JP2003253045A - Pneumatic radial tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire provided with a tread rubber composition which satisfies all of rolling resistance, bursting resistance, and abrasion resistance at high levels. <P>SOLUTION: The pneumatic radial tire is the one provided with a tread, a side wall, and a bead part, wherein the tread is of a laminate structure composed of a base rubber layer provided on the interior circumference side and a cap rubber layer provided on the exterior circumference side, the base layer being composed of a rubber composition containing (A) a rubber component containing at least 10 wt.% diene copolymer rubber having (a) ethylenically unsaturated nitrile monomer units (b) aromatic vinyl monomer units, and (c) conjugated monomer units and containing 5-45 wt.% units (a) and 10-50 wt.% units (b) based on the total amount of units (a), (b), and (c), and (B) at least one filler selected from carbon black and a white filler. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a pneumatic tire. More specifically, the present invention uses, as a rubber component of the tread base rubber layer, a conjugated diene-based copolymer rubber having a nitrile group having an improved affinity with a reinforcing filler, and has excellent running durability. It relates to a pneumatic radial tire.

[0002]

2. Description of the Related Art In recent years, the demand for low fuel consumption of automobiles has become more severe in response to the worldwide movement of carbon dioxide emission regulations accompanying the social demand for energy saving and the growing concern about environmental problems. It's starting. In order to meet such demands, it has been required to reduce rolling resistance in tire performance. As a method of reducing the rolling resistance of a tire, the most common method is to use a tire / tread with a cap / base composite structure and to use rubber advantageous for rolling resistance in the base rubber layer.

By the way, in order to obtain a rubber composition having a low heat build-up, many technical developments have been made so far to enhance the dispersibility of the filler used in the rubber composition. Among them, in particular, as a rubber component, a method of modifying the polymerization active terminal of a diene-based modified polymer obtained by anionic polymerization using an organolithium compound with a functional group having an interaction with a filler,
It is becoming the most popular, but due to the strong interaction between the polymer terminal functional group and silica, the dispersion of filler particles such as silica is insufficient, and therefore the reinforcing effect that the filler originally has. There was a problem that was not obtained enough.
On the other hand, as a filler for a rubber composition having a low heat generation property, a method of using silica instead of carbon black which has been generally used up to now has already been performed. However,
Silica particles tend to agglomerate due to hydrogen bonds of silanol groups, which are surface functional groups, and it is necessary to prolong the kneading time in order to improve the dispersion of silica particles in rubber. Further, in recent years, along with the high horsepower, high performance, and long life of automobiles, it is required for tires to have a high level of rolling resistance, fracture resistance, and wear resistance. Furthermore, it is desired to maintain these performances from the early stages of tire running to the middle and final stages.

[0004]

SUMMARY OF THE INVENTION The present invention provides a pneumatic radial tire having a tread rubber composition that satisfies all of rolling resistance, fracture resistance and wear resistance at high levels under such circumstances. It is intended to be provided.

[0005]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have found that a rubber component containing a specific conjugated diene copolymer rubber having a nitrile group as a tread base rubber. It was found that the object can be achieved by using. The present invention has been completed based on such findings.

That is, the present invention relates to a pneumatic tire having a tread, a sidewall and a bead portion,
The tread has a laminated structure composed of a base rubber layer arranged on the inner peripheral side and a cap rubber layer arranged on the outer peripheral side, and the base rubber layer is composed of (A) (a) ethylenically unsaturated nitrile monolayer. Having a monomer unit, (b) an aromatic vinyl monomer unit, and (c) a conjugated diene monomer unit, and based on the total amount of the above (a), (b) and (c) units ,
A rubber component containing at least 10% by weight of a diene copolymer rubber having (a) a unit of 5 to 45% by weight and (b) a unit of 10 to 50% by weight, and (B) at least a carbon black and a white filler. A pneumatic radial tire comprising a rubber composition containing a kind of filler.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the pneumatic radial tire of the present invention, the tread is composed of a base rubber layer and a cab rubber layer. Here, in the base rubber layer,
As the component (A), a rubber component containing the following conjugated diene-based copolymer rubber is used. The conjugated diene-based copolymer rubber comprises (A) (a) an ethylenically unsaturated nitrile monomer unit, (b) an aromatic vinyl monomer unit, and (c) a conjugated diene monomer unit. In addition, based on the total amount of the units (a), (b) and (c), it contains 5 to 45% by weight of the unit (a). When the content of the ethylenically unsaturated nitrile unit which is the unit (a) is less than 5% by weight, the dispersibility of the filler becomes poor, and the abrasion resistance, low heat generation property and fracture property may not be sufficiently improved. On the other hand, if this content exceeds 45% by weight, the glass transition point (Tg) of the conjugated diene-based copolymer rubber becomes too high, and the properties as a rubber elastic body are lost. The preferred content of this ethylenically unsaturated nitrile unit is 8 to 35% by weight, especially 9 to 2
0% by weight is preferred.

The content of the aromatic vinyl monomer unit which is the unit (b) is 10 to 50% by weight. If this content is less than 10% by weight, the abrasion resistance of the vulcanized rubber obtained may be insufficient, while if it exceeds 50% by weight, the rolling resistance of the vulcanized rubber obtained becomes large,
Tan tan tends to increase. The more preferable content of the aromatic vinyl monomer unit is 10 to 40% by weight.
Examples of the monomer forming the ethylenically unsaturated nitrile monomer unit include acrylonitrile and methacrylonitrile. Of these, acrylonitrile is preferable. These monomers may be used alone or in combination of two or more. Further, as the monomer forming the aromatic vinyl monomer unit,
For example, styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, α-methylstyrene, 2,
4-Dimethylstyrene, 2,4-diisopropylstyrene, 4-tert-butylstyrene, tert-butoxystyrene and the like can be mentioned, but among these, styrene is particularly preferable. These monomers may be used alone or in combination of two or more.

Further, examples of the monomer forming the conjugated diene monomer unit include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene and chloroprene. Of which 1,3-
Butadiene and isoprene are particularly preferred. These monomers may be used alone or in combination of two or more. If necessary, the conjugated diene-based copolymer rubber may be obtained by copolymerizing various ester-based monomers in addition to the above-mentioned monomers. Examples of the ester-based monomer include methyl (meth) acrylate,
Ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-
(Meth) such as amyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate and cyclohexyl (meth) acrylate
Examples thereof include acrylates and vinyl esters such as vinyl acetate. The content of the monomer unit formed from these ester-based monomers can be a ratio in the range that does not impair the properties of the conjugated diene-based copolymer rubber, but with respect to the total amount of the monomer unit. It is preferably 20% by weight or less. Examples of the conjugated diene-based copolymer rubber of the present invention include acrylonitrile-butadiene-styrene copolymer and the like.

The glass transition point of the conjugated diene-based copolymer rubber varies depending on the composition ratio of the monomers used.
STM D3418-82 (Peapproved 1
988), when measured by a differential scanning calorimeter (DSC) according to 988), -70 to 0 ° C is preferable, and further -60 to
It is preferably −10 ° C. Further, the difference between the extrapolation start temperature and the extrapolation end temperature of the glass transition is preferably 20 ° C or lower, more preferably 18 ° C or lower, and further preferably 15 ° C.
C. or lower, particularly preferably 13.degree. C. or lower. The lower limit is usually 5 ° C. When this temperature difference exceeds 20 ° C., the tan δ of the vulcanized rubber obtained also becomes large, which is not preferable. Further, it is preferable that the content of the monomer unit (a) is 9 to 20% by weight, and the difference between the extrapolation start temperature and the extrapolation end temperature of the glass transition is 13 ° C. or less, particularly 10 ° C. or less. .

Here, the extrapolation start temperature and extrapolation end temperature of the glass transition are ASTM D3418-82 (Peapp).
differential scanning calorimeter (DS)
According to C), it is measured as follows. That is,
The extrapolation start temperature is approximately the temperature between the straight line extending the low temperature side baseline and the inflection point P ₁ on the low temperature side and the inflection point P ₂ on the high temperature side in the temperature rising curve of the DSC shown in FIG. The extrapolation end temperature was determined as the temperature at the intersection of the straight line L and the extended straight line, and the extrapolation end temperature was obtained by extending the straight line L and the straight line extending the high temperature side baseline in the DSC heating curve shown in FIG. Obtained as the temperature at the point where the line intersects.

The Mooney viscosity [ML _{1 + 4} (100 ° C.)] of the conjugated diene-based copolymer rubber used in the present invention is 20 to 20.
0 is preferable, and 30 to 150 is more preferable. If the Mooney viscosity is less than 20, the vulcanized rubber obtained may have reduced wear resistance.
If it exceeds 0, the processability of the rubber composition containing the conjugated diene-based copolymer rubber may decrease. The weight average molecular weight of polystyrene of the conjugated diene copolymer rubber measured by GPC (gel permeation chromatography) is preferably 100,000 or more, particularly preferably 100,000 to 2,000.
It is 000. If this weight average molecular weight is less than 100,000, the abrasion resistance of the vulcanized rubber obtained tends to decrease, and tan δ may increase. on the other hand,
If it exceeds 2,000,000, the processability of the rubber composition containing the conjugated diene-based copolymer rubber may be lowered. This weight average molecular weight can be controlled during polymerization by using a chain transfer agent represented by alkyl mercaptan which is generally used in radical polymerization.

The conjugated diene-based copolymer rubber is produced by polymerizing the above-mentioned various essential monomers and optionally an ester-based monomer in a water-based medium by using a radical polymerization initiator. You can The polymerization method is not particularly limited, but emulsion polymerization is usually preferable. Emulsion polymerization may be a general method, for example, by emulsifying a predetermined monomer in an aqueous medium in the presence of an emulsifier, initiating polymerization with a radical polymerization initiator, and when a predetermined polymerization conversion rate is reached. A method of stopping the polymerization with a polymerization terminator can be mentioned.

In the present invention, the method of charging the above-mentioned ethylenically unsaturated nitrile monomer is important, and it is preferable to divide and add it to the polymerization system. It is preferable to add a part of the monomer before starting the polymerization and to add the rest intermittently or continuously to the polymerization system in the polymerization process.
Further, after the polymerization conversion rate of the total amount of the monomers charged measured during the polymerization is 10 to 95%, preferably 20 to 80%, the rest of the monomers are collectively or divided, Alternatively, it is preferable to add them continuously. When the whole amount of the monomer is charged into the polymerization system before the polymerization is initiated and copolymerized, the difference between the starting temperature and the ending temperature of the glass transition of the copolymer rubber tends to be larger than 20 ° C. Is not preferable. The initial charge amount of the monomer before the start of polymerization is preferably 20 with respect to the total amount of the monomer used.
˜95% by weight, more preferably 20 to 90% by weight, still more preferably 30 to 85% by weight.

As the emulsifier, an anionic surfactant,
Examples include nonionic surfactants, cationic surfactants and amphoteric surfactants. Further, a fluorinated surfactant can also be used. As these emulsifiers, anionic surfactants are frequently used, for example, capric acid, lauric acid, myristic acid, palmitic acid, oleic acid,
In addition to potassium salts or sodium salts of long-chain fatty acids having 10 or more carbon atoms such as stearic acid, rosin acid salts and the like can be used.

Radical polymerization initiators include benzoyl peroxide, lauroyl peroxide and tert.
-Butyl hydroperoxide, cumene hydroperoxide, paramenthane hydroperoxide, di-te
Organic peroxides such as rt-butyl hydroperoxide and dicumyl peroxide can be used. Further, an azo compound represented by azobisisobutyronitrile, an inorganic peroxide represented by potassium persulfate, and a redox catalyst represented by a combination of these peroxides and ferrous sulfate are used. You can also These radical polymerization initiators may be used alone or in combination of two or more.

In order to control the molecular weight of the conjugated diene copolymer rubber, a chain transfer agent such as alkyl mercaptans such as tert-dodecyl mercaptan and n-dodecyl mercaptan may be used as a chain transfer agent. Polymerization is carried out using a reactor from which oxygen is removed
It can be carried out at 0 ° C, and the polymerization temperature is particularly preferably 0 to 80 ° C. The polymerization system may be a continuous system or a batch system, and the polymerization temperature and the like or the operating conditions such as stirring and the like can be appropriately changed during the reaction. As the polymerization terminator, amine compounds such as hydroxylamine and diethylhydroxylamine can be used.
After the termination of the polymerization, the conjugated diene-based copolymer rubber latex was coagulated as a crumb from the produced conjugated diene-based copolymer rubber latex, the crumb was washed, dehydrated, and then dried with a dryer or the like to obtain a conjugated diene-based rubber. It can be a copolymer rubber.

Further, the conjugated diene-based copolymer rubber may contain an extending oil. In this case, the content of the extending oil is 100 parts by weight of the conjugated diene-based copolymer rubber. It is usually 10 to 60 parts by weight, preferably 20 to 50 parts by weight. If the amount of the extender oil is less than 10 parts by weight, the processability is not sufficiently improved, and if it exceeds 60 parts by weight, the amount ratio of the extender oil blended according to the required processability etc. at the time of preparing the rubber composition becomes large. It is not preferable because it is limited.
The Mooney viscosity [ML _{1 + 4} (100
[Deg.] C)] is preferably 20 to 180, particularly preferably 30.
~ 150. The extender oil is not particularly limited, and examples thereof include aromatic oils, naphthene oils, and paraffin oils. These may use only 1 type and may use 2 or more types together. Among these, aromatic extender oils are particularly preferable.

In the rubber composition used in the present invention, it is necessary that the conjugated diene-based copolymer rubber is contained in an amount of 10% by weight or more as the rubber component of the component (A). If this content is less than 10% by weight, a rubber composition having desired physical properties cannot be obtained, and the object of the present invention cannot be achieved. The content of the conjugated diene-based copolymer rubber in the rubber component is preferably 35% by weight or more, and particularly preferably 50 to 100% by weight. Examples of the rubber component used in combination with the conjugated diene-based copolymer rubber include natural rubber and diene-based synthetic rubber. Examples of the diene-based synthetic rubber include styrene-butadiene copolymer (SBR) and polybutadiene (B).
R), polyisoprene (IR), butyl rubber (II
R), ethylene-propylene copolymers and mixtures thereof. Of these, polybutadiene is preferred.

Next, as the component (B), carbon black or a white filler may be used alone, or a combination of carbon black / white filler may be used. Here, the carbon black is not particularly limited, and any carbon black can be selected and used from those conventionally used as a reinforcing filler for rubber. Examples of this carbon black include FEF and S
RF, HAF, ISAF, SAF and the like can be mentioned. Carbon black having an iodine adsorption amount (IA) of 60 mg / g or more and a dibutyl phthalate oil absorption amount (DBP) of 80 ml / 100 g or more is preferable. By using this carbon black, the effect of improving various physical properties becomes large, but especially HAF, I having excellent wear resistance is obtained.
SAF and SAF are preferred. On the other hand, although carbon black is usually used as a reinforcing agent, any carbon black generally used in the rubber industry can be used.

The white filler is not limited in its use as long as it has been conventionally used in the rubber industry. Examples of the white filler include silica, alumina, aluminum hydroxide, clay, calcium carbonate and the like. More preferably, the nitrogen adsorption specific surface area (N ₂ SA) is 190 to 300 m ² /
g silica or nitrogen adsorption specific surface area (N ₂ SA) is 1
Aluminum hydroxide of -20 m ² / g is preferred. As aluminum hydroxide having such N ₂ SA,
For example, there is a commercially available product as "Hijilite"[trademark; manufactured by Showa Denko KK]. The silica is not particularly limited and may be arbitrarily selected from those conventionally used as a reinforcing filler for rubber. Examples include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), calcium silicate, and aluminum silicate. Among them, the effect of improving fracture properties and the effect of achieving both wet grip and low rolling resistance are the most effective. Wet silica, which is prominent, is preferred.

Here, the total amount of the carbon black as the component (B) and the white filler is preferably 40 to 120 parts by weight per 100 parts by weight of the rubber. Outside of this range, it is difficult to obtain a rubber composition having the desired physical properties, and the object of the present invention may not be achieved. The total amount of carbon black and the white filler is preferably 100 parts by weight or less from the viewpoint of the compounding effect and the physical properties. Further, the white filler is preferably 20% by weight or more in the filler as the component (B), and more preferably 40 to 70% by weight. In the rubber composition used for the tire of the present invention, if desired,
A silane coupling agent can be blended as the component (C). The silane coupling agent is not particularly limited, and known silane coupling agents conventionally used in rubber compositions such as bis (3-triethoxysilylpropyl) polysulfide, γ-mercaptopropyltriethoxysilane, γ-aminopropyl are used. Triethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, N-
β (aminoethyl) -γ-aminopropyltrimethoxysilane or the like can be used.

The compounding amount of the silane coupling agent optionally used is usually 1 to 20 with respect to the filler.
It is selected within the range of weight%. If this amount is less than 1% by weight, it is difficult to sufficiently exert the effect as the coupling agent,
Further, if it exceeds 20% by weight, gelation of the rubber component may be caused. From the viewpoints of the effect as a coupling agent and the prevention of gelation, the preferable amount of the silane coupling agent is in the range of 5 to 15% by weight. In the rubber composition, if desired, various chemicals other than the above, which are usually used in the rubber industry, such as a vulcanizing agent, a vulcanization accelerator, an antiaging agent, and a scorch preventive agent, are used as long as the object of the present invention is not impaired. Agents, zinc white, stearic acid, etc. may be contained.

The tread portion of the pneumatic tire according to the present invention is composed of a composite rubber layer that divides into at least two parts, and the inner rubber layer on the belt layer side thereof has a rubber containing at least 10% by weight of the above diene copolymer rubber. It comprises a rubber composition containing components and a filler of carbon black or a white filler. Tire tread cap /
The base structure is not particularly limited and will be exemplified and described below. 2 to 4 are partial cross-sectional views of the tread according to the present invention. The carcass 1 and the belt portion 2 arranged in the circumferential direction at the crown portion of the carcass 1. The tread portion 3 is provided with a cap rubber layer 3a provided on the outer side in the tire radial direction and an inner side in the tire radial direction. And the base rubber layer 3b.

Here, the position of the upper surface of the base rubber layer (3b) between the grooves of the tread may be below the height of the groove bottom over the entire width of the tread (FIG. 2). The rubber layer (3b) may be corrugated so that its upper surface is higher than the groove bottom height (FIG. 3).
Further, the base rubber layer (3b) may have a structure in which a part of the base rubber layer (3b) is exposed on the tread surface in the tread central region (FIG. 4). In particular, in the structures of FIGS. 3 and 4, even after the middle period when the cap rubber is worn, due to the excellent properties of the base rubber layer in the present invention, it is possible to maintain the initial tire performance for a long time without at least degrading it. it can.

[0026]

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Various measurements on the vulcanized rubber were made by the following methods. (1) Rolling resistance The rolling resistance test was carried out in accordance with the Japan Automotive Tire Association (JATMA) regulation, and Comparative Example 1 was set as 100 and indicated as an index. The larger the number, the better. (2) Destruction resistance In accordance with JIS K6252, a tearing test was performed in an atmosphere of 100 ° C., and Comparative Example 1 was set to 100 and displayed as an index. The larger the number, the better. (3) Abrasion resistance prototype tires were mounted on passenger cars (Mark II, Soarer), and a running test of 50000 km was carried out in urban areas and on mountain slopes under a load equivalent to two passengers. Tread residual groove after running Was measured. For the measurement of the residual groove, the average value of 10 points on the circumference of the groove near the center was used, and Comparative Example 4 was set to 1
It was displayed as an index as 00. The larger the number, the better.

Production Example 1 (NSBR: Non-oil-extended conjugated diene rubber A) 200 parts by weight of water and 4.5 parts of rosin acid soap were placed in a polymerization vessel.
Parts by weight, 80 parts by weight of butadiene, 12 parts by weight of styrene, and 5 parts by weight of acrylonitrile were charged. Then, the temperature of the polymerization vessel was set to 5 ° C., and p-menthane hydroperoxide as a radical polymerization initiator was adjusted to 0.
03 parts by weight of ethylenediaminetetraacetic acid sodium salt was added.
02 parts by weight, 0.01 parts by weight of ferrous sulfate heptahydrate, and 0.02 parts of sodium formaldehyde sulfoxylate.
Polymerization was started by adding 3 parts by weight. Polymerization conversion rate is 30%
Then, 3 parts by weight of acrylonitrile was further added, and when the conversion of polymerization reached 60%, diethylhydroxylamine was added to terminate the polymerization. Then
Unreacted monomer is recovered by steam stripping,
A conjugated diene rubber latex was obtained. Then, this was solidified with sulfuric acid and sodium chloride to give crumb. Next, this crumb was dried by a hot air dryer to obtain a non-oil extended conjugated diene rubber A (NSBR). The conjugated diene rubber contained in the latex has a Mooney viscosity of 50, an acrylonitrile unit content of 10% by weight, a styrene unit content of 11% by weight, and a weight average molecular weight of 450,000.
0, the glass transition point was −60 ° C., and the difference between the extrapolation start temperature and the extrapolation end temperature of the glass transition was 12 ° C.

Production Example 2 (SBR: Non-oil-extended conjugated diene rubber B) 200 parts by weight of water and 4.5 parts of rosin acid soap were placed in a polymerization container.
Parts by weight, 72 parts by weight of butadiene and 28 parts by weight of styrene were charged. Then, the temperature of the polymerization vessel was set to 5 ° C., and as a radical polymerization initiator, 0.03 parts by weight of p-menthane hydroperoxide, 0.02 parts by weight of sodium ethylenediamine tetraacetate, and ferrous sulfate 7 hydrate were used. 0.01 part by weight of the product and 0.03 part by weight of sodium formaldehyde sulfoxylate were added to initiate polymerization.
When the conversion of the polymerization reached 60%, diethylhydroxylamine was added to terminate the polymerization. Then, unreacted monomers were recovered by steam stripping to obtain a conjugated diene rubber latex. Then, it is coagulated and dried in the same manner as in Production Example 1, and the non-oil extended conjugated diene rubber B (S
BR) was obtained. The conjugated diene rubber contained in the latex has a Mooney viscosity of 49 and a styrene unit content of 23.5.
% By weight, weight average molecular weight 440,000, glass transition point was -61 ° C.

Examples 1 to 4 and Comparative Examples 1 to 4 As rubber components, in the Examples, NSBR according to Production Example 1 was used.
In the comparative example, a rubber composition was prepared by using the SBR produced in Production Example 2 according to the formulation shown in Table 1. This rubber composition was vulcanized at 160 ° C. for 15 minutes, and the physical properties of the vulcanized rubber were measured. The results are shown in Table 1.

[0030]

[Table 1]

[Note] 1) Butadiene rubber: BR01 (trademark; manufactured by JSR, non-oil extended rubber) 2) Carbon black: ISAF grade, manufactured by Tokai Carbon Co., Ltd. 3) Silane coupling agent: "Si69" trademark, 4) Vulcanization accelerator DPG: diphenylguanidine 5) Vulcanization accelerator CZ: N-cyclohexyl-2-benzothiazolylsulfenamide 6) Vulcanization accelerator DM: Dibenzothiazyl disulfide In Example 1 and Example 1, carbon black was blended as a filler, and in Comparative Examples 1-5 and Examples 2-5, silica and carbon black were blended together as a filler. It is recognized that Examples 1 to 4 are extremely excellent in both rolling resistance and fracture resistance when compared with the corresponding Comparative Examples 1 to 4.

Example 5 and Comparative Example 5 A rubber composition was prepared according to the formulation shown in Table 1.
This rubber composition was vulcanized at 160 ° C. for 15 minutes,
The physical properties of the vulcanized rubber were measured. The results are shown in Table 1. Further, the above rubber composition was applied to the base rubber having the tread structure shown in FIG. 4, and tires of size 195 / 65R15 were manufactured by a conventional method. In this tire, the base rubber layer is disposed so as to be exposed on the tread surface in the central region of the tread, the belt layer has two steel cord layers, and the one layer layer covering the belt layer is used. It is a radial tire provided with (not shown). This prototype tire was subjected to an actual running test by the method described above to evaluate its wear resistance. The results are shown in Table 1. As a result of the above, it can be seen that Example 5 has not only improved rolling resistance and fracture resistance but also excellent abrasion resistance as compared with Comparative Example 5.

[0033]

INDUSTRIAL APPLICABILITY According to the present invention, as a tread base rubber, by applying a specific conjugated diene-based copolymer rubber having a nitrile group having an improved affinity with a reinforcing filler, rolling resistance and resistance are improved. It is possible to obtain a pneumatic radial tire that satisfies a high level of breaking performance and wear resistance.

[Brief description of drawings]

FIG. 1 is a DSC chart showing how to determine an extrapolation start temperature and an extrapolation end temperature of a glass transition of a conjugated diene-based copolymer rubber according to the present invention.

FIG. 2 is a partial cross-sectional view of a tire to which the present invention is applied.

FIG. 3 is a partial cross-sectional view of another tire to which the present invention is applied.

FIG. 4 is a partial cross-sectional view of another tire to which the present invention is applied.

[Explanation of symbols]

1: Carcass 2: Belt 3: Todd section 3a: Cap rubber layer 3b: Base rubber layer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hajime Kondo             3-1-1 Ogawa Higashi-cho, Kodaira-shi, Tokyo Stock market             Bridgestone Technology Center F term (reference) 4J002 AC081 BC061 BG101 BN141                       DA036 DE147 DE237 DJ017                       DJ037 FD017 GN01

Claims (10)

[Claims] 1. A pneumatic tire including a tread, a sidewall and a bead portion, wherein the tread has a laminated structure including a base rubber layer disposed on an inner peripheral side and a cap rubber layer disposed on an outer peripheral side. In addition, the base rubber layer has (A) (a) an ethylenically unsaturated nitrile monomer unit, (b) an aromatic vinyl monomer unit, and (c) a conjugated diene monomer unit. And based on the total amount of the above (a), (b) and (c) units, at least 5 to 45% by weight of the (a) unit and 10 to 50% by weight of the (b) unit of the diene copolymer rubber. A pneumatic radial tire comprising a rubber composition containing 10% by weight of a rubber component and (B) at least one kind of filler selected from carbon black and a white filler. 2. The conjugated diene-based copolymer rubber has a glass transition temperature of −70 to 0 ° C. and a Mooney viscosity [ML _{1 + 4} (10
0 ° C.)] 20 to 200. The pneumatic radial tire according to claim 1. 3. The pneumatic radial tire according to claim 1, wherein the conjugated diene polymer rubber has a difference between the extrapolation start temperature and the extrapolation end temperature of the glass transition of 20 ° C. or less. 4. The pneumatic radial tire according to claim 1, wherein the conjugated diene-based copolymer rubber is a copolymer of acrylonitrile, styrene and butadiene. 5. The white filler is 20% by weight in the component (B).
The pneumatic radial tire according to any one of claims 1 to 4, which is as described above. 6. The pneumatic radial tire according to claim 1, wherein the white filler as the component (B) is silica. 7. The filler as the component (B) is a rubber component 100.
The pneumatic radial tire according to any one of claims 1 to 6, which is 40 to 120 parts by weight per part by weight. 8. Further, for the filler of the component (B),
(C) The pneumatic radial tire according to any one of claims 1 to 7, which contains 1 to 20% by weight of a silane coupling agent. 9. The pneumatic tire according to claim 1, wherein the base rubber layer is arranged between the tread grooves in the tire width direction so that the uppermost surface position of the rubber layer is higher than the groove bottom height. Radial tires. 10. The pneumatic radial tire according to claim 1, wherein the base rubber layer has a structure exposed on the tread surface in the middle region of the tread width direction.