JP4084348B2 - Pneumatic radial tire - Google Patents

Description

  The present invention relates to a pneumatic radial tire capable of improving steering stability while maintaining crack growth resistance and riding comfort performance of a sidewall.

  In recent years, tires have been increasingly required to improve steering performance such as braking performance and riding comfort especially at high speeds. As a method for improving the braking performance of a tire, a method for increasing the longitudinal rigidity of the tire has been conventionally used, and for example, a method using a high-hardness sidewall is known.

  Patent Document 1 proposes a radial tire in which a rubber composite material layer containing organic single fibers oriented in the tire circumferential direction is arranged on a sidewall. According to the method of Patent Document 1, the rigidity in the tire circumferential direction is improved, but since the strength in the radial direction is not sufficient, it is difficult to obtain sufficient durability such as crack growth resistance.

  In Patent Document 2, the sidewall rubber is composed of an inner layer adjacent to the carcass and an outer layer that forms the outer wall surface outside the inner layer, and the inner layer includes a rubber composition including short fibers made of organic fibers. Pneumatic radial tires have been proposed. However, the organic fiber used in the method of Patent Document 2 is generally economically expensive because it is generally used by cutting a newly spun fiber for reinforcing short fibers.

Patent Document 3 uses a foamed rubber containing polybutadiene containing a predetermined amount of 1,2-syndio-polybutadiene crystals, and preferably has a complex elastic modulus E ₁ ^{* in} the circumferential direction of the tire and a complex elastic modulus in the radial direction of the tire. E ₂ ^* and the side wall to meet the ^{_{1.05 ≦ E 1 * / E 2}} * ≦ 1.25 is proposed. According to the method of Patent Document 3, the rolling resistance can be reduced and the weight can be reduced while maintaining the durability. However, since the entire sidewall is formed using the foamed rubber, in terms of cost and durability. There is room for improvement.

Patent Document 4 proposes a pneumatic radial tire in which the sidewall rubber is formed in a multilayer rubber structure, and the rubber modulus of the inner rubber layer of the sidewall rubber is set larger than the rubber modulus of the outer rubber layer. . According to the method of Patent Document 4, it is possible to improve the braking performance by increasing the longitudinal rigidity while avoiding the deterioration of the riding comfort performance, but there is still room for improvement in the crack growth resistance.
JP-A-4-191105 JP-A-6-255321 JP-A-8-85303 JP 2003-31213 A

  An object of the present invention is to solve the above-described problems and to provide a pneumatic radial tire that can improve steering stability while maintaining crack growth resistance and riding comfort performance of a sidewall.

  The present invention is a tire having two or more sidewall rubbers including at least an inner rubber layer and an outer rubber layer, wherein the tire is mounted on a rim and filled with a specified internal pressure at the tire maximum width position. The ratio E * a / E * b between the complex elastic modulus E * a in the tire circumferential direction of the inner rubber layer and the complex elastic modulus E * b in the radial direction is 1.5 or more, and the total amount of the sidewall rubber The tire relates to a tire in which the thickness of the inner rubber layer occupies 10 to 80%.

  The inner rubber layer in the present invention preferably contains paper fibers. In this case, the paper fiber is particularly preferably a kraft paper pulverized product.

  The compounding amount of the paper fiber in the inner rubber layer is preferably in the range of 3 to 30 parts by mass with respect to 100 parts by mass of the rubber component.

  In the present invention, it is preferable that the complex elastic modulus in the tire circumferential direction of the inner rubber layer is set to be larger than the complex elastic modulus in the tire circumferential direction of the outer rubber layer.

  In the present invention, under the measurement conditions of a temperature of 70 ° C., a frequency of 10 Hz, and a dynamic strain of ± 2%, the inner rubber layer has a complex elastic modulus E * a in the tire circumferential direction within a range of 5 to 40 MPa, and a radial direction. The complex elastic modulus E * b is preferably in the range of 3 to 10 MPa.

  According to the present invention, at least two or more sidewall rubbers are formed, and the rigidity is set so that the complex elastic modulus in the tire circumferential direction of the inner rubber layer is a certain level or more in relation to the complex elastic modulus in the radial direction. By doing so, it becomes possible to provide a pneumatic radial tire that maintains the crack growth resistance and the ride comfort performance while also improving the handling stability.

  The sidewall in the pneumatic tire of the present invention comprises two or more layers including at least an inner rubber layer and an outer rubber layer. The inner rubber layer has a complex elastic modulus E * a in the tire circumferential direction and a complex elastic modulus E in the radial direction. The ratio E * a / E * b to * b is 1.5 or more.

  In the present invention, the complex elastic modulus in the tire circumferential direction of the inner rubber layer is preferably set larger than the complex elastic modulus in the tire circumferential direction of the outer rubber layer. In this case, steering stability can be ensured by the contribution of the inner rubber layer having relatively high rigidity in the circumferential direction, and riding comfort performance can be ensured by the contribution of the outer rubber layer having relatively low rigidity in the radial direction. In particular, the complex elastic modulus E * a in the tire circumferential direction in the inner rubber layer is within the range of 5 to 40 MPa under the measurement conditions of a temperature of 70 ° C., a frequency of 10 Hz, and a dynamic strain of ± 2%, and the tire circumference of the outer rubber layer When the complex elastic modulus in the direction is within the range of 3 to 10 MPa under the measurement conditions of a temperature of 70 ° C., a frequency of 10 Hz, and a dynamic strain of ± 2%, it is preferable because steering stability and riding comfort performance are both excellent.

  The complex elastic modulus of the inner rubber layer and the outer rubber layer in the side wall rubber of the pneumatic tire of the present invention is measured at the tire maximum width position in a state where the tire is mounted on the rim and the specified internal pressure is filled.

  In the pneumatic tire of the present invention, the thickness of the inner rubber layer accounts for 10 to 80% of the total thickness of the sidewall rubber. If the thickness of the inner rubber layer relative to the total thickness of the sidewall rubber is 10% or more, the crack growth resistance and steering stability are good, and if it is 80% or less, the riding comfort performance is good.

  In the pneumatic tire of the present invention, it is preferable that paper fibers are blended in the inner rubber layer. Paper fiber refers to paper that has been shortened by grinding or the like. In the present invention, by adding paper fibers to the inner rubber layer, the rigidity of the inner rubber layer can be improved at low cost, and by appropriately setting the type and amount of the paper fibers, The rigidity of the inner rubber layer can be easily and arbitrarily controlled. In the inner rubber layer, the paper fiber is preferably blended within a range of 3 to 30 parts by mass with respect to 100 parts by mass of the rubber component. If the blending amount of the paper fiber is 3 parts by mass or more, the reinforcing effect of the inner rubber layer by blending the paper fiber is sufficiently obtained. If the blending amount is 30 parts by mass or less, the inner rubber layer is too hard. Deterioration of comfort performance can be prevented. The blending amount of the paper fibers is preferably 4 parts by mass or more, more preferably 5 parts by mass or more, and preferably 20 parts by mass or less, and further preferably 15 parts by mass or less.

  Paper fibers blended in the present invention include pulp obtained by pulping methods such as kraft pulp, semi-chemical pulp, mechanical pulp, non-wood pulp derived from kenaf, bagasse, bamboo, cotton, seaweed, etc., used copy It can be prepared using one or a mixture of two or more raw papers obtained from waste paper pulp obtained by deinking waste paper such as paper, old newspaper, and old corrugated paper. A paper fiber having a relatively large physical strength such as a pulverized product is preferably used. Kraft paper refers to all paper obtained by making kraft pulp (KP), and includes unbleached kraft paper and bleached kraft paper. Kraft pulp is the mainstream of those classified as chemical pulp, and since it has a relatively long fiber length, kraft paper is widely used for packaging applications and the like as paper having excellent strength. As the kraft pulp, either softwood kraft pulp or hardwood kraft pulp can be used, but softwood kraft pulp is preferable because of its relatively long fiber length.

  Kraft pulp is generally produced by the following method. First, impurities in the chip as a raw material are removed, and the thickness, length, etc. are made uniform within a certain range. Next, the chips are cooked with chemicals such as caustic soda and sodium sulfide at a high temperature of, for example, about 150 to 160 ° C. to elute mainly lignin in the chips and pulp. After passing through a washing step for separating the eluted lignin and chemicals from the pulp, the pulp is further treated with oxygen and alkali to further elute the remaining lignin in the pulp. Finally, foreign matter is removed and washed to obtain unbleached kraft pulp. Unbleached kraft pulp can be made bleached kraft pulp through a bleaching process. By making unbleached kraft pulp, unbleached kraft paper and bleached kraft pulp can be made by making paper.

  The average diameter of the paper fibers blended in the present invention is preferably in the range of 1 to 100 μm, for example, and the average length is preferably in the range of 1 to 10 μm, for example. In this case, the effect of reinforcing the inner rubber layer by the paper fibers can be sufficiently obtained, and poor dispersion of the paper fibers in the rubber composition forming the inner rubber layer can be prevented.

  The hardness of the inner rubber layer of the present invention is preferably set within a range of 60 to 80, for example. If the hardness is 60 or more, the desired degree of steering stability of the tire can be secured, and if it is 80 or less, the ride comfort is good. The hardness can be measured according to ISO-7619.

  Preferred examples of the rubber component used in the sidewall rubber of the present invention include natural rubber (NR) and / or diene synthetic rubber. Diene-based synthetic rubbers include styrene-butadiene rubber (SBR), polybutadiene rubber (BR), polyisoprene rubber (IR), ethylene-propylene-diene rubber (EPDM), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR). Butyl rubber (IIR) and the like, and rubber components containing one or more of these are preferred. The ethylene-propylene-diene rubber (EPDM) is an ethylene-propylene rubber (EPM) containing a third diene component. Examples of the third diene component include non-conjugated dienes having 5 to 20 carbon atoms such as 1,4-pentadiene, 1,4-hexadiene, 1,5-hexadiene, and 2,5-dimethyl-1,5. -Hexadiene and 1,4-octadiene, cyclic dienes such as 1,4-cyclohexadiene, cyclooctadiene, dicyclopentadiene, 5-ethylidene-2-norbornene, 5-butylidene-2-norbornene, 2-methallyl-5 Preferred examples include alkenyl norbornene such as -norbornene and 2-isopropenyl-5-norbornene. In particular, dicyclopentadiene, 5-ethylidene-2-norbornene and the like can be preferably used.

  The following components generally blended in other rubber products can be appropriately blended with the sidewall rubber in the present invention.

  As the filler, for example, silica can be blended in an amount of, for example, 5 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the rubber component. As the silica, those generally used for general-purpose rubber can be used, and examples thereof include dry method white carbon, wet method white carbon and colloidal silica used as a reinforcing material. Among these, wet method white carbon mainly containing hydrous silicic acid is preferable. If the compounding amount of silica is 5 parts by mass or more, the tire rubber composition has a satisfactory reinforcing effect by sufficiently obtaining a reinforcing effect on the tire rubber composition, and if it is 100 parts by mass or less, the tire rubber composition is used. It is possible to prevent a decrease in processability and an excessive increase in cost due to an increase in the viscosity of the unvulcanized rubber composition during the production of.

Nitrogen adsorption specific surface area (BET method) of silica used in the above, for example 50 to 300 m ² / g, it is preferably further in the range of 100 to 200 m ² / g. When the nitrogen adsorption specific surface area of silica is 50 m ² / g or more, a sufficient reinforcing effect on the tire rubber composition can be obtained, thereby improving the tire wear resistance. On the other hand, when the nitrogen adsorption specific surface area is 300 m ² / g or less, the processability of the rubber composition for tires is good, and the steering stability is sufficiently secured. Here, the nitrogen adsorption specific surface area is a value measured by the BET method according to ASTM D3037-81.

  When silica is blended in the rubber composition for tires of the present invention, a silane coupling agent, preferably a sulfur-containing silane coupling agent is blended in an amount of 1% by mass or more and 20% by mass or less with respect to the mass of silica. It is preferable. By adding a silane coupling agent, the wear resistance and steering stability of the tire can be improved. When the amount of the silane coupling agent is 1% by mass or more, the effect of improving the wear resistance and steering stability is good. Is obtained. Moreover, when the compounding quantity of a silane coupling agent is 20 mass% or less, there is little danger that the rubber | gum kneading | mixing and the burning (scorch) in an extrusion process will arise. As sulfur-containing silane coupling agents, 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyl-tetrasulfide, trimethoxysilylpropyl-mercaptobenzothiazole tetrasulfide, triethoxysilylpropyl-methacrylate-monosulfide, dimethoxymethyl Examples include silylpropyl-N, N-dimethylthiocarbamoyl-tetrasulfide, bis- [3- (triethoxysilyl) -propyl] tetrasulfide, 3-mercaptopropyltrimethoxysilane and the like.

  Other silane coupling agents include vinyltrichlorosilane, vinyltris (2-methoxyethoxy) silane, γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ- (2-aminoethyl) Aminopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and the like can be used.

  In the present invention, other coupling agents such as aluminate coupling agents and titanium coupling agents can be used alone or in combination with a silane coupling agent depending on the application.

  In addition, the sidewall rubber of the present invention may contain other fillers such as carbon black, clay, alumina, talc, calcium carbonate, magnesium carbonate, aluminum hydroxide, magnesium hydroxide, magnesium oxide, and titanium oxide alone or in combination. Can be used.

Here, the carbon black is preferably blended in an amount of 10 to 150 parts by mass with respect to 100 parts by mass of the rubber component. Here, the physical properties of carbon black are such that the nitrogen adsorption specific surface area (BET method) is in the range of 70 to 300 m ² / g, the DBP oil absorption is in the range of 5 to 300 ml / 100 g, and the iodine adsorption is in the range of 146 to 152 mg / g. The inner one is suitable in terms of the reinforcing effect on the tire rubber composition.

  In addition to the above, it is possible to add a vulcanizing agent, a vulcanization accelerator, a softening agent, a plasticizer, an anti-aging agent, a foaming agent, an anti-scorch agent, and the like to the sidewall rubber of the present invention.

  As the vulcanizing agent, an organic peroxide or a sulfur vulcanizing agent can be used. Examples of the organic peroxide include benzoyl peroxide, dicumyl peroxide, di-t-butyl peroxide, t-butyl cumyl peroxide, methyl ethyl ketone peroxide, cumene hydroperoxide, 2,5-dimethyl-2, 5-di (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne- 3 or 1,3-bis (t-butylperoxypropyl) benzene, di-t-butylperoxy-diisopropylbenzene, t-butylperoxybenzene, 2,4-dichlorobenzoyl peroxide, 1,1-di- t-butylperoxy-3,3,5-trimethylsiloxane, n-butyl-4,4 And the like can be used di -t- butyl peroxy valerate. Of these, dicumyl peroxide, t-butylperoxybenzene and di-t-butylperoxy-diisopropylbenzene are preferred. Moreover, as a sulfur type vulcanizing agent, sulfur, morpholine disulfide, etc. can be used, for example. Of these, sulfur is preferred.

  Vulcanization accelerators include sulfenamide, thiazole, thiuram, thiourea, guanidine, dithiocarbamic acid, aldehyde-amine or aldehyde-ammonia, imidazoline, or xanthate vulcanization accelerators. Those containing at least one of them can be used.

  Examples of the sulfenamide system include CBS (N-cyclohexyl-2-benzothiazylsulfenamide), TBBS (Nt-butyl-2-benzothiazylsulfenamide), N, N-dicyclohexyl-2- Examples thereof include sulfenamide compounds such as benzothiazylsulfenamide, N-oxydiethylene-2-benzothiazylsulfenamide, and N, N-diisopropyl-2-benzothiazolesulfenamide.

  Examples of the thiazole type include MBT (2-mercaptobenzothiazole), MBTS (dibenzothiazyl disulfide), sodium salt of 2-mercaptobenzothiazole, zinc salt, copper salt, cyclohexylamine salt, 2- (2,4-dinitro). Phenyl) mercaptobenzothiazole, 2- (2,6-diethyl-4-morpholinothio) benzothiazole and the like.

  Examples of thiurams include TMTD (tetramethylthiuram disulfide), tetraethylthiuram disulfide, tetramethylthiuram monosulfide, dipentamethylenethiuram disulfide, dipentamethylenethiuram monosulfide, dipentamethylenethiuram tetrasulfide, dipentamethylenethiuram hexasulfide. , Tetrabutyl thiuram disulfide, pentamethylene thiuram tetrasulfide and the like.

  Examples of thiourea compounds include thiourea compounds such as thiacarbamide, diethyl thiourea, dibutyl thiourea, trimethyl thiourea, and diortolyl thiourea.

  Examples of guanidine compounds include guanidine compounds such as diphenyl guanidine, diortolyl guanidine, triphenyl guanidine, orthotolyl biguanide, and diphenyl guanidine phthalate.

  Examples of dithiocarbamate include zinc ethylphenyldithiocarbamate, zinc butylphenyldithiocarbamate, sodium dimethyldithiocarbamate, zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate, zinc diamyldithiocarbamate, zinc dipropyldithiocarbamate , Complex salt of zinc pentamethylenedithiocarbamate and piperidine, zinc hexadecyl (or octadecyl) isopropyldithiocarbamate, zinc dibenzyldithiocarbamate, sodium diethyldithiocarbamate, piperidine pentamethylenedithiocarbamate, selenium dimethyldithiocarbamate, tellurium diethyldithiocarbamate, diamyl Di, such as cadmium dithiocarbamate Such Okarubamin acid compounds.

  Examples of the aldehyde-amine system or aldehyde-ammonia system include acetaldehyde-aniline reaction product, butyraldehyde-aniline condensate, hexamethylenetetramine, acetaldehyde-ammonia reaction product, and the like.

  As the anti-aging agent, amine-based, phenol-based, and imidazole-based compounds, carbamic acid metal salts, waxes, and the like can be appropriately selected and used.

  In the present invention, a softener may be used in combination in order to further improve kneading processability. Softeners include process oil, lubricating oil, paraffin, liquid paraffin, petroleum asphalt, petroleum jelly such as petroleum jelly, fatty oil softener such as castor oil, linseed oil, rapeseed oil, coconut oil, tall oil, , Waxes such as beeswax, carnauba wax and lanolin, and fatty acids such as linoleic acid, palmitic acid, stearic acid and lauric acid.

  Furthermore, a plasticizer can be blended in the sidewall rubber of the present invention as necessary. Specifically, DMP (dimethyl phthalate), DEP (diethyl phthalate), DBP (dibutyl phthalate), DHP (diheptyl phthalate), DOP (dioctyl phthalate), DINP (diisononyl phthalate), DIDP (phthalate) Acid diisodecyl), BBP (butyl benzyl phthalate), DLP (dilauryl phthalate), DCHP (dicyclohexyl phthalate), hydrophthalic anhydride, DOZ (di-2-ethylhexyl azelate), DBS (dibutyl sebacate), DOS (Dioctyl sebacate), acetyl triethyl citrate, acetyl tributyl citrate, DBM (dibutyl maleate), DOM (2-ethylhexyl maleate), DBF (dibutyl fumarate) and the like.

  For the side wall rubber of the present invention, as a scorch preventing agent for preventing or delaying scorch, for example, organic acids such as phthalic anhydride, salicylic acid, benzoic acid, nitroso compounds such as N-nitrosodiphenylamine, N-cyclohexylthiophthalimide Etc. can be used.

  FIG. 1 is a diagram illustrating the right half of a cross-sectional view of a pneumatic tire according to the present invention. The tire 1 includes a tread portion 2, a pair of sidewall portions 3 extending inward in the tire radial direction from both ends thereof, and a bead portion 4 positioned at an inner end of each sidewall portion 3. A carcass 5 is bridged between the bead portions 4 and 4, and a belt layer 6 having a tagging effect is disposed on the outer side in the radial direction of the carcass 5.

  The carcass 5 is formed of one or more carcass plies in which carcass cords are arranged at an angle of, for example, 70 to 90 ° with respect to the tire equator C. The carcass plies are beaded from the tread portion 2 through the sidewall portion 3. Around the bead core 7 of the portion 4 is folded back from the inner side to the outer side in the tire axial direction and is locked by the turned-up portion 5a.

  The belt layer 6 includes two or more belt plies in which belt cords are arranged at an angle of, for example, 45 ° or less with respect to the tire equator, and the belt cords are stacked in different directions so that the belt cords cross each other. . Further, a band layer (not shown) may be provided outside the belt layer 6. At this time, the band layer is formed by a continuous ply spirally wound with a low modulus organic fiber cord substantially parallel to the tire equator.

  In the present invention, the side wall portion 3 has a structure of two or more layers having at least the inner rubber layer 3a and the outer rubber layer 3b, and the inner rubber layer is formed using a predetermined rubber composition. It is possible to improve the steering stability while maintaining the crack growth resistance of the wall and the riding comfort performance. The structure of the pneumatic tire according to the present invention is not limited to that described above.

[Example]
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

  Of the blending components shown in Table 1, the components excluding sulfur and the vulcanization accelerator were kneaded at about 150 ° C. for 5 minutes using a banbury, and further added with sulfur and the vulcanization accelerator and about 80 using a biaxial open roll. A rubber composition was obtained by kneading at 5 ° C. for 5 minutes. A rubber sheet was produced using the rubber composition, molded as a tire sidewall, and vulcanized under conditions of 150 ° C., 30 minutes, 25 kgf (245.16625N) to produce a test tire.

(Complex modulus)
A strip sample having a width of 4 mm, a length of 30 mm, and a thickness of 1.5 mm was prepared, and a tire was used with a viscoelastic spectrometer manufactured by Iwamoto Seisakusho Co., Ltd. under conditions of a temperature of 70 ° C., a frequency of 10 Hz, and a dynamic strain of ± 2%. The complex elastic modulus was measured in the circumferential direction and the radial direction. The results are shown in Table 1.

(Flexible crack growth resistance)
In accordance with a flex crack test according to JIS-K6260, the crack growth property was tested using a dematcher flex crack tester. In the test, a sample was cut out from the tire, a prescribed crack was given, the number of bendings required for the crack to grow by 1 mm was measured, and the conventional example 1 was indicated as an index. The results are shown in Table 1.

(Maneuvering stability)
Wear tires of size 195 / 65R15 on the car, run at 40-100 km / h on the test course, evaluate steering stability by feeling test of steering wheel response, rigidity and grip, and ride comfort performance Evaluation was performed. The evaluation was performed based on the following criteria with a maximum of 5 points, and the average value of the three drivers was represented by an index with the conventional example 1 as 100. Larger values indicate better handling stability and ride comfort. The results are shown in Table 1.
5 points: Very good.
4 points: Good.
3 points: normal.
2 points: Slightly inferior.
1 point: Inferior.

Note 1: NR is “RSS # 3” made in Thailand.
Note 2: BR is “BR150B” manufactured by Ube Industries.
Note 3: N550 is “Seast SO” manufactured by Tokai Carbon Co., Ltd.
Note 4: Paper fiber is “Mill Five # 100” manufactured by Sankyo Flour Mills.
Note 5: Anti-aging agent 6C is “Ozonon 6C” manufactured by Seiko Chemical Co., Ltd.
Note 6: Wax is “Sannokk Wax” manufactured by Ouchi Shinsei Chemical Co., Ltd.
Note 7: Aroma oil is “Diana Process AH40” manufactured by Idemitsu Kosan Co., Ltd.
Note 8: Stearic acid is “paulownia” manufactured by NOF Corporation.
Note 9: Zinc oxide is “Ginbae R” manufactured by Toho Zinc Co., Ltd.
Note 10: Sulfur is manufactured by Tsurumi Chemical.
Note 11: The vulcanization accelerator is “Noxeller NS” (Nt-butyl 2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Co., Ltd.

  From the results shown in Table 1, Comparative Example 1 in which the ratio E * a / E * b of the complex elastic modulus E * a in the tire circumferential direction and the complex elastic modulus E * b in the radial direction in the inner rubber layer is smaller than 1.5 Compared with Comparative Example 3 and Comparative Example 2 in which the thickness of the inner rubber layer occupies 90% of the total thickness of the sidewall rubber, a sidewall comprising the inner rubber layer and the outer rubber layer according to the present invention was provided. In Examples 1 to 5, the crack growth resistance and the ride comfort were not lowered, but the steering stability was remarkably improved.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  An object of the present invention is to provide a pneumatic radial tire capable of improving the steering stability while maintaining the crack growth resistance and the like of the sidewall and the riding comfort performance.

It is the figure which illustrated the right half of the sectional view of the pneumatic tire concerning the present invention.

Explanation of symbols

  1 tire, 2 tread portion, 3 sidewall portion, 3a inner rubber layer, 3b outer rubber layer, 4 bead portion, 5 carcass, 5a folded portion, 6 belt layer, 7 bead core.

Claims (5)

A tire having two or more sidewall rubbers including at least an inner rubber layer and an outer rubber layer, wherein the inner rubber layer is in a tire maximum width position in a state where the tire is mounted on a rim and filled with a specified internal pressure. with paper fibers are blended, the ratio E * a / E * b of the complex elastic modulus E * b in the tire circumferential direction of the complex elastic modulus E * a and the radial direction of the inner rubber layer is located at least 1.5 A pneumatic radial tire in which the inner rubber layer occupies 10 to 80% of the total thickness of the sidewall rubber. The pneumatic radial tire according to claim 1 , wherein in the inner rubber layer, paper fibers are blended within a range of 3 to 30 parts by mass with respect to 100 parts by mass of the rubber component. The pneumatic radial tire according to claim 1 , wherein the paper fiber is a pulverized kraft paper. The pneumatic radial tire according to claim 1, wherein a complex elastic modulus E * a of the inner rubber layer in the tire circumferential direction is set to be larger than a complex elastic modulus of the outer rubber layer in the tire circumferential direction. Under the measurement conditions of a temperature of 70 ° C., a frequency of 10 Hz, and a dynamic strain of ± 2%, the complex elastic modulus E * a in the tire circumferential direction of the inner rubber layer is in the range of 5 to 40 MPa, and the complex elastic modulus E in the radial direction. The pneumatic radial tire according to claim 1, wherein * b is in a range of 3 to 10 MPa.

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