JP2000016010A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tire having a small electric resistance and a decreased rolling resistance without impairing the comfortableness. SOLUTION: This pneumatic tire is equipped with a carcass 6 ranging from the tread part 2 via a side wall part 3 to a bead core 6 of a bead part 4. The tread part 2 is equipped with a cap rubber body 11 to form a tread surface 2a and consisting of an insulating rubber material g1 reinforced with silica and a base rubber body 10 installed inside the cap body 11 in the wire radial direction and consisting of a conductive rubber material having a volume specific resistance of 1×108 Ωcm or less. The base rubber body 10 is equipped with a base layer 10a and a penetrative terminal part 10b which extends from the base layer 10a through the cap rubber body 11 and whose external end face 12 constitutes part of the tread grounding surface. The hardness Hs2 of the base rubber body 10 at 25 deg.C is smaller than the hardness Hs1 of the cap rubber body 11.

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 improving low rolling resistance and wet performance while maintaining ride comfort, and effectively discharging static electricity generated on a vehicle to a road surface.

[0002]

2. Description of the Related Art In recent years, tires using silica as a reinforcing agent for tread rubber have been proposed in order to enhance the fuel efficiency of automobiles and to reduce the amount of exhaust gas. I have. This product exhibits excellent wet performance because the hysteresis loss is kept high on the low temperature side, while it has low hysteresis loss on the high temperature side to reduce rolling resistance, and achieves both low rolling resistance performance and wet performance. There is an advantage that it can be improved.

[0003] On the other hand, however, silica has a high electric insulation property, so that when a tread rubber tire containing silica in place of carbon or with a reduced amount of carbon is used, static electricity tends to accumulate in a vehicle.
This accumulation of static electricity may cause sparks when the driver tries to open the fuel tank lid at a gas station, and may cause radio interference such as radio noise while the vehicle is running. It may cause malfunction.

In order to prevent such an electrical malfunction, Japanese Patent Application Laid-Open No. 8-120120 and US Pat.
No. 8055 proposes tires in which a conductive thin film mainly composed of carbon black is adhered to the surface of a tread rubber containing silica to improve the electric resistance. After the wear of the conductive thin film, the state of conduction with the road surface becomes extremely unstable.

The present invention has been devised in view of the above-mentioned problems, and comprises a cap rubber body made of an insulating rubber material having silica as a main reinforcing agent, wherein the cap rubber body made of a conductive rubber material and A base rubber body is provided that has a through terminal portion that rises through the rubber body and forms a part of the tread ground plane. Pneumatic that can effectively discharge static electricity generated on the vehicle to the road surface while maintaining rolling resistance performance and wet performance and without compromising ride comfort, and that can exhibit these characteristics stably from the initial use to the end of use It aims to provide tires.

[0006]

According to one aspect of the present invention, there is provided a pneumatic tire having a carcass extending from a tread portion to a sidewall portion to a bead core of a bead portion. Wherein the tread portion comprises a cap rubber body made of an insulating rubber material forming a tread surface and reinforced with silica, a base layer disposed radially inward of the cap rubber body in the tire direction, and a base layer formed from the cap rubber body. A base rubber body made of a conductive rubber material having a through terminal extending through the cap rubber body and having an outer end surface forming a part of a tread ground surface and having a volume resistivity of less than 1 × 10 ⁸ Ωcm. 25 ℃
A rubber hardness Hs2 of the base rubber body at a temperature of? Is smaller than a rubber hardness Hs1 of the cap rubber body.

According to a second aspect of the present invention, the insulating rubber material is 30 to 10 parts by weight based on 100 parts by weight of the rubber base material.
The conductive rubber material contains 0 parts by weight of silica and 3 to 20 parts by weight of carbon black,
2. The pneumatic tire according to claim 1, wherein the pneumatic tire contains 0 to 50 parts by weight of silica and 25 parts by weight or more of carbon black with respect to 00 parts by weight.

The invention according to claim 3 is the pneumatic tire according to claim 1 or 2, wherein the loss tangent tan δ of the base rubber body is equal to or less than the loss tangent tan δ of the cap rubber body. .

[0009] In this specification, the volume resistivity of rubber is determined by measuring a rubber sample of 15 cm square and 2 mm thick under the conditions of an applied voltage of 500 V, an air temperature of 25 ° C., and a humidity of 50%.
It is indicated by a value measured using an electric resistance measuring instrument of TESTER 8340A.

Further, the loss tangent (tan δ) of rubber is determined by cutting a sample into a predetermined strip-shaped sample,
The values are indicated using a viscoelastic spectrometer manufactured under the conditions of a temperature of 70 ° C., an initial extension of 10%, a dynamic strain of ± 1% and a frequency of 10 Hz.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a meridional section of a tire in a no-load state in which the rim is assembled to a regular rim J and filled with a regular internal pressure that can be determined by a standard.

The "regular rim" is a rim defined for each tire in a standard system including the standard on which the tire is based. For example, a standard rim for JATMA and a "Design Rim" for TRA Or ETRTO
Then "Measuring Rim".

[0013] The "normal internal pressure" is the air pressure specified for each tire in the standard system including the standard on which the tire is based. TIRE LOAD LIMITS AT VARIOU
Maximum value described in "S COLD INFLATION PRESSURES", ETR
If it is TO, it is "INFLATION PRESSURE".

The pneumatic tire 1 is, as shown in FIG.
From the tread portion 2 to the bead portion 4 through the sidewall portion 3
And a toroidal carcass 6 folded and locked by a bead core 5 and a belt layer 7 disposed radially outside the carcass 6 and inside the tread portion 2. You.

In the present embodiment, the carcass 6 is formed of one carcass ply, and a hard bead apex rubber 9 is disposed between the main body 6a and the folded portion 6b. The carcass ply is formed by arranging cords at an angle of 75 to 90 degrees with respect to the tire equator C. As the carcass cord, a polyester cord is employed in this example, but other nylon, rayon, aromatic polyamide Various kinds of organic fiber cords, steel cords and the like can be suitably used.

[0016] The belt layer 7 is made of a cord,
For example, two belt plies are arranged inside and outside in the radial direction arranged at an angle of 15 to 40 degrees, and the cords are arranged so as to intersect between the plies. In this example, a steel cord is used for the belt cord, and the belt layer 7 shows good conductivity.

The tread portion 2 has a tread surface 2a and a cap rubber body 11 made of an insulating rubber material g1 reinforced with silica, and a volume specific resistance disposed inside the cap rubber body 11 in the tire radial direction. Is 1 × 10 ⁸
Base rubber body 10 made of conductive rubber material g2 of less than Ωcm
And a two-layer structure having the following structure.

The base rubber body 10 has a substantially uniform thickness and extends in contact with the inner surface of the cap rubber body 11, and extends from the base layer 10a through the cap rubber body 11. In addition, the outer end surface 12 includes a through terminal portion 10b forming a part of the tread ground surface.

First, the cap rubber body 11 is formed so as to be exposed over most of the tread surface 2a, in this example, the entire ground area of the tread portion 2 except for the through terminal portion 10b, and has a significant effect on rolling resistance. . In the present invention, the cap rubber body 11 is made of a rubber material reinforced by blending silica. As a result, the rolling resistance on a dry road surface can be reduced, and the wet skid resistance on a wet road can be improved.

The cap rubber body 11 has a thickness greater than the depth of the drain tread groove G in this embodiment. Therefore, the low rolling resistance performance and the wet skid resistance performance on a wet road can be maintained even at the end of tire wear.

It is preferable that the cap rubber body 11 contains, for example, 30 to 100 parts by weight of silica with respect to 100 parts by weight of a rubber base material. Thereby, the cap rubber body 11 can achieve both the reduction of the rolling resistance of the tire and the wet performance at a higher level.

As the rubber substrate, natural rubber (N
R), butadiene rubber which is a polymer of butadiene (B
R), a so-called emulsion-polymerized styrene-butadiene rubber (E
-SBR), solution-polymerized styrene-butadiene rubber (S-
(SBR), synthetic polyisoprene rubber (IR) which is a polymer of isoprene, nitrile rubber (NBR) which is a copolymer of butadiene and acrylonitrile, and chloroprene rubber (CR) which is a polymer of chloroprene. It is preferable to use a rubber obtained by blending one or more of these.

The silica to be blended has a nitrogen adsorption specific surface area (BET) of 150 to 250 m ² / g.
And dibutyl phthalate (DBP) oil absorption of 180ml /
Those exhibiting a colloidal property of 100 g or more are preferable in terms of rubber reinforcing effect, rubber processability, and the like.

In order to obtain other physical properties required for the cap rubber body 11, for example, rubber elasticity, rubber hardness, heat generation, and the like, it is preferable to add carbon black supplementarily. The compounding amount of the carbon black is preferably 3 to 20 parts by weight based on 100 parts by weight of the diene rubber base material.

When the amount of the carbon black is more than 20 parts by weight, excellent effects such as low rolling resistance due to silica are reduced and the rubber tends to be hardened. It is difficult to obtain physical properties. If the compounding amount of the silica exceeds 100 parts by weight, it is difficult to compound 3 parts by weight or more of carbon black in order to obtain the other rubber physical properties, and the photooxidation-preventing effect is lowered and the weather resistance is significantly impaired. Absent.

The cap rubber body 11 is made of an insulating rubber material g1 having a volume resistivity of, for example, 1 × 10 ⁸ Ωcm or more, by blending silica.

The base layer 10a of the base rubber body 10
The through terminal portion 10b transfers static electricity generated from the vehicle to the road surface.
Plays an important role to release. In this example, the base layer 1
0a and the through terminal portion 10b are the same conductive rubber material g.
2 is formed from FIG. This conductive rubber material g2
Has a volume resistivity of 1 × 10
⁸Must be limited to less than Ωcm.

The base layer 10a has a substantially uniform thickness and extends in contact with the inner surface of the cap rubber body 11, and in this example, ends substantially coincident with both ends of the belt layer 7. . The cap rubber body 11, the base rubber body 10
The wing rubber body 15 is provided at both ends in the tire axial direction.

The through terminal portion 10b has an inner end 16 connected to the base layer 10a and extends radially outward through the cap rubber body 11 as shown in an enlarged view in FIG. The end portion 12 is formed so as to form a part of the tread surface 2a. In this specification, the tread surface 2a refers to a surface portion where the tread portion 2 comes into contact with a road surface, and excludes an outer surface of a tread groove G formed in the tread portion 2.

In the pneumatic tire 1, static electricity generated in the vehicle is transferred from the rim J to the outer rubber that forms the outer surfaces of the bead portion 4 and the sidewall portion 3 of the tire, and the belt layer 7.
Through terminal portion 10 of base rubber body 10
b to form a conductive path that discharges to the road surface. Generally, the sidewall portion 3 and the bead portion 4 located on the inner side in the tire radial direction with respect to the tread portion 2 are made of, for example, a normal rubber or structure not containing silica, but the portion has good conductive properties. For example, the skin rubber of the sidewall portion 3 and the bead portion 4 has a volume resistivity of less than 1 × 10 ⁸ Ωcm in this example.

As shown in FIGS. 2 and 3, the through terminal portion 10b of the present embodiment is formed in a ring shape substantially continuous at the tire equator C in the tire circumferential direction. For this reason, the through terminal portion 10b can be constantly grounded to the road surface during one rotation of the tire, so that the static electricity removing effect of the vehicle can be more reliably exerted, and the ground can be grounded both when traveling straight and when turning. Since the penetrating terminal portion 10b is provided at the position of the tire equator C where it is possible and the ground pressure is relatively high, it is preferable in that the effect of discharging static electricity to the road surface can be further enhanced.

As shown in FIG. 2, the through terminal portion 10b has a narrow portion 13 which is narrower than the inner end portion 16 thereof. The narrow portion 13 of the through terminal portion 10b
In the present example, the tapered shape extending toward the tread surface 2a while gradually reducing the width of the through terminal portion 10b in the tire axial direction, and having the minimum width with the tread surface 2a is shown.

As described above, when the through terminal portion 10b has the narrow portion 13 having a width smaller than the inner end portion 16, the strain can be concentrated on the narrow portion 13 having low rigidity. It is possible to effectively reduce the rubber crack at the end portion 16 and the rigidity step with the cap rubber body 11 which is a different kind of rubber. From such a viewpoint, the narrow portion 13
Is preferably 60 to 80% of the width Wa of the inner end portion 16 in the tire axial direction (Wb in this example).

The penetrating terminal portion 10b is connected to the tread surface 2
The width Wb (the minimum width of the narrow portion in the present example) of the outer end portion 12b appearing in FIG.
mm, more preferably in the range of 5 to 20 mm. If the width Wb of the outer end portion 12b of the through terminal portion 10b is less than 0.5 mm, the effect of energizing the road surface tends to decrease.
In some cases, the rubber physical properties of 0b affect the cap rubber body 11 to relatively lower the effect of improving low rolling resistance and wet performance.

The conductive rubber material g2 forming the base rubber body 10 is composed of 0 to 50 parts by weight of silica and 25 parts by weight or more based on 100 parts by weight of the rubber base material exemplified in the cap rubber body 11. And carbon black.

That is, 1 × 10 ⁸ Ω as the conductive rubber
In order to obtain an excellent conductivity of less than 25 cm, it is necessary to mix carbon black in an amount of 25 parts by weight or more.To obtain other rubber properties, silica may be added in an auxiliary manner. The amount is not more than 50 parts by weight. If the amount of silica in the conductive rubber material g2 exceeds 50 parts by weight, the abrasion resistance is inferior to that of rubber reinforced with carbon black, and the heat build-up due to the increase in rubber hardness increases to lower. It tends to impair rolling resistance.

The type of carbon black used in the conductive rubber material g2 is not particularly limited, but the blending amount Wc (parts by weight) of the carbon black and the average particle size N
The ratio (Wc / Nc) to c (unit nm) is preferably 1.5 or more. In general, the volume resistivity of the conductive rubber material g2 is related to the compounding amount Wc of carbon black and the average particle diameter Nc, and the volume resistivity decreases as Wc increases or Nc decreases. Therefore, the ratio (W
By regulating c / Nc) to 1.5 or more, the required conductivity can be guaranteed. Preferably, the average particle size N
Hard carbon having c of 30 nm or less is desirable.

When silica is used for the conductive rubber material g2, the type thereof is not particularly limited, and the same material as the insulating rubber material g1 constituting the cap rubber body 11 can be used. The embodiment exemplifies the case where the amount of silica is set to 0. The carbon black used for the insulating rubber material g1 is also the same as the base rubber body 10 described above.
Can be used as the conductive rubber material g2.

If necessary, a known vulcanizing agent, vulcanization accelerator, or the like may be added to the insulating rubber material g1 and the conductive rubber material g2.
Needless to say, a vulcanization accelerator, a plasticizer, an antioxidant, and a silane coupling agent can be appropriately added. As the silane coupling agent, bis (triethoxysilylpropyl) tetrasulfide and α-mercaptopropyltrimethoxysilane are preferable.

In the present invention, in a tire having such a silica-reinforced cap rubber body, the rubber hardness Hs2 of the base rubber body 10 at a temperature of 25 ° C.
One of the features is that the rubber hardness Hs1 of the cap rubber body 11 is smaller than that, that is, Hs1 (rubber hardness of the cap rubber body)> Hs2 (rubber hardness of the base rubber body).

As a result, excellent low rolling resistance and wet performance can be maintained, static electricity generated in the vehicle can be effectively discharged to the road surface, and vibration or impact acting on the cap rubber body 11 can be softened. And the ride comfort performance can be improved. It is particularly preferable that the difference in rubber hardness (Hs1-Hs2) is, for example, not less than 0 and not more than 5 °.

Since the rubber hardness changes depending on the temperature, the temperature for controlling the rubber hardness is set to 25 ° C. in consideration of the actual running conditions of the vehicle.

The rubber hardness Hs2 of the base rubber body 10 at a temperature of 25 ° C.
If the rubber hardness is Hs1 or more, ie, Hs1 (rubber hardness of the cap rubber body) ≦ Hs2 (rubber hardness of the base rubber body), in addition to the silica-reinforced cap rubber body 11,
Since the so-called waist strength of the base rubber body 10 becomes remarkable, a rugged feeling and a feeling of pushing up during driving tend to appear strongly, which tends to impair ride comfort, and the movement of the through terminal portion 10b follows the cap rubber body 11 Tends to be difficult.

In this embodiment, the base rubber body 1
0, the loss tangent tan δ of the conductive rubber g2 constituting the cap rubber body 11 is equal to or less than the loss tangent tan δ of the insulating rubber g1 constituting the cap rubber body 11. In this example, the value of the loss tangent tan δ of the conductive rubber g2 is represented by It is smaller than the value of the loss tangent of the material g1.

By setting the value of the loss tangent of the conductive rubber material g2 to be smaller than the value of the loss tangent of the insulating rubber material g1, the rolling resistance can be further reduced and the fuel consumption of the vehicle can be reduced. Excellent ride comfort can be secured. Further, when the value of the loss tangent of the conductive rubber material g2 is smaller than that of the insulating rubber material g1, it is preferable in that excessive heat generation inside the tread portion can be prevented.

The thickness h1 of the cap rubber body 11
And the thickness h2 of the base rubber body 10 can be variously determined in consideration of the rolling resistance and the electric resistance characteristics of the tire. For example, the ratio (h1 / h2) is set to 1.5 to 4.0. Is preferred. In this embodiment, as shown in FIG. 4, the insulating rubber material g1 forming the cap rubber body 11 and the conductive rubber material g2 forming the base rubber body 10 are integrated into a band from the die of the extruder. It is extruded, and both ends of this band are jointed to form a ring and used as tread rubber. This can prevent a decrease in tire productivity

In such a pneumatic tire, when the tire is new, it is assembled on a rim and filled with an internal pressure of 80% of the normal internal pressure. The electrical resistance between the part and the rim J can be less than 1 × 10 ⁸ Ωcm. In addition, even in a worn state after running the tire for 1000 km, the electric resistance can be regulated to 1 × 10 ⁹ Ωcm or less, and safe driving that prevents fire, radio interference, and the like caused by electrostatic spark can be performed at the beginning of use. Can be guaranteed from to the end.

The measurement of the electric resistance of the tire itself in the load state can be performed based on the “measurement procedure of the tire electric resistance under load” specified by Blatt3, WDK, Germany. As shown in the drawing, the tire 1 is vertically grounded under the above-mentioned load condition on a steel plate 31 to be mounted in an insulated state with respect to the base plate 30, and the electric resistance between the rim J and the steel plate 31 is set to an applied voltage of 500 V and air temperature. The measurement was performed at 25 ° C., 50% humidity, 2.0 kgf / cm ² internal pressure, and 450 kgf vertical load.

FIG. 5 shows another embodiment of the through terminal portion 10b. In this example, the through terminal portion 10b has the narrow portion 13 at a substantially central portion in the tire radial direction length,
The outer side in the radial direction of the narrow portion 13 widens again, and the outer end portion 12 has a width in the tire axial direction substantially equal to the inner end portion 16. In this case, the through terminal portion 10 is formed on the tread surface 2a.
b is preferable in that the ground area can be large, and the through terminal portion 10b has a small rigidity at the narrow portion 13 substantially at the center thereof.
A rigid step with the cap rubber body 11 can be reduced.

The through terminal portions 10b may be provided in a plurality of rows, for example, on both sides of the tire equator C, or may be formed as a columnar body having an outer end surface viewed from the tread surface 2a having a circular or rectangular shape other than a ring shape. It can be raised from the base layer 10a and can be sparsely distributed in the tire circumferential direction. In this case, it is preferable that one or more conductive portions are always grounded on the footprint where the tread surface is grounded when the tire makes one circuit. The through terminal portion 10b can be preferably implemented so that stress concentration at the inner end portion 16 is reduced by making the inner end portion 16 smoothly contact the base layer 10a by, for example, an arc.

[0051]

First, Table 1 shows examples of blending of the rubber material used for the cap rubber body and the rubber material used for the base rubber body.

[0052]

[Table 1]

* 1 to 8 in Table 1 are as follows. * 1 SL574 made of Japan Synthetic Rubber (S-SBR: Styrene content 15
%, Vinyl content 57%, non-oil exhibition) * 2 Nippon Zeon BR1220 (Hicis BR cis content 98%) * 3 Degusa Ultrasil VN-3 (silica: BET175
m ² / g, DBP lubrication amount 210ml / 100g) * 4 Mitsubishi Chemical carbon (primary particle diameter 16nm) * 5 Showa Cabot N351 carbon (primary particle diameter 28n
m) * 6 Degussa silane coupling agent (Si69: bis (3-triethoxysilylpropyl) tetrasulfide) * 7 Log display * 8 JISA hardness at 25 °

Next, a pneumatic tire (size: 175 / 70R13) having the structure shown in FIG. 1 was trial-produced by appropriately combining the rubbers shown in Table 1 as shown in Table 2, and the rolling resistance, wet performance, The tire electrical resistance (described above) under a load condition was measured and evaluated. In addition, bead part,
The volume resistivity of the rubber on the side wall is about 1
× 10 ⁷ Ωcm. The test method is as follows.

<Rolling Resistance> The rolling resistance was measured using a rolling resistance tester manufactured by Kobe Machinery Co., Ltd., and Comparative Example 1 was measured.
Is indicated by an index with 100 as the index. The higher the value, the better.

<Wet Performance> The wet performance was measured by mounting the sample tire on the front wheel of a passenger car at the standard rim specified by the JATMA standard and the maximum air pressure, and providing a puddle having a water depth of about 5 mm on an asphalt road surface having a radius of 50 m. The maximum lateral acceleration (lateral G) measured when the vehicle was running while increasing the speed in a stepwise manner was defined as the wet performance. The higher the value, the better.

<Ride Comfort Performance> The ride comfort performance is determined by comprehensively determining the driving performance of a vehicle on a dry asphalt road test course under the above-mentioned vehicle mounting condition and by the sensuality of the driver. Was evaluated. The higher the value, the better. Table 2 shows the test results.

[0058]

[Table 2]

As a result of the test, it was confirmed that all of the tires of the examples could improve the low rolling resistance performance and the wet performance, and also suppressed the electric resistance of the tires while improving the riding comfort performance.

[0060]

As described above, the pneumatic tire of the present invention can maintain the excellent low rolling resistance performance and wet performance obtained by blending silica, and can eliminate static electricity generated in a vehicle without impairing ride comfort. Discharge can be effectively performed on the road surface, and these characteristics can be stably exhibited from the initial use to the final use.

[Brief description of the drawings]

FIG. 1 is a sectional view of a pneumatic tire showing one embodiment of the present invention.

FIG. 2 is an enlarged partial cross-sectional view showing a through terminal portion.

FIG. 3 is a plan view of a tread portion showing an example of a tread pattern.

FIG. 4 is a partial sectional view showing an example of a tread rubber before molding.

FIG. 5 is a plan view of a tread portion showing another embodiment of the through terminal portion.

FIG. 6 is a diagram illustrating a method for measuring the electrical resistance of a tire in a load state.

[Explanation of symbols]

 Reference Signs List 2 Tread portion 2a Tread surface 3 Side wall portion 4 Bead portion 5 Bead core 6 Carcass 7 Belt layer 10 Base rubber body 10a Base layer 10b Penetration terminal section 11 Cap rubber body 12 Outer end of conductive part 16 Inner end of conductive part

Claims (3)

[Claims] 1. A pneumatic tire having a carcass extending from a tread portion to a bead core of a bead portion through a sidewall portion, wherein the tread portion has a tread surface and is an insulating rubber material reinforced by silica. A cap rubber body comprising: a base layer disposed radially inward of the cap rubber body in the tire radial direction; and a through terminal extending through the cap rubber body from the base layer and having an outer end surface forming part of a tread ground surface. And a volume resistivity of 1 × 10 ⁸ Ωcm
And a rubber hardness H of said base rubber body at a temperature of 25 ° C.
s2 is smaller than the rubber hardness Hs1 of the cap rubber body. 2. The rubber material according to claim 1, wherein said rubber material comprises 30 to 100 parts by weight of silica and 3 to 20 parts by weight based on 100 parts by weight of the rubber base material.
And the conductive rubber material contains 0 to 50 parts by weight of silica and 25 parts by weight or more of carbon black with respect to 100 parts by weight of the rubber base material. The pneumatic tire according to claim 1, wherein 3. The loss tangent tan δ of the base rubber body is as follows:
The pneumatic tire according to claim 1, wherein the loss tangent of the cap rubber body is tan δ or less.