JP2006315515A - Pneumatic radial tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To greatly improve high speed durability while maintaining ride quality in low speed running. <P>SOLUTION: A pneumatic radial tire is equipped with a belt reinforcing layer 6B covering both end parts of a belt 5. In the pneumatic radial tire, a polyketone fiber cord which satisfies the condition of formula (I): σ≥-0.01×E+1.2 and formula (II): σ≥0.02 is applied to the belt reinforcing layer 6B, and a tread rubber layer composed of a central part tread rubber layer 7A positioned at the center in the tire width direction, and a shoulder part tread rubber layer 7B positioned at the both outsides in the width direction is applied to a tread part 3, and tanδ of the shoulder part tread rubber layer 7B at 30°C is made larger than tanδ of the central part tread rubber layer 7A at 30°C (in the formulas, σ is thermal contraction stress (cN/dtex) at 177°C; E is an elastic modulus at a load of 49 N at 25°C). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a pneumatic radial tire, and more particularly to a pneumatic radial tire that has improved high-speed durability while maintaining riding comfort during low-speed traveling.

  At present, a belt generally used as a reinforcing member for a carcass forming a skeleton of a radial tire, particularly a reinforcing member for a crown portion of a carcass, is a belt mainly composed of a rubberized layer of a steel cord that is inclined with respect to the equator plane of the tire. Two or more layers are used, and the steel cords in these belt layers are configured to cross each other.

  Further, in order to improve the high-speed durability of the tire by suppressing the peeling that occurs remarkably at the end of the belt layer during high-speed running and the protrusion of the end of the belt, the tire circumference on the outer side in the tire radial direction of the belt A belt reinforcing layer formed by coating reinforcing cords arranged substantially parallel to a direction with a coating rubber may be provided. Further, by providing the belt reinforcing layer, it is possible to suppress the tire diameter growth and the belt end protrusion during high-speed running, and to improve the high-speed durability of the tire to some extent. However, when a cord having a relatively low elastic modulus such as a nylon cord is used as the reinforcing cord of the belt reinforcing layer, the effect of suppressing the tire diameter growth and the belt end protrusion is not sufficient, and further performance improvement is achieved. It was desired.

  On the other hand, a tire is proposed in which a high elastic modulus cord such as an aramid fiber cord is used as a reinforcing cord for the belt reinforcing layer. However, a tire using a high elastic modulus cord as a reinforcing cord for the belt reinforcement layer has a problem that the riding comfort during low-speed running deteriorates although the high-speed durability is high.

  On the other hand, Japanese Patent Application Laid-Open No. 2000-142025 (Patent Document 1) proposes a tire to which a polyketone fiber cord is applied as a reinforcing cord of the belt reinforcing layer. According to the gazette, a tire using a polyketone fiber cord as the reinforcement cord of the belt reinforcement layer is said to have a road noise greatly reduced and a high-speed durability greatly improved.

JP 2000-142525 A

  However, as a result of examination by the present inventor, even for the radial tire disclosed in Japanese Patent Application Laid-Open No. 2000-142025, the high speed durability of the tire due to the recent increase in the speed of the vehicle is required. There is a need to develop tires that are not sufficiently durable and have improved high-speed durability.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a pneumatic radial tire in which high-speed durability is greatly improved while maintaining riding comfort during low-speed traveling.

  As a result of earnest studies to achieve the above object, the inventor of the present invention is a pneumatic radial tire including a pair of belt reinforcing layers on the outer side in the tire radial direction at both ends of the belt. After using a polyketone fiber cord having heat shrinkage stress and elastic modulus, a pair of tread rubber layers located at the center in the tire width direction and a pair of tread rubber layers located at both outer sides in the tire width direction of the center tread rubber layer A tread rubber layer consisting of a shoulder tread rubber layer is arranged, and the loss tangent (tan δ) of the shoulder tread rubber layer is made larger than the loss tangent of the center tread rubber layer, so that the tread as during low-speed running When the section is at a relatively low temperature, the polyketone fiber cord does not develop heat shrinkage stress, so the riding comfort during low-speed driving is good, while high When the tread part becomes relatively hot during running, the polyketone fiber cord quickly develops heat shrinkage stress and suppresses tire diameter growth and belt end protrusion, resulting in high tire speeds. The inventors have found that the durability is greatly improved and have completed the present invention.

That is, the pneumatic radial tire of the present invention has a pair of bead portions and a pair of sidewall portions, a tread portion connected to both sidewall portions, and a toroid-like extension between the pair of bead portions. A carcass to be reinforced, a belt disposed on the outer side in the tire radial direction of the crown portion of the carcass, and a reinforcing cord arranged substantially parallel to the tire circumferential direction is coated with a coating rubber, and the tire of the belt In a pneumatic radial tire comprising a pair of belt reinforcing layers arranged so as to cover both ends of the belt radially outside,
The belt reinforcing layer has the following formula (I) and formula (II):
σ ≧ -0.01 × E + 1.2 (I)
σ ≥ 0.02 (II)
[In the formula, σ is a heat shrinkage stress (cN / dtex) at 177 ° C .; E is an elastic modulus at 49 N load (cN / dtex) at 25 ° C.] ,
The tread portion has a tread rubber layer on the outer side in the tire radial direction of the belt and the belt reinforcing layer, the tread rubber layer is located at the center in the tire width direction, and the tire of the central tread rubber layer It comprises a pair of shoulder tread rubber layers located on both outer sides in the width direction, characterized in that tan δ at 30 ° C. of the shoulder tread rubber layer is larger than tan δ at 30 ° C. of the central tread rubber layer. To do.

  Here, the heat shrinkage stress σ at 177 ° C. of the polyketone fiber cord is a stress generated in the cord at 177 ° C. by heating a 25 cm length fixed sample at a temperature rising speed of 5 ° C./min. The elastic modulus E of the polyketone fiber cord under a load of 49 N at 25 ° C. is an elastic modulus in a unit cN / dtex calculated from a tangent at 49 N of the SS curve by a JIS cord tensile test.

  In a preferred example of the pneumatic radial tire of the present invention, tan δ at 30 ° C. of the shoulder tread rubber layer is 0.4 or more. In this case, the temperature of the shoulder tread rubber layer rises rapidly during high-speed running, the temperature of the polyketone fiber cord in the belt reinforcement layer rises quickly, and the tire diameter grows and the belt end protrudes during high-speed running. Can be reliably suppressed, and the high-speed durability of the tire can be sufficiently improved.

  In the pneumatic radial tire of the present invention, the polyketone fiber cord preferably has a heat shrinkage stress σ at 177 ° C. of 0.3 cN / dtex or more, and more preferably 0.5 cN / dtex or more. In this case, the polyketone fiber cord expresses a large heat shrinkage stress during high-speed running, and the high-speed durability of the tire can be further improved.

  ADVANTAGE OF THE INVENTION According to this invention, the pneumatic radial tire which improved the high-speed durability significantly can be provided, maintaining the riding comfort at the time of low speed driving | running | working.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view of one embodiment of the pneumatic radial tire of the present invention.

  The radial tire shown in FIG. 1 has a pair of bead portions 1 and a pair of sidewall portions 2, a tread portion 3 connected to both sidewall portions 2, and a toroidal shape extending between the pair of bead portions 1. A radial carcass 4 that reinforces each of the parts 1, 2, 3, a belt 5 that is disposed on the outer side in the tire radial direction of the crown part of the radial carcass 4, and the belt 5 that covers the entire belt 5 on the outer side in the tire radial direction. A belt reinforcing layer 6A disposed in the tire, a pair of belt reinforcing layers 6B disposed so as to cover both ends of the belt 5 on the outer side in the tire radial direction of the belt reinforcing layer 6A, and the belt 5 and the belt of the tread portion 3 And tread rubber layers 7A and 7B disposed on the outer side in the tire radial direction of the reinforcing layers 6A and 6B.

  A radial carcass 4 of a radial tire shown in FIG. 1 is composed of two carcass plies, and a main body portion extending in a toroidal shape between a pair of bead cores 8 embedded in the bead portion 1, respectively. Each bead core 8 includes a folded portion wound radially outward from the inner side to the outer side in the tire width direction. In the pneumatic radial tire of the present invention, the number of plies and the structure of the radial carcass 4 are as follows. It is not limited to.

  The radial tire shown in FIG. 1 includes a bead filler 9 on the outer side in the tire radial direction of the ring-shaped bead core 8 embedded in the bead portion 1. The pneumatic radial tire of the present invention includes the bead filler 9. It does not have to be provided.

  Further, the radial tire shown in FIG. 1 includes a belt 5 formed of two belt layers on the outer side in the tire radial direction of the crown portion of the radial carcass 4. 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 further, two belt layers are formed of the belt layer. The belt 5 is formed by laminating the cords constituting the belt 5 so as to cross each other with the tire equator plane interposed therebetween. The belt 5 in the figure is composed of two belt layers. However, in the pneumatic radial tire of the present invention, the number of belt layers constituting the belt 5 is not limited to this.

  Furthermore, the radial tire shown in FIG. 1 covers a belt reinforcing layer 6A that covers the entire belt 5 on the outer side in the tire radial direction of the belt 5, and covers both ends of the belt 5 on the outer side in the tire radial direction of the belt reinforcing layer 6A. The pneumatic radial tire of the present invention may not have the belt reinforcing layer 6A that covers the entire belt 5. Further, in the illustrated tire, the pair of belt reinforcing layers 6B covering the end of the belt 5 is composed of one layer, but may be composed of a plurality of layers. Here, the belt reinforcing layers 6A and 6B are usually formed by coating a cord arranged substantially parallel to the tire circumferential direction with a coating rubber.

In the pneumatic radial tire of the present invention, the pair of belt reinforcing layers 6B covering the end portion of the belt 5 has the following formulas (I) and (II):
σ ≧ -0.01 × E + 1.2 (I)
σ ≥ 0.02 (II)
[In the formula, σ is a heat shrinkage stress (cN / dtex) at 177 ° C .; E is an elastic modulus (cN / dtex) at a load of 49 N at 25 ° C.] It takes a thing. When the pneumatic radial tire of the present invention has a belt reinforcing layer 6A that covers the entire belt 5 in addition to the pair of belt reinforcing layers 6B that covers the end of the belt 5, the reinforcing cord used for the belt reinforcing layer 6A is The cord is not particularly limited, and may be a polyketone fiber cord or another cord.

  The polyketone fiber cord shrinks at a high temperature to express a large heat shrinkage stress, and has a reversibility that expands when returned to room temperature. Since the polyketone fiber cord has a large thermal shrinkage stress at high temperatures, the tire diameter growth and the protrusion of the end of the belt 5 are surely suppressed during high-speed running when the tire is at a high temperature. Can improve sex. Further, since the polyketone fiber cord does not develop heat shrinkage stress at low temperatures, the riding comfort of the tire during low speed running is not deteriorated.

  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, a tire at high speed running as in the case of applying a nylon cord When a cord having a high elastic modulus E but a small heat shrinkage stress σ is used, the aramid cannot be sufficiently suppressed. Similar to the case where the cord is applied, the tire ride comfort during low-speed driving deteriorates.

  Further, when the cord used does not satisfy the relationship of the above formula (II), the high speed durability of the tire cannot be sufficiently improved. From the viewpoint of further improving the high-speed durability of the tire, the heat shrinkage stress σ at 177 ° C. of the polyketone fiber cord is preferably 0.3 cN / dtex or more, and more preferably 0.5 cN / dtex or more.

  In the pneumatic radial tire of the present invention, the tread portion 3 has tread rubber layers 7A and 7B on the outer side in the tire radial direction of the belt 5 and the belt reinforcing layers 6A and 6B, and the tread rubber layers 7A and 7B are tires. The center tread rubber layer 7A located in the center in the width direction and a pair of shoulder tread rubber layers 7B located on both outer sides in the tire width direction of the center tread rubber layer 7A. It is necessary that tan δ at 30 ° C. is larger than tan δ at 30 ° C. of the central tread rubber layer 7A. In this case, since the hysteresis loss of the shoulder tread rubber layer 7B close to the belt reinforcing layer 6B covering the end of the belt 5 is large, the temperature of the shoulder tread rubber layer 7B rises rapidly during high speed running, and the polyketone fiber The cord quickly becomes hot and immediately develops a large heat shrink stress. As a result, the polyketone fiber cord in the belt reinforcing layer 6B sufficiently suppresses the growth of the tire diameter and the protrusion of the end of the belt 5 during high speed running, and the high speed durability of the tire is greatly improved.

  Here, from the viewpoint of increasing the temperature of the polyketone fiber cord sufficiently quickly during high-speed running, the shoulder tread rubber layer 7B preferably covers 50% or more of the outer side in the tire radial direction of the belt reinforcing layer 6B. More preferably, the entire surface is covered. The boundary between the shoulder tread rubber layer 7B and the central tread rubber layer 7A is more preferably 7 mm or more from the inner end in the tire width direction of the belt reinforcing layer 6B from the center in the tire width direction.

  In the pneumatic radial tire according to the present invention, the tan δ of the shoulder tread rubber layer 7B is made larger than the tan δ of the central tread rubber layer 7A, thereby preventing a change in performance of the tire at high speed and gripping properties. The effect which improves is also acquired.

  In the pneumatic radial tire of the present invention, tan δ at 30 ° C. of the shoulder tread rubber layer 7B is preferably 0.4 or more. If the tan δ at 30 ° C. of the shoulder tread rubber layer 7B is 0.4 or more, the temperature of the shoulder tread rubber layer 7B rises more rapidly during high speed running, and the temperature of the polyketone fiber cord in the belt reinforcing layer 6B is increased. Furthermore, it can raise rapidly. On the other hand, tan δ at 30 ° C. of the central tread rubber layer 7A is not particularly limited as long as it is lower than tan δ at 30 ° C. of the shoulder tread rubber layer 7B, but is preferably 0.4 or less.

  Further, in the pneumatic radial tire of the present invention, a central tread rubber layer 7A having a smaller hysteresis loss, that is, a low heat generating property, is disposed between the pair of shoulder tread rubber layers 7B having a large hysteresis loss. Therefore, an increase in rolling resistance of the tire due to the shoulder tread rubber layer 7B is suppressed. Therefore, it is superior in terms of fuel efficiency compared to a tire in which high-loss rubber is applied to the entire tread rubber layer.

  In the belt reinforcing layer 6B including the polyketone fiber cord, the number of driven polyketone fiber cords is preferably in the range of 35 to 60 (lines / 50 mm). If the number of driven polyketone fiber cords is less than 35 (lines / 50 mm), the strength of the belt reinforcing layer 6B is insufficient and the durability is insufficient. In addition, even if the number of driving exceeds 60 (pieces / 50 mm), there is no particular limitation as long as the driving can be performed.

  The polyketone fiber cord is preferably formed by twisting a plurality of filament bundles made of polyketone having a fineness of 500 to 2000 dtex, and more preferably by twisting two or three strands. If the fineness of the filament bundle used for the polyketone fiber cord is less than 500 dtex, both the elastic modulus and the heat shrinkage stress are insufficient, and if it exceeds 2000 dtex, the cord diameter becomes thick and the driving cannot be made dense.

［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ポリケトンが好ましい。また、該ポリケトンの中でも、繰り返し単位の97モル％以上が１-オキソトリメチレン［−ＣＨ₂−ＣＨ₂−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。 The polyketone used as the raw material for the polyketone fiber cord is represented by the following formula (III):

[Wherein, A is a portion derived from an unsaturated compound polymerized by an unsaturated bond, and may be the same or different in each repeating unit], and a polyketone substantially consisting of a repeating unit represented by 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 preferred, and a polyketone in which 100 mol% is 1-oxotrimethylene is most preferred.

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

  In the formula (III), 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-vinyl pyrrolidone, diethyl ester of sulphonylphosphonic acid , A compound containing an unsaturated bond, such as sodium styrenesulfonate, sodium allylsulfonate, vinylpyrrolidone, and vinyl chloride.

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

[Wherein, t and T are the flow times of a viscosity tube at 25 ° C. of a diluted solution of hexafluoroisopropanol having a purity of 98% or more and a polyketone dissolved in the hexafluoroisopropanol; C is 100 mL of the diluted solution It is preferable that the intrinsic viscosity [η] defined by the mass (g) of the solute in the range is 1 to 20 dL / g, more preferably 2 to 10 dL / g, and 3 to Even more preferably 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 drawing. 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 -Unstretched polyketone yarn can be obtained by removing the solvent in a non-solvent bath such as hexane, isooctane, acetone, methyl ethyl ketone, and washing.

  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, etc. at a concentration of 2 to 30% by mass, and a spinning nozzle is used 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 performed by the method of (1) above, the temperature in the final stretching step of the multistage thermal stretching is in the range of 110 ° C to (stretching temperature in the stretching step one step before the final stretching step-3 ° C). 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 (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 ° C / The cooling end temperature in the rapid cooling is preferably 50 ° C. or lower. Here, the method for rapidly cooling the heat-stretched polyketone fiber is not particularly limited, and a conventionally known method can be adopted. Specifically, a cooling method using a roll is preferable. In addition, since the polyketone fiber obtained in this way has a large residual elastic strain, it is usually preferable to perform relaxation heat treatment so that the fiber length is shorter than the fiber length after hot drawing. Here, the temperature of the relaxation heat treatment is preferably in the range of 50 to 100 ° C., and the relaxation ratio is preferably in the range of 0.980 to 0.999 times.

  Preferably, the polyketone fiber cord can be produced by twisting a plurality of filament bundles made of the polyketone, more preferably two or three, more specifically, for example, a filament made of the polyketone. A twisted cord having a double twisted structure can be obtained by applying a lower twist to the bundle, then combining a plurality of the bundles and applying an upper twist in the opposite direction. The polyketone fiber cord may be a single twisted cord bundle formed by twisting one filament bundle made of the polyketone. In this case, the filament bundle made of the polyketone is gathered, A twisted cord can be obtained by twisting in the direction.

  The cord / rubber composite used for the belt reinforcing layer 6B can be obtained by coating the polyketone fiber cord obtained as described above with a coating rubber. Here, there is no restriction | limiting in particular as coating rubber of a polyketone fiber cord, The coating rubber used for the 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 radial tire of the present invention, a cord / rubber composite formed by coating the above polyketone fiber cord with a coating rubber is applied to the belt reinforcing layer 6B, and the tread rubber layer 7A and the shoulder tread are formed on the tread portion 3. A tread rubber layer composed of the rubber layer 7B is disposed, and the shoulder tread rubber layer 7B is manufactured according to a conventional method except that the tan δ at 30 ° C. is larger than the tan δ at 30 ° C. of the central tread rubber layer 7A. be able to. The belt reinforcing layer 6B is, for example, a ribbon-like cord / rubber composite formed by coating one or more polyketone fiber cords having a width smaller than the width of the belt reinforcing layer 6B with a coating rubber. It is preferably formed by spiral winding a plurality of times in the circumferential direction of the tire until a predetermined width dimension is reached. In this case, a joint part does not occur in the tire circumferential direction, and the belt 5 can be reinforced uniformly. In the pneumatic radial tire of the present invention, as the gas filled in the tire, normal or air having a changed oxygen partial pressure, or an inert gas such as nitrogen can be used.

  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.

  A radial tire of size 225 / 45R17 having the structure shown in FIG. 1 was produced according to a conventional method. Each test tire is the same except for the type, structure and physical properties of the cord used for the belt reinforcing layer, and the physical properties of the rubber used for the shoulder tread rubber layer. Table 1 shows the type, structure and physical properties of the cords used, and tan δ measured under the conditions of the shoulder tread rubber layer and the central tread rubber layer: 30 ° C., frequency: 52 Hz, and strain: 1%.

  Further, the belt of each test tire is composed of two steel belt layers, the belt layer on the inner side in the tire radial direction has a width of 190 mm, and the belt layer on the outer side in the tire radial direction has a width of 180 mm. Further, a belt reinforcing layer 6A adjacent to the belt and covering the entire belt is arranged so as to protrude 5 mm from the belt end outward in the tire width direction, and further, both end portions of the belt at the outer side in the tire radial direction of the belt reinforcing layer 6A. The belt reinforcing layer 6B that covers only the belt was disposed with a width of 25 mm from the end of the belt reinforcing layer 6A to the inside in the tire width direction. Furthermore, the width in the tire width direction of the central tread rubber layer 7A of the tire of the example is 130 mm, the width of the shoulder tread rubber layer 7B is 45 mm, the shoulder tread rubber layer 7B and the central tread rubber layer. The boundary with 7A is 10 mm from the center in the tire width direction from the inner end in the tire width direction of the belt reinforcing layer 6B. The tires thus produced were evaluated for high-speed durability and riding comfort by the following methods. The results are shown in Table 1.

(1) High-speed durability Drum tests were conducted on the test tires, and the speed was increased by 10 km / h to measure the speed at the time of failure. The higher the speed at the time of the failure, the higher the durability limit speed and the higher the high speed durability.

(2) Ride comfort The load-deflection curve of the test tire was measured, and the tangential slope at a certain load on the obtained load-deflection curve was defined as the longitudinal spring constant for the load, and the longitudinal spring constant of the tire of Comparative Example 1 The value was expressed as an index with the value of 100 being 100. A larger index value indicates a larger longitudinal spring constant.

  As apparent from Table 1, the polyketone fiber cord satisfying the above formulas (I) and (II) is applied to the belt reinforcing layer, and then the tread rubber layer is divided in the width direction to form the shoulder tread rubber layer 7B. By making tan δ at 30 ° C. higher than tan δ at 30 ° C. of the central tread rubber layer 7A, the high-speed durability of the tire can be improved without deteriorating the riding comfort during low-speed traveling.

It is sectional drawing of one embodiment of the pneumatic radial tire of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Bead part 2 Side wall part 3 Tread part 4 Radial carcass 5 Belt 6A Belt reinforcement layer which covers the whole belt 6B Belt reinforcement layer which covers the edge part of a belt 7A Center part tread rubber layer 7B Shoulder part tread rubber layer 8 Bead core 9 Bead Filler

Claims (4)

A pair of bead portions and a pair of sidewall portions, a tread portion connected to both sidewall portions, a carcass extending in a toroidal shape between the pair of bead portions to reinforce these portions, and a crown portion of the carcass A belt disposed on the outer side in the tire radial direction and a reinforcing cord arranged substantially parallel to the tire circumferential direction are coated with a coating rubber so as to cover both ends of the belt on the outer side in the tire radial direction of the belt. In a pneumatic radial tire comprising a pair of belt reinforcement layers arranged in
The belt reinforcing layer has the following formula (I) and formula (II):
σ ≧ -0.01 × E + 1.2 (I)
σ ≥ 0.02 (II)
[In the formula, σ is a heat shrinkage stress (cN / dtex) at 177 ° C .; E is an elastic modulus at 49 N load (cN / dtex) at 25 ° C.] ,
The tread portion has a tread rubber layer on the outer side in the tire radial direction of the belt and the belt reinforcing layer, the tread rubber layer is located at the center in the tire width direction, and the tire of the central tread rubber layer It comprises a pair of shoulder tread rubber layers located on both outer sides in the width direction, characterized in that tan δ at 30 ° C. of the shoulder tread rubber layer is larger than tan δ at 30 ° C. of the central tread rubber layer. Pneumatic radial tire.   2. The pneumatic radial tire according to claim 1, wherein tan δ at 30 ° C. of the shoulder tread rubber layer is 0.4 or more.   2. The pneumatic radial tire according to claim 1, wherein the polyketone fiber cord has a heat shrinkage stress σ at 177 ° C. of 0.3 cN / dtex or more. The pneumatic radial tire according to claim 3, wherein the heat shrinkage stress σ at 177 ° C of the polyketone fiber cord is 0.5 cN / dtex or more.

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