JP2000343916A - Pneumatic tire and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tire using a tread rubber of a two-layer structure comprising a non-conductive rubber and a conductive rubber, having superior electrical conductivity and having no wavy wear or exfoliation by improving an arrangement or a shape of a conductive part penetrating a cap rubber layer. SOLUTION: In this tire, a tread rubber 1 has a two-layer structure comprising a non-conductive cap rubber layer 11 on the tire tread face side and a conductive base rubber layer 12 on the inner side. A bar-like protrusion 6 having a relatively small cross section wherein a rubber 11a of the cap rubber layer 11 covers the peripheral side face of a rubber part 12a extending from a tread lower layer part to the tire tread face side and extending from the base rubber layer 12 is formed in a ground contact face area of the tread rubber 1 such that the tip surface of the protrusion 6 is positioned in a nearly same level as a land part 5 surface with an air space formed around the bar-like protrusion 6 in a groove or the land part 5, while the rubber part 12a on the inner side is exposed at the tip surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive pneumatic tire having a two-layer structure of a non-conductive rubber and a conductive rubber, and a method of manufacturing the same.

[0002]

2. Description of the Related Art When a pneumatic tire in a vehicle is non-conductive (insulating), static electricity easily accumulates in the vehicle body. Such accumulation of static electricity may cause spark discharge or adversely affect electronic components such as a car radio, and may cause discomfort due to being grounded to a human body. For this reason, the tire itself usually has an appropriate conductivity so that static electricity can be grounded to the road surface through the tire. The conductivity as a tire can be obtained by blending a large amount of carbon black as a filler in a rubber composition used for the tire.

[0003] In recent years, in order to improve the required performance and characteristics of tires such as abrasion resistance, fuel efficiency and wet resistance, a rubber material containing a high proportion of silica or the like as a filler instead of carbon as a filler. It has been developed to use. In this case, there is a problem that the conductivity of the tire cannot be obtained and the tire is easily charged. In order to solve this, a conductive rubber having a low electric resistance containing a large amount of carbon black etc. is used as a base rubber layer, and a part of the conductive rubber is penetrated through a cap rubber layer on the tire tread side made of non-conductive rubber to form a tread tread. It has been proposed to provide an exposed through conductive portion (for example, Japanese Patent Application Laid-Open No. 9-71112).

[0004] This is because a non-conductive rubber having a high electric resistance is used as a cap rubber layer, and a conductive rubber having a low electric resistance is partially exposed to thereby ensure the characteristics obtained by blending a silica filler or the like. At the same time, conductivity is ensured, and grounding prevents charging.

When the penetrating conductive portion is provided continuously in the tire circumferential direction at a land portion such as a block or a rib of a tread pattern, for example, a joint boundary portion between the two rubbers exposed on the land portion surface. In this case, uneven wear due to a difference in rubber quality, a difference in rigidity, or the like occurs, which adversely affects tire performance. Therefore, the conductive portion is
It is preferable to provide them at required intervals in the tire circumferential direction, and it is desirable that the diameter be small as long as conductivity can be ensured.

However, the smaller the diameter of the penetrated conductive part, the more difficult it is to provide the conductive part. For example, a hole is formed in a part of the extruded tread rubber and the conductive rubber is filled. Requires cumbersome work.

Further, as a method of providing the penetrating conductive portion, a part of a land portion such as a block is vulcanized and formed by a mold formed deeper than other land portions, and a base rubber layer is formed at the deep portion by another vulcanization. It is also proposed that the conductive portion penetrated is exposed by sucking the land portion above the land portion and, after vulcanization, processing the formed land portion so as to have the same height as the other land portions. (Japanese Patent Laid-Open No. 11-115)
414).

However, also in this case, the conductive portion extending from the base rubber layer made of the conductive rubber and penetrating the cap rubber layer is integrated with the cap rubber layer constituting the land portion, so that both ends are formed on the land surface. The bonding boundary portion of the rubber is exposed with a length in the tire circumferential direction, and step wear and peeling are likely to occur at the bonding boundary portion.

The present invention has been made in view of the above, and has a tread rubber having a two-layer structure of a non-conductive rubber and a conductive rubber, and exposing a part of the conductive rubber to a tire tread surface so as to be conductive. In pneumatic tires that have ensured lubricity, by improving the arrangement and shape of the conductive portion that penetrates the cap rubber layer, it is possible to ensure good conductivity and to cause step wear and peeling of the boundary between both rubbers. It is intended to provide a tire that does not have such a tire, and to provide a manufacturing method capable of easily and efficiently obtaining the tire.

[0010]

SUMMARY OF THE INVENTION The present invention provides a tread,
A pneumatic tire having a two-layer structure of a cap rubber layer made of a non-conductive rubber on the tire tread side and a base rubber layer made of a conductive rubber disposed inside the cap rubber layer, wherein a tread contact In the ground area, a relatively small-section rod-shaped protrusion extending from the tread lower layer portion toward the tire tread side, and having the rubber portion extending from the base rubber layer inside and covering the peripheral side surface with the rubber of the cap rubber layer, The tip surface is provided so as to be at substantially the same height as the land surface, and the rubber portion inside the rod-shaped projection is exposed to the tip surface. For example, a non-conductive (insulating) rubber composition having an electrical resistance value of 100 MΩ · cm or more due to rubber compounding with a large amount of silica as a reinforcing filler, and the conductive rubber is mainly With filler for reinforcement Electric resistance by blending a large amount of rubber of carbon Te refers to a conductive rubber composition of less than 100 M.OMEGA · cm.

The pneumatic tire according to the present invention has bar-shaped projections extending from the tread lower layer portion toward the tire tread side at required intervals in the tire circumferential direction within the ground contact surface area on the outer periphery of the tread. Since the rubber portion extending from the base rubber layer of the conductive rubber is exposed at the tip end surface, the conductivity required for the tire can be secured thereby, and the tire performance is required by the cap rubber layer of the non-conductive rubber. Good characteristics such as abrasion resistance, low fuel consumption and wet resistance can be ensured.

[0012] In particular, the rod-shaped projections themselves have an appropriate elasticity, have good followability to unevenness of the road surface, are not easily broken, and have excellent durability.

[0013] As in the second aspect of the present invention, the rod-shaped projection may be provided so as to be substantially flush with the tire tread surface from the bottom of the groove in the tread pattern. In this case, there is no risk of step wear or cracks occurring on land portions such as blocks and ribs of the tread pattern, and there is no effect on tire characteristics such as reduction in rigidity of land portions.

According to a third aspect of the present invention, the rod-like projection is provided in a land portion in a tread pattern.
It may extend from the vicinity of the base rubber layer toward the tire tread side, and the periphery may be provided separated from the land portion by a narrow groove. Also in this case, the rod-shaped projection can be elastically deformed independently of the land by the narrow groove around the rod-shaped projection, the projection itself is not easily broken, and the stepped wear at the boundary between the two rubbers at the land is reduced. There is no fear of peeling.

The bar-like projection has a tip with a cross-sectional area of 2 to 8 mm.
A rod-shaped member having a range of 0 mm ² is preferable. That is, when the cross-sectional area of the rod-shaped protrusion is smaller than the above, the inner rubber portion extending from the base rubber layer is too thin,
In some cases, sufficient conductivity cannot be ensured, and when the cross-sectional area is larger than the above range, the rubber of the base rubber layer may not be sufficiently sucked up during vulcanization, and the tire performance may be affected.

According to a fifth aspect of the present invention, there is provided a method of manufacturing the above pneumatic tire, wherein a cap rubber layer made of a non-conductive rubber is disposed on the tire tread side, and a base rubber layer made of a conductive rubber is disposed therebelow. When vulcanizing a green tire having a tread having a two-layer structure with a mold, the groove extends from the groove bottom forming surface to a deeper position than the land portion forming concave portion at a required portion of the groove forming convex portion in the contact surface area of the tread pattern. Vulcanization molding is performed using a mold provided with a projection molding hole, and both rubber layers are allowed to flow with the base rubber layer inside in the projection molding hole, and after vulcanization, molded by the projection molding hole. The distal end of the rod-shaped projection protruding from the land surface is cut off to expose the inner rubber portion extending from the base rubber layer to the distal end surface.

Thus, by vulcanization molding from a green tire having a simple two-layer structure of a non-conductive rubber and a conductive rubber, the conductive rubber portion continuous from the base rubber layer is placed on the inner side and the peripheral side surface is covered with a cap. A bar-shaped projection covered with rubber in the rubber layer can be provided at the bottom of the groove, and a pneumatic tire exhibiting the above effects can be easily manufactured.

In particular, at the time of the vulcanization, the contact flow resistance of the cap rubber layer in contact with the wall surface of the projection forming hole is large, so that the inflow of rubber into the cap rubber layer is suppressed.
The rubber of the base rubber layer is sucked up to a position deeper than the land-forming concave portion of the projection-forming hole. Therefore, after vulcanization, by cutting off the tip of the bar-shaped projection protruding from the surface of the land, the inner rubber portion can be exposed at the tip.

According to a sixth aspect of the present invention, when the same green tire is vulcanized and molded by a mold, the land forming concave portion in the ground contact surface area of the tread pattern is substantially provided with a groove forming convex portion. A pipe having the same height is protruded, and the inner hole of the pipe is extended to a position deeper than the land forming recess, and vulcanization molding is performed using a mold that is a projection forming hole, and a base is formed in the pipe. Both rubber layers are allowed to flow with the rubber layer inside, and after vulcanization, the tip of the rod-shaped projection protruding from the land surface by the pipe is cut off to remove the inner rubber portion extending from the base rubber layer. It is characterized in that it is exposed on the tip end surface.

Also in this method, the contact flow resistance of the cap rubber layer in contact with the pipe during vulcanization is large, and the flow of the cap rubber layer into the pipe is suppressed. Since it is sucked up to a position deeper than the concave portion, the inside rubber portion can be exposed on the front end surface by cutting off the front end portion after vulcanization. Therefore, in land parts such as blocks and ribs of the tread pattern, stick-shaped projections whose peripheral sides are covered with rubber of the cap rubber layer with the rubber part continuous from the base rubber layer inside, An independently provided pneumatic tire can be easily manufactured.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described based on embodiments shown in the drawings.

FIG. 1 is a sectional view of a tread of a pneumatic tire according to an embodiment of the present invention, FIG. 2 is a partially enlarged perspective view of FIG.
FIG. 4 is an enlarged sectional view of a bar-shaped projection, FIG. 4 is another embodiment in which a bar-shaped projection is provided in a groove, and FIG. 5 is a partially enlarged perspective view showing an example in which the bar-shaped projection is provided on a land portion. 6 is an enlarged cross-sectional view of the rod-like projection portion of the above.

The pneumatic tire, which is not shown in detail, has a bead portion having bead cores on both sides, a sidewall portion extending radially outward from the bead portion, and a tread (1) connecting the upper end thereof. And a carcass (8) whose both ends are folded back by a bead core and supported along the inner circumference, and a belt layer 9 disposed between the tread (1) and the carcass (8), and its reinforcing structure is provided. Is similar to that of a general radial tire.

In the case of the tire of this embodiment, the tread (1) has a tread pattern on the tire tread side as follows:
The tire tread surface (2) has a main groove (3) as a vertical groove extending linearly or slightly zigzag in the tire circumferential direction (vertical direction), and a main groove (3) in a direction intersecting the main groove (3). It has a horizontal groove (4), which defines a predetermined block-shaped land portion (5), and shows a case of a block pattern. In FIG. 1, auxiliary grooves, auxiliary grooves, and the like other than the main groove are omitted.

The tread pattern is not limited to the block pattern described above. For example, a left-right symmetric or asymmetric pattern provided with two or more main grooves, a left-right symmetric or asymmetric pattern provided with one main groove, Further, any of a rib pattern and a rib / block pattern in which blocks and ribs coexist may be used.

The tread (1) of this tire is
As a basic structure thereof, for example, a cap rubber layer (11) made of a non-conductive rubber having a high electric resistance value due to a rubber compound having a high filling degree of silica and arranged on the tire tread side;
It is composed of a conductive rubber having a large amount of carbon and a low electric resistance, and a base rubber layer (12) disposed below the cap rubber layer (11).

In the ground contact area of the tread (1), a bar-shaped projection (6) having a small cross section extending from the lower layer of the tread toward the tread of the tire at every required interval in the circumferential direction of the tire has an air gap around it. It is provided as follows. In particular, the rod-like projection (6) is formed of a base rubber layer (1) made of the conductive rubber.
The conductive rubber portion (12a) extending continuously from 2) is placed inside, and the peripheral side surface is covered with a non-conductive rubber (11a) continuous from the cap rubber layer (11). (6) is provided such that the tip surface is at the same height as the surface of the land (5) such as a block or a rib,
The rubber portion (12a) inside the rod-shaped projection (6) is exposed at the distal end surface.

For example, in the first embodiment shown in FIGS. 1 to 3, the rod-like projections (6) are formed in grooves in the tread pattern, usually in the main grooves (3) as shown in FIG. The protruding portion is spaced apart from the land portion (5) so as to be substantially flush with the surface of the tire tread surface (2), that is, the land portion (5) from the bottom portion (3a). The rod-shaped projection (6) can be provided in another groove such as a lateral groove.

When the bar-like projection (6) is provided in a groove such as the main groove (3) as in this embodiment, for example, the lengthwise direction of the groove (mainly (A circumferential direction of the tire) to form a flat rectangular or elliptical rod having a small width in the groove width direction, or to widen the groove width near the rod-like projection (6) as shown in FIG. Is preferred.
(3b) shows a widened portion of the main groove (3).

In the second embodiment shown in FIGS. 5 and 6, the rod-like projections (6) are provided in the base rubber layer (12) in the land portions (5) such as blocks and ribs in the tread pattern. From the vicinity of the tire tread surface (2) side, the periphery is separated from the main body of the land portion (5) by a narrow groove (7), and is provided at the same height as the land portion (5). Is shown. Although not shown, it is also possible to provide the rod-shaped projection of the first embodiment and the rod-shaped projection of the second embodiment in combination.

In each of the above embodiments, the arrangement interval in the circumferential direction of the tire is shorter than the ground contact length of the tire so that one of the rod-like projections (6) can always contact the ground. The rod-shaped projection (6) has a conductive rubber portion (12a) continuous from the base rubber layer (12) on the inner side thereof, and the rubber portion (12a) is exposed on the tip end surface. In the state, the tire is passed from the vehicle body wheel through a conductive lower structure such as a belt layer and a sidewall portion, and further through a base rubber layer (12) of conductive rubber and a rubber portion (12a) in the rod-shaped protrusion (6). Conductivity up to the tread (2) can be ensured.

The shape of the rod-shaped projection (6) can be tapered as shown in FIGS. 1 to 3 in addition to a rod having the same diameter in the height direction, and a rod having a circular cross section. Not limited,
The cross section may be a bar having an arbitrary cross section such as a rectangle such as a rectangle or a square, or an ellipse. Further, it may be formed in a rod shape inclined with respect to the tire radial direction. In the case of the inclined rod-shaped projection (6), depending on its form, the tip surface is at a position lower than the surface of the land portion (5) when the running is stopped, and the tip surface rises by centrifugal force during running and the tip surface is raised on the surface of the land portion (5). It can also be provided so as to be at the same height as.

The rod-like projection (6) has a cross-sectional area of 2 to 8 at the tip in consideration of a manufacturing method, conductivity, and the like to be described later.
0 mm ^2, more preferably to a rod of relatively small cross-section in the range of 7~30mm ^2.

Next, a method of manufacturing the tire of the embodiment shown in FIGS.

First, a cap rubber layer (11) made of a non-conductive rubber compounded with silica is arranged on the surface portion on the tread tread (2) side, and a base rubber layer (11) made of a conductive rubber compounded with carbon is placed below the cap rubber layer (11). A green tire (unvulcanized tire) including a tread (1) having a two-layer structure provided with 12) is manufactured in advance. In this case, the thickness of the cap rubber layer (11) is slightly larger than the depth of the main groove (3) of the tread pattern, for example, about 3 to 10 mm. This green tire can be manufactured by extrusion molding in the same manner as the conventional tread (1) having a two-layer structure, or by layering the tread on a forming drum.

The green tire is vulcanized and molded using a vulcanizing mold (20) having the following structure as shown in FIG.

That is, the vulcanization mold (2
0), a groove in the ground surface area of the tread pattern, for example, a groove bottom forming surface (23a) of a groove forming protrusion (23) for forming the main groove (3) is provided at a required position. Projection forming hole (2) extending deeper from land forming recess (25) from 23a).
6) is provided. The depth and diameter of the projection forming hole (26) are set so that the rubber of the base rubber layer (12) can be sucked higher than the land portion (5) as described later. The projection-forming hole (26) may be formed as a projection-forming hole in a pipe by embedding a pipe in addition to a case where the projection-forming hole (23) is drilled as shown in the figure. Can be. Further, if necessary, the projection forming hole (26) can be a tapered hole.

When the green tire is vulcanized and molded using the mold (20), the tread rubber flows into the projection forming hole (26) during vulcanization. Since the flow resistance is increased, the flow of the rubber in the cap rubber layer (11) around the opening of the projection forming hole (26) is suppressed, and the flow velocity of the rubber becomes faster in the center portion. The rubber of the base rubber layer (12) slightly below the opening of the projection forming hole (26) flows inside (center portion) of the rubber (11a) of the cap rubber layer (11) in contact with the hole wall surface. As a result, the water flows into the inner part of the projection forming hole (26) deeper than the land forming recess (25), that is, is sucked up. In particular, the sucking action of the rubber portion (12a) of the base rubber layer (12)
The cross-sectional area of the projection forming hole (26) is 2 to 80 m.
m ^2, more preferably the case of the range of 7~30mm ^2, are particularly well done. When a spew hole or a vent hole is formed continuously to the projection forming hole (26), the above-mentioned suction is performed more favorably.

By vulcanization molding in this way, as shown in FIG. 8, a bar-like projection (6) projecting higher than the land portion (5) is formed in the main groove (3). In this state,
The rod-shaped protrusion (6) is covered with a non-conductive rubber (11a) extending from the cap rubber layer (11), and an inner rubber portion (12a) extending from the base rubber layer (12).
Is not exposed. Therefore, after the vulcanization, the distal end of the rod-shaped projection (6) is cut off by means such as cutting or buffing so as to be substantially flush with the surface of the tire tread (2), that is, the surface of the land (5). I do. This allows the inner rubber part (12
a) is exposed at the tip end surface, and the tire of the embodiment shown in FIGS. 1 to 3 is obtained.

When the tire shown in the embodiment of FIGS. 5 and 6 is manufactured, a vulcanizing mold (20) is provided at a required portion of a land forming concave portion (25) in a tread pattern ground contact area. A pipe (27) having substantially the same height as the groove forming projection (23) is projected by welding means or the like, and the pipe inner hole is extended to a position deeper than the land forming recess (25). Using a mold formed as a molding hole (26), vulcanization molding is performed as shown in FIG.

Regarding the diameter and depth of the hole (26) for forming a projection by the pipe (27), the base rubber layer (12)
In order to be able to suck the rubber higher than the land,
For example, it is set so that a protrusion having a cross-sectional area of ² to 80 mm ² can be formed. The thickness of the pipe (27) is 1 to 5
mm, preferably around 2 mm. Further, the green tire to be vulcanized is provided with a tread (1) having a two-layer structure of a cap rubber layer (11) made of the same non-conductive rubber and a base rubber layer (12) made of a conductive rubber. It shall be assumed.

At the time of vulcanization by the mold (20), since the rubber contact flow resistance is large in the projection forming hole (26) in the pipe (27), the cap rubber around the opening of the pipe (27) is formed. As a result of suppressing the inflow of the layer (11), the flow velocity of the rubber at the center of the pipe is increased, and the rubber (12a) of the base rubber layer (12) is formed inside the rubber (11a) of the cap rubber layer (11). The protrusion forming hole (26)
It easily flows into the inside, and is sucked up to a position deeper than the land portion forming concave portion (25), that is, an inner depth portion higher than the land portion (5).

The vulcanized tire thus obtained is
As shown in FIG. 10, the land portion (5) such as a block protrudes higher than the surface of the land portion (5), and its periphery is formed by a narrow groove (7) corresponding to the pipe (27). A bar-shaped projection (6) separated from the main body of (5) is formed. However, the surface of the rod-shaped projection (6) is covered with a non-conductive rubber (11a) extending from the cap rubber layer (11). Therefore, the tip of the rod-shaped projection (6) is cut off by means such as cutting or buffing so as to be substantially the same height as the land portion (5), so that the inner conductive rubber portion (12a) is cut off. ) Is exposed on the tip surface. In this way, it is possible to obtain a tire having the rod-shaped projections (6) of the embodiment shown in FIGS.

The pneumatic tire described above has a cap rubber layer (11) made of a non-conductive rubber on the outer periphery of the tread (1) to reduce the rolling resistance required for the tire performance when the tire is used in a vehicle. Wet resistance,
Characteristics such as abrasion resistance can be secured. In addition, at every required interval in the tire circumferential direction within the ground contact surface of the tire tread surface (2), at the tip end surface of the bar-like projection (6) provided in the main groove (3) or the land portion (5) such as a block or a rib. ,
Since the conductive rubber portion (12a) continuously extending from the base rubber layer (12) is exposed, the conductivity required for a tire can be secured thereby.

Particularly, the rod-shaped projection (6) has a cap rubber layer (11) with its peripheral side facing the rubber portion (12a) inside.
Of a non-conductive rubber and a conductive rubber due to the difference in rubber qualities and the difference in rigidity, and the separation of the joint interface Does not occur. Further, the bar-shaped projection (6) is easily connected to the cap rubber layer (11) only at the base thereof, easily deforms elastically, can easily follow irregularities on the running road surface, and is not easily damaged.

[0046]

As described above, according to the pneumatic tire of the present invention, the tread rubber has a two-layer structure of a cap rubber layer made of non-conductive rubber and a base rubber layer made of conductive rubber. As a conductive part penetrating through the rubber layer, a relatively small-section rod-shaped part extending from the tread lower layer part toward the tire tread side and covering the peripheral side with the rubber part of the cap rubber layer with the rubber part extending from the base rubber layer inside. Protrusions are provided in grooves such as main grooves or on land portions such as blocks or ribs, and the inner conductive rubber portion is exposed on the tip end surface, so that the conductivity required as a tire can be secured, The cap rubber layer of non-conductive rubber not only ensures the characteristics required for tire performance, but also eliminates step wear and peeling due to differences in rubber quality and rigidity. Possess reasonably resilient, not easily broken, excellent in durability.

According to the pneumatic tire manufacturing method of the present invention, the rod-like projections are formed by vulcanization molding from a green tire having a simple two-layer tread rubber of a non-conductive rubber and a conductive rubber. Tires can be easily and reliably manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a tread in a tire transverse direction showing one embodiment of a pneumatic tire according to the present invention.

FIG. 2 is an enlarged perspective view of a part of the above.

FIG. 3 is an enlarged cross-sectional view of a rod-shaped protrusion of the above.

FIG. 4 is a partially enlarged perspective view showing another embodiment in which a bar-shaped projection is provided in a groove.

FIG. 5 is a partially enlarged perspective view showing an example in which a bar-shaped projection is provided on a land portion.

FIG. 6 is an enlarged cross-sectional view of a rod-shaped projection portion of the same.

FIG. 7 is a partial cross-sectional view during vulcanization molding in the manufacture of the tire of the first embodiment.

FIG. 8 is a cross-sectional view of a part of the tire after vulcanization according to the first embodiment.

FIG. 9 is a partial cross-sectional view during vulcanization molding in the manufacture of a tire according to a second embodiment.

FIG. 10 is a cross-sectional view of a part of the tire after vulcanization according to the first embodiment.

[Explanation of symbols]

 (1) Tread (2) Tire tread (3) Main groove (3a) Groove bottom (4) Lateral groove (5) Land (6) Rod-like projection (7) Narrow groove (11) Non-conductive cap rubber layer (11a) ) Rubber (12) Conductive base rubber layer (12a) Rubber part (20) Die (23) Convex part for groove formation (25) Concavity for land part formation (26) Hole for protrusion formation (27) Pipe

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B60C 11/00 B60C 11/00 A B 11/04 11/12 C 11/13 B60C 11/04 H 11 / 12 // B29K 21:00 105: 24 B29L 30:00 F term (reference) 4F202 AE03 AG05 AG28 AH20 CA21 CU02 CU14 CY01 CY30 4F203 AE03 AG05 AG28 AH20 DA11 DB01 DC01 DF02 DK05 DK07 4F212 AE03 AG05 AG28 AH20 VA03 VC06 VC02 VL27 VP37

Claims (6)

[Claims] 1. A pneumatic tire having a two-layer structure in which a tread includes a cap rubber layer made of a non-conductive rubber on the tire tread side and a base rubber layer made of a conductive rubber disposed inside the cap layer. In the ground contact surface area of the tread, the rubber is extended from the lower part of the tread toward the tread side of the tread, and the peripheral side is covered with the rubber of the cap rubber layer with the rubber part extending from the base rubber layer being inside. A pneumatic tire having a bar-shaped projection having a small cross section, and a rubber portion inside the rod-shaped projection being exposed to the tip end surface. 2. The pneumatic tire according to claim 1, wherein the rod-shaped projection is provided so as to be substantially flush with the tire tread surface from the bottom of the groove in the tread pattern. 3. The method according to claim 1, wherein the bar-shaped protrusion extends from the vicinity of the base rubber layer toward the tire tread surface in the land portion of the tread pattern, and is provided so as to be separated from the land portion by a narrow groove. The pneumatic tire as described. 4. The cross-sectional area of the tip of the rod-shaped projection is 2 to 80.
The pneumatic tire according to claim 1 in the range of mm ^2. 5. In the manufacture of a tire, a green tire provided with a tread having a two-layer structure of a cap rubber layer made of a non-conductive rubber and a base rubber layer made of a conductive rubber disposed thereunder on the tire tread side. At the time of vulcanization molding with a mold, a mold provided with a projection molding hole extending from the groove bottom molding surface deeper than the land molding concave portion at a required location of the groove molding convex portion in the tread pattern ground contact surface area The vulcanization molding is carried out, and the two rubber layers are caused to flow with the base rubber layer inward in the projection molding hole, and after vulcanization, a rod-like molded from the projection molding hole and protruding from the land surface. A method for manufacturing a pneumatic tire, comprising cutting off a tip portion of a projection to expose an inner rubber portion extending from a base rubber layer to a tip surface. 6. In the manufacture of a tire, a green tire provided with a tread having a two-layer structure of a cap rubber layer made of a non-conductive rubber and a base rubber layer made of a conductive rubber disposed thereunder on the tire tread side. At the time of vulcanization molding with a mold, a pipe having substantially the same height as the groove forming projection is protrudingly provided at a required portion of the land forming recess in the ground contact surface area of the tread pattern, and the pipe inner hole is formed. The vulcanization molding is performed by using a mold that is extended to a position deeper than the land-shaped molding concave portion and formed as a projection molding hole, and both rubber layers are caused to flow with the base rubber layer inside in the pipe, and after vulcanization, A method of manufacturing a pneumatic tire, comprising cutting off the tip of a rod-like projection projecting from a land portion surface with the pipe, and exposing an inner rubber portion extending from a base rubber layer to the tip surface.