JP5712189B2 - Rubber composition for tire and pneumatic tire - Google Patents

Description

The present invention relates to a rubber composition for tires and a pneumatic tire using the same.

In recent years, for the purpose of reducing the rolling resistance of a tire while maintaining wet grip performance, a compound containing silica as a main component has been used particularly in the tread portion of the tire. In such a situation, in order to further reduce rolling resistance, the other components such as breakers and sidewall portions are changed from the composition containing carbon black as the main component of the reinforcing filler, and silica is filled for reinforcement. The use of a formulation with the main component of the agent is beginning to be studied.

However, when silica is compounded in place of carbon black in each member of the tire, silica has a high electrical insulating property and tends to increase the electrical resistance of the tire, so that there is a drawback that static electricity tends to accumulate in the vehicle. Due to the accumulation of static electricity, for example, radio noise or the like is likely to be generated, or when the vehicle is refueled, a spark due to static electricity may be generated and the fuel may be ignited.

In Patent Document 1, in the tread part, the sidewall part, the breaker part or the ply part, the volume resistivity is 1 × 10 ⁹ Ω · cm or more, and the content of silica in the reinforcing filler is 70% by mass or more. A tire having a conductive rubber layer is described together with the tire member. However, regarding the kneading method of the rubber composition used for the conductive layer, there is only a description of simple X-F kneading consisting of a base kneading step and a finishing kneading step. Changes in electrical resistance and durability have not been studied in detail. In addition, since only styrene butadiene rubber is used as the rubber component of the rubber composition used in the conductive layer, there is a problem that the bending crack resistance is poor and sufficient durability cannot be obtained.

Patent Document 2 describes a pneumatic tire in which the volume specific resistances of the internal conductive layer, conductive rubber, covering rubber, energizing rubber, and bead rubber are all less than 1 × 10 ⁸ Ω · cm. However, the dispersibility of carbon black, the change in electrical resistance of the tire over time, and durability have not been studied in detail.

JP 2007-8269 A JP 2011-88458 A

The present invention solves the above-described problems, suppresses rolling resistance to a low level, prevents accumulation of static electricity during running of the tire, suppresses an increase in electrical resistance of the tire over time, and improves an inner layer sidewall that can improve durability. An object is to provide a rubber composition for cushions and a pneumatic tire using the rubber composition.

The present invention includes 5 to 30 parts by mass of carbon black having a nitrogen adsorption specific surface area of 400 m ² / g or more with respect to 100 parts by mass of a rubber component containing two or more kinds of diene rubbers, JIS K 6812 “polyolefin tube, The present invention relates to a rubber composition for inner-layer sidewalls and / or cushions having a carbon black dispersion ratio of 90% or more determined by counting aggregates according to “Method for evaluating pigment dispersion or carbon dispersion of joints and compounds”.

The rubber composition is obtained by a base kneading step 1 and a base kneading step 1 in which a rubber containing a diene rubber having the lowest SP value among the two or more types of diene rubbers and the carbon black are kneaded. The kneaded product and a base kneading step 2 for kneading a rubber containing a diene rubber having the highest SP value among the two or more types of diene rubbers are preferably obtained.

The rubber composition is preferably obtained by a production method further including a re-kneading step of kneading the kneaded material obtained in the base kneading step 2 again.

The present invention also relates to a pneumatic tire having an inner side wall rubber and / or a cushion rubber produced using the rubber composition.

The pneumatic tire includes a tread portion, a sidewall portion, a bead portion, a carcass from the tread portion through the sidewall portion to the bead portion, and a breaker portion on the outer side in the tire radial direction of the carcass. The volume specific resistance of the tread rubber, breaker rubber, and sidewall rubber formed in the tread portion, the breaker portion, and the sidewall portion, respectively, is 1 × 10 ⁸ Ω · cm or more. The pneumatic tire includes an inner-layer sidewall rubber disposed between the carcass and the sidewall rubber, a cushion rubber disposed in a lower region at both ends of the breaker in contact with the inner-layer sidewall rubber, Covered with cushion rubber and contact area and arranged to cover upper side of breaker part Rubber, current-carrying rubber embedded in the tread portion so as to be in contact with the covering rubber and partly exposed on the surface of the tread, bead portion rubber disposed in a region in contact with the inner side wall rubber and in contact with the rim flange of the bead portion The volume specific resistance of the inner layer side wall rubber, the cushion rubber, the covering rubber, the energizing rubber, and the bead rubber is preferably less than 1 × 10 ⁸ Ω · cm.

In the pneumatic tire, the inner layer side wall rubber preferably has a thickness of 0.2 to 1.0 mm.

The bead rubber is preferably clinch rubber or chafer rubber.

The energizing rubber is preferably formed continuously in the tire circumferential direction.

According to the present invention, 5 to 30 parts by mass of carbon black having a nitrogen adsorption specific surface area of 400 m ² / g or more is contained per 100 parts by mass of a rubber component containing two or more types of diene rubber, and JIS K 6812 “polyolefin” In accordance with the method for evaluating the pigment dispersion or carbon dispersion of pipes, joints and compounds, a rubber composition for an inner layer sidewall and / or cushion having a carbon black dispersion obtained by counting aggregates of 90% or more. Therefore, while keeping the rolling resistance low, it can prevent the accumulation of static electricity during running of the tire and also suppress the increase of the tire's electrical resistance over time, durability (high-speed durability, durability against repeated fatigue (crack resistance) Performance)) can also be improved. Therefore, it is possible to provide a pneumatic tire that is excellent in fuel efficiency, can prevent accumulation of static electricity during tire travel throughout the life of the tire, and has excellent durability.
In the present specification, when simply described as durability, both high-speed durability and durability against repeated fatigue (crack resistance performance) are included.

It is a figure which shows the upper right half of sectional drawing of the pneumatic tire of this invention. 1 is a schematic cross-sectional view conceptually showing a tire electrical resistance measuring device.

The rubber composition for inner wall and / or cushion of the present invention (also referred to as the rubber composition of the present invention) has a nitrogen adsorption specific surface area of 400 m with respect to 100 parts by mass of a rubber component containing two or more kinds of diene rubbers. ^Of carbon black obtained by counting aggregates in accordance with JIS K 6812 "Evaluation method of pigment dispersion or carbon dispersion of polyolefin pipes, joints and compounds". The dispersion ratio is 90% or more.

In the present invention, in order to ensure durability, a rubber composition containing two or more types of diene rubber is used, and further, carbon black having high conductivity and a nitrogen adsorption specific surface area of a specific value or more (high specific surface area carbon). A specific amount of black) is also added. Furthermore, regarding the dispersibility of this carbon black, the accumulation of static electricity is maintained while keeping the rolling resistance low by setting the carbon black dispersion obtained by counting aggregates to a specific value or more according to JIS K 6812. Can be effectively prevented, the accumulation of static electricity can be effectively prevented throughout the life of the tire, and the durability can be improved.

Conventionally, with regard to the design of a conductive rubber for preventing the accumulation of static electricity in a tire, studies have been made focusing only on how to conduct with a small amount of high specific surface area carbon black. For this reason, the electrical resistance of the tire may increase due to the use of the tire or the aging of the tire, or the tire may be used in a dispersed state with good conductivity (that is, a state where the high specific surface area carbon black is not sufficiently dispersed in the rubber composition). Thus, high speed durability and various durability over time have not been sufficiently studied. In addition, it has not been considered that the electrical resistance of the tire increases due to the use of the tire or aging.

In view of the fact that it is very difficult to satisfactorily disperse carbon black having a nitrogen adsorption specific surface area of a specific value or more in a rubber composition, the present invention improves rolling resistance by improving the dispersibility of the carbon black. It is possible to suppress the accumulation of static electricity during tire travel, and also to suppress the increase in tire electrical resistance over time, which has not been noticed at all, and the accumulation of static electricity during tire travel throughout the tire life. Can be effectively prevented, and the durability can be improved.

(Rubber composition for inner side wall and / or cushion)
The rubber composition of the present invention contains two or more diene rubbers as a rubber component. Thereby, durability can be improved. The diene rubber usable in the present invention is not particularly limited, and natural rubber (NR), epoxidized natural rubber (ENR), diene synthetic rubber (isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber. (SBR), styrene isoprene butadiene rubber (SIBR), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), ethylene propylene diene rubber (EPDM), butyl rubber (IIR), halogenated butyl rubber (X-IIR), etc. used. Among them, because it shows good strength, flex crack growth resistance and crack resistance, durability can be improved, and because it is used for tires and its cost is relatively low, NR , ENR, BR and SBR are preferred, NR, ENR and BR are more preferred, and it is further preferred to use ENR and / or BR together with NR.

When BR is used together with NR, the rolling resistance is further reduced, the dispersibility of carbon black is further improved, and the durability is further improved. Moreover, the bending crack growth resistance and crack resistance can be further improved. In addition, when ENR is used together with NR, the resistance to flex crack growth and crack resistance can be improved to some extent, and at the same time, the environment can be considered more by using a natural material.

The NR is not particularly limited, and for example, those commonly used in the tire industry such as SIR20, RSS # 3, TSR20, and the like can be used.

When NR is contained, the content of NR in 100% by mass of the rubber component is preferably 40% by mass or more, more preferably 50% by mass or more. If it is less than 40% by mass, it may be difficult to obtain sufficient mechanical strength. The NR content is preferably 80% by mass or less, more preferably 70% by mass or less. If it exceeds 80% by mass, the blend ratio of other blend rubbers such as BR and ENR becomes too low, and there is a possibility that problems arise in the resistance to flex crack growth and crack resistance.

As the ENR, a commercially available epoxidized natural rubber may be used, or natural rubber may be epoxidized. The method for epoxidizing natural rubber is not particularly limited, and can be carried out using a method such as a chlorohydrin method, a direct oxidation method, a hydrogen peroxide method, an alkyl hydroperoxide method, or a peracid method. Examples thereof include a method of reacting natural rubber with an organic peracid such as peracetic acid or performic acid.

The epoxidation rate of ENR is preferably 5 mol% or more, and more preferably 10 mol% or more. If the epoxidation ratio of ENR is less than 5 mol%, the effect of epoxidation cannot be obtained, and even if blended with NR or the like, it may be difficult to sufficiently improve the flex crack growth resistance. The epoxidation rate of ENR is preferably 60 mol% or less, and more preferably 40 mol% or less. When the epoxidation rate of ENR exceeds 60 mol%, the polymer component tends to gel. In addition, when carbon black or silica is blended, it may be difficult to obtain good dispersion. The epoxidation rate can be calculated by nuclear magnetic resonance (NMR) spectroscopy.

When ENR is contained, the content of ENR in 100% by mass of the rubber component is preferably 20% by mass or more, more preferably 30% by mass or more. If it is less than 20% by mass, it may be difficult to sufficiently improve the bending crack growth resistance even when blended with NR or the like. The content of the ENR is preferably 60% by mass or less, more preferably 50% by mass or less. If it exceeds 60% by mass, the blending amount of the low SP value polymer is relatively small, and when carbon black or silica is blended, it may be difficult to obtain good dispersion.

It is not particularly limited as BR, for example, BR1220 manufactured by Nippon Zeon Co., Ltd., BR130B manufactured by Ube Industries, Ltd., BR150B having high cis content such as BR150B, VCR412 manufactured by Ube Industries, Ltd., VCR617, etc. BR containing syndiotactic polybutadiene crystals can be used. Among them, the cis content of BR is preferably 90% by mass or more because the mechanical strength, durability, and rolling resistance characteristics are good.

When BR is contained, the content of BR in 100% by mass of the rubber component is preferably 20% by mass or more, more preferably 30% by mass or more. If it is less than 20% by mass, it may be difficult to sufficiently improve the bending crack growth resistance and crack resistance. The BR content is preferably 60% by mass or less, more preferably 50% by mass or less. If it exceeds 60% by mass, the NR and the like are relatively decreased, so that the mechanical strength may be lowered.

In the present invention, carbon black (high specific surface area carbon black) having a nitrogen adsorption specific surface area (N ₂ SA) of 400 m ² / g or more is used. The nitrogen adsorption specific surface area of the carbon black is at 400 meters ² / g or more, preferably 500 meters ² / g or more, more preferably at least ^{700m 2 / g, 900m 2 /} g or more is more preferred, 1100 m ² / g or more and particularly preferable. If it is less than 400 m < ² > / g, there exists a possibility that the improvement of a rolling resistance characteristic at the time of mix | blending carbon black required in order to obtain sufficient electroconductivity (prevention of accumulation of static electricity) and the same electroconductivity may not be obtained. The _N 2 SA is preferably 2000 m ² / g or less, more preferably 1500 m ² / g, more preferably not more than 1350 m ² / g. When it exceeds 2000 m ² / g, it becomes difficult to disperse, fuel efficiency and durability deteriorate, and the electrical resistance of the tire over time tends to increase. It is difficult to produce such carbon black, which may unnecessarily increase costs. In the present invention, N ₂ SA of carbon black is determined according to JIS K 6217-2: 2001.

The carbon black has a dibutyl phthalate oil absorption (DBP) of preferably 180 ml / 100 g or more, more preferably 300 ml / 100 g or more, still more preferably 400 ml / 100 g or more, and particularly preferably 450 ml / 100 g or more. Thereby, it is possible to achieve both good antistatic (preventing accumulation of static electricity) characteristics and rolling resistance characteristics, and it is possible to suppress the increase in the viscosity of the rubber composition and maintain good processability. The DBP of carbon black is preferably 1000 ml / 100 g or less, more preferably 500 ml / 100 g or less.
Carbon blacks exceeding 1000 ml / 100 g are difficult to produce and may increase costs.
The DBP of carbon black is measured according to JIS K6217-4: 2001.

Content of the said carbon black is 5 mass parts or more with respect to 100 mass parts of rubber components, Preferably it is 8 mass parts or more. If the amount is less than 5 parts by mass, sufficient conductivity may not be obtained. The content is 30 parts by mass or less, preferably 25 parts by mass or less, more preferably 15 parts by mass or less. If it exceeds 30 parts by mass, dispersibility may deteriorate, fuel economy and durability may deteriorate, and the electrical resistance of the tire over time may increase.

The rubber composition of the present invention preferably further contains silica. Silica is not particularly limited, and silica prepared by a wet method or a dry method can be used. By blending silica, it is possible to keep rolling resistance lower while ensuring reinforcement, and to ensure the flex crack growth resistance, mechanical strength, etc. required for inner layer side wall rubber and cushion rubber it can. Moreover, the scorch resistance of a rubber composition can also be improved by mix | blending a silica.

The nitrogen adsorption specific surface area (BET method) of silica is preferably in the range of, for example, 50 to 300 m ² / g, and more preferably 70 to 250 m ² / g. In the present invention, the nitrogen adsorption specific surface area of silica is measured by the BET method according to ASTM D3037-81.

When silica is contained, the content of silica is preferably 2-55 parts by mass, more preferably 5-40 parts by mass, still more preferably 10-35 parts by mass, particularly preferably 100 parts by mass of the rubber component. 15 to 30 parts by mass. When the content of silica is within the above range, the effects of the present invention can be obtained more suitably.

When silica is contained, it is preferable to mix a silane coupling agent with silica. As the silane coupling agent, any silane coupling agent conventionally used in combination with silica can be used in the rubber industry. For example, sulfide systems such as bis (3-triethoxysilylpropyl) tetrasulfide, 3 -Mercapto type such as mercaptopropyltrimethoxysilane, vinyl type such as vinyltriethoxysilane, amino type such as 3-aminopropyltriethoxysilane, glycidoxy type of γ-glycidoxypropyltriethoxysilane, 3-nitropropyltri Examples thereof include nitro compounds such as methoxysilane, and chloro compounds such as 3-chloropropyltrimethoxysilane. Among these, sulfide type is preferable, and bis (3-triethoxysilylpropyl) tetrasulfide is more preferable. In addition, as for the compounding quantity of a silane coupling agent, 5-15 mass parts is preferable with respect to 100 mass parts of silica.

In addition to the above components, the rubber composition of the present invention includes compounding agents generally used in the production of rubber compositions, such as reinforcing fillers such as clay, zinc oxide, stearic acid, processing aids, various aging An inhibitor, a softener, a plasticizer, a tackifier, a vulcanizing agent such as sulfur, a vulcanization accelerator, and the like can be appropriately blended.

As the vulcanizing agent, an organic peroxide or a sulfur-based vulcanizing agent can be used. As the organic peroxide, for example, dicumyl peroxide, t-butylperoxybenzene, di-t-butylperoxy-diisopropylbenzene can be preferably used. Moreover, as a sulfur type vulcanizing agent, sulfur, morpholine disulfide, etc. can be used, for example, and sulfur can be used conveniently.

Examples of vulcanization accelerators include sulfenamide, thiazole, thiuram, thiourea, guanidine, dithiocarbamic acid, aldehyde-amine or aldehyde-ammonia, imidazoline, and xanthate vulcanization accelerators. It is done.

The rubber composition of the present invention is produced by a general method. That is, it can be produced by a method of kneading the above components with a Banbury mixer, a kneader, an open roll or the like and then vulcanizing.

The rubber composition of the present invention has a volume resistivity measured at 10 V of less than 1 × 10 ⁸ Ω · cm, more preferably 1 × 10 ⁷ Ω · cm or less, and even more preferably 1 × 10 ^6.5 Ω · cm or less. Particularly preferably, it is 1 × 10 ⁶ Ω · cm or less. Further, it is preferably 1 × 10 ³ Ω · cm or more, more preferably 1 × 10 ⁴ Ω · cm or more. If the volume resistivity is within the above range, the effect of the present invention can be obtained more suitably. In the present invention, the volume resistivity can be measured by the method described in the examples. Hereinafter, in the present invention, when the volume resistivity is simply described, it means the volume resistivity measured at 10V.

The rubber composition of the present invention has a carbon black dispersion ratio of 90% or more obtained by counting agglomerates according to JIS K 6812 “Evaluation Method for Pigment Dispersion or Carbon Dispersion of Polyolefin Tubes, Joints and Compounds”. Preferably it is 92% or more, More preferably, it is 95% or more. If it is less than 90%, the dispersibility of carbon black is low, the fuel efficiency and durability deteriorate, and the electrical resistance of the tire over time tends to increase. In addition, the dispersion rate of carbon black can be measured by the method described in Examples.

Since high specific surface area carbon black has very poor dispersibility, normally, when high specific surface area carbon black is blended, the dispersion ratio of carbon black becomes less than 90%, fuel efficiency and durability deteriorate, and over time The increase in electrical resistance of tires tends to increase.

Examples of the method for setting the carbon black dispersion ratio to a specific value or more when the high specific surface area carbon black is blended include the following methods.

Generally, the SP value of carbon black is said to be 9.6 to 10.5, and is higher than the SP value of diene rubber used for tires. Therefore, unless the diene rubber having a lower SP value is first kneaded with the high specific surface area carbon black, the carbon black is unevenly distributed in the diene rubber having a high SP value, and the dispersibility of the carbon black is greatly deteriorated. Therefore, the rubber composition of the present invention contains two or more types of diene rubbers. First, a rubber containing a diene rubber having a low SP value and a high specific surface area carbon black are kneaded to a certain extent. It is preferably obtained by a production method in which a high specific surface area carbon black is dispersed in a rubber containing a low diene rubber, and then a rubber containing a diene rubber having a high SP value is added and kneaded. Thereby, the dispersion ratio of the carbon black can be made a specific value or more.

Specifically, the base kneading step 1 for kneading a rubber containing the diene rubber having the lowest SP value among the two or more types of diene rubbers and the high specific surface area carbon black, and the base kneading step 1 are used. It is preferably obtained by a production method including a kneaded product obtained and a base kneading step 2 in which a rubber containing a diene rubber having the highest SP value among the two or more kinds of diene rubbers is kneaded. For example, when NR and BR and / or ENR are blended as a diene rubber, a rubber containing NR and a high specific surface area carbon black are kneaded in the base kneading step 1 and obtained by the base kneading step 1. The kneaded material and rubber containing BR and / or ENR may be kneaded in the base kneading step 2.

After the completion of the base kneading step 2, a finishing kneading step is performed in which a vulcanizing agent or a vulcanization accelerator is added to the kneaded product obtained in the base kneading step 2 and kneaded. In this way, a rubber composition having a carbon black dispersion ratio equal to or higher than a specific value is obtained.
In addition, it is more preferable to obtain by the manufacturing method which further includes the re-kneading process which knead | mixes again the kneaded material obtained by the base kneading process 2 before moving to a finishing kneading process. By performing the re-milling step, the dispersibility of the carbon black can be further improved, fuel efficiency and durability can be further improved, and an increase in the electrical resistance of the tire over time can be suitably suppressed.

In the rubber composition, the dispersion ratio of carbon black to the diene rubber phase having the highest SP value (SPM method) is preferably 1 or more. The dispersion ratio is preferably 5 or less, more preferably 3 or less, still more preferably 2 or less, and particularly preferably 1.5 or less. When the dispersion ratio is within the above range, it indicates that carbon black can be dispersed well in a rubber composition containing two or more diene rubbers. The dispersion ratio can be measured by the method described in the examples.

In the rubber composition, the dispersion ratio (volume%, NMR method) of carbon black in the diene rubber phase having the highest SP value is preferably 40 or more, more preferably 42 or more. The dispersion ratio is preferably 80 or less, more preferably 65 or less, and still more preferably 57 or less. When the dispersion ratio is within the above range, it indicates that carbon black can be dispersed well in a rubber composition containing two or more diene rubbers. The dispersion ratio can be measured by the method described in the examples.

The method for setting the carbon black dispersion ratio to a specific value or more is not limited to the above method, and other than the above method, for example, high specific surface area carbon black is used in advance as a master batch (particularly, wet master batch). And a method of repeatedly kneading until the dispersibility of the carbon black becomes a specific value or more.

(Pneumatic tire)
The pneumatic tire of the present invention is produced by a usual method using the rubber composition.
That is, a rubber composition containing the above components is extruded in accordance with the shape of each tire member such as an inner layer side wall rubber and / or cushion rubber at an unvulcanized stage, together with other tire members, a tire molding machine An unvulcanized tire is formed by molding in the usual manner. The unvulcanized tire is heated and pressurized in a vulcanizer to obtain a tire.

The pneumatic tire of the present invention is used as a passenger car tire, truck / bus tire, motorcycle tire, high-performance tire, and the like. In addition, the high-performance tire in this specification is a tire that is particularly excellent in grip performance, and is a concept that includes a competition tire used in a competition vehicle.

Below, an example of the pneumatic tire of the present invention is explained using a drawing.
<Basic structure>
The structure of the pneumatic tire of the present invention is exemplified in the upper right half of the tire cross section in FIG. The tire 1 includes a tread rubber 7 constituting a tread portion, a pair of sidewall rubbers 8 constituting a pair of sidewall portions extending inward in the tire radial direction from both ends thereof, and a clinch positioned at an inner end of each sidewall portion. A clinch rubber 3 constituting the part and a chafer rubber 2 constituting the chafer part located at the upper part of the rim. A carcass 10 is bridged between the clinch portion and the chafer portion, and a breaker rubber 9 constituting a breaker portion is disposed on the outer side of the carcass 10 in the tire radial direction. The carcass 10 is formed of one or more carcass plies on which carcass cords are arranged. The carcass ply includes a bead core 13 and a bead extending from the upper end of the bead core 13 toward the side wall through a sidewall portion. The area around the apex 11 is folded from the inner side to the outer side in the tire axial direction and is locked by the folded portion. The breaker portion is composed of two or more breaker plies in which breaker cords are arranged, and the breaker cords are stacked in different directions so that the breaker cords intersect each other. In the pneumatic tire of the present invention, although not limited thereto, for example, a covering rubber (under tread) 5 that covers the upper side of the breaker portion is provided between the tread portion (tread rubber, base tread) and the breaker portion. Provided. The cushion rubber 4 is disposed between the carcass ply and both ends of the breaker portion and the sidewall portion, having a contact area with the covering rubber 5. An energizing rubber 6 is disposed in the tread rubber 7 so as to be in contact with the covering rubber 5 and partially exposed to the grounding surface. In addition, an inner side wall rubber 14 having a contact area with the cushion rubber 4 and extending between at least the cushion rubber 4 and the clinch rubber 3 or the chafer rubber 2 is disposed between the carcass 10 and the side wall rubber 8. Is done. In the pneumatic tire 1, the energizing rubber 6, the covering rubber 5, the cushion rubber 4, the inner side wall rubber 14, the clinch rubber 3 or the chafer rubber 2 are electrically connected.

By adopting the above structure, the bead rubber located in the contact area with the rim during running of the tire or the static electricity generated in the ground contact area is electrically connected to the outside of the tire through the electrically connected conductive rubber member inside the tire. To be released. Therefore, even if silica is used for the tread rubber, breaker rubber, and sidewall rubber, the electrical resistance of the tire can be lowered.

<Tread rubber, breaker rubber, sidewall rubber>
The volume specific resistances of the tread rubber, breaker rubber, and sidewall rubber constituting the tire are all set to 1 × 10 ⁸ Ω · cm or more. Conventionally, carbon black has been used as a rubber reinforcing agent (filler), but rolling resistance can be reduced by replacing this with silica. Furthermore, since silica is not a material derived from fossil fuels such as petroleum, it is preferably used from the viewpoint of environmental problems as compared with carbon black, which is generally a material derived from petroleum or coal. However, when silica is used, the volume resistivity tends to increase. According to the present invention, the volume specific resistance of the rubber composition is 1 by the above-mentioned electrically connected structure while maintaining the basic characteristics such as the reduction of the rolling resistance of the tire and the processability of the rubber by using the silica compound as a base. The problem of high electric resistance of × 10 ⁸ Ω · cm or more can be improved.

In the pneumatic tire of the present invention, it is preferable that 50% by mass or more of the filler contained in each of the tread rubber, breaker rubber, and sidewall rubber is silica. When silica accounts for 50 mass% or more of the filler, the effect of reducing the rolling resistance of the tire is good. The proportion of silica in the filler is more preferably 70% by mass or more, and still more preferably 90% by mass or more. All of the above fillers may be silica, but other fillers may be used in combination for the purpose of adjusting the electrical conductivity and mechanical strength of the tread rubber, breaker rubber and sidewall rubber.

Silica can be blended in an amount of, for example, 5 to 100 parts by mass with respect to 100 parts by mass of the rubber component in each of the tread rubber, breaker rubber, and sidewall rubber. When it is 5 parts by mass or more, the rolling resistance of the tire can be reduced, and when it is 100 parts by mass or less, the workability due to the increase in viscosity of the unvulcanized rubber composition at the production of tread rubber, breaker rubber and sidewall rubber is improved. Reduction and excessive increase in cost can be prevented well.

As the silica, those similar to those used in the rubber composition of the present invention can be used.

Tread rubber, breaker rubber and the nitrogen adsorption specific surface area of silica used in the sidewall rubber (BET method), for example 100 to 300 m ² / g, it is preferable that further the range of 150 to 250 ² / g. When it is 100 m ² / g or more, the abrasion resistance of the tire is improved satisfactorily by obtaining a sufficient reinforcing effect. On the other hand, when it is 300 m ² / g or less, the processability during production of each rubber is good, and the steering stability of the tire is also ensured.

<Coating rubber>
The covering rubber 5 in the present invention is made of rubber having a volume specific resistance set to be less than 1 × 10 ⁸ Ω · cm so as to be in contact with the cushion rubber 4 and the energizing rubber 6 and cover the upper portion of the breaker portion. . If the volume resistivity is less than 1 × 10 ⁸ Ω · cm, the desired effect of improving the conductivity of the tire can be obtained. The volume resistivity is preferably set to 1 × 10 ⁷ Ω · cm or less, more preferably 1 × 10 ⁶ Ω · cm or less, and further preferably 1 × 10 ^5.5 Ω · cm or less, Further, it is preferably set to 1 × 10 ³ Ω · cm or more, more preferably 1 × 10 ⁴ Ω · cm or more.

If the thickness of the covering rubber 5 is 0.2 mm or more, the desired effect of improving the tire conductivity is obtained, and if it is 3.0 mm or less, the rolling resistance of the tire is not greatly deteriorated. The thickness of the cushion rubber is preferably 0.5 to 2.0 mm, particularly preferably 0.9 to 1.5 mm. The covering rubber 5 only needs to have a portion in contact with the cushion rubber and the current-carrying rubber, and is provided over the entire surface between the tread portion and the breaker portion, or up to or beyond the position where the current-carrying rubber is disposed. It can be provided partially.

Further, with respect to the portion where the covering rubber, the cushion rubber and the current-carrying rubber are in contact with each other, it is preferable that the cushion rubber has a portion that is in contact with the belt in the tire circumferential direction with a width of 5 mm or more. Is more preferable. By bringing the cushion rubber and the covering rubber into contact with each other under the above conditions, the tire conductive effect can be sufficiently obtained. The contact with the current-carrying rubber is preferably in contact with the entire surface of the current-carrying rubber in the tire width direction and / or the circumferential direction.

In the present invention, the coated rubber preferably contains 5 to 80 parts by mass of carbon black, more preferably 10 to 60 parts by mass, and more preferably 20 to 50 parts by mass with respect to 100 parts by mass of the rubber component. More preferably. When 5 parts by mass or more of carbon black is blended, the conductivity of the coated rubber can be increased.

It is preferable that the nitrogen adsorption specific surface area of carbon black used for the covering rubber is 70 to 2000 m ² / g. Thereby, the mechanical strength of the coated rubber is good, which is also preferable in terms of ensuring processability during production. Nitrogen adsorption specific surface ^area, 100m ² / ^g~1500m 2 / g is more preferable. Moreover, wood tar carbon black etc. which are resources other than petroleum can also be suitably employ | adopted for carbon black. Further, the high specific surface area carbon black used in the present invention may be used alone or in combination with another carbon black for the coating rubber.

The coated rubber may contain silica as a filler in addition to carbon black.
In the coated rubber, the content of silica is preferably 5 to 60 parts by mass and more preferably 20 to 40 parts by mass with respect to 100 parts by mass of the rubber component. When the amount is 5 parts by mass or more, the rolling resistance of the tire can be reduced. When the amount exceeds 60 parts by mass, the rolling resistance and workability may be deteriorated.

The nitrogen adsorption specific surface area (BET method) of silica used for the coated rubber is preferably in the range of 80 to 250 m ² / g, for example. When it is 80 m ² / g or more, the durability of the tire is favorably improved by sufficiently obtaining the reinforcing effect.

<Cushion rubber>
The cushion rubber 4 according to the present invention has a contact region between the inner side wall rubber 14 and a contact region between a carcass ply constituting a carcass 10 to be described later and an edge portion and a side wall portion of the breaker portion and at a lower region of both end portions of the breaker. It is made of rubber having a volume resistivity set to be less than 1 × 10 ⁸ Ω · cm. If the volume eigenvalue is less than 1 × 10 ⁸ Ω · cm, an effect of improving the conductivity of the tire can be obtained. The volume resistivity of the cushion rubber 4 is preferably set to 1 × 10 ⁷ Ω · cm or less, more preferably 1 × 10 ^6.5 Ω · cm or less, and further preferably 1 × 10 ⁶ Ω · cm or less. Preferably, it is set to 1 × 10 ³ Ω · cm or more, more preferably 1 × 10 ⁴ Ω · cm or more.

The cushion rubber may be formed continuously or discontinuously in the tire circumferential direction between the carcass ply constituting the carcass and the edge portion and the sidewall of the breaker portion as described above. There is no limit.

The cushion rubber 4 is preferably produced using the above-described cushion rubber composition of the present invention.

<Electric rubber>
In the present invention, the current-carrying rubber is embedded in the tread part, and a part thereof is exposed to the tire ground contact surface, and the other part is connected (contacted) with the covering rubber, so that the static electricity generated during the running of the pneumatic tire is connected. Effectively release to the ground. In FIG. 1, the current-carrying rubber 6 is shown as a structure embedded in one central portion of the tread portion, but a plurality of current-carrying rubbers can also be buried. And the width | variety of the electricity supply rubber | gum of a tire width direction is 0.2-10 mm, for example, Preferably it is 0.9-1.5 mm. If it is less than 0.2 mm, the current-carrying effect is small. On the other hand, if it exceeds 10 mm, the grounding area of the current-carrying rubber in the tread portion increases relatively, and the grounding characteristics are impaired, and the rolling resistance characteristics and wear resistance are impaired. There is a risk. Moreover, although it is preferable to form the current carrying rubber as a continuous layer in the tire circumferential direction, it can also be formed intermittently in the tire circumferential direction.

The volume specific resistance of the current-carrying rubber is set lower than that of the tread rubber, breaker rubber, and sidewall rubber, and is less than 1 × 10 ⁸ Ω · cm. When the volume resistivity is less than 1 × 10 ⁸ Ω · cm, the conductivity of the tire is improved and the effect of discharging static electricity is obtained. The volume specific resistance of the conductive rubber is more preferably 1 × 10 ⁷ Ω · cm or less, further preferably 1 × 10 ⁶ Ω · cm or less, and particularly preferably 1 × 10 ^5.5 Ω · cm or less. The lower limit of the volume resistivity of the energizing rubber is not particularly limited.

The electrically conductive rubber can also employ a composition substantially similar to that of the cushion rubber, and the same carbon black or silica as described above may be blended. Moreover, it is also possible to employ | adopt the compounding design which provides electroconductivity based on the mixing | blending of a tread rubber from a viewpoint of improving a grounding characteristic.

<Inner side wall rubber>
The inner side wall rubber 14 in the present invention has a contact region with the cushion rubber 4 and extends between the carcass 10 and the side wall rubber 8 at least from the cushion rubber 4 to a position in contact with the clinch rubber 3 or the chafer rubber 2. For example, the upper end portion of the inner layer side wall rubber 14 is electrically connected to the cushion rubber 4 and the lower end portion thereof is electrically connected to the clinch rubber 3 or the chafer rubber 2. The volume resistivity of the inner side wall rubber 14 is set to less than 1 × 10 ⁸ Ω · cm. If the volume eigenvalue is less than 1 × 10 ⁸ Ω · cm, an effect of improving the conductivity of the tire can be obtained. The volume resistivity of the inner-layer side wall rubber 14 is preferably 1 × 10 ⁷ Ω · cm or less, more preferably 1 × 10 ^6.5 Ω · cm or less, still more preferably 1 × 10 ⁶ Ω · cm or less, particularly Preferably, it is set to 1 × 10 ^5.5 Ω · cm or less. When a rubber composition containing a large amount of a conductive component is employed, the electrical resistance decreases, but on the other hand, the electrochemical reaction in the region where the tire is in contact with the rim is promoted and the rim is likely to rust. To avoid this, the volume resistivity of the inner layer sidewall rubber is set preferably 1 × 10 ³ Ω · cm or more, more preferably more than 1 × 10 ⁴ Ω · cm.

If the thickness of the inner side wall rubber 14 is 0.2 mm or more, a desired effect of improving tire conductivity is obtained, and if it is 1.0 mm or less, the rolling resistance of the tire is not greatly deteriorated. The thickness of the cushion rubber is particularly preferably in the range of 0.5 to 1.0 mm. The inner layer side wall rubber 14 is disposed between the carcass 10 and the side wall rubber 8 (for example, disposed adjacent to the outer side of the carcass 10 and the inner side of the side wall rubber 8), and cushion rubber and bead portion rubber. What is necessary is just to have a part which touches. A part of the inner layer sidewall rubber 14 may be disposed between the carcass and the breaker, and may be formed continuously or discontinuously in the tire circumferential direction.

Further, with respect to the portion where the inner side wall rubber is in contact with the cushion rubber and the bead rubber, it is preferable that the cushion rubber has a portion in contact with the belt in the tire circumferential direction with a width of 5 mm or more. More preferably. By bringing the inner side wall rubber and the cushion rubber into contact with each other under the above conditions, the tire conductive effect can be sufficiently obtained. The contact with the bead rubber is preferably a portion in contact with the width of 5 mm or more along the carcass shape, and more preferably 10 mm or more.

The inner side wall rubber is preferably produced using the rubber composition for an inner side wall of the present invention described above.

In the present invention, static electricity can be effectively discharged through an electrical connection path as shown in FIG. 1, and crack resistance performance can be improved by using the rubber composition for the inner layer side wall rubber having the above composition. Therefore, the generation of cracks starting from the ply-winding portion can be prevented, and the occurrence of cracks on the sidewall surface and the inner liner surface can also be prevented.

<Bead rubber>
In the present invention, the bead rubber disposed in the region of the bead that contacts the rim flange is a concept including clinch rubber, chafer, and rubber chafer. When the tire travels, driving force is transmitted from the rim via the bead rubber, and at this time, static electricity is easily generated due to friction between the rim and the bead rubber. Since the bead rubber has a contact area with the inner side wall rubber, static electricity is effectively discharged to the ground plane through the inner side wall rubber. In FIG. 1, a clinch rubber, a chafer or a rubber chafer is electrically connected to the inner side wall rubber 14.

Here, the volume resistivity of the bead rubber is less than 1 × 10 ⁸ Ω · cm. Good electrical conductivity of the tire can be obtained by setting the volume resistivity to less than 1 × 10 ⁸ Ω · cm. The volume resistivity of the bead rubber is preferably 1 × 10 ⁷ Ω · cm or less, more preferably 1 × 10 ^6.5 Ω · cm or less, still more preferably 1 × 10 ⁶ Ω · cm or less, and particularly preferably 1 × 10 ^5.5 Ω · cm or less. The lower limit of the volume resistivity of the bead rubber is not particularly limited. Since the bead rubber, that is, clinch rubber, chafer, and rubber chafer is required to have wear resistance, rigidity, and hardness, in addition to such a compounding design, the electric resistance is adjusted by the compounding method of the cushion rubber and the current-carrying rubber. be able to. Further, the high specific surface area carbon black is 5 to 30 mass with respect to 100 mass parts of the rubber component containing two or more kinds of diene rubbers, similar to the rubber composition for the inner side wall and / or cushion of the present invention. Composition having a carbon black dispersion ratio of 90% or more obtained by counting agglomerates according to JIS K 6812 "Evaluation method of pigment dispersion or carbon dispersion of polyolefin pipes, joints and compounds" It is preferable to produce using.

<Carcass>
The carcass 10 extending from the tread portion to the bead portion through the sidewall portion in the present invention is composed of one or more carcass plies on which carcass cords are arranged. The carcass ply has a configuration in which carcass cords are aligned in parallel and embedded in rubber. Examples of the fiber material constituting the carcass cord include rayon, nylon, polyester, and aramid. These may be used alone or in combination of two or more. For the purpose of considering the environment, rayon may be used because it is a natural resource material. In this case, it is preferable to mix 90% by mass or more of rayon with respect to the fiber material constituting the carcass cord.

Although the volume specific resistance of the ply rubber is not particularly limited, it can be set similarly to the tread rubber, breaker rubber and sidewall rubber. In addition, the volume resistivity of the ply rubber can be set to less than 1 × 10 ⁸ Ω · cm, which, in combination with the adjacent inner layer side wall rubber, improves the conductivity of the tire and has the effect of discharging static electricity. can get. In this case, the volume resistivity of the ply rubber can be set to preferably 1 × 10 ⁷ Ω · cm or less, more preferably 1 × 10 ⁶ Ω · cm or less, and even more preferably 1 × 10 ^5.5 Ω · cm or less. . The lower limit of the volume resistivity of the ply rubber is not particularly limited.

The ply rubber in the present invention can be blended substantially the same as the coating rubber, and may be blended with carbon black or silica similar to the above. Further, from the viewpoint of improving the adhesion with the carcass cord, it is possible to impart conductivity by blending carbon black or the like based on the basic blend of conventional ply rubber.

In the present invention, the volume resistivity of the tread rubber, breaker rubber and sidewall rubber is set to 1 × 10 ⁸ Ω · cm or more, while maintaining the tire performance such as rolling resistance and durability, the inner layer sidewall rubber, The volume specific resistances of the cushion rubber, the covering rubber, the energizing rubber, and the bead rubber that are electrically connected thereto are adjusted to be lower. Therefore, static electricity generated in the pneumatic tire can be effectively discharged through the electrical connection passage formed by these.

Furthermore, since the inner layer side wall rubber and / or cushion rubber is produced using the rubber composition of the present invention, it is possible to suppress the rolling resistance and prevent the accumulation of static electricity during running of the tire. The increase in the electrical resistance of the tire can be suppressed, the accumulation of static electricity during running of the tire can be effectively prevented throughout the life of the tire, and the durability can be improved. Further, when the bead rubber (more preferably clinch rubber and / or chafer rubber) is also produced using the rubber composition of the present invention, the effects of the present invention can be obtained more suitably.

<Rubber composition of covering rubber, electric rubber, chafer rubber, clinch rubber, tread rubber, breaker rubber, and sidewall rubber>
The covering rubber, current-carrying rubber, chafer rubber, clinch rubber, tread rubber, breaker rubber, and sidewall rubber in the pneumatic tire of the present invention are composed of, for example, the following rubber compositions.

Examples of the rubber component used in these rubber compositions include those listed in the rubber composition of the present invention. Diene rubber is preferable as a rubber component used for covering rubber, cushion rubber, current-carrying rubber, chafer rubber, and clinch rubber. Among them, natural rubber, styrene-butadiene rubber, butadiene rubber, isoprene rubber, epoxidized natural rubber, etc. preferable.

In the rubber composition, the following compounding agents generally employed in tire rubber compounding can be appropriately compounded.

In the present invention, as described above, it is preferable to add silica to the tread rubber, breaker rubber, and sidewall rubber. When silica is blended in the rubber composition, it is preferable to blend 1 to 20 parts by mass of the silane coupling agent with respect to 100 parts by mass of silica, for example. By blending 1 part by mass or more, the wear resistance of the tire is improved and the rolling resistance can be reduced. On the other hand, in the case of 20 parts by mass or less, there is little risk of occurrence of scorch in rubber kneading and extruding processes and unnecessary increase in cost. Examples of the silane coupling agent include those similar to the above.

In addition to the above components, the rubber composition generally includes a compounding agent generally used in the production of a rubber composition, for example, a reinforcing filler such as clay, zinc oxide, stearic acid, a processing aid, various anti-aging agents, A softener, a plasticizer, a tackifier, a vulcanizing agent such as sulfur, a vulcanization accelerator, and the like can be appropriately blended.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
<Material>
NR (natural rubber): RSS # 3 (SP value 7.9)
BR (butadiene rubber): BR150B manufactured by Ube Industries, Ltd. (cis content: 95% by mass) (SP value 8.4)
ENR25 (epoxidized natural rubber): ENR25 (epoxidized natural rubber having an epoxidation rate of 25 mol%) manufactured by Kumpulan Guthrie Berhad (Malaysia) (SP value 9)
Silica: Ultrasil VN3 manufactured by Degussa (N ₂ SA: 175 m ² / g)
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Degussa
Carbon Black 1: Show Black N330 manufactured by Cabot Japan Co., Ltd. (N ₂ SA: 75 m ² / g, DBP: 102 ml / 100 g)
Carbon Black 2: Ketjen Black EC600JD (N ₂ SA: 1270 m ² / g, DBP: 495 ml / 100 g) manufactured by Ketjen Black International Co., Ltd.
Carbon black 3: PRINTEX XE2B manufactured by Degussa (N ₂ SA: 1000 m ² / g, DBP: 420 ml / 100 g)
Carbon black 4: Ketjen Black EC300J manufactured by Ketjen Black International Co., Ltd. (N ₂ SA: 800 m ² / g, DBP: 360 ml / 100 g)
Aroma oil: Process X-140 manufactured by Japan Energy Co., Ltd.
Petroleum-based resin: SP1068 resin stearic acid manufactured by Nippon Shokubai Co., Ltd .: Stearic acid “paulownia” manufactured by NOF Corporation
Zinc oxide: Zinc oxide type 2 anti-aging agent manufactured by Mitsui Mining & Smelting Co., Ltd .: NOCRACK 6C (N- (1,3-dimethylbutyl) -N'-phenyl-p- manufactured by Ouchi Shinsei Chemical Co., Ltd.) Phenylenediamine)
Wax: Ozoace 0355 manufactured by Nippon Seiwa Co., Ltd.
Sulfur: Powder sulfur vulcanization accelerator manufactured by Tsurumi Chemical Co., Ltd. NS: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfanamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
SBR1502: SBR1502 manufactured by Sumitomo Chemical Co., Ltd.
SBR1500: SBR1500 manufactured by Sumitomo Chemical Co., Ltd.
Carbon Black N220: Dia Black I (N ₂ SA: 114 m ² / g) manufactured by Mitsubishi Chemical Corporation
Cobalt stearate: COST-S manufactured by Nikko Metal Co., Ltd.
Insoluble sulfur: Sanfel EX from Sanshin Chemical Co., Ltd.

<Preparation of inner side wall rubber and cushion rubber>
(Example and Comparative Example 8)
Among the blended components shown in Table 1, the components shown in step 1 were kneaded for 4 minutes using a closed Banbury mixer so that the discharge temperature was 150 ° C. (base kneading step 1). Next, the kneaded product obtained in the base kneading step 1 and the components shown in step 2 were kneaded for 3 minutes using a closed Banbury mixer so that the discharge temperature was 150 ° C. (base kneading step 2). Further, for Examples 3 to 6 and Comparative Example 8, the kneaded material obtained in the base kneading step 2 was kneaded for 3 minutes using a closed Banbury mixer so that the discharge temperature was 140 ° C. (rekneading step) ). Next, sulfur and a vulcanization accelerator are added to the kneaded product obtained in the base kneading step 2 or the re-kneading step and further kneaded for 3 minutes so that the discharge temperature becomes 100 ° C. Through an extrusion process and a calendering process, an inner layer side wall rubber composition and a cushion rubber composition were prepared.
(Comparative Examples 1-7)
Kneading the ingredients excluding sulfur and vulcanization accelerators shown in Table 1 for 4 minutes using an enclosed Banbury mixer so that the discharge temperature is 150 ° C, then adding sulfur and vulcanization accelerators. Then, the mixture was further kneaded for 3 minutes so that the discharge temperature was 100 ° C., and an inner layer side wall rubber composition and a cushion rubber composition were prepared through an extrusion process and a calendar process by a conventional method.

<Preparation of coated rubber and conductive rubber>
The components excluding sulfur and vulcanization accelerators shown in Tables 2 and 3 are kneaded for 4 minutes using a closed Banbury mixer so that the discharge temperature is 150 ° C., and then sulfur and vulcanization accelerators. Then, the mixture was further kneaded for 3 minutes so that the discharge temperature became 100 ° C., and the coated rubber composition (under tread rubber composition) and the current-carrying rubber composition were prepared through an extrusion process and a calendar process by a conventional method.

<Preparation of tread rubber, sidewall rubber, breaker rubber>
After knead | mixing the component except a sulfur and a vulcanization accelerator among the compounding components shown to Tables 4-6 for 4 minutes so that discharge | emission temperature may be 150 degreeC using an enclosed Banbury mixer, sulfur and a vulcanization accelerator. Was added, and the mixture was further kneaded for 3 minutes so that the discharge temperature became 100 ° C., and a tread rubber composition, a sidewall rubber composition, and a breaker rubber composition were prepared through an extrusion process and a calendar process by a conventional method.

<Preparation of clinch rubber and chafer rubber>
Among the blended components shown in Table 7, the components shown in step 1 were kneaded for 4 minutes using a closed Banbury mixer so that the discharge temperature was 150 ° C. (base kneading step 1). Next, the kneaded material obtained in the base kneading step 1 and the components shown in the step 2 were kneaded for 3 minutes using a closed Banbury mixer so that the discharge temperature was 150 ° C. (base kneading step 2). Furthermore, the kneaded material obtained in the base kneading step 2 was kneaded for 3 minutes using a closed Banbury mixer so that the discharge temperature was 140 ° C. (re-kneading step). Next, sulfur and a vulcanization accelerator are added to the kneaded product obtained by the re-kneading process, and further kneaded for 3 minutes so that the discharge temperature becomes 100 ° C., and after the extrusion process and calendar process by the conventional method, the clinch rubber A composition and a chafer rubber composition were prepared.

<Preparation of test vulcanized rubber slab>
Vulcanized rubber slab sheets (2 mm × 130 mm × 130 mm) were prepared by vulcanizing each rubber composition shown in Tables 1 to 7 at 160 ° C. for 20 minutes. The following evaluation was performed using this vulcanized rubber slab sheet. The results are shown in Tables 1-7.

<Volume specific resistance of rubber composition>
A test piece having a thickness of 2 mm and 15 cm × 15 cm was prepared using the vulcanized rubber slab sheet (each rubber composition shown in Tables 1 to 7), and a voltage of 10 V and an air temperature of 23 using an electrical resistance measurement R8340A manufactured by ADVANTEST. The volume resistivity of the rubber composition was measured under the conditions of ° C. and humidity of 55%. The common logarithm of the result is shown in Tables 1-7. The larger the value, the higher the volume resistivity of the rubber composition, indicating poorer conductivity.

<Dispersion rate of carbon black>
A test piece for measurement was cut out from the above vulcanized rubber slab sheet (each rubber composition in Tables 1 and 7) and applied according to JIS K 6812 “Evaluation method for pigment dispersion or carbon dispersion of polyolefin pipes, joints and compounds”. The carbon black aggregates in the vulcanized rubber composition were counted, and the carbon black dispersion (%) was calculated. The larger the dispersion rate, the better the dispersibility of carbon black.

<Carbon dispersion ratio in polymer phase with high SP value (SPM method)>
A test specimen for measurement was cut out from the vulcanized rubber slab sheet (each rubber composition in Table 1), and the dispersion volume ratio of carbon black dispersed in each polymer phase was analyzed by image analysis using SPM (scanning probe microscope). The dispersion ratio of carbon black in the polymer phase having the highest SP value was calculated based on the following formula. The smaller this value, the more uniformly the carbon black is dispersed throughout.
(Dispersion ratio of carbon black to polymer phase with highest SP value)
= (Dispersion volume ratio of carbon black in the polymer phase having the highest SP value) / (Average dispersion volume ratio of carbon black in all phases except the polymer phase having the highest SP value)

<Carbon dispersion ratio in polymer phase with high SP value (volume%, NMR method)>
In addition to the above method, NMR also measured the dispersion volume ratio of carbon black dispersed in each polymer phase by the following method.
Specifically, the carbon black content dispersed in each rubber phase was quantified for each rubber phase from the line width of the spectrum measured by the ¹³ C-NMR DD / MAS method as described below.
Samples were prepared by blending each polymer used in Examples and Comparative Examples alone (NR, BR, ENR25) with carbon black used in the present invention in variable amounts. That is, 100% by mass of NR was used as a rubber component, and carbon black used in the present invention was blended in variable amounts to prepare a plurality of samples. Similarly, a plurality of samples each using 100% by mass of BR and ENR25 were prepared.
And the correlation of the line width of the peak in each polymer measured by < ¹³ > C-NMR and the amount of carbon black was analyzed using this sample.
For example, the attribution of the following five peaks observed in the DD / MAS ¹³ C-NMR spectrum of the vulcanized NR rubber at different carbon black blending amounts (0 to 70 phr) is as follows.
_{NR (C1) - C H 2} -C (CH 3) = CH-CH 2 -; 33ppm
NR (C2) —CH ₂ —C (CH ₃ ) ═CH—CH ₂ —; 135 ppm
_{NR (C3) -CH 2 -C (} CH 3) = C H-CH 2 -; 126ppm
_{NR (C4) -CH 2 -C (} CH 3) = CH- C H 2 -; 27ppm
_{NR (C5) -CH 2 -C (} C H 3) = CH-CH 2 -; 24ppm
As the amount of carbon black increases, the present inventors have found that the peak line width increases with a certain correlation, and using this, a correlation curve between the peak line width and the carbon black amount is created. did. (Similar correlation was observed with 5 peaks.)
The solid ¹³ C-NMR measurement conditions are as follows.
Device: Bruker Avance 400
13C resonance frequency: 100.6 MHz
MAS rotation speed: 5 kHz (± 1 Hz)
Measurement mode: DD / MAS
Measurement temperature: 25 ° C
Sample amount: A correlation curve between the peak line width and the amount of carbon black was prepared for BR and ENR25 using a method similar to ¼ capacity of the zirconia rotor. And about each vulcanized rubber slab sheet of an example and a comparative example, it measured using solid ^13C -NMR and calculated the ratio of carbon black distributed to each polymer phase using the above-mentioned correlation curve. .
According to this method, more accurate quantification is possible.

<Rolling resistance test>
A test piece for measurement was cut out from the vulcanized rubber slab sheet (each rubber composition in Table 1), and the temperature was 50 ° C., initial strain was 10%, dynamic using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho). The tan δ of each test rubber composition was measured under the conditions of a strain of 2% and a frequency of 10 Hz. The rolling resistance index of Comparative Example 3 was set to 100, and the rolling resistance characteristics were indicated by an index using the following formula. The smaller the index, the lower the rolling resistance and the better.
(Rolling resistance index) = (tan δ of each formulation / tan δ of Comparative Example 3) × 100

<Preparation of pneumatic tire>
The rubber composition prepared in each formulation shown in Table 1 is applied to the inner sidewall rubber and cushion rubber, and the rubber composition prepared in the rubber formulation in Tables 2 to 7 is tread rubber, sidewall rubber, breaker rubber, clinch rubber, The tire was applied to chafer rubber, coated rubber, and current-carrying rubber, and vulcanized by a conventional method to produce a size 195 / 65R15 pneumatic tire (test tire) having the structure shown in FIG.

Here, the basic structure of the test tire is as follows.
<Carcass ply>
Cord angle: 90 degrees in the tire circumferential direction Cord material: Polyester 1670 dtex / 2
<Breaker>
Cord angle: 24 degrees x 24 degrees in the tire circumferential direction Cord material: Steel cord (2 + 2 x 0.25)

The inner side wall rubber had a thickness of 0.5 mm, the covering rubber had a thickness of 1 mm, the cushion rubber had a thickness of 1 mm, and the current-carrying rubber had a width of 3 mm and a continuous structure in the tire circumferential direction.
Also, the contact between the covering rubber and the cushion rubber is a belt-like 5 mm width in the tire circumferential direction, the contact between the covering rubber and the energizing rubber is the entire surface of the energizing rubber in the tire width direction, and the contact between the inner side wall rubber and the cushion rubber is in the tire circumferential direction. Further, a belt-like structure having a width of 5 mm and a contact between the inner side wall rubber and the clinch rubber having a width of 5 mm or more along the carcass shape was adopted.

The following evaluation was performed using this test tire. The results are shown in Table 1.

<High-speed tire endurance test>
The test tire prepared above was subjected to a high-speed durability test, and the durability was judged based on the traveling speed (km / h) at which it was damaged. Using the tires, (1) 200 km / h-10 minutes, (2) 210 km / h-10 minutes, (3) 220 km / h-10 minutes in order, increasing the running speed in order, and damage. The running speed (km / h) was confirmed. That is, a tire that can travel to a higher speed (km / h) region is excellent in high-speed durability.

<Electric resistance of tire>
As shown in FIG. 2, the insulating plate 50 and (the electric resistance value is 10 ¹² Omega higher) plate metal installation surface is polished on a 51 (electric resistance 10Ω or less), tire rim assembly The electrical resistance value of the tire and rim assembly was measured in accordance with JATMA regulations using a measuring device including a conductive tire mounting shaft 52 for holding the tire and an electrical resistance measuring device 53. In addition, each test tire used the thing from which the mold release agent and dirt of the surface were fully removed beforehand, and fully dried. Other conditions are as follows.
Rim: Aluminum alloy 15 × 6JJ
Internal pressure: 200 kPa
Load: 5.3kN
Test environment temperature (test room temperature): 25 ° C
Humidity: 50%
Measuring range of electric resistance measuring device: 10 ^{3 to} 1.6 × 10 ¹⁶ Ω
Test voltage (applied voltage): 1000V
The test procedure is as follows.
(1) A test tire is mounted on a rim to prepare a tire / rim assembly. At this time, soapy water is used as a lubricant at the contact portion between the two.
(2) The tire / rim assembly is allowed to stand in the test room for 2 hours and then attached to the tire mounting shaft 52.
(3) The tire / rim assembly is loaded with the load for 0.5 minutes, and further for 0.5 minutes after being released and for 2 minutes after being released.
(4) When the test voltage is applied and 5 minutes have passed, the electrical resistance value between the tire mounting shaft 52 and the metal plate 51 is measured by the electrical resistance measuring device 53. The measurement is performed at four positions at 90 ° intervals in the tire circumferential direction, and the maximum value among them is taken as the electrical resistance value (measured value) of the tire.
This measurement was performed before traveling (new tire) and after traveling 20,000 km, and the common logarithm of each electric resistance value is summarized in Table 1. The common logarithm is preferably 8 or less. Further, the electrical resistance value of the tire before traveling and after traveling 20,000 km was compared, and the increase value of the electrical resistance value due to traveling 20,000 km was also shown. A lower increase value indicates that the accumulation of static electricity during tire travel can be prevented throughout the life of the tire.

<Crack resistance>
The test tire prepared above was mounted and run at 30000 km at a speed of 80 km / h and a load of 4.7 kN, and the crack growth amount of the inner-layer sidewall rubber was measured to evaluate the crack resistance performance. In addition, when the growth amount was less than 1 mm, the case where the growth amount was 1 mm or more and 5 mm or less was Δ, and the case where the growth amount was more than 5 mm was evaluated as x.

From Table 1, in all the examples, carbon black having a nitrogen adsorption specific surface area of 400 m ² / g or more is blended, the dispersion is good, the volume specific resistance as a rubber composition is low, and the tire is running. Can prevent the accumulation of static electricity. In addition to keeping the rolling resistance low, the high-speed durability was good, and the electrical resistance value of the tire not only in the initial stage but also after running 20,000 km was low and good. Moreover, the crack resistance performance in the tire was also good.

Further, in Examples 3 and 4 in which re-kneading was performed, the dispersibility of carbon black was further higher than in the corresponding Examples 1 and 2 without re-kneading, and thereby, rolling resistance characteristics and high speed were increased. Durability was further improved, and the difference in tire electrical resistance after the initial run and after running 20,000 km was also reduced. In Examples 5 and 6, equivalent volume resistivity and electrical resistance values were obtained with a smaller amount of carbon black, and the rolling resistance characteristics were further improved, albeit slightly.

Moreover, in Examples 1, 3, and 5, by blending BR, the dispersibility of carbon black was higher than in corresponding Examples 2, 4, and 6, and the rolling resistance characteristics were good. Furthermore, high-speed durability was also good.

On the other hand, carbon black is not blended in Comparative Example 1, and the volume specific resistance of the composition for inner layer sidewall rubber and cushion rubber and the electrical resistance value of the tire are very high, and the problem of static electricity accumulation cannot be solved. It was. Moreover, high-speed durability and crack resistance were also inferior.

Further, in Comparative Example 6, since carbon black having a nitrogen adsorption specific surface area of less than 400 m ² / g was blended, even when blending 30 parts by mass of the upper limit of the amount of carbon black of the present invention, the inner layer side wall rubber and cushion rubber The volume resistivity of the composition and the electrical resistance of the tire were very high, and the problem of static electricity accumulation could not be solved. By blending two or more diene rubbers (NR and BR in this case), the crack resistance performance and high-speed durability were improved, but the rolling resistance characteristics were considerably deteriorated.

In Comparative Examples 2 to 4, since only one diene rubber (NR in this case) was blended as a rubber component, the crack resistance performance was poor and the high-speed durability was very poor or somewhat poor. Further, the increase in the electrical resistance value of the tire due to running was large or somewhat large.

Further, in Comparative Examples 2 and 3, since the kneading method of carbon black having a nitrogen adsorption specific surface area of 400 m ² / g or more was not devised, its dispersion was poor, so the crack resistance performance and high-speed durability were poor. Also, the increase in the electrical resistance value of the tire was particularly large, and in Comparative Example 2, the electrical resistance value after running 20,000 km was poor even though the initial electrical resistance value was good. In Comparative Example 4, since carbon black having a nitrogen adsorption specific surface area of less than 400 m ² / g was blended, the rolling resistance characteristics were poor, and the electric resistance value after running for 20,000 km was not so good.

In Comparative Examples 4 and 5, since carbon black having a nitrogen adsorption specific surface area of less than 400 m ² / g was blended, in order to obtain volume resistivity and tire electrical resistance, an amount equal to or more than the upper limit of the specified range of 50 parts by mass. Therefore, the rolling resistance was deteriorated. Further, although a large amount of carbon black was blended, the volume resistivity of the inner layer side wall rubber and cushion rubber composition and the tire electrical resistance value were slightly high. In addition, the increase in the electrical resistance value of the tire due to running was great.

In Comparative Example 7, since the kneading method was not devised using carbon black having a nitrogen adsorption specific surface area of 400 m ² / g or more, its dispersibility was poor, and as a result, high-speed durability and crack resistance were somewhat poor. It was. In addition, the increase in electrical resistance due to traveling was very large, and even though the initial electrical resistance value was good, the electrical resistance value after traveling 20,000 km was poor.

In Comparative Example 8, carbon black having a nitrogen adsorption specific surface area of 400 m ² / g or more was used. However, contrary to the examples, since carbon kneaded with a polymer having a high SP value, carbon black was added to the polymer having a high SP value. It was unevenly distributed, and the dispersibility of carbon black was very poor. Although re-kneading was also carried out, the dispersibility of the carbon black was very poor and did not recover, and the high-speed durability, crack resistance, and rolling resistance were poor. In addition, the increase in electrical resistance due to running was even greater.

DESCRIPTION OF SYMBOLS 1 Tire 2 Chafer rubber 3 Clinch rubber 4 Cushion rubber 5 Cover rubber 6 Electric conduction rubber 7 Tread rubber 8 Side wall rubber 9 Breaker rubber 10 Carcass 11 Bead apex 12 Band 13 Bead core 14 Inner layer side wall rubber

Claims (8)

Containing 5 to 30 parts by mass of carbon black having a nitrogen adsorption specific surface area of 400 m ² / g or more with respect to 100 parts by mass of a rubber component containing two or more kinds of diene rubbers, JIS K 6812 “polyolefin pipes, joints and compounds of A rubber composition for an inner layer sidewall and / or cushion, wherein the carbon black dispersion obtained by counting aggregates is 90% or more according to “Evaluation method of pigment dispersion or carbon dispersion”. A base kneading step 1 for kneading a rubber containing a diene rubber having the lowest SP value among the two or more diene rubbers, and the carbon black;
Claim obtained by a production method comprising a kneaded product obtained by the base kneading step 1 and a base kneading step 2 for kneading a rubber containing a diene rubber having the highest SP value among the two or more kinds of diene rubbers. Item 8. The rubber composition for an inner layer sidewall and / or cushion according to Item 1. The inner layer sidewall and / or cushion rubber composition according to claim 2, obtained by a production method further comprising a re-kneading step of kneading the kneaded material obtained in the base kneading step 2 again. A pneumatic tire having an inner-layer sidewall rubber and / or cushion rubber produced using the rubber composition according to claim 1. A pneumatic tire comprising a tread portion, a sidewall portion, a bead portion, a carcass from the tread portion through the sidewall portion to the bead portion, and a breaker portion on the outer side in the tire radial direction of the carcass. And
Volume specific resistance of the tread rubber, breaker rubber and sidewall rubber respectively formed in the tread portion, the breaker portion and the sidewall portion is 1 × 10 ⁸ Ω · cm or more,
The pneumatic tire includes an inner-layer sidewall rubber disposed between the carcass and the sidewall rubber, a cushion rubber disposed in a lower region at both ends of the breaker in contact with the inner-layer sidewall rubber, and the cushion rubber. Coated rubber having a contact area and arranged to cover the upper side of the breaker part, current-carrying rubber embedded in the tread part so as to be in contact with the coated rubber and partly exposed on the surface of the tread, the inner layer side wall Provided with a bead rubber disposed in a region in contact with the rubber and in contact with the rim flange of the bead,
5. The pneumatic tire according to claim 4, wherein volume resistivity of each of the inner layer side wall rubber, the cushion rubber, the covering rubber, the energizing rubber, and the bead rubber is less than 1 × 10 ⁸ Ω · cm. The pneumatic tire according to claim 4 or 5, wherein the inner side wall rubber has a thickness of 0.2 to 1.0 mm. The pneumatic tire according to claim 5 , wherein the bead rubber is a clinch rubber or a chafer rubber. The pneumatic tire according to claim 5, wherein the conductive rubber is formed continuously in a tire circumferential direction.

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