JP6809099B2 - Pneumatic tires - Google Patents

Description

The present invention relates to a pneumatic tire having a thin under-groove gauge for reducing rolling resistance. More specifically, even if the under-groove gauge is thin, it is possible to prevent the occurrence of groove cracks and to improve steering stability. Regarding pneumatic tires that can be maintained well.

In recent years, in order to reduce rolling resistance and improve fuel efficiency, the gauge (under-groove gauge) of the rubber layer forming the lower part of the main groove extending in the tire circumferential direction has been thinned in the tread portion ( For example, see Patent Document 1). However, when the under-groove gauge becomes extremely thin, the rigidity of the rubber layer constituting the lower part of the main groove becomes significantly smaller than that of the reinforcing layer including the reinforcing cord such as the belt layer and the belt reinforcing layer, and the bottom of the main groove There is a problem that stress tends to be concentrated on the tire, and when the tire is used for a long period of time and deteriorates over time, groove cracks are likely to occur.

On the other hand, the entire tread rubber layer is required to have a low heat generation and high hardness in order to improve the steering stability in addition to the fuel efficiency of the tire. Such a rubber composition is generally used. There is a problem that it is difficult to stretch, fatigue resistance to deformation stress during running is insufficient, and groove crack resistance is inferior. Based on the above, even when thinning the grooved gauge to reduce rolling resistance and improve fuel efficiency, measures are required to prevent the occurrence of groove cracks without deteriorating steering stability. Has been done.

Japanese Unexamined Patent Publication No. 2013-039864

An object of the present invention is air that can prevent the occurrence of groove cracks and maintain good steering stability even when the under-groove gauge is thinned to reduce rolling resistance. It is to provide tires with wheels.

The pneumatic tire of the present invention for achieving the above object has a tread portion extending in the tire circumferential direction to form an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and these sidewall portions. A pair of bead portions arranged inside in the tire radial direction, a carcass layer mounted between the pair of bead portions, a reinforcing layer arranged on the outer peripheral side of the carcass layer in the tread portion, and the tread. The carcass layer and the tread rubber layer arranged on the outer peripheral side of the reinforcing layer are provided in the portion, and a main groove extending in the tire circumferential direction and a land portion partitioned by the main groove are formed on the outer surface of the tread portion. In the pneumatic tire, the distance from the bottom surface of the main groove to the outer peripheral surface of the reinforcing layer is 5 mm or less, and the subgrooved rubber is made of a rubber composition different from the rubber composition constituting the tread rubber layer. A layer is provided so as to cover at least the bottom surface of the main groove, and the subgroove rubber layer passes through each of the end points on the tread surface of the pair of land portions adjacent to the main groove and from each end point to the reinforcing layer. The subgroove rubber layer exists only in the region between the pair of virtual lines having an angle of 95 ° formed with the reinforcing layer, which is inclined toward the outside of the main groove with respect to the vertical line lowered toward. The rubber composition to be composed contains a diene rubber, a filler and an antiaging agent, the filler is blended in an amount of 90 parts by weight or less with respect to 100 parts by weight of the diene rubber, and the antiaging agent is an aromatic amine compound. The elastic coefficient of the rubber composition constituting the grooved rubber layer is 16 MPa or less, and the elastic coefficient of the rubber composition constituting the tread rubber layer is the elasticity of the rubber composition constituting the grooved rubber layer. It is characterized in that it is 1.5 times or more and 5.0 times or less of the rate.

In the pneumatic tire of the present invention, the distance from the bottom surface of the main groove to the outer peripheral surface of the reinforcing layer is reduced to 5 mm or less to reduce rolling resistance, while having the above characteristics, being flexible and resistant to distortion. Since the subgroove rubber layer made of a rubber composition that can be flexibly dealt with is provided, the occurrence of groove cracks can be suppressed. At this time, since the subgroove rubber layer is arranged only in the above-mentioned region, the rigidity of the entire tread portion (particularly the rigidity of the land portion) is not reduced, and the steering stability is maintained well. be able to. In the present invention, the elastic modulus refers to the conditions of a frequency of 20 Hz, an initial strain of 10%, a dynamic strain of ± 2%, and a temperature of 20 ° C. using a viscoelastic spectrometer (manufactured by Toyo Seiki Seisakusho) in accordance with JIS K6394. It means the storage elastic modulus (E') measured in.

In the present invention, the diene rubber is preferably a diene rubber containing at least a butadiene structure. In particular, it is preferable that the diene rubber contains at least polybutadiene. By limiting the rubber components of the rubber composition constituting the grooved rubber layer to those having excellent fatigue and heat generation properties in this way, the fatigue resistance of the grooved rubber layer is improved, and rolling resistance is reduced. , It is advantageous to balance the prevention of groove cracks and the maintenance of steering stability.

In the present invention, it is preferable to contain carbon black having a CTAB adsorption specific surface area of 130 m ² / g or less as the filler. By limiting the types of fillers in this way, the balance between heat generation and elastic modulus of the rubber layer under the groove is improved, and both prevention of groove cracks and maintenance of heat generation and steering stability are balanced. Will be advantageous. In the present invention, the CTAB adsorption specific surface area of the filler shall be measured in accordance with JIS K6217-3.

In the present invention, the elastic modulus of the rubber composition constituting the grooved rubber layer is preferably 1.0 MPa to 15.0 MPa. By using the subgroove rubber layer having such physical characteristics, it is advantageous to prevent the occurrence of groove cracks without impairing the steering stability.

In the present invention, the blending amount of the anti-aging agent is preferably 1 part by weight to 5 parts by weight with respect to 100 parts by weight of the diene rubber. By limiting the amount of the anti-aging agent compounded in this way, it is advantageous to improve fatigue without impairing the elastic modulus of the rubber layer under the groove, and to achieve both prevention of groove cracks and steering stability in a well-balanced manner. Become.

In the present invention, the tread rubber layer is composed of a cap tread rubber layer in which the tread rubber layer is exposed on the surface of the tread portion and an under tread rubber layer laminated on the inner peripheral side thereof, and the rubber composition and the under tread forming the cap tread rubber layer are formed. It is preferable that the rubber composition constituting the tread rubber layer is different from the rubber composition constituting the grooved rubber layer. As a result, the grooved rubber layer is a rubber composition that emphasizes groove crack resistance without impairing steering stability by optimizing the elastic modulus ratio with the cap tread rubber layer, and the cap tread layer emphasizes steering stability. The rubber composition, the under and the red rubber layer can be a rubber composition that emphasizes heat generation, and the balance of the entire tire can be optimized.

It is a meridian cross-sectional view of the pneumatic tire which comprises embodiment of this invention. It is a cross-sectional view of the meridian which shows the tread part of FIG. 1 enlarged. FIG. 5 is an enlarged meridian sectional view showing a tread portion of a pneumatic tire according to another embodiment of the present invention. FIG. 5 is an enlarged meridian sectional view showing a tread portion of a pneumatic tire according to another embodiment of the present invention. FIG. 5 is an enlarged meridian sectional view showing a tread portion of a pneumatic tire according to another embodiment of the present invention. FIG. 5 is an enlarged meridian sectional view showing a tread portion of a pneumatic tire according to another embodiment of the present invention. FIG. 5 is an enlarged meridian sectional view showing a tread portion of a pneumatic tire according to another embodiment of the present invention.

Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIG. 1, the pneumatic tire of the present invention includes a tread portion 1 extending in the tire circumferential direction to form an annular shape, a pair of sidewall portions 2 arranged on both sides of the tread portion 1, and side surfaces. It includes a pair of bead portions 3 arranged inside the wall portion 2 in the tire radial direction. In FIG. 1, CL indicates the tire equator.

A carcass layer 4 is mounted between the pair of left and right bead portions 3. The carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction, and is folded back from the inside to the outside of the vehicle around the bead core 5 arranged in each bead portion 3. Further, a bead filler 6 is arranged on the outer periphery of the bead core 5, and the bead filler 6 is wrapped by a main body portion and a folded portion of the carcass layer 4.

A belt layer 7a (two belt layers 7a in the example of FIG. 1) is embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. Each belt layer 7a includes a plurality of reinforcing cords that are inclined with respect to the tire circumferential direction, and the reinforcing cords are arranged so as to intersect each other between the layers. In these belt layers 7a, the inclination angle of the reinforcing cord with respect to the tire circumferential direction is set in the range of, for example, 10 ° to 40 °. Further, a belt reinforcing layer 7b (two layers of belt reinforcing layers 7b in the example of FIG. 1) is provided on the outer peripheral side of the belt layer 7a. The belt reinforcing layer 7b contains an organic fiber cord oriented in the tire circumferential direction. In the belt reinforcing layer 7b, the angle of the organic fiber cord with respect to the tire circumferential direction is set to, for example, 0 ° to 5 °. In the present invention, the belt layer 7a and the belt reinforcing layer 7b are collectively referred to as the "reinforcing layer 7". In the present invention, the belt layer 7a is an essential element, but the belt reinforcing layer 7b is an arbitrary element. Therefore, in addition to the case where the belt layer 7a and the belt reinforcing layer 7b are provided as shown in the figure, the reinforcing layer 7 It is possible that only the belt layer 7a is provided.

On the outer surface of the tread portion 1, main grooves 8 extending in the tire circumferential direction (four main grooves 8 in FIG. 1) are provided, and the main grooves 8 provide land portions 9 (5 rows of land portions 9 in FIG. 1). ) Is partitioned. The land portion 9 may be either a rib extending continuously over the entire circumference of the tire or a block defined by a lug groove (not shown) extending in the tire width direction. At this time, the distance G (hereinafter, referred to as the under-groove gauge G) from the bottom surface of the main groove 8 to the outer peripheral surface of the reinforcing layer 7 is set to 5 mm or less. The grooved gauge G is the distance from the bottom surface of the main groove 8 to the outer peripheral surface of the belt layer 7a when only the belt layer 7a is provided as the reinforcing layer 7, and is the distance between the belt layer 7a and the belt reinforcing layer 7b. Is provided, it is the distance from the bottom surface of the main groove 8 to the outer peripheral surface of the belt reinforcing layer 7b. Further, the outer peripheral surface of the reinforcing layer 7 (belt layer 7a, belt reinforcing layer 7b) is a reinforcing cord constituting the reinforcing layer 7 (belt cord in the case of the belt layer 7a, organic fiber cord in the case of the belt reinforcing layer 7b). This is the outer surface of the coated rubber covering the tire in the radial direction of the tire.

A tread rubber layer 10 is arranged on the outer peripheral side of the carcass layer 4 in the tread portion 1, and a side rubber layer 20 is arranged on the outer peripheral side (outside in the tire width direction) of the carcass layer 4 in the sidewall portion 2 in the bead portion 3. A rim cushion rubber layer 30 is arranged on the outer peripheral side (outside in the tire width direction) of the carcass layer 4. The tread rubber layer 10 may have a structure in which two types of rubber layers having different physical properties (cap tread rubber layer 11 and under tread rubber layer 12) are laminated in the tire radial direction.

In the present invention, in such a general pneumatic tire, the subgroove rubber layer 40 is provided under the groove of the main groove 8 as described later. Therefore, the basic cross-sectional structure of the pneumatic tire excluding the grooved rubber layer 40 is not limited to the above-mentioned structure. Therefore, for example, the subgrooved rubber layer 40 of the present invention can be applied to a so-called run-flat tire in which a side reinforcing layer having a crescent-shaped cross section is provided inside the carcass layer 4 in the sidewall portion 2 in the tire width direction. it can.

In the present invention, as shown in FIG. 2, the subgroove rubber layer 40 is provided under the groove of the main groove 8. That is, the tread portion 1 is composed of a tread rubber layer 10 that occupies most of the tread portion 1 and a tread rubber layer 10 that is locally provided under the groove of the main groove 8. The subgroove rubber layer 40 is provided so as to cover at least the bottom surface of the main groove 8. Further, a vertical line drawn from each end point P toward the reinforcing layer 7 by passing through the end points P on the treads of the pair of land portions 9 adjacent to one main groove 8, that is, the area shown by the diagonal line in FIG. It exists in the region between the pair of virtual lines L having an angle θ formed with the reinforcing layer 7 that is inclined toward the outside of the main groove 8 (dotted line in the figure) and is 95 °. In the illustrated example, the subgroove rubber layer 40 reaches from the bottom surface of the main groove 8 to the reinforcing layer 7, and divides the tread rubber layer 10 in the tire width direction.

The grooved rubber layer 40 is composed of a rubber composition different from the rubber composition constituting the tread rubber layer 10. Specifically, it contains a diene rubber, a filler, and an antioxidant, and the filler is blended in an amount of 90 parts by weight or less with respect to 100 parts by weight of the diene rubber, and the antioxidant is an aromatic secondary amine. It is composed of a rubber composition which is an aromatic amine compound such as. Further, the rubber composition constituting the grooved rubber layer 40 has an elastic modulus E1 of 16 MPa or less. When the elastic modulus of the rubber composition constituting the grooved rubber layer 40 is E1 and the elastic modulus of the rubber composition constituting the tread rubber layer 10 is E2, the ratio of these elastic moduli E2 / E1 is 5. It is set to 0 or less.

Since the grooved rubber layer 40 made of the rubber composition having such characteristics is softer than the tread rubber layer 10 and can flexibly follow the strain, the groove is formed by the presence of the grooved rubber layer 40 at the above-mentioned position. The occurrence of cracks can be suppressed. In particular, even if the grooved gauge G is set thin to 5 mm or less in order to reduce rolling resistance and groove cracks tend to occur, the grooved rubber layer 40 is provided as described above. Groove cracks can be prevented. At this time, since the grooved rubber layer 40 is provided only in the above-mentioned region, the rigidity of the entire tread portion 1 (particularly the rigidity of the land portion 9) is not lowered, and the steering stability is good. Can be maintained.

When the grooved rubber layer 40 is provided outside the above range, the ratio of the grooved rubber layer 40 to the tread portion 1 increases, the rigidity of the tread portion 1 decreases, and steering stability is improved. It becomes difficult to maintain. The sub-groove rubber layer 40 does not need to be provided in the entire region (hatched portion in FIG. 3), and is present at least below the flat portion of the bottom surface of the main groove 8 as shown in FIG. Just do it. In the illustrated example, the grooved rubber layer 40 divides the tread rubber layer 10, but as shown in FIG. 4, the grooved rubber layer 40 does not reach the reinforcing layer 7, and the tread rubber layer 10 is the reinforcing layer. It may be continuous in the tire width direction on the 7 side. Further, when the tread rubber layer 10 is composed of the cap tread rubber layer 11 and the under tread rubber layer 12 as described above, the grooved rubber layer 40 reaches the reinforcing layer 7 as shown in FIG. The cap tread rubber layer 11 and the under tread rubber layer 12 may be separated from each other, and as shown in FIG. 6, the cap tread rubber layer 11 and the under tread rubber layer 12 may be separated without reaching the reinforcing layer 7. May be divided. Alternatively, as shown in FIG. 7, both the cap tread rubber layer 11 and the under tread rubber layer 12 remain between the grooved rubber layer 40 and the reinforcing layer 7 in a state where the grooved rubber layer 40 does not reach the reinforcing layer 7. You may be doing it.

When the grooved rubber layer 40 is provided over the entire shaded portion of FIG. 3, the virtual line L coincides with the boundary between the grooved rubber layer 40 and the tread rubber layer 10. Therefore, under the above-mentioned condition, the boundary between the grooved rubber layer 40 and the tread rubber layer 10 passes through the end point P on the tread surface of the land portion 9, and the angle θ on the tread rubber layer 10 side formed by this boundary and the reinforcing layer 7. Can be rephrased as 95 ° or less. From this point of view, when the angle θ of the boundary between the grooved rubber layer 40 and the tread rubber layer 10 exceeds 95 °, the grooved rubber layer 40 expands outward from the above range (hatched portion in FIG. 3). Therefore, it becomes difficult to maintain good steering stability as described above.

If the elastic modulus E1 of the grooved rubber layer 40 is larger than 16 MPa, the grooved rubber layer 40 is not sufficiently flexible, and the occurrence of groove cracks cannot be appropriately suppressed. Mizoshita rubber layer 40
The elastic modulus E1 of is preferably 1.0 MPa to 15.0 MPa. Mizoshita rubber layer 40
When the ratio E 2 / E 1 of the elastic modulus of the tread rubber layer 10 is larger than 5.0, the grooved rubber layer 40
The physical properties of the tread rubber layer 10 and the tread rubber layer 10 are unbalanced, and it becomes difficult to achieve both prevention of groove cracks and maintenance of steering stability in a well-balanced manner. Mizoshita rubber layer 40 and tread rubber layer 1
The elastic modulus ratio of 0 E 2 / E 1 is preferably 4.5 to 1.5.

As the rubber composition constituting the tread rubber layer 10, a rubber composition (elastic modulus E2 of, for example, 4 MPa to 20 MPa) usually used as the tread rubber layer 10 in a general pneumatic tire can be used. As described above, the tread rubber layer 10 may be composed of a cap tread rubber layer and an under tread rubber layer. In that case, the grooved rubber layer 40 is a cap tread rubber layer and an under tread rubber layer. It is composed of a rubber composition different from both. Assuming that the elastic modulus of the rubber composition constituting the cap tread rubber layer is E2c and the elastic modulus of the rubber composition constituting the undertread rubber layer is E2u, E2c / E1 and E2u / E1 are 5.0 or less, respectively. ..

In the rubber composition constituting the grooved rubber layer 40, the rubber component contains a diene-based rubber as described above. As the diene rubber, rubbers usually used in rubber compositions for tires such as natural rubber, butadiene rubber, styrene butadiene rubber, isoprene rubber, modified butadiene rubber having modified molecular ends, and modified styrene butadiene rubber are used. be able to. Among the above-mentioned diene-based rubbers, those containing a butadiene structure (for example, butadiene rubber, styrene-butadiene rubber, modified butadiene rubber having a modified molecular end, modified styrene-butadiene rubber), and among them, those having a polybutadiene structure (butadiene). Rubber) can be preferably used. The butadiene rubber may be modified with a modifier, and the catalyst used at the time of polymerization is not limited, and a butadiene rubber produced by a catalyst such as nickel, titanium, chromium, neogeim, or lithium may be used. These diene rubbers can be used alone or as any blend. By using such a rubber component, the fatigue and heat generation of the subgroove rubber layer 40 are improved, and the reduction of rolling resistance, the prevention of groove cracks, and the maintenance of steering stability are balanced. Will be advantageous.

The rubber composition constituting the grooved rubber layer 40 always contains a filler as described above, but when the blending amount of the filler exceeds 90 parts by weight with respect to 100 parts by weight of the diene rubber, the grooved rubber layer As 40, not only is it not possible to obtain sufficient flexibility and the effect of suppressing the occurrence of groove cracks is not sufficiently obtained, but also the heat generation property is greatly deteriorated. The blending amount of the filler is preferably 85 parts by weight to 40 parts by weight with respect to 100 parts by weight of the diene rubber. As the filler, carbon black usually used in rubber compositions for tires can be used, and as silica, those manufactured by a wet method or a dry method such as precipitated silica can be used, and as a commercially available product, Ultrasil 7000GR ( Evonik), Ultrasil 9100GR (Evonik), Zeosil 1165MP (Solvay), Zeosil Premium 200MP (Solvay), Zeosil 115GR (Solvay), Zeosil 115GR (Solvay), Ultra (Manufactured by Evonik) can be used. In particular, the present invention, CTAB adsorption specific surface area is preferably not more than 130m ² / g as a filler, may more preferably comprise carbon black as a 129m ² / g~30m ² / g. By including such carbon black, the physical properties of the subgrooved rubber layer 40 are improved, and it is advantageous to achieve a good balance between reducing rolling resistance, preventing groove cracks, and maintaining steering stability. ..

The rubber composition constituting the grooved rubber layer 40 always contains an aromatic amine compound such as an aromatic secondary amine as an antioxidant as described above, and more preferably N- (1,3-dimethylbutyl). -N'-Phenyl-p-phenylenediamine is preferred. The blending amount of the anti-aging agent is preferably, for example, 1 part by weight to 5 parts by weight with respect to 100 parts by weight of the diene rubber. By blending the anti-aging agent in this way, the aging resistance of the grooved rubber layer 40 is improved, and it is advantageous to balance the prevention of groove cracks and the maintenance of steering stability.

A compounding agent other than the above can be added to the rubber composition constituting the grooved rubber layer 40. Other compounding agents include fillers other than carbon black, vulcanization or cross-linking agents, vulcanization accelerators, liquid polymers, thermosetting resins, thermoplastic resins, etc., which are generally used for pneumatic tires. Various compounding agents can be exemplified. The blending amount of these blending agents can be a conventional general blending amount as long as it does not contradict the object of the present invention.

First, 10 types of rubber compositions for tires (rubbers 1 to 10) having the formulations shown in Table 1 were prepared. In preparing these rubber compositions, the components excluding sulfur and the vulcanization accelerator were weighed, kneaded in a 1.8 L closed mixer at 160 ° C. for 5 minutes, and then the masterbatch was released. This masterbatch was kneaded with an open roll, sulfur and a vulcanization accelerator were added, and the mixture was mixed to obtain each rubber composition. In Table 1, in accordance with JIS K6394, measurements were made using a viscoelastic spectrometer (manufactured by Toyo Seiki Seisakusho) under the conditions of frequency 20 Hz, initial strain 10%, dynamic strain ± 2%, and temperature 20 ° C. The elastic modulus of each rubber composition is also shown.

The types of raw materials used in Table 1 are shown below.
・ SBR: Styrene butadiene rubber, Nippon Zeon Nipol 1502
-BR: butadiene rubber, Nippon Zeon Corporation Nipol BR 1220
・ NR: Natural rubber, STR20
CB1: Carbon black, VULCAN 10H manufactured by CABOT (CTAB adsorption specific surface area: 129 m ² / g)
-CB2: Carbon black, VULCAN M manufactured by CABOT (CTAB adsorption specific surface area 95 m ² / g)
-Silica: Evonik's Ultrasil VN3GR
-Coupling agent: Si69 manufactured by Evonik Industries
・ Oil: Showa Shell Sekiyu Co., Ltd. Extract No. 4 S
・ Stearic acid: NOF Beads stearic acid ・ Zinc white: Zinc oxide 3 types manufactured by Shodo Chemical Industry Co., Ltd. ・ Anti-aging agent: PILFLEX 13 manufactured by NICOL LIMITED
・ Sulfur: Tsurumi Kagaku Kogyo Co., Ltd. with Jinhua Ink Oil Fine powder sulfur ・ Vulcanization accelerator: FLEXSYS Co., Ltd. SANTOCURE CBS

Next, using the above-mentioned rubber composition for tires (rubbers 1 to 10), the type of rubber composition having a tire size of 245 / 50R18, having the basic structure shown in FIG. 1, and constituting the grooved rubber layer. (Type of under-groove rubber), Type of rubber composition constituting the tread rubber layer (Type of tread rubber), Elasticity E1 of the rubber composition constituting the under-groove rubber layer, and rubber composition constituting the tread rubber layer Comparative Examples 1 to 7 and Examples 1 to 5 in which the ratio E2 / E1 to the elasticity E2, the grooved gauge, and the angle θ of the boundary between the grooved rubber layer and the tread rubber layer were set as shown in Table 2. Pneumatic tires of various types were produced (in addition, among Examples 1 to 5, Examples 1 to 2, 4 to 5 in which the ratio E2 / E1 is out of the range of 1.5 to 4.5 are reference examples, respectively. ) .

In the column of "Type of subgrooved rubber" in Table 2, the elastic modulus of the rubber composition constituting the subgrooved rubber layer is also shown. Comparative Example 1 and Comparative Example 2 are examples in which the entire tread portion is composed of a single rubber composition, but in Table 1, the grooved rubber layer and the tread rubber layer are composed of the same rubber composition. Numerical values and the like are shown, but the angle θ is left blank because the boundary between the grooved rubber layer and the tread rubber layer cannot be discriminated.

Groove crack resistance, steering stability, and heat generation were evaluated for these 12 types of pneumatic tires by the following evaluation methods, and the results are also shown in Table 2.

Groove crack resistance Each test tire is assembled on a wheel with a rim size of 18 x 8JJ, filled with an air pressure of 50 kPa, left in a container irradiated with 100 ppmh of ozone at a temperature of 50 ° C. for one day, and then on the bottom surface of the main groove. The crack occurrence state was visually confirmed, and the result of Comparative Example 1 was evaluated on a 5-point scale with 2 points (reference).

Steering stability Each test tire (245 / 50R18) is assembled to a rim 18x8JJ wheel, mounted on a test vehicle with a displacement of 2.5L class with an air pressure of 230kPa, and a test driver on a circuit course consisting of a dry road surface. The sensory evaluation was performed by. The evaluation result is shown by an index with Comparative Example 1 as 100. The larger this index value is, the better the steering stability is. If this index value is "97" or more, it means that the conventional level is maintained and sufficiently good steering stability is maintained.

Heat generation The rubber composition used for the grooved rubber layer in each test tire was press-vulcanized at 160 ° C. for 30 minutes in a predetermined mold to prepare a test piece, and tan δ at 60 ° C. of this test piece was obtained. , A viscoelastic spectrometer (manufactured by Toyo Seiki Seisakusho Co., Ltd.) was used to measure under the conditions of initial strain of 10%, amplitude of ± 2%, frequency of 20 Hz, and atmospheric temperature of 60 ° C. The evaluation result is shown by an index in which the reciprocal of the measured value of Comparative Example 1 is 100. The larger the index value, the smaller the tan δ at 60 ° C., which means that the heat generation is low.

As is clear from Table 2, in each of Examples 1 to 5, the groove crack resistance was improved as compared with Comparative Example 1 while maintaining or reducing steering stability and heat generation. On the other hand, in Comparative Example 2, since the under-groove gauge was large, it was excellent in groove crack resistance, but steering stability and heat generation were deteriorated. In Comparative Example 3, since the angle θ was large and the proportion of the rubber layer under the groove occupied in the tread portion was large, the steering stability was deteriorated. In Comparative Example 4, since rubber (rubber 3) having a remarkably large elastic modulus was used as the subgroove rubber layer, the groove crack resistance could not be improved and the heat generation property was also deteriorated. In Comparative Example 5, since the elastic modulus ratio E2 / E1 is excessive, the elastic modulus of the grooved rubber layer is low, and the elastic modulus of the tread rubber layer is high, the steering stability balance is deteriorated and the steering stability is deteriorated. did. In Comparative Example 6, since the rubber composition (rubber 6) containing an excessive amount of the filler (carbon black) was used as the subgrooved rubber layer, the heat generating property was deteriorated. In Comparative Example 7, since a rubber composition (rubber 7) containing no antioxidant was used as the subgroove rubber layer, the groove crack resistance was deteriorated.

1 tread part 2 sidewall part 3 bead part 4 carcass layer 5 bead core 6 bead filler 7 reinforcement layer 7a belt layer 7b belt reinforcement layer 8 main groove 9 land part 10 tread rubber layer 11 cap tread rubber layer 12 under tread rubber layer 20 side rubber Layer 30 Rim cushion rubber layer 40 Under-groove rubber layer CL Tire equatorial line

Claims (7)

A tread portion extending in the tire circumferential direction to form an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and a pair of bead portions arranged inside the tire radial direction of these sidewall portions. A carcass layer mounted between the pair of bead portions, a reinforcing layer arranged on the outer peripheral side of the carcass layer in the tread portion, and a reinforcing layer arranged on the outer peripheral side of the carcass layer and the reinforcing layer in the tread portion. In a pneumatic tire having a tread rubber layer and having a main groove extending in the tire circumferential direction and a land portion partitioned by the main groove formed on the outer surface of the tread portion.
The distance from the bottom surface of the main groove to the outer peripheral surface of the reinforcing layer is 5 mm or less, and the subgroove rubber layer made of a rubber composition different from the rubber composition constituting the tread rubber layer is at least the main groove. The subgroove rubber layer is provided so as to cover the bottom surface, and the rubber layer under the groove passes through each of the end points of the pair of treads of the land portion adjacent to the main groove and is drawn from each end point toward the reinforcing layer. Also exists only in the region between the pair of virtual lines inclined toward the outside of the main groove and forming an angle with the reinforcing layer at 95 °, and the rubber composition constituting the subgroove rubber layer is diene. It contains a rubber system, a filler, and an antioxidant, and the filler is blended in an amount of 90 parts by weight or less with respect to 100 parts by weight of the diene rubber. The antioxidant is an aromatic amine compound, and the grooved rubber The elastic coefficient of the rubber composition constituting the layer is 16 MPa or less, and the elastic coefficient of the rubber composition constituting the tread rubber layer is 1.5 times or more the elastic coefficient of the rubber composition constituting the grooved rubber layer. Pneumatic tires characterized by being 5.0 times or less. The pneumatic tire according to claim 1, wherein the diene rubber is a diene rubber containing at least a butadiene structure. The pneumatic tire according to claim 2, wherein the diene rubber contains at least polybutadiene. The pneumatic tire according to any one of claims 1 to 3, wherein the filler contains carbon black having a CTAB adsorption specific surface area of 130 m ² / g or less. The pneumatic tire according to any one of claims 1 to 4, wherein the elastic modulus of the rubber composition constituting the grooved rubber layer is 1.0 MPa to 15.0 MPa or less. The pneumatic tire according to any one of claims 1 to 5, wherein the amount of the antiaging agent blended is 1 part to 5 parts by weight with respect to 100 parts by weight of the diene rubber. The tread rubber layer is composed of a cap tread rubber layer exposed on the surface of the tread portion and an under tread rubber layer laminated on the inner peripheral side thereof, and the rubber composition constituting the cap tread rubber layer and the under tread. The pneumatic tire according to any one of claims 1 to 6, wherein the rubber composition constituting the rubber layer is different from the rubber composition constituting the grooved rubber layer.

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