JP6325305B2 - Pneumatic tire - Google Patents

Description

The present invention relates to a pneumatic tire.

In general, raw materials derived from petroleum resources such as butadiene rubber and carbon black are widely used in tire rubber compositions, but the regulations on the suppression of carbon dioxide emissions have been tightened, and the existing amount of petroleum is limited. In view of the limited use, it is considered to replace some or all of the raw materials derived from petroleum resources with raw materials derived from non-petroleum resources such as natural rubber, silica, white fillers such as calcium carbonate.

For example, when silica is blended in a tire member, silica has high electrical insulation and tends to increase the electrical resistance of the tire, so that static electricity tends to accumulate in the vehicle, and sparks due to static electricity are generated when refueling and the fuel is ignited. there is a possibility. Furthermore, due to the strong demand for fuel efficiency in recent years, if the use of a single case, thinner gauges on the side walls, and weight reduction of fillers are promoted, it may become more difficult to ensure the electrical conductivity (conductivity) of the tire. is there.

In addition, the steering stability deteriorates due to the single case and the thin gauge of the side wall. Therefore, it is desired to provide a tire that has good fuel efficiency, energization performance, and handling stability, and that has secured properties such as crack growth resistance.

Patent Document 1 discloses a tire that has improved conductivity and low fuel consumption by including a sidewall inner conductive layer connected to a clinch, a tread inner conductive layer having a specific composition connected to the sidewall inner conductive layer, and the like. However, there is still room for improvement in terms of improving performance such as low fuel consumption, energization performance, steering stability, and crack growth resistance.

JP 2013-6571 A

An object of the present invention is to solve the above-mentioned problems and to provide a pneumatic tire excellent in energization performance, low fuel consumption, steering stability, and crack growth resistance.

According to the present invention, the tread portion, the sidewall portion, the bead portion provided with a clinch in the region in contact with the rim, and the tread portion and the sidewall portion pass through the inside of the tire in the radial direction so as to reach the bead portion. A pneumatic tire including a carcass disposed in the tire and a breaker disposed between the tread portion and the carcass, and further connected to the clinch and the breaker, and the carcass and the sidewall portion A sidewall inner conductive layer disposed between and an electrically conductive rubber disposed to be exposed to a surface of the tread portion connected to the breaker, the clinch, the sidewall inner conductive layer, breakers and volume resistivity of the conduction rubber are both less 1 × 10 ⁸ Ω · cm, the side wall inner conductive layer A high-cis butadiene rubber (a) and a 1,2-syndiotactic polybutadiene crystal, the melting point of which is 90 to 140 ° C., and a weight average molecular weight of 50,000 to 500,000 butadiene rubber (b) The present invention relates to a pneumatic tire manufactured using a rubber composition for a sidewall inner conductive layer in which 1 to 10 parts by mass of conductive carbon black is blended with 100 parts by mass of a rubber component.

The high cis-butadiene rubber (a) preferably has a cis content of 96% by mass or more, a Mooney viscosity of 35 to 75, and a weight average molecular weight (Mw) / number average molecular weight (Mn) of 2.7 or less.
The conductive carbon black preferably has a dibutyl phthalate oil absorption of 300 ml / 100 g or more.

According to the present invention, a high-cis butadiene rubber (a) and 1,2-syndiotactic polybutadiene crystals having a melting point of 90 to 140 ° C. and a weight average molecular weight of 50,000 to 500,000 butadiene rubber ( b) and a pneumatic component having a specific structure in which a sidewall inner conductive layer in which 1 to 10 parts by mass of conductive carbon black is blended with respect to 100 parts by mass of the rubber component including Low fuel consumption, handling stability and crack growth resistance can be secured.

It is a figure which shows the upper right half of sectional drawing of the pneumatic tire of this invention.

<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 rubber positioned at an inner end of each sidewall portion. 3 and a chafer rubber 2 located at the top of the rim. A carcass 10 is bridged between the clinch and the chafer, and a breaker rubber 9 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 extending from a tread portion through a sidewall portion, and a bead apex extending from the upper end of the bead core 13 toward the sidewall. 11 is folded from the inner side to the outer side in the tire axial direction, and is locked by the folded portion. In the tire of the present invention, sufficient performance can be obtained even with the carcass 10 formed from one carcass ply. The breaker rubber 9 is composed of two or more breaker plies in which breaker cords are arranged, and the breaker cords 9 are stacked in different directions so that the breaker cords cross between the breaker plies.

Between the tread rubber 7 and the breaker rubber 9, a covering rubber (under tread) 5 is disposed inside the tread rubber 7, and a band 12 having a jointless structure is disposed inside the covering rubber 5. The current-carrying rubber 6 is disposed in the tread rubber 7 so as to be in contact with the breaker rubber 9 and partly exposed to the grounding surface. In addition, a sidewall inner conductive layer 14 having a contact region with the breaker rubber 9 and extending from at least the breaker rubber 9 to a position in contact with the clinch rubber 3 is disposed between the carcass 10 and the sidewall rubber 8. In the pneumatic tire 1, the current-carrying rubber 6, the breaker rubber 9, the sidewall inner conductive layer 14, and the clinch rubber 3 are electrically connected.

By adopting the above structure, clinch rubber located in the contact area with the rim when the tire is running, and static electricity generated in the ground contact area have a low volume resistivity, and are electrically connected to the clinch rubber 3 and sidewalls inside the tire. It is discharged to the outside of the tire through the respective conductive rubbers of the inner conductive layer 14, the breaker rubber 9 and the current-carrying rubber 6. Therefore, the electrical resistance of the tire can be reduced.

The pneumatic tire of the present invention can be used as tires for various vehicles such as passenger cars, trucks and buses, and heavy machinery.

Next, the rubber composition used for each tire member will be described.

<Side wall inner conductive layer>
The sidewall inner conductive layer 14 has a contact region with the breaker rubber 9 and is disposed between the carcass 10 and the sidewall rubber 8 at least from the breaker rubber 9 to a position in contact with the clinch rubber 3. The inner conductive layer 14 is electrically connected to the breaker rubber 9 at the upper end and the clinch rubber 3 at the lower end. The volume resistivity of the sidewall inner conductive layer 14 is 1 × 10 ⁸ Ω · cm or less, preferably 1 × 10 ⁷ Ω · cm or less, more preferably 1 × 10 ⁶ Ω · cm or less. If it is 1 × 10 ⁸ Ω · cm or less, good electrical conductivity can be obtained for the tire. The volume resistivity is preferably 1 × 10 ³ Ω · cm or more, more preferably 1 × 10 ⁴ Ω, in order to avoid an electrochemical reaction in a region where the tire is in contact with the rim and avoid the rim from being easily rusted.・ Set to cm or more.

The thickness of the sidewall inner conductive layer 14 is preferably 0.2 mm or more, more preferably 0.3 mm or more, and further preferably 0.5 mm or more, from the viewpoint of reducing the rolling resistance of the tire. Is 3.0 mm or less, more preferably 2.0 mm or less, still more preferably 1.5 mm or less. The layer thickness in the present invention is the minimum thickness.

The sidewall inner conductive layer 14 is disposed between the carcass 10 and the sidewall rubber 8 (for example, disposed on the outside of the carcass 10 and adjacent to the inside of the sidewall rubber 8), and the breaker rubber 9 and What is necessary is just to have a part which touches the clinch rubber 3. Moreover, a part may be arrange | positioned between a carcass and a breaker, and you may form continuously or discontinuously in a tire peripheral direction.

Regarding the portion where the sidewall inner conductive layer 14 is in contact with the breaker rubber 9 and the clinch rubber 3, it is preferable that the inner conductive layer 14 has a portion that is in contact with the belt at a width of 5 mm or more in the tire circumferential direction. More preferably, the contact is 10 mm or more. By bringing the inner conductive layer 14 and the breaker rubber 9 into contact with each other under the above conditions, the tire conductive effect can be sufficiently obtained. The contact with the clinch rubber 3 is preferably a portion that is in contact with the width of 5 mm or more along the carcass shape, and more preferably 10 mm or more.

The sidewall inner conductive layer 14 includes high-cis butadiene (a) and 1,2-syndiotactic polybutadiene crystals, the melting point of which is 90 to 140 ° C., and the weight average molecular weight of 50,000 to 500,000 butadiene rubber. The rubber composition for the sidewall inner conductive layer containing (b) and conductive carbon black is used.

Using high-cis butadiene (a) and butadiene rubber (b) as rubber components, and by adding a relatively small amount of conductive carbon black as a filler, the loss elastic modulus (E ″) is reduced and stored. Improved conductivity and crack growth resistance while suppressing increase in elastic modulus (E ') and increase in tan δ, resulting in energization performance, low fuel consumption, handling stability, crack growth resistance Can provide excellent tires.

As the high cis butadiene rubber (a), for example, a butadiene rubber having a cis content of 96% by mass or more, a Mooney viscosity of 35 to 75, and a weight average molecular weight (Mw) / number average molecular weight (Mn) of 2.7 or less is suitable. Can be used for

When the cis content of the high cis-butadiene rubber (a) is less than 96% by mass, the crack growth resistance improving effect tends not to be obtained.
The cis content can be measured by infrared absorption spectrum analysis.

The Mooney viscosity (Mooney viscosity ML _{1 + 4} (100 ° C.)) measured at 100 ° C. of the high-cis butadiene rubber (a) is 35 to 75, preferably 37 to 65, and more preferably 40 to 55. When the Mooney viscosity is within the above range, good fuel economy, crack growth resistance and steering stability can be obtained.
The Mooney viscosity is measured according to ISO 289 and JIS K6300.

The weight average molecular weight (Mw) / number average molecular weight (Mn) of the high cis-butadiene rubber (a) is 2.7 or less, preferably 2.5 or less, more preferably 2.3 or less. The lower limit of Mw / Mn is not particularly limited, but is preferably 1.9 or more, more preferably 2.0 or more. When Mw / Mn is within the above range, good fuel economy, crack growth resistance and steering stability can be obtained.
In the present specification, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are gel permeation chromatograph (GPC) (GPC-8000 series, manufactured by Tosoh Corporation), detector: differential refractometer, column: It calculated | required by standard polystyrene conversion based on the measured value by Tosoh Corp. TSKGEL SUPERMALTPORE HZ-M.

The vinyl content of the high-cis butadiene rubber (a) is preferably 1.8% by mass or less, more preferably 1.0% by mass or less, still more preferably 0.5% by mass or less, and particularly preferably 0.3% by mass or less. It is. When it exceeds 1.8 mass%, there exists a tendency for low-fuel-consumption property to deteriorate. The lower limit of the vinyl content is not particularly limited.
In the present specification, the vinyl content (1,2-bond butadiene unit amount) can be measured by infrared absorption spectrum analysis.

The method for preparing the high cis butadiene rubber (a) is not particularly limited, and once the desired characteristics of the high cis butadiene rubber (a) are determined, those skilled in the art can easily obtain the high cis butadiene rubber ( a) can be prepared. Among them, the high cis butadiene rubber (a) is preferably synthesized using a rare earth element-based catalyst. Thereby, the high cis-butadiene rubber (a) having the above characteristics can be more suitably prepared.

As the rare earth element-based catalyst, known catalysts can be used, and examples thereof include lanthanum series rare earth element compounds, organoaluminum compounds, aluminoxanes, halogen-containing compounds, and catalysts containing a Lewis base as necessary. Among these, an Nd-based catalyst using a neodymium (Nd) -containing compound as a lanthanum series rare earth element compound is particularly preferable.

Examples of the lanthanum series rare earth element compounds include halides, carboxylates, alcoholates, thioalcolates, amides, and the like of rare earth metals having an atomic number of 57 to 71. Among these, the use of an Nd-based catalyst is preferable in that a BR having a high cis content and a low vinyl content can be obtained.

The organoaluminum compound is represented by AlR ^a R ^b R ^c (wherein R ^a , R ^b and R ^c are the same or different and represent hydrogen or a hydrocarbon group having 1 to 8 carbon atoms). Things can be used. Examples of aluminosans include chain aluminoxanes and cyclic aluminoxanes. As the halogen-containing compound, AlX _k R ^d _3-k (wherein X is a halogen, R ^d is an alkyl group having 1 to 20 carbon atoms, an aryl group or an aralkyl group, k is 1, 1.5, 2 or 3) Aluminum halides represented by: Me ₃ SrCl, Me ₂ SrCl ₂ , strontium halides such as MeSrHCl ₂ , MeSrCl ₃ ; metal halides such as silicon tetrachloride, tin tetrachloride, titanium tetrachloride, etc. . The Lewis base is used for complexing a lanthanum series rare earth element compound, and acetylacetone, ketone, alcohol and the like are preferably used.

The rare earth element-based catalyst may be used in the state of being dissolved in an organic solvent (n-hexane, cyclohexane, n-heptane, toluene, xylene, benzene, etc.) during the polymerization of butadiene, silica, magnesia, magnesium chloride, etc. These may be used by being supported on a suitable carrier. The polymerization conditions may be either solution polymerization or bulk polymerization. The preferable polymerization temperature is -30 to 150 ° C, and the polymerization pressure may be arbitrarily selected depending on other conditions.

As the butadiene rubber (a), commercially available products such as JSR BR51, T700, BR730 manufactured by JSR Corporation, and CB24 manufactured by LANXESS may be used.

In the rubber composition for the sidewall inner conductive layer, the content of the high-cis butadiene rubber (a) in 100% by mass of the rubber component is 10% by mass or more, preferably 30% by mass or more. If it is less than 10% by mass, sufficient fuel economy and crack growth resistance may not be obtained. The content is 90% by mass or less, preferably 80% by mass or less, and more preferably 70% by mass or less. If it exceeds 90% by mass, sufficient processability and low fuel consumption may not be obtained.

The rubber composition for the sidewall inner conductive layer contains 1,2-syndiotactic polybutadiene crystal (SPB) as a rubber component together with the high-cis butadiene rubber (a), and the melting point of the crystal is 90 to 140 ° C. Yes, butadiene rubber (b) (SPB-containing BR) having a weight average molecular weight (Mw) of 50,000 to 500,000 is included.

The melting point of 1,2-syndiotactic polybutadiene crystal is 90 ° C. or higher, preferably 100 ° C. or higher, more preferably 110 ° C. or higher. The melting point is 140 ° C. or lower, preferably 130 ° C. or lower. When the melting point of SPB is within the above range, good steering stability, low fuel consumption and crack growth resistance can be obtained.

In the butadiene rubber (b), the content of 1,2-syndiotactic polybutadiene crystals is preferably 15% by mass or more, more preferably 20% by mass or more. The content is preferably 45% by mass or less, more preferably 40% by mass or less. When the SPB content is within the above range, good steering stability, low fuel consumption, and crack growth resistance can be obtained.

The weight average molecular weight (Mw) of the butadiene rubber (b) is 50,000 or more, preferably 70,000 or more, more preferably 100,000 or more, and further preferably 150,000 or more. The Mw is 500,000 or less, preferably 400,000 or less, more preferably 300,000 or less. When the Mw of the butadiene rubber (b) is within the above range, good steering stability, low fuel consumption, and crack growth resistance can be obtained.

The method for preparing the butadiene rubber (b) is not particularly limited. If the desired characteristics of the butadiene rubber (b) are determined, those skilled in the art can easily prepare the butadiene rubber (b) having the above characteristics.

As the butadiene rubber (b), commercially available products such as RB840, RB830, and RB820 manufactured by JSR Corporation may be used.

In the rubber composition for the sidewall inner conductive layer, the content of the butadiene rubber (b) in 100% by mass of the rubber component is 5% by mass or more, preferably 10% by mass or more. If it is less than 5% by mass, sufficient steering stability, fuel economy and crack growth resistance may not be obtained. The content is 40% by mass or less, preferably 35% by mass or less. If it exceeds 40% by mass, sufficient crack growth resistance may not be obtained.

In the rubber composition for the sidewall inner conductive layer, the total content of butadiene rubber (a) and butadiene rubber (b) in 100% by mass of the rubber component is preferably 30 to 90% by mass, more preferably 35 to 70% by mass. %. When the total content is within the above range, good handling stability, low fuel consumption, and crack growth resistance can be obtained.

In the rubber composition for the side wall inner conductive layer, it is preferable to blend isoprene-based rubber as the rubber component together with the butadiene rubber (a) and the butadiene rubber (b).

Examples of the isoprene-based rubber include isoprene rubber (IR), natural rubber (NR), and modified natural rubber. NR includes deproteinized natural rubber (DPNR) and high-purity natural rubber (HPNR). Modified natural rubber includes epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber. Etc. Moreover, as NR, what is common in tire industry, such as SIR20, RSS # 3, TSR20, can be used, for example. Among isoprene-based rubbers, NR is preferable because the effects of the present invention can be obtained more suitably.

In the rubber composition for a sidewall inner conductive layer, the content of isoprene-based rubber in 100% by mass of the rubber component is preferably 20% by mass or more, more preferably 30% by mass or more. The content of the isoprene-based rubber is preferably 70% by mass or less, more preferably 50% by mass or less. If it is out of the above range, sufficient steering stability, low fuel consumption and crack growth resistance may not be obtained.

The total content of the high-cis butadiene rubber (a), the butadiene rubber (b) and the isoprene-based rubber in 100% by mass of the rubber component is preferably 50% by mass or more, more preferably 75% by mass or more, and still more preferably. It is 90 mass% or more, and may be 100 mass%. When the total content is within the above range, good handling stability, low fuel consumption, and crack growth resistance can be obtained.

In the rubber composition for the sidewall inner conductive layer, as the rubber component, in addition to the high cis butadiene rubber (a), the butadiene rubber (b), and the isoprene-based rubber, for example, styrene butadiene rubber (SBR), styrene isoprene butadiene rubber ( SIBR), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR) and other diene rubbers may be used.

The rubber composition for the sidewall inner conductive layer contains conductive carbon black. Thereby, favorable electroconductivity is acquired and the effect of this invention is acquired favorably. As the conductive carbon black, commercially available products such as Lionite manufactured by Lion Co., Ltd. and Kechen Black EC600JD, EC300JD manufactured by Lion Co., Ltd. can be used.

The conductive carbon black has a dibutyl phthalate oil absorption (DBP) of preferably 300 ml / 100 g or more, more preferably 350 ml / 100 g or more. If it is less than 300 ml / 100 g, sufficient conductivity may not be imparted. The DBP of the conductive carbon black is preferably 600 ml / 100 g or less, more preferably 500 ml / 100 g or less, still more preferably 400 ml / 100 g or less. If it exceeds 600 ml / 100 g, crack growth resistance and steering stability may be lowered.
In the present specification, the DBP of carbon black is measured according to JIS K6217-4: 2001.

The nitrogen adsorption specific surface area (N ₂ SA) of the conductive carbon black is preferably 700 m ² / g or more, and more preferably 800 m ² / g or more. If it is less than 700 m < ² > / g, there exists a possibility that sufficient electroconductivity cannot be provided. The _N 2 SA is preferably at most 1200 m ² / g, more preferably at most 1100 m ² / g. If it exceeds 1200 m ² / g, fuel economy and crack growth resistance may be deteriorated.
In this specification, _N 2 SA of carbon black, JIS K 6217-2: determined by 2001.

Content of electroconductive carbon black is 1 mass part or more with respect to 100 mass parts of rubber components, Preferably it is 2 mass parts or more. If it is less than 1 part by mass, sufficient conductivity may not be imparted. Moreover, this content is 10 mass parts or less, Preferably it is 5 mass parts or less. If it exceeds 10 parts by mass, fuel economy and crack growth resistance may be reduced.

The rubber composition for the sidewall inner conductive layer preferably contains carbon black other than the conductive carbon black (hereinafter also referred to as “normal carbon black”) together with the conductive carbon black. Thereby, a favorable reinforcement property is obtained and the improvement effect of the present invention is obtained synergistically. Further, by blending conductive carbon black with normal carbon black, conductivity can be suitably imparted only by blending a small amount of conductive carbon black.

Ordinary carbon black has a nitrogen adsorption specific surface area (N ₂ SA) of preferably 20 m ² / g or more, more preferably 30 m ² / g or more. When it is less than 20 m ² / g, the reinforcing property is lowered and the desired performance tends not to be obtained. The N ₂ SA is 150 m ² / g or less, preferably 105 m ² / g or less, more preferably 60 m ² / g or less. If it exceeds 150 m ² / g, the fuel efficiency tends to deteriorate.

Ordinary carbon black has a dibutyl phthalate (DBP) oil absorption of 70 ml / 100 g or more, preferably 100 ml / 100 g or more. If it is less than 70 ml / 100 g, the reinforcing property is lowered and the desired performance may not be obtained. The DBP oil absorption is preferably 180 ml / 100 g or less, more preferably 140 ml / 100 g or less, and still more preferably 120 ml / 100 g or less. If it exceeds 180 ml / 100 g, the crack growth resistance tends to decrease.

The content of normal carbon black is preferably 20 parts by mass or more, more preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 20 parts by mass, the reinforcing property may not be ensured. The content is preferably 70 parts by mass or less, more preferably 50 parts by mass or less. If it exceeds 70 parts by mass, tan δ (rolling resistance characteristics) tends to deteriorate.

You may mix | blend a softener with the rubber composition for side wall inner side conductive layers. Examples of the softening agent include process oils such as paraffinic process oil, naphthenic process oil, and aromatic process oil (aromatic process oil). 1-30 mass parts is preferable with respect to 100 mass parts of rubber components, as for content of a softening agent, 3-20 mass parts is more preferable, and 3-10 mass parts is still more preferable.

In addition to the components described above, the rubber composition generally includes compounding agents commonly used in the production of rubber compositions, such as other reinforcing fillers, zinc oxide, stearic acid, various anti-aging agents, tackifiers, Vulcanizing agents such as wax and sulfur, vulcanization accelerators and the like can be appropriately blended.

<Bead rubber>
The bead portion has a clinch rubber 3 in a region in contact with the rim flange, and a chafer rubber 2 is also provided. When the tire travels, driving force is transmitted from the rim through the bead portion. At this time, static electricity is likely to be generated due to friction between the rim and the bead portion rubber. Since the clinch rubber 3 has a contact region with the sidewall inner conductive layer 14, static electricity is effectively discharged to the ground plane through the inner conductive layer. In FIG. 1, the clinch rubber 3 is electrically connected to the sidewall inner conductive layer 14.

Here, the volume resistivity of the clinch rubber 3 is 1 × 10 ⁸ Ω · cm or less, preferably 1 × 10 ⁷ Ω · cm or less, more preferably 1 × 10 ⁶ Ω · cm or less. By setting it to 1 × 10 ⁸ Ω · cm or less, good electrical conductivity of the tire can be obtained.

The clinching rubber 3 is made of a clinching rubber composition containing a rubber component, carbon black and the like.

In the rubber composition for clinch, examples of the rubber component include those described above, and NR, SBR, and the like can be preferably used. In this case, in the rubber composition for clinch, the content of NR is preferably 10 to 60% by mass, more preferably 20 to 40% by mass, and the content of SBR is preferably 100 parts by mass of the rubber component. 30-90 mass%, More preferably, it is 60-80 mass%.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black used for the rubber composition for clinch is preferably 40 to 120 m ² / g, more preferably 60 to 90 m ² / g. Further, the content of the carbon black is preferably 20 to 120 parts by mass, more preferably 40 to 80 parts by mass with respect to 100 parts by mass of the rubber component.

<Breaker rubber>
The breaker rubber 9 is in contact with the sidewall inner conductive layer 14 and the current-carrying rubber 6 and is disposed between the tread rubber 7 and the carcass 10 to ensure electrical conductivity, so that the volume specific resistance is 1 × 10 ⁸ Ω · cm or less. It is set. The volume resistivity is preferably 1 × 10 ⁷ Ω · cm or less, more preferably 1 × 10 ⁶ Ω · cm or less.

The breaker rubber 9 is made of a rubber composition for breakers containing a rubber component, carbon black and the like.

In the rubber composition for a breaker, examples of the rubber component include those described above, and NR or the like can be preferably used. In this case, in the rubber composition for a breaker, the content of NR is preferably 50% by mass or more, more preferably 80% by mass or more, and may be 100% by mass with respect to 100 parts by mass of the rubber component.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black used in the rubber composition for breakers is preferably 40 to 120 m ² / g, more preferably 60 to 90 m ² / g. Further, the content of the carbon black is preferably 20 to 120 parts by mass, more preferably 40 to 80 parts by mass with respect to 100 parts by mass of the rubber component.

<Electric rubber>
The current-carrying rubber 6 is embedded in the tread portion, part of which is exposed to the tire ground contact surface, and the other part is connected (contacted) with the breaker rubber 9 so that the static electricity generated during the running of the pneumatic tire is grounded. To effectively release. 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 the thickness 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 is relatively increased, which may impair the grounding characteristics. 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 conductive rubber 6 is 1 × 10 ⁸ Ω · cm or less. In the case of 1 × 10 ⁸ Ω · cm or less, the conductivity of the tire is improved and the effect of discharging static electricity is obtained. Preferably it is 1 × 10 ⁷ Ω · cm or less, more preferably 1 × 10 ⁶ Ω · cm or less.

The current-carrying rubber 6 is made of a rubber component, carbon black, and the like using a rubber composition for current-carrying rubber.

In the rubber composition for current-carrying rubber, examples of the rubber component include those described above, and SBR, BR, and the like can be suitably used. In this case, in the rubber composition for the current-carrying rubber, the SBR content is preferably 20 to 80% by mass, more preferably 50 to 70% by mass, and the BR content is preferably 100 parts by mass of the rubber component. Is 10-70 mass%, More preferably, it is 30-50 mass%.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black used for the rubber composition for the current-carrying rubber is preferably 60 to 150 m ² / g, more preferably 90 to 120 m ² / g. The carbon black content is preferably 20 to 120 parts by mass, and more preferably 40 to 70 parts by mass with respect to 100 parts by mass of the rubber component.

<Tread rubber, sidewall rubber, carcass>
The tread rubber, sidewall rubber, and carcass (carcass topping rubber) in the pneumatic tire of the present invention are composed of, for example, a rubber composition containing the following rubber components, fillers, and the like.

Examples of the rubber component include those described above. For example, NR can be suitably used for tread rubber, NR or BR can be used for sidewall rubber, and NR or SBR can be used for carcass. As the filler, carbon black, silica or the like can be used.

Even if the volume resistivity of tread rubber, sidewall rubber, and carcass is set to 1 × 10 ⁸ Ω · cm or more, while maintaining tire performance such as rolling resistance and steering stability, The volume resistivity of the clinch, breaker, and current-carrying rubber that are electrically connected to this is adjusted to be low. Therefore, static electricity generated in the pneumatic tire can be effectively discharged through the electrical connection passage formed by these. Furthermore, since the sidewall inner conductive layer having a specific composition is disposed, it is possible to obtain excellent rolling resistance characteristics, steering stability, and crack growth resistance at the same time.

The pneumatic tire of this invention is manufactured by a normal method using the rubber composition which comprises each tire member. That is, the rubber composition for each tire member blended with the above components is extruded in accordance with the shape of the tire member at an unvulcanized stage, and is molded together with other tire members by a normal method on a tire molding machine. By doing so, an unvulcanized tire is formed. The unvulcanized tire is heated and pressurized in a vulcanizer to obtain a tire.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.
The various chemicals used in the examples are described below.
<Material>
NR: TSR20
BR730: BR730 manufactured by JSR Corporation (high cis BR, BR synthesized using an Nd-based catalyst, cis content: 97% by mass, Mooney viscosity (100 ° C.): 55, Mw / Mn: 2.51, vinyl content : 0.9% by mass (equivalent to high-cis butadiene rubber (a))
BR1250H: BR1250H (low-cis butadiene rubber) manufactured by Nippon Zeon Co., Ltd.
RB840: RB840 (SPB-containing BR) manufactured by JSR Corporation (SPB crystal melting point: 126 ° C., SPB crystal content: 36 mass%, Mw: 200000 (corresponding to butadiene rubber (b)))
VCR617: UBEPOL VCR617 manufactured by Ube Industries, Ltd. (SPB-containing BR, SPB crystal melting point: 200 ° C., SPB crystal content: 17 mass%, Mw: 450,000)
RB810: RB810 manufactured by JSR Corporation (SPB-containing BR, melting point of SPB crystal: 71 ° C., SPB crystal content: 18% by mass, Mw: 200000)
BR150B: UBEPOL BR150B manufactured by Ube Industries, Ltd. (high cis BR, BR synthesized using a Ni-based catalyst, cis content: 95% by mass, Mooney viscosity (100 ° C.): 40, Mw / Mn: 2.78, Vinyl content: 2.0% by mass)
SBR1502: SBR1502 manufactured by Sumitomo Chemical Co., Ltd. (styrene content: 23.5% by mass)
Carbon Black N550: N550 manufactured by Cabot Japan Co., Ltd. (N ₂ SA: 41 m ² / g, DBP: 115 ml / 100 g)
Carbon black N220: N220 manufactured by Cabot Japan Co., Ltd. (N ₂ SA: 114 m ² / g, DBP: 114 ml / 100 g)
Carbon black N330: N330 manufactured by Cabot Japan Co., Ltd. (N ₂ SA: 75 m ² / g, DBP: 102 ml / 100 g)
Conductive carbon black: Kechen Black EC300J (DBP: 365 ml / 100 g, N ₂ SA: 800 m ² / g) manufactured by LION Co., Ltd.
Silica: Ultrasil VN3 manufactured by Degussa (N ₂ SA: 175 m ² / g)
Silane coupling agent: Si266 manufactured by Degussa
Oil: Process X-140 manufactured by Japan Energy Co., Ltd.
Anti-aging agent: NOCRACK 6C manufactured by Ouchi Shinsei Chemical Co., Ltd.
Stearic acid: Tsubaki stearic acid manufactured by NOF Corporation
Zinc oxide: Zinc oxide wax manufactured by Mitsui Mining & Smelting Co., Ltd .: Sunnock N manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Cobalt stearate: COST-S manufactured by Nikko Metal Co., Ltd.
Sulfur: Powder sulfur vulcanization accelerator manufactured by Tsurumi Chemical Co., Ltd .: Soxinol CZ manufactured by Sumitomo Chemical Co., Ltd.

<Preparation of side wall inner conductive layer, clinch rubber, breaker rubber, energizing rubber, tread rubber, side wall rubber, carcass rubber>
Ingredients shown in Tables 1 to 7 excluding sulfur and vulcanization accelerator are kneaded at 150 ° C. for 5 minutes using a closed Banbury mixer, and then added with sulfur and vulcanization accelerator to open roll. And kneaded at 80 ° C. for 3 minutes, unvulcanized side wall inner conductive layer rubber compositions A-1 to A-4, a-1 to a-14, clinch rubber composition B, breaker rubber composition C A conductive rubber composition D, a tread rubber composition E, a sidewall rubber composition F, and a carcass rubber composition G were prepared.
Each unvulcanized rubber composition was vulcanized to prepare a vulcanized rubber composition.

<Volume specific resistance of rubber composition>
Test pieces having a thickness of 2 mm and 15 cm × 15 cm were prepared using the rubber compositions A-1 to G of Tables 1 to 7, and a voltage of 500 V, an air temperature of 25 ° C., and a humidity of 50 using an electrical resistance measurement R8340A manufactured by ADVANTEST. % Was measured. The results are shown in Tables 1-7. The larger the value, the higher the volume resistivity of the rubber composition.

<Processability>
The uncured sidewall inner conductive layer rubber compositions A-1 to A-4 and a-1 to a-14 were measured for Mooney viscosity at 130 ° C. according to JIS K6300. The Mooney viscosity (ML _{1 + 4} ) of the reference comparative example was assumed to be 100, and the index was expressed by the following formula. The larger the index, the lower the Mooney viscosity and the better the processability. The results are shown in Table 1.
(Workability index) = (ML _{1 + 4} of Comparative Example 1) / (ML _{1 + 4 of} each formulation) × 100

<Viscoelasticity test>
Using a viscoelastic spectrometer VES manufactured by Iwamoto Seisakusho Co., Ltd., the loss elastic modulus and storage elastic modulus of the vulcanized rubber composition under conditions of a temperature of 70 ° C., a frequency of 10 Hz, an initial strain of 10%, and a dynamic strain of 2%. Was measured. The loss elastic modulus and the storage elastic modulus of Comparative Example 1 were set to 100, and the values were respectively indicated (low fuel consumption index and stiffness index). The greater the index, the better the fuel economy and driving stability. The results are shown in Table 1.

<Crack growth resistance test>
In accordance with the test method of “Dematcher bending crack growth test method for vulcanized rubber and thermoplastic rubber” of JIS-K6260, the sample (side wall inner conductive layer rubber composition A-1 to A-4) , A-1 to a-14), the number of times until 1 mm breakage occurred was measured, and the number of times obtained was expressed logarithmically. The larger the value, the better the crack growth resistance. The results are shown in Table 1.

(Examples and comparative examples)
The rubber compositions prepared with the rubber blends shown in Tables 1 to 7 were used in the combinations shown in Table 8, respectively, and applied to the sidewall inner conductive layer, clinch rubber, breaker rubber, energizing rubber, tread rubber, sidewall rubber, carcass rubber, A 195 / 65R15 pneumatic tire having the structure shown in FIG.

Here, the basic structure of the prototype tire is as follows.
<Carcass ply (1 sheet)>
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 sidewall inner conductive layer had a thickness of 0.5 mm, the current-carrying rubber had a width of 3 mm, and a continuous structure in the tire circumferential direction was adopted.
Also, the contact between the breaker rubber and the sidewall inner conductive layer is a belt-like width of 5 mm in the tire circumferential direction, the contact between the breaker rubber and the energized rubber is the entire surface of the energized rubber in the tire width direction, A structure with a width of 5 mm or more along the carcass shape was adopted. In addition, the side wall used what was produced by the inner side, the outer side, and clinch by extrusion.

<Tire conductivity>
The pneumatic tire produced above is mounted on a regular rim, filled with a specified internal pressure of 2.0 MPa, the tread portion is grounded to the iron plate with a load of 4.7 kN, and the volume between the tire rim portion and the iron plate at an applied voltage of 100 V. The resistance value was measured. The results are shown in Table 8.

<Rolling resistance>
The pneumatic tire produced above was mounted on a regular rim, filled with a specified internal pressure of 2.0 MPa, and the rolling resistance was measured at a speed of 80 km / h and a load of 4.7 kN using a rolling resistance tester manufactured by STL. . With respect to the rolling resistance coefficient (RRC) obtained by dividing the measured value of rolling resistance by the load, the rolling resistance of each tire was indicated by an index with Comparative Example 1 as 100 by the following formula. The larger the value, the smaller the rolling resistance and the better the performance. The results are shown in Table 8.
(Rolling resistance index) = (Rolling resistance coefficient of Comparative Example 1) / (Rolling resistance coefficient of each tire) × 100

<Crack resistance>
The 195 / 65R15 pneumatic tire produced as described above was mounted, traveled at 30000 km at a speed of 80 km / h and a load of 4.7 kN, the amount of crack growth in the sidewall inner conductive layer was measured, and the crack resistance performance was evaluated. The comparative example 1 was set to 100 and indicated as an index. The larger the value, the better the crack resistance performance. The results are shown in Table 8.

<Steering stability>
The 195 / 65R15 pneumatic tire produced above was mounted and the vehicle was run on the test course, and the steering stability was evaluated by sensory evaluation of the driver. The steering stability of Comparative Example 1 was taken as 100, and the index was displayed. The larger the value, the better the steering stability. The results are shown in Table 8.

From Tables 1 and 8, the tires of the examples in which the blends A-1 to A-4, in which a relatively small amount of conductive carbon black was added to the high-sis BR and the predetermined SPB-containing BR, were used for the sidewall inner conductive layer, Property, rolling resistance, steering stability and crack growth resistance (crack resistance) were good. On the other hand, the performance of the tire of Comparative Example 1-3 that did not use these components was inferior.

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

Claims (3)

The tread portion, the sidewall portion, the bead portion having a clinch in the region that contacts the rim, and the tread portion and the sidewall portion are arranged so as to pass through the inside in the radial direction of the tire and reach the bead portion. A pneumatic tire comprising a carcass and a breaker disposed between the tread portion and the carcass,
Further, it is connected to the clinch and the breaker, and is disposed so as to be exposed to the surface of the tread portion, connected to the side wall inner conductive layer disposed between the carcass and the sidewall portion, and the breaker. With the electrified rubber
The volume specific resistance values of the clinch, the sidewall inner conductive layer, the breaker, and the conductive rubber are all 1 × 10 ⁸ Ω · cm or less,
The sidewall inner conductive layer includes a high-cis butadiene rubber (a) and 1,2-syndiotactic polybutadiene crystal, the crystal having a melting point of 90 to 140 ° C., and a weight average molecular weight of 50,000 to 500,000. 1 to 10 parts by mass of conductive carbon black having a nitrogen adsorption specific surface area of 700 m ² / g or more and carbon black having a nitrogen adsorption specific surface area of 150 m ² / g or less to 100 parts by mass of the rubber component containing rubber (b). A pneumatic tire manufactured using a rubber composition for a sidewall inner side conductive layer containing 20 to 70 parts by mass . The high-cis butadiene rubber (a) has a cis content of 96% by mass or more, a Mooney viscosity of 35 to 75, and a weight average molecular weight (Mw) / number average molecular weight (Mn) of 2.7 or less. Pneumatic tire. The pneumatic tire according to claim 1 or 2, wherein the conductive carbon black has a dibutyl phthalate oil absorption of 300 ml / 100 g or more.

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