US20130092300A1

US20130092300A1 - Pneumatic tire

Info

Publication number: US20130092300A1
Application number: US13/693,611
Authority: US
Inventors: Tetsuya Kunisawa; Keiichi Nakadera
Original assignee: Sumitomo Rubber Industries Ltd
Current assignee: Sumitomo Rubber Industries Ltd
Priority date: 2007-06-15
Filing date: 2012-12-04
Publication date: 2013-04-18
Also published as: US20140299241A1; KR101091489B1; EP2014488A1; US8869856B2; KR20110089390A; US20080308203A1; EP2014488B1; DE602008003716D1; KR20080110534A

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 1×10⁸Ω·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 10⁸Ω·cm.

Description

This application is a Divisional of U.S. application Ser. No. 12/155,295, filed Jun. 2, 2008, claiming priority of Japanese Patent Application No. 2007-159029 filed on Jun. 15, 2007, No. 2007-172695 filed on Jun. 29, 2007, Nos. 2007-188542 and 2007-188547 filed on Jul. 19, 2007, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a pneumatic tire improved in safety by keeping low rolling resistance and reducing static electricity generated during tire running.
2. Description of the Background Art
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.
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 reinforcing agent; a rubber component forming a sidewall part contains 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.
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 1×10⁸Ω·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 1×10⁸Ω·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.
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 m²/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 m²/g or less, and a silane coupling agent in an amount capable of controlling a reactive factor within a specific range.
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 10⁸Ω·cm or less and a low resistivity.
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

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.
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 1×10⁸Ω·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 m²/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 m²/g or more and 250 m²/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 1×10⁸∩·cm.
A ketjen black is suitably used as the carbon black. The bead part rubber preferably has a volume specific resistivity of less than 1×10⁸Ω·cm. A thickness of the side part electroconductive rubber is preferably adjusted to a range of 0.2 to 2 mm.
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

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

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.
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.
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.
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.

Each volume specific resistivity of the tread rubber, the breaker rubber, and the sidewall rubber forming the tire is set to 1×10⁸Ω·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 1×10⁸Ω·cm or more of a rubber composition is improved.
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.
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.
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.
The nitrogen adsorption specific surface area of silica (BET method) is preferably in the range of from 100 to 300 m²/g, more preferably 150 to 250 m²/g. In the case where the nitrogen adsorption specific surface area is 100 m²/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 m²/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 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 1×10⁸Ω·cm. It is possible to achieve a desired degree of tire electroconductivity improvement effect when the volume specific resistivity is less than 1×10⁸Ω·cm. Also, the volume specific resistivity may be set in the same manner as in the side part electroconductive rubber and is preferably 1×10⁷Ω·cm or less, more preferably 1×10⁶Ω·cm or less and is preferably 1×10³Ω·cm or more, more preferably 1×10⁴Ω·cm or more.
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.
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.
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 of the 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.
The nitrogen adsorption specific surface area of carbon black contained in the coating rubber is preferably 600 m²/g or more and 1,500 m²/g or less. Mechanical strength of the coating rubber is good when the nitrogen adsorption specific surface area is 600 m²/g or more. The nitrogen adsorption specific surface area of 1,500 m²/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 m²/g or more and is preferably 1,300 m²/g or less, more preferably 1,000 m²/g or less. As carbon black, wood tar carbon black that is not an oil-derived stock is suitably used.
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.
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.
The nitrogen adsorption specific surface area of silica (BET method) is preferably in the range of from 70 to 250 m²/g, more preferably 80 to 240 m²/g. In the case where the nitrogen adsorption specific surface area is 70 m²/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 m²/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.

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 1×10⁸Ω·cm. When the volume specific resistivity of side part electroconductive rubber 14 is less than 1×10⁸Ω·cm, it is possible to achieve an effect of improving tire electroconductivity. The volume specific resistivity of the ply rubber is preferably set to 1×10⁷Ω·cm or less, more preferably 1×10⁶Ω·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 1×10³Ω·cm or more, more preferably 1×10⁴Ω·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 or discontinuously in the tire circumferential direction.
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.

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 of the 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. 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.
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 1×10⁸Ω·cm. In the case where the volume specific resistivity of the conduction rubber is less than 1×10⁸Ω·cm, electroconductivity of the tire is improved to achieve effect of discharging static electricity. The volume specific resistivity of the conduction rubber is preferably 1×10⁷Ω·cm or less, more preferably 1×10⁶Ω·cm or less.
In the present invention, when the volume specific resistivity of the tread rubber, the breaker rubber, and the sidewall rubber are set to 1×10⁸Ω·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.
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.

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.
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.
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.
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 is less than 1×10⁸Ω·cm. Good electroconductivity of the tire is achieved by maintaining the volume specific resistivity of the bead part rubber to less than 1×10⁸Ω·cm. The volume specific resistivity of the bead part rubber is preferably less than 1×10⁷Ω·cm, more preferably 1×10⁶Ω·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 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.
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 1×10⁸Ω·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 1×10⁷Ω·cm or less, more preferably 1×10⁶Ω·cm or less.
In the present invention, when the volume specific resistivity of the breaker rubber and the sidewall rubber are set to 1×10⁸Ω·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).
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.

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.
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 (IIR), 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.
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.
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.
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. 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.
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, γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-(2-aminoethyl)aminopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and the like.
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.
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.
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.
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.
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.
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.
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.
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.
As the anti-scorching agent for preventing or delaying scorching, organic acid such 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

Hereinafter, the present invention will be described in more details based on examples, and the present invention is not limited to the example.

Examples 1 and 2 and Comparative Examples 1 and 2

Side Part Electroconductive Rubber, Coating Rubber, and Conduction Rubber

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° C. for 4 minutes, sulfur and the vulcanizing agent were added to be mixed and kneaded at 95° 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.

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° C. for 4 minutes, sulfur and the vulcanizing agent were added to be mixed and kneaded at 95° 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 1

	Coating Rubber/Conduction Rubber	Side Part Electroconductive Rubber

Blending	A2	B2	C2	D2	E2	F2	G2	H2

Diene-Based	NR (TSR20 grade)	100	100	100	100	100	100	100	100
Rubber
Carbon	N330(product of Mitsubishi	55	—	—	—	50	—	—	—
	Chemical Corporation)
Silica	VN3 (product of Degussa	—	55	50	40	—	50	45	35
	Corporation)
Carbon	Printex XE2B (product of	—	—	5	15	—	—	5	15
	Degussa Corporation)
Processed Oil	Diana Process PS32 (product	5	—	—	—	10	—	—	—
	of Idemitsu Kosan Co., Ltd.)
Soybean Oil	Soybean Refined Oil (product	—	5	5	5	—	10	10	10
	of Nissin Oillio Group, Ltd.)
Wax	Sunnoc Wax (product of Ouchi	2	2	2	2	—	—	—	—
	Shinko Chemical
	Industrial Co., Ltd.)
Anti-Aging Agent	Santflex 13 (Product of Flexsys)	2	2	2	2	4	4	4	4
Stearic Acid	KM (product of NOF Corporation)	2	2	2	2	2	2	2	2
Zinc Flower	Zinc Oxide No. 1 (product of	5	5	5	5	5	5	5	5
	Mitsui Mining & Smelting
	Co., Ltd.)
Coupling Agent	Si75 (product of Degussa	—	5	4	3	—	5	4	3
	Corporation)
Sulfur	Crystex HSOT20 (Product of	5	5	5	5	1.5	1.5	1.5	1.5
	Flexsys)
Vulcanization	Nocceler (product of Ouchi	2	2	2	2	0.75	0.75	0.75	0.75
Accelerator	Shinko Chemical Industrial
	Co., Ltd.)
Volume Specific	log₁₀R	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	63	94	92	87	63	95	92	87
Petroleum (%)

In Table 1, a nitrogen adsorption specific surface area of the carbon (Printex XE2B) is 880 m²/g.

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 (Ω · cm)	1 × 10⁶

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 (Ω · cm)	1 × 10¹¹

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 (Ω · cm)	1 × 10¹¹

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 (Ω · cm)	1 × 10¹¹

In Tables 2 to 5, details of the blending agents are as follows.
Note 1: natural rubber is TSR20 (trade name) made in Thailand.
Note 2: SBR1500 is styrene-butadiene rubber manufactured by JSR Corporation.
Note 3: N220 is carbon black manufactured by Cabot Japan K.K. (nitrogen adsorption specific surface area: 111 m²/g; DBP oil absorption amount: 115 ml/100 g)
Note 4: N330 is carbon black manufactured by Mitsubishi Chemical Corporation (nitrogen adsorption specific surface area: 79 m²/g; DBP oil absorption amount: 105 ml/100 g).
Note 5: Silica VN3 is VN3 (trade name) manufactured by Degussa Corporation (nitrogen adsorption specific surface area: 210 m²/g).
Note 6: A silane coupling agent is Si69 (trade name) manufactured by Degussa Corporation.
Note 7: Aromatic oil is X140 (trade name) manufactured by Japan Energy Corporation.
Note 8: Wax is Sunnoc N (trade name) manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.
Note 9: An anti-aging agent is Antigen6C manufactured by Sumitomo Chemical Co., Ltd.
Note 10: Stearic acid is Stearic Acid Tsubaki (trade name) manufactured by NOF Corporation.
Note 11: Zinc flower is zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd.
Note 12: Sulfur is Sulfur Powder (trade name) manufactured by Karuizawa Seirensha K.K.
Note 13: A vulcanizing agent 1 is Nocceler NS-P (trade name) manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.
Note 14: Insoluble sulfur is Myuclon OT20 (trade name) manufactured by Shikoku Chemicals Corporation.
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:

Cord angle: 90 degrees in tire circumferential direction.
Cord material: polyester (1500 denier, 1670 dtex/2)

Breaker:

Cord angle: 24×24 degrees in tire circumferential direction.
Cord material: steel
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.

Volume Specific Resistivity

Sample pieces each having a thickness of 2 mm and a size of 15 cm×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° 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

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:
Rollin resistance(RR)=(RRC of Comparative Example 1/RRC of each of Examples 1 and 2 and Comparative Example 2)×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

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 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	G2	H2	E2	F2
Electroconductive
Rubber
Clinch Rubber	I2	I2	I2	I2
Tread Rubber	J2	J2	J2	J2
Sidewall Rubber	K2	K2	K2	K2
Breaker Rubber	L2	L2	L2	L2
Tire
	1 × 10⁷	1 × 10⁶	1 × 10⁷	1 × 10¹¹
Electroconductivity
Rolling Resistance	106	104	100	103

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.
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 1×10⁸Ω·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 1×10⁸Ω·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.
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.
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.

Claims

What is claimed is:

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 1×10^{8 Ω·cm or more,}

said pneumatic tire further comprising side part electroconductive rubber extending from at least both edges of said breaker part to the bead part along the outside of said carcass, 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 have 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 and each have a volume specific resistivity of less than 1×10⁸Ω·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 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 1×10^{8 Ω·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 m²/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 m²/g or more and 250 m²/g or less in an amount of 10 to 55 parts by mass with respect to 100 parts by mass of a rubber component.