JPH10329508A - Fiber cord with high strength and dip cord - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide fiber cord with a high strength and high elastic modulus excellent in the anti-fatigue property having an excellent dimensional stability. SOLUTION: This fiber cord with high strength is a twist yarn cord consisting of a fiber, the strength of whose original yarn cord is 35 g/d or more and the twist coefficient Kd of a lower twist is 700 or less and the twist coefficient Ku of an upper twist is 700 or more, and the ratio Ku/Kd between the upper twist coefficient and the lower twist coefficient is 1.5 or more and 10.0 or less. It is favorable that the original yarn of the cord is a polybenzazole fiber. The dip cord is made by giving the adhesive for the rubber to the fiber cord with a high strength.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength fiber cord having improved strength utilization and fatigue resistance and extremely high strength of a raw yarn.

[0002]

2. Description of the Related Art Conventionally, fibers used as rubber reinforcing materials for tires, hoses, belts and the like have mainly been nylon fibers, polyester fibers, glass fibers and steel fibers. Aromatic polyamide fibers represented by Kevlar have been used as various rubber reinforcing materials.

[0003] Polybenzazole fibers, which have much higher strength and elastic modulus than the aromatic polyamide fibers, and are also excellent in heat resistance and dimensional stability, are attracting attention as rubber reinforcing materials. In the field of rubber materials, the use of conventional organic fibers as reinforcement fibers in applications requiring higher strength and higher heat resistance, which has been insufficient in performance, has been studied.

[0004] Such high-strength fibers are represented by polybenzazole fibers and the like.
Since it has twice the tensile strength and tensile modulus, when it is used as a carcass material for, for example, a tire for a passenger car, it is possible to achieve a remarkable weight reduction that could not be achieved conventionally.

[0005] However, such ultra-high-strength fibers generally have a high modulus of elasticity as seen in polybenzazole fibers, and therefore have extremely low critical strain for compression. In the case of polybenzbisoxazole or the like, the critical compression strain is as low as 0.22%, and therefore, there is a problem that the compression fatigue resistance is inferior to other organic fibers under conditions where a large compression strain is applied. Therefore, as one means for improving this fatigue resistance, as described in JP-A-9-49139, polybenzazole fibers exhibit extremely good fatigue resistance on the low twisting side with a single twist. It is known that a relatively high coefficient is required, especially when used for a carcass of a radial tire where fatigue resistance is required,
In such a case, the fatigue resistance was not always sufficient.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned drawbacks of polybenzazole fiber, that is, the problem of poor fatigue resistance in a region where a large amount of compressive strain is applied as a rubber reinforcing material. High strength fiber cords such as polybenzazole fiber which have high strength, high elastic modulus, high heat resistance and excellent dimensional stability, and have excellent fatigue resistance It will not be provided.

[0007]

Conventionally, the number of ply twists and the number of ply twists in plied yarns are generally defined as a balance twist and a ply twist called a balanced twist in order to prevent cord deformation caused by residual torque of a cord such as snal. In the opposite direction were given almost equal values.

However, in the ultra-high strength fiber cord, the twisted cord necessarily includes the filament outside the cord in the longitudinal direction and always exists at the center of the cord. This is called the migration of the filament in the cord.If the twist coefficient of the lower twist is high, the migration of each filament is not always uniform, and especially when the twist is given, the part where the cord bends at an acute angle etc. It occurs easily, and stress concentration occurs in such places. Therefore, in a cord having a high elastic modulus, the strength utilization rate of the twisted cord is reduced, and the fatigue property is also below the expected value. The present inventors have conducted intensive studies and found that in the case of ultra-high strength fibers,
If the twist coefficient of the lower twist is low, the migration of each filament in the cord is uniform, and even if the cord is given a high twist coefficient, the uniformity of the filament migration is maintained and the cord is distorted. In this case, it was found that non-uniform migration did not occur, the stress concentration was small, the strength retention rate was clearly higher than that of the balanced twisted cord, and the fatigue resistance was significantly improved.

That is, the present invention relates to 35
After twisting high-strength fiber with a strength of g / d or more,
When a plurality of the cords are aligned and a ply twist is applied in the opposite direction to the ply twist, the ply twist coefficient Kd is set to 700 or less, the ply twist coefficient Ku is set to 700 or more, and the ply twist coefficient is set to A high-strength fiber cord characterized in that the ratio Ku / Kd to the twisting coefficient is 1.5 or more and 10 or less, more preferably 2.3 or more and 7.0 or less. Further, it is a high-strength fiber dip cord obtained by applying a rubber adhesive to the high-strength fiber cord.

Hereinafter, the present invention will be described in detail. The high-strength fiber in the present invention refers to a fiber having a strength of 35 g / d or more, such as an ultra-high molecular weight polyolefin fiber or a polybenzazole fiber. Here, the polybenzazole fiber refers to a fiber made of a polybenzazole polymer, and the polybenzazole (PBZ) refers to a polybenzoxazole (PBO) homopolymer and a polybenzothiazole (P
BT) Homopolymers and their PBO, random, sequential or block copolymers of PBT. Here, polybenzoxazole, polybenzothiazole and their random, sequential or block copolymers are described, for example, in "Liqu
id Crystalline Polymer Compositions, Process and P
roducts] U.S. Pat. No. 4,703,103 (Jan. 1987)
027), “Liquid Crystalline Polymer Composi
tions, Process and Products "US Patent No. 45336
No. 92 (August 6, 1985), "Liquid Crystalline
Poly (2,6-Benzothiazole) Compositions, Process and
Products, U.S. Pat. No. 4,533,724 (August 6, 1985), "Liquid Crystalline Polymer Composite"
ons, Process and Products "U.S. Pat.
No. 3 (August 6, 1985), Evers "Thermooxidat
ively Stable Articulated p-Benzobisoxazole and-Be
nzobisthiazole Polymers "U.S. Patent No. 4,539,567
No. (November 16, 1982), Tsai et al.
making Heterocyclic Block Copolymer ”US Patent No. 4
No. 578432 (March 25, 1986). As the structural unit contained in the PBZ polymer,
Preferably selected from lyotropic liquid crystal polymers. The monomer units consist of the monomer units described in structural formulas (a) to (h), and more preferably consist essentially of the monomer units selected from structural formulas (a) to (c).

[0011]

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[0012]

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Suitable solvents for forming the dope of the PBZ polymer include cresol and non-oxidizing acids capable of dissolving the polymer. Examples of suitable acid solvents include polyphosphoric acid, methanesulfonic acid and concentrated sulfuric acid or mixtures thereof. Further suitable solvents are polyphosphoric acid and methanesulfonic acid. The most suitable solvent is polyphosphoric acid.

The concentration of the polymer in the solvent is preferably at least about 7% by weight, more preferably at least 1% by weight.
0% by weight, most preferably at least 14% by weight. The maximum concentration is limited by practical handling properties such as, for example, polymer solubility and dope viscosity. Because of these limiting factors, the polymer concentration usually does not exceed 20% by weight.

[0015] Suitable polymers, copolymers or dopes are synthesized by known techniques. See, eg, Wolfe et al., US Pat. No. 4,533,693 (August 6, 1985), Sy.
U.S. Pat. No. 4,772,678 to S. bert et al. (September 20, 1988); U.S. Pat.
(July 11, 1989). P
BZ polymers are disclosed in US Pat. No. 5,085,959 to Gregory et al.
According to No. 1 (February 8, 1992), it is possible to increase the molecular weight at a high reaction rate under a relatively high temperature and high shear condition in a dehydrating acid solvent.

From the polymerized dope, a polybenzazole fiber having a high strength and a high elastic modulus is produced by a known means. For example, US Pat. No. 5,294,390 (1)
The dry-wet spinning method described on May 15, 994) is suitable.

The polybenzazole fiber is twisted using a ring twister or the like from the viewpoint of improving fatigue resistance. Detailed studies by the present inventors have confirmed that when the twist coefficient of the lower twist of the polybenzazole fiber exceeds 700, a large number of kink bands of the filaments constituting the cord are generated. Therefore, in the case of a twisted structure that receives a strain equal to or more than the compression limit strain (0.22%), its strength and elastic modulus are significantly reduced. Further, in order to improve the strength of the cord, it is necessary to give a certain number of twists. Therefore, it is important that the twist coefficient Kd of the lower twist is 700 or less, and preferably 100 or more. Further, it is important that the lower limit of the twisting coefficient Ku of the upper twist is 700 or more, more preferably 1000 or more, in order to improve the fatigue resistance. 200
0 or less, more preferably 1500 or less, and the twist balance Ku / Kd at this time is 1.5 or more and 10 or less, preferably 2.3 or less.
Not less than 7.0. The twist coefficient (K) is defined by the following equation. K = Tw (Den / ρ) ^1/2 Tw: Twist number (t / 10 cm) Den: Total denier ρ: Fiber density (g / cm ³ )

The twisted cord is provided with a so-called dip in order to improve the adhesion to rubber. Examples of the treatment liquid include (A) an aqueous dispersion of an epoxy resin, (B) an aqueous dispersion of a blocked isocyanate, (C) an aqueous dispersion of a rubber latex, and (D) a mixed solution of a resorcinol-formaldehyde resin and a rubber latex. In general, the treatment is performed in a single step or in a multi-step treatment of two or more steps in combination or alone. However, other prescriptions may of course be used. In particular, in this formulation, uniformity of migration of each filament in the cord is particularly important for enhancing fatigue resistance and utilization of strength and elastic modulus.

The polybenzazole fiber cord thus obtained has a high degree of utilization of the strength and elastic modulus, and has a twist coefficient Kd of the lower twist of 100 to 700, preferably 200 to 500, and a twist coefficient Ku of the upper twist of 700 or more. It is 2000 or less, preferably 1000 or more and 1500 or less, and Ku / Kd is 1.5 or more and 10 or less, preferably 2.3 or more and 7 or less. As a result, it has good fatigue resistance, has high strength and elastic modulus that cannot be realized by conventional organic fibers, and has novel features of excellent fatigue resistance.

Next, the effects of the present invention will be described with reference to examples. Of course, the present invention is not limited to the embodiments.

EXAMPLE A 1000-denier polybenzbisoxazole fiber was twisted and then twisted to form a cord. The characteristics of the obtained cord are shown in Table 1 and FIGS.

[0021]

[Table 1]

As can be seen from FIGS. 1 and 2, when the lower twisting coefficient is 700 or more, the strength and elastic modulus of the upper twisted cord are remarkably reduced, and the excellent mechanical properties of the polybenzbisoxazole fiber are considered as cord properties. It can be seen that it cannot be reflected on Further, when the twisting coefficient becomes 1500 or more, the elastic modulus shows a lower limit value, and the excellent properties of the polybenzbisoxazole fiber cannot be utilized.

Next, a two-step dipping process was performed on each raw code to create a dip code. The first-stage dipping solution was an aqueous dispersion of an epoxy resin, and the processing temperature was 240 ° C., and the second-stage dipping solution was an RFL solution, and the processing temperature was 235 ° C. Table 1 shows the characteristics of the obtained cord. This result is shown in FIG. 3 as the strength before and after fatigue. As described above, it can be seen that the fiber of the present invention has a higher strength retention and a significantly higher fatigue resistance than the comparative example as shown in the examples. Further, as shown in FIG. 4, the tendency that the higher the twisting coefficient is, the higher the fatigue is, but it is clear that this is limited to the case where Ku / Kd is 1.5 or more. ADVANTAGE OF THE INVENTION By this invention, it became possible to provide the code | cord | chord which can achieve high strong retention | maintenance, maintaining the fatigue resistance excellent compared with the cord of a balance twist.

[0024]

According to the present invention, a cord which simultaneously satisfies both mechanical properties and fatigue resistance at a level which could not be achieved as a practical cord by utilizing the excellent mechanical properties of high-strength fibers. And to provide dip code.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a lower twist coefficient and a cord strength.

FIG. 2 is a diagram showing a relationship between a lower twist coefficient and a cord elastic modulus.

FIG. 3 is a diagram showing the relationship between the strength of a product of the present invention and a comparative product before and after a fatigue test.

FIG. 4 is a view showing the relationship between the twisting coefficient of the product of the present invention and the comparative product and the cord strength after fatigue.

Claims (4)

[Claims] 1. A twisted cord made of a fiber having a strength of 35 g / d or more, and a twist coefficient Kd of a lower twist.
Is 700 or less, the twist coefficient Ku of the ply twist is 700 or more, and the ratio Ku / Kd of the ply twist coefficient and the ply twist coefficient is 1.5.
A high-strength fiber cord characterized by being at least 10.0. 2. A high-strength fiber cord wherein the ratio Ku / Kd of the twisting coefficient and the lower twisting coefficient of the twisted cord is 2.3 or more and 7.0 or less. 3. The high-strength fiber cord according to claim 1, wherein the raw yarn of the cord is a polybenzazole fiber. 4. A high-strength fiber dip cord obtained by applying a rubber adhesive to the high-strength fiber cord according to claim 1.