U.S. patent application number 14/309612 was filed with the patent office on 2014-10-09 for pneumatic tire.
The applicant listed for this patent is SUMITOMO RUBBER INDUSTRIES, LTD.. Invention is credited to Tetsuya KUNISAWA, Keiichi NAKADERA.
Application Number | 20140299241 14/309612 |
Document ID | / |
Family ID | 39737076 |
Filed Date | 2014-10-09 |
United States Patent
Application |
20140299241 |
Kind Code |
A1 |
KUNISAWA; Tetsuya ; et
al. |
October 9, 2014 |
PNEUMATIC TIRE
Abstract
A pneumatic tire capable of reducing rolling resistance and
discharging static electricity generated during running, wherein
each of a tread rubber, a breaker rubber, and a sidewall,
respectively, has a volume specific resistivity of 1.times.10.sup.8
.OMEGA.cm or more, the pneumatic tire further including a
conduction rubber embedded in the tread part so as to be at least
partially exposed to a surface of the tread part, a coating rubber
disposed on the upper part of the breaker part, a bead part rubber,
and side part electroconductive rubber electrically connecting the
conduction rubber to the beat part rubber, wherein each of the
conduction rubber, the bead part rubber, the coating rubber and the
side part electroconductive rubber has a volume specific
resistivity of less than 10.sup.8 .OMEGA.cm.
Inventors: |
KUNISAWA; Tetsuya;
(Kobe-shi, JP) ; NAKADERA; Keiichi; (Kobe-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SUMITOMO RUBBER INDUSTRIES, LTD. |
Kobe-shi |
|
JP |
|
|
Family ID: |
39737076 |
Appl. No.: |
14/309612 |
Filed: |
June 19, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13693611 |
Dec 4, 2012 |
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14309612 |
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12155295 |
Jun 2, 2008 |
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13693611 |
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Current U.S.
Class: |
152/152.1 |
Current CPC
Class: |
B60C 19/08 20130101;
Y10T 152/10819 20150115; B60C 19/088 20130101; Y02T 10/86 20130101;
B60C 19/082 20130101; Y10T 152/1081 20150115; Y10T 152/10765
20150115; B60C 19/086 20130101; Y10T 152/10846 20150115; Y10T
152/10864 20150115 |
Class at
Publication: |
152/152.1 |
International
Class: |
B60C 19/08 20060101
B60C019/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 15, 2007 |
JP |
2007-159029 |
Jun 29, 2007 |
JP |
2007-172695 |
Jul 19, 2007 |
JP |
2007-188542 |
Jul 19, 2007 |
JP |
2007-188547 |
Claims
1. A pneumatic tire comprising a tread part, a sidewall part, a
bead part, a carcass extending from said tread part to said bead
part through said sidewall part, and a breaker part disposed at an
outside of said carcass in a tire radial direction, wherein each of
a tread rubber, a breaker rubber, and a sidewall rubber formed on
said tread part, said breaker part, and said sidewall part,
respectively, has a volume specific resistivity of 1.times.10.sup.8
.OMEGA.cm or more, said pneumatic tire further comprising side part
electroconductive rubber extending continuously in the tire
circumferential direction from at least both edges of said breaker
part to the bead part along the outside of said carcass wherein a
part thereof is disposed between the carcass and the edges of the
breaker part, a coating rubber having a region for contact with
said side part electroconductive rubber and disposed so as to coat
an upper part of the breaker part, a conduction rubber contacting
the coating rubber and embedded in said tread part so as to be
partially exposed to a surface of a tread, and a bead part rubber
contacting a lower end of said side part electroconductive rubber
and disposed at a region contacting a rim flange of said bead part,
wherein said conduction rubber is formed in the tire
circumferential direction, and has a width from 0.2 to 10 mm in a
tire width direction, said coating rubber has a thickness from 0.2
mm or more and 3.0 mm or less, and has a contact part in a
circumferential direction with the side part electroconductive
rubber in width of 5 mm or more, and said side part
electroconductive rubber, said coating rubber, and said conduction
rubber each have a volume specific resistivity of less than
1.times.10.sup.8 .OMEGA.cm, and one bead part is electrically
connected with the other bead part through said side part
electroconductive rubber and said coating rubber.
2. The pneumatic tire according to claim 1, wherein said tire
comprises carbon black and said carbon black is a ketjen black.
3. The pneumatic tire according to claim 1, wherein said bead part
rubber has a volume specific resistivity of less than
1.times.10.sup.8 .OMEGA.cm.
4. The pneumatic tire according to claim 1, wherein said side part
electroconductive rubber has a thickness in a range of from 0.2 to
2 mm.
5. The pneumatic tire according to claim 1, wherein said side part
electroconductive rubber, said coating rubber, and said conduction
rubber contain carbon black having a nitrogen adsorption specific
surface area of 600 m.sup.2/g or more in an amount of 5 parts by
mass or more with respect to 100 parts by mass of a rubber
component and a silica having a nitrogen adsorption specific
surface area of 70 m.sup.2/g or more and 250 m.sup.2/g or less in
an amount of 10 to 55 parts by mass with respect to 100 parts by
mass of a rubber component.
Description
[0001] This application is a continuation of application Ser. No.
13/693,611, filed Dec. 4, 2012. Application Ser. No. 13/693,611 is
a divisional of application Ser. No. 12/155,295, filed Jun. 2,
2008. Application Ser. No. 12/155,295 claims priority to: Japanese
Patent Application No. 2007-159029 filed Jun. 15, 2007; Japanese
Patent Application No 2007-172695, filed Jun. 29, 2007; Japanese
Patent Application No. 2007-188542, filed Jul. 19, 2007; and
Japanese Patent Application No. 2007-188547, filed Jul. 19, 2007.
The entire contents of all of the foregoing applications are hereby
incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a pneumatic tire improved
in safety by keeping low rolling resistance and reducing static
electricity generated during tire running.
DESCRIPTION OF THE BACKGROUND ART
[0003] In recent years, various methods for using silica for a
tread part, a breaker, a sidewall part, or the like of a tire have
been proposed for the purpose of reduction in tire rolling
resistance as well as of maintenance of wet grip performance.
However, a problem of lack in safety is raised in the case where
silica is contained in a large amount since electrical resistance
of the tire is increased to generate spark due to static
electricity, for example, during supply of fuel for a vehicle, so
that the fuel catches fire. Therefore, there is a demand for a tire
that realizes of a reduction in rolling resistance and maintenance
of wet grip performance and is capable of preventing static
electricity from being generated.
[0004] Japanese Patent Laying-Open No. 08-230407 discloses, as a
pneumatic tire capable of improving electroconductivity and
preventing discharge phenomenon caused by accumulation of static
electricity in a vehicle body, a tire wherein: a rubber composition
forming a tread part contains carbon black in a blending amount of
50 parts by weight or less with respect to 100 parts by weight of a
rubber component and a non-carbon black in a blending amount of 40
parts by weight or less with respect to 100 parts by weight of a
rubber component; and an electroconductive thin film is disposed on
the tread part and the sidewall part. It is disclosed in the
publication that a rubber component forming the electroconductive
thin film contains carbon black in a blending amount of 60 parts by
weight or more with respect to 100 parts by weight of a rubber
component and in a ratio of 35 wt % of the whole rubber
composition.
[0005] Japanese Patent Laying-Open No. 2000-190709 proposes a
pneumatic tire capable of maintaining excellent wet grip
performance and effectively reducing tire electrical resistance as
well as of stably exhibiting such characteristics from an initial
use to a wear limit of the tire. The publication proposes a
pneumatic tire, wherein a tread rubber includes a main tread rubber
part that is made from an insulating rubber material having a
volume specific resistivity of 1.times.10.sup.8 .OMEGA.cm or more
and an outer electroconductive part that is made from a shoulder
part electroconductive rubber material having a volume specific
resistivity of less than 1.times.10.sup.8 .OMEGA.cm, forms a
contact area together with a main tread part, and ends with a gap
of 3% to 35% of a contact area margin in a tire axially inner
direction from an edge of the contact area, the outer
electroconductive part is in the form of a sheet having a thickness
of 0.01 to 1.0 mm, exposed to a treat outer surface including a
groove wall and a groove bottom of a lateral groove to be
continuous in a tire circumferential direction; a wing rubber, a
sidewall rubber, and a clinch rubber are formed of the shoulder
part electroconductive rubber material; and the outer
electroconductive part is continued to the wing rubber.
[0006] Japanese Patent Laying-Open No. 10-036559 proposes, as a
tire sidewall rubber composition capable of rendering a tire having
small rolling resistance, wear resistance, excellent wet
performance, and small electrical resistance, a tire sidewall
rubber composition obtainable by mixing and kneading 100 parts by
weight of a specific diene-based rubber, 5 to 50 parts by weight of
carbon black having a DBP oil absorption amount of 120 ml/100 g or
less and a CTAB surface area of 130 m.sup.2/g or less, 10 to 60
parts by weight of precipitated silica having a DBP oil absorption
amount of 200 ml/100 g or more and a BET nitrogen adsorption
specific surface area of 180 m.sup.2/g or less, and a silane
coupling agent in an amount capable of controlling a reactive
factor within a specific range.
[0007] Japanese Patent Laying-Open No. 08-034204 proposes a tire
tread including a strip that is made from a tire tread rubber
composition having a high resistivity by using silica as a
reinforcing agent and has a predetermined side width while
extending in a length direction and an electroconductive strip that
spreads in the length direction in the side width and made from a
tire rubber composition having a volume resistivity of 10.sup.8
.OMEGA.cm or less and a low resistivity.
[0008] However, in view of the methods in Japanese Patent
Laying-Open Nos. 08-230407, 2000-190709, 10-036559, and 08-034204,
there is a demand for improvement in satisfactory and excellent
valance between low rolling resistance and high safety.
SUMMARY OF THE INVENTION
[0009] The present invention keeps low rolling resistance and
effectively prevents accumulation of static electricity generated
in a tire contact area or a region where a tire contacts a rim
during tire running.
[0010] According to the present invention, there is provided a
pneumatic tire including a tread part, a sidewall part, a bead
part, a carcass extending from the tread part to the bead part
through the sidewall part, and a breaker part disposed at an
outside of the carcass in a tire radial direction, wherein each of
a tread rubber, a breaker rubber, and a sidewall rubber formed on
the tread part, the breaker part, and the sidewall part,
respectively, has a volume specific resistivity of 1.times.10.sup.8
.OMEGA.cm or more, the pneumatic tire further including a side part
electroconductive rubber extending from at least both edges of the
breaker part to the bead along the outside of the carcass, a
coating rubber having a region for contact with the side part
electroconductive rubber and disposed so as to coat an upper part
of the breaker, a conduction rubber contacting the coating rubber
and embedded in the tread part so as to be partially exposed to a
surface of a tread, and a bead part rubber contacting a lower end
of the side part electroconductive rubber and disposed at a region
contacting a rim flange of the bead part, wherein the side part
electroconductive rubber, the coating rubber, and the conduction
rubber contain carbon black having a nitrogen adsorption specific
surface area of 600 m.sup.2/g or more in an amount of 5 parts by
mass or more with respect to 100 parts by mass of a rubber
component and a silica having a nitrogen adsorption specific
surface area of 70 m.sup.2/g or more and 250 m.sup.2/g or less with
respect to 100 parts by mass of the rubber component, and each of
the side part electroconductive rubber, the coating rubber, and the
conduction rubber each have a volume specific resistivity of less
than 1.times.10.sup.8 .OMEGA.cm.
[0011] A ketjen black is suitably used as the carbon black. The
bead part rubber preferably has a volume specific resistivity of
less than 1.times.10.sup.8 .OMEGA.m. A thickness of the side part
electroconductive rubber is preferably adjusted to a range of 0.2
to 2 mm.
[0012] In the pneumatic tire according to the present invention,
rubber blending having small rolling resistance is used for the
tread part, the breaker part, and the sidewall part. On the other
hand, the pneumatic tire has a structure in which the bead part
rubber is connected to the coating rubber disposed on the upper
part of the breaker part with the side part electroconductive
rubber interposed therebetween, and is electrically connected to
the conduction rubber embedded in the tread part so as to contact a
road surface. By employing such a structure, it is possible to
reduce tire rolling resistance and to effectively reduce
accumulation of static electricity generated in a tire contact area
or a region where the tire contacts the rim during tire rubbing.
Therefore, it is possible to provide the pneumatic tire that
maintains a low fuel consumption tire property and is improved in
safety in use.
BRIEF DESCRIPTION OF THE DRAWING
[0013] FIG. 1 shows a right half of a sectional view of a pneumatic
tire according to Embodiment 1 of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
<Basic Structure>
[0014] One example of a structure of the pneumatic tire of the
present invention is as in FIG. 1 in which the upper right half of
the cross section of the tire is shown. Tire 1 is provided with
tread rubber 7 forming a tread part, sidewall rubber 8 forming a
pair of sidewall parts extending from both ends of tread rubber 7
in a tire radially inward direction, clinch rubber 3 forming a
clinch part located at an inner end of the sidewall parts, and
chafer rubber 2 forming chafer part located at an upper part of a
rim. Carcass 10 is bridged over the beat parts on both sides, and a
breaker rubber forming a breaker part is disposed at a tire
radially outside of carcass 10.
[0015] Carcass 10 is formed of at least one carcass ply for
aligning a carcass cord, and the carcass ply is folded back from an
inner part to an outside in a tire axial direction around bead core
13 and bead apex 11 extending from an upper end of bead core 13 to
a sidewall direction through from the tread part and the sidewall
part and locked by a locking part. Breaker part 9 is formed of at
least two breaker plies that are aligned breaker cords, and the
breaker cords are overlapped with orientations thereof being
alternated so that the breaker cords intersects with each other. In
the pneumatic tire of the present invention, a coating rubber 5 is
provided between the tread part and the breaker part.
[0016] The embodiment of the present invention is characterized in
that a side part electroconductive rubber 14 having a region for
contacting coating rubber 5, being adjacent to carcass 10, and
extending from at least the both ends of the breaker part to a
position contacting clinch rubber 3 is disposed. Conduction rubber
6 is disposed in tread rubber 7 so as to contact coating rubber 5
and be partially exposed to the contact area and has a structure in
which conduction rubber 6 is electrically connected to coating
rubber 5, side part electroconductive rubber 14, and clinch rubber
3.
[0017] By employing the above structure, it is possible to
discharge static electricity generated in the bead part rubber
located at the region contacting the rim or the contact region
during tire rubbing to the outside of the tire through the
electroconductive rubber members.
<Tread Rubber, Breaker Rubber, and Sidewall Rubber>
[0018] Each volume specific resistivity of the tread rubber, the
breaker rubber, and the sidewall rubber forming the tire is set to
1.times.10.sup.8 .OMEGA.cm or more. Though carbon black has
heretofore been used as a rubber reinforcing agent, it is possible
to reduce rolling resistance by using silica in place of the carbon
black. Further, since the silica is not an oil-derived material,
silica is preferably used from the view point of environment
problems as compared to the carbon that is the oil-derived
material. However, in the case of using silica, the volume specific
resistivity tends to be increased. In the present invention, a
reduction in tire rolling resistance and the basic characteristics
such as rubber processability are maintained by basically
containing silica, and the problem of high electrical resistance of
a volume specific resistivity of 1.times.10.sup.8 .OMEGA.cm or more
of a rubber composition is improved.
[0019] In the pneumatic tire of the present invention, 50 mass % or
more of the above-described filler contained in each of the tread
rubber, the breaker rubber, and the sidewall rubber is preferably a
silica. In the case where 50 mass % or more of the filler is the
silica, an effect of reducing the tire rolling resistance is good.
A ratio of the silica in the filler is preferably 70 mass % or
more, more preferably 90 mass % or more. In the present invention,
all of the filler may be the silica, but other fillers are used in
combination for the purpose of adjusting electroconductivity and
mechanical strength of each of the tread rubber, the breaker
rubber, and the sidewall rubber.
[0020] The silica may be contained in an amount of 5 parts by mass
or more and 100 parts by mass or less with respect to 100 parts by
mass of a rubber component in each of the tread rubber, the breaker
rubber, and the sidewall rubber. In the case where the silica
blending amount is 5 parts by mass or more with respect to 100
parts by mass of the rubber component, it is to possible to reduce
tire rolling resistance. In the case where the silica compounding
amount is 100 parts by mass or less, it is possible to favorably
prevent a reduction in processability due to viscosity increase of
an unvulcanized rubber composition and excessive increase in
cost.
[0021] As the silica, it is possible to use those generally used
rubbers, and examples thereof include dry method white carbon, wet
method white carbon, colloidal silica, and the like. Among others,
the wet method white carbon mainly containing hydrous silicic acid
is preferable.
[0022] The nitrogen adsorption specific surface area of silica (BET
method) is preferably in the range of from 100 to 300 m.sup.2/g,
more preferably 150 to 250 m.sup.2/g. In the case where the
nitrogen adsorption specific surface area is 100 m.sup.2/g or more,
a satisfactory reinforcing effect is achieved to favorably improve
wear resistance of the tire. On the other hand, in the case where
the nitrogen adsorption specific surface area is 300 m.sup.2/g or
less, processability of the rubbers during production is good, and
good tire driving stability is ensured. The nitrogen adsorption
specific surface area is measured by the BET method in accordance
with ASTM D3037-81.
<Coating Rubber>
[0023] Coating rubber 5 in the present invention is provided
disposed so as to contact side part electroconductive rubber 4 and
conduction rubber 6 and made from a rubber having a volume specific
resistivity set to less than 1.times.10.sup.8 .OMEGA.cm. It is
possible to achieve a desired degree of tire electroconductivity
improvement effect when the volume specific resistivity is less
than 1.times.10.sup.8 .OMEGA.cm. Also, the volume specific
resistivity may be set in the same manner as in the side part
electroconductive rubber and is preferably 1.times.10.sup.7
.OMEGA.cm or less, more preferably 1.times.10.sup.6 .OMEGA.cm or
less and is preferably 1.times.10.sup.3 .OMEGA.cm or more, more
preferably 1.times.10.sup.4 .OMEGA.cm or more.
[0024] It is possible to achieve a desired degree of the tire
electroconductivity improvement effect when a thickness of coating
rubber 5 is 0.2 mm or more, and the tire rolling resistance is not
deteriorated by a large degree when the thickness is 3.0 mm or
less. The thickness of the side part electroconductive rubber is
preferably 0.5 to 2.0 mm, particularly preferably in the range of
from 0.9 to 1.5 mm. It is sufficient that coating rubber 5 has the
part contacting with the side part electroconductive rubber and the
conduction rubber, and it is also possible to provide coating
rubber 5 allover the portion between the tread part and the breaker
part or to partially provide to a position at which the conduction
rubber is disposed or to a range exceeding the position.
[0025] The part of the coating rubber contacting the side part
electroconductive rubber is preferably in the form of a strip
extending in a tire circumferential direction and having a width of
5 mm or more, more preferably 10 mm or more. By contacting the side
part electroconductive rubber and the coating rubber under the
above-described conditions, it is possible to achieve a
satisfactory tire electroconductive effect. The contact of the side
part electroconductive rubber with the conduction rubber is
preferably the contact with the whole part of the conduction rubber
in a tire width direction.
[0026] In the present invention, the coating rubber may preferably
contain carbon black that is contained in the range of from 30 to
100 parts by mass with respect to 100 arts by mass of a rubber
component. In the case where 30 parts by mass or more of carbon
black is contained with respect to 100 parts by mass of the rubber
component, electroconductivity ofthe coating rubber is increased.
In the case where the blending amount of carbon black is 100 parts
by mass or less with respect to 100 parts by mass of the rubber
component, durability is improved.The blending amount of carbon
black with respect to 100 parts by mass of the rubber component is
preferably 35 parts by mass or more, more preferably 40 parts or
more by mass and is preferably 80 parts by mass or less, more
preferably 70 parts by mass or less.
[0027] The nitrogen adsorption specific surface area of carbon
black contained in the coating rubber is preferably 600 m.sup.2/g
or more and 1,500 m.sup.2/g or less. Mechanical strength of the
coating rubber is good when the nitrogen adsorption specific
surface area is 600 m.sup.2/g or more. The nitrogen adsorption
specific surface area of 1,500 m.sup.2/g or less is preferred from
the view point of ensuring processability during production. The
nitrogen adsorption specific surface area may more preferably be
650 m.sup.2/g or more and is preferably 1,300 m.sup.2/g or less,
more preferably 1,000 m.sup.2/g or less. As carbon black, wood tar
carbon black that is not an oil-derived stock is suitably used.
[0028] Silica or the like, for example, may be contained as a
filler in the coating rubber in addition to carbon black, but, from
the view point of imparting good electroconductivity, carbon black
may preferably occupy 8 mass %, more preferably 15 mass % or more,
further preferably 100 mass % or more of the fillers.
[0029] In the case where the coating rubber contains silica, the
blending amount of silica is 10 parts by mass or more and 55 parts
by mass or less, for example, with respect to 100 parts by mass of
the rubber component. It is possible to reduce the tire rolling
resistance when the silica blending amount is 10 parts by mass or
more with respect to 100 parts by mass of the rubber component, and
the rolling resistance is deteriorated when the silica blending
amount exceeds 55 parts by mass.
[0030] The nitrogen adsorption specific surface area of silica (BET
method) is preferably in the range of from 70 to 250 m.sup.2/g,
more preferably 80 to 240 m.sup.2/g. In the case where the nitrogen
adsorption specific surface area is 70 m.sup.2/g or more, a
satisfactory reinforcing effect is achieved to favorably improve
wear resistance of the tire. In the case where the nitrogen
adsorption specific surface area is less than 250 m.sup.2/g,
processability of the rubbers during production is good, and good
tire driving stability is ensured. The nitrogen adsorption specific
surface area is measured by the BET method in accordance with ASTM
D3037-81.
<Side Part Electroconductive Rubber>
[0031] A Side part electroconductive rubber 14 in the present
invention has a structure in which side part electroconductive
rubber 14 is adjacent to an outside of carcass 10 and extends to
the bead part from the both ends of the breaker part through the
sidewall part, so that a lower end of side part electroconductive
rubber 14 is electrically connected to clinch rubber 3. The volume
specific resistivity of the side part electroconductive rubber is
set to less than 1.times.10.sup.8 .OMEGA.cm. When the volume
specific resistivity of side part electroconductive rubber 14 is
less than 1.times.10.sup.8 .OMEGA.cm, it is possible to achieve an
effect of improving tire electroconductivity. The volume specific
resistivity of the ply rubber is preferably set to 1.times.10.sup.7
.OMEGA.cm or less, more preferably 1.times.10.sup.6 .OMEGA.cm or
less. When a rubber composition containing an electroconductive
component in a large amount is used, it is possible to reduce
electrical resistance, while the rim is easily subjected to rusting
due to promotion of an electrochemical reaction in a region at
which the tire contacts the rim. In order to avoid the rusting, the
volume specific resistivity of the side part electroconductive
rubber is preferably set to 1.times.10.sup.3 .OMEGA.cm or more,
more preferably 1.times.10.sup.4 .OMEGA.cm or more. The side part
electroconductive rubber is disposed adjacent to the outside of the
carcass, and a part thereof may be disposed between the carcass and
the breaker and may be formed continuously in the tire
circumferential direction.
[0032] As the rubber blending of side part electroconductive rubber
14, the blending substantially the same as that of the coating
rubber may be used, and, from the view point of reducing rubber
detachment at both ends of the breaker, it is possible to use a
composition wherein rubber hardness and the like are adjusted.
<Conduction Rubber>
[0033] In the present invention, the conduction rubber is embedded
into the tread part, be partially exposed to a tire contact area,
and another part is coupled to the coating rubber to effectively
discharge static electricity generated during running of the
pneumatic tire to the contact area. Though conduction rubber 6
shown in FIG. 1 is embedded at a position at a central part of
tread part 7, it is possible to embed a plurality ofthe conduction
rubbers. The width W of the conduction rubber in a tire width
direction may be 0.2 to 10 mm, preferably 0.9 to 1.5 mm.
[0034] Conduction effect is small when the width is less than 0.2
mm, while the contact region of the conduction rubber in the tread
part is relatively increased when the width exceeds 10 mm to impair
the contact characteristics. Though it is preferable to form the
conduction rubber as a continuous layer in the tire circumferential
direction, the conduction rubber may be formed discontinuously in
the tire circumferential direction.
[0035] The volume specific resistivity of the conduction rubber is
set to a value smaller than those of the tread rubber, the breaker
rubber, and the sidewall rubber. The volume specific resistivity of
the conduction rubber is less than 1.times.10.sup.8 .OMEGA.cm. In
the case where the volume specific resistivity of the conduction
rubber is less than 1.times.10.sup.8 .OMEGA.m, electroconductivity
of the tire is improved to achieve effect of discharging static
electricity. The volume specific resistivity of the conduction
rubber is preferably 1.times.10.sup.7 .OMEGA.cm or less, more
preferably 1.times.10.sup.6 .OMEGA.cm or less.
[0036] In the present invention, when the volume specific
resistivity of the tread rubber, the breaker rubber, and the
sidewall rubber are set to 1.times.10.sup.8 .OMEGA.cm or more,
since the volume specific resistivity of the side part
electroconductive rubber, the coating rubber and the conduction
rubber coupled to the coating rubber are set to values lower than
those of the tread rubber, the breaker rubber, and the sidewall
rubbers while maintaining the tire performance such as rolling
resistance and durability, it is possible to effectively discharge
the static electricity generated in the pneumatic tire through the
electrical connection passage by the coating rubber, the side part
electroconductive rubber, the conduction rubber, and the like.
[0037] It is possible to impart electroconductivity to the
conduction rubber of the present invention by adding thereto carbon
black or metal foil in the same manner as in the coating rubber as
well as to employ blending design for imparting electroconductivity
based on the blending of the tread rubber from the view point of
improving the contact characteristics.
<Bead Part Rubber>
[0038] As used herein, the bead part rubber means the clinch rubber
or the chafer rubber. Static electricity is generated in a driving
mechanism during running of the tire, and the static electricity is
accumulated in the car and also inside the tire through the rim and
the bead part rubber. It is necessary to effectively discharge the
static electricity to the contact area through the side part
electroconductive rubber.
[0039] Referring to FIG. 1, it is desirable that the bead part
rubber, namely the clinch rubber or the chafer rubber, is
electrically connected to the side part electroconductive rubber.
In FIG. 1, the clinch rubber is a rubber layer denoted by reference
numeral 3, of which an outside contacts the rim flange in a tire
bead part, while an inner part contacts the folding edge of carcass
10.
[0040] In FIG. 1, the chafer rubber is so disposed on a bead part
outer surface as to contact the flange part from a base part of the
rim. As used herein, chafer rubber 2 means a rubber forming a
chafer. That is, chafer rubber 2 means a cord coating rubber in the
case where the chafer is a cord ply layer or means a rubber of a
rubber chafer in the case where the chafer is a rubber chafer.
Chafer rubber 2 in FIG. 1 is shown as the one including the
above-described meanings.
[0041] The present invention includes at least one of the clinch
rubber and the chafer rubber as the bead part rubber. The volume
specific resistivity of the bead part rubber 10.sup.8 is less than
1.times.10.sup.8 .OMEGA.cm. Good electroconductivity of the tire is
achieved by maintaining the volume specific resistivity of the bead
part rubber to less than 1.times.10.sup.8 .OMEGA.cm. The volume
specific resistivity of the bead part rubber is preferably less
than 1.times.10.sup.7 .OMEGA.cm, more preferably 1.times.10.sup.6
.OMEGA.cm. Since the bead part rubber, i.e., the cling rubber and
the chafer rubber, is required to have abrasion resistance,
rigidity, and hardness, it is possible to adjust electrical
resistance by a blending method of imparting electroconductivity by
adding carbon black or metal foil in the same manner as in the side
part electroconductive rubber or the conduction rubber.
<Carcass>
[0042] Carcass 10 in the present invention is formed of at least
one carcass ply aligning a carcass cord. The carcass ply has a
structure wherein the carcass cords that are aligned in parallel to
each other are embedded in the rubber. Examples of a fiber material
for forming the carcass cord include rayon, nylon, polyester,
aramid, and the like, and these may be used alone or in combination
of two or more. Among the above materials, it is preferable to use
rayon since rayon is a natural stock material, and it is preferable
to contain 90 mass % or more of rayon with respect to the fiber
materials forming the carcass cord.
[0043] Though the volume specific resistivity of the ply rubber is
not particularly limited, the volume specific resistivity may be
set in the same manner a in the tread rubber, the breaker rubber,
and the sidewall rubber. When the volume specific resistivity is
less than 1.times.10.sup.8 .OMEGA.cm, it is possible to improve
tire electroconductivity to achieve static electricity discharge
effect in cooperation with the adjacent side part electroconductive
rubber. In this case, the volume specific resistivity of the ply
rubber may be set to 1.times.10.sup.7 .OMEGA.cm or less, more
preferably 1.times.10.sup.6 .OMEGA.cm or less.
[0044] In the present invention, when the volume specific
resistivity of the breaker rubber and the sidewall rubber are set
to 1.times.10.sup.8 .OMEGA.cm or more, since the volume specific
resistivity of the coating rubber, the side part electroconductive
rubber, and the conduction rubber are set to the value lower than
those of the breaker rubber and the sidewall rubber while
maintaining tire performance such as rolling resistance and
durability, it is possible to further improve tire
electroconductivity of the tire in cooperation with the coating
rubber, the side electroconductive rubber, the conduction rubber,
and the like (the static electricity generated in the pneumatic
tire).
[0045] Further, the side part electroconductive rubber is disposed
so as to also contact the bead part rubber. Since the bead part
rubber having the low volume specific resistivity and the side part
electroconductive rubber and the like are contact with each other
in addition to the structure wherein the side part
electroconductive rubber, the coating rubber, and the conduction
rubber are continuous, it is possible to remarkably improve static
electricity discharge efficiency through the rim.
<Blending Design of Rubber Component>
[0046] The coating rubber, the side part electroconductive rubber,
the conduction rubber, the ply rubber the chafer rubber, the clinch
rubber, the tread rubber, the breaker rubber, and the sidewall
rubber is formed of the following rubber compositions, for
example.
[0047] Preferred examples of the rubber component include a natural
rubber (NR), an epoxidized natural rubber, a deproteined natural
rubber, and a diene-based synthetic rubber. Examples of the
diene-based synthetic rubber include a styrene-butadiene rubber
(SBR), a polybutadiene rubber (BR), a polyisoprene rubber (IR), an
ethylene-propylene-diene rubber (EPDM), a chloroprene rubber (CR),
an acrylonitrile-butadiene rubber (NBR), a butyl rubber (DR), and
the like, and a rubber component containing one or more of the
diene-based synthetic rubbers is suitably used. The
ethylene-propylene-diene rubber (EPDM) means a rubber containing
ethylene-propylene rubber (EPM) and a third diene component.
Examples of the third diene component include a non-conjugated
diene having 5 to 20 carbon atoms, such as 1,4-pentadiene,
1,4-hexadiene, 1,5-hexadiene, 2,5-dimethyl-1,5-hexadiene, and
1,4-octadiene, or a cyclic diene such as 1,4-cyclohexadiene,
cyclooctadiene, dicyclopentadiene, an alkenylnorbornene such as
5-ethylidene-2-norbornene, 5-butylidene-2-norbornene,
2-methallyl-5-norbornene, and 2-isopropenyl-5-norbornene, and the
like. Particularly, dicyclopentadiene, 5-ethylidene-2-norbornene,
and the like are preferred.
[0048] As the rubber component used for the coating rubber, the
side part electroconductive rubber, the conduction rubber, the
chafer rubber, and the clinch rubber, the diene-based rubber is
preferred, and, among others, the natural rubber (NR), the
styrene-butadiene rubber (SBR), the polybutadiene rubber (BR), the
polyisoprene rubber (IR), and the epoxidized natural rubber (ENR),
the deproteined natural rubber, and the like are preferred.
[0049] To the above-described rubber components, it is possible to
add the following compounding agents that are generally used in
tire rubber compositions as required.
[0050] In the present invention, it is preferable to add silica to
the tread rubber, the breaker rubber, and the sidewall rubber as
described above. In the case of adding silica to the rubber
composition, it is preferable to add a silane-based coupling agent,
preferably a sulfur-containing silane coupling agent, in an amount
of 1 mass % or more and 20 mass % or less to a silica mass.
[0051] By adding 1 mass % or more of the silane coupling agent,
tire abrasion resistance is improved to thereby achieve a reduction
in rolling resistance.When the blending amount of the silane
coupling agent is 20 mass % or less, the risk for occurrence of
scorching during steps for mixing and kneading and extruding the
rubber is reduced.
[0052] Examples of the sulfur-containing silane coupling agent
include
3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoil-tetrasulfide,
trimethoxysilylpropyl-mercaptobenzothiazoletetrasulfide,
triethoxysilylpropyl-methacylate-monosulfide,
dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoil-tetrasulfide,
bis-[3-(triethoxysilyl)-propyl]tetrasulfide,
3-mercaptopropyltrimethoxysilane, and the like. Other usable
examples of the silane-based coupling agent include
vinyltrichlorosilane, vinyltris(2-methoxyethoxy)silane,
.gamma.-glycidoxypropyltrimethoxysilane,
.gamma.-methacryloxypropyltrimethoxysilane,
.gamma.-(2-aminoethyl)aminopropyltrimethoxysilane,
.gamma.-chloropropyltrimethoxysilane,
.gamma.-aminopropyltriethoxysilane, and the like.
[0053] In the present invention, it is possible to use another
coupling agent in accordance with the usage, such as an
aluminate-based coupling agent, a titanium-based coupling agent, or
the like alone or in combination with the silane-based coupling
agent.
[0054] It is possible to use for the rubber component another
filler such as carbon black, clay, alumina, talc, calcium
carbonate, magnesium carbonate, aluminum hydroxide, magnesium
hydroxide, magnesium oxide, titanium oxide, and the like alone or
in combination of two or more.
[0055] It is possible to add a vulcanizing agent, vulcanization
accelerator, a softening agent, a plasticizer, an anti-aging agent,
a foaming agent, an anti-scorching agent, and the like in addition
to the above-described substances.
[0056] An organic peroxide or a sulfur-based vulcanizing agent may
be used as the vulcanizing agent. Examples of the organic peroxide
include benzoyl peroxide, dicumyl peroxide, di-t-butyl peroxide,
t-butyl-cumyl peroxide, methylethylketone peroxide, cumene
hydroperoxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane,
2,5-dimethyl-2,5-di(benzoylperoxy)hexane,
2,5-dimethyl-2,5-di(t-butylperoxy)hexine-3 or
1,3-bis(t-butylperoxypropyl)benzene,
di-t-butylperoxy-diisopropylbenzene, t-butylperoxybenzene,
2,4-dichlorobenzoylperoxide,
1,1-di-t-butylperoxy-3,3,5-trimethylcyloxane,
n-butyl-4,4-di-t-butylperoxyvalelate, and the like. Among the above
organic peroxides, dicumyl peroxide, t-butylperoxybenzene, and
di-t-butylperoxy-diisopropylbenzene are preferred. As the
sulfur-based vulcanizing agent, sulfur, morpholinedisulfide, and
the like may be used. Among the above sulfur-based vulcanizing
agents, sulfur is preferred.
[0057] As the vulcanization accelerator, it is possible to use
those containing at least one of sulfenamide-based, thiazole-based,
thiuram-based, thiourea-based, guanidine-based,
dithiocarbamine-based, aldehyde-amine-based or
aldehyde-ammonia-based, imidazoline-based, and xantate-based
vulcanization accelerators.
[0058] As the anti-aging agent, it is possible to select from
amine-based, phenol-based, imidazole-based compounds, a carbamic
acid metal salt, and a wax as required.
[0059] In the present invention, a softener may be used in
combination in order to further improve kneading processability.
Examples of the softener include a petroleum softener such as
process oil, lubricant oil, paraffin, liquid paraffin, petroleum
asphalt, and vaseline, a fatty oil-based softener such as caster
oil, flaxseed oil, rapeseed oil, and coconut oil, wax such as tall
oil, beeswax, carnauba wax, and lanoline, fatty acid such as
linoleic acid, palmitic acid, a stearic acid, and lauric acid, and
the like.
[0060] Examples of the plasticizer include DMP (dimethyl
phthalate), DEP (diethyl phthalate), DBP (dibutyl phthalate), DHP
(diheptyl phthalate), DOP (dioctyl phthalate), DINP (diisononyl
phthalate), DIDP (diisodecyl phthalate), BBP (butylbenzyl
phthalate), DLP (dilauryl phthalate), DCHP (dicyclohexyl
phthalate), anhydrous hydrophthalate ester, DOZ (di-2-ethylhexyl
azelate), DBS (dibutyl sebacate), DOS (dioctyl sebacate),
acetyltriethyl citrate, acetyltributyl citrate, DBM (dibutyl
maleate), DOM (2-ethylhexyl maleate), DBF (dibutyl fumarate), and
the like.
[0061] As the anti-scorching agent for preventing or delaying
scorching, organic acidsuch as anhydrous phthalic acid, salicylic
acid, and benzoic acid, a nitroso compound such as
N-nitrosodiphenylamine, N-cyclohexylthiophthalimide, and the like
may be used.
EXAMPLES
[0062] Hereinafter, the present invention will be described in more
details based on examples, and the present invention is not limited
to the examples.
Examples 1 and 2 and Comparative Examples 1 and 2
<Side Part Electroconductive Rubber, Coating Rubber, and
Conduction Rubber>
[0063] Ingredients other than sulfur and the vulcanizing agent of
each of blending ingredients shown in Table 1 were mixed and
kneaded using an airtight bunbury mixer at 150.degree. C. for 4
minutes, sulfur and the vulcanizing agent were added to be mixed
and kneaded at 95.degree. C. for 2 minutes, followed by performing
an extrusion step and a calendar step in accordance with a
conventional method to thereby prepare compositions of side part
electroconductive rubber, coating rubber, conduction rubber and
clinch rubber A2 to H2.
<Preparation of Tread Rubber, Sidewall Rubber, Breaker Rubber,
and Clinch Rubber>
[0064] Ingredients other than sulfur and the vulcanizing agent of
each of blending ingredients shown in Table 2 to 5 were mixed and
kneaded using an airtight bunbury mixer at 140.degree. C. for 4
minutes, sulfur and the vulcanizing agent were added to be mixed
and kneaded at 95.degree. C. for 2 minutes, followed by performing
an extrusion step and a calendar step in accordance with a
conventional method to thereby prepare the compositions of tread
rubber J2,sidewall rubber K2, breaker rubber L2, and clinch rubber
I2.
TABLE-US-00001 TABLE 1 Coating Rubber/ Side Part Conduction Rubber
Electroconductive Rubber Blending A2 B2 C2 D2 E2 F2 G2 H2
Diene-Based Rubber NR (TSR20 grade) 100 100 100 100 100 100 100 100
Carbon N330(product of Mitsubishi Chemical Corporation) 55 -- -- --
50 -- -- -- Silica VN3 (product of Degussa Corporation) -- 55 50 40
-- 50 45 35 Carbon Printex XE2B (product of Degussa Corporation) --
-- 5 15 -- -- 5 15 Processed Oil Diana Process PS32 (product of
Idemitsu Kosan 5 -- -- -- 10 -- -- -- Co., Ltd.) Soybean Oil
Soybean Refined Oil (product of Nissin Oillio -- 5 5 5 -- 10 10 10
Group, Ltd.) Wax Sunnoc Wax (product of Ouchi Shinko Chemical 2 2 2
2 -- -- -- -- Industrial Co., Ltd.) Anti-Aging Agent Santflex 13
(Product of Flexsys) 2 2 2 2 4 4 4 4 Stearic Acid Kiri (product of
NOF Corporation) 2 2 2 2 2 2 2 2 Zinc Flower Zinc Oxide No. 1
(product of Mitsui Mining & 5 5 5 5 5 5 5 5 Smelting Co., Ltd.)
Coupling Agent Si75 (product of Degussa Corporation) -- 5 4 3 -- 5
4 3 Sulfur Crystex HSOT20 (Product of Flexsys) 5 5 5 5 1.5 1.5 1.5
1.5 Vulcanization Nocceler (product of Ouchi Shinko Chemical 2 2 2
2 0.75 0.75 0.75 0.75 Accelerator Industrial Co., Ltd.) Volume
Specific log.sub.10R 4.8 10.5 7.8 5.8 5.0 11.1 7.1 5.3 Resistivity
Ratio of Materials Derived from Stocks other than Petroleum (%) 63
94 92 87 63 95 92 87
[0065] In Table 1, a nitrogen adsorption specific surface area of
the carbon (Printex XE2B) is 880 m.sup.2/g.
TABLE-US-00002 TABLE 2 Clinch Rubber Blending I2 Natural Rubber 20
SBR1500 80 N220 50 Aromatic Oil 5 Wax 1.5 Anti-Aging Agent 1
Stearic Acid 1.5 Zinc Flower 3.5 Sulfur 1.6 Accelerator 0.8 Volume
specific resistivity (.OMEGA. cm) 1 .times. 10.sup.6
TABLE-US-00003 TABLE 3 Tread Rubber Blending J2 Natural Rubber 100
Silica VN3 50 Silane Coupling Agent 5 Wax 1 Anti-Aging Agent 2
Stearic Acid 1 Zinc Flower 3 Sulfur 1.5 Accelerator 1 Volume
specific resistivity (.OMEGA. cm) 1 .times. 10.sup.11
TABLE-US-00004 TABLE 4 Sidewall Rubber Blending K2 Natural Rubber
100 Silica VN3 45 Silane Coupling Agent 4.5 Wax 1 Anti-Aging Agent
3 Stearic Acid 1 Zinc Flower 3 Sulfur 2 Accelerator 1 Volume
specific resistivity (.OMEGA. cm) 1 .times. 10.sup.11
TABLE-US-00005 TABLE 5 Breaker Rubber Blending L2 Natural Rubber
100 N330 -- Silica VN3 55 Silane Coupling Agent 5.5 Anti-Aging
Agent 2 Cobalt Stearate 2 Stearic Acid 1 Zinc Flower 10 Insoluble
Sulfur 5.5 Accelerator 0.9 Volume specific resistivity (.OMEGA. cm)
1 .times. 10.sup.11
[0066] In Tables 2 to 5, details of the blending agents are as
follows. [0067] Note 1: natural rubber is TSR20 (trade name) made
in Thailand. [0068] Note 2: SBR1500 is styrene-butadiene rubber
manufactured by JSR Corporation. [0069] Note 3: N220 is carbon
black manufactured by Cabot Japan K.K. (nitrogen adsorption
specific surface area: 111 m.sup.2/g; DBP oil absorption amount:
115 ml/100 g) [0070] Note 4: N330 is carbon black manufactured by
Mitsubishi Chemical Corporation (nitrogen adsorption specific
surface area: 79 m.sup.2/g; DBP oil absorption amount: 105 ml/100
g). [0071] Note 5: Silica VN3 is VN3 (trade name) manufactured by
Degussa Corporation (nitrogen adsorption specific surface area: 210
m.sup.2/g). [0072] Note 6: A silane coupling agent is Si69 (trade
name) manufactured by Degussa Corporation. [0073] Note 7: Aromatic
oil is X140 (trade name) manufactured by Japan Energy Corporation.
[0074] Note 8: Wax is Sunnoc N (trade name) manufactured by Ouchi
Shinko Chemical Industrial Co., Ltd. [0075] Note 9: An anti-aging
agent is Antigen6C manufactured by Sumitomo Chemical Co., Ltd.
[0076] Note 10: Stearic acid is Stearic Acid Tsubaki (trade name)
manufactured by NOF Corporation. [0077] Note 11: Zinc flower is
zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd.
[0078] Note 12: Sulfur is Sulfur Powder (trade name) manufactured
by Karuizawa Seirensha K.K. [0079] Note 13: A vulcanizing agent 1
is Nocceler NS-P (trade name) manufactured by Ouchi Shinko Chemical
Industrial Co., Ltd. [0080] Note 14: Insoluble sulfur is Myuclon
OT20 (trade name) manufactured by Shikoku Chemicals
Corporation.
[0081] Pneumatic tires (Examples 1 and 2 and Comparative Examples 1
and 2) each having the structure shown in FIG. 1 and the size of
195/65R15 were produced by using the rubber compositions shown in
Tables 1 to 5 in combinations shown in Table 6 for a tread part, a
sidewall part, a breaker, a clinch rubber, a chafer rubber, a side
part electroconductive rubber, and a conduction rubber by an
ordinary vulcanization molding method. Basic structure of the
sample tires are as follows. Carcass ply:
[0082] Cord angle: 90 degrees in tire circumferential
direction.
[0083] Cord material: polyester (1500 denier, 1670 dtex/2)
Breaker:
[0084] Cord angle: 24.times.24 degrees in tire circumferential
direction.
[0085] Cord material: steel
[0086] The thickness of the coating rubber was 0.8 mm, the
thickness of the side part electroconductive rubber was 1 mm, and
the width of the conduction rubber was 1.5 mm and continuous in the
tire circumferential direction.
<Evaluation of Tire Performance>
Volume Specific Resistivity
[0087] Sample pieces each having a thickness of 2 mm and a size of
15 cm.times.15 cm by using the rubber compositions of Tables 1 to 5
were produced, and each volume specific resistivity was measured by
using an electrical resistance meter R8340A (product of ADVANTEST)
under the conditions of a voltage of 500 V, a temperature of
25.degree. C., and a moisture of 50%. The results are shown in
Tables 1 to 5. The larger the value is, the higher the volume
specific resistivity of the rubber composition.
Rolling Resistance
[0088] The pneumatic tires produced as described above were mounted
to regular rims, and then a regular inner pressure of 2.0 MPa was
charged. Rolling resistance was measured by using a rolling
resistance tester manufactured by STL at a speed of 80 km/h and a
load of 4.7 kN. By using a rolling resistance coefficient (RRC)
obtained by dividing the detected rolling resistance (RR) by the
load, rolling resistance (RR) of each of Examples 1 and 2 and
Comparative Examples 1 and 2 was calculated by way of the following
expression: [0089] Rolling resistance (RR)=(RRC of Comparative
Example 1/RRC of each of Examples 1 and 2 and Comparative Example
2).times.100, with the rolling resistance of the Comparative
Example 1 being set to 100. The smaller the value, the smaller the
rolling resistance and better the performance. The results are
shown in Table 6.
Tire Electroconductivity
[0090] The pneumatic tires produced as described above were mounted
to regular rims, and then a regular inner pressure of 2.0 MPa was
charged. Each of the tread parts was brought into contact with an
iron plate at a load of 4.7 kN to measure an electrical resistance
value between the tire rim part and the iron plate at an applied
voltage of 100 V. The results are shown in Table 6.
TABLE-US-00006 TABLE 6 Comparative Comparative Example 1 Example 2
Example 1 Example 2 Coating Rubber C2 D2 A2 B2 Conduction Rubber C2
D2 A2 B2 Side Part Electro- G2 H2 .sup. E2 .sup. F2 conductive
Rubber Clinch Rubber I2 .sup. I2 .sup. I2 I2 Tread Rubber J2 J2 J2
J2 Sidewall Rubber K2 K2 K2 K2 Breaker Rubber L2 .sup. L2 .sup. L2
L2 Tire Electro- 1 .times. 10.sup.7 1 .times. 10.sup.6 1 .times.
10.sup.7 1 .times. 10.sup.11 conductivity Rolling Resistance 106
104 100 103
[0091] Referring to Table 6, Comparative Example 1 does not contain
any silica and electroconductive carbon black in the coating
rubber, the conduction rubber, and the side electroconductive
rubber. Comparative Example 2 is an example of not contain any
carbon black in the coating rubber, the conduction rubber and the
side electroconductive rubber.
[0092] Examples 1 and 2 achieved both of improvements in rolling
resistance and tire electroconductivity since the electroconductive
rubber composition having the volume specific resistivity of less
than 1.times.10.sup.8 .OMEGA.cm was used for the coating rubber,
the conduction rubber, and the side part electroconductive rubber,
and since the volume specific resistivity of the tread part, the
breaker, and the sidewall part was set to 1.times.10.sup.8
.OMEGA.cm or more, from which it is apparent that the pneumatic
tires according to the present invention are excellent in both of
the rolling resistance and electroconductivity.
[0093] The pneumatic tire of the present invention capable of
suppressing the rolling resistance and effectively discharging
static electricity generated in tire during tire rubbing is
suitably used for vehicles such as cars, tracks, buses, and heavy
machineries.
[0094] Although the present invention has been described and
illustrated in detail, it is clearly understood that the same is by
way of illustration and example only and is not to be taken by way
of limitation, the scope of the present invention being interpreted
by the terms of the appended claims.
* * * * *