JP3160370B2 - 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 the improvement of pneumatic tires, in particular, tires called all-season tires. It sufficiently enhances the performance on ice after the middle stage of wear.

[0002]

2. Description of the Related Art Conventional all-season tires applicable to not only general roads and highways but also snow-covered roads and ice-covered roads are different from ordinary summer tires in the selection of block size and the size of each block. Some tread rubbers use a rubber composition with a compounded composition that focuses on improving the performance on snow and ice, making the block rigidity relatively small due to the formation of sipes, etc. In consideration of durability and the like, the tread rubber is made into two layers inside and outside in the tire radial direction, the outside rubber layer is made of a rubber composition that can improve the performance on ice and snow, and the inside rubber layer is made of low rubber. There is one that employs a so-called cap and base structure in which heat-generating rubber compositions are provided.

[0003]

The all-season radial tire has various advantages because it is designed to be able to run on any road surface.
Since the history of all-season tires themselves is short,
There are also many points that need to be improved, and among them, it is most important to prevent the deterioration of on-ice performance after the middle period of tread wear and the occurrence of so-called shoulder wear caused by running on various road surfaces. It has become a challenge.

[0004] The cause of the deterioration of the performance on ice after the middle stage of wear is that the depth of the main groove defining the block becomes shallow due to the wear, and the oil and the like in the tread rubber are gradually removed with time. Along with the transfer to other components, the scattering causes the rubber to degrade, which in turn causes an increase in the block rigidity, whereby the flexibility of the block is reduced and the road surface grip force is reduced.

Accordingly, the present invention effectively improves the performance on ice after the middle period of wear without sacrificing wear resistance, steering performance, etc., and sufficiently prevents the occurrence of shoulder drop wear. Provided is a pneumatic tire that can improve the riding comfort in the middle period and thereafter.

[0006]

A pneumatic tire according to the present invention has a tread portion, in particular, a straight line, a zigzag shape, and other two pieces which extend continuously in the circumferential direction of the tread with a tire equatorial plane interposed therebetween. A pair of circumferential main grooves are provided, and the tread portion of the central area sandwiched between the pair of circumferential main grooves is formed on the innermost rubber layer located on the innermost side in the radial direction and on the outermost side in the radial direction. The rubber layer is composed of at least three layers: an intermediate rubber layer positioned on the outer rubber layer and an outer rubber layer positioned further on the outer peripheral side of the intermediate rubber layer. Of the inner rubber layer, the thickness of the inner rubber layer measured from the bottom of the circumferential main groove is 70% or less of the depth of the circumferential main groove. 2mm or more The sum of the thickness of the side rubber layer and the thickness of the intermediate rubber layer is 90% or less of the circumferential main groove and 4 mm or more.

[0007] Preferably, the outer rubber layer is formed at a temperature of -20 ° C.
Formed by a rubber composition having a dynamic elastic modulus in the range of 15 × 10 ⁷ to 40 × 10 ⁷ dyn / cm ² . Also preferably, the dynamic elastic modulus of each of the inner rubber layer and the intermediate rubber layer is smaller than that of the outer rubber layer, and the foaming rate of the outer rubber layer is 0 to 10%, and the foaming rate of the intermediate rubber layer is 3-40%, and the foaming rate of the inner rubber layer is in the range of 5-50%. In addition, it is preferable that the cells of the foamed rubber forming the inner rubber layer are substantially closed cells.

Preferably, the outer rubber layer in the central area and the side rubber layer forming the tread portion in the side area are each formed of the same rubber composition.

[0009] More preferably, the side rubber layer is formed by combining a rubber composition for a general all-season tire and a rubber composition for a general summer tire in order to improve the abrasion resistance. Use together.

[0010] More preferably, the JIS hardness of each rubber layer in the central area is set to a relative relationship of inner rubber layer ≦ intermediate rubber layer <outer rubber layer, and more preferably, their JIS hardness is determined by the inner rubber layer. 45-70 degrees for the middle rubber layer and 55-70 degrees for the outer rubber layer.

Preferably, each of the outer rubber layer and the side rubber layer is formed of non-foamed rubber.

[0012] Preferably, an additional auxiliary rubber layer covering the outer surface of each side rubber layer in the tread width direction is provided, and the rubber characteristics of the additional auxiliary rubber layer are the same as those of the side wall rubber. The amount of oil mixed into the intermediate rubber layer and the inner rubber layer is reduced by at least 10 parts by weight from the amount of oil mixed into other rubber layers located around those rubber layers.

[0013] Even more preferably in such a tire, the tread portion of the side section is constituted by a respective rubber layer substantially identical to the respective layer of the central section with respect to the composition and the foaming ratio.

[0014]

In the pneumatic tire according to the present invention, the rubber layer in the central area of the tread portion is made at least three layers inward and outward in the radial direction, and the rubber layer having a high foaming rate is exposed as the wear of the tread portion progresses. In particular,
It is possible to effectively prevent deterioration of performance mainly on ice after the middle stage of wear. Also, the thickness of the inner rubber layer measured from the groove bottom of the circumferential main groove is set to 70% or less of the depth of the circumferential main groove and 2 mm or more, thereby lowering the performance on ice after the middle stage of wear. , And effectively prevents a decrease in block rigidity.

That is, if it exceeds 70%, the block rigidity becomes too small, which is not preferable in terms of abrasion resistance and the like. If it is less than 2 mm, the performance on ice after the middle stage of abrasion is greatly reduced. Become.

Preferably, the sum of the thickness of the inner rubber layer and the thickness of the intermediate rubber layer is 90% of the circumferential main groove depth.
% And 4 mm or more. This is because when the sum of the thicknesses exceeds 90%, the block stiffness and the like become small, and wear resistance from the middle stage of wear tends to be a problem. When the thickness is less than 4 mm, the performance on ice after the middle stage of wear is greatly reduced. Will do.

Preferably, the outer rubber layer in the central area is formed of a non-foamed rubber composition having excellent performance on ice and snow. That is, when the tire is new, in addition to the deep main groove depth, based on the fact that the oil in the rubber layer is less scattered, the block rigidity is relatively small, and the flexibility of the block is high, The outer rubber layer
It is preferable to use a non-foamed rubber having better wear resistance than a foamed rubber.

On the other hand, in the state of progress of wear to the extent that the intermediate rubber layer and the inner rubber layer are exposed, the depth of the main groove is already sufficiently small, so that the rigidity of the block itself and, consequently, the wear resistance Is greatly increased, so that even if those layers are formed of foam rubber having low wear resistance, there is no possibility that an extreme decrease in wear resistance occurs.

Preferably, the side rubber layer in the side area is formed of a usual non-foamed rubber composition to effectively prevent occurrence of shoulder dropping wear and deterioration of steering performance. In this tire, of the rubber composition forming the outer rubber layer,
When the dynamic elastic modulus at −20 ° C. is in the range of 15 × 10 ⁷ to 40 × 10 ⁷ dyu / cm ² , excellent performance on ice and snow can be obtained without deteriorating the abrasion resistance at the beginning of wear. Can be secured.

If the dynamic elastic modulus of each of the inner rubber layer and the intermediate rubber layer is smaller than that of the outer rubber layer, the internal rubber tends to deteriorate in the middle of wear. As a result, sufficient flexibility can be ensured, and a decrease in performance on ice can be prevented.

Further, the foaming ratio of the outer rubber layer is 0 to 10
%, The foaming rate of the intermediate rubber layer is in the range of 3 to 40%, and the foaming rate of the foamed rubber forming the inner rubber layer is in the range of 5 to 50%. As a result, the decrease in rubber flexibility caused by the deterioration of the rubber due to the deterioration of the rubber can be covered by the foamed rubber layer, and the decrease in performance on ice can be effectively prevented. Here, when the cells of the foamed rubber are closed cells, the rubber layer can be effectively protected from freezing water in the cells and the like. That is, when the bubbles are open continuous cells, moisture or the like is likely to enter the deep portion of the todd rubber layer due to a phenomenon similar to a capillary phenomenon, which may cause rubber breakage due to freezing or the like.

By the way, J of each rubber layer in the central area
The IS hardness is preferably a relative relationship of inner rubber layer ≦ intermediate rubber layer <outer rubber layer. In other words, as the wear progresses, the rubber undergoes aging and deteriorates, deteriorating the performance on ice, whereas when the inner rubber layer has a lower hardness,
Flexibility can be secured more sufficiently, and excellent performance on ice can be secured.

More preferably, an additional auxiliary rubber layer is provided to cover the outer surface of the side rubber layer in the tread width direction, and the rubber characteristic of the additional auxiliary rubber layer is made the same as that of the side wall rubber, so that the tread portion is formed. Cracks are effectively prevented at the joint interface between the rubber and the sidewall portion, particularly at the joint surface with the tread rubber. And also preferably,
The amount of oil blended into the intermediate rubber layer and the inner rubber layer is reduced by at least 10 parts by weight from the amount of blended oil into the other rubber layers located around the inner rubber layer. Prevent deterioration more.

[0024]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional view in the tread width direction showing one embodiment of the present invention. In FIG.
Indicates a side wall portion connected to the tread portion 1, and 3 indicates a bead portion continuous to the radially inner end of each side wall portion 2.

In this tire having a size of 175 / 65R14, reference numeral 4 denotes a carcass. The carcass 4 comprises a single ply of an organic fiber cord extending at an angle of substantially 90 ° C. with respect to the tire circumferential direction. The respective side end portions of the tire 4 are wound around the respective bead cores 5 from the inside to the outside of the tire and fixed by winding.

On the outer peripheral side of the bead core 5, a high hardness bead filler 6 having a JIS hardness in the range of 70 to 90 degrees, for example, is brought into contact with the bead core 5 between the main body portion and the folded end portion of the carcass 4. Is arranged on the outer peripheral side of the crown portion of the carcass 4 with respect to the tire circumferential direction.
Two belt layers 7, 8 of respective steel cords extending in opposite directions at an angle of 21 degrees are provided.

Here, a pair of two circumferentially extending tread portions 1 and 2 extending continuously in the circumferential direction of the tread are arranged on the tread portion 1 provided on the outer peripheral side of the belt layers 7 and 8 with the tire equatorial plane XX interposed therebetween. Grooves 9 are provided, respectively, and these circumferential main grooves 9 allow the tread portion 1 to have a central area 10 sandwiched between them and a side area 11 located outside the circumferential main grooves 9 in the tread width direction outside. And partition.

Here, each of the circumferential main grooves 9
Can extend in a straight, zigzag or other desired shape, and the width of each of the central section 10 and the side section 11 is about 50% and about 25% with respect to the tread tread width W. It can be.

In this example, the tread portion of the central section 10 is divided into an inner rubber layer 12 located on the innermost peripheral side in the radial direction of the tire, and an intermediate rubber layer 13 located on the outer peripheral side of the inner rubber layer 12. , An outer rubber layer 14 located on the outer peripheral side of the intermediate rubber layer 13 and a three-layer rubber layer.
Having a hardness and a blending composition shown in Table 1,
With 20% foam rubber, the intermediate rubber layer 13 has the hardness and composition shown in Table 2. Each of the foamed rubber having a foaming rate of 10% was formed, and the outer rubber layer 14 was formed as shown in Table 3.
And a general non-foam rubber having excellent performance on ice and snow.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

[Table 3]

The inner rubber layer 12 has a thickness h _{1 of} 3 mm as measured from the bottom of the circumferential main groove 9 having a depth h of 8 mm, and the inner rubber layer 12 and the intermediate rubber layer 13 have a thickness h _{1 of} 3 mm. And the sum of the thicknesses h ₂ of each is 6 mm

The foaming rate of the foamed rubber forming the inner rubber layer 12 is 5 to 50%, and the foaming rate of the intermediate rubber layer 13 is 3 to 50%.
The foaming ratio of the outer rubber layer 14 is preferably in the range of 0 to 10%, and the cells of the foamed rubber are preferably substantially closed cells.

Here, the side rubber layer 15 constituting the tread portion of the side section 11 can be formed of a general non-foam rubber which is used for summer tires and emphasizes abrasion resistance. is there.

In such a tire, preferably, the compounded oil amount of the inner rubber layer 12 and the intermediate rubber layer 13 is made smaller than that of the tread constituent members around the inner rubber layer 12 and the intermediate rubber layer 13 so that the rubber deterioration of those rubber layers after the middle stage of wear is caused. To prevent a decrease in flexibility.

Incidentally, in this example, the oil amount of each of the inner rubber layer 12 and the intermediate rubber layer 13 was set to 5 parts by weight, which was extremely smaller than 30 parts by weight of the outer rubber layer.
According to this, the oil which has migrated from the surroundings of the rubber layers 12 and 13 to those layers can sufficiently maintain the flexibility of the rubber while minimizing the influence of the aging of the rubber layer after the middle stage of wear. .

Here, the inner rubber layer 12 and the intermediate rubber
The dynamic elastic modulus and the JIS hardness of the outer rubber layer 14 are preferably smaller than those of the outer rubber layer 14 in order to prevent a decrease in performance on ice after the middle stage of wear.
Regarding the IS hardness, it is preferable that the inner rubber layer 12 has a range of 45 to 70 degrees, the intermediate rubber layer 13 has a range of 55 to 70 degrees, and the outer rubber layer 14 has a range of 55 to 70 degrees.

Further, in the illustrated example, the side rubber layer in the side area
15 each with a respective rubber layer 12,
Inner layer with the same foaming ratio and composition as 13 and 14
15a, an intermediate layer portion 15b, and an outer layer portion 15c. In the case of such a configuration, the belt layers 7, 8
Inner layer portion 15a made of foamed rubber bonded to the side end portion of
Here, since the breaking strength is slightly lower than that of the non-foamed rubber and it is not preferable in preventing the belt end peeling, the heat generation between the side end portions of the belt layers 7 and 8 and the inner portion 15a is low. A non-foamed protective rubber layer 16 is interposed.

In addition, in this example, the outer surface of each side rubber layer 15 in the tread width direction is covered with an additional auxiliary rubber layer 17 having a substantially triangular cross section. This additional rubber layer
17 is a rubber forming the side wall portion 2, that is,
It is made of a rubber composition that is substantially the same as the sand rubber, and increases the bonding force between the side end portions of the side rubber layers 15 and the side walls to increase the bonding strength between the side wall rubber and the side rubber layers 15. Functions to prevent cracks.

The additional auxiliary rubber layer 17 here is
Together with the center area tread part and the side area tread part as other constituent members of the tread part 1, for example, integral molding by simultaneous extrusion enhances production efficiency and also enhances bonding strength to the side rubber layer 15. It is preferable in increasing the value.

According to the tire constructed as described above, the performance on ice and snow during the early to middle stages of wear is affected by the action of the outer rubber layer 14 and the outer layer portion 15c, and the middle and later stages of wear. The performance on ice is the intermediate and inner rubber layers 13 and 12 made of foamed rubber, and the intermediate and inner layer portions 15.
Under the respective actions of b and 15a, both can be sufficiently effectively exerted. Also, the occurrence of shoulder drop abrasion and the deterioration of steering performance are caused by the outer layer portion 15 of the side rubber layer 15.
It can be effectively prevented by appropriately selecting the composition of c and the like.

(Comparative Example) Hereinafter, comparative tests of the inventive tire, the conventional tire, and the comparative tire will be described with respect to the initial wear performance on ice, the middle wear performance on ice, shoulder wear, and steering performance. ◎ Test tire size is 175 / 65R14 ・ Invented tire A tire having the configuration shown in FIG. -Conventional tire A tire in which the entire tread portion is made of the all-season rubber composition shown in Table 3. However, the additional auxiliary rubber layer is the same as the inventive tire. -Comparative tire A tire in which the entire tread portion is made of the foamed rubber shown in Table 1. However, the additional auxiliary rubber layer is the same as the inventive tire.

Test Method The performance on ice was evaluated by measuring mu on ice. The performance on ice in the middle stage of wear was evaluated in a state where the depth of the main groove was reduced to about half. Shoulder wear is 1000
Evaluation by measuring the difference in the amount of wear after traveling 0 km,
The steering performance was evaluated by measuring cornering power with an indoor drum.

試 験 Test Results The results of the above tests are shown in Table 4 by index using the conventional tire as a control. The larger the index value, the better the result.

[Table 4] According to Table 4, it is clear that the invented tire can exhibit excellent on-ice performance after the middle stage of wear without causing shoulder drop wear, deterioration in steering performance, and the like.

[0046]

As is clear from the above comparative example, according to the present invention, the performance on ice, especially in the middle stage of wear, can be obtained without sacrificing shoulder drop wear and steering performance. It can be greatly improved in comparison with the above.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view in a tread width direction showing an embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Carcass 7, 8 Belt layer 9 Circumferential main groove 10 Central area 11 Side area 12 Inner rubber layer 13 Intermediate rubber layer 14 Outer rubber layer 15 Side rubber layer 15a Inner layer part 15b intermediate layer portion 15c outer portion 16 the protective rubber layer 17 additional auxiliary rubber layer X-X equatorial plane W tread width h main groove depth h _1, h ₂ thickness

Claims (11)

(57) [Claims] 1. A carcass comprising a tread portion, a pair of sidewall portions and a bead portion, and comprising a cord extending at an angle of substantially 90 ° with respect to a tread circumferential direction, and an outer peripheral side of a crown portion of the carcass. Is arranged in
At least two belt layers each having a cord extending in a direction opposite to the circumferential direction of the tread, and extending continuously in the circumferential direction of the tread at a position separated by a tire equatorial plane on the tread portion. A pair of two circumferential main grooves are provided, and a tread portion of a central area sandwiched between these circumferential main grooves is formed by a radially innermost inner rubber layer and an outer circumferential side of the inner rubber layer. An intermediate rubber layer located at
When the rubber layer is composed of at least three layers with the outermost rubber layer located on the outermost side in the radial direction, the rubber characteristics of each of these rubber layers are made different from each other, and the foaming rate of each layer is changed in the radial direction. The thickness of the inner rubber layer measured from the bottom of the circumferential main groove is set to 70% or less of the depth of the circumferential main groove, and the thickness of the inner rubber layer is increased. The sum of the thickness of the layer and the thickness of the intermediate rubber layer is calculated as the depth of the circumferential main groove.
A pneumatic tire that is 90% or less and 4 mm or more. 2. The rubber composition according to claim 1, wherein the outer rubber layer is formed of a rubber composition having a dynamic elastic modulus at −20 ° C. in the range of 15 × 10 ⁷ to 40 × 10 ⁷ dyn / cm ² . Pneumatic tire. 3. The pneumatic tire according to claim 1, wherein a dynamic elastic modulus of each of the inner rubber layer and the intermediate rubber layer is smaller than that of the outer rubber layer. 4. The foaming rate of the outer rubber is 0-10%, the foaming rate of the intermediate rubber layer is 3-40%, and the foaming rate of the inner rubber layer is 5-5%.
The pneumatic tire according to any one of claims 1 to 3, which has a range of 50%. 5. The pneumatic tire according to claim 1, wherein the cells of the foamed rubber are substantially closed cells. 6. A side rubber layer constituting a tread portion of a side section located outside the circumferential main groove in a tread width direction, and the outer rubber layer are each formed of the same rubber composition. A pneumatic tire according to any one of claims 1 to 5. 7. The pneumatic tire according to claim 1, wherein the JIS hardness of each of the rubber layers in the central area is such that: inner rubber layer ≦ intermediate rubber layer <outer rubber layer. 8. The outer rubber layer and the side rubber layer are each formed of a non-foamed rubber.
A pneumatic tire according to any one of claims 1 to 7. 9. An additional auxiliary rubber layer which covers the outer surface of each side rubber layer in the tread width direction, wherein the rubber characteristic of the additional auxiliary rubber layer is the same as that of the side wall rubber. 8. The pneumatic tire according to any one of 8 above. 10. The compounded oil amount of the intermediate rubber layer and the inner rubber layer is reduced by at least 10 parts by weight from the compounded oil amount of other rubber layers located around those rubber layers. 10. The pneumatic tire according to any one of 9 above. 11. The tread portion in a side section located outside the circumferential main groove in the tread width direction is formed of each rubber layer substantially identical to each layer of the central section. Pneumatic tires.