JPS6157404A - Tire with polyester carcass reinforcement layer - Google Patents

Abstract

PURPOSE:To improve confortableness by imbedding the carcass ply of a radial tire in the rubber that is provided with natural rubber and synthetic rubber at a specific ratio using multi-filament twisted yarn made of polyethyleneterephthalate with specifically physical properties. CONSTITUTION:A radial tire has a carcass ply 1 that is folded from the inside to the outside so that both ends can enclose a pair of bead cores 7. In this case, the carcass ply 1 consists of polyethyleneterephthalate with at least 0.8 maximum viscosity. The ply is formed with multi-filament twisted yarn whose intermediate elasticity is less than 6% when 2.3g/d load is applied, in which the sum between this intermediate elasticity and the dry heat shrinkage factor is less than 8.5%, and in which the temperature indicating the maximum of the loss tangent (tandelta) when dynamic viscous elasticity is measured at a frequency of 10Hz is 120-135 deg.C. Then, the carcass ply 1 is imbedded in the rubber consisting of natural rubber to 50-80wt% and synthetic rubber of 50-20wt%.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a passenger car tire that immediately improves handling performance. The present invention relates to a radial tire for a passenger car that prevents a decrease in rigidity of a polyester cord.

(Prior art) As shown in Figure 2, a radial tire for a passenger car has a carcass ply (1) consisting of a rubber matrix and a reinforcing organic iron fiber cord embedded in the rubber matrix, which connects the hood and the tire equator. A plurality of belt plies consisting of a large number of mutually parallel steel cords embedded in a rubber matrix while arranged so that they are substantially perpendicular to each other (B), Q2)
・・・・・・The steel cord is the tire equator and 10
It has a structure in which a belt (1υ) formed by cross-polymerizing at an angle of ~30° is laminated on the top of the carcass ply (1), and the carcass is twisted and responds to the lateral acceleration during handling. A high bead filler (8) is arranged on the bead core (7) of the tire bead part to form a bead core assembly (9) so as not to deteriorate the characteristics, and a carcass ply (1 ) is folded back from the inside to the outside to form this folded part (3).
is attached to the outside of the carcass ply (1) and terminates.

This type of radial tire has better handling stability, braking performance, high-speed durability, and wear resistance than bias tires.

Due to its excellent load durability, it has become increasingly used in recent years, but in order to further improve the driving safety of vehicles, tires have been added to the tread section with the intention of further improving the handling performance of the tire. By using a rubber composition with a large coefficient of friction, or by reducing the tire aspect ratio (ratio of tire height to tire width) to increase the contact area,
Flat radial tires are popular because of their improved grip on the road.

However, even if the road gripping force increases, the steering response must also increase accordingly, and in order to improve driving performance, the rigidity of the carcass must also be increased. However, if the rigidity of the carcass becomes excessive, a dilemma arises in that riding comfort deteriorates.

Generally, polyester cords are commonly used for the carcass of flat radial tires.In order to produce cords with high rigidity, for example, a method of improving the stretching process disclosed in JP-A-56-15430, or a special Showa 58-
Many attempts have been made, such as the method proposed in Japanese Patent No. 81111, in which the degree of polymerization of polyester is made relatively low. In addition, once the material, spinning conditions, and twisting structure of polyester cord are determined, the intermediate elongation (the elongation when a load of 2,3'A is applied, which is different from the breaking elongation) and the elongation at 100°C can be determined. There is a property that the sum of the dry heat shrinkage rate (hereinafter referred to as dry heat shrinkage rate) and the dry heat shrinkage rate (hereinafter referred to as dimensional change coefficient) at different temperatures is constant, and the ratio can be changed within a limited range by changing the heat setting conditions. Can be selected arbitrarily. The broken line (T) in FIG. 3 shows the relationship between the intermediate elongation and the dry heat shrinkage rate of the conventional high polymerization degree polyester cord. As is clear from this diagram (1), the dimensional change coefficient shows a constant value of about 8.5%. The Young's modulus of such a cord increases as the intermediate elongation decreases. Therefore, in order to obtain high rigidity, it is sufficient to increase the stretch, perform heat setting under tension, and reduce the intermediate elongation, but conversely, the dry heat shrinkage rate increases.

The ester cord prepared in this way is embedded in a rubber matrix to form a carcass ply, but prior to embedding it is usually
After being immersed in resorcinol/formalin/latex and dried, the cord is stretched by 2 to 10% in an atmosphere of 210 to 250°C and heat set' to fix the cord under tension, further increasing its rigidity.

However, in a tire where the carcass ply (1) surrounds and terminates in the vicinity of the bead core assembly (9) as shown in Figure 2, the cord with a high heat shrinkage rate as described above cannot be used by folding the carcass ply. Part (3) 6 is held only by the adhesive force of the rubber, so when the rubber is plasticized during high temperature treatment in the vulcanization process, the holding force of the rubber can resist the contraction force of the hood. The cords contract as they slide against each other on the bonded surface, and move to the upper left of the diagram above the broken line (1) in Figure 3, and while the dry heat shrinkage rate decreases, the intermediate elongation increases, As a result, the rigidity of the tire decreases, making it possible to sufficiently improve maneuverability, and the unevenness of the sidewall increases.
A uniform shape cannot be obtained.

On the other hand, JP-A-54-25001 and JP-A-58-17400
4, No. 59-2908, No. 59-40903, and No. 59-81208, etc., the end of the carcass ply 1JPV as shown in FIG.
fr: The tire whose end is sandwiched between the carcass bridle (1) and the belt bridle (b) is unlikely to shift around the bead core assembly (9), so the cord will shrink during vulcanization. As the cord is heated under the action of tension that counteracts the stress, there is little decrease in modulus and the handling response is improved. Since the vibration is transmitted to the rim without significant attenuation, the ride quality deteriorates.

Furthermore, since the lower side of the carcass folded portion (3) is subjected to repeated compressive stress, the cord in that portion is susceptible to fatigue. Therefore, in order to prevent this, there is a need for a cord that is less tiring. In addition, a steel cord reinforcing layer (5) made of steel cord or high elastic modulus cord is arranged between the bead core assembly (9) and the carcass folded part (3), so that the neutral line of bending deformation is set at the carcass folded part (3). Attempts have been made to approach 3) and reduce the effect of compressive stress.

In addition, tires with a small aspect ratio that emphasizes maneuverability have a cross-sectional shape where the angle between the neutral line at the bottom of the side and the tire radial direction is small, so the vertical vector component of vibration transmitted through the cord becomes large. This not only causes a deterioration in riding comfort, but also because the radius of curvature at the maximum width position is small, compressive stress acts strongly on the inner cord, causing fatigue and a decrease in strength.

Moreover, this also means that the tread thickness decreases in this area, and since the belt ends, the rigidity usually changes discontinuously in that area. Therefore, when the tire touches the ground, stress is concentrated in that area and the tire is significantly deformed. Therefore, since a forward-flowing tire with a small aspect ratio has good road surface grip, a structure is used in which the carcass rigidity of the above-mentioned part increases accordingly, and in order to increase the rigidity of the lower side half, the neutral line of the carcass is The angle with respect to the tire's radial direction was made smaller. As a result, the height at the maximum width position of the carcass is 65-70% of the carcass height, and the radius of curvature in the vicinity becomes small and the 7-rex zone of the carcass is narrow, stress is concentrated and the inside A strong compressive stress acts on the cord, causing a decrease in the strength of the cord.

In view of the current situation where it is desired to develop a radial tire that has both good riding comfort and driving performance, the present inventors have proposed a radial tire with a particularly small aspect ratio by Japanese Patent Application No. 50-91458. In this method, by specifying the folding end position of the carcass ply and limiting the height range of the carcass maximum width position, both ride comfort and driving performance are improved, and fatigue due to compression of the cord is reduced. Successful.

(Problems to be Solved by the Invention) The present inventors achieved a significant improvement in the function of flat radial tires by the invention proposed in the above-mentioned Japanese Patent Application No. 59-91458. As a result of detailed research into the characteristics of cord and its behavior during the tire manufacturing process, we found that polyester cord with specific physical properties provides a carcass with high fatigue resistance and high rigidity, and that By embedding it in a matrix of In addition, we have found that the invention already proposed above can be further improved.

That is, an object of the present invention is to provide a radial tire that is excellent in both driving performance and ride comfort. Another object of the present invention is to provide a flat radial tire that improves both driving performance and ride comfort and has excellent road grip (means for solving problems). A carcass ply made of an organic fiber cord embedded in the tire is arranged so that the cord and the tire equator are substantially perpendicular to each other, and both ends of the carcass ply are folded back from the inside to the outside so as to wrap around each of the pair of bead fur assemblies. The belt plies are made up of a number of steel cords parallel to each other and terminated along the outside of the carcass ply, and further embedded in the rubber.
In a tire having a radial structure in which bells formed by cross-polymerizing at an angle of 30° are laminated on the top of the carcass ply, the organic fiber cord of the carcass ply incorporated into the tire comprises at least It is made of substantially polyethylene terephthalate having an intrinsic viscosity of 0.8, has an intermediate elongation of 6% or less, a dimensional change coefficient of 8.5% or less, and has a dynamic viscoelastic property using a testing machine. The loss tangent (t
It is a multifilament twisted yarn with a maximum temperature of 120 to 135°C, and the rubber in which the cord is embedded contains 50 to 80% by weight of natural rubber and 50 to 135% by weight of natural rubber.
% by weight of synthetic rubber.

゛ It should be noted here that the characteristics of the cord, i.e. intermediate elongation and heat shrinkage, are related to the history of heat and tension, and vary depending on the condition of the raw cord, the cord that has been processed by the depping process, and the cord that is incorporated into the tire. However, each of the numerical values in the present invention mentioned above particularly applies to the organic fiber cord of the carcass ply incorporated into the tire.

The organic fiber cord applied to the present invention has an intrinsic viscosity [η] of at least 0.8 when measured at a temperature of 25° C. using orthochlorophenol as a solvent. Preferably 0.8-1
．． It is a multifilament twisted yarn made by melt-spinning and drawing substantially polyethylene terephthalate. here,
Substantial polyethylene terephthalate means that at least 85 mol% is ethylene terephthalate units, and the remaining 15 mol% is aromatic dicarboxylic acids such as isophthalic acid, naphthalene dicarboxylic acid, diphenyldicarboxylic acid, propylene glycol, butylene glycol. This means that it can be a random copolymer, a block copolymer, or a blend polymer in which a diol component such as P-oxybenzoic acid, an oxyacid such as P-oxybenzoic acid, etc. are copolymerized. If the content of ester units other than ethylene terephthalate exceeds 15 mol %, the heat setting properties of the resulting fibers will decrease, resulting in a decrease in the dimensional stability against heat and the initial modulus of the cord. In order to ensure the thermal stability of the cord, it is most preferable that the cord contains 100% ethylene terephthalate units.

If the intrinsic viscosity [η] is less than 0.8, the strength of the cord will be insufficient and the fatigue resistance will be poor, so it is not acceptable.

Moreover, if it exceeds 1.2, melt spinning becomes considerably difficult, so it is not recommended.

The above-mentioned polyester melt is disclosed in, for example, JP-A-58-15
The method described in Publication No. 6017, i.e. about 0.75-2
A filament is formed by extrusion from a spinneret equipped with a large number of 51 nM large-diameter oleices, and the quenching of the filament is delayed by a quenching delay collar directly below the spinneret. A high-strength polyester yarn is obtained by winding the yarn on a winder at a speed of 1/2 min and then drawing it continuously or discontinuously at 215 to 230°C. In addition, the stretching process is performed in JP-A-59-
It is also useful to carry out the method according to the method described in Japanese Patent No. 1714 in order to obtain a code applicable to the present invention.

That is, the spun undrawn yarn is supplied as the undrawn yarn first.

Pre-stretch to 1.10 times or less between the roller and the unstretched second supply roller maintained at 100°C or lower, and then apply high-temperature pressurized steam at 200°C or higher between the first stretching port and the The stretching point is fixed at that position, and the first stage stretching is performed at 40% or more of the total stretching ratio. , stretched by passing through a slit heater at 17G to 420°C for 0.3 seconds or more in a non-gamma contact state, and then stretched by 10% at 280 to 165°C.
Dimensional stability is further improved by performing the following relaxation process. The thus obtained filament threads are combined and twisted so that the total number of filaments is approximately 0.000 to 1.000 to form a reinforcing coat for the carcass ply used in the tire K of the present invention.

The spinning and drawing conditions for the above polyester yarn are based on the loss tangent (tan δ) obtained by measuring the dynamic viscoelasticity of the obtained filament at a frequency of 10 Hz while changing the temperature using a dynamic viscoelasticity tester. The maximum temperature (hereinafter referred to as tan)
The temperature is appropriately selected so that the peak temperature (referred to as δ peak temperature) is in the range of 120 to 135°C. That is, the tan δ peak temperature correlates with the fine structure of the filament, particularly the orientation of molecular chains in the amorphous portion, and increases as the orientation progresses. Therefore, the conditions of the spinning and drawing processes that affect the orientation, such as the spinning draft ratio, spinning speed, cooling rate of spun yarn, drawing temperature, and drawing ratio, are selected within the range of the above-mentioned process conditions to obtain an appropriate tan δ peak. It is easy to set the temperature.

In particular, under the above spinning conditions, since tension is applied to the yarn and it is stretched during cooling, the temperature difference between the surface layer and the center of the spun filament becomes a factor that inhibits spinnability and drawability. Sometimes. Therefore, it is desirable to reduce the diameter of the spun filament in order to minimize the cooling delay in the center and eliminate the above-mentioned inhibiting factors. Finally, while the conventional yarn has a single yarn fineness of 4 to 10 d, the preferable single yarn fineness of the yarn applied to the present invention is about 1 to 6 d.

A cord having a tan δ peak temperature of 120 to 135° C. has a high Young's modulus, and a typical example of the relationship between its intermediate elongation and dry heat shrinkage rate is shown by the solid line (It) in FIG. 3. If you compare this with the dashed line (1) that shows the dimensional change coefficient of the conventional code, you can clearly understand that in this example, the dimensional change coefficient is around 7%, while that of the conventional code is about 9%.
Therefore, even when the cord applied to the present invention is heat-set under conditions where the intermediate elongation is small, the dry heat shrinkage rate is significantly lower than that of the conventional cord. Therefore, the conventional phenomenon that the cord contracts during vulcanization and increases the intermediate elongation, resulting in a decrease in the rigidity of the carcass and the inability to obtain the expected handling performance, is almost eliminated.

The code whose tan δ peak temperature is less than 120°C is
Since the degree of molecular chain orientation has not reached a sufficient value and is therefore composed of filaments with low strength and Young's modulus,
Tires using this tire have low strength and poor handling performance, and do not meet the purpose of the present invention.

On the other hand, a cord with a tan δ peak temperature exceeding 185°C has a large dimensional change coefficient as shown by the broken line (1) in Figure 3, and the intermediate elongation of the cord is small due to the high rigidity of the kerosene. Even if heat-set under these conditions, the cord will contract during the tire curing process and the intermediate elongation will increase, resulting in a lack of carcass rigidity and reduced handling performance. It is not possible to terminate the tire between the carcass ply and the belt, as this will not only reduce the fatigue resistance but also impair the commercial value of the tire, which still has noticeable unevenness in the sidewall portion.

After the cord obtained as described above is made into a blind weave, it is elongated by 2 to 10% by applying a rubber adhesive such as resorcinol, 7-ormarin, latex, and heated to approximately 210 to 250°C. Heat setting is performed at an ambient temperature, and further relaxation treatment is performed at an ambient temperature of 200 to 240°C, resulting in shrinkage of approximately 0 to 2%. Even when the cord subjected to such treatment is set in a tensioned state, thermal shrinkage is small, and its dimensional change coefficient is still maintained at the state shown by the solid line (If) in FIG. 3.

Next, a cord with a tan δ peak temperature of 120 to 135 °C has a higher fatigue resistance than a cord with a higher tan δ peak temperature (under condition 1, the fatigue resistance is about 10% better, but the degree of molecular chain orientation is low, so it is difficult to hydrolyze). Since the cord of the present invention has a slightly lower tan δ peak temperature than conventional cords, the heat generation associated with tire rotation accelerates the hydrolysis of the polyester filament, resulting in improved aging resistance. This hydrolysis reaction is greatly affected by the concentration of free carboxyl end groups in the polyester, so in order to make the concentration of free carboxyl end groups on paper, it is necessary to It is desirable to add an end capping agent such as a carbonate compound to provide resistance to hydrolysis.

However, the resistance provided by the above method is still not sufficient, and impurities in natural rubber and code tffl
Since the vulcanization accelerator blended into the rubber matrix generally exhibits a catalytic effect on hydrolysis, consideration must be given to the composition of the rubber and the selection of the vulcanization accelerator.

In other words, the lower the natural rubber content in the rubber matrix, the smaller the hydrolysis effect of the cord, but on the other hand,
The green strength of the tire decreases, making it difficult to manufacture the tire. Therefore, the natural rubber content that maintains appropriate green strength and suppresses the action of promoting cord hydrolysis within an acceptable range is 50 to 80%, preferably 6%.
0 to 7% by weight, 50 to 20% by weight of the remainder,
Preferably 40-30% by weight is at least one synthetic rubber selected from the group consisting of styrene-butadiene rubber, butadiene rubber and imprene rubber. In particular,
The styrene content is 10-20% by weight, 35-50% by weight of the butadiene component is 12 bonds, and the remainder is 1.
Solution-polymerized styrene or butadiene rubber having four bonds is particularly preferred because it has high fluidity and can be easily filled into the hood gap.

The vulcanization accelerator to be added to the rubber matrix is preferably one that has a small catalytic effect on the hydrolysis of the polyester cord and has a property of increasing the initial modulus of the synthetic rubber. A compound belonging to the sulf7enamide group in which all the hydrogens bonded to the nitrogen atoms of the sul7enamide group have been replaced, such as N-oxydiethylene-2-benzothiazolylsulf7enamide.

Examples include N,N'-dicyclohexylbenzothiazol-7-enamide.

(Example) Hereinafter, the tire of the present invention will be further described with reference to Examples and Comparative Examples.

The size of the tires manufactured here was 195/60R15, and the respective measuring methods and testing methods were based on the following.

(1) Loss tangent (tan δ) Using a viscoelasticity tester manufactured by Iwamoto Seisakusho, the vibration frequency IGHz,
Dynamic viscoelasticity was measured under a load of 9 weights and 0.5 fA.

Cz) Intermediate elongation, elongation rate when a load of 2.3 cm is applied according to TIS-L-1017.

(3) Dry heat shrinkage rate Shrinkage rate when left at a temperature of 150°C for 30 minutes according to JIS-L-1017.

(4) Tilt force retention rate after running After running the tire for 10,000 times, it is dismantled and the strength of the cord is measured.The strength of the cord is compared with the strength of the cord before molding, and the result is expressed as the retention rate.

(5) Maneuvering response established by Japan Society of Automotive Engineers of Japan, automobile standard, TASO-Z・1
10 Test vehicle speed 1001 (@/h) Input the steering force periodically to cause a periodic change in the direction of travel of the car, detect the phase delay and the magnitude of the change, and set the vehicle tire speed to 1001 The index is displayed so that the better one is larger.

(6) Ride comfort A road surface with triangular pillars attached perpendicular to the direction of travel of the vehicle is
The amplitude of vertical vibration when passing at a speed of Kg/b is measured, and the ratio of its reciprocal is t - the conventional tire (comparative example 2) is Z
Display index as oo.

(7) Average value of side unevenness depth of 10 to 100 tires. In addition, the second
Table 1 shows the cord embedding rubber formulations applied in the examples and comparative examples shown in the table.

Table 1 Embedded rubber compound v-sBu: Solution polymerization SBR of bound styrene 18i 1%, butadiene component vinyl bond 48% by weight Accelerator az2Hcyclohexyl2benzothiacylsul7
Enamide accelerator MsA: N-oxydiethylene 2benzothiacylsul-7enamide accelerator Dz: N,N dicyclohexylhensothiazol-sul-7enamide (hereinafter referred to as the margin) However, in Table 2 above, at the top end position of the winding [1uldJ
means "1 up, 1 down", and one of the two carcass plies is rolled up from the inside to the outside against the bead core, and the remaining one is rolled up against the bead core from the outside to the inside. It means to wrap around.

In addition, l' [HTUJ is an abbreviation for high turn up, in which one carcass ply is rolled up from the inside to the outside around the bead core, and the end reaches a part of the shoulder, as shown in Figure 1. .

From the above test results, the following becomes clear.

(1) Tire numbers 2 to 5 (embodiments of the present invention) are 8.
A polyester cord with a small dimensional change coefficient of 5% or less, a tan δ peak temperature of 122 to 133°C, and an intermediate elongation of 5.6 or less was used, and the embedded rubber was made of natural rubber and synthetic rubber.
60/4. Or tires using a compound with a ratio of 7% 0, all exhibit high strength retention after running, steering response, 1 ride comfort index, and side unevenness values are extremely small compared to other tires. It shows.

(2) Tire No. 6 has the same cord as Tire No. 2, but is an example of different tire manufacturing conditions, with the cord's intermediate elongation exceeding 6%, poor steering response, and large side irregularities.

(3) Tire number 7 is an example in which a cord with low intermediate elongation is embedded in a rubber matrix made of 100% natural rubber.
It shows a low strength retention rate.

(4) Tire No. 8 has a tan δ peak temperature that is too low and a low degree of orientation, so the intermediate elongation is large and the steering response is extremely poor.

(5) Tire number 9 is an example of polyester having a low intrinsic viscosity, and exhibits an extremely low value of tenacity retention.

(Effects of the Invention) As detailed above, the tire of the present invention has excellent driving performance such as handling response due to the carcass having high rigidity.
Despite its high rigidity, carcass ply has extremely low dry heat shrinkage, so both ends of the carcass ply wrap around the bead core assembly and are folded back from the inside to the outside, and are attached to the outside of the car and waste. Even with a tartar structure that is not held between belts, the rigidity of the carcass ply is well maintained without causing the folded part to shift during the rubber vulcanization process and increasing the intermediate elongation. The carcass, in which the folded end does not extend to the belt part and has a relatively thin sidewall part, provides a tire that has both excellent driving performance and a comfortable ride due to its high rigidity and appropriate elasticity.

The flat radial tire has a structure in which the folded end of the carcass ply extends along the outside of the carcass and is sandwiched between the carcass ply and the belt, and the height at the maximum width of the carcass is 55 to 55% of the carcass height. 65%, that is, the present inventors have
If the present invention is applied to the tire proposed in No. 458, it will have great grip on the road surface, and will have excellent driving performance and ride comfort.
Moreover, a tire with good fatigue resistance can be obtained. Furthermore, the tire of the present invention has a unique rubber composition and an appropriate vulcanization accelerator, which suppresses hydrolysis of the polyester cord, prevents loss of strength and decrease in adhesion, and increases the durability of the tire. At the same time, the tire has a uniform shape and quality with fewer irregularities on the sidewall.

As described above, the tire of the present invention has 2. excellent driving performance.

It combines a comfortable ride with great fatigue resistance and durability, and is effective in improving vehicle driving safety and reducing passenger fatigue, and its practical application is highly anticipated in the future. nru.

[Brief explanation of the drawing]

FIG. 1 is a left half sectional view showing an example of a tire according to the present invention;
FIG. 2 is a sectional view of the left half of an example of a conventional tire, and FIG. 3 is a diagram showing the relationship between intermediate elongation and dry heat shrinkage of polyester cord for reinforcing carcass ply.
) indicates the dimensional change coefficient of the conventional polyester cord, and (It) indicates the dimensional change coefficient of the polyester cord applied to the present invention. (1), Direct carcass ply. (3)...Carcass ply folded part. (4)... Carcass ply end. (5)... Steel cord reinforcement layer. (9)... Bead core assembly. 01)... Belt. (1 smell, (ka...belt ply. Patent applicant: Toyo Tire & Rubber Industries Co., Ltd.)

Claims (1)

[Claims] 1. A carcass ply made of an organic fiber cord embedded in rubber is arranged so that the cord and the tire equator are substantially orthogonal, and both ends of the carcass ply are connected to each of a pair of bead core assemblies. The belt plies are folded from the inside to the outside so as to wrap around the carcass ply and terminate along the outside of the carcass ply, and are further embedded in the rubber and are made up of a number of mutually parallel steel cords. In a tire having a radial structure in which a belt formed by cross-polymerizing at an angle of 30° is laminated on the top of the carcass ply, the organic fiber cord of the carcass ply incorporated into the tire has at least 0 It is substantially made of polyethylene terephthalate having an intrinsic viscosity of .8, and has an intermediate elongation of 6% or less when a load of 2.3 g/d is applied, and has a
The sum of the dry heat shrinkage rate at a temperature of 50°C is 8.5% or less, and the dynamic viscoelasticity is measured at a frequency of 10 using a testing machine.
It is a multifilament twisted yarn whose temperature exhibiting the maximum loss tangent (tan δ) when measured in Hz is in the range of 120 to 135°C, and the rubber in which the cord is embedded has a temperature of 50 to 135°C.
A tire having a polyester carcass reinforcing layer comprising 80% by weight of natural rubber and 50 to 20% by weight of synthetic rubber. 2. Both ends of the carcass ply wrap around a pair of bead core assemblies and a steel cord reinforcing layer polymerized on the outside of each, and further extend along the outside of the carcass ply, and the end ends between the belt and the carcass ply. A tire comprising a polyester carcass reinforcing layer according to claim 1, which is sandwiched between the tires.