JP3477289B2 - 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 preventing generation of fine wrinkles, cracks and the like at the groove bottom portion of a vertical main groove formed in a tread portion.

[0002]

2. Description of the Related Art In recent years, automobile tires have been improved in performance with the increase in horsepower of automobiles. For example, as a high-performance tire, a flat radial tire in which the land area is increased and the steering stability performance and the grip performance are improved by flattening the width of the tire to be less than 60% or widening the tread width can be given.

Further, in order to satisfy not only dry performance but also wet performance at a high level, a high-performance tire is generally a longitudinal main groove that extends continuously in a straight line in the tire circumferential direction with a relatively wide width on the tread surface. It is common practice to place

[0004]

By the way, when such a high performance tire as described above is used for a long period of time, cracks such as fine wrinkles and cracks may occur at the groove bottom of the vertical main groove. Such cracks have fine wrinkles and the like and generally do not affect various running performances of the tire, but as a result of the vertical main grooves being formed with a wide width, they are easily noticeable to the eyes and the appearance of the tire is improved. There is a problem of damage.

The present inventor conducted various experiments in order to prevent the occurrence of such cracks. First, paying attention to how the rubber physical property values of the tread portion change with the passage of time, as shown in FIG. 6, in the tread rubber g, the surface inner portion b of the groove bottom portion of the vertical main groove a is shown. ,and,
The complex elastic modulus of the inner portion c of the tread surface was measured by cutting out a sample from each site with the passage of time. The tread rubber g is formed of one kind of rubber having a uniform composition, and t1 = t2 = 1 mm in the figure.

The measurement results are shown in FIG. From this result, the complex elastic modulus E1 ^* of the surface inner part b of the groove bottom and
The complex elastic modulus E2 ^* of the inner portion c of the tread becomes large with the passage of time, and the elasticity deteriorates. The change of the complex elastic modulus, that is, the deterioration of elasticity is caused by the inner portion b of the groove bottom surface. Is larger, even when the tire is new, it has already been found that the inner surface portion b of the groove bottom portion has a larger complex elastic modulus despite having the same rubber composition. did.

Further, as a result of further research on the above, when the tire raw cover is vulcanized with a vulcanizing die, vertical main grooves are formed, or when a tread profile is extruded in advance, the vertical main When a large pressure acts on the groove bottom portion of the groove, the complex elastic modulus E1 of the groove bottom portion is
It turns out that ^* is large. It was also found that the ratio (E1 ^* / E2 ^* ) of the complex elastic modulus is usually about 2.0 when the tire is new.

Next, the remaining amount of the amine-based or phenol-based rubber anti-aging agent at each of the above-mentioned sites was measured over time, and as shown in FIG. 5 (B),
It was found that the groove width was remarkably reduced in the inner surface portion b of the groove bottom portion.

Further, when the amount of acetone extracted at each of the above-mentioned sites was measured with the lapse of time, as shown in FIG. 5 (C), a remarkable decrease was also observed at the inner surface b of the groove bottom. This means that the mineral oil and the softening agent in the rubber have decreased with the passage of time.

From the above experimental results, firstly, with respect to the tread rubber g, as the tire is used for a long period of time, the antiaging agent, the softening agent, etc. are reduced, for example, by migrating to the belt layer side, and the ozone resistance is greatly increased. By decreasing, the crack is likely to occur. Secondly, in the groove bottom portion of the vertical main groove a having a relatively thin rubber thickness, the migration of the antioxidant and the like is performed more quickly than other portions. Thirdly, it has been found that the increase in complex elastic modulus is also affected by the decrease in the antioxidant, softening agent, oil component and the like.

Further, as shown in FIG. 6, when the linear main groove a extending in a straight line is provided especially in the tire shoulder portion, only the rib d on the inner side of the vertical main groove a in the axial direction of the tire is provided as compared with the zigzag groove. The vertical main groove a is likely to be widened, and the cracks are likely to occur even in such a situation.

The present inventor has conducted extensive studies based on the above experimental results. As a result, it is basically determined that the complex elastic modulus E1 ^* of the groove bottom portion of the vertical main groove is smaller than that of the conventional tire when the tire is new. It has been found that it is possible to prevent the elasticity of the groove bottom portion from increasing after a lapse of time and improve the crack resistance and the like.

As described above, the present invention provides a pneumatic tire which prevents cracks generated in the groove bottom portion of the vertical main groove provided in the tread portion and does not impair the appearance even during long-term use. Has an aim.

[0014]

The invention according to claim 1 of the present invention is a carcass which is locked by folding back around a bead core of a bead portion from a tread portion to a sidewall portion,
A pneumatic tire having a belt layer arranged radially outside and inside the tread portion of the carcass, and further, in the tread portion, a vertical main groove extending from the tread portion surface to the tire circumferential direction is provided. Tire axial direction and tire
Multiple rubber sheets with the same rubber composition divided in the radial direction
It is possible to form a groove corresponding to the vertical main groove of the finished tire.
Sea urchins are laminated on a raw tire cover and vulcanized with a vulcanization mold.
When the tire is new, the tread rubber that forms the tread portion and is disposed on the outer side in the tire radial direction of the belt layer by further integrating is a complex elastic modulus E1 of the inner surface portion of the groove bottom portion of the vertical main groove. The ratio of * to the complex elastic modulus E2 * of the inner surface of the tread (E1 * / E2 *)
And 1.0 or more and 1.5 or less, and the tread portion is made of a rubber composition formed of a substantially uniform composition as a whole, and the invention according to claim 2
The invention according to claim 1 uses a plurality of rubber sheets.
A small rubber strip extruded by an extruder against
The rubber strip on the rotating raw tire cover.
While sequentially moving the loops, it is possible to wind and stack one after another.
Has a groove corresponding to the vertical main groove of the finished tire
It is characterized by forming a tread rubber.

In the invention according to claim 3 , the tread rubber is 100 parts by weight of a rubber base material in which a polymer of one kind or a combination of two or more kinds of natural rubber, butadiene rubber, styrene butadiene rubber or isoprene rubber is mixed. It is characterized in that 60 parts by weight or more and 100 parts by weight or less of carbon black and 30 parts by weight or less of a petroleum-based softening agent are mixed with each part.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, the pneumatic tire 1 is
Bead part 4 from tread part 2 to sidewall part 3
A carcass 6 which is folded back and locked around the bead core 5 is bridged, and a tough belt layer 7 is wound on the outer side of the carcass 6 in the radial direction and inward of the tread portion 2. It gives a hoop effect to the tire shape.

Further, in this example, as a pneumatic tire, the flatness ratio, which is the ratio of the tire cross-section height to the tire maximum width, is 0.8 or less, for example, JIS D420.
2 illustrates an example of a radial tire for passenger cars specified in 2.

The carcass 6 comprises at least one carcass ply 6A having a so-called radial structure in which the carcass cords are arranged at an angle of 75 ° to 90 ° with respect to the tire equator C. The carcass cords are, for example, steel cords. Alternatively, an organic fiber cord such as nylon, rayon or polyester can be preferably used.

The belt layer 7 has one or more belt cords arranged at an angle of about 10 ° to 35 ° with respect to the tire equator C, and in this embodiment, two belt plies 7A and 7B.
Each of the plies 7A and 7B is placed in a different direction so that the belt cords intersect each other.
For this belt cord, like the carcass cord,
Organic fiber cords such as nylon, polyester and rayon, and more preferably high elastic cords such as steel can be appropriately used.

A bead apex 1 made of hard rubber is provided from the bead core 5 toward the outer side in the tire radial direction.
3 are provided to reinforce the bead portion 4.

In the present embodiment, a total of four vertical main grooves 9 extending linearly and continuously in the tire circumferential direction (only two are shown, but symmetrical) are provided in the tread portion 2. , An example in which five land portions 10 can be formed on the tread surface is shown, but these vertical main grooves 9 can be appropriately bent other than a linear shape, and the number thereof is appropriately set to other than four. can do. When the vertical main groove 9 extends in a straight line, as described above, the width is widened and cracks are likely to occur.
The effect of the present invention is further exerted in such a case.

The vertical main groove 9 is formed so that the groove width measured on the surface of the tread surface is, for example, 5 mm or more and 20 mm or less, and the groove depth is, for example, 5 mm or more and 18 mm or less. You can

In each land portion 10 divided by the vertical main groove 9, a large number of lateral grooves extending in a direction intersecting with the vertical main groove 9, for example, siping having a groove width of 1 mm or less, or inside the land portion 10 is formed. It is possible to appropriately dispose a lug groove or the like that is interrupted by.

Next, a tread rubber 11 which forms the tread portion 2 and is arranged outside the belt layer 7 in the tire radial direction.
Is a complex elastic modulus E1 ^* of the surface inner portion G1 of the groove bottom portion of the vertical main groove 9 and a complex elastic modulus E2 ^* of the surface inner portion G2 of the tread portion 2 (land portion 10) when the tire is new ^.
And the ratio (E1 ^* / E2 ^* ) is 1.0 or more and 1.5 or less, and the tread rubber 11 is composed of a rubber composition formed of a substantially uniform composition as a whole. There is.

Here, the tread rubber 11 is at least radially outside the belt layer 7 (when a reinforcing layer having a cord is provided on the outside in the radial direction of the belt layer 7, the reinforcing layer), and moreover, it is regular. It is defined as the area between the outer end points E of the ground contact width TW in the normal state in which the internal pressure is filled and the normal load is applied.

Conventionally, in the tread rubber 11, in order to make the complex elastic modulus different between the groove bottom of the vertical main groove and the tread surface, a technique of so-called two-layer tread structure is disclosed in, for example, Japanese Patent Laid-Open No. 60-255505. Japanese Patent Laid-Open No. 62-1
Although proposed by Japanese Patent Publication No. 91202, etc., the present application is significantly different from these proposals in that the material cost can be reduced by using a tread rubber as a single layer structure.

When the tire is new, the ratio (E
The reason why 1 ^* / E2 ^* ) is 1.0 or more and 1.5 or less is that when this ratio exceeds 1.5, there is no great difference from the conventional tire, and the occurrence of cracks cannot be sufficiently prevented.
Therefore, it is desirable to set the upper limit of the ratio to 1.25. The lower limit of the ratio is ideally the same for the complex elastic modulus because the rubber compositions are originally the same, and for this reason, it is set to 1.0.

Next, when the tire is new, the complex elastic modulus E1 ^* of the surface inner portion G1 of the groove bottom portion of the vertical main groove 9 and
Complex elastic modulus E2 of the inner surface portion G2 of the tread portion 2
^There are various methods for setting the ratio (E1 ^* / E2 ^* ) to ^* to 1.0 or more and 1.5 or less, but it is important to set the vertical main groove 9 at a large pressure or heat. Forming with minimal deformation.

Generally, as shown in FIGS. 3A and 3B, the die plate used when the tread rubber 11 is extruded from the extruder is of a type (D1) in which a tread profile is not formed, and a tread profile is prepared in advance. There are two types, that is, the type (D2) in which is formed. And
In the case where the tread profile can be formed in advance, a large pressure acts on the groove bottom of the concave groove 14 corresponding to the vertical main groove 9 as compared with other portions, and the complex elastic modulus increases.

In FIG. 3C, in the tread rubber 11 having a tread profile formed in advance, the groove 1
4 shows the results of measuring the complex elastic moduli of the groove bottom inner part of 4 and the surface inner part of the tread land portion. As is clear from the figure, it can be seen that the inner part of the groove bottom shows a higher value than the inner part of the surface of the tread land, and the elastic modulus is increased.

Therefore, when the tire is new, the ratio (E1 ^* /
As a specific method for making E2 ^* ) 1.0 or more and 1.5 or less, for example, as shown in FIG. 2A, a plurality of rubber sheets 11A to 11D divided in the tire axial direction and the tire radial direction are used. The tire raw cover 1 is made of the same rubber composition so that the concave groove 14 corresponding to the vertical main groove 9 can be formed.
5 and the like, and integrating this in a vulcanization mold.

By reducing the number of divisions of the tread rubber 11 as much as possible, the productivity of the tire can be improved, and the concave groove 14 corresponding to the longitudinal main groove is formed in advance before vulcanization. It is preferable in that the mold during vulcanization can prevent a large pressure from acting on the groove bottom portion of the concave groove 14, and thus can prevent the groove bottom portion of the vertical main groove of the finished tire from having a high modulus.

Further, for example, as shown in FIG.
While extruding a narrow rubber strip 16 from an extruder (not shown), the rubber strip 16 is sequentially wound and laminated on the rotating tire raw cover 15 while being appropriately moved, as shown in the figure. The groove 1
The tread rubber 11 having No. 4 is formed, and thereafter, the tread rubber 11 is integrated by vulcanization with a vulcanization mold.

It is desirable to make the difference between the height of the protrusion forming the money-shaped vertical main groove and the concave groove 14 small, for example, about 1 to 3 mm. Further, the lamination control of the rubber strip 16 is preferable. Are configured to be able to follow the movements previously stored in the computer.

As described above, the tread rubber 11 is formed with a substantially uniform composition as a whole, and various rubber compositions conventionally used can be adopted. And, for example, as a composition for high performance tires, natural rubber,
60 parts by weight or more and 100 parts by weight or less of carbon black, and 30 parts by weight, based on 100 parts by weight of a rubber base material mixed with a polymer of one kind or a combination of two or more kinds of butadiene rubber, styrene butadiene rubber or isoprene rubber. A rubber composition containing the following petroleum-based softening agent may be preferably used.

Generally, the above-mentioned high-performance tires contain a relatively large amount of petroleum-based softeners, and in many cases rubber compositions having a large complex elastic modulus are used from the beginning. Therefore, in the tread rubber using such a rubber composition, due to the migration of the antioxidant, oil, etc. due to the above-mentioned aging, as shown in FIG. It becomes inferior in cracking property.

Therefore, by limiting the amount of the petroleum-based softening agent such as paraffin-based, naphthene-based or aromatic-based softener to 30 parts by weight or less, the change in the complex elastic modulus can be reduced. In the first place, since the softening agent facilitates the rubber processing operation at the time of production rather than the tire running performance, it can be configured not to be added at all, but if added, it is about 10 to 30 parts by weight. desirable.

[0038]

Example A tire having a tire size of 205 / 55R15 and a structure as shown in FIG. 1 was experimentally manufactured by the following method and tested for crack resistance and the like. EXAMPLE A rubber strip was laminated along a profile of a tread on a tire raw cover having a radial structure (see FIG. 2).
(B)), which was molded with a vulcanization mold. Comparative Example 1 A tread rubber extruded from a non-profile die head on a tire raw cover having a radial structure (see FIG. 3).
(A)) was wound and molded with a vulcanization mold. Therefore, the vertical main groove is first formed by molding with a vulcanizing mold. Comparative Example 2 On a tire raw cover having a radial structure, a tread rubber extruded from a die head having a profile (see FIG. 3).
(B)) was wound and molded with a vulcanization mold. In addition,
The internal structure of each sample tire and the rubber composition of the tread rubber are the same, and they are not affected. The test method is as follows.

(A) Crack resistance After the test tire was aged in an oven at 70 ° C for 10 days, it was assembled on a regular rim (internal pressure 2.3 kgf / c).
m ² ), the state of cracks in the vertical main groove was observed by leaving it in an ozone chamber having an ozone concentration of 50 pphm. Evaluation,
It is as follows. ◯: No cracks occurred at all Δ: Wrinkles or fine cracks occurred ×: Clearly cracks occurred, impairing aesthetics

B) Complex modulus of elasticity For each sample tire, the complex modulus of elasticity E1 ^* of the inner surface portion G1 of the groove bottom portion of the vertical main groove of the tread rubber and the inside of the surface of the tread portion were measured when the tire was new and after heat aging. The complex elastic modulus E2 ^* of the side part G2 is 1 mm from the surface part.
At the inner position, a strip sample with a width of 4 mm, a length of 30 mm, and a length of 1.5 mm is cut out, and a viscoelastic spectrometer manufactured by Iwamoto Seisakusho Co., Ltd. is used to measure a temperature of 70 ° C., a frequency of 10 Hz, and a dynamic strain of ± 2%. It was measured under the conditions. The test results are shown in Table 1.

[0041]

[Table 1]

As a result of the test, it was confirmed that the tires of the examples had a small complex elastic modulus E1 ^* inwardly of the groove bottom when new, and were smaller than those of the other comparative tires even if they were highly elasticized by heat aged. It was Based on this, it was confirmed that crack resistance did not cause cracking for two weeks or more even in a harsh environment such as an ozone chamber. It should be noted that, after a lapse of one month, slight cracks began to occur, but the appearance was not spoiled.

On the contrary, in each of the tires of Comparative Examples 1 and 2, fine cracks were formed after 2 weeks, and a large number of obvious cracks were formed after 1 month, which markedly impaired the appearance.

When the tire laminated with the divided rubber sheets described in the embodiment of the invention was also tested, the value of the ratio of complex elastic modulus (E1 ^* / E2 ^* ) and the crack resistance were the same as above. It was also confirmed that the same performance as that of the example tire could be exhibited.

[0045]

As described above, the pneumatic tire of the present invention is
By suppressing the increase in elasticity of rubber at the groove bottom portion of the vertical main groove when the tire is new, it is possible to prevent the occurrence of cracks at the groove bottom portion and maintain the appearance of the tire for a long period of time.

[Brief description of drawings]

FIG. 1 is a tire cross-sectional view showing an embodiment of the present invention.

2A and 2B are cross-sectional views showing an example of a tread rubber.

3A and 3B are cross-sectional views showing an example of a die plate, and FIG. 3C is a cross-sectional view showing the measurement results of the complex elastic modulus of tread rubber.

FIG. 4 is a graph showing changes over time in complex elastic moduli of high-performance and general-purpose rubbers.

FIG. 5A is a graph showing a time-dependent change in complex elastic modulus of the tread rubber, FIG. 5B is a graph showing a time-dependent change in the amount of the antioxidant remaining in the tread rubber, and FIG. 5C is a tread rubber. 5 is a graph showing the change over time in the amount of extracted acetone in.

FIG. 6 is a cross-sectional view for explaining a conventional technique.

[Explanation of symbols]

2 tread portion 3 sidewall portion 4 bead portion 5 bead core 6 carcass 7 belt layer 9 vertical main groove 10 land portion 11 tread rubber G1 surface inward portion of groove bottom portion of vertical main groove G2 surface inward of tread portion (land portion) Part E1 ^* , E2 ^* Complex elastic modulus

Continuation of the front page (58) Fields investigated (Int.Cl. ⁷ , DB name) B60C 11 / 00,1 / 00 B29D 30/52-30/68

Claims (3)

(57) [Claims] 1. A carcass which is locked by folding back around a bead core of a bead part from a tread part through a sidewall part, and a belt layer which is arranged radially outside the carcass and inside the tread part, Moreover, a pneumatic tire having a vertical main groove extending in the tire circumferential direction, which is recessed from the surface of the tread portion, is provided in the tread portion, and the same tire divided in the tire axial direction and the tire radial direction is used.
Multiple rubber sheets with different rubber composition are aligned with the vertical main grooves of the finished tire.
Laminated on the tire raw cover so that a corresponding groove can be formed
And, by integrating by vulcanization with a vulcanizing mold, the tread rubber that forms the tread portion and is arranged on the outer side in the tire radial direction of the belt layer, when the tire is new,
Complex elastic modulus E1 * of the inner surface of the bottom of the vertical main groove
And the complex elastic modulus E2 * of the inner part of the surface of the tread part
And the ratio (E1 * / E2 *) is 1.0 or more and 1.5 or less, and the tread portion is made of a rubber composition formed of a substantially uniform composition as a whole. Pneumatic tires. 2. A tread portion and a sidewall portion
A car that is locked by folding back around the bead core of the cord part
The dust and the outside of the carcass in the radial direction and inside the tread portion
And a belt layer disposed on one side of the tread portion.
The vertical main part that is recessed from the tread surface and extends in the tire circumferential direction.
It is a pneumatic tire with grooves and rotates a small rubber strip extruded by an extruder.
Move the rubber strips appropriately on the tire cover.
By sequentially winding and stacking while moving,
Treadgo having a groove corresponding to the longitudinal main groove of the finished tire
Of the vulcanization mold and can be integrated by vulcanization with a vulcanization mold.
And the outer side of the belt layer in the tire radial direction by forming the tread portion.
The tread rubber placed on the side is
Complex elastic modulus E1 * of the inner surface of the bottom of the vertical main groove
And the complex elastic modulus E2 * of the inner part of the surface of the tread part
The ratio (E1 * / E2 *) to 1.0 or more and 1.5 or less
And, moreover, a tread portion, a substantially uniform composition as a whole
Air comprising a rubber composition formed by
Included tires . 3. The tread rubber is 60 parts by weight or more based on 100 parts by weight of a rubber base material in which a polymer of one kind or a combination of two or more kinds of natural rubber, butadiene rubber, styrene butadiene rubber or isoprene rubber is mixed. And 10
The pneumatic tire according to claim 1 or 2, wherein 0 part by weight or less of carbon black and 30 parts by weight or less of a petroleum-based softening agent are blended.