JP4966554B2 - Pneumatic radial tire - Google Patents

Description

  The present invention relates to a pneumatic radial tire, and more particularly to a pneumatic radial tire that is improved in handling stability and riding comfort during high-speed traveling while reducing the weight of the tire.

  In recent years, with increasing environmental problems, there is an urgent need to develop tires with low rolling resistance, that is, lightweight tires that contribute to fuel efficiency reduction of automobiles. In order to reduce the weight of the tire, a method of reducing the steel cord having a large specific gravity used as a belt cord of the tire, that is, applying an organic fiber cord to the belt cord is performed.

  In detail, application of a belt cord made of organic fibers such as aramid, polyester and polyketone has been attempted as a steel substitute material. However, since the belt to which the cord made of polyester fiber is applied has low in-plane rigidity, the grip force tends to be lowered and the handling stability tends to be deteriorated as compared with the belt to which the cord made of steel or aramid is applied. Furthermore, organic fibers such as polyester fibers tend to have lower handling stability when traveling at high speed because their elastic modulus decreases mainly with an increase in temperature. Therefore, the use of aramid fibers, which are highly elastic and less likely to decrease the modulus of elasticity when heated, solves the above problems. However, aramid has no heat shrinkage stress and does not adhere to rubber. In particular, there is a problem with durability when the vehicle runs at a high speed and the temperature rises. Aramid is also very expensive.

  Attempts have been made to use polyketone fibers as carcass cords or belt cords instead of polyester fibers and aramid fibers having these disadvantages (see Patent Documents 1 to 3). However, in recent years, there has been a demand for higher performance tires. In addition to excellent high-speed durability, driving at a low speed (about 40 km / hour) and at a high speed (about 200 km / hour). There is a need to develop tires that are excellent in handling stability and riding comfort at any time, and that have improved handling stability and riding comfort especially during high-speed driving.

JP 2000-202111 A JP 2001-334807 A JP 2001-341505 A

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a pneumatic radial tire that solves the above-mentioned problems of the prior art and improves the handling stability and ride comfort especially at high speed while reducing the weight of the tire. It is in.

  As a result of intensive studies to achieve the above object, the present inventor has found that a 49N elastic modulus E (cN / dtex) of 25 ° C. and a heat contraction stress σ (cN / dtex) of 177 ° C. are specified as the tire belt cord. By using a cord having a heat shrinkage force satisfying the relational expression for the belt, it has been found that it is possible to obtain a tire with improved handling stability and riding comfort particularly at high speeds compared to the conventional one, and the present invention. It came to complete.

That is, the pneumatic radial tire of the present invention includes a carcass made of a ply of a radial arrangement cord extending in a toroidal shape between a pair of bead portions, and two or more belt layers arranged radially outside the crown portion of the carcass A pneumatic radial tire comprising a belt comprising: a cord in which at least one of the belt layers is a cord formed by twisting two filament bundles made of polyketone fibers; 49N elastic modulus E (cN / dtex) and 177 ° C. heat shrinkage stress σ (cN / dtex) are represented by the following formulas (I) and (II):
σ ≧ −0.01E + 1.2 (I)
σ ≧ 0.02 (II)
It is characterized by satisfying.

  Here, the 177 ° C. heat shrinkage stress σ of the cord composed of the above polyketone fiber is a temperature increase of 5 ° C./min of a 25 cm long fixed sample of the polyketone fiber cord before vulcanization subjected to general Dip treatment. This is the stress generated in the cord at 177 ° C when heated at speed, and the 49N elastic modulus E at 25 ° C of the cord composed of the above polyketone fiber is the tangent at 49N of the SS curve according to the cord tension test of JIS The elastic modulus in unit cN / dtex calculated from

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

(Wherein A is a portion derived from an unsaturated compound polymerized by an unsaturated bond, and each repeating unit may be the same or different) and is characterized by consisting essentially of repeating units represented by .

  In another preferred embodiment of the pneumatic radial tire of the present invention, A in the general formula (III) is an ethylene group.

Oite the pneumatic radial tire of the present invention, the Suitable end count of cords of the belt layer is Ri forty / 50Mm～70 present / 50 mm der, more preferably fifty / 50Mm～70 present / 50 mm And particularly preferably 55/50 mm to 70/50 mm.

  According to the present invention, in the pneumatic radial tire, the polyketone fiber cord having a specific heat shrinkage stress and elastic modulus is used for at least one layer of the belt, so that the weight of the tire can be greatly reduced. There is an advantageous effect that it is possible to provide a pneumatic radial tire with improved handling stability and ride comfort than before.

  Details of the present invention will be described below. The pneumatic radial tire of the present invention is a belt comprising a carcass made of a ply of a radial arrangement code extending in a toroidal shape between a pair of bead portions, and two or more belt layers arranged radially outside the crown portion of the carcass. Is provided. The cords of the belt layer are inclined and arranged at a cord angle with respect to the equator plane of the tire. When there are two belt layers, the cords in these layers are laminated so as to cross each other.

  The cord used for at least one of the belt layers is a cord obtained by twisting two filament bundles composed of polyketone fibers (hereinafter referred to as polyketone fiber cord), and has a 49N elastic modulus E (cN / dtex) at 25 ° C. ) And 177 ° C. heat shrinkage stress σ (cN / dtex) must satisfy the above formulas (I) and (II). The polyketone fiber cord is lightweight and has an appropriate stretchability. If the above formula (I) is not satisfied, it is inappropriate to apply to the belt cord because of its low elastic modulus. Even if the above formula (I) is satisfied, if the above formula (II) is not satisfied, the heat shrinkage Therefore, the steering stability and riding comfort at high speed are inferior. The heat shrinkage stress σ is preferably 0.05 or more, more preferably 0.15 or more, and even more preferably 0.4 or more, in order to make the tread protrusion suppression effect at a high speed sufficient. . For the same reason, the elastic modulus E is preferably 60 or more, and more preferably 100 or more. Here, if the heat shrinkage stress σ is 1.5 or more, the shrinkage force at the time of vulcanization becomes too large, resulting in the disorder of the cord inside the tire and the disorder of the rubber arrangement, resulting in deterioration of durability and uniformity. May be incurred. From the viewpoint of further preventing the cord arrangement disorder during tire vulcanization, the heat shrinkage stress σ is preferably 1.30 or less, and more preferably 0.90 or less.

  Since the polyketone fiber cord satisfying the above formulas (I) and (II) has a reversibility that shrinks at a high temperature and expands when returned to room temperature, a tire in which the polyketone fiber cord is applied to a belt is used at low speed running. It is excellent in handling stability and ride comfort in any of the high-speed running characteristics. In particular, the tire has improved driving stability and ride comfort when traveling at a higher speed and the temperature rises than a tire having a belt using a conventional organic fiber cord. In addition, by using a reversible polyketone fiber cord having a difference in heat shrinkage stress between 20 ° C. and 177 ° C. of 0.20 cN / dtex or more, preferably 0.25 cN / dtex or more, at low speed running and high speed running It is possible to achieve both excellent driving stability and ride comfort.

The starting polyketone is preferably a polyketone substantially composed of the repeating unit represented by the general formula (III). Among the polyketones, polyketones in which 97 mol% or more of repeating units are 1-oxotrimethylene [—CH ₂ —CH ₂ —CO—] are preferable, and polyketones in which 99 mol% or more are 1-oxo trimethylene. Is more preferable, and a polyketone in which 100 mol% is 1-oxotrimethylene is most preferable.

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

  In the general formula (III), the unsaturated compound forming A is most preferably ethylene, but propylene, butene, pentene, cyclopentene, hexene, cyclohexene, heptene, octene, nonene, decene, dodecene, styrene, Unsaturated hydrocarbons other than ethylene such as acetylene and allene, and diethyls of methyl acrylate, methyl methacrylate, vinyl acetate, acrylamide, hydroxyethyl methacrylate, undecenoic acid, undecenol, 6-chlorohexene, N-vinylpyrrolidone, and sulfonyl phosphonic acid It may be a compound containing an unsaturated bond such as ester, sodium styrenesulfonate, sodium allylsulfonate, vinylpyrrolidone and vinyl chloride.

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

(Wherein t and T are the flow time of a viscosity tube at 25 ° C. of a diluted solution of hexafluoroisopropanol having a purity of 98% or more and a polyketone dissolved in the hexafluoroisopropanol; The intrinsic viscosity [η] defined by the mass (g) of the solute is preferably in the range of 1 to 20 dL / g, more preferably in the range of 2 to 10 dL / g, More preferably, it is in the range of 8. When the intrinsic viscosity is less than 1 dL / g, it is difficult to obtain a high-strength polyketone fiber cord because the molecular weight is too small, and troubles such as fluff and yarn breakage occur frequently during spinning, drying and stretching. On the other hand, if the intrinsic viscosity exceeds 20 dL / g, it takes time and cost to synthesize the polymer, and it becomes difficult to uniformly dissolve the polymer, which may adversely affect the spinnability and physical properties.

  As the method for fiberizing the polyketone, (1) after spinning an unstretched yarn, performing multi-stage heat stretching, and stretching at a specific temperature and magnification in the final stretching step of the multi-stage heat stretching, (2 ) A method in which after the undrawn yarn is spun, hot drawing is performed, and the fiber after completion of the hot drawing is rapidly cooled with high tension applied. A desired filament suitable for production of the polyketone fiber cord can be obtained by fiberizing the polyketone by the method (1) or (2).

  Here, the spinning method of the unstretched yarn of the polyketone is not particularly limited, and a conventionally known method can be employed. Specifically, JP-A-2-112413, JP-A-4-228613, Wet spinning method using an organic solvent such as hexafluoroisopropanol and m-cresol as described in JP-A-4-505344, WO99 / 18143, WO00 / 09611, JP2001-164422 No., JP-A No. 2004-218189, JP-A No. 2004-285221, and the wet spinning method using an aqueous solution of zinc salt, calcium salt, thiocyanate, iron salt, etc., among these, A wet spinning method using an aqueous solution of is preferred.

  For example, in a wet spinning method using an organic solvent, a polyketone polymer is dissolved in hexafluoroisopropanol or m-cresol at a concentration of 0.25 to 20% by mass, extruded from a spinning nozzle to be fiberized, and then toluene, ethanol, isopropanol , N-hexane, isooctane, acetone, methyl ethyl ketone, etc., a solvent can be removed and washed in a non-solvent bath to obtain a polyketone undrawn yarn.

  On the other hand, in the wet spinning method using an aqueous solution, for example, a polyketone polymer is dissolved in an aqueous solution of zinc salt, calcium salt, thiocyanate, iron salt or the like at a concentration of 2 to 30% by mass, and a spinning nozzle is formed at 50 to 130 ° C. Then, it is extruded into a coagulation bath and subjected to gel spinning, followed by desalting and drying to obtain an undrawn polyketone yarn. Here, in the aqueous solution in which the polyketone polymer is dissolved, it is preferable to use a mixture of zinc halide and a halogenated alkali metal salt or a halogenated alkaline earth metal salt. An organic solvent such as an aqueous solution, acetone, or methanol can be used.

  Further, as a drawing method of the obtained undrawn yarn, a hot drawing method in which the undrawn yarn is heated and drawn to a temperature higher than the glass transition temperature of the undrawn yarn is preferable. The method (2) may be carried out in one stage, but it is preferably carried out in multiple stages. There is no restriction | limiting in particular as this heat drawing method, For example, the method etc. which run a thread | yarn on a heating roll or a heating plate are employable. Here, the heat stretching temperature is preferably in the range of 110 ° C. to (melting point of polyketone), and the total stretching ratio is preferably 10 times or more.

  When polyketone fiberization is carried out by the method of (1) above, the temperature in the final stretching step of the multistage hot stretching is in the range of 110 ° C. to (the stretching temperature of the stretching step one step before the final stretching step). Moreover, the draw ratio in the final drawing step of multistage hot drawing is preferably in the range of 1.01 to 1.5 times. On the other hand, when polyketone fiberization is carried out by the method of (2) above, the tension applied to the fiber after completion of the hot drawing is preferably in the range of 0.5 to 4 cN / dtex, and the cooling rate in rapid cooling is 30 The cooling end temperature in the rapid cooling is preferably 50 ° C. or lower. Here, there is no restriction | limiting in particular as a rapid cooling method of the heat-stretched polyketone fiber, A conventionally well-known method can be employ | adopted, Specifically, the cooling method using a roll is preferable. In addition, since the polyketone fiber obtained in this way has a large residual elastic strain, it is usually preferable to perform relaxation heat treatment so that the fiber length is shorter than the fiber length after hot drawing. Here, the temperature of the relaxation heat treatment is preferably in the range of 50 to 100 ° C., and the relaxation ratio is preferably in the range of 0.980 to 0.999 times.

  The polyketone fiber cord used for the belt of the tire of the present invention is formed by twisting two filament bundles of the polyketone fiber by an ordinary method.

  In addition, when the rubber is coated on the polyketone fiber cord, an adhesive such as RFL (resorcin-formalin-latex) liquid is usually applied to the fiber cord in order to ensure adhesion between the fiber cord and the rubber. Thereafter, heat treatment is performed.

  In the belt to which the polyketone fiber cord is applied, the number of driven polyketone fiber cords is preferably 40/50 mm to 70/50 mm. If the number of belt cords to be driven is less than 40/50 mm, the elastic modulus of the rubber composite material is low, which is inappropriate. If it exceeds 70/50 mm, the weight increases, which is inappropriate. Preferably, the number of driven belt cords is 50/50 mm to 60/50 mm.

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

  Steel cords having the structure shown in Table 1, and cords of aramid fibers, polyethylene terephthalate (PET) fibers, and polyketone (PK) fibers were prototyped, and tires of size 195 / 65R15 using each cord as a belt were prototyped. The prototype tire was provided with two layers of belts, and the angles of the belt cords to the equator plane of the tires were all 70 degrees, and the steel cords or the organic fiber cords were used for all the two layers of belts.

  Further, as the heat shrinkage stress σ at 177 ° C. of the cord used, a 25 cm length fixed sample was heated at a heating rate of 5 ° C./min, and the stress generated in the cord at 177 ° C. was measured. As the elastic modulus E at 49 N load at 25 ° C. of the used cord, the elastic modulus in unit cN / dtex calculated from the tangent line at 49 N of the SS curve by the JIS cord tensile test was measured.

  The tires obtained as described above were evaluated for adhesion between organic fiber cords and rubber, steering stability, riding comfort, and high-speed durability by the following methods. In addition, the weight of each tire obtained was indicated as an index with the weight of the conventional tire as 100. The smaller the number, the lighter the tire. These results are shown in Table 1.

(1) Evaluation method of adhesion between organic fiber cord and rubber The cord is embedded in unvulcanized rubber and vulcanized at 160 ° C for 20 minutes under a pressure of 1.9 MPa, and the cord is dug up from the resulting vulcanizate. The cord was peeled from the vulcanizate at a speed of 300 mm / min, and the peel resistance at that time was defined as the adhesive strength (N / piece).

(2) Steering stability evaluation method Each test tire was mounted on a 2000cc class passenger car, and after a preliminary run over 80km for 3 minutes, an actual vehicle feeling test was conducted at a speed of 40 to 200km / hr. , (I) Straight stability, (ii) Turning stability, (iii) Rigidity, (iv) Handling, etc., give a score of 1-10 points, and each item is averaged to give a steering stability score. did. Two professional drivers performed, the average of the scores of the two drivers was determined, and the result of the test tire of Conventional Example 1 was taken as 100 and indicated by an index. A larger index value than 100 indicates higher steering stability and better performance.

(3) Ride Comfort Evaluation Method Similar to the above-described steering stability evaluation method, each tire is mounted on a passenger car and subjected to a sensory test for ride comfort, and the result of the test tire of Conventional Example 1 is 100. As an index. As the index value is larger than 100, the ride comfort is higher and better.

(4) High-speed durability evaluation method A test tire is mounted on a testing machine having a drum diameter of 1707 mm, a high-speed durability test specified in JIS-D4230 is performed, and further 10 km / hour is accelerated every 30 minutes. The distance traveled was measured. The measurement results were expressed as an index when the running distance of the conventional tire was set to 100. The larger the index value, the higher the durability and the better.

  In Table 1, when comparing the conventional example with the comparative example 1, the comparative example 1 uses the aramid fiber as an alternative to the steel belt, so that the weight of the tire is greatly reduced, but the heat shrinkage stress at high temperature is quite low. However, since the adhesiveness is lowered, the steering stability and the high-speed durability at the time of traveling at 180 km / hour are lowered. Although the tire weight is reduced in Comparative Example 2 due to the use of PET fiber, the elastic modulus is low and the belt rigidity is insufficient. As a result, the handling stability, ride comfort, and high-speed durability are all deteriorated. In particular, steering stability and ride comfort during traveling at 180 km / hour and high-speed durability are greatly reduced. On the other hand, Examples 1-3 using the polyketone fiber for the belt have a larger adhesive force and heat shrinkage stress at high temperature than the above Comparative Examples 1 and 2, and therefore when running at 180 km / hour. The steering stability and ride comfort are improved, and particularly high-speed durability is very good. Also, these Examples 1 to 3 differ from Comparative Examples 1 and 2 in that the driving stability and riding comfort are at a low speed of 40 km / hour even at a high speed of 180 km / hour. There is no further deterioration, and it is improving. Further, comparing these Examples 1 to 3 with the conventional example, in Examples 1 to 3, the steering stability is maintained almost equal to that of the conventional example, but the ride comfort is improved as compared with the conventional example. .

  On the other hand, although the PK fiber cord is used, Comparative Example 3 using the PK fiber cord that does not have the physical properties defined in the present application is inferior in handling stability and riding comfort as compared with Examples 1 to 3. Moreover, the improvement effect of the steering stability at the time of the above high-speed driving | running | working seen in Examples 1-3 and riding comfort was not seen.

Claims (6)

A pneumatic radial tire comprising a carcass made of a ply of a radial arrangement code extending in a toroidal shape between a pair of bead parts, and a belt made of two or more belt layers arranged radially outside the crown part of the carcass. And at least one of the belt layers is made of a cord obtained by twisting two filament bundles composed of polyketone fibers, and the cord has a 49N elastic modulus E (cN / dtex) of 177 at 25 ° C. The heat shrinkage stress σ (cN / dtex) at 0 ° C. is represented by the following formulas (I) and (II):
σ ≧ −0.01E + 1.2 (I)
σ ≧ 0.02 (II)
Said pneumatic radial tire characterized by satisfying. The polyketone is represented by the following general formula (III):

(Wherein A is a portion derived from an unsaturated compound polymerized by an unsaturated bond, and each repeating unit may be the same or different) and is characterized by consisting essentially of repeating units represented by The pneumatic radial tire according to claim 1.   The pneumatic radial tire according to claim 2, wherein A in the general formula (III) is an ethylene group.   The pneumatic radial tire according to any one of claims 1 to 3, wherein the number of driven cords is 40/50 mm to 70/50 mm. 5. The pneumatic radial tire according to claim 4, wherein the number of driven cords is 50/50 mm to 70/50 mm. The pneumatic radial tire according to claim 5, wherein the number of driven cords is 55/50 mm to 70/50 mm.