JP2008273265A - Run flat tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a run flat tire capable of outstandingly enhancing durability in run flat traveling without impairing riding comfortability in usual traveling and improving tire uniformity. <P>SOLUTION: The run flat tire is provided with a side reinforcement rubber layer in which a meridian cross section is a crescent shape over the whole area or the approximately whole area of both side parts along an inner surface of a carcass ply. The carcass ply cord includes at least 50 mass% or more of polyketone fiber and has the maximum thermal contraction stress of 0.1-0.9 cN/dtec as the dipped cord. The thermal contraction ratio at 150°C×30 min. dry heat treatment of the polyketone fiber is within a range of 3.0%-6.5%, and single yarn fineness of the polyketone fiber is 1.5-15 dtex. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a run-flat tire, and more particularly, to a side-reinforced run-flat tire in which durability during run-flat running is greatly improved without impairing riding comfort during normal running.

  As a so-called run-flat tire, the inner surface of the carcass in the side wall portion of the tire can be safely run over a certain distance without losing the load bearing capacity even when the internal pressure of the tire is reduced due to puncture or the like. In addition, a crescent-shaped side reinforcing rubber layer with a relatively high modulus is arranged to improve the rigidity of the sidewall part so that the load can be borne without excessively increasing the deformation of the sidewall part when the internal pressure decreases. Various types of side-reinforced run-flat tires such as tires and tires whose sidewall portions are reinforced with various reinforcing members have been proposed (see Patent Documents 1 to 4).

  On the other hand, cellulosic fibers such as rayon have been used as a reinforcing material for various rubber articles including tire reinforcing cords because they are highly elastic at room temperature and have high adhesion to rubber. In addition, the cellulosic fiber has a higher Young's modulus at room temperature and higher temperature than polyester such as PET, and has a high thermal dimensional stability with a heat shrinkage at 177 ° C. of 0.65 to 1.0%. Yes. Therefore, the cellulosic fiber has been used as a carcass reinforcing cord of the side reinforcing type run-flat tire.

  However, conventional side-reinforced type run-flat tires using cellulosic fiber cords such as rayon as carcass reinforcement cords are not sufficiently high in the elastic modulus of cellulosic fibers, so that the tire is bent during run-flat running. When the tire becomes large due to the run-flat running and the temperature of the tire becomes high, the rigidity of the carcass ply is lowered and the deflection of the tire is further increased. For this reason, the main cause of tire failure at the end of run-flat driving is due to the cracking of the side-reinforcing rubber layer with a crescent-shaped cross section, and conventional side-reinforced run-flat tires have a long-running running distance. There was a problem of being short.

  On the other hand, if the sidewall is reinforced by increasing the gauge of the side reinforcing rubber layer, etc., in order to extend the durability distance of the tire during run-flat running, the tire weight increases or the tire runs during normal running. There is a problem that the vertical spring rises and the riding comfort during normal running deteriorates.

In order to solve such a problem, the applicant previously used a polyketone fiber cord having specific heat shrinkage stress and elastic modulus as a carcass reinforcement cord of a side reinforcement type run-flat tire in Patent Document 5, It has been reported that tire deflection during run-flat driving can be suppressed without increasing tire weight, and as a result, tire run-flat durability can be greatly improved without deteriorating riding comfort during normal driving. ing.
JP 2000-264012 A Special table 2002-500587 gazette Japanese translation of PCT publication No. 2002-500589 JP 2004-306658 A JP 2006-224952 A

  In the run-flat tire described in Patent Document 5, the run-flat durability of the tire can be greatly improved without deteriorating the riding comfort during normal running. However, since the longitudinal spring of the tire during normal running is large, there is a problem that the uniformity of the tire is worse than that of a general tire. In addition, the polyketone obtained by wet spinning described as a suitable example in Patent Document 5 has a single yarn fineness of about 0.5 to 2 dtex because the solvent needs to be dried, and this was used for the carcass ply. In some cases, there was still room for improvement in tire performance due to the soft stiffness of the ply treat.

  Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, greatly improve the durability during run-flat driving without impairing the riding comfort during normal driving, and improve tire uniformity. The object is to provide an improved pneumatic tire.

  As a result of intensive studies to achieve the above object, the present inventors have used a polyketone fiber cord having physical properties such as specific heat shrinkage characteristics as a carcass reinforcement cord of a side-reinforced type run-flat tire. Without increasing the weight, it is possible to suppress the deflection of the tire during run-flat driving, and as a result, while significantly improving the tire run-flat durability without deteriorating the riding comfort during normal driving, The inventors have found that the uniformity of direction can be improved and the deterioration of uniformity can be suppressed, and the present invention has been completed.

That is, the run-flat tire of the present invention includes a pair of left and right bead portions, a carcass ply extending from the crown portion to both bead portions through both side portions, and the entire or almost entire region of both side portions along the inner surface of the carcass ply. In a run flat tire having a side reinforcing rubber layer having a crescent-shaped meridional cross section,
The carcass ply cord contains at least 50% by mass of polyketone fiber, and has a maximum heat shrinkage stress of 0.1 to 0.9 cN / dtex as a dip-treated cord and a heat shrinkage rate of 3.0% at 150 ° C. for 30 minutes. Has 6.5%,
The polyketone fiber has a single yarn fineness of 1.5 to 15 dtex,
It is characterized by this.

  In the run-flat tire of the present invention, the polyketone fiber is obtained by melting the polyketone and discharging it from a spinneret and winding it once or stretching it without winding it. The polyketone fiber has a strength of 5 cN / dtex or more. It is preferable that Preferably, the carcass ply includes a weft that intersects a cord arranged in a substantially radial direction, and the weft is cut at a plurality of locations in the tire circumferential direction at substantially constant intervals, more preferably the weft. The cutting pitch A is in the range of 5 to 30 mm. Further, the weft is preferably made of cellulosic fiber or vinylon fiber, and the weft is preferably spun yarn.

Here, the maximum heat shrinkage stress of the cord means that a 25 cm long fixed sample of a carcass ply cord before vulcanization subjected to a general dip treatment is heated at a heating rate of 5 ° C./min. It is the maximum stress (unit: cN / dtex) generated in the cord at ° C. The heat shrinkage rate during dry heat treatment is the same dip-treated cord, which is subjected to a dry heat treatment at 150 ° C. for 30 minutes in an oven, and the cord length before and after the heat treatment is a load of 1/30 (cN / dtex). This is a value obtained by measuring with
Thermal shrinkage during dry heat treatment (%) = {(Lb−La) / Lb} × 100
However, Lb is the cord length before heat treatment, and La is the cord length after heat treatment. The tensile strength and tensile modulus of the polyketone fiber are values obtained by measurement according to JIS-L-1013. The tensile modulus is the load at an elongation of 0.1% and the elongation of 0.2%. It is the value of the initial elastic modulus calculated from the load at.

  According to the present invention, it is possible to provide a pneumatic tire that can greatly improve the durability during run-flat travel without impairing the ride comfort during normal travel and also has improved tire uniformity.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a partial cross-sectional view of an 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 sidewall portions 2 and a tread portion 3 connected to both sidewall portions 2, and extends in a toroidal shape between the pair of bead portions 1. A radial carcass 4 made of one or more carcass plies that reinforce each of these parts 1, 2, and 3, and a pair of crescent-shaped side reinforcing rubber layers 5 disposed inside the radial carcass 4 of the sidewall part 2. Prepare.

  In the illustrated tire, a bead filler 7 is disposed on the outer side in the tire radial direction of the ring-shaped bead core 6 embedded in the bead portion 1, and further, on the outer side in the tire radial direction of the crown portion of the radial carcass 4. In addition to the belt 8 composed of two belt layers, a belt reinforcing layer 9A is arranged so as to cover the entire belt 8 outside the belt 8 in the tire radial direction. A pair of belt reinforcing layers 9B is arranged so as to cover only both end portions of the layer 9A. 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 belt reinforcing layers 9A and 9B are usually made of rubberized layers of cords arranged substantially parallel to the tire circumferential direction.

  The radial carcass 4 in the illustrated example is composed of a single carcass ply formed by coating a plurality of reinforcing cords arranged in parallel with a coating rubber, and each of the radial carcass 4 is in the bead portion 1. The present invention comprises a main body portion extending in a toroidal shape between a pair of embedded bead cores 6 and a folded portion wound around each bead core 6 radially outward from the inner side to the outer side in the tire width direction. In the pneumatic tire, the number of plies and the structure of the radial carcass 4 are not limited to this. Furthermore, although the belt 8 in the illustrated example comprises two belt layers, the number of belt layers constituting the belt 8 is not limited to this in the pneumatic tire of the present invention. Furthermore, in the pneumatic tire of the present invention, it is not essential to dispose the belt reinforcing layers 9A and 9B, and a belt reinforcing layer having a different structure can be disposed.

  In the present invention, it is desirable that the carcass ply cord of the radial carcass 4 includes at least 50% by mass, preferably 70% by mass or more, more preferably 100% by mass of polyketone fiber. If it is less than 50% by mass, the performance of any of the strength, heat resistance, and adhesion to rubber as a tire becomes insufficient.

  Further, the carcass ply cord of the radial carcass 4 has a maximum heat shrinkage stress of 0.1 to 0.9 cN / dtex, more preferably 0.2 to 0.6 cN / dtex as a dip-treated cord. Is desirable. When the maximum heat shrinkage stress is less than 0.1 cN / dtex, the run flat running durability cannot be sufficiently improved. On the other hand, when the maximum heat shrinkage stress exceeds 0.9 cN / dtex, the cord is remarkably contracted by heating at the time of tire manufacture, so that there is a concern that the finished tire shape may be deteriorated.

  Furthermore, the carcass ply cord of the radial carcass 4 has a heat shrinkage ratio in the range of 3.0% to 6.5%, preferably 3.5% to 5. It is desirable to be in the range of 0%. When the heat shrinkage rate during dry heat treatment at 150 ° C. for 30 minutes is less than 3.0%, the alignment efficiency by heating at the time of tire production is remarkably lowered, and the strength as a tire becomes insufficient. On the other hand, when the thermal shrinkage rate during dry heat treatment at 150 ° C. for 30 minutes exceeds 6.5%, the cord is significantly shrunk by heating during tire manufacture, and there is a concern that the finished tire shape may be deteriorated.

  Furthermore, the single yarn fineness of the polyketone fiber is 1.5 to 15 dtex, preferably 2 to 9 dtex. When the single yarn fineness is less than 1.5 dtex, the stiffness of the ply treat is soft, so that the workability at the time of molding the raw tire is inferior, whereas when it exceeds 15 dtex, the fatigue property is inferior.

  Furthermore, the polyketone fiber contained in the carcass ply cord of the radial carcass 4 preferably has a tensile strength of 5 cN / dtex or more, more preferably 7 cN / dtex or more. When the tensile strength is less than 5 cN / dtex, the strength as a tire is insufficient.

  Furthermore, as shown in FIG. 2, the carcass ply includes a weft 11 intersecting with the carcass ply cord 10 arranged in a substantially radial direction, and the weft 11 is cut at a plurality of locations in the tire circumferential direction. preferable. As means for cutting the weft 11, it can be performed by a known pick breaker process described in Japanese Patent Laid-Open No. 5-208458, but of course, the weft can be cut using other methods. It is.

  Furthermore, as shown in FIG. 2, the cutting pitch A of the weft 11 is preferably in the range of 5 to 30 mm, more preferably in the range of 7 to 15 mm. When the cutting pitch A is less than 5 mm, the carcass cord may be damaged in the cutting process. On the other hand, when it exceeds 30 mm, the uniformity in the tire circumferential direction cannot be sufficiently improved.

  Furthermore, the weft 11 preferably has a cutting elongation of 5 to 20% and a cutting strength of 200 to 1000 g. When the cutting elongation is less than 5% or the cutting strength is 200 g or less, unexpected weft 11 cutting occurs before the step of topping the rubber, and the shape as a braided fabric cannot be maintained. On the other hand, if the cut elongation is greater than 20% or the cut strength exceeds 1000 g, it becomes difficult to cut the weft 11 in the cutting step, and the uniformity in the tire circumferential direction cannot be sufficiently improved.

  Furthermore, it is desirable that the weft 11 is made of a cellulosic fiber or a vinylon fiber, and more preferably a spun yarn. Such a fiber can be designed to satisfy the above-described cutting elongation and cutting strength.

  Next, a carcass ply cord containing at least 50 mass% or more of polyketone fibers (hereinafter abbreviated as “PK fibers”) that can be used in the present invention will be described in detail.

  Examples of fibers other than PK fibers that can be used in the present invention include nylon, ester, rayon, polynosic, lyocell, and vinylon.

（式中、Ｔは撚り数（回／１００ｍｍ）、Ｄはコードの総繊度（ｄｔｅｘ）、ρはコードに使用される繊維素材の密度（ｇ／ｃｍ^３）である）で定義される撚り係数αが０．２５〜１．２５の範囲であることが好ましい。ＰＫ繊維コードの撚り係数αが０．２５未満では、熱収縮応力が十分に確保できず、一方、１．２５を超えると、弾性率が十分に確保できず、補強能が小さくなる。 Further, the above code further includes the following formula (I),

(Where T is the number of twists (times / 100 mm), D is the total fineness of the cord (dtex), and ρ is the density of the fiber material used in the cord (g / cm ³ )) α is preferably in the range of 0.25 to 1.25. If the twist coefficient α of the PK fiber cord is less than 0.25, the heat shrinkage stress cannot be sufficiently ensured. On the other hand, if it exceeds 1.25, the elastic modulus cannot be sufficiently ensured and the reinforcing ability is reduced.

（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あって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ものが好適であり、その中でも、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。 As a polyketone as a raw material of the PK fiber, the following general formula (II),

(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). Among them, a polyketone in which 97 mol% or more of repeating units is 1-oxotrimethylene [—CH ₂ —CH ₂ —CO—] is preferable, and a polyketone in which 99 mol% or more is 1-oxo trimethylene is preferable. Is more preferable, and a polyketone in which 100 mol% is 1-oxotrimethylene is most preferable.

  In such polyketones, the ketone groups may be partially bonded to each other and the portions derived from the unsaturated compound may be bonded to each other, but the proportion of the portions in which the unsaturated compound-derived portions and the ketone groups are alternately arranged is 90 mass. % Or more, preferably 97% by mass or more, and most preferably 100% by mass.

  In the formula (II), 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, and methyl acrylate, methyl methacrylate, vinyl acetate, acrylamide, hydroxyethyl methacrylate, undecenoic acid, undecenol, 6-chlorohexene, N-vinylpyrrolidone, diethyl ester of sulphonylphosphonic acid Further, it may be a compound containing an unsaturated bond such as sodium styrene sulfonate, sodium allyl sulfonate, vinyl pyrrolidone and vinyl chloride.

（上記式中、ｔおよびＴは、純度９８％以上のヘキサフルオロイソプロパノールおよ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の範囲内にあることが好ましく、３〜８ｄＬ／ｇの範囲内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、乾燥時およ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およ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、紡糸性およ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 (III),

(In the above formula, 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, and c is the diluted solution. The intrinsic viscosity [η] defined by the mass (g) of solute in 100 mL) is preferably in the range of 1 to 20 dL / g, more preferably in the range of 3 to 8 dL / g. Even more preferred. 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.

  Furthermore, the PK fiber preferably has a crystal structure with a crystallinity of 50 to 90% and a crystal orientation of 95% or more. If the degree of crystallinity is less than 50%, the structure of the fiber is not sufficiently formed and sufficient strength cannot be obtained, and the shrinkage characteristics and dimensional stability during heating may be unstable. For this reason, the crystallinity is preferably 50 to 90%, more preferably 60 to 85%.

  The polyketone fiber according to the present invention can be preferably produced by melt spinning the polyketone, and specifically, the melt spinning method described in Japanese Patent No. 2676379 can be adopted. That is, a molten polyketone fiber composed of an alternating copolymer type of olefinically unsaturated hydrocarbon and carbon monoxide (a copolymer in which CO units in a macromolecule are alternately arranged with units derived from olefins) has a small average molecular weight. 2000 alternating copolymers of carbon monoxide and olefinically unsaturated compounds are melt-spun at a temperature of minimum (T + 20) K and then stretched at a temperature of maximum (T-10) K, where T is the crystalline melting point of the polymer. In other words, it is possible to obtain a desired balance of a combination of tensile strength, bending modulus, and adhesion to rubber having excellent desired characteristics. In this case, the draw ratio of the draw is preferably at least 3: 1, more preferably at least 7: 1 and most preferably 15: 1. A preferred stretching temperature is a temperature that is at least 40K below the crystalline melting point of the polymer, and a preferred melt spinning temperature is a temperature that is at least 40K above the crystalline melting point of the polymer.

  Alternatively, as described in JP-A-2005-105470, it is known that when a silicon atom is introduced into a molecular chain, melt spinnability is imparted. The melted polyketone may be used for melt spinning. That is, in addition to the ethylenically unsaturated compound and carbon monoxide, the polyketone obtained by reacting the silicon compound as the third component is melted and discharged from the spinneret, and is wound up or stretched without being wound up. Thus, a desired polyketone fiber can be obtained. The obtained polyketone fiber has a strength of 5 cN / dtex or more.

  In order to make the most effective use of the high heat shrinkage characteristics of PK fiber cords, the processing temperature during processing and the temperature of the molded product during use are close to the temperature indicating the maximum heat shrinkage stress (maximum heat shrinkage temperature). It is desirable to be temperature. Specifically, the processing temperature such as the RFL processing temperature and the vulcanization temperature in the adhesive processing performed as necessary is 100 to 250 ° C., and when the tire material generates heat due to repeated use or high speed rotation. Since the temperature can be as high as 100 to 200 ° C, the maximum heat shrink temperature is preferably in the range of 100 to 250 ° C, more preferably in the range of 150 to 240 ° C.

  The coating rubber for covering the carcass ply cord according to the present invention can have various shapes. Typically, it is a film, a sheet or the like. Moreover, a known rubber composition can be appropriately employed as the coating rubber, and it is not particularly limited.

  The run flat tire of the present invention can be manufactured by a conventional method by applying the above-mentioned carcass ply as the radial carcass 4. In the pneumatic tire of the present invention, as the gas filled in the tire, normal or air with a changed oxygen partial pressure, or an inert gas such as nitrogen can be used.

Hereinafter, the present invention will be specifically described based on examples.
(PK fiber preparation example 1: melt spinning)
A fiber grade of alternating copolymer of 8 mol% propylene ethylene (CE) based on carbon monoxide, ethylene and ethylene was melt spun. The copolymer had a molecular weight of 10,000 to 25,000 and a crystalline melting point of 493K. The melt spinning was drawn at a draw ratio of 6: 1. Further, the stretching temperature of the alternating copolymer was 207 ° C., and the melt spinning temperature was 280 ° C.

(PK fiber preparation example 2: wet spinning)
A polyketone polymer with an intrinsic viscosity of 5.3, which is a completely alternating copolymer of ethylene and carbon monoxide, prepared by a conventional method is added to an aqueous solution containing 65% by weight of zinc chloride / 10% by weight of sodium chloride, and stirred at 80 ° C. for 2 hours. It melt | dissolved and the dope with a polymer concentration of 8 weight% was obtained.

  This dope is heated to 80 ° C., filtered through a 20 μm sintered filter, passed through a 10 mm air gap from a 50-hole nozzle with a diameter of 0.10 mmφ kept at 80 ° C., and 5% by weight of zinc chloride. Was extruded at a rate of discharge of 2.5 cc / min into water at 18 ° C. containing a coagulated yarn while being drawn at a speed of 3.2 m / min.

Subsequently, the coagulated yarn was washed with an aqueous sulfuric acid solution having a concentration of 2% by weight and a temperature of 25 ° C., and further washed with water at 30 ° C., and then the coagulated yarn was wound at a speed of 3.2 m / min.
The coagulated yarn was impregnated with IRGANOX 1098 (manufactured by Ciba Specialty Chemicals) and IRGANOX 1076 (manufactured by Ciba Specialty Chemicals) in an amount of 0.05% by weight (with respect to the polyketone polymer), and then dried at 240 ° C. or higher. A finishing agent was added to obtain an undrawn yarn. The heat shrinkage rate can be adjusted by appropriately controlling the drying temperature.

A finishing agent having the following composition was used.
Oleic acid lauryl ester / bisoxyethyl bisphenol A / polyether (propylene oxide / ethylene oxide = 35/65: molecular weight 20000) / polyethylene oxide 10 mol addition oleyl ether / polyethylene oxide 10 mol addition castor oil ether / sodium stearylsulfonate / dioctyllin Sodium acid = 30/30/10/5/23/1/1 (weight% ratio).

  The obtained undrawn yarn was drawn at 240 ° C. in the first stage, followed by the second stage at 258 ° C., the third stage at 268 ° C., the fourth stage at 272 ° C., and then the second stage at 200 ° C. The film was stretched five times at 1.08 times (stretching tension 1.8 cN / dtex) and wound with a winder. The total draw ratio from the undrawn yarn to the five-stage drawn yarn was 17.1 times. This fiber yarn had high physical properties of strength 15.6 cN / dtex, elongation 4.2%, and elastic modulus 347 cN / dtex. In addition, the heat shrinkage rate during dry heat treatment at 150 ° C. for 30 minutes was 1.9%. The PK fiber thus obtained was used as a cord under the following conditions.

(Examples 1-9, Comparative Examples 1-3, Conventional Example)
Fiber cords having the materials, thickness, spinning method, heat shrinkage stress, dry heat shrinkage rate and single yarn fineness shown in Tables 1 to 3 below are arranged in parallel by the number of shots (90/100 mm) and covered with coating rubber Later, wefts are cut to produce a cord / rubber composite, and the cord / rubber composite is used as a carcass ply to produce a side-reinforcement type run-flat tire of size 215 / 45ZR17 having the structure shown in FIG. did. Further, the longitudinal spring and run-flat durability of the obtained tire were evaluated by the following methods, and the results shown in Table 3 were obtained.

(1) Longitudinal spring A load-deflection curve of a test tire filled with an internal pressure of 230 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 with respect to the load. The value of the longitudinal spring constant of the tire was taken as 100 and indicated as an index. 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 4.17kN, a speed of 89km / h, and a temperature of 38 ° C without filling the test tire with internal pressure. The distance measured until the failure of the conventional tire was measured 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.

(3) Tire uniformity RFV (Radial Force Variation) and LFV (Lateral Force Variation) of the test tire filled with an internal pressure of 230 kPa were measured, and the value of the longitudinal spring constant of the tire of the conventional example was expressed as an index. The smaller the index value, the better the uniformity.

  From Table 1 above, it can be seen that the tire using the PK fiber produced by the melt spinning method for the carcass ply is superior in the conventional rayon carcass ply cord and the PK fiber by wet spinning, and the uniformity. Furthermore, it can be seen that the uniformity of the tire using the melt-spun PK fiber is further improved by performing the pick break.

It is sectional drawing of the right half of an example of the pneumatic tire of this invention. FIG. 3 is a cross-sectional view of a portion including a carcass cord and a weft that intersects the carcass ply in the carcass ply.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Bead part 2 Side wall part 3 Tread part 4 Radial carcass 5 Side reinforcement rubber layer 6 Bead core 7 Bead filler 8 Belt 9A, 9B Belt reinforcement layer 10 Carcass ply cord 11 Weft A Weft cut pitch

Claims (6)

A pair of left and right bead parts, a carcass ply extending from the crown part to both bead parts through both side parts, and a side reinforcing rubber having a crescent-shaped meridional section over the entire area of the both side parts along the inner surface of the carcass ply In a run flat tire comprising a layer,
The carcass ply cord contains at least 50% by mass of polyketone fiber, and has a maximum heat shrinkage stress of 0.1 to 0.9 cN / dtex as a dip-treated cord and a heat shrinkage rate of 3.0% at 150 ° C. for 30 minutes. Has 6.5%,
The polyketone fiber has a single yarn fineness of 1.5 to 15 dtex,
A run-flat tire characterized by that.   2. The run flat according to claim 1, wherein the polyketone fiber is a polyketone fiber having a strength of 5 cN / dtex or more obtained by melting a polyketone and discharging it from a spinneret and winding it once or drawing without winding. tire.   The run-flat tire according to claim 1 or 2, wherein the carcass ply includes a weft that intersects with a cord arranged in a substantially radial direction, and the weft is cut at a plurality of locations in the tire circumferential direction at substantially constant intervals.   The run-flat tire according to claim 3, wherein the weft cut pitch A is in the range of 5 to 30 mm.   The run-flat tire according to claim 3 or 4, wherein the weft is made of a cellulose fiber or a vinylon fiber.   The run-flat tire according to any one of claims 3 to 5, wherein the weft is a spun yarn.

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