks is used.
This sipe is attached by embedding a thin plate-like protrusion, commonly called a blade, in the base material of a tread molding die of a vulcanizer, etc., and a raw tire is attached to this, and the raw tire is heated from the inside. Then, it is formed by expanding and deforming and pressure bonding (see Patent Document 1).

FIG. 4 is a cross-sectional view schematically showing a main part of a mold 70 of a vulcanizer having a tread molding mold in which a blade 60 is embedded.
The mold 70 includes upper and lower molds 72a and 72b, and upper and lower molds 74a and 74b for forming a tread. Numerous blades for sipe formation are embedded or implanted on the surfaces of the upper and lower molds 74a and 74b.
By the way, in a radial tire having a tread pattern partitioned by such a sipe, although not described in the patent literature, a cap rubber layered with a cap rubber layer made of foamed rubber and a base rubber layer made of a non-foamed rubber layer is laminated. Those having a tread with a Pooh base structure are known. The foamed rubber in this structure is designed in accordance with, for example, a foaming rate of about 25% at normal temperature and a design specification.

When a tire having this foam rubber layer is vulcanized and molded, the tire temperature is about 170 ° C at the end of vulcanization, and the volume of foam rubber on the cap side is very expanded at this temperature. There is considerable resistance to pull away from the vulcanizing mold.
On the other hand, the tread mold of the vulcanization mold has a large number of three-dimensional blades for sipe formation. When these three-dimensional blades are separated from the mold, the narrow sub-blocks partitioned by the sipe are The deformed sub-block is locally deformed by the tensile resistance of the blade, and the deformed sub-block may thermally expand at the temperature at the end of vulcanization and may be in close contact with the adjacent sub-block.

When the expansion ratio of the foamed rubber is 25% at normal temperature as described above, when the adjacent sub-block expands and comes into close contact as described above, the tire continues to maintain its close contact state even at normal temperature, That part remains as irregularities on the tread surface of the tire. Although the unevenness hardly affects the durability and other performances of the tire, there is a problem that the commercial value is lowered in a tire such as a passenger car in which the quality of appearance is important.
In order to solve this problem, the thickness of the blade forming the sipe is increased to widen the sipe, and when the vulcanized tire is released from the mold, the adhesion between the sub-blocks can be prevented. If the thickness of the sipe is increased as it is, the width of the sipe reaches the non-foamed rubber layer, resulting in a new problem that the rigidity of the tire is lowered and the steering stability is sacrificed.
Therefore, conventionally, in order to prevent the surface unevenness, the blade implantation shape is changed at the sacrifice of the tire performance as described above, or the foaming rate of the foamed rubber is set low to prevent the surface unevenness.
Japanese Patent Laid-Open No. 8-1672

The first object of the present invention is to prevent the adjacent sub-blocks made of foamed rubber from adhering to each other without sacrificing the steering stability of the tire, and to provide unevenness on the tread surface of the tire. Is to prevent the occurrence of
In addition, the second object is to enable a sipe having a width necessary for suppressing the occurrence of unevenness to be formed without manufacturing restrictions.

The invention of claim 1 is a pneumatic tire having a tread portion having a block pattern and each block divided into narrow sub-blocks by a plurality of sipes, wherein the tread portion is a radially outer cap rubber layer. The base rubber layer has a structure in which the inner base rubber layer is laminated, and the sipe has a certain wide width so that the adjacent sub-blocks do not adhere to each other at the time of mold release after vulcanization in the cap rubber layer, and the tread in the base rubber layer. The pneumatic tire is configured to have a constant width that is narrower than the cap rubber layer so as to maintain rigidity.
According to a second aspect of the present invention, in the tire according to the first aspect, the hardness of the cap rubber layer is smaller than that of the base rubber layer.
The pneumatic tire according to claim 1 or 2, wherein the cap rubber layer is a foam rubber layer, and the base rubber layer is a non-foam rubber layer. This is a tire .

  The pneumatic tire of the present invention is provided with a wide sipe groove in the cap tread portion made of foamed rubber, so that the sub-blocks can be prevented from coming into close contact with each other during vulcanization. Occurrence is suppressed. Further, since the base tread portion of the tire is non-foamable rubber and has a higher hardness than the cap tread portion made of foamable rubber, the block rigidity is not lowered and the steering stability is excellent. Moreover, the width of the sipe can be freely set to a width where adjacent sub-blocks are not in close contact with each other at the time of mold release after vulcanization without being restricted in production.

FIG. 1 is a development view of a tread having a block pattern according to an embodiment of a pneumatic tire of the present invention.
The tire tread 10 includes two main grooves 20a and two narrow grooves 20b formed in the tire circumferential direction, and a plurality of lug grooves 30 arranged in the tire width direction at equal intervals in the tire circumferential direction. And a plurality of blocks 40 that are partitioned and a shoulder block 42 disposed at an end in the width direction of the tire.
The plurality of blocks 40 are each formed with a plurality of sipes 50 each having a very narrow groove in a substantially width direction of the tire in a substantially zigzag manner. As described above, this sipe is formed by, for example, a stainless steel blade 60 embedded in a tread mold during vulcanization of the tire.

2 shows a blade 60 for forming a sipe, FIG. 2A is a sectional view thereof, and FIG. 2B is a perspective view thereof.
As shown in the side view of FIG. 2B, the sipe forming blade 60 has a width B portion 62 on the front end side when attached to the tread mold, and a width A portion on the end side thereof, that is, on the tread surface side of the tire. 64, and an inclined surface 66 whose width changes continuously from A to B in the middle portion thereof. Further, the blade 60 is formed in a zigzag shape with a predetermined length as shown in FIG. 1B in order to form a sipe that is bent in a zigzag shape substantially in the width direction of the tire.
Here, the width A portion is the sipe molding portion 64 of the cap rubber layer 12 (FIG. 3) made of foamed rubber, and the width B portion is a base made of non-foamed rubber having a narrower width than the sipe molding portion. It is the sipe molding part 62 of the rubber layer 14 (FIG. 3). These widths are selected from a certain numerical range depending on the foaming rate and the hardness of the foamed rubber, but the width A is preferably 0.5 mm to 2 mm, and the width B is preferably 0.3 to 1 mm. If the width A is narrower than the above range, the adjacent sub-blocks of the formed sipe are likely to be in close contact with each other, and if the width B is wider than the above range, the formed sipe has insufficient rigidity of the non-compressed rubber, resulting in stable maneuverability. Adversely affect.

Next, an example of this blade will be described. Table 1 shows specific dimensions of the blade according to the present invention. Here, three types of blades are shown according to the product foaming rate of the foam rubber of the cap rubber layer of the tire according to the present embodiment.
The type 1 blade is for forming a sipe in a tire cap rubber layer and a base rubber layer having a product foaming rate (foaming rate of foamed rubber at room temperature) of 10%. The A dimension of this blade, i.e., the width of the wide part, the L dimension, i.e. its length, is 0.5 mm and 3.5 mm, respectively, and the B dimension, i.e., the width of the narrow part, M dimension, i.e. its length, They are 0.4 mm and 3.0 mm, respectively.
Hereinafter, the same applies to Type 2 and Type 3, and the specific numerical values are as shown in Table 1. As the product foaming rate increases, the A dimension of the blade, that is, the width of the sipe-molded portion of the foam rubber is increased. . This is because, since the product foaming rate is increased, the thermal expansion of the foamed rubber at the time of mold release after the vulcanization of the tire is increased.

  Therefore, by using this blade 60, a wide groove is formed in the foamed rubber layer of the tread and a narrow groove is formed in a zigzag shape in the substantially width direction of the tire during the vulcanization molding of the tire. It is formed. As a matter of course, the sipe is not limited to the zigzag shape, but may be a straight line or another line shape.

FIG. 3 shows a cross-sectional shape of a main part of the tread 10 of the tire according to the present embodiment.
As shown in the figure, the tread 10 has a cross-sectional structure in which a foam rubber layer or cap rubber layer 12 on the outer side in the radial direction of the tire and a non-foam rubber layer or base rubber layer 14 on the inner side thereof are laminated. A tapered shape is formed from the surface of the tread 10 toward the bottom of the tread, that is, the cap rubber layer 12 is formed as a wide groove and the base rubber layer 14 is formed as a narrow groove. Here, the hardness of the cap rubber is set to be smaller than that of the base rubber. Using a durometer hardness test / type A tester according to JIS K 6253-1993, the cap rubber is measured at a test temperature of 25 ° C. The hardness is preferably about 38, for example, and the base rubber preferably has a hardness of about 58.
By forming the groove width of the sipe 50 as described above, when releasing the tire at the end of vulcanization, the sub-blocks are separated from each other so that they do not adhere to each other. On the other hand, a base made of non-foamed rubber Since the rubber layer 14 has a narrow width, sufficient rigidity can be maintained.
Therefore, the steering stability of the tire is not impaired.

Next, the results of performance tests conducted on a tire molded using a blade according to an embodiment of the present invention having the above configuration and a comparative tire molded using a conventional blade will be described.
For comparison with a tire molded with the blade according to the present invention, tires molded with the conventional blades 1 and 2 were prepared.
Here, the conventional blade 1 has a uniform thickness of 0.4 mm, and the conventional blade 2 has a uniform thickness of 0.7 mm. In contrast, in the blade according to the present invention, the thickness of the cap portion is 0.7 mm and the thickness of the base portion is 0.4 mm.
The tire size was 205 / 65R15, and all the conditions were the same except for the point of molding by the blades.
Steering stability test is a straight circuit, lane change performance at a speed from 80 km / h to 140 km / h on a circumferential circuit (dry road surface) consisting of 4 km per lap, and S-shaped installed on the course The cornering evaluation was judged on the handling roads. This was comprehensively judged by feeling evaluation of skilled drivers. The evaluation results are shown in Table 2.

As shown in Table 2, in the tire in which the sipe was formed using the conventional blade 1 (referred to as the conventional tire 1), the maximum unevenness amount was 1.9 mm, and the average number of unevennesses of 1 mm or more was 121 on average per tire. . In addition, in a tire formed with a sipe using a conventional blade 2 (referred to as a conventional tire 2), the maximum unevenness amount is 1.1 mm, and the number of unevennesses of 1 mm or more is reduced to an average of 17 locations per tire. When the stability is evaluated on a five-point scale, the conventional tire 1 has a value of 3.5 compared to the conventional tire 1, which is clearly inferior in steering stability. This seems to be due to the fact that a wide sipe was formed even in a base rubber layer made of non-foamed rubber, resulting in a decrease in tire rigidity.
On the other hand, when the sipe is formed using the blade according to the present invention, the maximum unevenness amount is 1.2 mm, and the number of unevennesses of 1 mm or more is 16, which is almost the same as that of the conventional tire 2. Is evaluated as 5 similarly to the conventional tire 1.
As described above, the pneumatic tire according to the present invention has excellent steering stability in addition to an excellent appearance with a small number of irregularities of 1 mm or more on the tread surface.

It is an expanded view of the principal part of the tread part of the pneumatic tire which concerns on embodiment of this invention. 2 shows one embodiment of a three-dimensional blade for forming the sipe of the pneumatic tire of FIG. 1, FIG. 2A is its immediate sectional view, and FIG. 2B is its perspective view. It is an expanded sectional view of the sub block of the pneumatic tire of FIG. It is sectional drawing which showed the conventional metal mold | die for tire vulcanization schematically.

Explanation of symbols

  10 ... tread, 12 ... cap rubber layer (foamed rubber layer), 14 ... base rubber layer (non-foamed rubber layer), 20a ... main groove, 20b ... narrow groove, 30 ... Lug groove, 40 ... block, 50 ... sipe, 60 ... blade, 70 ... mold of vulcanizer.

Claims (3)

In a pneumatic tire having a tread portion that has a block pattern and each block is divided into narrow sub-blocks by a plurality of sipes,
The tread portion has a structure in which a radially outer cap rubber layer and an inner base rubber layer are laminated, and the sipe is constant so that adjacent sub-blocks do not adhere to each other when the cap rubber layer is released after vulcanization. The pneumatic tire is characterized in that the base rubber layer has a constant width narrower than that of the cap rubber layer so that the base rubber layer can maintain the rigidity of the tread. In the tire according to claim 1,
The pneumatic tire according to claim 1, wherein the hardness of the cap rubber layer is smaller than that of the base rubber layer. In the pneumatic tire according to claim 1 or 2,
The pneumatic tire according to claim 1, wherein the cap rubber layer is a foam rubber layer, and the base rubber layer is a non-foam rubber layer.

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