JP5054899B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire excellent in ride comfort and run-flat durability during normal internal pressure running.

  Conventionally, as one of so-called run flat tires that can safely travel a certain distance even when the internal pressure of the tire is reduced due to puncture or the like, for example, a sidewall of a tire as in Patent Document 1 There is known a run flat tire in which a side reinforcing rubber layer having a crescent cross section is disposed on the innermost side surface of the carcass, so-called side reinforcing type run flat tire. In such a side-reinforced run-flat tire, the load of the vehicle is supported by the inherent rigidity of the sidewall portion reinforced by the side reinforcing rubber layer when the tire internal pressure is reduced due to puncture, that is, during the run-flat running. It is possible to travel a considerably long distance to the repair place or the exchange place. However, during run flat running, not only the sidewall portion but also the tread grounding end portion bends, so further improvement in the run flat durability of the side reinforcing run flat tire is required.

  In addition, in order to prevent separation of the belt layer constituting the belt, particularly separation that occurs remarkably at the end of the belt layer, an organic fiber cord such as a nylon fiber cord covering each end in the width direction of the belt is rubberized. A pair of belt reinforcing layers is disposed outside the belt in the tire radial direction. The tire provided with the pair of belt reinforcing layers is not sufficient to suppress the bending of the tread ground end, and further increases the number of belt reinforcing layers to increase the rigidity of the tread ground end. Thus, it is possible to improve the run flat durability by suppressing the bending of the tread ground contact end during the run flat running and reducing the bending of the entire tire. However, in the tire with the increased number of belt reinforcing layers as described above, the vibration riding comfort is deteriorated when there is protrusion input from the road surface during normal internal pressure traveling with the increase in the rigidity of the tread ground contact end. There is a problem of doing.

Japanese Patent Laid-Open No. 11-254919

  Accordingly, an object of the present invention is to solve these problems of the prior art and to provide a pneumatic tire with improved run-flat durability without impairing riding comfort during normal internal pressure traveling.

  As a result of intensive studies focusing on the material of the cord constituting the belt reinforcing layer in order to achieve the above object, the present inventor has found that the cord constituting the belt reinforcing layer has a 49N elastic modulus E (cN / dtex) and 177 ° C. heat shrinkage stress σ (cN / dtex) satisfying a specific relational expression, using a polyketone fiber cord, the tread grounding end during run-flat running without impairing riding comfort during normal internal pressure running It has been found that a tire with improved run-flat durability can be obtained by suppressing the bending of the portion, and the present invention has been completed.

That is, the pneumatic tire of the present invention has a pair of bead portions, a pair of sidewall portions, and a tread portion connected to both sidewall portions, and extends in a toroidal shape between the pair of bead portions. A radial carcass formed of at least one carcass ply, a pair of side reinforcing rubber layers disposed inside the radial carcass of the sidewall portion, and at least two or more sheets disposed inside the tread portion. And a rubberized layer of a cord arranged on the outer side in the tire radial direction of the belt and covering at least each end in the width direction of the belt and arranged substantially parallel to the circumferential direction of the tire In a pneumatic tire comprising at least one pair of belt reinforcing layers,
The width of the belt reinforcing layer is a width of 20 mm or more as viewed from the belt end,
The cord constituting the belt reinforcing layer 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 ≧ 0.3 (II)
[Wherein, 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.].

  Here, the heat shrinkage stress σ at 177 ° C. of the cord made of the above polyketone fiber is a stress generated in the cord during measurement at 177 ° C. by heating a 25 cm length sample at a heating rate of 5 ° C./min. In addition, the elastic modulus E at 49 N load at 25 ° C. of the polyketone fiber cord is an elastic modulus in a unit cN / dtex calculated from a tangent line at 49 N of the SS curve by a JIS cord tensile test.

Another preferred embodiment of the pneumatic tire according to the present invention is substantially outside of the belt in the tire radial direction and is disposed between the belt and the belt reinforcing layer and covers at least the entire belt. At least one auxiliary belt layer made of a rubberized layer of cords arranged in parallel to the belt, and the width of the auxiliary belt layer is 95% to 105% of the belt, and the cord constituting the auxiliary belt layer Is a polyketone fiber cord obtained by twisting a plurality of filament bundles made of polyketone, and the polyketone fiber cord constituting the auxiliary belt layer has the following formulas (I) and (II):
σ ≧ −0.01E + 1.2 (I)
σ ≧ 0.3 (II)
[Wherein, 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.] is preferably satisfied.

（式中、Ａは不飽和結合によって重合された不飽和化合物由来の部分であり、各繰り返し単位において同一でも異なっていてもよい）で表される繰り返し単位から実質的になることが好ましい。 In the pneumatic tire of the present invention, the polyketone has the following general formula (III):

(In the formula, A is a portion derived from an unsaturated compound polymerized by an unsaturated bond, and each repeating unit may be the same or different) and is preferably substantially composed of a repeating unit.

  In the pneumatic tire of the present invention, it is preferable that A in the general formula (III) is an ethylene group.

  According to the present invention, in the pneumatic tire, as a cord constituting at least one pair of belt reinforcing layers disposed on the outer side in the tire radial direction of the belt and covering each end in the width direction of the belt, a specific heat shrinkage stress and Since the polyketone fiber cord with elastic modulus is applied, it is natural to suppress separation at the belt end compared to conventional nylon fiber cord, and run flat durability without impairing riding comfort during normal internal pressure running There is an advantageous effect that an improved pneumatic tire can be provided.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view in the width direction showing an embodiment of the pneumatic tire of the present invention, and FIG. 2 is a cross-sectional view in the width direction showing a modification of the pneumatic tire of the present invention.

  The tire shown in FIG. 1 has a pair of left and right bead portions 1, a pair of sidewall portions 2, and a tread portion 3 connected to both sidewall portions 2, and is embedded in each of the bead portions 1. A radial carcass 5 made of at least one carcass ply that extends in a toroidal shape between the pair of bead cores 4 and reinforces each of these parts 1, 2, 3, and an inner side of the radial carcass 5 of the sidewall part 2. A pair of arranged crescent-shaped side reinforcing rubber layers 6, a belt 7 composed of at least two belt layers arranged inside the tread portion 3, and an outer side in the tire radial direction of the belt 7. And at least one pair of belt reinforcing layers 8 covering at least each end of the belt 7 in the width direction.

  The radial carcass 5 in the illustrated example is composed of a single carcass ply, and has a main body portion extending in a toroidal shape between a pair of bead cores 4, and an outer side from the inside in the tire width direction around each bead core 4. However, in the pneumatic tire of the present invention, the number of plies and the structure of the radial carcass 4 are not limited to these.

  The belt layer constituting the belt 7 in the illustrated example is usually composed of a rubberized layer of a cord that extends obliquely with respect to the tire equatorial plane, preferably a rubberized layer of a steel cord, and further includes two belt layers. However, the cords constituting the belt layer are laminated so as to intersect with each other across the equator plane. Although the belt 7 in the illustrated example is composed of two belt layers, in the pneumatic tire of the present invention, the number of belt layers constituting the belt 7 may be three or more.

In the pneumatic tire of the present invention, the belt reinforcing layer 8 is composed of a rubberized layer of a cord arranged substantially parallel to the tire circumferential direction, and the cord is formed by twisting a plurality of filament bundles made of polyketone. A polyketone fiber cord, wherein the polyketone fiber cord is represented by the following formulas (I) and (II):
σ ≧ −0.01E + 1.2 (I)
σ ≧ 0.02 (II)
[Wherein, 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.].

  Since the polyketone fiber cord has a large heat shrinkage stress at a high temperature, when the tire temperature rises due to run-flat running, the polyketone fiber cord in the belt reinforcing layer 8 exhibits the large heat shrinkage stress, and the tread portion grounding end. Since the rigidity of the portion is improved, the bending of the tread grounding end portion is suppressed and at the same time the bending of the entire tire is suppressed, and as a result, the run-flat durability of the tire is improved. On the other hand, at low temperatures, that is, when running at normal internal pressure, the heat shrinkage stress of the polyketone fiber cord is small, and therefore the improvement in rigidity is small. The riding comfort of the tire at the time is not impaired.

  If the cord to be used does not satisfy the relationship of the above formula (I), if a cord having a large thermal shrinkage stress σ but a low elastic modulus E is used, the rigidity of the tread portion and the tread grounding end portion during run flat running Since the rise is not so great, the effect of improving the run-flat durability is small. On the other hand, when a cord having a high elastic modulus E but a small heat shrinkage stress σ is used, not only the effect of improving the run-flat durability is small, but also the ride comfort during normal running is deteriorated. Further, when the heat shrinkage stress σ at 177 ° C. of the cord used is less than 0.02 cN / dtex, the expected increase in the rigidity of the tread grounding end is not obtained at the time of run flat running, and the effect of improving the run flat durability is small. . In addition, from the viewpoint of variation in run-flat running conditions and appropriate tire size, the heat shrinkage stress σ (cN / dtex) at 177 ° C. of the polyketone fiber cord is preferably 0.3 or more.

The cord constituting the belt reinforcing layer 8 of the pneumatic tire of the present invention is required to be composed of a polyketone fiber cord obtained by twisting a plurality of filament bundles composed of polyketone. A polyketone substantially consisting of repeating units represented by the formula (III) is preferred. Among the polyketones, polyketones in which 97 mol% or more of repeating units are 1-oxotrimethylene [—CH ₂ —CH ₂ —CO—] are preferable, and polyketones in which 99 mol% or more are 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 general formula (III), the unsaturated compound forming A is most preferably ethylene, but propylene, butene, pentene, cyclopentene, hexene, cyclohexene, heptene, octene, nonene, decene, dodecene, styrene, Unsaturated hydrocarbons other than ethylene such as acetylene and allene, and diethyls of methyl acrylate, methyl methacrylate, vinyl acetate, acrylamide, hydroxyethyl methacrylate, undecenoic acid, undecenol, 6-chlorohexene, N-vinylpyrrolidone, and sulfonyl phosphonic acid It may be a compound containing an unsaturated bond such as ester, 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 the polymerization degree of the polyketone, the following formula:

(Wherein t and T are the flow time 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 mass (g) of the solute 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. When the intrinsic viscosity is less than 1 dL / g, it is difficult to obtain a high-strength polyketone fiber cord because the molecular weight is too small, 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 a wet spinning method using an organic solvent, a polyketone polymer is dissolved in hexafluoroisopropanol or m-cresol 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., a 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 (melting point of 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 lower. Here, there is no restriction | limiting in particular as a rapid cooling method of the heat-stretched polyketone fiber, A conventionally well-known method can be employ | adopted, Specifically, the 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. For example, the filament bundle made of 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 belt reinforcing layer 8 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 a coating rubber of a polyketone fiber cord, The coating rubber used for the conventional belt reinforcement layer 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.

  The pneumatic tire of the present invention is manufactured by applying a cord / rubber composite in which the above-mentioned polyketone fiber cord is disposed in parallel to the tire circumferential direction and coated with a coating rubber on the belt reinforcing layer 8 and is manufactured by a conventional method. can do. Further, in the pneumatic tire of the present invention, as the gas filled in the tire, normal or changed oxygen partial pressure, or an inert gas such as nitrogen can be used.

The width of the belt reinforcing layer 8 needs to be 20 mm or more when viewed from the belt end. Further, in the illustrated pneumatic tire, the number of belt reinforcing layers 8 is one pair, but two or more pairs may be used. By increasing the number of belt reinforcing layers 8, the run-flat durability is improved. . From the viewpoint of ride comfort during normal running, the number of belt reinforcing layers is preferably up to two pairs.

  As shown in FIG. 2, the pneumatic tire of the present invention is disposed between the belt 7 and the belt reinforcing layer 8 on the outer side in the tire radial direction of the belt 7 and covers at least the entire belt 7 in the tire circumferential direction. Alternatively, at least one auxiliary belt layer 9 made of a rubberized layer of cords arranged substantially parallel to the cord may be provided. By applying this auxiliary belt layer 9 to the tire, separation at the belt end can be further suppressed. The material of the cord constituting the auxiliary belt layer 9 is not particularly limited, and examples of the material of the cord include steel, organic fibers such as nylon, polyester, aramid, and polyketone. From the viewpoint of the effect of suppressing the buckling in the tire width direction of the tread portion, the cord constituting the auxiliary belt layer 9 is preferably a polyketone fiber cord obtained by twisting a plurality of filament bundles made of polyketone, and in particular, the polyketone fiber The cord is preferably a polyketone fiber cord satisfying the above formulas (I) and (II), and more preferably a polyketone fiber cord having a heat shrinkage stress σ (cN / dtex) at 177 ° C. of 0.3 or more.

  The width of the auxiliary belt layer 9 is preferably 95% to 105% of the width of the belt. In the illustrated pneumatic tire, the number of auxiliary belt layers is one, but may be two or more.

  In the pneumatic tire of the present invention, examples of combinations of the number of the belt reinforcing layers 8 and the auxiliary belt layers 9 include, for example, a pair of belt reinforcing layers 8 and one auxiliary belt layer 9, two pairs of belt reinforcing layers 8 and an auxiliary belt layer 9. One combination is listed. From the viewpoint of achieving both run-flat durability and riding comfort during normal running, a combination of a pair of belt reinforcing layers 8 and one auxiliary belt layer 9 is preferable.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

Example 1
A size 235 / 45R17 run-flat tire having the structure shown in FIG. The test tire belt is composed of two steel belt layers. In the belt reinforcement layer 8, polyketone fiber cords having the structure shown in Table 1 are arranged in parallel with the number of drivings shown in Table 1, and coated rubber is used. The cord / rubber composites produced by coating were applied respectively. The polyketone fiber cord satisfies the above formulas (I) and (II), almost 100% is composed of repeating units represented by the formula (III), and 97 mol% or more of repeating units are 1-oxotrimethylene. It consists of a polyketone.

(Examples 2 and 3)
The auxiliary belt layer 9 having the material and structure cords shown in Table 1 was arranged in the same manner as in Example 1 except that the auxiliary belt layer 9 was arranged between the belt 7 and the belt reinforcing layer 8 outside the belt 7 in the tire radial direction. A run-flat tire of size 235 / 45R17 having the structure shown in FIG. The polyketone fiber cord applied to the auxiliary belt layer 9 of Example 3 satisfies the above formulas (I) and (II), and almost 100% is composed of repeating units represented by the formula (III). 97 mol% or more consists of a polyketone in which 1-oxotrimethylene is used.

(Comparative Examples 1 and 2)
A run-flat tire of size 245 / 40R18 having the structure shown in FIG. 1 was made in the same manner as in Example 1 except that the cord having the material and structure shown in Table 1 was used as the cord constituting the belt reinforcing layer 8. The polyketone fiber cord applied to the belt reinforcing layer 8 of Comparative Example 2 is a polyketone fiber cord not satisfying the above formulas (I) and (II), and is composed of repeating units represented by the formula (III). , A is mainly composed of polyketone (containing about 6% propylene) which is ethylene group.

(Comparative Example 3)
The size 235 / 45R17 of the structure shown in FIG. 2 is the same as in Examples 2 and 3 except that the nylon fiber cord having the structure shown in Table 1 is applied as the cord constituting the belt reinforcing layer 8 and the auxiliary belt layer 9. Prototype run-flat tires.

(Comparative Example 4)
A run-flat tire of size 235 / 45R17 having the structure shown in FIG. 2 was made in the same manner as in Comparative Example 3 except that two pairs of belt reinforcing layers 8 were provided.

(Performance evaluation)
The longitudinal springs and run-flat durability of the tires of Examples 1 and 2 and Comparative Examples 1 to 3 were evaluated by the following methods, and the results shown in Table 1 were obtained.

(1) Longitudinal spring A load-deflection curve of a test tire filled with an internal pressure of 250 kPa is measured, and the inclination of a tangent at a certain load on the obtained load-deflection curve is defined as a longitudinal spring constant for the load. The value of the vertical spring constant of the tire was expressed as an index with the value being 100. A larger index value indicates a larger longitudinal spring constant.

(2) Run-flat durability A drum test was performed in an environment with a load of 5.25kN, a speed of 90km / h, and a temperature of 38 ° C without filling the test tire with internal pressure. The distance measured until the failure of the tire of Comparative Example 1 was taken as 100, and displayed as an index. The larger the index value, the longer the distance traveled until failure, and the better the run-flat durability.

  From Table 1, in the tire of the example in which the polyketone fiber cord satisfying the above formulas (I) and (II) is applied to the belt reinforcing layer 8, the longitudinal spring, that is, the riding comfort during normal internal pressure running is a nylon fiber cord. It was maintained at substantially the same level as Comparative Example 1 applied to the reinforcing layer 8, and the run-flat durability was significantly improved as compared with Comparative Example 1.

  On the other hand, in the tire of Comparative Example 2 using the polyketone fiber cord not satisfying the above formulas (I) and (II), the riding comfort at the time of normal internal pressure accompanying was the same as that of Comparative Example 1, but Example 1 The run flat durability was not obtained.

  Further, in addition to the belt reinforcing layer 8 to which the polyketone fiber cord satisfying the above formulas (I) and (II) is applied, an auxiliary belt layer 9 to which the nylon fiber cord is applied is further provided, and the above formula (I) In Example 3 in which the polyketone fiber cord satisfying (II) and (II) is applied to the belt reinforcing layer 8 and the auxiliary belt layer 9, the longitudinal spring is a comparative example in which the nylon fiber cord is applied to the belt reinforcing layer 8 and the auxiliary belt layer 9. The run-flat durability was significantly improved as compared with Comparative Example 3. Further, the vertical springs of Examples 2 and 3 were almost the same as those of Example 1 in which the auxiliary belt layer 9 was not provided, and the vertical springs due to the auxiliary belt layer 9 were not increased.

  On the other hand, in the comparative example 4 in which another pair of belt reinforcing layers 8 to which the nylon fiber cords are applied are arranged on the tire of the comparative example 3 and the number of the belt reinforcing layers 8 is two pairs, the run flat durability is high. The run-flat durability was not improved as much as in Examples 2 and 3 in which the belt reinforcement layer 8 to which the polyketone fiber cord was applied was provided, although it was improved over Comparative Example 3 in which the belt reinforcement layer 8 was provided in a pair. . Further, the vertical spring of Comparative Example 4 was significantly higher than Comparative Example 3, and the riding comfort during normal internal pressure traveling was degraded.

1 is a cross-sectional view in the width direction showing one embodiment of a pneumatic tire of the present invention. It is sectional drawing of the width direction which shows the modification of the pneumatic tire of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Bead part 2 Side wall part 3 Tread part 4 Bead core 5 Radial carcass 6 Side reinforcement rubber layer 7 Belt 8 Belt reinforcement layer 9 Auxiliary belt layer

Claims (4)

A pair of bead portions, a pair of sidewall portions, and a tread portion connected to both sidewall portions; and at least one carcass ply extending in a toroidal shape between the pair of bead portions. A belt composed of a radial carcass, a pair of side reinforcing rubber layers disposed inside the radial carcass of the sidewall portion, and at least two belt layers disposed inside the tread portion, and the belt At least one pair of belt reinforcing layers made of rubberized layers of cords arranged substantially parallel to the tire circumferential direction and covering at least each end portion in the width direction of the belt. In pneumatic tires,
The width of the belt reinforcing layer is a width of 20 mm or more as viewed from the belt end,
The cord constituting the belt reinforcing layer 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 ≧ 0.3 (II)
[Wherein, 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.] . At least an outer layer in the tire radial direction of the belt, which is disposed between the belt and the belt reinforcing layer and includes at least a rubberized layer of a cord arranged to be substantially parallel to the tire circumferential direction and covering at least the entire belt. A further auxiliary belt layer;
The width of the auxiliary belt layer is 95% to 105% of the belt,
The cord constituting the auxiliary belt layer is a polyketone fiber cord obtained by twisting a plurality of filament bundles made of polyketone,
The polyketone fiber cord constituting the auxiliary belt layer has the following formulas (I) and (II):
σ ≧ −0.01E + 1.2 (I)
σ ≧ 0.3 (II)
Wherein, sigma is the thermal shrinkage stress at 177 ℃ (cN / dtex), E is the elastic modulus at 49N load at 25 ° C. is (cN / dtex)] claim 1, characterized in that meet the pneumatic tire according to. The polyketone is represented by the following general formula (III):

(Wherein A is a portion derived from an unsaturated compound polymerized by an unsaturated bond, and each repeating unit may be the same or different) and is characterized by consisting essentially of repeating units represented by The pneumatic tire according to claim 1 or 2 . The pneumatic tire according to claim 3, wherein A in the general formula (III) is an ethylene group.

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