KR920008999B1 - Process for the production of aromatic polyamide short fibers - Google Patents

Abstract

The method for producing aromatic polyamide staple fiber whose draw ratio is 2.0-300 comprises: feeding liq. crystal prepolymers into axially circulating apparatus; dispersion extruding them through nozzles formed along the circumference of circulating apparatus by centrifugal force into flowing polymerization accelerating precipitator flowed vertically along the wall of outer vessel whose radius is 1.1-5.0 times that of circulating apparatus; thus letting them contact, mixed and flow together; solidifying to form staple fiber; and finally retrieving solidified staple fiber and polymerization accelerating solvents.

Description

Method for producing aromatic polyamide short fibers

1 is a schematic diagram of a short fiber manufacturing process according to the present invention.

* Explanation of symbols for the main parts of the drawings

1: Inlet 2: Nozzle

3: injector 4: rotating belt

5: outer cylinder 6: polymerization accelerator

7: inlet port 8: receiving container

9: transfer filter 10, 10 ': recovery part

11: outlet

The present invention relates to a method for preparing aromatic polyamide short fibers, and more particularly, to continuously disperse aromatic polyamide short fibers having excellent physical properties by dispersing and dispersing them in a polymerization accelerator precipitant while rotating the liquid crystal prepolymer. It relates to a method that can be produced.

In general, pulp-like short fibers made of wholly aromatic polyamide are not only light, but also have high strength, high elasticity, heat resistance, abrasion resistance, and electrical insulation, and thus are not only special industries such as aircraft, automobile, or composite materials and building materials. It is also usefully used for leisure sports goods. Due to this availability, various methods for producing short fibers on the wholly aromatic polyamide pulp have been studied.

For example, US Pat. No. 3,869,429 and US Pat. No. 3,869,430, when preparing aromatic polyamide short fibers, polymerize an inorganic salt, aromatic diamine and aromatic dieside chloride in an amide solvent, and then wash and dry the polymer. The dope is dissolved in 98% or more sulfuric acid solvent to form a dope, and then the dope is spun through water or methanol to obtain a wholly aromatic polyamide fiber. In general, short fibers were prepared again by cutting or pulverizing such fibers.

However, this manufacturing method requires a multi-step process in which the polymer is separated, washed with water, dried, dissolved in a sulfuric acid solvent, spun, cut and pulverized, thus increasing manufacturing costs, and the manufacturing apparatus in the process is corroded due to the use of the sulfuric acid solvent. Various problems appeared.

In addition, U.S. Patent No. 4,511,623 discloses the use of tertiary amines such as pyridine during the polymerization of aromatic polyamides to sharply increase the reaction rate during the polymerization, and at the instant of gelation, mechanical shearing force, resulting in high orientation and high Although a method for preparing high strength polyamide pulp-like short fibers having an intrinsic viscosity of 5 to 7 while having a degree of polymerization has been introduced, in the case of preparing pulp-like short fibers using this method, it is also possible to produce Since a large amount of tertiary amine is added at the same time, the polymerization is terminated within 10 seconds due to the rapid increase in viscosity when the polymerization is finally performed by terephthaloyl chloride. It is difficult to continuously produce because it requires ripening time.

Accordingly, the present invention, in order to solve such a conventional problem, by discharging and dispersing the liquid crystal prepolymer in the flow of the polymerization accelerator precipitate while rotating, and by contact solidification to recover the formed short fibers continuously, the physical properties in a simpler process It is an object of the present invention to provide a method for continuously producing excellent aromatic polyamide short fibers.

The present invention will be described in detail as follows.

The present invention provides a method for producing an aromatic polyamide short fiber, comprising: supplying a liquid crystal prepolymer into a rotating means for axial rotation, discharging and dispersing the liquid crystal prepolymer into a flowing polymerization precipitating agent by rotating the rotating means; , Wherein the dispersed liquid crystal prepolymer is solidified while flowing together with the polymerization accelerator to form short fibers, and recovering the solidified short fibers and the polymerization promoter. It is a manufacturing method.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

1 is a view schematically showing a process for producing aromatic polyamide short fibers according to the present invention. First, the liquid crystal prepolymer according to the present invention is applied to the rotating means, that is, the circumferential surface through the inlet 1. A plurality of nozzles 2 are formed and supplied to the inside of the cylindrical injector 3 capable of axial rotation.

Herein, the liquid crystal prepolymer to be introduced through the inlet 1 is manufactured through the following process. That is, what is necessary is just to melt | dissolve a metal salt in an amide solvent, and to make an aromatic mole of aromatic diamine and aromatic dieside chloride, and to react at low temperature.

As the amide solvent in the present invention, for example, N-methyl-2-pyrrolidine (NMP), N, N-dimethylacetamide (DMAC), hexamethylphosphoramide (HMPA), N, N-dimethyl At least one selected from formamide (DMF) and dimethyl sulfoxide (DMSO) may be used. Meanwhile, as the metal salt used to increase the solubility of the polymer, for example, calcium chloride (CaCl ₂ ), lithium chloride (LiCl), sodium chloride (NaCl) or potassium chloride (KCl) may be used, and the amount of the metal salt may be used in the amide system. It is good to use it at 0.5 to 15 weight% with respect to a solvent.

For example, after dissolving the metal salt in the above amide solvent alone or a mixed solvent thereof, and then adding an equimolar amount of aromatic diamine and aromatic dieside chloride to the solution, at a low temperature of 30 ℃ or less, during the polymerization An optical effervescent liquid crystal prepolymer having a viscosity of 5 to 100,000 poise at the point after the steeroperation and before gelation is prepared.

Cylindrical injector (3) into which the prepolymer prepared by the above method is introduced is axially rotated by the rotary belt (4) installed in the central portion of the inlet (1) as shown in the figure.

The liquid crystal prepolymer introduced into the cylindrical injector 3 is externally, ie, the inner wall surface of the outer cylinder 5 described below through the nozzle 2 formed in the circumferential portion thereof by the axial rotation as described above. The discharge is dispersed.

At this time, the polymerization accelerator precipitant 6 is flowed (flows) directly on the inner wall surface of the cylindrical outer cylinder 5 which accommodates the cylindrical injector 3, so that the discharge-dispersed liquid crystal prepolymer is promoted. It comes into contact with the precipitant 6.

Here, the polymerization accelerator precipitater significantly improves the degree of polymerization (molecular weight) of the liquid crystal prepolymer to complete the polymerization, and at the same time, an amide bond and a hydrogen bond are formed in the polymer, thereby producing a wholly aromatic polyamide short fiber having excellent physical properties. . At this time, the polymerization accelerator used in the embodiment of the present invention may include tertiary amines, for example, pyridine, triethylamine, t-butylamine, picoline, quinoline, pyrimidine, pyrazine, quinoxaline Although, one or more of the acpyridine may be selected and used, pyridine may be said to be effective in obtaining high intrinsic viscosity and orientation as the most suitable polymerization accelerator.

In addition, the supply of the polymerization accelerator to the inside of the outer cylinder 5 should be continuously supplied through the inlet port 7, but should be supplied to overflow from the receiving barrel 8 attached to the inner wall of the outer cylinder 5.

In this way, when the polymerization accelerator precipitate 6 continuously overflows from the receiving barrel 8, they flow down the wall of the outer cylinder 5 and come into contact with the liquid crystal prepolymer dispersed in the injector 3. .

It should be noted that the inlet 7 and the receiving barrel 8 must be installed above the horizontal line of the injector 3 when the liquid crystal prepolymer is dispersed from the cylindrical injector 3 toward the inner wall surface of the outer cylinder 5. The molecular weight is increased by solidification by the polymerization accelerator 6 flowing down directly along the wall surface of the outer cylinder 5. At this time, the stretching ratio is changed according to the rotational speed of the injector (3) and the radius of the outer cylinder (5).

As described above, when the liquid crystal prepolymer dispersed from the injector 3 comes into contact with the flowing polymerization accelerator, short fibers as cut and dispersed are obtained.

In the process of forming short fibers as described above, it is sometimes easy to bundle bundles of short fibers together. When such a bundle is formed, if there is an obstacle in the discharge portion of the short fibers, bundles of short fibers accumulate on this obstacle and continuous production is not achieved. Will not. However, in the process according to the present invention, even if short fibers are bundled, there is no obstacle in the discharge portion, so that continuous production is not impeded, and thus high fibers can be continuously produced while providing a high stretch.

On the other hand, the stretching according to the process of the present invention is the initial length (l1) of the liquid crystal prepolymer discharged from the nozzle for a predetermined time (Δt) is the discharge speed from the nozzle to the normal direction is Vp, l1 = Vp × Δt Can be displayed.

The liquid crystal prepolymer discharged for a predetermined time (Δt) is solidified after contact with the polymerization accelerator precipitant flowing downward while forming a radius R as shown in FIG. 2, where the final length of the discharged liquid crystal prepolymer (L2) = RωΔ It can be expressed as t. Where ω is the rotational angular velocity of the nozzle. Under the above conditions, the draw ratio D becomes D = l 2 / l 1 = Rω / Vp.

That is, the draw ratio D can be adjusted by the radius R of the outer cylinder, the rotational angular velocity ω of the nozzle, and the discharge rate Vp of the liquid crystal prepolymer.

According to this formula, it is preferable that the draw ratio according to the present invention be 2.0 to 300. If the draw ratio is less than 2.0, the drawing effect cannot be expected, and the degree of crystallinity is also lowered. Not only do not achieve the powder form but also the physical properties are reduced.

In addition, as shown in FIG. 2 of the accompanying drawings, R (radius of the outer cylinder) / r (radius of the injector) is preferably set to 1.1 to 5.0. If the ratio is less than 1.1, the discharge of the liquid crystal prepolymer is In case of exceeding 5.0, the liquid crystal prepolymer discharged from the nozzle is solidified before contacting the polymerization accelerator, and the effect of using the polymerization promoter is lost.

On the other hand, if the short fiber according to the present invention through the above process is formed on the wall surface of the outer cylinder (5), the short fiber falls down along the wall surface of the outer cylinder (5) to the bottom of the outer cylinder (5) It is recovered to the short fiber recovery section 10 by the transfer filter 9 installed, and the polymerization accelerator precipitant used to solidify the liquid crystal prepolymer is recovered to the solvent recovery section 10 'and the solvent outflow pipe 11 ) Is used again as a solvent in the next process.

When the short fibers recovered through the above process are washed and dried in a conventional manner, the aromatic polyamide short fibers of the present invention are obtained.

On the other hand, the intrinsic viscosity of short fibers as final polymers is obtained from the following relationship.

Intrinsic Viscosity (IV) = ln (η _rel ) / C

Where C is the concentration of the polymerization solution and? Rel is the flow time ratio of the solution and the solvent in a capillary viscometer maintained at 30 ° C as relative viscosity.

The diameter of the short fibers as the final polymer is averaged over 50 samples using an electron scanning microscope, and the degree of crystallinity (Xc) is calculated from the scattering pattern of the scattering group.

The method according to the present invention is applicable to all liquid crystalline polymers of aromatic polyamides having a viscosity of 5 to 100,000 poise and allows the production to be controlled by all scales, that is, the number of nozzles, the size of the nozzles, the size of the inlet, etc. do.

In addition, the method according to the invention is easy to feed the liquid crystal prepolymer to the nozzle. That is, the centrifugal force generated by the rotation of the injector facilitates the discharge from the nozzle, and the draw ratio can be easily adjusted by adjusting the ratio of Vp and Rω, and the stretched and solidified in the process of the present invention is directly below the polymerization accelerator. Because it falls, the continuous process management is very easy, and because the separation of the short fibers and the solvent using a transport filter has an effect that can improve the recovery rate of the solvent.

Hereinafter, the present invention will be described in detail with reference to Examples.

[Examples 1 to 8]

The reaction tank was thoroughly purged with nitrogen to completely remove water, and 5000 ml of N-methyl-2-pyrrolidone was added thereto as an amide solvent, and the temperature was raised to 80 ° C., followed by calcium chloride (CaCl ₂ ) as a metal halide salt. 10.0% is added and stirred for 30 minutes to dissolve. 207.6 g of p-phenylenediamine (PPD) was added to the amide-based polymerization solvent in which such an inorganic salt was dissolved. The mixture was dissolved while stirring for 10 minutes, and 391.6 g of terephthaloyl chloride (TPC) was added at a low temperature of 30 ° C. or lower. Stir. After the addition, the liquid crystal prepolymer obtained by stopping the stirring at about 8 minutes was supplied from the polymerization vessel to the liquid crystal prepolymer inlet by using a gear pump.

At this time, the nozzle diameter was 0.3mm, the discharge speed Vp at the nozzle was 0.5m / sec, the radius r of the injector was 100mm, the distance R from the rotating shaft to the polymerization accelerator precipitate solvent was 200 mm and the inside of the outer cylinder was nitrogen. Infused it. Among these conditions, the physical properties of the short fibers obtained by changing the rotational angular velocity ω of the cylinder are shown in Table 1.

As a result, the crystallinity degree of the obtained short fiber was 45% or more.

TABLE 1

[Comparative Examples 1 to 5]

The physical properties of the short fibers obtained by experimenting the liquid crystal prepolymer prepared in the same manner as in Example 1 under low or high rotational angular velocity ω are shown in Table 2 below. Other experimental conditions are the same as in Example 1. As a result of the experiment, when the draw ratio is 2.0 or less, the crystallinity degree Xc, which is an important property of short fibers, is lowered. In addition, when the draw ratio is 300 or more, the fiber is not in the form of a powder, and the physical properties are also reduced.

TABLE 2

[Examples 9 to 15]

After the polymerization in the same manner as in Example 1, when the liquid crystal prepolymer is introduced into the nozzle, the rotational angular velocity ω is constant at 2000 rpm, and then the physical properties of the short fibers obtained by changing the distance R from the rotation axis to the polymerization accelerator precipitate are shown. 3 is shown.

TABLE 3

[Comparative Examples 6 to 7]

Experiments were carried out in the same manner as in Example 9, but the results of experiments with R increased are shown in Table 4. When the ratio of R / r was 6.0 or more, the liquid crystal prepolymer discharged from the nozzle was solidified before contacting the polymerization accelerator. Thus, the effect of using the polymerization accelerator was lowered.

TABLE 4

Claims (5)

In preparing the aromatic polyamide short fibers, supplying the liquid crystal prepolymer into the rotating means for axial rotation, discharging and dispersing the liquid crystal prepolymer into the flowing polymerization promoting precipitate in the rotating means; The liquid crystal prepolymer is solidified while flowing together with the polymerization accelerator precipitated to form short fibers, and the method for producing an aromatic polyamide short fibers characterized in that the step of recovering the solidified short fibers and the polymerization promoter. The method of claim 1, wherein the liquid crystal prepolymer is discharge-dispersed by centrifugal force through a nozzle formed in the circumference of the rotating means. The method according to claim 1, wherein the polymerization accelerator precipitant is made to be in contact with the liquid crystal prepolymer while flowing downward along the wall surface of the outer cylinder. The method of claim 3, wherein the outer cylinder has a radius of 1.1 to 5.0 with respect to the radius of the rotating means. The method for producing an aromatic polyamide short fiber according to claim 1, wherein the draw ratio of the short fiber is to be in the range of 2.0 to 300.

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