JP2000079805A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small tire capable of decreasing rolling resistance without impairing riding comfort, and of having a small electrical resistance. SOLUTION: This pneumatic tire is provided with a carcass 6, and a belt layer 7 formed out of steel cords arranged to the outer side in the tire radial direction of the carcass 6. A tread rubber 9 at the outer side in the tire radial direction of the belt layer 7 consists of the main part of a tread ground contacting surface 29, and includes a main tread rubber part 10 reinforced by silica, and plural through terminal parts 11 formed out of conductive rubber materials the main tread rubber part 10 from the outer surface of the belt layer 7 to extend its outer end terminal surfaces 11a to be a part of the tread ground contacting surface 2a. In the conductive rubber material, its loss tangent δat 70 deg.C is 0.10 to 0.25, and the peak temperature of its loss tangent is in a range of -10 to -35 deg.C.

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 reducing rolling resistance and improving wet grip performance and effectively discharging static electricity generated on a vehicle to a road surface.

[0002]

2. Description of the Related Art In recent years, fillers for reinforcing tread rubber have been replaced by silica instead of carbon black in order to enhance the fuel efficiency of automobiles and promote reduction of exhaust gas. It has been proposed. Generally, carbon black and rubber make physical so-called surface bonding, so that rubber is difficult to move,
Silica is firmly chemically bonded to rubber via a binder. Therefore, the tread rubber reinforced with silica has reduced rolling resistance and increased wear resistance. Also,
Since the rubber and the silica are bonded at a so-called point, the rubber is easy to move and has a high adhesive strength, so that excellent wet grip performance can be exhibited.

However, such a tire has a drawback that the amount of carbon in the rubber is reduced, and silica has a high electrical insulating property, so that the electrical resistance of the tire tends to increase, and static electricity tends to accumulate in the vehicle. . Such accumulation of static electricity may cause sparks when, for example, trying to open the fuel tank lid of a vehicle at a gas station, and may cause radio interference such as radio noise while the vehicle is running. It may cause a malfunction.

In order to prevent electrical malfunction due to static electricity accumulated in a vehicle, for example, Japanese Patent Application Laid-Open No. Hei 8-120120 and US Pat. No. 5,518,055 disclose that tread rubber containing silica is mainly made of carbon black. Tires have been proposed in which a conductive thin film is adhered and the electrical resistance of the tire is improved.However, in these tires, the state of conduction with the road surface is extremely unstable after the outer conductive thin film is worn. Become. That is, the conductivity of the tire changes as the tire wears.

The present invention has been devised in view of the above-mentioned problems, and the tread rubber on the outer side in the tire radial direction of the belt layer made of a steel cord forms a main part of a tread contact surface and is mainly reinforced with silica. A main tread rubber portion and a plurality of through terminal portions made of a conductive rubber material that extends through the main tread rubber portion from the outer surface of the belt layer and whose outer end surface forms a part of the tread ground surface, In addition, this conductive rubber material is based on the use of rubber with a limited loss tangent tan δ and its peak temperature, which reduces rolling resistance and enhances wet grip performance while effectively discharging static electricity generated on the vehicle to the road surface. It is an object of the present invention to provide a pneumatic tire that can exhibit these characteristics stably from the initial stage to the final stage of use.

[0006]

In order to achieve the above object, according to the first aspect of the present invention, there is provided a carcass extending from a tread portion to a side wall portion to a bead core of a bead portion, and a tire of the carcass. A pneumatic tire having a belt layer arranged radially outward and inward of the tread portion and further arranged with steel cords inclined with respect to the tire equator, wherein the tread rubber in the tire radial direction outside of the belt layer is A main tread rubber part which forms the main part of the tread ground contact surface and contains 30 to 100 parts by weight of silica with respect to 100 parts by weight of the rubber base material, and penetrates the main tread rubber part from the outer surface of the belt layer. The volume resistivity is 1 × 10 and the outer end surface forms a part of the tread contact surface.
^A plurality of penetrating terminals made of a conductive rubber material of less than ⁸ (Ωcm), and the conductive rubber material has a loss tangent tan δ of 0.10 to 0.25 at 70 ° C. and a peak temperature of the loss tangent. Is in the range of -10 to -35 ° C.

According to a second aspect of the present invention, the conductive rubber material contains at least 25 parts by weight of carbon black based on 100 parts by weight of the rubber base material.
It is a pneumatic tire of the statement.

According to a third aspect of the present invention, the through terminal portion has a substantially ring shape extending in the tire circumferential direction with a width of 0.5 to 2.0 mm in the tire axial direction, and has a width of 5 mm in the tire axial direction. 3. The pneumatic tire according to claim 1, wherein 3 to 10 tires are formed within the tread contact width at a distance of 30 mm.

[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.

[0010] The loss tangent (tan δ) of rubber is determined by cutting a rubber into a predetermined strip-shaped sample and measuring the loss tangent.
Using a viscoelastic spectrometer made of
%, Dynamic strain ± 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 normal state in which a normal rim J is rim-assembled and filled with a normal internal pressure and no load is applied. Here, the “regular rim” is a rim defined for each tire in the standard system including the standard on which the tire is based. For example, a standard rim for JATMA, a “Design Rim” for TRA, or For ETRTO, "Measur
ing Rim ". 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, and the maximum air pressure and TRA for JATMA. Ba Table "TIRE LOAD LIMITS AT
VARIOUS COLD INFLATION PRESSURES "
For ETRTO, it is "INFLATION PRESSURE".

A pneumatic tire 1 shown in FIG.
And a toroidal carcass 6 reaching the bead core 5 of the bead portion 4 through the side wall portion 3 and a belt layer 7 made of a steel cord disposed radially outside the carcass 6 in the tire tread portion 2. For passenger cars.

In the present embodiment, the carcass 6 includes a main body 6a extending between the bead cores 5 and 5;
A carcass ply 6A comprising a folded portion 6b which is continuous with both ends of the bead core 5 and is turned around the bead core 5 from inside to outside in the tire axial direction is shown. In addition, between the main body 6a and the folded portion 6b,
Hard bead apex rubber 8 is arranged, and bead portion 4
Has been reinforced.

The carcass ply 6A has a radial structure in which carcass cords are arranged at an angle of 75 to 90 degrees with respect to the tire equator C, for example. , Rayon, aromatic polyamide, and other organic fiber cords, steel cords, and the like.

The belt layer 7 comprises, for example, two belt plies 7A and 7B in the radial direction, in which steel cords are arranged at an angle of 15 to 40 degrees with respect to the tire equator C. The codes are superimposed in a direction that intersects each other. Each belt ply 7A, 7B
Is formed by coating both sides of an array of steel cords with thin topping rubber. Such a belt layer 7
Since the steel cord is included, it has good conductivity in the tire circumferential direction.

As shown in the enlarged view of FIG. 2, the tread rubber 9 outside the belt layer 7 in the tire radial direction forms an essential part of the tread contact surface 2a and is an insulating rubber material reinforced with silica in this embodiment. Main tread rubber part 1 consisting of g1
And a plurality of conductive rubber materials g2 extending from the outer surface of the belt ply 7B outside the belt layer 7 through the main tread rubber portion 10 and the outer end surface 11a forms a part of the tread ground surface 2a. An example including the through terminal portion 11 is illustrated.

The main tread rubber portion 10 reinforced by silica forms a main portion of the tread ground surface 2a as shown in FIGS. 1 and 2 and FIG. 3 which is a developed view of the tread portion 2. The tread contact surface 2a is in the normal state,
The contact surface is a tread contact surface between the tread contact ends e, e when a normal load determined by the standard is applied.
Then, "the main tread rubber portion 10 is connected to the tread ground surface 2a.
"The main part of the tread" means that the total contact area of the main tread rubber part 10 per tire circumference occupies at least 50% or more of the total area of the tread contact surface, preferably 60% or more, and more preferably 60% or more. Preferably, it occupies 70% or more.

In the present embodiment, the main tread rubber portion 10 is divided in the tire axial direction (10A, 10A, 10B, 10B, 1B) by a plurality of through terminal portions 11 extending in the tire circumferential direction.
0C, 10C), but is formed so as to be exposed over the entire area of the tread ground surface 2a except for the through terminal portion 11. Further, in the present embodiment, the main tread rubber portion 10 is provided between the outer surface of the outer belt ply 7B and the tread contact surface 2a.
With such a thickness, low rolling characteristics and wet grip performance by silica can be further improved.

The main tread rubber portion 10 contains 30 to 100 parts by weight of silica with respect to 100 parts by weight of a rubber base material to improve low rolling resistance and wet grip performance. In the examples, those containing 3 to 20 parts by weight of carbon black are exemplified. Such a main tread rubber portion 10 forms a main portion of the tread ground contact surface 2a, and furthermore, the entire thickness of the tread rubber 9 as in this example, so that the rolling resistance of the tire becomes smaller,
The wet grip performance is greatly improved.

The rubber base material used for the main tread rubber portion 10 includes natural rubber (NR), butadiene rubber (BR) which is a polymer of butadiene, styrene-butadiene rubber (E-SBR) of so-called emulsion polymerization, and solution polymerization. Styrene-butadiene rubber (S-SBR), synthetic polyisoprene rubber (IR) which is a polymer of isoprene, and nitrile rubber (N which is a copolymer of butadiene and acrylonitrile)
BR), chloroprene rubber (CR), which is a polymer of chloroprene, and the like.
Rubber blends of more than one species may also be used.

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. If the amount of silica exceeds 100 parts by weight, it is not preferable because, for example, the compounding of carbon black becomes difficult in order to obtain the other rubber properties described above, and the effect of preventing photooxidation is reduced and the weather resistance is significantly impaired.

In order to further improve other physical properties required for the main tread rubber portion 10, for example, rubber elasticity, rubber hardness, heat generation, dry grip performance, etc., carbon black is used in an amount of 3 to 20 parts by weight. It is preferable to mix them appropriately. If the compounding amount of the carbon black exceeds 20 parts by weight, excellent effects such as low rolling resistance by silica are reduced, and the movement of the rubber is hindered and the tackiness tends to be reduced. It is difficult to obtain satisfactory rubber properties. Note that such carbon black can be omitted.

The main tread rubber portion 10 has a reduced carbon content and a highly electrically insulating silica compound.
For example, the insulating rubber material g1 has a volume resistivity of 1 × 10 ⁸ (Ωcm) or more.

The through terminal portion 11 itself is made of a conductive rubber material g2, extends from the outer surface of the highly conductive belt layer 7 through the main tread rubber portion 10, and has an outer end surface 11a in contact with the tread. It forms part of the ground 2a. Thereby, the penetrating terminal portion 11 discharges static electricity generated from the vehicle to the road surface via the belt layer 7. In this example, the plurality of through terminal portions 11 are all formed of the same conductive rubber material g2, and have a volume resistivity of 1 × 10 ⁸ (Ωcm).
Less than.

A wing rubber body 12 is provided at each end of the tread rubber 9 in the tire axial direction, and a sidewall rubber 13, a bead rubber 14 and the like are adhered to the wing rubber body 12 in succession. Each of these rubbers does not contain silica, and has good electrical conductivity with a volume resistivity of less than 1 × 10 ⁸ (Ωcm).

In such a pneumatic tire 1, static electricity generated in the vehicle is transferred from the rim J to the bead rubber 14 of the tire,
A conductive path that discharges from the through terminal portion 11 to the road surface via the sidewall rubber 13 and the belt layer 7 can be formed.

As shown in FIG. 2, in the present embodiment, the through terminal portion 11 has a substantially equal width and extends in the tire radial direction. Also, as shown in FIG. 1 and FIG.
5 is formed of a central through terminal portion 11A passing through the position, a through terminal portion 11B, 11B in both sides thereof, and an outer through terminal portion 11C, 11C outside the through terminal portion.

Each of the through terminal portions 11 has a width W in the tire axial direction at the outer end portion 11a of 0.5 to 2.0 mm, for example.
More preferably, it is formed in a small width of 1.0 to 1.5 mm. The width W at the outer end of the through terminal 11
If it is less than 0.5 mm, the effect of discharging to the road surface tends to decrease. Conversely, if it exceeds 2.0 mm, the rubber properties of the through terminal portion 11 affect the main tread rubber portion 10 to reduce the rolling resistance. In addition, the effect of improving the wet performance is relatively easily reduced.

Further, in this embodiment, the through terminal portion 11 has a substantially ring shape extending in the tire circumferential direction.
In addition, since it is "substantially ring-shaped," the through terminal portion 11 may be interrupted by, for example, a tread groove extending in the tire axial direction. As described above, since the through terminal portion 11 has a substantially ring shape, more of the through terminal portion 11 can be grounded to the road surface during one rotation of the tire, and the static electricity removing effect of the vehicle can be more reliably exerted.

Each through terminal 11 is, for example, 3 to 10 mm apart from the tread contact width at a distance of 5 to 30 mm in the tire axial direction.
It is desirable that five or eight books are formed. By arranging the plurality of penetrating terminals 11 in the tire axial direction in this manner, an opportunity to ground the penetrating terminals 11 is ensured during both straight traveling and turning. In particular, when the center through terminal portion 11A is provided at the position of the tire equator C where the ground pressure is relatively high, the effect of discharging static electricity to the road surface can be further enhanced.

In the present embodiment, the conductive rubber material g2 constituting the penetrating terminal portion 11 is 25 parts by weight or more based on 100 parts by weight of the rubber base material exemplified in the main tread rubber portion 10. Exemplifies the case where conductivity is imparted by compounding the compound.

That is, 1 × 1 as the conductive rubber material g2
In order to obtain an excellent conductivity of less than 0 ⁸ (Ωcm), it is desirable to mix carbon black in an amount of 25 parts by weight or more, preferably 30 parts by weight or more, more preferably 45 parts by weight or more. Here, the type of carbon black used in the conductive rubber material g2 is not particularly limited. It is preferably at least 0.5. In general, the volume resistivity of the conductive rubber material g2 is related to the blending amount Wc of carbon black and its average particle diameter Nc, and the volume resistivity tends to decrease as Wc increases or Nc decreases. Therefore, the ratio (Wc /
By regulating Nc) to 1.5 or more, favorable conductivity can be guaranteed. Preferably, the average particle diameter Nc
Is preferably 30 nm or less.

In this embodiment, the conductive rubber material g2
Shows an example in which the amount of silica is set to 0, but a small amount of silica can be added as long as the conductivity is not impaired. The same carbon black as the conductive rubber material g2 can be used for the insulating rubber material g1. If necessary, a known vulcanizing agent, vulcanization accelerator, vulcanization accelerator, plasticizer, antioxidant, oil, or silane cup may be added to the insulating rubber material g1 and the conductive rubber material g2. Needless to say, a ring agent or the like can be appropriately added. As the silane coupling agent, bis (triethoxysilylpropyl) tetrasulfide and α-mercaptopropyltrimethoxysilane are preferable.

The conductive rubber material g2 must have a loss tangent tan δ at 70 ° C. of 0.10 to 0.25 and a peak loss tangent temperature of -10 to −35 ° C. FIG. 4 shows an example of the conductive rubber material g2.
5 is a graph showing the relationship between the loss tangent tan δ and the temperature (° C.), and has a peak at about −30 ° C. in this example.

Loss tangent tan δ of the conductive rubber material g2
Is less than 0.10, the penetration terminal portion 11 has relatively high elasticity, and the wet grip performance of the main tread rubber portion 10 having improved adhesion by silica is reduced, or Cracks and the like at the interface. Conversely, if the loss tangent tan δ exceeds 0.25, the penetrating terminal portion 11 becomes relatively viscous and the wet grip performance can be enhanced, but the energy loss increases and the rolling resistance cannot be reduced.

If the peak temperature of the loss tangent of the conductive rubber material g2 is higher than -10 ° C., the abrasion resistance is reduced, and the abrasion is larger than that of the main tread rubber portion 10. Worsens. If the peak temperature of the loss tangent is lower than −35 ° C., the wet grip performance deteriorates.

The loss tangent tan δ at 70 ° C. of the insulating rubber material g1 forming the main tread rubber portion 11 is preferably, for example, 0.05 to 0.20.

In this embodiment, as shown in FIG.
The insulating rubber material g1 forming the main tread rubber portion 10 and the conductive rubber material g2 forming the through terminal portion 11 are integrally extruded into a band from a die of an extruder, and both ends of the band are joined. To form a tread rubber 9. This can prevent a decrease in tire productivity. In addition, as shown by a one-dot chain line in the figure,
Under-tread rubber 1 with a small thickness
6 may be connected. Such an undertread rubber 16 has a thickness of 2.0 mm or less, preferably 0.5 to 1.5 mm, and is preferably made of the same conductive rubber material g2 as the through terminal portion 11.

Further, such a pneumatic tire is mounted on a rim at the time of a new article, and a tire filled with an internal pressure of 80% of the normal internal pressure is loaded with 80% of the tire maximum load. The electric resistance between the ground portion and the rim J can be less than 1 × 10 ⁸ (Ω). Also in the wear state after 1000km running of the tire, it said to the electrical resistance no 1 × 10 ⁹ (Ω) or less can be restricted to less than 1 × 10 ⁹ (Ω), the fire caused by sparks static, Telecommunications Safe driving with no obstacles can be guaranteed from the beginning to the end of use.

The measurement of the electric resistance of the tire itself in the loaded state can be measured based on the "Procedure for measuring the electric resistance of a tire under a load" specified by WTT, Blatt3 in 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.

As described above, the embodiment of the present invention has been described in detail. However, the through terminal portion 11 is not limited to a substantially ring shape, but may be a columnar body having an outer end surface viewed from the tread surface having a circular or rectangular shape, for example. It can be started from the belt layer 7 and can be sparsely distributed in the tire circumferential direction. In this case, it is preferable that at least one through terminal portion is always grounded on a footprint where the tread portion is grounded when the tire makes one circuit.

[0042]

First, Table 1 shows an example of the combination of the rubber material used for the main tread rubber portion and the rubber material used for the through terminal portion.

[0043]

[Table 1]

* 1 to 9 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 NS116 made by Nippon Zeon (S-SBR: styrene content 20%,
* 3 SBR1502 manufactured by Sumitomo Chemical (E-SBR: 23.5% styrene)
* 18% of vinyl, non-oil exhibition) * 4 Nippon Zeon BR1220 (high cis BR cis content 98%) * 5 Degusa Ultrasil VN-3 (silica: BET175)
m ² / g, DBP lubrication amount 210ml / 100g) * 6 Mitsubishi Chemical carbon (primary particle diameter 16nm) * 7 Showa Cabot N351 carbon (primary particle diameter 28n
m) * 8 Degussa silane coupling agent (Si69: bis (triethoxysilylpropyl) tetrasulfide) * 9 Log display

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 5 was obtained.
Is indicated by an index with 100 as the index. The higher the value, the better.

<Wet Grip Performance> The wet performance was measured by measuring the speed on a course provided with a puddle of about 5 mm depth on an asphalt road surface by mounting the test tire on a traction test vehicle at the standard rim specified by JATMA standard and the maximum air pressure. The maximum coefficient of friction when traveling at 64 km / H was measured and evaluated by an index with Comparative Example 5 being 100. The higher the value, the better. Table 2 shows the test results.

[0048]

[Table 2]

As a result of the test, it was confirmed that all of the tires of the examples reduced the electric resistance of the tire while improving the low rolling resistance performance and the wet grip performance.

[0050]

As described above, the pneumatic tire of the present invention can maintain excellent low rolling resistance performance and wet performance obtained by blending silica, and effectively discharge static electricity generated in a vehicle to a road surface. These characteristics can be exhibited stably from the initial stage to the final stage of 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 a partially enlarged view of a tread portion.

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

FIG. 4 is a graph showing the relationship between the loss tangent of the conductive rubber material and the temperature.

FIG. 5 is a partial sectional view showing another embodiment of the tread rubber before molding.

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

[Explanation of symbols]

 2 Tread portion 2a Tread ground surface 3 Side wall portion 4 Bead portion 5 Bead core 6 Carcass 7 Belt layer 10 Main tread rubber portion 11 Through terminal portion

Claims (3)

[Claims] 1. A carcass extending from a tread portion to a bead core of a bead portion from a sidewall portion to a bead core of a bead portion, and a carcass disposed radially outward of the carcass and inward of a tread portion and having a steel cord inclined with respect to the tire equator. A pneumatic tire including an arrayed belt layer, wherein the tread rubber on the tire radial outer side of the belt layer is
A main tread rubber part which forms a main part of the tread ground contact surface and contains 30 to 100 parts by weight of silica with respect to 100 parts by weight of the rubber base material; and a penetrating through the main tread rubber part from the outer surface of the belt layer. And a plurality of through terminal portions made of a conductive rubber material having a volume resistivity of less than 1 × 10 ⁸ (Ωcm), the outer end surface of which forms a part of the tread ground surface, and the conductive rubber material has a temperature of 70 ° C. Of the loss tangent is 0.10 to 0.25, and the peak temperature of the loss tangent is -1.
A pneumatic tire, which is in the range of 0 to -35 ° C. 2. The pneumatic tire according to claim 1, wherein the conductive rubber material contains at least 25 parts by weight of carbon black based on 100 parts by weight of the rubber base material. 3. The through terminal portion has a substantially ring shape extending in the tire circumferential direction with a width in the tire axial direction of 0.5 to 2.0 mm, and is tread grounded at a distance of 5 to 30 mm in the tire axial direction. The pneumatic tire according to claim 1, wherein three to ten tires are formed in the width.