JPH1120409A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the electrification up to the end ofd traveling by applying a conductive rubber layer having a specific resistivity value and a prescribed physical property to a prescribed position of a treated part to form an energized path. SOLUTION: In this pneumatic tire, a conductive rubber layer 2 is present on the cap layer 1 of a tire tread having a resistivity value of 10<8> Ω.cm or more so as to be circumferentially continued from the tread to a base layer 3. The rubber layer 2 has a center X ranging from W/4 or more to 3W/4 or less to the direction of tread width W. When X is within this range, the conductive rubber layer 2 is surely situated in grounding area, and a sufficient electrification effect can be provided. The thickness after vulcanization of the conductive rubber layer 2 is set to 0.5 mm or more, more preferably, 1.0-2.0 mm, considering the durability to the end of traveling.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire that can reliably prevent static charge until the end of traveling without impairing abrasion resistance and fuel efficiency.

[0002]

2. Description of the Related Art In a conventional pneumatic tire, an appropriate amount of carbon black is contained in a tread rubber, and there has been no problem relating to the electric resistance of the tire or the problem relating to accumulation of a charge amount. However, in recent years, environmental issues have been widely taken up, and the movement to reduce fuel consumption has been accelerated. In order to achieve low fuel consumption, that is, reduction of rolling resistance by improving tread rubber, it is necessary to reduce carbon black which causes loss.Today, carbon black is used as a tread rubber excellent in low fuel consumption performance. Tread rubber containing silica by reducing the blending amount has attracted attention, and in order to achieve a high level of both tire kinetic performance and low fuel consumption performance, especially in pneumatic radial tires having a cap / base structure, a large amount of silica is blended. There is a tendency for the use of rubber for the cap layer to increase. As a result, problems relating to electric resistance and problems relating to accumulation of the amount of charge have newly emerged.

As a method for solving such a problem, the following methods have been mainly known. One is to sandwich a thick conductive rubber sheet from the tread surface to the tread lower rubber at the center in the tread width direction or a thin conductive rubber sheet from the tread shoulder to the inside of the side (for example, EP 658 452). Issue specification,
U.S. Pat. No. 5,518,055 and JP-A-8-3
No. 4204).

[0004] Another method is to use a tread rubber mixed with carbon black excellent in conductivity, which is different from carbon black usually used in tires.

[0005] Still another method is to coat a conductive material, for example, cement obtained by mixing a conductive carbon black with a water-based rubber composition at the time of extruding the tread during tire production. (For example, see Japanese Patent Application Laid-Open No. 8-120120). According to this method, even when the product tire after tire vulcanization is mounted on a passenger car and the tread portion is worn, the conductive coating material remains on the sidewalls of many grooves carved as a pattern of the tread portion. Thereby, the static electricity charged on the entire tire can be dissipated to the road surface.

[0006]

However, each of the above methods has problems in manufacturing and quality as described below, and has not always been sufficiently satisfactory. For example, in a rubber sheet or a contact rubber layer as disclosed in the above-mentioned European Patent No. 658 452, the effect is maintained at the initial stage of running, but when general-purpose carbon black is used as a filler, In the latter case, there is a problem that the current-carrying path is cut off due to the promotion of abrasion of the conductive layer at the end of traveling, and the antistatic effect is lost. In particular, with the improvement of the wear resistance of the tread cap by the silica compound rubber composition, in order to maintain such an effect until the end of traveling, the wear resistance of the conductive rubber sheet and the contact rubber layer is improved similarly to the tread cap rubber. Otherwise, only the cap rubber is grounded at the end of traveling, and as a result, the antistatic effect cannot be obtained.

[0007] Further, a rubber component 1 is added to the tire tread rubber.
When several parts by weight of the conductive carbon black are added to 00 parts by weight, the specific resistance value of the tread is reduced, but the fuel efficiency, which is the original purpose of the tire, is significantly deteriorated. Since the reinforcing property with the polymer is extremely low, there is a problem that the wear resistance of the tire tread is reduced as a result.

Further, the method of coating a water-based cement containing conductive carbon black on the rubber surface of the cap layer is extremely inferior in workability due to the extremely high adhesive strength of the cement material, and the cement material itself There is a problem with the storage stability of the rubber composition, there is a risk of phase separation, and various stabilizers are required to prevent foaming at the time of coating. It reduces the durability of the product and causes mold contamination during vulcanization. Furthermore, the rubber composition of the cap layer is hydrophobic, and it takes a long time to dry when applying the above-mentioned water-based cement, and also causes uneven coating, resulting in poor durability of the coated film. Furthermore, at the time of vulcanization, the interfacial adhesive force between the rubber of the cap layer and the rubber coated with the water-based cement is reduced, interfacial peeling occurs during traveling, and at the end of traveling, the current path is cut off, and an antistatic effect is obtained. There is a problem that can not be.

It is an object of the present invention to provide a pneumatic tire that can reliably prevent electrification until the end of traveling without impairing abrasion resistance and fuel economy.

[0010]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventor has found that a conductive rubber layer having a specific specific resistance value and predetermined physical properties is provided on a tread portion of a tread portion of a pneumatic tire. The present inventors have found that the above object can be achieved by applying a current to the portion to form an energization path, and have completed the present invention.

That is, the pneumatic tire of the present invention is as follows. (1) A conductive rubber layer having a specific resistance of 10 ⁶ Ω · cm or less, which is exposed on the tread surface and forms an energization path with the tire grounding surface, is partially provided in the width direction of the annular tread of the product tire in the tire circumferential direction. Wherein the shrinkage in the thickness direction of the conductive rubber layer at the time of vulcanization is equal to or smaller than the shrinkage in the thickness direction of another extruded tread rubber. Tires.

(2) A conductive rubber layer having a specific resistance value of 10 ⁶ Ω · cm or less, which is exposed on the tread surface and forms an energization path with the tire grounding surface in a part of the annular tread in the width direction of the product tire, is formed in the tire circumferential direction. Exist continuously and / or intermittently in
A pneumatic tire, wherein the widthwise shrinkage of the conductive rubber layer during vulcanization is equal to or greater than the widthwise shrinkage of another extruded tread rubber.

(3) In the pneumatic tire, the annular tread has a two-layer structure including a cap layer on the tire tread side and a base layer adjacent inside the cap layer, and the cap layer has a specific resistance value of 10 ^8. It is a pneumatic tire made of a rubber of Ω · cm or more.

(4) The pneumatic tire according to the present invention, wherein the conductive rubber layer has a contraction ratio in the thickness direction smaller than that of the cap layer.

(5) In the pneumatic tire, the conductive rubber layer has a center X in the tread width W direction in a range represented by the following formula: W / 4 ≦ X ≦ 3W / 4. Tires.

(6) In the pneumatic tire, the width of the conductive rubber layer along the tread width W direction is 0.5 to 2.
It is a pneumatic tire that is 0 mm.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the specific resistance value is 1
0 diene rubber used in the rubber composition for a ⁶ Omega · cm or less conductive rubber layer is styrene-butadiene rubber (SB
R), butadiene rubber (BR) or natural rubber (NR)
It is more preferable to include at least one of the above from the viewpoint of durability.

Further, the rubber composition for a conductive rubber layer includes:
Nitrogen adsorption specific surface area (N ₂ SA) is 130 m ² / g or more and dibutyl phthalate oil absorption (DBP) is 110 ml
/ 100 g or more of carbon black is preferably used. In this rubber composition, by using such a small particle size and high structure carbon black, the durability of the rubber layer forming the current path is improved, and the antistatic effect can be exerted until the end of running of the tire. To Here, N ₂ SA is described in ASTM D3037-89 and D
BP is a value determined in accordance with ASTM D2414-90, respectively.

When the compounding amount of the carbon black is less than 40 parts by weight based on 100 parts by weight of the diene rubber, the reinforcing property is not sufficient. On the other hand, when the amount exceeds 100 parts by weight, when the softening agent is small, it becomes hard after vulcanization. Overheating, cracking, etc., and when the amount of the softening agent is large, abrasion resistance decreases. As the compounding agent other than carbon black, compounding agents usually used in rubber products, for example, vulcanizing agents, vulcanization accelerators, vulcanization accelerating assistants, softeners, antioxidants, etc. It is appropriately blended.

In one embodiment of the pneumatic tire of the present invention, in the tread having the cap / base structure shown in FIG. 1, the contraction rate of the extruded conductive rubber during vulcanization is smaller than the contraction rate of the rubber of the cap layer. Equal or smaller. When the contraction rate of the extruded conductive rubber at the time of vulcanization is larger than the contraction rate of the rubber of the cap layer, as shown in FIG.
Even when the conductive rubber layer 2 is exposed on the tread surface at the time of extrusion, the rubber of the cap layer 1 flows into the gap after shrinkage of the conductive rubber layer 2 during vulcanization, so that the conductive rubber layer 2 on the tread surface is hidden. May be lost. On the other hand, if the contraction rate of the extruded conductive rubber layer 2 at the time of vulcanization is equal to or smaller than the contraction rate of the rubber of the cap layer 1, FIG.
As shown in (b), the conductive layer can be favorably exposed on the tread surface. The same can be said for the tread type shown in FIGS. The type shown in FIG. 3 is an example in which the conductive rubber layer 2 extends from the surface of the cap layer 1 to the bottom surface of the base layer 3, and the type shown in FIG. This is an example of reaching the base layer 3.

Even if the contraction rate in the thickness direction of the conductive rubber layer 2 during vulcanization is greater than the contraction rate in the thickness direction of the other extruded tread rubber, as shown in FIG. By increasing the thickness of the base only at point 2, it is possible to manufacture a tire that can achieve the intended purpose.

Next, the structure of one embodiment of the pneumatic tire of the present invention will be specifically described. FIG. 1 shows a tread having a cap / base structure. As shown in FIG. 1, in the pneumatic tire of the present invention, the conductive rubber layer 2 surrounds the cap layer 1 of the tire tread having a specific resistance of 10 ⁸ Ω · cm or more until it reaches the base layer 3 from the tread surface. It exists continuously in the direction.

In the conductive rubber layer, the center X of the conductive rubber layer in the direction of the tread width W is within a range represented by the following formula: W / 4 ≦ X ≦ 3W / 4. When X is in the range of not less than W / 4 and not more than 3W / 4, the conductive rubber layer surely enters the ground area, and a sufficient antistatic effect can be obtained.

The thickness of the conductive rubber layer after vulcanization is 0.5 mm or more, more preferably 1.0 to 2.0 mm, considering durability until the end of running. This thickness is 0.
If it is less than 5 mm, there is a possibility that the workability at the time of feeding a thin sheet and the rubber layer at the time of vulcanization may interrupt the conductive layer. On the other hand, if it exceeds 4.0 mm, the rolling resistance of the tire deteriorates, and in addition to promoting the occurrence of uneven wear, a peeling phenomenon due to a difference in elastic modulus from the tread cap rubber tends to occur. It becomes difficult to maintain a low electric resistance value stably.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on examples, conventional examples and comparative examples. According to the formulation shown in Tables 1 and 2 below, rubber compositions to be used for the tread cap rubber and the conductive rubber layer of the pneumatic radial tire were respectively prepared.

(Table 1: Tread Cap Rubber) Cap Rubber Styrene Butadiene Rubber ^* 196 (parts by weight) Butadiene Rubber ^{* 2} 30 SiO ₂ ^* 360 Carbon Black (N234) ^{* 4} 20 Silane Coupling Agent ^{* 5} 6 ZnO 3 Stearic acid 2 Aroma oil 10 Vulcanization accelerator (CBS) ^{* 6} 1.5 Vulcanization accelerator (DPG) ^{* 7} 2 Sulfur 1.5 * 1 SBR1712 manufactured by Nippon Synthetic Rubber Co., Ltd. * 2 96% cis bond * 3 Nipsil VN3 * 4 N ₂ SA: 126 m ² / g DBP: 125 ml / 100 g * 5 Si69 manufactured by DEGUSSA * 6 N-cyclohexyl-2-benzothiazylsulfenamide * 7 Diphenylguanidine

(Table 2: conductive rubber) Rubber composition Natural rubber 40 (parts by weight) Styrene butadiene rubber ^* 860 Carbon black (N134) ^* 960 Aroma oil 15 ZnO 2 Antioxidant ^{* 10} 1 Vulcanization accelerator ( DPG) 0.2 Vulcanization accelerator (NS) ^{* 11} 0.8 Sulfur 1.5 * 8 NBR manufactured by Nippon Synthetic Rubber Co., Ltd. * 9 N ₂ SA: 146 m ² / g DBP: 127 ml / 100 g * 10 N- (1 , 3-Dimethylbutyl) -N'-phenyl-p-phenylenediamine * 11 N-tert-butyl-2-benzothiazolylsulfenamide

Using the obtained conductive rubber as the conductive rubber layer 2 as shown in FIG. 1, the cap layer 1 of the pneumatic radial tire having a size of 195 / 65R15 has a width W / 2 (a half of the tread width W). ) Was continuously arranged in the tire circumferential direction until it reached the base layer 3 (Example 1). Further, the same conductive rubber is continuously applied in the tire circumferential direction at a position of W / 2 (a half of the tread width W) of the pneumatic radial tire of the same size as shown in FIG. (Example 2). Further, as shown in FIG. 4, the same conductive rubber was continuously arranged in the tire circumferential direction on both sides of the pneumatic radial tire of the same size as the mini-side 4 until it reached the base layer 3 (Example 3). The gauge of the conductive rubber layer 2 in the new tire after vulcanization is as shown in Table 3 below. As a conventional example, a tire without the conductive rubber 2 was manufactured in the same manner. Further, as comparative examples, tires similar to Example 1 were all manufactured except that the ratio of the shrinkage ratio between the cap rubber and the conductive rubber was 0.9.

The resistance value (electric resistance value) of these tires
Was determined as follows. That is, GERMAN ASSOCIATION
Using the high resistance meter of Model HP4339A manufactured by Hewlett Packard (HEWLETT PACKARD) in accordance with WdK 110 Sheet 3 of OF RUBBER INDUSTRY,
The measurement was performed as shown in FIG. In the figure, 11 is a tire, 12
Is a steel plate, 13 is an insulating plate, and 14 is a high resistance meter, which was measured by applying a current of 1000 V between the steel plate 12 on the insulating plate 13 and the rim of the tire 11.

The specific resistance of the conductive layer 2 was determined as follows. That is, a disk-shaped sample is prepared, and the electric resistance value R at a portion having a radius of r = 2.5 cm and a thickness of t = 0.2 cm is measured using an insulation resistance test box manufactured by Advance Corporation shown in FIG. Then, the specific resistance value ρ was calculated by the following equation. ρ = (a / t) R where a is the cross-sectional area (= π × r ² ), and t is the thickness. In FIG. 7, A indicates the main electrode, B indicates the counter electrode, C indicates the guard electrode, and t indicates the thickness of the sample.

Further, the measurement of the rubber shrinkage was measured using a workability tester (MPT) manufactured by Monsanto. Table 3 below shows the resistance values when new and 50% worn.

(Table 3)

[0033]

As described above, in the pneumatic radial tire of the present invention, the conductive rubber layer having a specific specific resistance value and a specific physical property is provided with a cap / base structure in which a predetermined number of pneumatic radial tires are used. As a result, the antistatic effect was sufficiently ensured until the end of traveling without deteriorating wear resistance and low fuel consumption performance.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a tread of an example pneumatic tire of the present invention.

FIG. 2 is an explanatory diagram showing changes during vulcanization of a conductive rubber inserted in a tread of a pneumatic tire.

FIG. 3 is a sectional view showing a tread of another example pneumatic tire of the present invention.

FIG. 4 is a sectional view showing a tread of still another example pneumatic tire of the present invention.

FIG. 5 is an explanatory view showing a pneumatic tire manufacturing method for the purpose of preventing electrification.

FIG. 6 is a schematic diagram of a specific resistance value measuring device used in Examples.

FIG. 7 is an explanatory diagram showing a method for measuring an electric resistance value R of a disc-shaped sample.

[Explanation of symbols]

 Reference Signs List 1 cap layer 2 conductive rubber layer 3 base layer 4 mini side 11 tire 12 steel plate 13 insulating plate 14 high resistance meter

Claims (6)

[Claims] 1. A conductive rubber layer having a specific resistance of 10 ⁶ Ω · cm or less, which is exposed on the tread surface and forms an energization path with a tire grounding surface, is partially provided in a width direction of an annular tread of a product tire. The conductive rubber layer is present continuously or intermittently in the circumferential direction, and the shrinkage in the thickness direction of the conductive rubber layer during vulcanization is equal to or smaller than the shrinkage in the thickness direction of another extruded tread rubber. Pneumatic tire. 2. A conductive rubber layer having a specific resistance value of 10 ⁶ Ω · cm or less, which is exposed on the tread surface and forms an energization path with the tire grounding surface, is partially provided in the width direction of the annular tread of the product tire. Exist continuously and / or intermittently in the direction,
A pneumatic tire, wherein the widthwise shrinkage of the conductive rubber layer during vulcanization is equal to or greater than the widthwise shrinkage of another extruded tread rubber. 3. The annular tread has a two-layer structure including a cap layer on the tire tread side and a base layer adjacent to the inside thereof, and the cap layer has a specific resistance value of 10 ⁸ Ω · cm.
The pneumatic tire according to claim 1, comprising the rubber. 4. The pneumatic tire according to claim 3, wherein a contraction ratio in a thickness direction of the conductive rubber layer is smaller than a contraction ratio in a thickness direction of the cap layer. 5. The conductive rubber layer according to claim 1, wherein a center X of the conductive rubber layer is located in a range represented by the following equation: W / 4 ≦ X ≦ 3W / 4. The pneumatic tire according to one of the preceding claims. 6. The pneumatic tire according to claim 1, wherein the width of the conductive rubber layer along the tread width W direction is 0.5 to 2.0 mm.