JP2010143293A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire in which a run-flat durability and a high-speed durability under a normal state are improved and eccentric wears at the central part and both ends of a tread are restricted. <P>SOLUTION: This pneumatic tire comprises a bead part 1, a carcass layer 4 extending through both sides 2 up to both beads 1, a belt ply 8 of at least two or more layers, a peripheral belt reinforcing ply 9, and a side reinforcing rubber ply 5. The peripheral belt reinforcing ply 9 is divided into three areas of a central area 9A and both side areas 9B, a cord constituting both side areas 9B is a polyketone fiber cord having several filament twisted bundles of polyketone, wherein the polyketone fiber cord fulfills formula (I): σ≥-0.01E+1.2 and formula (II): σ≥0.02 and cords constituting a central area A are organic fiber cords having a lower tensile strength at the time of extension by 2% at 150°C as compared with that of polyketone fiber, and a higher tensile strength at the time of extension by 2% at 25°C. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a pneumatic tire (hereinafter, also simply referred to as “tire”), and more specifically, air in which run-flat durability and normal high-speed durability are improved and uneven wear at the center and both ends of a tread is suppressed. Related to tires.

  In a conventional run flat tire, a structure in which a crescent-shaped side reinforcing rubber is arranged inside a tire radius of a carcass layer in a side portion is common. In the run-flat tire, since side reinforcing rubber is present, there is a problem that the contact pressure at both ends (shoulder portions) is increased due to the small amount of deflection in the side region, and high-speed durability is deteriorated. Further, the side reinforcing rubber is generally disposed under the steel belt, and heat storage increases due to traveling at the end of the steel belt, which is highly distorted during high-speed traveling, which contributes to deterioration of high-speed durability.

  In addition, when traveling in a puncture state (internal pressure: 0 kPa), the steel belt layer is in a buckling state (the center part is lifted from the grounding surface and the vehicle weight is held only at both ends), and the vehicle weight is held. The ground contact pressure at both ends (shoulder region) is increased, deteriorating run-flat durability. As described above, in the run flat tire, it has been a problem to achieve both high-speed durability when not punctured and run-flat durability during puncturing.

Furthermore, for the purpose of achieving both a high level of run-flat durability and ride comfort, a method of using a cord made of polyketone fiber having a large heat shrinkage stress as the material of the radial ply has been proposed (for example, Patent Documents 1 and 2). This is intended to improve the case holding force by utilizing the high heat shrinkage stress when the entire side portion generates heat by the run flat running.
JP 2006-321275 A JP 2007-253826 A

  On the other hand, in recent years, suppression of uneven wear is also required from the viewpoint of improving tire durability. As a countermeasure, it is conceivable to increase the number of belts installed and improve the rigidity of the tire center. However, increasing the number of belts leads to an increase in tire weight, resulting in a new problem that leads to deterioration in fuel consumption.

  Accordingly, an object of the present invention is to provide a pneumatic tire in which run-flat durability and normal high-speed durability are improved and uneven wear at the center and both ends of the tread is suppressed.

  As a result of intensive studies to solve the above problems, the present inventor has found that the above problems can be solved by setting the circumferential belt reinforcing layer to a predetermined configuration, and has completed the present invention.

That is, the pneumatic tire of the present invention includes a pair of left and right bead portions, a carcass layer extending from the crown portion to both bead portions through both side portions, and at least two belt layers on the outer side in the tire radial direction of the carcass layer. And a circumferential belt reinforcing layer on the outer side in the tire radial direction of the belt layer, and a side reinforcing rubber layer having a crescent-shaped meridional section over the entire region or almost the entire region of both side portions along the inner side of the carcass layer. In pneumatic tires,
The circumferential belt reinforcing layer is divided into three regions, a central region and both side regions, and a plurality of filament bundles made of polyketone are twisted by the cords constituting the circumferential belt reinforcing layer both side regions Polyketone fiber cord, wherein the polyketone fiber cord has the following formulas (I) and (II),
σ ≧ −0.01E + 1.2 (I)
σ ≧ 0.02 (II)
Where σ is the heat shrinkage stress (cN / dtex) at 177 ° C. and E is the elastic modulus (cN / dtex) at 49 N load at 25 ° C.
The cord constituting the central region of the circumferential belt reinforcing layer has a smaller tensile strength at 2% elongation at 150 ° C. and a larger tensile strength at 2% elongation at 25 ° C. compared to the polyketone fiber. It is an organic fiber cord.

  Here, the heat shrinkage stress σ at 177 ° C. of the polyketone fiber cord is obtained by heating a 25 cm long fixed sample of the polyketone fiber cord before vulcanization subjected to a general dip treatment at a heating rate of 5 ° C./min. The stress generated in the cord at 177 ° C, and the elastic modulus E at 49N load at 25 ° C of the polyketone fiber cord is a unit calculated from the tangent at 49N of the SS curve according to the JIS cord tensile test. Elastic modulus at cN / dtex.

  In the present invention, both side regions of the circumferential belt reinforcing layer extend at least 2 mm or more outside the end of the belt layer in the tire width direction, and both side region lengths of the circumferential belt reinforcing layer are 10 The organic fiber cord is preferably aramid or a composite cord composed of aramid and nylon.

  According to the present invention, it is possible to provide a pneumatic tire that can improve run-flat durability and normal-time high-speed durability, and suppress uneven wear at the center and both ends of the tread.

DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a partial cross-sectional view of a preferred example of the pneumatic tire of the present invention. The tire shown in FIG. 1 has a pair of left and right bead portions 1 and a pair of side portions 2, and a tread portion 3 connected to both side portions 2, and extends between the pair of bead portions 1 in a toroidal shape. A carcass layer composed of one or more carcass plies 4 that reinforce each of the parts 1, 2, and 3 and a pair of crescent-shaped side reinforcing rubber layers 5 arranged inside the carcass ply 4 of the side part 2 are provided.

  In the illustrated tire, a bead filler 7 is disposed on the outer side in the tire radial direction of each of the ring-shaped bead cores 6 embedded in the bead portion 1, and the outer side in the tire radial direction of the tread portion of the carcass ply 4. A belt 8 composed of two belt layers is disposed in the belt. Further, a circumferential belt reinforcing layer 9 is disposed so as to cover the entire belt 8 outside the belt 8 in the tire radial direction. Here, the belt layer is usually composed of a rubberized layer of a cord extending in an inclined manner with respect to the tire equatorial plane, preferably a rubberized layer of a steel cord, and the two belt layers constitute the belt layer. The belt 8 is formed by laminating the cords so as to cross each other with the equator plane interposed therebetween. The circumferential belt reinforcing layer 9 is usually composed of a rubberized layer of cords arranged substantially parallel to the tire circumferential direction.

In the present invention, the circumferential belt reinforcing layer 9 is divided into three regions, a central region 9A and both side regions 9B. Further, the cord constituting both side regions B of the circumferential belt reinforcing layer 9 is a polyketone fiber cord obtained by twisting a plurality of filament bundles made of polyketone, and the polyketone fiber cord has the following formulas (I) and (II),
σ ≧ −0.01E + 1.2 (I)
σ ≧ 0.02 (II)
It is important that σ is a heat shrinkage stress (cN / dtex) at 177 ° C., and E is an elastic modulus (cN / dtex) at a load of 49 N at 25 ° C.

  If cords made of polyketone fibers that satisfy the above requirements are installed at both ends of the crown, the cord shrinkage stress will increase if the temperature inside the tire at the belt ends rises during both high-speed running and run-flat running. As the temperature increases, the belt expands in the circumferential direction at both ends, and the belt expansion can be suppressed. As a result, the circumferential tension at both ends increases, and high-speed durability can be improved by reducing the contact pressure at the belt end, and run-flat durability can be improved by suppressing belt buckling.

  As shown in FIG. 2, the circumferential belt reinforcing layer 9 has only one layer (a), two layers and two layers for the polyketone layer disposed in the both side regions 9B in consideration of tire wear performance, actual vehicle maneuverability, and the like. A structure in which the layer width is the same (b), two layers and one layer width is narrower than the other one layer (c) can be employed as appropriate. Thereby, compatibility with other performances becomes possible. For example, in a tire with a narrow tire width, a buckling suppression effect can be sufficiently obtained with one layer, but on the contrary, a tire with a wide tire width, a tire with a speed symbol of W range or more, etc. can be applied with a two-layer structure. The effect of the present invention is exhibited. Further, in a tire in which a two-layer structure is desirable, a technique in which one layer width is narrower than the other one layer in consideration of wear is also effective.

  If the cord to be used does not satisfy the relationship of the above formula (I), the use of a cord having a large heat shrinkage stress σ but a low elastic modulus E sufficiently suppresses the deflection of the tire during run-flat running. If a cord with a high elastic modulus E but a small heat shrinkage stress σ is used, the vertical spring of the tire during normal running increases, and the tire during normal running The ride comfort is worse. Further, when the heat shrinkage stress σ at 177 ° C. of the cord to be used is less than 0.02 cN / dtex, the amount of deflection at the time of run-flat running becomes large and the run-flat durability distance becomes insufficient.

  Here, the polyketone fiber cord preferably has a heat shrinkage stress σ at 177 ° C. of 1.5 cN / dtex or less. When the heat shrinkage stress σ of polyketone fiber cords at 177 ° C exceeds 1.5 cN / dtex, the shrinkage force during vulcanization becomes too large, resulting in the damage of the cord inside the tire and the placement of the rubber. It will cause deterioration of sex and uniformity. The polyketone fiber cord preferably has a heat shrinkage stress σ at 177 ° C. of 0.20 cN / dtex or more from the viewpoint of sufficiently suppressing deformation of the tire during run flat running. From the viewpoint of surely suppressing deformation of the heat shrinkage stress σ at 177 ° C. is more preferably 0.30 cN / dtex or more, and further preferably more than 0.4 cN / dtex. In addition, the effect which suppresses the deformation | transformation of the tire at the time of run flat running is so high that heat contraction stress (sigma) is high. Further, the polyketone fiber cord preferably has an elastic modulus E at a load of 49 N at 25 ° C. of 30 cN / dtex or more from the viewpoint of sufficiently suppressing deformation of the tire during run flat running. From the viewpoint of reliably suppressing the deformation of the tire, the elastic modulus E at a load of 49 N is more preferably 80 cN / dtex or more. Furthermore, the polyketone fiber cord preferably has an elastic modulus E at a load of 49 N at 25 ° C. of 170 cN / dtex or less from the viewpoint of sufficiently ensuring fatigue resistance, and from the viewpoint of improving fatigue resistance. More preferably, the elastic modulus E at a load of 49 N is 150 cN / dtex or less.

［式中、Ｎは撚り数（回／１０ｃｍ）で、ρはコードの比重（ｇ／ｃｍ^３）で、Ｄはコードの総デシテックス数（ｄｔｅｘ）である］で定義される撚り係数（Ｎｔ）が０．２５以上であることが好ましい。ポリケトン繊維コードの撚り係数（Ｎｔ）が０．２５未満では、疲労性が低下して、耐久性が不足する。 The polyketone fiber cord used for both side regions 9B of the circumferential belt reinforcing layer is represented by the following formula (III),

Where N is the number of twists (times / 10 cm), ρ is the specific gravity of the cord (g / cm ³ ), and D is the total decitex number (dtex) of the cord. Is preferably 0.25 or more. When the twist coefficient (Nt) of the polyketone fiber cord is less than 0.25, the fatigue property is lowered and the durability is insufficient.

  In both side regions 9B of the circumferential belt reinforcing layer of the pneumatic tire of the present invention, the number of driven polyketone fiber cords is preferably in the range of 5 to 60 (lines / 50 mm). When the number of polyketone fiber cords driven in both side regions 9B of the circumferential belt reinforcing layer is less than 5 (lines / 50 mm), the tire deflection during run-flat running cannot be sufficiently suppressed, and the tire run-flat durability However, if it exceeds 60 (50 / 50mm), the vertical spring of the tire during normal driving will rise, and the riding comfort of the tire during normal driving will deteriorate. Tend to.

  Moreover, it is preferable that the polyketone fiber cord used for the both side regions 9B of the circumferential belt reinforcing layer is formed by twisting two or three filament bundles made of polyketone having a fineness of 500 to 2000 dtex. If the fineness of the filament bundle used for the polyketone fiber cord is less than 500 dtex, both the elastic modulus and the heat shrinkage stress are insufficient, and if it exceeds 2000 dtex, the cord diameter becomes thick and the driving cannot be made dense. In addition, even if the number of filament bundles made of polyketone is 4 or more, there is no particular limitation as long as the relationship of the above formulas (I) and (II) can be satisfied.

  The polyketone fiber cord used for both side regions 9B of the circumferential belt reinforcing layer preferably has a reversibility that shrinks at a high temperature and expands when returned to room temperature. In this case, the rigidity increases as the polyketone fiber cords in the both side regions 9B of the circumferential belt reinforcing layer contract during high-temperature running, that is, during run-flat running, so that the rigidity increases and the deflection of the sidewall portion 2 of the tire can be suppressed. Up, at low temperature, that is, during normal running, the polyketone fiber cords in both side regions 9B of the circumferential belt reinforcing layer 9 tend to stretch, the rigidity is lowered, the tire's longitudinal spring is lowered, and the tire is running during normal running. Deterioration of ride comfort can be suppressed. Further, by using a reversible polyketone fiber cord having a difference in heat shrinkage stress between 20 ° C. and 177 ° C. of 0.20 cN / dtex or more, preferably 0.25 cN / dtex or more, during normal running and run flat running Both effects can be achieved.

で表される繰り返し単位から実質的になるポリケトンが好ましい。また、該ポリケトンの中でも、繰り返し単位の９７モル％以上が１−オキソトリメチレン［−ＣＨ_２−ＣＨ_２−ＣＯ−］であるポリケトンが好ましく、９９モル％以上が１−オキソトリメチレンであるポリケトンが更に好ましく、１００モル％が１−オキソトリメチレンであるポリケトンが最も好ましい。 Both side regions 9B of the circumferential belt reinforcing layer 9 of the pneumatic tire of the present invention are formed by coating a polyketone fiber cord obtained by twisting a plurality of filament bundles made of polyketone with a coating rubber. As the polyketone, the following formula (IV),

A polyketone substantially consisting of repeating units represented by Among the polyketones, a polyketone in which 97 mol% or more of repeating units is 1-oxotrimethylene [—CH ₂ —CH ₂ —CO—] is preferable, and polyketone in which 99 mol% or more is 1-oxo trimethylene. Is more preferable, and a polyketone in which 100 mol% is 1-oxotrimethylene is most preferable.

  The polyketone as the raw material of the polyketone fiber cord may be partially bonded with ketone groups and with unsaturated compounds. However, the unsaturated compound-derived portions and ketone groups are alternately arranged. Is preferably 90% by mass or more, more preferably 97% by mass or more, and most preferably 100% by mass.

  In the formula (IV), the unsaturated compound forming A is most preferably ethylene, but propylene, butene, pentene, cyclopentene, hexene, cyclohexene, heptene, octene, nonene, decene, dodecene, styrene, acetylene. , Unsaturated hydrocarbons other than ethylene, such as allene, methyl acrylate, methyl methacrylate, vinyl acetate, acrylamide, hydroxyethyl methacrylate, undecenoic acid, undecenol, 6-chlorohexene, N-vinylpyrrolidone, diethyl ester of sulphonylphosphonic acid , A compound containing an unsaturated bond, such as sodium styrenesulfonate, sodium allylsulfonate, vinylpyrrolidone, and vinyl chloride.

［式中、ｔ及びＴは、純度９８％以上のヘキサフルオロイソプロパノール及び該ヘキ
サフルオロイソプロパノールに溶解したポリケトンの希釈溶液の２５℃での粘度管の流過時間であり；Ｃは、上記希釈溶液１００ｍＬ中の溶質の質量（ｇ）である］で定義される極限粘度［η］が１〜２０ｄＬ／ｇの範囲にあることが好ましく、２〜１０ｄＬ／ｇの範囲にあることが更に好ましく、３〜８の範囲にあることがより一層好ましい。極限粘度が１ｄＬ／ｇ未満では、分子量が小さ過ぎて、高強度のポリケトン繊維コードを得ることが難しくなる上、紡糸時、乾燥時及び延伸時に毛羽や糸切れ等の工程上のトラブルが多発することがあり、一方、極限粘度が２０ｄＬ／ｇを超えると、ポリマーの合成に時間及びコストがかかる上、ポリマーを均一に溶解させることが難しくなり、紡糸性及び物性に悪影響が出ることがある。 Furthermore, as a polymerization degree of the said polyketone, following formula (V),

[Wherein t and T are the flow times of a viscosity tube at 25 ° C. of a diluted solution of hexafluoroisopropanol having a purity of 98% or more and a polyketone dissolved in the hexafluoroisopropanol; The intrinsic viscosity [η] defined by the solute mass (g) is preferably in the range of 1 to 20 dL / g, more preferably in the range of 2 to 10 dL / g, More preferably, it is in the range of 8. If the intrinsic viscosity is less than 1 dL / g, the molecular weight is too small to obtain a high-strength polyketone fiber cord, and troubles such as fluff and yarn breakage occur frequently during spinning, drying and stretching. On the other hand, if the intrinsic viscosity exceeds 20 dL / g, it takes time and cost to synthesize the polymer, and it becomes difficult to uniformly dissolve the polymer, which may adversely affect the spinnability and physical properties.

  As the method for fiberizing the polyketone, (1) after spinning an unstretched yarn, performing multi-stage heat stretching, and stretching at a specific temperature and magnification in the final stretching step of the multi-stage heat stretching, (2 ) A method in which after the undrawn yarn is spun, hot drawing is performed, and the fiber after completion of the hot drawing is rapidly cooled with high tension applied. A desired filament suitable for production of the polyketone fiber cord can be obtained by fiberizing the polyketone by the method (1) or (2).

  Here, the spinning method of the unstretched yarn of the polyketone is not particularly limited, and a conventionally known method can be employed. Specifically, JP-A-2-112413, JP-A-4-228613, Wet spinning method using an organic solvent such as hexafluoroisopropanol and m-cresol as described in JP-A-4-505344, WO99 / 18143, WO00 / 09611, JP2001-164422 No., JP-A No. 2004-218189, JP-A No. 2004-285221, and the wet spinning method using an aqueous solution of zinc salt, calcium salt, thiocyanate, iron salt, etc., among these, A wet spinning method using an aqueous solution of is preferred.

  For example, in the wet spinning method using an organic solvent, a polyketone polymer is dissolved in hexafluoroisopropanol, m-cresol, or the like at a concentration of 0.25 to 20% by mass, extruded from a spinning nozzle to be fiberized, and then toluene, ethanol, isopropanol , N-hexane, isooctane, acetone, methyl ethyl ketone, etc., the solvent can be removed and washed in a non-solvent bath to obtain a polyketone undrawn yarn.

  On the other hand, in the wet spinning method using an aqueous solution, for example, a polyketone polymer is dissolved in an aqueous solution of zinc salt, calcium salt, thiocyanate, iron salt or the like at a concentration of 2 to 30% by mass, and a spinning nozzle is formed at 50 to 130 ° C. Then, it is extruded into a coagulation bath and subjected to gel spinning, followed by desalting and drying to obtain an undrawn polyketone yarn. Here, in the aqueous solution in which the polyketone polymer is dissolved, it is preferable to use a mixture of zinc halide and a halogenated alkali metal salt or a halogenated alkaline earth metal salt. An organic solvent such as an aqueous solution, acetone, or methanol can be used.

  Further, as a drawing method of the obtained undrawn yarn, a hot drawing method in which the undrawn yarn is heated and drawn to a temperature higher than the glass transition temperature of the undrawn yarn is preferable. The method (2) may be carried out in one stage, but it is preferably carried out in multiple stages. There is no restriction | limiting in particular as this heat drawing method, For example, the method etc. which run a thread | yarn on a heating roll or a heating plate are employable. Here, the heat stretching temperature is preferably in the range of 110 ° C. to (the melting point of the polyketone), and the total stretching ratio is preferably 10 times or more.

  When polyketone fiberization is carried out by the method of (1) above, the temperature in the final stretching step of the multistage hot stretching is in the range of 110 ° C. to (the stretching temperature of the stretching step one step before the final stretching step). Moreover, the draw ratio in the final drawing step of multistage hot drawing is preferably in the range of 1.01 to 1.5 times. On the other hand, when polyketone fiberization is carried out by the method of (2) above, the tension applied to the fiber after completion of the hot drawing is preferably in the range of 0.5 to 4 cN / dtex, and the cooling rate in rapid cooling is 30 The cooling end temperature in the rapid cooling is preferably 50 ° C. or less. Here, the method for rapidly cooling the heat-stretched polyketone fiber is not particularly limited, and a conventionally known method can be adopted. Specifically, a cooling method using a roll is preferable. In addition, since the polyketone fiber obtained in this way has a large residual elastic strain, it is usually preferable to perform relaxation heat treatment so that the fiber length is shorter than the fiber length after hot drawing. Here, the temperature of the relaxation heat treatment is preferably in the range of 50 to 100 ° C., and the relaxation ratio is preferably in the range of 0.980 to 0.999 times.

  The polyketone fiber cord is formed by twisting a plurality of filament bundles made of the polyketone, preferably two or three strands. For example, the filament bundle made of the polyketone is twisted, and then a plurality of the bundles are joined together. By applying an upper twist in the opposite direction, it can be obtained as a twisted cord having a double twist structure.

  A cord / rubber composite used for the reinforcing cord layer can be obtained by coating the polyketone fiber cord obtained as described above with a coating rubber. Here, there is no restriction | limiting in particular as coating rubber of a polyketone fiber cord, The coating rubber used for the cord / rubber composite for the conventional tire can be used. Prior to coating the polyketone fiber cord with the coating rubber, the polyketone fiber cord may be subjected to an adhesive treatment to improve the adhesion to the coating rubber.

  Further, in the present invention, the cord constituting the central region 9A of the circumferential belt reinforcing layer 9 has a smaller tensile strength at 2% elongation at 150 ° C. than the polyketone fiber used for both side regions B, It is also important that the organic fiber cord has a large tensile strength at 2% elongation at 25 ° C. During normal running, in high-performance tires, as a cord for the circumferential belt reinforcing layer 9A, by using a cord having higher elasticity than the polyketone cord used for both side regions B at room temperature (25 ° C.), By suppressing the protrusion of the center portion, it is possible to improve the high-speed durability and suppress the wear difference (uneven wear) between the center portion and both sides. In the present invention, the tensile strength at the time of 2% elongation at 150 ° C. of the cord constituting the central region 9A of the circumferential belt reinforcing layer 9 is preferably 25 to 50 N, and 2% at 25 ° C. The tensile strength during stretching is preferably 100 to 300N.

  FIG. 3 shows an elongation-strong correlation image of an aramid cord, an aramid and nylon composite cord, and a polyketone (PK) cord at room temperature (25 ° C.). As shown in the figure, the aramid cord and the composite cord of aramid and nylon have a high tensile strength at 2% elongation at 25 ° C. Therefore, an aramid cord and a composite cord of aramid and nylon can be preferably used in the present invention.

  In the present invention, both side regions 9B of the circumferential belt reinforcing layer 9 extend at least 2 mm or more outward in the tire width direction at the end of the belt layer 8, and both side regions 9B of the circumferential belt reinforcing layer 9 are It is preferable that it is 10-50 mm. This considers the influence on other performance such as wear performance and actual vehicle handling performance.

  The pneumatic tire of the present invention is only required to satisfy the above requirements, and the details and materials of the tire structure other than the above are not particularly limited, and can be manufactured by a conventional method. Moreover, as gas with which a tire is filled, normal or changed oxygen partial pressure, or inert gas such as nitrogen can be used.

Hereinafter, the present invention will be described in more detail with reference to examples.
(Examples 1 and 2 and Comparative Examples 1 to 3)
A side reinforcing type run flat tire shown in FIG. 1 was produced with a tire size of 215 / 45R17. The configuration of the circumferential belt reinforcing layer of each test tire is as shown in Table 1 below. Each of the obtained test tires was tested for high speed durability, run flat durability and uneven wear. The obtained results are also shown in Table 1. The test methods for high-speed durability, run-flat durability and uneven wear properties are as follows.

<High speed durability>
After assembling each of the test tires on a rim having a rim size of 7 J × 17, a high-speed durability drum test was performed under the conditions of an internal pressure of 200 kPa and a load of 4.0 kN. Under the above conditions, the drum was started from 120 km / h, the speed was increased by 10 km / h every 5 minutes, and the speed until the tire failed was measured and evaluated by this measured value. The evaluation was performed as an index display with the failure occurrence rate of Comparative Example 1 as 100. The results are also shown in Table 1.

<Runflat durability>
After assembling each of the above test tires on a rim having a rim size of 7J × 17, the valve core was pulled out to 0 kPa, a load of 4.0 kN was applied, and the drum was measured for how many minutes to run at 80 km / h until this failure occurred. Evaluation was based on measured values. The evaluation was performed by indicating each failure occurrence time as an index, with the failure occurrence time of Comparative Example 1 being 100. The results are also shown in Table 1.

<Uneven wear>
Each of the above test tires was assembled on a rim having a rim size of 7J × 17 and then mounted on a passenger car. Thereafter, the reciprocal of the difference between the most worn portion and the non-weared portion in the tire cross-sectional shape after traveling 5000 km on the paved road was obtained and indicated by an index display when Comparative Example 1 was set as 100. The higher the value, the better the wear resistance.

  From Table 1, it can be seen that the pneumatic tire of the present invention has improved high-speed durability, run-flat durability and uneven wear.

It is sectional drawing of an example of the pneumatic tire of this invention. It is a figure which shows the example of the circumferential belt reinforcement layer which concerns on this invention. It is the figure which showed the relationship between the extension | stretching of the code | cord | chord which comprises the center part area | region of the circumferential belt reinforcement layer in 25 degreeC, and strength.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Bead part 2 Side part 3 Tread part 4 Carcass ply 5 Side reinforcement rubber 6 Bead core 7 Bead filler 8 Belt layer 9 Circumferential belt reinforcement layer 9A Central area | region of the circumferential belt reinforcement layer 9B Side area of the circumferential belt reinforcement layer

Claims (3)

A pair of left and right bead portions, a carcass layer extending from the crown portion to both bead portions through both side portions, at least two belt layers on the outer side in the tire radial direction of the carcass layer, and on the outer side in the tire radial direction of the belt layer In a pneumatic tire comprising: a circumferential belt reinforcing layer; and a side reinforcing rubber layer having a crescent-shaped meridional shape over the entire region or almost the entire region of both side portions along the inside of the carcass layer,
The circumferential belt reinforcing layer is divided into three regions, a central region and both side regions, and a plurality of filament bundles made of polyketone are twisted by the cords constituting the circumferential belt reinforcing layer both side regions Polyketone fiber cord, wherein the polyketone fiber cord has the following formulas (I) and (II),
σ ≧ −0.01E + 1.2 (I)
σ ≧ 0.02 (II)
Where σ is the heat shrinkage stress (cN / dtex) at 177 ° C. and E is the elastic modulus (cN / dtex) at 49 N load at 25 ° C.
The cord constituting the central region of the circumferential belt reinforcing layer has a smaller tensile strength at 2% elongation at 150 ° C. and a larger tensile strength at 2% elongation at 25 ° C. compared to the polyketone fiber. A pneumatic tire characterized by being an organic fiber cord.   Both side regions of the circumferential belt reinforcing layer extend at least 2 mm outward in the tire width direction at the end of the belt layer, and both side region lengths of the circumferential belt reinforcing layer are 10 to 50 mm. Item 2. The pneumatic tire according to Item 1.   The pneumatic tire according to claim 1 or 2, wherein the organic fiber cord is aramid or a composite cord made of aramid and nylon.

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