JP2009190727A - Pneumatic radial tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic radial tire providing excellent high-speed durability and low rolling resistance without causing other problems such as increase in manufacturing costs and increase in the weight of the tire. <P>SOLUTION: The pneumatic radial tire 10 is equipped with: a bead core 1; a carcass ply 2; a belt 3; a belt reinforcement layer 4 arranged approximately in the tire-equator direction; and a tread 5. A fiber cord forming the belt reinforcement layer 4 is a single-twisted cord containing PK fibers of at least 90 mass% or more. The maximum thermal shrinkage stress as a dipped cord is 15 N/yarn or less. The maximum value of a distance between the fiber cord of the belt reinforcement layer 4 and a steel cord in the outermost belt layer of the belt 3 is 0.4 mm or smaller in a tire center part. The minimum value of the distance between the fiber cord of the belt reinforcement layer 4 and the steel cord of the outermost belt layer is 0.3 mm or larger within a range from an end part of the outermost belt layer to 10 mm inside of the end part. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a pneumatic radial tire (hereinafter also simply referred to as “tire”), and more particularly, to a pneumatic radial tire according to an improvement in a reinforcing cord used for a belt reinforcing layer.

  In general, in a pneumatic radial tire for high-speed traveling, a belt reinforcing layer that covers at least both ends of the belt layer is disposed outside the belt layer in the tire radial direction. This belt reinforcing layer has an effect of improving the high-speed durability of the tire by suppressing the rising of both ends of the belt layer caused by the centrifugal force during high-speed rotation by the tagging effect.

  Conventionally, the cord constituting the belt reinforcing layer is mainly an organic fiber cord having a double twist structure in which a plurality of strands (so-called strands) of organic fibers subjected to a lower twist are further twisted by an upper twist. in use. In addition, for the purpose of reducing manufacturing cost and tire weight, it has also been proposed to use a cord having a single-stranded structure composed of only one strand (for example, Patent Documents 1 and 2).

Japanese Examined Patent Publication No. 59-1601 JP 2002-154304 A

  Conventionally, as a cord material of the belt reinforcing layer, organic fibers having a low elastic modulus such as nylon are mainly used. However, such a low elastic modulus organic fiber cord has a problem that sufficient high-speed durability may not be obtained in a tire that has been flattened and enlarged in recent years.

  On the other hand, it has been proposed to improve the high-speed durability of a flattened and enlarged tire by using a polyketone fiber having a high elastic modulus as a belt reinforcing layer cord. However, with such a high elastic modulus cord, it is difficult to ensure a sufficient gap between the belt reinforcing layer cord and the belt layer cord disposed on the inner side in the tire radial direction during tire manufacture. For this reason, in order to ensure sufficient high-speed durability, a method such as inserting a rubber strip between the belt layer and the belt reinforcing layer is necessary, which leads to an increase in manufacturing cost and an increase in tire weight. there were. Furthermore, in a pneumatic radial tire, it is also important to have a low rolling resistance that contributes to low fuel consumption.

  Accordingly, an object of the present invention is to provide a pneumatic radial tire that achieves excellent high-speed durability and low rolling resistance without solving the above problems and causing other problems such as an increase in manufacturing cost and an increase in tire weight. It is to provide.

  As a result of intensive studies, the present inventor has found that the above problem can be solved by using a predetermined piece-twisted polyketone fiber cord as the cord used for the belt reinforcing layer, and has completed the present invention.

That is, the pneumatic radial tire of the present invention includes a bead core provided on each of a pair of left and right bead portions, and a radial cord layer extending from the crown portion to both bead portions via both sidewall portions and anchored to the bead core. A carcass ply; a belt disposed radially outward of the crown portion of the carcass ply; a belt reinforcing layer disposed substantially outside the belt in a tire equator direction; and a tread disposed outside the belt reinforcing layer. In a pneumatic radial tire comprising
The fiber cord forming the belt reinforcing layer is a single twist cord containing at least 90% by mass of polyketone fiber, and the maximum heat shrinkage stress as a dip-treated cord is 15 N / line or less,
In the tire center portion, the maximum value of the distance between the fiber cord forming the belt reinforcing layer and the steel cord forming the outermost belt layer of the belt is 0.4 mm or less, and
The minimum value of the distance between the fiber cord forming the belt reinforcing layer and the steel cord forming the outermost belt layer is 0.3 mm within the range from the end of the outermost belt layer to 10 mm inside thereof. The above is a feature.

  In the present invention, it is preferable that the fiber cord forming the belt reinforcing layer has a heat shrinkage rate of 0.6% or more and less than 2% at 177 ° C. for 30 minutes as a dip-treated cord at the time of dry heat treatment. The total fineness of the fiber cord forming the belt reinforcing layer is preferably 800 dtex or more and 3400 dtex or less, and the number of twists of the fiber cord forming the belt reinforcing layer is 120 times / 1 m or more and 480 times / 1 m or less. It is also preferable. Furthermore, the gap between the fiber cord forming the belt reinforcing layer and the adjacent fiber cord is preferably 0.35 mm or less. Furthermore, in the present invention, it is preferable that a rubber sheet having a thickness of 0.2 mm or more and a width of 10 mm or more is inserted between the fiber cord forming the belt reinforcing layer and the belt.

Here, the maximum heat shrinkage stress of the cord means that a 25 cm long fixed sample of a belt reinforced 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: N / piece) generated in the cord at the time of ° C. The heat shrinkage rate during dry heat treatment is the same as that of the dip-treated cord after dry heat treatment at 177 ° C. for 30 minutes in an oven, and the cord length before and after the heat treatment is measured by applying a load of 50 g. This is a value obtained by an expression.
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.

  In the present invention, the predetermined single twist polyketone fiber cord is used as the fiber cord for forming the belt reinforcing layer, so that the heat shrinkage stress of the cord can be reduced, and the cord due to the shrinkage during vulcanization can be suppressed. Biting in can be prevented. As a result, the gap between the belt reinforcing layer cord and the belt layer cord can be secured without using a rubber strip or the like, and it is excellent without causing other problems such as an increase in manufacturing cost and an increase in tire weight. In addition, it has become possible to realize a pneumatic radial tire having high-speed durability and low rolling resistance, which can contribute to low fuel consumption. In other words, since the single twisted cord is twisted only in one direction (no twist is added), para-aramid with poor heat setability is easy to return due to the tension action at the time of manufacture. In the past, it was applied only to nylon, but polyketone fiber has good setability even when heat is applied, so workability does not deteriorate even when single twist is applied. The code can be applied.

1 is a cross-sectional view in the width direction showing a pneumatic radial tire according to an embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
In FIG. 1, the one-side cross section figure of the pneumatic radial tire of an example of this invention is shown. As shown in the figure, a pneumatic radial tire 10 according to the present invention includes a bead core 1 provided on each of a pair of left and right bead portions 11 and a bead core 1 extending from a crown portion 12 to both bead portions 11 via both side wall portions 13. A moored carcass ply 2 made of a radial cord layer, a belt 3 arranged radially outward of the crown portion, a belt reinforcing layer 4 arranged substantially in the tire equator direction on the outer side, and further arranged on the outer side thereof Tread 5.

  In the present invention, among these, the fiber cord forming the belt reinforcing layer 4 is a single twisted cord containing at least 90% by mass or more of polyketone fiber. Thereby, weight reduction of a tire and reduction of manufacturing cost can be aimed at, ensuring sufficient high-speed durability of a flat and large sized tire.

  Further, the maximum heat shrinkage stress of the fiber cord as a dip-treated cord is 15 N / line or less, preferably 10 N / line or less, more preferably 5 to 8 N / line. When the maximum heat shrinkage stress exceeds 15 N, a sufficient gap can be secured between the fiber cord and the belt layer cord disposed inside the belt reinforcing layer due to heat shrinkage generated during tire manufacture. It becomes difficult.

  Furthermore, in the present invention, in the tire center portion, the maximum value of the distance between the fiber cord forming the belt reinforcing layer 4 and the steel cord forming the outermost belt layer of the belt 3 is 0.4 mm. Hereinafter, it is preferably 0.2 to 0.3 mm. If the maximum value of the distance between the fiber cord forming the belt reinforcing layer 4 and the steel cord forming the outermost belt layer is greater than 0.4 mm in the tire center portion, the rolling resistance reduction effect is reduced. Here, in the present invention, the outermost layer belt layer means a belt layer constituting the belt 3 adjacent to the belt reinforcing layer 4, and in the case of the belt 3 composed of a two-layer belt layer as illustrated. Is the second belt layer.

  Furthermore, in the present invention, the distance between the fiber cord forming the belt reinforcing layer 4 and the steel cord forming the outermost belt layer is within a range from the end of the outermost belt layer to the inner 10 mm thereof. The minimum value is 0.3 mm or more, preferably 0.4 to 0.6 mm. Within the above range, if the minimum value of the distance between the fiber cord forming the belt reinforcing layer 4 and the steel cord forming the outermost belt layer is less than 0.3 mm, there is a concern that durability may deteriorate during high-speed running. is there. In the present invention, the distance between the belt reinforcing layer cord and the belt layer cord can be measured by cutting the tire in the meridian direction and observing the cross section with a microscope.

  Furthermore, the fiber cord forming the belt reinforcing layer 4 preferably has a heat shrinkage rate of 177 ° C. × 30 minutes as a dip-treated cord at the time of dry heat treatment of 0.6% or more and less than 2%. Preferably, it is 0.8% or more and less than 1.6%. If this thermal shrinkage is less than 0.6%, sufficient residual tension is not generated during tire manufacture, and it may be difficult to ensure sufficient high-speed durability. On the other hand, if it exceeds 2%, it becomes difficult to ensure a sufficient gap between the fiber cord and the belt layer cord disposed inside the belt reinforcing layer due to heat shrinkage that occurs during tire manufacture.

  Furthermore, the total fineness of the fiber cords forming the belt reinforcing layer 4 is preferably 800 dtex or more and 3400 dtex or less, more preferably 1100 dtex or 2200 dtex or less. If the total fineness of the fiber cord is less than 800 dtex, the cord diameter becomes thin and the bending rigidity is remarkably reduced, which causes a problem that workability at the time of manufacturing the tire is deteriorated. On the other hand, if the total fineness exceeds 3400 dtex, the thickness of the belt reinforcing layer becomes excessive and the amount of rubber used increases, resulting in problems such as an increase in tire weight and deterioration in rolling resistance.

  Furthermore, the number of twists of the fiber cord forming the belt reinforcing layer 4 is preferably 120 times / 1 m or more and 480 times / 1 m or less, more preferably 150 times / 1 m or more and 200 times / 1 m or less. When the number of twists of the fiber cord is less than 120 times / 1 m, the convergence of the filament is remarkably lowered, and the rigidity utilization rate may be lowered. On the other hand, when the number of twists exceeds 480 times / 1 m, it is necessary to use more fibers in order to ensure sufficient rigidity, which may result in an increase in tire weight and manufacturing cost. Furthermore, since the untwisting torque is remarkably increased, there is a concern that it may cause untwisting or defective properties during production.

  Furthermore, in the present invention, the gap between the fiber cord forming the belt reinforcing layer 4 and the adjacent fiber cord is preferably 0.35 mm or less, more preferably 0.2 to 0.3 mm. is there. If this gap is larger than 0.35 mm, the fiber cord will bite into the inside of the tire due to expansion and thermal contraction during product manufacture, and as a result, it will not be possible to secure a sufficient gap between the belt reinforcing layer and the belt, and high speed running will occur. There is a concern that will lead to deterioration of durability at times.

  Next, a single-strand cord for belt reinforcement layer (hereinafter referred to as PK fiber cord) containing at least 90% by mass of polyketone fiber (hereinafter abbreviated as “PK fiber”) 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０．１〜０．８８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０．１未満では、熱収縮応力が十分に確保できず、一方、０．８８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。 The PK fiber cord has 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 0.1 to 0.88. When the twist coefficient α of the PK fiber cord is less than 0.1, the heat shrinkage stress cannot be sufficiently ensured. On the other hand, when it exceeds 0.88, 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%.

  As the method for fiberizing the polyketone, (1) after spinning an unstretched yarn, performing multistage hot drawing, and drawing at a specific temperature and magnification in the final drawing step of the multistage hot drawing, (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 the 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, JP-A-2004-218189, JP-A-2004-285221, and the wet spinning method using an aqueous solution of zinc salt, calcium salt, thiocyanate, iron salt, etc. Among these, the wet spinning method using an aqueous solution of the above salt is preferable.

  For example, in a wet spinning method using an organic solvent, a polyketone polymer is dissolved in hexafluoroisopropanol, m-cresol, or the like at a concentration of 0.25 to 20% by mass, extruded from a spinning nozzle to be fiberized, and then toluene, ethanol, isopropanol The unstretched yarn of polyketone can be obtained by removing and washing the solvent in a non-solvent bath such as n-hexane, isooctane, acetone or methyl ethyl ketone.

  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, and further desalting and drying can be performed to obtain unstretched polyketone. 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 a method of heat drawing, 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 suitably 10 times or more.

  When polyketone fiberization is carried out by the method of (1) above, the temperature in the final stretching step of the multistage hot stretching is in the range of 110 ° C. to (the stretching temperature of the stretching step one step before the final stretching step). Moreover, the draw ratio in the final drawing step of multistage hot drawing is preferably in the range of 1.01 to 1.5 times. On the other hand, when polyketone fiberization is carried out by the method of (2) above, the tension applied to the fiber after completion of the hot drawing is preferably in the range of 0.5 to 4 cN / dtex, and the cooling rate in rapid cooling is 30 The cooling end temperature in the rapid cooling is preferably 50 ° C. or less. 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.

  In order to make the most effective use of the high heat shrinkage characteristics of single twisted cords containing PK fibers, the processing temperature at the time of processing and the temperature of the molded product at the time of use are the temperatures that exhibit the maximum heat shrinkage stress (maximum heat shrinkage). It is desirable that the temperature be close to (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.

  By cording the PK fiber cord obtained as described above, a cord / rubber composite used for the belt reinforcing layer 4 can be obtained. Here, there is no restriction | limiting in particular as coating rubber of PK fiber cord, The coating rubber used for the conventional belt reinforcement layer can be used. Prior to rubberizing the PK fiber cord, the PK fiber cord may be subjected to an adhesive treatment to improve the adhesion to the coating rubber.

  In the tire of the present invention, other points are not particularly limited as long as the belt reinforcing layer 4 is made of a PK fiber cord satisfying the above conditions. For example, although the belt reinforcing layer 4 is provided with substantially the same width as the belt 3 in the illustrated example, the belt reinforcing layer 4 is not limited to this and may be any one that covers at least both end portions and the center portion of the belt 3. The belt reinforcing layer 4 is made of the fiber cord and a coating rubber covering the fiber cord, and is disposed substantially in parallel with the tire equator direction. The number of layers is one in the illustrated example, but may be two or more, and is not particularly limited.

  The carcass 2 includes a radial cord layer formed by coating a plurality of reinforcing cords arranged in parallel in a substantially radial direction with a coating rubber. In the illustrated example, the carcass 2 extends from the crown portion 12 to both bead portions 11 through both side wall portions 13, wound around the bead core 1 and moored to the bead portion 11, but the carcass ply constituting the carcass 1 is a so-called envelope structure in which at least one ply is folded around the bead core 1 from the inner side to the outer side in the tire width direction and the folded end is located between the belt 3 and the crown portion of the carcass 2. You may have. The number of carcass 2 is two in the illustrated example, but may be one or three or more, and is not particularly limited.

  In the illustrated example, the belt 3 includes two belt layers. However, in the tire of the present invention, the number of belt layers constituting the belt 3 is not limited thereto. The belt 3 is usually composed of a rubberized layer of cords extending in an inclined manner with respect to the tire equatorial plane, preferably a rubberized layer of steel cords, and the two belt layers are composed of each cord constituting the belt layer. The belt 3 is formed by being laminated so as to intersect with each other across the equator plane.

  Furthermore, in the present invention, it is preferable to insert a rubber sheet having a thickness of 0.2 mm or more and a width of 10 mm or more between the fiber cord forming the belt reinforcing layer 4 and the belt 3 disposed inside thereof. . Since a sufficient distance can be maintained between the belt and the belt reinforcing layer by inserting the rubber sheet, durability is improved. For example, a rubber sheet having a thickness of 0.4 to 1.0 mm and a width of 10 to 40 mm can be suitably used. When the thickness of the rubber sheet is less than 0.2 mm, it is difficult to obtain the effect of inserting the rubber sheet, and when the width is less than 10 mm, handling during manufacture becomes difficult.

  In the pneumatic radial 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.

Hereinafter, the present invention will be described in more detail with reference to examples.
(Preparation example of PK fiber)
A polyketone polymer having an intrinsic viscosity of 5.3, which is prepared by a conventional method and is completely alternatingly copolymerized with ethylene and carbon monoxide, is added to an aqueous solution containing 65% by mass of zinc chloride / 10% by mass of sodium chloride, and 2 at 80 ° C. The mixture was dissolved with stirring for a time to obtain a dope having a polymer concentration of 8% by mass.

  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 spout diameter maintained 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 a sulfuric acid aqueous solution having a concentration of 2 mass% 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.
After impregnating IRGANOX 1098 (manufactured by Ciba Specialty Chemicals) and IRGANOX 1076 (manufactured by Ciba Specialty Chemicals) in an amount of 0.05% by mass (with respect to polyketone polymer), the coagulated yarn was 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 (mass% 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. The PK fiber thus obtained was used as a cord under the following conditions.

(Production of test tire)
A pneumatic radial tire with a tire size of 225 / 45R17 was prototyped according to the specifications shown in the following table, and evaluated for high-speed durability and rolling resistance. The evaluation results are shown in the table below together with the characteristics of the fiber cords of the belt reinforcing layer used for each test tire.

  As shown in FIG. 1, each test tire extends to the bead core 1 extending from the crown portion 12 to both bead portions 11 via the bead core 1 provided on the pair of left and right bead portions 11, and to the bead core 1. Further, two carcass plies made of a radial cord layer, a belt 3 made of two belt layers arranged on the outer side in the radial direction of the crown portion, and a single layer belt arranged on the outer side in a substantially tire equator direction. A reinforcing layer 4 and a tread 5 disposed further outside are provided. Of these, the belt 3 is composed of a steel cord having a 1 × 5 structure and a coating rubber covering the steel cord, and the cord angle is ± 35 ° with respect to the tire circumferential direction. The belt reinforcing layer 4 was composed of a single twisted cord shown in the following table and a coating rubber covering it.

(Heat shrinkage during dry heat treatment)
The heat shrinkage rate during the dry heat treatment of the cord used for the belt reinforcement layer was measured by subjecting each cord after the dipping treatment to a dry heat treatment at 177 ° C. for 30 minutes in an oven and applying a 50 g load to the cord length before and after the heat treatment. And calculated by the following formula.
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.)

(Maximum heat shrinkage stress)
The maximum heat shrinkage stress of the cord used for the belt reinforcement layer is determined by heating a 25 cm long fixed sample of the belt reinforcement cord after dip treatment before vulcanization at a heating rate of 5 ° C./min. Measured as the maximum stress (unit: N / piece) generated in.

<High speed durability>
Each test tire was assembled on a rim having a rim size of 7.5J-17, filled with an internal pressure of 300 kPa, and then the speed until a tire failure occurred was measured by a step speed method according to the test method of JATMA standard. The results are shown as an index with the conventional failure rate as 100. The larger the index value, the higher the endurance limit speed and the higher the durability at high speed.

<Rolling resistance>
The rolling resistance was evaluated by directly measuring the resistance of each test tire in a drum test at a speed of 80 km / h. The results are shown as an index with the resistance of the conventional example taken as 100. The smaller the index value, the smaller the rolling resistance and the better.

  From the results in the above table, in the test tires of the examples using the predetermined single twisted PK fiber cords as the fiber cords forming the belt reinforcing layer, the test tires of the conventional example and the comparative example that do not satisfy such conditions It is clear that excellent high-speed durability and rolling resistance are obtained as compared with the above.

1 Bead core 2 Carcass 3 Belt 4 Belt reinforcement layer 5 Tread 11 Bead portion 12 Crown portion 13 Side wall portion

Claims (6)

A bead core provided on each of the pair of right and left bead parts, a carcass ply made of a radial cord layer extending from the crown part to both bead parts through both side wall parts and anchored to the bead core, and a crown part radial of the carcass ply In a pneumatic radial tire comprising: a belt disposed outside in the direction; a belt reinforcing layer disposed substantially outside the belt in the tire equator direction; and a tread disposed outside the belt reinforcing layer.
The fiber cord forming the belt reinforcing layer is a single twist cord containing at least 90% by mass of polyketone fiber, and the maximum heat shrinkage stress as a dip-treated cord is 15 N / line or less,
In the tire center portion, the maximum value of the distance between the fiber cord forming the belt reinforcing layer and the steel cord forming the outermost belt layer of the belt is 0.4 mm or less, and
The minimum value of the distance between the fiber cord forming the belt reinforcing layer and the steel cord forming the outermost belt layer is 0.3 mm within the range from the end of the outermost belt layer to 10 mm inside thereof. A pneumatic radial tire characterized by the above.   2. The pneumatic radial tire according to claim 1, wherein the fiber cord forming the belt reinforcing layer has a heat shrinkage rate of 177 ° C. for 30 minutes as a dip-treated cord at the time of a dry heat treatment of 0.6% or more and less than 2%.   The pneumatic radial tire according to claim 1 or 2, wherein the total fineness of the fiber cord forming the belt reinforcing layer is 800 dtex or more and 3400 dtex or less.   The pneumatic radial tire according to any one of claims 1 to 3, wherein the number of twists of the fiber cord forming the belt reinforcing layer is 120 times / 1 m or more and 480 times / 1 m or less.   The pneumatic radial tire according to any one of claims 1 to 4, wherein a gap between a fiber cord forming the belt reinforcing layer and an adjacent fiber cord is 0.35 mm or less.   A pneumatic sheet according to any one of claims 1 to 5, wherein a rubber sheet having a thickness of 0.2 mm or more and a width of 10 mm or more is inserted between the fiber cord forming the belt reinforcing layer and the belt. Radial tire.

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