JPH062216A - Ultrafine aramide fiber and its production - Google Patents

Abstract

PURPOSE:To obtain the subject fiber having a high strength, improved in flexibility and in wear resistance, and useful for ropes, braids, etc., by extruding a liquid- crystalline para-oriented aramide polymer solution into an inert gas under specific conditions, bringing the extruded solution into contact with a coagulation solution, washing the produced fibers and subsequently drying the washed fibers. CONSTITUTION:A solution of a liquid-crystalline para-oriented aramide polymer (e.g. poly para-phenylene terephthalamide) in a solvent such as N-methyl-2-pyrrolidone is once extruded into an inert gas, brought into contact with a coagulating solution (e.g. 35% aqueous solution of sulfuric acid) having a solvent concentration of 32-45wt.% and installed at a place apart from the lower surface of a spinneret at a spinneret surface-coagulating solution surface distance of 6 times the distance between the nozzles of the spinneret, washed with water, and subsequently dried to provide the objective ultrafine aramide fibers having a single filament fineness of 0.1-1 denier, a strength of >=18g/de, an elongation of >=2.5% an initial modulus of >=450g/d, and a peak temperature A value of <=60 deg.C in a moisture-absorbed fiber linear expansion curve formed by plotting the differences between the 0-300 deg.C CTMA curve of a fiber specimen immersed in water and the 0-300 deg.C CTMA curve of a fiber specimen absolutely dried with phosphorus pentaoxide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrafine aramid fiber which is excellent in abrasion resistance and has a soft texture and a method for producing the same.

[0002]

2. Description of the Related Art Para-oriented aramid fibers have excellent properties such as high strength, high modulus and high heat resistance. These fibers are applied to industrial applications and general clothing applications, and are used as high-performance materials for lightweight reinforcing materials, ropes, fishing nets, protective clothing, and the like.

However, the performance required for fibers is not only strength and modulus but also various application characteristics. In particular, high-strength fibers are often hard and difficult to handle, and often become fibrillated and damaged when worn. Particularly in the fields of ropes, braids, and clothing, there has been a demand for ultrafine, high-strength aramid fibers that are flexible and have good wear resistance.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide an ultrafine aramid fiber having improved flexibility and abrasion resistance while maintaining the high strength, which is an original feature of para-aramid fiber, and its efficient use. It is to provide a manufacturing method.

[0005]

When the microstructure of any fiber is examined, there are many aggregates of highly oriented polymer chains called microfibrils. Of course, not all are microfibrils, and there are some places where the polymer chains are folded or the sequence is incomplete. In order to increase the strength of the fiber, the polymer chains must be arranged linearly, which naturally increases the amount of microfibrils. As can be seen from the morphology, microfibrils are strong in the direction of the fiber axis, but weak in the direction perpendicular to the fiber axis and tend to fall apart. In particular, when there are voids between the microfibrils or the intermolecular force between the microfibrils is weak, the microfibrils are more likely to be separated. In fact, when the fibers are rubbed with each other or the fibers are rubbed with a metal, one filament is divided into finer fibrils. When this tendency is strong, it is expressed as “having a bundle-like microfibril structure” or “strong fibril structure”. In general, the liquid crystalline aramid fiber has a non-uniform structure in the fiber cross section, and the outer layer and the inner layer have different fine structures, and are likely to have a bundled microfibril structure.

The inventors of the present invention have made extensive studies as to a technique for uniformizing a fine structure in which a bundle-like microfibril structure is difficult to be obtained when spinning from a liquid crystal para-aligned aramid polymer, and as a result, by adopting a specific spinning condition, The coagulation state is uniform and the independence of bundled microfibrils is reduced,
The present invention has been accomplished in which ultrafine aramid fibers that are flexible and have excellent abrasion resistance can be obtained.

That is, according to the present invention, 1 is an ultrafine aramid fiber characterized by having a single yarn fineness of 0.1 denier or more and less than 1 denier and mechanical properties within the following range: Strength: 18 g / de or more Degree: 2.5% or more Initial modulus: 450 g / de or more The peak temperature A value of the hygroscopic yarn linear expansion curve defined in the text is 60 ° C. or less 2 The aromatic polyamide fiber has 90 mol% or more of the repeating units of the polymer. The aramid fiber according to claim 1, comprising the following repeating unit (1).

[0008]

[Chemical 2]

3 A liquid crystalline para-aligned aramid polymer solution is once discharged into an inert gas and brought into contact with a coagulating liquid,
Then, when a predetermined aramid fiber is produced by washing with water and drying, the following relations (1) and (2) are simultaneously satisfied. (1) The distance between the die surface and the coagulating liquid surface is not more than 6 times the die nozzle interval. (2) The solvent concentration in the coagulating liquid with which the spun filaments come into contact is 32 to 45% by weight.

The present invention will be described in detail below. The aramid fiber targeted by the present invention is preferably a para-oriented aramid fiber composed of the following repeating unit (1) and has the following physical properties.

[0011]

[Chemical 3]

The single yarn fineness is 0.1 denier or more and less than 1 denier. The spinning amount of less than 0.1 denier has a small discharge amount in the spinneret, the spinnability is unstable, and it is extremely difficult to obtain a fiber having good uniformity in the length direction. When it is 1 denier or more, the difference in the fine structure of the fiber cross section becomes large. That is, the surface layer is composed of microfibrils having an extremely high degree of orientation, and the inner layer is composed of a bundle of bundled microfibrils having many voids between the microfibrils. When such a two-layer structure is developed, fibrils are easily formed against friction and wear resistance is reduced.

Regarding strength, 18 g / de or more is required. If it is less than 18 g / de, the value as a high-strength fiber is remarkably reduced, and even if the flexibility and abrasion resistance are improved, it cannot be widely used.

The elongation is 2.5% or more. Liquid crystalline para-aligned aramid fibers generally have low elongation, but at least 2.
If it is not more than 5%, the strength at the time of twisting will be reduced, and the durability will be deteriorated during repeated use.

The initial modulus is 450 g / de or more. When this value is less than 450 g / de, the features of the high modulus fiber are lost.

The peak temperature A value of the hygroscopic yarn linear expansion curve defined below is 60 ° C. or less. The sample length of the fiber is 2cm, and the measurement is 0.003g to obtain the linear expansion curve of the hygroscopic yarn.
It is performed under a load of / de. As a preparation, a sample that has been completely immersed in water for 5 hours or more and two types of fibers that have been completely dried with phosphorus pentoxide are prepared. Definition of the peak temperature A value of the hygroscopic yarn linear expansion curve; The curve plotted against this is defined as the hygroscopic linear expansion curve. The hygroscopic yarn linear expansion curve increases once when the temperature rises from room temperature (20 ° C.), reaches a peak value, and decreases when the temperature further rises. Alternatively, it may remain flat after reaching the peak value. The temperature that takes this peak value is defined as the peak temperature A value.

FIGS. 1 and 2 show an example of obtaining this A value, and the sample used is one obtained in Experiment No. 1 of Example 1 described later. FIG. 1 shows TMA curves of the fiber and the absolutely dried fiber which were immersed in water and completely absorbed water. The difference between these two curves was found to have a peak at a temperature of 58 ° C. in the hygroscopic yarn linear expansion curve of FIG. Therefore, the A value is 58 ° C.

From the above findings, it has been found that liquid crystalline para-oriented aramid fibers having a single yarn fineness of less than 1 denier have a small difference in fine structure in the cross-sectional direction and have good wear resistance. Since the discharge amount of the ultrafine denier is remarkably small technically, the spinnability is deteriorated, the single yarn is broken, or the single yarns are adhered to each other, so that stable continuous yarn production is difficult. Further, violent mass transfer occurs in the course of the coagulation bath, so that the yarn is easily broken especially when the single yarn is thin. In order to overcome these difficulties, the following conditions are necessary.

That is, first of all, the distance between the die and the surface of the coagulating liquid should be 6 times or less than the nozzle interval of the die. When the coagulation bath is in a state of flow like a wetting wall, the distance between the point where the yarn comes out of the die and the point where the yarn first comes into contact with the coagulating liquid is 6 times or less than the nozzle interval of the die. Should.
When spinning ultrafine fibers, the nozzle spacing of the spinneret must be as small as possible and the yarn groups must be densely packed. This is to reduce the fluid resistance when the unwound yarn comes into contact with the coagulation bath. This is particularly important for ultrafine fibers because the single yarn is weak. However, if the nozzle interval of the spinneret is made smaller, the yarns that come out will come into close contact with each other before the yarns come into contact with the coagulating liquid, and cause yarn breakage. Therefore, the distance between the die and the surface of the coagulating liquid must be optimized according to the die interval. The interval between the die and the surface of the coagulating liquid should be 6 times or less than the interval between the die nozzles. Further, the interval between spinneret nozzles for spinning the ultrafine fibers of the present invention is preferably 3 mm or less.

The concentration of solvent in the coagulation bath with which the spun filaments come into contact must be 32-45% by weight. Solvents include sulfuric acid, chlorosulfuric acid and fluorosulfuric acid, but sulfuric acid is the most common. Generally, the lower the solvent concentration of the coagulation bath is, the more advantageous it is for strong expression. However, in the ultrafine fibers of the present invention, if it is less than 32% by weight, the abrasion resistance is deteriorated because the skin core structure becomes large. On the other hand, if the solvent concentration exceeds 45%, the coagulation becomes insufficient and the spinning tone deteriorates remarkably.

[0021]

As described above, according to the present invention, it is possible to stably produce a para-oriented aromatic polyamide fiber having a uniform fiber structure and a small single yarn fineness. The fibers have improved abrasion resistance in air and seawater, and their applications are greatly expanded in the fields of ropes, nets and cloths for general clothing.

The present invention will be described below with reference to examples.
The spinning dope used in the spinning test was prepared by the following polymerization method.

Preparation of spinning dope Paraphenylenediamine was dissolved in a solvent of N-methyl-2-pyrrolidone containing a small amount of calcium chloride, and then equimolar amount of terephthalic acid dichloride was added to carry out a polymerization reaction to produce polyparaphenylene terephthalamide (hereinafter PPTA
Called). The PPTA polymer was dissolved in the above-mentioned polymerization solvent, and water was added to this to make a slurry, and the hydrochloric acid produced as a by-product was neutralized with sodium hydroxide. The PPTA was completely washed with water, dried and then redissolved in 99.6% sulfuric acid to prepare a spinning dope having a polymer concentration of 15% by weight. The P
The relative viscosity of PTA was 0.9% when dissolved in 98% sulfuric acid.
It was 5.3 when measured at 5 g / 100 ml and a temperature of 30 ° C. The spinning dope was filtered through a metal fine wire filter having an opening of 20 microns and sent to a spinning head by a gear pump.

[0024]

Example 1 Using the spinning dope prepared by the above-mentioned polymerization method, yarns having different single yarn fineness were produced. The nozzle diameter of the spinneret was 0.04 mm, the nozzle interval was 1.5 mm, and the spinning speed was 100 m / min. As the coagulating liquid, a 35 wt% sulfuric acid aqueous solution was used. The space between the spinneret and the coagulation bath surface is 4
It was mm. Therefore, the ratio of the distance between the die surface and the coagulation bath surface to the die nozzle interval (hereinafter referred to as the air gap ratio) was 2.7.

Experiment NO1 is an example of the present invention with a single yarn fineness of 0.75 de, and Experiments NO2 and NO3 are comparative examples with a single yarn fineness of 1.5 de and 2.5 de, respectively. Table 1 shows various properties of these fibers. The abrasion resistance was evaluated by the following method.

The F / F wear is a measurement of the number of times until the wear is broken by repeatedly rubbing the fibers together, and 30 fibers obtained in each experiment are combined to make 3000 de, and then 50
It was carried out under a tension of 0.6 g / de after twisting at a rate of 1 turn / m. The yarn of 3000 de is twisted once and the crossing points are repeatedly rubbed against each other. For edge wear, reciprocal rubbing was repeated at the edge of Tungaloy metal, and the number of rubbing until cutting was measured.

As can be seen from Table 1, when the single yarn fineness exceeds 1 de, the abrasion resistance is considerably lowered. Conventional wisdom has been that the larger the single yarn fineness is, the better the abrasion resistance is. However, surprisingly, the smaller the single yarn fineness is, on the contrary, the better abrasion resistance is exhibited. This is presumed to be due to the difference in the microstructure generated during the molding of the fiber, and in fact the structural parameters such as the peak temperature A value of the hygroscopic yarn linear expansion curve also have different values. The fiber of Example Experiment No. 1 of the present invention is soft and has a good texture, and is also excellent in abrasion resistance, so that it is easy to use for delicate ropes and clothes.

[0028]

[Table 1]

[0029]

Example 2 In this example, the spinnability and fiber physical properties were examined by changing the air gap ratio. The nozzle diameter of the spinneret is 0.04 mm, the nozzle spacing is 1.5 mm, and the spinning speed is 10.
It was 0 m / min. The coagulation bath used was a 35% by weight aqueous sulfuric acid solution. The experimental results are shown in Table 2.

Examples of the present invention In the experiments NO4, NO5 and NO6, the mechanical properties and abrasion resistance of the fiber were good, and the spinning tone was also good. Comparative example experiment N in which the air gap ratio exceeds 6
In O7, the single yarns were in close contact with each other, and the spinning was unsatisfactory. Further, in the example experiment NO4 of the present invention, the control of the coagulating liquid was somewhat unstable because the air gap was as narrow as 2 mm. Preferably 3
The device design becomes easier if it is more than mm.

[0031]

[Table 2]

[0032]

Example 3 In this example, the fiber concentration and spinning tone were examined by changing the solvent concentration in the coagulation bath. The nozzle diameter of the spinneret is 0.05 mm, the nozzle spacing is 2 mm, the air gap is 5 mm, the spinning speed is 100 m / min, and the single yarn fineness is 0.75 de.
And The coagulation bath is a sulfuric acid water bath and the concentration is 0 to 50% by weight.
Changed. The experimental results are shown in Table 3.

Experiment No. 8 is water containing substantially no solvent in the coagulation bath, but the coagulation is too rapid, and the A value is too large, resulting in poor abrasion resistance and a large number of spun yarns. Experiment NO
In No. 9, when the coagulation bath concentration was 30%, the yarn physical properties and abrasion resistance were considerably improved, but the spinning breakage did not reach the satisfactory range. Experiments NO10 and NO11 in the examples of the present invention have coagulation bath concentrations of 35 and 40% by weight, respectively, but in both cases, the mechanical properties and abrasion resistance of the obtained fibers are good, and the spinning breakage rate is extremely low. When the concentration of the coagulation bath is further increased to 50% by weight, the coagulation is insufficient and the yarn breakage remarkably increases.

[0034]

[Table 3]

[0035]

[Embodiment 4] In this embodiment, a study was conducted to make the single yarn fineness smaller than 0.75 de. Although it is preferable that the nozzle diameter be decreased along with the single yarn fineness, it was practically difficult to make it smaller than 0.02 mmφ. The other spinning conditions were the same as in Example 1.

The performance of the spun yarn is shown in Table 4. As can be seen from the table, examples of the present invention experiment NO13 and NO
No. 14 had a single yarn fineness of 0.5 de and 0.33 de, respectively, but the performance of the yarn was good in both mechanical properties and abrasion resistance, and there was no problem in spinning tone. Example Experiment No. 15 of the present invention has a single-filament fineness of 0.17 de and tends to increase the number of spun yarns, but can be spun and has good yarn performance. However, reducing the single yarn fineness to 0.08 de was
As shown in column 16, the spinning was extremely difficult and the yarn that could be evaluated was not able to be spun. In addition, since the yarn of Experiment NO15 is 50 de, in the case of the abrasion resistance test, 60 yarns were combined and a yarn of 3000 de was prepared and then measured.

[0037]

[Table 4]

[Brief description of drawings]

[Figure 1] TMA curve of water-immersed yarn and absolutely dried yarn

[Figure 2] Hygroscopic yarn linear expansion curve

Claims (3)

[Claims] 1. An ultrafine aramid fiber having a single yarn fineness of 0.1 denier or more and less than 1 denier and a mechanical property within the following range. Strength: 18 g / de or more Elongation: 2.5% or more Initial modulus: 450 g / d or more Peak temperature A value of the hygroscopic linear expansion curve defined in the text is 60 ° C or less 2. The ultrafine aramid fiber according to claim 1, wherein 90 mol% or more of the repeating unit of aramid is composed of the following repeating unit (1). [Chemical 1] 3. A liquid crystal para-aligned aramid polymer solution is once discharged into an inert gas, brought into contact with a coagulation liquid, and then washed with water and dried to produce a predetermined aramid fiber. A method for producing an ultrafine aramid fiber, which simultaneously satisfies the relationship (2). (1) The distance between the die surface and the coagulating liquid surface is not more than 6 times the die nozzle interval (2) The solvent concentration in the coagulating liquid with which the spun filaments come into contact is 32 to 45% by weight.