JPH0791716B2 - Pneumatic radial tires - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a pneumatic radial tire for passenger cars, and more specifically, to an improved polyester cord used as a reinforcing cord for a carcass layer and / or a belt layer. By doing so, the present invention relates to a pneumatic radial tire for passenger cars having improved durability.

(Prior Art) Rayon, polyamide and polyester are well known as organic fibers as a carcass reinforcing material for radial tires for passenger cars. Of these, the use of rayon has reached its limit due to problems of raw material resources, bad odor in the manufacturing process, wastewater treatment, and the like. Polyamide has excellent durability, but is inferior in creep property, and further has problems such as occurrence of flat spots. For this reason, in recent years, polyester has become the mainstream as a reinforcing material for radial tires for passenger cars.

However, since polyester has lower strength than polyamide, many cords must be used to secure the safety factor of the carcass in the tire using polyester as the carcass reinforcing material. In addition, since polyester is inferior in heat resistance to polyamide, it is easy to cause separation between the cord and the rubber, and inferior in fatigue resistance, there is a problem of cord breakage due to carcass durability.
Therefore, in order to solve such problems, many improved techniques have been proposed. For example, JP-A-53-58031
As disclosed in JP-A No. 53-58032 and JP-A No. 53-58032, the value of birefringence as a microstructure is 160 × 10 ^{−3 to} 189 ×.
There is known a technique aiming at improving fatigue resistance by setting the crystallinity within the range of 10 ^{-3 and} the crystallinity within the range of 45 to 55%. Further, JP-A-55-116816 discloses a polyester in which the content of terminal carboxyl groups in the polymer is reduced in order to improve heat resistance. Furthermore, improve the microstructure of polyester, specify the swelling grade concentration of topping rubber when applying this cord to tires, and reduce the terminal carboxyl group content in the polyester polymer to improve durability. Attempts are also being made.

(Problems to be Solved by the Invention) As described above, in an attempt to improve the fatigue resistance of a carcass, for example, a polyester cord having excellent mechanical fatigue resistance is adopted in the conventional technology. The high stress spun polyester disclosed in the prior art as an excellent polyester has a problem that it has lower strength than ordinary polyester and its heat resistance is significantly inferior because of its micro characteristics. For this reason, if the amount of cords used is increased in order to secure the safety factor of the carcass, not only the tire weight becomes heavy but also the economical efficiency becomes poor. Further, the use of a large number of cords causes a problem that heat generation from the cords itself becomes large during high-speed running, and thus thermal deterioration of the polyester is promoted, and breakage between the cords and rubber, that is, separation easily occurs. .

On the other hand, in the conventional technique for reducing the terminal carboxyl groups of the polyester polymer in order to improve the heat resistance, there is a problem that if the number of the terminal carboxyl groups is too small, the adhesiveness decreases, and the polyester for high stress spinning is used. Even if it was combined with, the strength could not be solved. As a means for improving the strength of polyester, a means of increasing the polymerization degree of the polymer, increasing the draw ratio, etc. are known, but using such means alone will improve the strength but significantly increase the fatigue resistance. Therefore, the durability of the tire will decrease. Not only that, but as a characteristic of such a cord, since the heat shrinkage is usually large, the good characteristics such as the high elastic modulus and low heat shrinkage inherent in polyester are also lost.

Therefore, an object of the present invention is to have a high elastic modulus inherent in polyester,
We have improved the durability of tires by manufacturing dip cords that have high strength and fatigue resistance while maintaining the property of low heat shrinkage and have excellent heat resistance, and apply these dip cords to radial tires. It is to plan.

Here, the dip code means a code that has been treated with an adhesive.

(Means for Solving Problems) The inventors of the present invention have a mutual relationship among the primary structure, secondary structure and dip treatment of a polyester polymer in order to improve the durability of a radial tire using a polyester cord as a reinforcing material. As a result of diligent research focusing on clarifying that, it is possible to obtain a polyester dip cord with high strength and excellent fatigue resistance and heat resistance without impairing the original properties of polyester under these predetermined relationships. The present invention has led to the completion of the invention of a radial tire having excellent durability.

The structure of the present invention is as follows.

In a pneumatic radial tire having a carcass reinforced with a belt arranged inside the tread portion, at least one of the belt and the ply of the carcass is reinforced with a polyethylene terephthalate fiber cord, and the polyethylene terephthalate fiber cord is , The dip cord obtained by setting the cord tension of the hot stretching zone to 1 to 2.5 g / d and the cord tension of the normalizing zone to 0.5 to 1.5 g / d as the dip treatment condition, and the following formula: strength ( S) 7.0 (g / d) Long period of small angle X-ray (L _p ) 160 (Å) Terminal carboxyl group content (C) 15 (Equivalent / 10 ⁶ g polymer) Diethylene glycol content in polymer (DEG)
It is characterized by satisfying the relationship of 1.5 (% by weight).

(Operation) The inventors of the present invention studied the relationship between the reinforcing material cord of the radial tire and the tire durability performance, and obtained the following findings.

When a polyester cord was used as a reinforcing material in a radial tire for passenger cars, it failed at a level one to two steps lower than in the case where a polyamide cord was used, in an endurance test on an indoor drum until the breakdown caused a failure. . As a result of detailed analysis and investigation of this cause, the tire using polyester cord as a reinforcing material has high heat generation of the tire during running, and when the temperature near the interface between the cord and rubber reaches 120 ° C or more, the cord suddenly increases. It was found that the heat deterioration of the product progresses and the separation fails. Furthermore,
The heat generation property of this cord has shown a phenomenon that the heat generation amount increases in proportion to the increase in the amount of the cord used in one tire. That is, from this phenomenon, it was estimated that when the amount of the cord used as the reinforcing material is large, the amount of heat generated from the cord itself increases, and as a result, the temperature of the tire rises. Therefore, it was considered important to reduce the amount of cords used as much as possible in order to improve the durability of the tire. However, if the amount of cord used is reduced, the reinforcement effect will also decrease in proportion to this,
The safety factor of the tire as an air container decreases, and eventually the cord is destroyed by various stimuli received while driving,
That is, there is a risk of a shock burst, or a cut burst depending on sharp stone fragments. Therefore, the polyester cord as a reinforcing material needs to have a certain strength or more. Then, as a result of diligent study on the necessary limit of the strength, it was found that the strength (S) of the reinforcing polyester cord used in the tire should be 7.0 g / d or more. If it is less than this range, the cut burst resistance performance is lowered as described in detail in the following examples, which is not preferable.

On the other hand, it was found that the following conditions must be satisfied in order to maintain this strength and improve fatigue resistance and heat resistance.

That is, the polyethylene terephthalate fiber constituting the cord as the tire reinforcing material is a value measured at 25 ° C. using o-chlorophenol in which 90 mol% or more of all repeating units of the molecular chain are composed of polyethylene terephthalate units. The intrinsic viscosity calculated by the above is 0.8 or more, preferably 0.9 or more. Further, in the present invention, it is an important point that the content of diethylene glycol which is a side reaction product contained in the main chain of the polymer is 1.5% by weight or less. The reason for this is that if the diethylene glycol content exceeds 1.5 parts by weight, the strength decreases during the dip heat treatment, and sufficient strength cannot be obtained.

Further, in the present invention, the terminal carboxyl group content in the polymer is 15 equivalents / 10 ⁶ g or less, preferably 1
It must be 0 equivalent / 10 ⁶ g polymer or less. The reason for this is that if a polymer containing more than 15 equivalents / 10 ⁶ g polymer of carboxyl end groups is used, the heat resistance will decrease, so only the one with poor durability can be obtained due to the heat deterioration caused by the heat generated during high-speed running. Because there is no.

Next, high stress spinning was performed using this polymer. As a result of studying the relationship between the fatigue properties of polyethylene terephthalate cords and the fiber internal structure in order to improve the mechanical fatigue properties of the obtained cords, it was found that the cord fatigue properties were determined by the long period L of X-ray diffraction.
We found that there is a relation with _p (Å)
It has been found that the object of the present invention can be achieved when _p (Å) satisfies the relationship of the following equation: Lp160.

Polyethylene terephthalate-based fiber cords satisfying all the above conditions are obtained by, for example, solid-phase polymerizing polymer (intrinsic viscosity 1.31) in the raw yarn manufacturing process being rapidly cooled under a spinneret in a gas atmosphere of 10 to 60 ° C. It can be obtained by selecting the optimum conditions within the range of 1500 to 2000 m / min and the draw ratio of 2.30 to 2.50.

In the present invention, the cord tension of the hot threading zone is 1 to 2.5 g / d as the dip heat treatment condition,
And the cord tension in the normalizing zone is 0.5 to 1.5 g /
It must be within the range of d. The reason for this is that it is presumed that the high stress-spun polyethylene terephthalate fiber cord is likely to cause a decrease in strength during dip heat treatment because the orientation disorder of the amorphous portion is large as a microstructure characteristic of the fiber. The reason is that the tension applied to the cord is increased until the drying is sufficiently completed to prevent the molecular strength of the amorphous portion from being lowered in the tension state. still,
After sufficiently drying, the tension may be adjusted so that the required physical properties are obtained.

By combining the above technologies, a dip cord with high strength, high fatigue resistance and excellent heat resistance can be obtained. Therefore, when such a cord is applied to a tire, the amount of reinforcing material used is small. Thus, a radial tire having excellent heat resistance, low heat buildup, light weight and durability can be obtained.

(Example) Next, the present invention will be described with reference to Examples and Comparative Examples.

Intrinsic viscosity (IV) 1.31, diethylene glycol content (DE
G) 0.8% by weight and terminal carboxyl group content (C) 8 equivalents
/ 10 using polyethylene terephthalate having ⁶ g polymer value, then rapidly cooled spinneret under a temperature 25 ° C. in a gas atmosphere wound up by spinning at乍Ra spinning speed 2000 m / min and then stretched to 2.40 times in the stretching step Then, a polyethylene terephthalate raw yarn 1000d / 192 filament was prepared.

Using the obtained raw yarn, ply-twisted with 49 twists / 10 cm,
Next, two of these yarns were combined and twisted in the opposite direction at the number of twists of 49 times / 10 cm to obtain a twisted cord. Then this code 65
As the woven fabric having the number of nails per 5 cm, a dip treatment was performed under the following dip treatment conditions. However, for Comparative Examples 5 to 7 in Table 1 below, the dip processing was performed under different dip processing conditions as shown in Table 1.

The adhesive was mixed with resorcinol-polysulfide and resorcinol-rich resorcinol-formaldehyde condensate at a solid content ratio of 20: 100, and 18 parts of the solid content were taken out from the mixture, and 9 parts of 28% ammonia water was added thereto. , And the whole
Water was added to make 50 parts to completely dissolve it, and then 50 parts of resorcin-formaldehyde condensate / latex (RFL) was added and used as an adhesive solution.

Here, this RFL was prepared in the following composition and aged for 48 hours or more.

Water 518.8 (parts by weight) Resorcin 11.0 Formalin (37%) 16.2 Ammonium hydroxide (28%) 10.0 Vinyl pyridine-styrene-butazine copolymer latex (41%) 244.0 For the raw cord and dip cord thus prepared The strength (S), intrinsic viscosity (IV), diethylene glycol content (DEG), carboxyl group content and small-angle X-ray long period (L _p ) are also shown in Table 1, respectively.

The above-mentioned diethylene glycol content (DEG), terminal carboxyl group content (C), strength (S) and small angle X-ray long period (L _p ) were measured as follows.

Diethylene glycol content (DEG) 0.5 g of the sample was refluxed and decomposed in 25 ml of a 1N NaOH / 80% methanol solution, and the excess alkali was neutralized, followed by standing. Then, inject the supernatant into gas chromatography (glass column 3 mmφ x 1500 mm, filled with PEG 20M 5%, 80-100 mesh) and calculate the peak height ratio of DEG / EG (ethylene glycol) to obtain the calibration curve. The DEG (% by weight) was calculated from the above.

Terminal carboxyl group content (C) A sample of 1 g was dissolved in 20 ml of o-cresol, completely dissolved and cooled, and then 40 ml of chloroform was added, and potentiometric titration was performed with a methanol solution of NaOH.

Strength (S) From the tensile strength SD (gf) of the raw cord (or dip cord) before dip treatment and the positive fineness D _N (d) of the raw cord, the following formula: It was calculated according to. The tensile strength SD of raw cord (or dip cord) is measured by JIS-L1017 standard time test method,
The measurement of the true fineness D _N of the raw cord was also carried out by the method of JIS-L1017.

Small-angle X-ray long period (L _p ) Scattering angle (2θ) is calculated from the geometrical condition of the camera radius (R = 400 mm), from the inter-interference distance (Smm) in the fiber axis direction of four-point interference on the small-angle scattering photographic film. The long period L _p (Å) was obtained from the Bragg equation.

Next, after the rubber is put on the above-mentioned dip-cord woven fabric, it is cut into a predetermined length and used as a carcass layer, and a size 165 SR 13 having two steel cord layers as a belt layer is used. Created a radial tire. The obtained tire was subjected to a high-speed durability drum test, a low internal pressure and high load durability drum test, and a tire side plunger test. Hereinafter, these test methods will be described.

High-speed durability drum test method Using a drum tester with a smooth drum surface made of steel and a diameter of 1.707m, the ambient temperature was controlled at 38 ± 3 ℃, rim size 4 1/2 J-13, test internal pressure 2.1. After running for 120 minutes at a speed of 81 km / hour under the conditions of kg / cm ² and a load of 425 kg, and after cooling for 3 hours or more, the test air pressure was readjusted and the main running was started.

The actual running was started from a speed of 121 km / hour, the speed was gradually increased by 8 km / hour every 30 minutes, and the speed at which the failure occurred and the running time were measured.

According to past results, if you can not complete 30 minutes at a speed of 185 km / hour, there may be a problem in the market.

Low internal pressure and high load durability drum test method Using a drum tester similar to the high speed durability drum test, the ambient temperature was controlled to 30 ± 3 ° C, and the rim size was 4 1/2 J
-13, test internal pressure 1.0kg / cm ² , load 470kg under conditions of failure occurred or run up to 10,000km.

From the past results, if you do not complete 10 million km, there may be a problem in the market.

Side plunger test method Tires are assembled with a rim size of 4 1/2 J-13 and air pressure of 1.9 kgf / cm ² and fixed to the tester with no load, and the tip of the plunger is hemispherical (φ19 mm). Push the pin vertically to the maximum tire width position at 50 ± 2.5 mm / min. The plunger movement amount Y (cm) from the time the plunger contacts the tire to the time when it breaks, and the plunger pushing force when the tire breaks F
From (kg) the following formula: Plunger energy (PE) was calculated in accordance with. This test result is related to the side cut resistance in the market,
It is predicted that 500 kg / cm will be required based on past results.

The results of the above tests are also shown in Table 1.

(Effects of the Invention) As is clear from the test results shown in Table 1, in the pneumatic radial tire using the dip cord satisfying all the conditions of the present invention, a dip that lacks any of the conditions of the present invention. It was extremely durable compared to pneumatic radial tires using cords.

Continuation of front page (56) Reference JP 61-89322 (JP, A) JP 58-98419 (JP, A) JP 57-154410 (JP, A) JP 58-23914 (JP , A) JP-A-60-246811 (JP, A)

Claims (1)

[Claims] 1. A pneumatic radial tire having a carcass reinforced with a belt arranged inside a tread portion, wherein at least one of the belt and the ply of the carcass is reinforced with a polyethylene terephthalate fiber cord. The terephthalate fiber cord is a dip cord obtained by setting the cord tension of the hot stretching zone to 1 to 2.5 g / d and the cord tension of the normalizing zone to 0.5 to 1.5 g / d as the dip treatment condition, Formula: Strength (S) 7.0 (g / d) Long period of small angle X-ray (L _p ) 160 (Å) Terminal carboxyl group content (C) 15 (Equivalent / 10 ⁶ g polymer) Diethylene glycol content in the polymer (DEG)
A pneumatic radial tire characterized by satisfying the relationship of 1.5 (% by weight).