JP4734027B2 - 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 by puncture or the like, a cross-section is formed on the innermost side surface of the carcass of the sidewall portion of the tire. A run flat tire having a crescent-shaped side reinforcing rubber layer, a so-called side reinforcing type run flat tire is known.

  When such a side-reinforced run-flat tire travels in a run-flat state, it is known that so-called buckling occurs, which is a phenomenon in which the center of the tread surface rises from the road surface. In a tire in which buckling occurs, the contact pressure of the tread shoulder portion increases, and as a result, the heat generated by the reinforcing rubber disposed near the shoulder portion increases, so that the tire may be broken.

  For this reason, side-reinforced run-flat tires with improved durability by suppressing buckling during run-flat running in side-reinforced run-flat tires are desired, and various studies have been made on these.

  For example, Patent Document 1 discloses a number of belts substantially perpendicular to the tire equatorial plane between a belt and a belt reinforcing layer made of an organic fiber cord such as nylon fiber or aramid fiber disposed on the outer periphery of the belt. A tire is described in which at least one reinforcing layer is provided in a cord arrangement. By arranging the reinforcing layer in this way, it is possible to suppress the buckling and improve the run flat durability. However, with the increase in the rigidity of the entire tread portion due to the arrangement of the reinforcing layer, normal internal pressure running There was a problem that the vibration ride comfort deteriorated when there was projection input from the road surface.

  In Patent Document 2, the outermost belt layer of the belt layers constituting the belt is composed of a pair of left and right small belt members, and the deformation of the tread portion is particularly large when buckling occurs. The occurrence of buckling can be suppressed without overlapping both small belt members in the range of 20 to 50% of the tread contact width and increasing the out-of-plane bending rigidity of the belt outside the overlapped range. As a result, a tire is described that has improved durability during run-flat running without sacrificing ride comfort. However, such a tire has a problem that the manufacturing process is complicated because the structure of the belt layer is complicated.

JP-A-6-191243 JP 2004-359145 A

  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 running.

  As a result of earnest study focusing on the material of the cord constituting the belt reinforcing layer in order to achieve the above object, the present inventor has found 25 as a cord constituting the belt reinforcing layer disposed on the outer side in the tire radial direction of the belt. By applying a polyketone fiber cord in which 49 ° C. elastic modulus E (cN / dtex) at ° C. and 177 ° C. heat shrinkage stress σ (cN / dtex) satisfy a specific relational expression, the riding comfort during normal internal pressure running is not impaired. In addition, the inventors have found that a tire with improved run-flat durability can be obtained by suppressing the occurrence of a buckling phenomenon during run-flat running, 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 composed of at least one existing carcass ply, a pair of side reinforcing rubber layers disposed inside the radial carcass of the sidewall portion, and at least two layers disposed inside the tread portion A pneumatic tire comprising: a belt comprising a belt layer; and at least one belt reinforcing layer comprising a rubberized layer of a cord disposed outside the belt in the tire radial direction and arranged substantially parallel to the tire circumferential direction In
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.

  In a preferred embodiment of the pneumatic tire of the present invention, the width of the belt reinforcing layer is in a range of 95 to 105% of the width of the belt.

  Another preferred embodiment of the pneumatic tire of the present invention is at least one cord reinforcing layer comprising a rubberized layer of cords arranged inside the belt in the tire radial direction and arranged substantially parallel to the tire width direction. Is further provided.

  In the pneumatic tire of the present invention, the cord constituting the cord reinforcing layer is preferably a polyketone fiber cord obtained by twisting a plurality of filament bundles made of polyketone.

In the pneumatic tire of the present invention, the polyketone fiber cord constituting the cord reinforcing layer has 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.] is preferably satisfied.

  In the pneumatic tire of the present invention, the polyketone fiber cord constituting the cord reinforcing layer preferably has a heat shrinkage stress σ (cN / dtex) at 177 ° C. of 0.3 or more.

（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 a pneumatic tire, a polyketone fiber cord having a specific heat shrinkage stress and an elastic modulus is applied as a cord constituting a belt reinforcing layer disposed on the outer side in the tire radial direction of the belt. There is an advantageous effect that it is possible to provide a pneumatic tire with improved run-flat durability without impairing ride comfort.

  According to the present invention, in the pneumatic tire provided with the belt reinforcing layer, at least one piece of a rubberized layer of cords arranged substantially parallel to the tire width direction on the inner side in the tire radial direction of the belt. Since the cord reinforcing layer is further provided, the buckling in the tire width direction during the run flat running is further suppressed, and as a result, the run flat durability can be further improved.

  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. Further, at least one belt reinforcing layer, in the illustrated example, a first belt reinforcing layer 8 disposed so as to cover the entire belt 7, and the width direction of the belt 7 on the outer side in the tire radial direction of the first belt reinforcing layer 8 And a second belt reinforcing layer 9 of a pair arranged so as to cover each end.

  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 first belt reinforcing layer 8 is composed of a rubberized layer of cords arranged substantially parallel to the tire circumferential direction, and the cord twists a plurality of filament bundles made of polyketone. A combined polyketone fiber cord, wherein the polyketone fiber cord is represented by the following formulas (I) and (II):
σ ≧ −0.01E + 1.2 (I)
σ ≧ 0.3 (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.].

  Since the polyketone fiber cord has a large heat shrinkage stress at a high temperature, when the temperature of the tire rises due to run-flat running, the polyketone fiber cord in the first belt reinforcing layer 8 exhibits the large heat shrinkage stress, and the tread portion By improving the overall rigidity, the occurrence of the tire buckling phenomenon 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 hardly exerted and the rigidity is hardly improved, so the vertical spring of the tire during normal internal pressure running does not rise so much, and normal internal pressure The riding comfort of the tire during driving is not impaired.

When the cord to be used does not satisfy the relationship of the above formula (I), if a cord having a large heat shrinkage stress σ but a low elastic modulus E is used, the rigidity improvement effect of the entire tread portion is small during run flat running. Therefore, the run-flat durability improvement effect is also small. On the other hand, when a cord having a high elastic modulus E but a small heat shrinkage stress σ is used, although the run-flat durability is improved, the riding comfort of the tire during normal internal pressure running deteriorates. Further, when the heat shrinkage stress σ at 177 ° C. of the cord to be used is less than 0.02 cN / dtex, although there is a buckling suppressing effect, a sufficient effect may not be obtained due to a difference in tire size and usage conditions. The heat shrinkage stress σ (cN / dtex) at 177 ° C. of the polyketone fiber cord is 0.3 or more .

The cord constituting the first belt reinforcing layer 8 of the pneumatic tire of the present invention needs to be composed of a polyketone fiber cord obtained by twisting a plurality of filament bundles composed of polyketone, and as a polyketone as a raw material of the polyketone fiber cord A polyketone substantially consisting of repeating units represented by the above 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.

  The cord / rubber composite used for the first 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.

  In the pneumatic tire of the present invention, a cord / rubber composite in which the above-mentioned polyketone fiber cord is arranged in parallel to the tire circumferential direction and coated with a coating rubber is applied to the first belt reinforcing layer 8, Can be manufactured. 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 first belt reinforcing layer 8 is preferably in the range of 95 to 105% of the width of the belt 8.

  As shown in FIG. 1, the pneumatic tire of the present invention is a single second belt arranged on the outer side in the tire radial direction of the belt 7 so as to cover each end in the width direction of the belt 7. Although the reinforcing layer 9 is provided, the arrangement of the second belt reinforcing layer 9 is not essential. The second belt reinforcing layer 9 is composed of a rubberized layer of cords arranged substantially in parallel with the tire circumferential direction, like the first belt reinforcing layer 8, but the material of the cords is not particularly limited. Examples of the material of the cord include steel, and organic fibers such as nylon, polyester, aramid, and polyketone. Since higher run flat durability can be obtained, the cord constituting the second belt reinforcing 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 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 second belt reinforcing layer 9 is preferably 20 mm or more when viewed from the belt end in order to ensure a run-flat durability effect. Further, the width of the second belt reinforcing layer 9 may be the same as the width of the first belt reinforcing layer 8.

  In addition, as shown in FIG. 2, the pneumatic tire of the present invention is at least one piece of a rubberized layer of a cord that is arranged on the inner side in the tire radial direction of the belt 7 and arranged substantially parallel to the tire width direction. The cord reinforcing layer 10 may be further provided. By applying the cord reinforcing layer 10 to a tire, buckling in the tire width direction during run-flat running can be suppressed, and the run-flat durability of the tire can be further improved. The material of the cord constituting the cord reinforcing layer 10 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 achieving both run-flat durability and riding comfort during normal internal pressure running, the cord constituting the cord reinforcing layer 10 is preferably a polyketone fiber cord in which a plurality of filament bundles made of polyketone are twisted, particularly The polyketone fiber cord is preferably a polyketone fiber cord satisfying the above formulas (I) and (II), and has a heat shrinkage stress σ (cN / dtex) at 177 ° C. of 0.3 or more. Is more 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.

(Examples 1 and 2)
A run-flat tire of size 245 / 40R18 having the structure shown in FIG. Note that the belt of the test tire is composed of two steel belt layers, and polyketone fiber cords having the structure shown in Table 1 are driven into the first belt reinforcing layer 8 and the second belt reinforcing layer 9 as shown in Table 1, respectively. The cord / rubber composites prepared in parallel by number and coated with coating rubber 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 3 and 4)
The size 245 / of the structure shown in FIG. 2 is the same as in Examples 1 and 2, except that the cord reinforcing layer 10 having the polyketone fiber cord having the structure shown in Table 1 is disposed on the inner side in the tire radial direction of the belt 7. A 40R18 run-flat tire was prototyped. In addition, the cord reinforcement layer 10 in Example 3, 4 consists of the rubberized layer of the cord of the material and structure shown in Table 1 arranged substantially parallel to the tire width direction. 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.

(Comparative Examples 1 and 2)
As the cords constituting the first belt reinforcing layer 8 and the second belt reinforcing layer 9, the cords having the structure shown in FIG. A run-flat tire of size 245 / 40R18 was prototyped. The polyketone fiber cord used in Comparative Example 2 is a polyketone fiber cord not satisfying the above formulas (I) and (II), which is composed of repeating units represented by the formula (III), and A is mainly ethylene. It consists of a polyketone (containing about 6% propylene).

(Comparative Example 3)
As in Examples 3 and 4 except that aramid fiber cords having the structure shown in Table 1 were used as the cords constituting the first belt reinforcing layer 8, the second belt reinforcing layer 9, and the cord reinforcing layer 10, respectively. A run-flat tire of size 245 / 40R18 having the structure shown in FIG.

(Performance evaluation)
The longitudinal springs and run-flat durability of the tires of Examples 1 to 4 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 230 kPa was measured, and the inclination of a tangent at a certain load on the obtained load-deflection curve was defined as a longitudinal spring constant with respect to 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.
(Please replenish the internal pressure of the tire when measuring the vertical spring.)

(2) Run-flat durability A drum test is performed in an environment with a load of 5.24kN, 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 indicated 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 Example 1 in which the polyketone fiber cord satisfying the above formulas (I) and (II) is applied to the first belt reinforcing layer 8, the longitudinal spring, that is, the riding comfort during normal internal pressure running is nylon fiber. Although it was almost the same as Comparative Example 1 in which the cord was applied to the first belt reinforcing layer 8, 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 during running at normal internal pressure was almost the same as in Comparative Example 1, The improvement in run flat durability as in Example 1 was not obtained.

  Further, in Examples 2 to 4 in which the reinforcing layer was added, the run-flat durability was further improved although the ride comfort was slightly inferior to that in Example 1. In addition, when Example 4 and the comparative example 3 which has the same structure as Example 4 are applied instead of an aramid fiber cord instead of the polyketone fiber cord applied to Example 4, Example 4 and Comparative Example 3 are compared. Although the run-flat durability was comparable, the vertical spring of Example 4 was smaller than Comparative Example 3, that is, the ride comfort during normal internal pressure traveling of Example 4 was superior to Comparative Example 3.

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 1st belt reinforcement layer 9 2nd belt reinforcement layer 10 Cord reinforcement layer

Claims (5)

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 arranged inside the radial carcass of the sidewall portion, and at least two belt layers arranged inside the tread portion, and the belt In a pneumatic tire provided with at least one belt reinforcing layer made of a rubberized layer of cords arranged on the outer side in the tire radial direction of the cord and arranged substantially parallel to the tire circumferential direction,
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.] .   The pneumatic tire according to claim 1, wherein the width of the belt reinforcing layer is in a range of 95 to 105% of the width of the belt. At least one cord reinforcing layer comprising a rubberized layer of polyketone fiber cords , which is arranged on the inner side in the tire radial direction of the belt and twisted together a plurality of filament bundles made of polyketone arranged substantially parallel to the tire width direction The polyketone fiber cord has the following formulas (I) and (II):
σ ≧ −0.01E + 1.2 (I)
σ ≧ 0.3 (II)
2. In the formula, 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. Or the pneumatic tire of 2. 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 3 . The pneumatic tire according to claim 4, wherein A in the general formula (III) is an ethylene group.

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