JPH0967732A - Polyester monofilament for rubber reinforcement and pneumatic radial tire using the same - Google Patents

Abstract

(57) [PROBLEMS] To provide an adhesive-treated polyester monofilament cord having excellent fatigue resistance in rubber, and a pneumatic radial tire using the same, which has excellent durability and steering stability around a bead portion. To do. A monofilament cord made of polyethylene terephthalate or polyester containing the same as a main component, which simultaneously satisfies the following characteristics, is an adhesive-treated polyester monofilament for rubber reinforcement. (A) Intrinsic viscosity (IV): 0.90 or more, (b) Birefringence Δn: 0.185 or more, (c) Crystal orientation degree: 0.90 or more, (d) Amorphous orientation degree: 0.42 Hereinafter, (e) density (g
/ Cm ^3): 1.400 or more, (f) fineness (denier): 2000~5000, (g) Strength: 6 g / d or more, (h) Initial Modulus: 70 g / d or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adhesive-treated polyester monofilament cord for rubber reinforcement, which has high strength and high elasticity but is excellent in fatigue resistance in rubber, and a bead portion using the cord as a ply cord. The present invention relates to a pneumatic radial tire having excellent durability and steering stability around the periphery.

[0002]

2. Description of the Related Art Conventionally, as rubber reinforcing cords for tires, conveyor belts, etc., a large number of very small denier filaments such as polyester, polyamide, rayon, etc. are bundled, and twisted yarns consisting of lower twist and upper twist, A twisted cord is used that has improved yarn gathering properties and fatigue resistance.

[0003] On the other hand, with the intention of omitting the twisting step in the converging property, an attempt has been made to apply a cord composed of one filament, that is, a so-called monofilament cord to a rubber reinforcing material such as a tire. In terms of physical properties, this monofilament cord has higher elasticity and lower shrinkage than conventional twisted cords if it is made of the same material, and not only can improvement in the performance of the rubber reinforcement be expected, but even inside the twisted cord. Since the adhesive is not impregnated, the amount of the adhesive used can be greatly reduced, which is a great advantage in practical use.

For example, Japanese Patent Laid-Open No. 52-11 of 1970's
Japanese Patent No. 0918 discloses a method for producing a nylon monofilament cord, and is disclosed in US Pat. No. 4,360,050.
Japanese Patent Application Laid-Open Publication No. 1994-242242 discloses applying a polyester thick denier monofilament cord to a tire. Further, in the above publication, there is a description of a monofilament cord having an oval cross section or a rectangular cross section, and it is considered that the fatigue resistance of the monofilament cord was considered from this. That is, since the monofilament cord cannot disperse the force with respect to an external force like the twisted cord, it has a drawback that the twisted cord has poor fatigue resistance. In the case of multi-filament twisted cord, even if compressive strain stress acts, it has a twist angle 1
Since the ultra-fine filament of each book is bent and deformed, it moves in a direction that relaxes and absorbs the compressive strain input, resulting in excellent fatigue resistance, but in the case of a monofilament cord, it is directly subjected to the compressive strain input. become.

Further, as can be seen from the disclosures of JP-A-2-99610 and JP-A-2-127507,
It can be seen that the application of the nylon monofilament cord having the cord surface modified by steam was attempted to various tires. Regarding the production of the monofilament cord by the steam heating method, the above-mentioned JP-A-52-110918 is used.
Further, the nylon monofilament cord is not excellent in both elastic modulus and heat shrinkage rate, as compared with the polyester multifilament twisted cord which is widely used at present, and the nylon monofilament cord has a fatigue resistance. Although it is at a practical level, it has not yet been put into practical use as a tire cord. That is, nylon is superior to polyester in terms of fatigue properties in the tire, but has a lower elastic modulus and a basic property of higher heat shrinkability,
All of these characteristics adversely affect the steering stability of the tire. Even if nylon is used as a monofilament cord, each property does not reach that of polyester multifilament twisted cord.

As long as a nylon monofilament cord is used, it is impossible to satisfy the high elastic modulus and low heat shrinkage rate as a carcass ply cord, which is indispensable for realizing a tire which is required to have excellent steering stability in recent years. The current situation.

In order to improve this point, it has been proposed to use a polyester monofilament cord for a tire. For example, Japanese Patent Application Laid-Open No. 3-185111 discloses that a monofilament cord to which a low carboxyl group polyester fiber material is applied is used in a tire carcass. This low-carboxylated polyester is expected to be improved against deterioration due to amines transferred from the rubber composition, but its fatigue resistance to physical fatigue in the tire is insufficient, and a failure occurs in the cord part during running. It may occur, which is a practical problem.

Further, Japanese Patent Application Laid-Open No. 4-232102 discloses that a polyester monofilament cord obtained by steam heating is applied to a tire. Techniques to reduce the birefringence of the outer layer of the cross section of the yarn by steam heating compared to the inner layer, and to make the cross section oval to increase flexibility against bending and improve fatigue resistance, are applied to actual tires. In this case, however, there is a problem that when the strain of the tire increases due to a high load, the cord breakage around the bead portion occurs at a relatively early stage, and it has not yet been put into practical use.

In all of the conventional techniques described above, the raw yarn manufacturing process and the raw yarn characteristics are defined. As is well known, the rubber reinforcing cord is treated with an adhesive dip using RFL resin or the like before use. Is always done. This treatment is performed at a high temperature and a long-term heat treatment under high tension. Therefore, the change in the microstructure of the cord is very large, and merely improving the characteristics of the raw yarn does not necessarily lead to the improvement of the fatigue resistance in rubber.

As described above, the monofilament cord mainly composed of nylon yarn has a limit in increasing its elastic modulus, and has a drawback that it cannot exhibit an elastic modulus higher than that of a conventional polyester twisted cord. On the other hand, monofilament cords mainly composed of polyester have the advantage of exhibiting a higher elastic modulus than conventional polyester twisted cords, but have poor fatigue resistance, and it is important to improve this fatigue resistance. It is an obstacle.

[0011]

SUMMARY OF THE INVENTION The present invention was created in order to solve the problems of the prior art as described above, and the purpose thereof is to have excellent fatigue resistance in rubber. An object of the present invention is to provide an adhesive-treated polyester monofilament cord and a pneumatic radial tire using the same, which has excellent durability and steering stability around the bead portion.

[0012]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the inventor achieved the above-mentioned object by giving a polyester monofilament treated with an adhesive with specific characteristics. The inventors have found that they can be achieved and have completed the present invention. That is, the cord of the present invention is a polyester monofilament cord for rubber reinforcement, which is made of polyethylene terephthalate or polyester containing this as a main component, and which has been treated with an adhesive agent in advance, and is characterized by simultaneously satisfying the following characteristics.

(A) Intrinsic viscosity (IV): 0.90 or more (b) Birefringence Δn: 0.185 or more (c) Crystal orientation degree: 0.93 or more (d) Amorphous orientation degree: 0.38 Following (e) Density (g / cm ³ ): 1.400 or more (f) Fineness (denier): 2000 to 5000 (g) Strength: 6 g / d or more (h) Initial elastic modulus: 70 g / d or more

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The contents of each element constituting the present invention and the effects thereof will be described in detail below.

According to the results of studies by the present inventors, for example, when a polyester monofilament is used as a ply material for a radial tire and a high load drum test is performed, a very large compressive stress is applied to the bead turn-back portion, which is a relatively early stage. It has been found that there is a problem that a failure due to a cord break occurs. Observing the fracture mode, the monofilament cord has a bending point due to stress concentration, and a remarkable increase in diameter occurs before fracture. Rubber,
When the adhesive is removed, the cord is observed to whiten. It is considered from these facts that the monofilament cord undergoes repeated compressive stress to cause interfacial fracture inside the filament, generally called fibrillation, and lead to fracture from the inside to the whole.

In order to improve the fatigue strength against such compressive stress to a practical level, the monofilament after the adhesive treatment has an intrinsic viscosity of 0.90 or more, preferably 0.93.
As described above, more preferably 0.96 or more is required. Here, the adhesive treatment is a normal adhesive dipping treatment (hereinafter simply referred to as dipping treatment) in which the filament is immersed in the adhesive to improve adhesion with rubber after the monofilament is formed and heat treatment is performed. The treatment method is not particularly limited, but, for example, dip treatment with a resocil / formalin / latex (RFL) solution is generally performed.

The intrinsic viscosity of the monofilament will be described in detail. The higher the intrinsic viscosity of the monofilament is, the higher the fibril peeling resistance and the rubber adhesion are, and the mechanical fatigue resistance is improved. Although the upper limit of the intrinsic viscosity is not particularly limited, it is practically 1.
It is preferably 2 or less.

The dip-treated polyester monofilament was embedded in rubber, vulcanized, and then
When a general adhesion test of pulling the cord out of the rubber with a tensile tester is performed, it is observed that the monofilament having a low intrinsic viscosity of less than 0.90 peels off the outer layer portion and remains in the rubber. In the worst case, this peeling progresses to the inside,
Causes a cord break. However, in the sample whose intrinsic viscosity is within the range of the present invention, the amount of peeling is obviously reduced, or peeling does not occur at all, and the rubber adhesive strength is further increased. It is considered that this is because the internal fibril peeling resistance is excellent and the bonding strength between the adhesive layer and the cord surface is improved due to the increase in the number of entangled molecules. The intrinsic viscosity of the monofilament means that the monofilament is dissolved in a mixed solvent of p-chlorophenol / tetrachloroethane (weight ratio 3: 1) so as to be 0.5% by weight, and the automatic IV measurement manufactured by Scott at 30 ° C. RH is performed. Device A
The value measured using VS500 (trade name). The intrinsic viscosity of the monofilament can be adjusted by, for example, solid-state polymerization conditions before spinning, melting conditions during spinning, and the like.

In addition, the monofilament cord of the present invention
In addition, the degree of amorphous orientation is 0.38 or less, preferably 0.35
The following is more preferably 0.20 to 0.32
is important. The present inventors examined and found that the same unique
Even with a dip code that has viscosity, this difference in the degree of amorphous orientation is
Fatigue varies greatly depending on the situation. This repeats
When the strain is applied to the cord, the deformation is
As the dip code is low,
The amorphous molecules are
Orientation distribution becomes uniform, and it is more flexible as the starting point of fibrillation.
This is to reduce the probability of occurrence of internal cracks
It is inferred. However, to maintain high strength
Monofilament birefringence is 0.185 or more, preferably
Is 0.187 or more, more preferably 0.190 or more.
And the crystal orientation is 0.93 or more, preferably
0.935 or more, more preferably 0.94 or more,
Monofilament density 1.400 g / cm^ThreeAbove, good
More preferably 1.401 g / cm ^ThreeAbove, more preferably
1.402 g / cm^Three~ 1.410 g / cm^ThreeWho
Is good. That is, the molecular orientation in the crystalline region is higher and
The molecular orientation in the crystal region should be lower,
Orientation creates high strength and fatigue resistance.
It is important to have a code.

The microstructure of such a monofilament is
It is expressed by optimizing the drawing conditions or dipping conditions of the raw yarn. That is, in the raw yarn manufacturing process, under high tension before performing the relaxation treatment, a high temperature (for example, non-contact such that the surface temperature of the filament becomes 220 to 260 ° C.) so that the highly oriented molecular region can be sufficiently crystallized. Heating should be performed) for a relatively long time, and the density should be 1.390 g / cm ³ or more at this stage.
This is important not only for increasing the crystal orientation and crystallinity but also for reducing the structure distribution of the yarn cross section. Since the fine structure of the yarn can be formed only in a limited range in the dipping process, the structure formation in the raw yarn manufacturing process is very important.

In the dipping process, generally, the drying process after the adhesive dipping (impregnation) treatment has one drying zone and two curing zones, but the curing zone is heated to a high temperature (for example, 250 ° C.). ) Or a low tension of the first curing zone (for example, the tension of the first curing zone: the tension of the second curing zone is 1:
1.5 to 1: 3) is a good direction. Increasing the temperature promotes the development of crystal parts, the crystal orientation becomes high, and the amorphous orientation becomes relatively low. Decreasing the tension of the first curing zone increases the relaxation rate of the zone and promotes relaxation of orientation in the amorphous region, thus promoting polarization of orientation. Since the final zone is a part that determines the final elastic modulus (intermediate elongation) and cutting elongation of the dip cord, the tension condition should be set according to the tire application condition.

The intent of the present invention is to improve the fatigue resistance while ensuring the physical properties of the polyester monofilament in actual use, and the polyester monofilament obtained has the above-mentioned microstructure characteristics. And having a strength of 6.0 g / d or more, an initial elastic modulus of 70 g / d or more, preferably a strength of 6.5 g / d or more, an initial elastic modulus of 75 g / d or more, more preferably a strength of 70 g / d or more, an initial elastic modulus. It should satisfy 80 g / d or more. For example, no matter how good the fatigue strength is, if the initial strength is low, the probability of cord breakage eventually increases, which is not preferable. There is no particular upper limit to the initial elastic modulus, but it is practically about 70 g / d to 120 g / d.

The fineness of the monofilament is 2000 to 50, which is the same as that of an ordinary twisted cord, when it is used for a tire or the like.
A denier of 00 is preferred.

The cross-sectional shape of the polyester monofilament is not particularly limited in the present invention. As a result of a test conducted by the present inventor, a circular cross section had better fatigue properties under an environment with a larger compressive stress, and an elliptical shape had better fatigue properties under an environment with a small compressive stress and rather rather a simple bending. This is because the presence of the stress concentration points as described above is involved, and under high compressive stress, the elliptical shape tends to concentrate the bending point at one point and tends to increase the strain. In an environment where stress concentration points do not occur, an elliptical shape having a smaller diameter in the bending direction has better fatigue resistance. Therefore, this cross-sectional shape should be determined in consideration of the environment in which the monofilament cord is used.

The raw material of the polyester monofilament used in the present invention is polyethylene terephthalate or polyethylene terephthalate as a main component, that is, 80
Polyester, which is contained by weight% or more, is preferable. Examples of polyester components other than polyethylene terephthalate include polybutylene terephthalate and polyethylene naphthalate, which are blended and used as desired. Alternatively, 10% by weight or less of a copolymerization component, for example,
Adipic acid, isophthalic acid, naphthalene dicarboxylic acid,
It is possible to use those obtained by adding a dicarboxylic acid such as diphenyldicarboxylic acid or the like, a diol component such as propylene glycol, putylene glycol, diethylene glycol or the like to form a copolymer with polyester.

Further, with respect to this polyester component,
Known additives such as a softening agent and a stabilizer can be added within a range that does not impair the effects of the present invention, for example, 10% by weight or less.

The adhesive used for the monofilament of the present invention is not particularly limited, and may be, for example, a mixture of resorcyl / formalin / latex (RFL) liquid commonly used for the adhesive treatment of polyester yarn, or The RFL solution may be applied to the monofilament after pretreatment with an epoxy compound or the like.

As detailed above, the adhesive-treated polyester monofilament of the present invention has an intrinsic viscosity (I
V): 0.90 or more, birefringence Δn: 0.185 or more, crystal orientation: 0.93 or more, amorphous orientation: 0.38 or less,
Density: 1.400 g / cm ³ or more, Fineness: 2000 d-
5000d, strength: 6g / d or more, initial elastic modulus: 70g
By having a specific property of / d or more, the fibril peeling property inside the cord is improved, and the fatigue resistance in rubber can be significantly improved while maintaining the high strength and high elasticity merit of the conventional polyester monofilament. . Due to this effect, for example, even when used in tire ply cords requiring the most severe fatigue resistance and safety, and in a high load drum endurance test described later, fatigue resistance at a practically acceptable level was exhibited.

Of course, the monofilament cord of the present invention is useful not only as a ply cord but also as a reinforcing material for various parts of a tire such as a belt cord.

[0030]

Next, the present invention will be described in detail with reference to examples and comparative examples, but the present invention is not limited to these examples. (Examples 1 to 4 and Comparative Examples 1 to 6) Table 1 below shows the microstructure, physical properties, fibril resistance, and tire fatigue test results of adhesive-treated polyester monofilaments. still,
The material of the cord used in the experiment was 100% polyethylene terephthalate, the cross-sectional shape was circular, and the filament fineness before treatment was about 3000 denier.

The monofilament PET raw material chips are
It had an intrinsic viscosity of 0.6 and was prepared by performing solid phase polymerization at 240 ° C. under vacuum to raise the degree of polymerization to a target chip intrinsic viscosity. This chip was put into a screw-type melt extruder from a hopper in a nitrogen atmosphere, melted at a spinning temperature of 305 ° C., then extruded from a circular nozzle while maintaining a constant amount with a gear pump, and passed through an air gap,
Rapidly solidify in a water cooling bath 70 cm below the nozzle,
After further removing water, the yarn is once wound around a bobbin as an undrawn yarn. This undrawn yarn is drawn on a separate line drawing machine.
The total draw ratio is 5.4-
A two-stage stretching of 6.8 times was performed. As a heater,
A non-contact type electric heater was used for both 1st and 2nd stage drawing, and the temperature conditions were changed depending on the sample.

For the adhesive treatment, the same dip solution was used,
It was performed using a Ritzler code processor. The component composition of such a dipping solution is as follows.

Resorcin 14.9 (parts by weight) Formaldehyde 37% aqueous solution 19.0 Sodium hydroxide 10% aqueous solution 18.2 Vinyl viridine latex ^{* 1} 190.5 Styrene-butadiene copolymer latex ^{* 2} 195.4 Soft water 562. 0 1000.0 * 1: Latex JSR0680 manufactured by Japan Synthetic Rubber Co., Ltd. * 2: Latex JSR2108 manufactured by Japan Synthetic Rubber Co., Ltd. As a method for adjusting this dip solution, first, soft water 372.5
After dissolving resorcin in g, sodium hydroxide 10
% Aqueous solution with stirring, 37% aqueous formaldehyde solution was added, and the mixture was aged at 25 ° C. for 6 hours to obtain a solution A. On the other hand, latex was added to the remaining 189.5 g of soft water, the mixed solution was designated as solution B, and the solution A was added to this solution B and further aged at 25 ° C. for 24 hours to prepare a conventional RFL dip solution. . R of this dip solution
F / L is 16% by weight, solid content is 18% by weight, and VP
/ (VP + SBR) was 7.5% by weight.

A filament is dipped in this solution in a dip bath and dried at a temperature of 130 ° C. and a temperature of each of the first and second curing zones of 220 to 250 ° C., 120 and 40, respectively.
An exposure time of 40 seconds was processed. The intermediate elongation at 2.25 g / d is set to 4%, and the tension in the final zone is set to 0.
Although it was set to 85 kg, the other zones were adjusted with samples in the range of 0.4 to 1.7 kg.

The microstructure analysis, physical property test, fibril resistance, and tire fatigue test were carried out by the following methods. However, a dip code using water instead of the adhesive was used for the fineness measurement and the fine structure analysis.

The results of these characteristics and performance evaluations are shown in Tables 1 and 2 below. (1) Cord tensile test According to JIS L 1017, an autograph manufactured by Shimadzu Corporation is used to perform tensile at a constant speed under room temperature conditions of 25 ° C ± 2 ° C to obtain the load when the cord is cut. The cord strength is obtained by dividing by the cord fineness. Further, the initial elastic modulus is obtained from the rising slope of the initial SS curve. (2) Fineness A cord with a length of 9 m (without adhesive) is measured and the temperature is 125 ° C.
Measure the weight after drying for 30 minutes in the environment and
By multiplying it by 0, the cord weight per 9000m (g),
That is, denier. (3) Measurement of Intrinsic Viscosity A p-chlorophenol / tetrachloroethane (3: 1) mixed solvent is used as a solvent, and measurement is performed at 30 ° C. using an automatic IV measuring device manufactured by Scott. (4) Birefringence measurement By using an interference microscope manufactured by Carl Zeiss Co., Ltd., the fiber axis direction refractive index and the vertical direction refractive index of a sample immersed in a refractive index preparation liquid manufactured by Japan Geoscience Co., Ltd. are measured and subtracted. Ask.
The refractive index of the immersion liquid at room temperature is measured using a 4T type Abbe refractometer manufactured by Atago. (5) Crystal Region Orientation Degree Measurement The measurement is performed using a wide-angle X-ray diffraction device manufactured by Rigaku Denki Co., Ltd. and software. The integral width of the peak obtained by scanning the (010) plane from the β angle of 0 to 360 degrees is calculated, and the crystal orientation degree is calculated by the following formula.

Degree of crystal orientation = 1−Σ (integral width) / 360 (6) Degree of orientation of amorphous region Obtained from the following formula.

[0038]

[Equation 1] However, fa: degree of orientation of amorphous region Δn: birefringence X: degree of crystallinity fc: degree of orientation of crystalline region Δnc: intrinsic birefringence of crystal (= 0.290) Δna: intrinsic birefringence of amorphous (= 0.204) Here, the crystallinity X is obtained from the following formula using the density (ρ: g / cm ³ ).

[0039]

[Equation 2] However, ρc: Crystal density (= 1.455 g / cm ³ ) ρa: Amorphous density (= 1.335 g / cm ³ ) (7) Density measurement Carbon tetrachloride / n-heptane mixed solvent system kept at 25 ° C. The sample and the glass float of known density are placed in the density odor pipe of (4) and allowed to stand for 24 hours for measurement. (8) Cord peeling resistance test The adhesive-treated cord was embedded in an unvulcanized compounded rubber composition and vulcanized at 170 ° C. for 30 minutes under a pressure of 20 kg / cm ² , and the vulcanized product obtained was used. The cord was pulled out at a constant speed, and the amount of the peeled product of the cord left in the vulcanized rubber was visually evaluated as follows.

◯: None or almost none △: Somewhat X: Yes or ruptured by peeling (9) Durability of high-load drum of trial tire (preparation of trial tire) The trial tire 10 has a tread portion as shown in FIG. 12, a pair of side portions 14 continuous on both sides of the tread portion 12, and bead portions 16 formed inside the side portions 14, respectively, and carcass ply cords 18A are arranged in the radial direction of the tire. The pneumatic radial tire 10 is reinforced by a carcass ply 18 and a belt layer 20 that surrounds the carcass ply 18 and is buried inside the tread portion 12, and the sizes thereof are all 165 / 70R13. An adhesive-treated polyester monofilament was used as a carcass cord, and the carcass cord driving number and tire structure were the same in each of the examples and comparative examples.

(Evaluation of durability of high load drum) After preparing a trial tire in a room at 25 ° C ± 2 ° C to the maximum air pressure of JIS standard, after leaving it for 24 hours, the air pressure was re-adjusted and
The tire is loaded with a load twice the maximum load of the S standard and run on a drum having a diameter of 1.7 m at a speed of 60 km / hour up to a target of 20,000 km. After that, take out the cord from the tire after the test so as not to damage it, measure the ply cord strength (generally called residual strength) of the bead turnback part,
Obtain the retention rate (strength retention rate%) for dip code strength.

[0042]

[Table 1]

[0043]

[Table 2]

From Tables 1 and 2, the following was confirmed. In Comparative Examples 1 and 2, the cord had poor peeling resistance because of its low inherent viscosity, and the cord was almost broken even in the high load drum test. Although Comparative Examples 3, 4, and 5 have high intrinsic viscosity, they have a problem that many cords are broken at the end of the high-load drum or the residual strength is low because the amorphous orientation is high. Comparative Example 6 is not preferable because the dip code strength is low because the birefringence is low.

The first, second, third, and fourth embodiments satisfy the conditions of the present invention. It can be seen that the higher the intrinsic viscosity is, the higher the peeling resistance is and the higher the residual strength after running the high load drum is. Further, in the case of the same molecular weight, those having a low amorphous orientation are excellent in fatigue resistance. As a result, in each of the examples, even after the end of the high-load drum, the residual strength is more than half of the dip cord, and it is judged that it can withstand practical use sufficiently.

[0046]

EFFECT OF THE INVENTION Since the adhesive-treated polyester monofilament of the present invention is constructed as described above, the fatigue resistance in rubber can be improved while maintaining the high strength and high elasticity merit of the conventional polyester monofilament. The excellent effect of remarkably improving was shown. Further, the pneumatic radial tire of the present invention using this polyester monofilament as a carcass ply cord,
The effect was excellent in durability and steering stability.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing a trial tire used in an example.

[Explanation of Codes] 10 Prototype tire (pneumatic radial tire) 12 Tread portion 18 Carcass ply 18A Carcass ply cord

Claims (2)

[Claims] 1. A rubber-reinforcing polyester monofilament, which is a monofilament cord made of polyethylene terephthalate or polyester containing this as a main component, and which has been previously treated with an adhesive and which simultaneously satisfies the following characteristics. (A) Intrinsic viscosity (IV): 0.90 or more (b) Birefringence Δn: 0.185 or more (c) Crystal orientation degree: 0.93 or more (d) Amorphous orientation degree: 0.38 or less (e ) Density (g / cm ³ ): 1.400 or more (f) Fineness (denier): 2000 to 5000 (g) Strength: 6 g / d or more (h) Initial elastic modulus: 70 g / d or more 2. A carcass ply cord is arranged in a radial direction of a tire, comprising a tread portion, a pair of side portions continuous on both sides of the tread portion, and a pair of bead portions respectively formed inside the side portions. In a radial tire reinforced by a carcass ply and a belt layer that surrounds the carcass ply and is buried inside a tread portion, the carcass ply cord is made of the rubber-reinforced polyester monofilament according to claim 1. A pneumatic radial tire characterized by the following.