JPH09137319A - Polyester fiber - Google Patents

Abstract

(57) Abstract: To provide a polyester fiber having high strength and thermal dimensional stability comparable to that of rayon, which is suitable as a fiber for rubber reinforcement. A polyester fiber made of polyethylene terephthalate having an intrinsic viscosity of 0.85 or more, a strength of 6 g / de or more and an elongation of 12% or more, and a fine crystal volume of 2.5 × 10 ² nm ³ or more. , A crystal melting endothermic curve has a main peak at a temperature of 270 to 280 ° C. and a sub peak at a temperature of 255 to 270 ° C., and a birefringence difference (|
A polyester fiber having a fiber microstructure in which Δn (0.9) −Δn (0) |) is 0.005 or less.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polyester fiber suitable for reinforcing a rubber structure having high strength and excellent thermal dimensional stability.

[0002]

2. Description of the Related Art Polyester fiber not only exhibits excellent mechanical properties such as strength and elasticity, but also has excellent dimensional stability and durability. Therefore, it is a fiber for rubber reinforcement of belts, tires, etc. Is widely used as. However, in recent years, further improvement in thermal dimensional stability has been particularly required as a material to replace rayon used for high-end automobiles and for the purpose of omitting post-cure inflation during tire molding.

Conventionally, in order to improve thermal dimensional stability,
For example, JP-B-63-528 and JP-B-63-5.
The method of drawing a partially oriented yarn proposed in Japanese Patent No. 29 was adopted, but it is still insufficient in comparison with rayon.
Further, a method has been proposed in which the unstretched yarn is highly oriented and crystallized by increasing the spinning speed to further improve the method (JP-A-61-41320, JP-A-62-6).
9819, JP-A-63-159518).

However, the methods for producing highly oriented crystal undrawn yarns proposed in these papers merely increase the spinning speed, so that cooling unevenness between filaments due to yarn wobbling occurs, and thus fluff occurs during drawing. However, there is a problem that thread breakage occurs frequently and a high-strength thread sufficient for rubber reinforcement cannot be obtained. In addition, since increasing the spinning speed makes the difference in orientation between the fiber inner and outer layers abnormally large, the molecular orientation of the fiber inner and outer layers at the time of stretching becomes uneven, and it becomes impossible to perform high-strength drawing to obtain sufficient strength.

In order to reduce the unevenness of orientation of the inner and outer layers of the fiber, Japanese Patent Publication No. 64-2685 and Japanese Patent Publication No. 1-28.
In JP 127, there is proposed a method in which the cooling air is set to 50 to 80 ° C. to delay the cooling rate to reduce the temperature difference between the fiber inner and outer layers and suppress the alignment unevenness. However, in this method, since crystallization proceeds excessively during spinning, the mobility of the molecular chain for stretching is impaired, and high-strength yarn cannot be obtained, making it difficult to obtain a high-strength yarn. Further, as another method for reducing the orientation unevenness of the fiber inner and outer layers, a method of disturbing the orientation of the fiber surface layer portion by using high-temperature heated steam as a heating means for hot drawing to raise the orientation degree of the entire fiber has been proposed. However, in this method, the intrinsic viscosity of the polyester in the fiber surface layer portion is lowered, so that the durability of the obtained fiber is likely to be insufficient, and crystallization of the fiber inner layer portion is likely to occur during stretching, so that high-strength drawing is also difficult. It is easy to become. Further, JP-A-5-311512 and JP-A-5-3115
In JP-A-13, a method is proposed in which heated steam is introduced under the spinneret to reduce the intrinsic viscosity of the outer layer polyester of the spun yarn and suppress the orientation unevenness of the fiber inner and outer layers. As described above, the intrinsic viscosity of the polyester is lowered, so that the strength of the fiber is likely to be insufficient, which is insufficient as a rubber-reinforcing fiber.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a polyester fiber having high strength and thermal dimensional stability comparable to that of rayon, which is particularly suitable as a fiber for reinforcing a rubber.

[0007]

Means for Solving the Problems As a result of intensive studies aimed at achieving the above-mentioned object, the present inventors have found that the high-draft-spun highly-oriented undrawn yarn has a small difference in orientation between the inner and outer layers of the fiber, and thus has a high draw ratio. High-strength fibers can be easily obtained by stretching, and the obtained fibers have a large crystallite volume and a fiber structure in which the melting point peaks show the main peak and the sub-peaks, so the thermal dimensional stability The present invention has been achieved as a result of further studies based on such findings.

Thus, according to the present invention, the intrinsic viscosity of ethylene terephthalate as a main repeating unit is 0.
A polyester fiber having a breaking strength of 6 g / de or more, a breaking elongation of 12% or more, and satisfying the following properties (1) to (5) at the same time is provided. The crystallite volume (V) is 2.5 × 10 ² nm ³ or more, the crystal melting endothermic curve has a main peak at a temperature of 270 to 280 ° C. and a sub-peak of a temperature of 255 to 270 ° C., and a birefringence index in the transverse direction of the fiber. Difference (| Δn (0.9)-
Δn (0) |) is 0.005 or less, where Δn (r) is the birefringence at the position of the standardized radius r, and Δn (0) is the birefringence at the fiber axis center.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the polymer constituting the polyester fiber of the present invention, it is important that the main repeating unit of the polyester is ethylene terephthalate, preferably 95% or more thereof, and particularly preferably polyethylene terephthalate. In addition, the intrinsic viscosity of polyester (25
C, calculated from o-chlorophenol solution) is 0.85 or more, preferably 0.9 to 1.0, and when less than 0.85, its durability for use as rubber reinforcement Not only becomes insufficient, but also has a cutting strength of 6 g /
This is not preferable because the stretching ratio required for high strength such as de or more becomes large, and only one peak appears in the melting endothermic curve described later, and the thermal dimensional stability decreases.

Next, the polyester fiber of the present invention is required to have a breaking strength of 6.0 g / de or more and a breaking elongation of 12% or more. However, if the breaking strength becomes too large, the volume of microcrystals described later becomes large. However, if the cutting elongation is too high, it becomes difficult to satisfy the cutting strength. Therefore, the cutting strength is 6.5 to 7.0 g /
The range of de is preferable, and the cutting elongation is particularly preferably in the range of 14 to 20%. If the cutting strength is less than 6.0 g / de, the strength is insufficient for rubber reinforcement and a sufficient reinforcing effect cannot be obtained. On the other hand, if the cutting elongation is less than 12%, it is used for rubber reinforcement. When used, the strength is greatly reduced in the twisting process usually performed, and the durability is also deteriorated, which is not preferable.

The polyester fiber of the present invention preferably has a fineness (single yarn fineness) in the range of 1.0 to 3.0 denier, and when it is less than 1.0 denier, the fiber characteristics described later are simultaneously obtained. It becomes difficult to stably spin a satisfying fiber. On the other hand, when it exceeds 3.0 denier, it is difficult to reduce the orientation difference between the inner and outer layers of the fiber, and it is difficult to simultaneously achieve high strength and thermal dimensional stability. Becomes

In addition to the above-mentioned characteristics, the polyester fiber of the present invention has the following characteristics, the crystallite volume (V) is 2.5 × 10 ² nm ³ or more, and the crystal melting endothermic curve has a temperature of 270 to 280 ° C. There is a main peak and a sub-peak at a temperature of 255 to 270 ° C., and the birefringence difference in the fiber cross-section direction (| Δn (0.9) −
It is important that Δn (0) |) is 0.005 or less at the same time. Here, the crystallite volume (V) is determined by X-ray diffraction (010), (10)
0), which is represented by the product of crystal sizes calculated from the half-width of the interference peak of the (−105) plane using Scherrer's formula, and when this value is less than 2.5 × 10 ² nm ^3. Has
As shown in FIG. 4, the thermal dimensional stability becomes insufficient, so that the object of the present invention cannot be achieved. The crystal melting endothermic curve was measured by using a differential scanning calorimeter at a temperature rising rate of 20 ° C./min under a nitrogen stream, and the sub-peak of the melting endothermic peak was decreased when the draw ratio was increased. It is presumed that the crystal component of the peak relaxes the stress concentration because the molecular chain is fixed relatively loosely than the crystal component of the main peak. Therefore, when this sub-peak is not present, the fiber strength and the elongation are lowered and the toughness becomes insufficient, which is not preferable. Further, by setting the birefringence difference in the cross-sectional direction of the fiber to 0.005 or less, the stretchability during fiber production is improved and a fiber with excellent physical properties is obtained. However, if this value is too large, it is stable. There is a tendency that the fiber cannot be stretched and the strength and elongation of the entire fiber are lowered and the toughness becomes insufficient.

The polyester fiber of the present invention detailed above can be obtained, for example, by the following method, but the present invention is not limited to this method.

In producing the fiber of the present invention, the spinning tension is increased to obtain an undrawn yarn of high orientation and high crystallinity, and the cooling method is limited to eliminate the cooling rate difference between the inner and outer layers of the fiber. Etc. are important, and for that purpose the intrinsic viscosity of the polymer used and the spin-drawing process are important. That is, when melt-spinning a polyester having an intrinsic viscosity of 0.85 or more, the spinning draft is set in the range of 1000 to 3000, and the fineness of the obtained undrawn yarn is 10 denier or less, preferably 2 to 5
Denier and take-off speed 2500m /
Min., Preferably 3000 to 4000 m / min. By doing so, the birefringence difference between the fiber inner layer portion and the outer layer portion is small, and the crystals are large and a plurality of melting endothermic peaks appear. A drawn yarn is obtained. The obtained unstretched yarn has a uniform orientation in the cross section of the fiber and thus can be stretched at a high ratio.However, if the stretching ratio is made too large, the crystallite volume becomes too small or the endothermic peak sub-peak disappears. On the other hand, if the stretching ratio is too small, the strength becomes insufficient. Therefore, stretching is performed at a maximum stretching ratio of 0.85 to 0.93 times. Here, the stretching is preferably performed in two or more stages, in which case the first stage stretching is preferably performed at a temperature as low as possible in order to suppress crystallization, and when performing direct spinning, different from the case of separate stretching. Since the warp yarn temperature is high, it is desirable that the first stage preheating roll is not heated. The drawn yarn is
In order to improve its dimensional stability, it can be heat-fixed and further subjected to relaxation heat treatment.

The measuring method of each parameter for specifying the structure and physical properties of the polyester fiber of the present invention is as follows. Cutting strength and elongation Based on JIS L 1017. Microcrystal volume (010), (100), (-10 in wide angle X-ray diffraction
5) The product of the crystal sizes in each direction calculated using the Scherrer's formula from the half width of the diffraction peak of the plane. Crystal melting endothermic curve Differential scanning calorimeter (DSC-I manufactured by Perkin Elmer Co., Ltd.
Using a mold) at a heating rate of 20 ° C./min under a nitrogen stream.
The endothermic peak temperature was defined as the crystal melting point. Birefringence difference in cross section of fiber Interference microscope (Interfero-interference microscope manufactured by Carl Zeiss Jena, Inc. was used to determine by interference fringe method. Immersion solution was methylene iodide, α-bromonaphthalene, clove oil,
A combination of dibutyl phthalate and a desired refractive index was used. From the photograph of the obtained interference fringes, the average refractive index was calculated from the interval and the deviation of the interference fringes by the following formula. λd / D = (n−N) t However, d: deviation of interference fringes, D: interval of interference fringes, λ: wavelength of light source to be measured, n: refractive index of sample, N: refractive index of solution, t: of sample Wire diameter In this analysis, the normalized radius (r = a / A) when the radius of the fiber is A and the distance from the center axis is a (r = a / A) 10 points at 0.1 intervals between 0 and 0.9 "Technology for measuring fibers and polymers" edited by the Society: Conducted in accordance with the method published by Asakura Shoten, and the refractive index in the direction parallel to the fiber axis direction of the sample and the vertical direction It was calculated. Δn (r) = refractive index in parallel direction (r) −refractive index in vertical direction (r)

[0016]

In the polyester fiber of the present invention, the molecular chains are fixed by relatively large crystallites, so that the molecular chain fixation between crystals is more three-dimensionally constituted than that of the one having a small crystallite size. As a result, the thermal mobility of the molecular chains in the amorphous structure is suppressed, and the dimensional stability becomes extremely excellent. Furthermore, since the birefringence difference in the fiber cross-section direction and the melting endothermic peak satisfy the above requirements, the breaking strength is 6.0 g /
Even if it is larger than de, the distortion in the fiber structure does not become so large, so that the dimensional stability becomes good, and moreover, the good quality fiber with few fluff is stably maintained without lowering the process stability during the yarn making. It is presumed that such an effect that it can be easily obtained is exhibited.

[0017]

The present invention will be described in more detail with reference to the following examples. Polyethylene terephthalate having an intrinsic viscosity of 1.01 is melted at about 300 ° C., and is discharged from a spinneret having 500 nozzles having the hole diameters shown in Table 1 at a rate such that the fineness of fibers obtained after drawing is as shown in Table 1. After that, Table 1
After passing through the heating zone below the mouthpiece described above, cool air at 25 ° C
After spraying at a rate of Nm ³ / min to cool and solidify, apply an oil agent with an oiling nozzle, and then take off at a speed shown in Table 1,
Without being wound once, two-stage drawing was carried out and wound up.

Here, the feed roll for the first stage drawing is not heated, the preheating temperature for the second stage drawing is 100 ° C., and then 20
Heat set at 0 ° C. The first stage draw ratio was the natural draw ratio, and the second stage draw ratio was such that the total draw ratio was as shown in Table 1.

The polyester fiber obtained has a total fineness of 3
Plural yarns for 50 times / 10
cm after twisting, and three of them are combined 50 times / 1
A twist of 0 cm was applied, the obtained cord was subjected to an adhesive treatment using a resorcin / formalin / latex adhesive liquid (RFL liquid), and heat treated at 245 ° C. for 2 minutes under a tension of 2 g / de to obtain a treated cord. Table 1 shows the results. In the table, the thermal dimensional stability is represented by the sum of the elongation at 2.25 g / de load and the dry heat shrinkage at 150 ° C.

[0020]

[Table 1]

As is clear from Table 1, when the intrinsic viscosity of the polyester is low, the strength and elongation are significantly deteriorated when the polyester is treated, and it is not preferable for rubber reinforcement. It is also understood that when the cutting strength is low, the strength for rubber reinforcement is insufficient, and when the crystallite volume is small, the dimensional stability is insufficient.

[0022]

Since the polyester fiber of the present invention has a dimensional stability as good as rayon, it can be used particularly suitably as a reinforcing cord for rubbers, but it may of course be used for other purposes.

[Brief description of the drawings]

FIG. 1 is a crystal melting endothermic curve of a drawn yarn (a) and an undrawn yarn (b) obtained in Example 1.

2 is a crystal melting endothermic curve of the drawn yarn obtained in Comparative Example 2. FIG.

FIG. 3 shows the refractive index distributions of the drawn yarn (a) and the undrawn yarn (b) obtained in Example 1 in the cross-sectional fiber direction (after normalization).

FIG. 4 is a graph showing the relationship between crystallite volume and thermal dimensional stability.

Claims (3)

[Claims] 1. A fiber comprising a polyester having ethylene terephthalate as a main repeating unit and having an intrinsic viscosity of 0.85 or more, a breaking strength of 6 g / de or more, a breaking elongation of 12% or more, and the following: A polyester fiber characterized by simultaneously satisfying the properties of. The crystallite volume (V) is 2.5 × 10 ² nm ³ or more, the crystal melting endothermic curve has a main peak at a temperature of 270 to 280 ° C. and a sub-peak of a temperature of 255 to 270 ° C., and a birefringence index in the transverse direction of the fiber. Difference (| Δn (0.9)-
Δn (0) |) is 0.005 or less, where Δn (r) is the birefringence at the position of the standardized radius r, and Δn (0) is the birefringence at the fiber axis center. 2. The polyester fiber according to claim 1, wherein the sub-peak value of the crystal melting endothermic curve is 0.5 times or more the main peak value. 3. The polyester fiber according to claim 1, which has a single yarn fineness of 1.0 to 3.0 denier.