JP3415871B2 - Tread structure of radial tire - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a tread structure of a radial tire. [0002] Tires used in heavy-duty vehicles that require a particularly long wear life have a thick tread rubber composed of a rubber composition having high wear resistance. However, generally, a rubber composition excellent in abrasion resistance generates a large amount of heat, so that a large amount of heat is generated in a tread portion and separation tends to occur easily. [0003] Therefore, the tread structure of the conventional radial tire has a so-called cap-base structure in which a cap portion is formed of a rubber composition having excellent wear resistance and a base portion is formed of a low heat-generating rubber to prevent separation. I was [0004] However, in order to reduce the heat generation of the rubber composition, a method of using a small amount of carbon black or using carbon black having a large particle diameter is used. When this kind of rubber is used for the base portion, the movement of the cap rubber becomes large and uneven wear is likely to occur because the hardness is low. Japanese Patent Application Laid-Open No. 63-61202 discloses a method for improving the above-mentioned problem by using a low-heat-generating, high-hardness rubber composition reinforced with a resin for the cap portion and the base portion to reduce the movement of the cap rubber and to bias the movement. Although a method for reducing wear has been proposed, it is not always satisfactory. SUMMARY OF THE INVENTION An object of the present invention is to provide a tread structure for a radial tire in which uneven wear in a tread portion can be reduced as much as possible. Means for Solving the Problems When the tire is in contact with the ground, the surface of the rotating tire is out of phase with the belt due to friction with the road surface, and the land portions of the ribs, blocks and lugs are sheared. Deform. Based on the belt, this deformation means that constant movement occurs in the tire circumferential direction and width direction on the tire surface, but uneven wear occurs because the magnitude of this movement is the position in the tread. It is considered that the part with large movement is worn early, and the part with small movement is worn late. This tendency is greater because the movement increases as the depth of the groove increases. In addition, if uneven wear occurs once in the initial stage of tread wear, uneven wear is accelerated because the quickly worn part becomes more mobile, and this state is maintained to the end, and despite the fact that most of the grooves remain, The tire must be removed. It is considered that uneven wear occurs and progresses due to the above-mentioned causes. A point to be noted here is that the cap rubber of the conventional tire is entirely of the same material. That is, although the wear proceeds unevenly, the wear resistance of the cap rubber is the same. Therefore, even if a rubber composition having excellent wear resistance is used, the life of the tire must be shortened unless the progress of uneven wear is fundamentally prevented. Based on the above findings, the present invention has developed means for adjusting uneven progress of wear with a multilayer structure having a plurality of layers having different wear indices and different thicknesses. That is, in the present invention, the tread has a multilayer structure of a plurality of layers, and the interface between the surface layer as the first layer and the adjacent second layer is located within a range of 30 to 80% of the main groove depth when viewed from the groove bottom. And a tread structure for a radial tire, wherein the ratio of the pico abrasion index of the surface layer to the second layer is 0.7 to 0.9. In the case where the tread has a three-layer laminated structure, the interface between the second layer and the third layer is located at 10% or less of the depth of the main groove as viewed from the groove bottom, in addition to the above structure. And the ratio of the pico abrasion index of the third layer to the second layer is 0.5 to
0.95 is desirable. Since the present invention is as described above, even if the surface layer is unevenly worn, the wear at the position where the second layer having good abrasion resistance is quickly worn out is exposed when the second layer having good wear resistance is exposed. In addition, the wear at the remaining position is relatively quick, and the uneven wear is adjusted as a whole. However, if the interface between the surface layer and the second layer is located at more than 80% of the depth of the main groove as viewed from the groove bottom, the proportion of the surface layer is too small, so that the surface layer as the first layer is The role of adjusting uneven wear relatively cannot be exerted in the second layer, and uneven wear occurs in the second layer. Conversely, when the interface between the surface layer and the second layer is located within a range of less than 30% of the main groove depth when viewed from the groove bottom, the proportion of the surface layer is large, so that the wear of the tire as a whole is accelerated, and Life is shortened. If the ratio of the pico abrasion index of the surface layer to the second layer is less than 0.7, the wear of the surface layer is too fast to control uneven wear satisfactorily, thereby shortening the tire life. On the other hand, if the ratio of the pico abrasion index exceeds 0.9, the adjusting effect due to the abrasion difference is not sufficient. Since the third layer is made of a rubber composition having less wear resistance than the second layer, heat generation can be reduced. However, the interface between the second layer and the third layer is mainly viewed from the groove bottom. Groove depth 1
If it exceeds 0%, the thickness of the third layer is so large that the third layer is exposed in the middle of its life, and uneven wear occurs in the third layer. If it is 10% or less, the removal limit is reached, so even if the abrasion resistance is inferior, the influence is small. When the ratio of the pico abrasion index of the third layer to the second layer is less than 0.5, there is too much difference in abrasion, and when the third layer is exposed, the abrasion is accelerated and uneven wear occurs, so that the timing of removal is accelerated. On the other hand, if it is larger than 0.95, the heat generation becomes large, and the benefit of providing the third layer is poor. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic sectional view showing a tread structure according to the present invention, wherein 1 is a tread, and 2 is a main groove formed in the tread. The tread 1 has a three-layer structure as shown in the figure, and the surface layer 1a as the first layer is the second layer 1
The third layer 1c is made of a rubber having a low abrasion resistance and has a low abrasion resistance to reduce the heat generation of the second layer 1b having a relatively high abrasion resistance. It is composed of Reference numeral 3 denotes an interface between the surface layer 1a and the second layer 1b, and reference numeral 4 denotes an interface between the second layer 1b and the third layer 1c. Next, the groove depth of the main groove is d, the height of the interface 3 from the groove bottom of the main groove 2 is d ₁ , and the height of the interface 4 from the same point is d.
_2, P ₁ pico wear index of the surface layer 1a, the Pico abrasion index of the second layer 1b P _2, the Pico abrasion index of the third layer 1c as P _3, tires of size 10.00R20 14PR shown in Table 1 Was made as a prototype, and its removal life and uneven wear were evaluated. The results are shown in Table 1. The removal life shown in the table refers to the distance traveled from when the tire was mounted on a truck and the tread was worn and the remaining depth of one of the grooves in the tread pattern reached 2 mm. Is displayed as a control, and uneven wear is visually inspected for the depth of each groove at the time of this removal,
Those having a large difference between a deep part and a shallow part of the groove depth are indicated as having uneven wear. For pico wear test,
Measured according to American Society for Testing and Materials Standard ASTM D 2228. [Table 1] In Table 1, the prototype No. 3 and No. 3 4 is real
This is an example. From Table 1, adjusting the respective interface positions between the surface layer, the second layer and the third layer and the ratio of the wear index between adjacent layers within a certain range improves the life of the tire and prevents uneven wear. It is recognized that it can be done. The present invention is not limited to the above embodiment. As described above, according to the present invention, the tread has a laminated structure of a plurality of layers, and the interface between the surface layer as the first layer and the second layer adjacent thereto is viewed from the bottom of the groove and the depth of the main groove. 30-80
%, And the ratio of the pico abrasion index of the surface layer to the second layer is set to 0.7 to 0.9. Therefore, even if the surface layer is worn unevenly, the adjustment is performed by the second layer. Therefore, uneven wear of the tread as a whole can be prevented. Further, the third layer has a lower abrasion resistance than the second layer.
Low heat generation due to the use of a rubber composition
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BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial schematic cross-sectional view showing one embodiment of a tread structure according to the present invention. [Description of Signs] 1 Tread 1a Surface layer 1b Second layer 1c Third layer 2 Main groove 3 Interface 4 Interface

Claims (1)

(57) [Claims 1] The tread has a laminated structure of a plurality of layers, and the interface between the surface layer which is the first layer and the second layer adjacent thereto is viewed from the bottom of the groove to determine the depth of the main groove. Within the range of 30-80%, the second
The ratio of the pico wear index of the surface layer to the layer is 0.7 to 0.9.
The position of the interface between the second layer and the third layer is located at 10% or less of the depth of the main groove as viewed from the groove bottom , and the ratio of the pico abrasion index of the third layer to the second layer is 0.5 to 0.95. Radial tire tread structure.