WO1995004174A1

WO1995004174A1 - A process for preparing wholly aromatic polyamide filaments

Info

Publication number: WO1995004174A1
Application number: PCT/KR1994/000104
Authority: WO
Inventors: Jong Tae Park; Won Jun Choe; Myung Hwan Lee
Original assignee: Kolon Industries, Inc.
Priority date: 1993-08-03
Filing date: 1994-08-02
Publication date: 1995-02-09
Also published as: KR950006037A; KR960000780B1

Abstract

A process for preparing wholly aromatic polyamide filament comprising the steps: (a) providing a 13 ∩ 22 wt. % of anisotropic spinning solution by dissolving an aromatic polyamide polymer having an inherent viscosity of more than 4.5 in a sulfuric acid solvent; (b) preparing filaments by extrusion of said spinning solution through a spinneret into a coagulant in which water or a sulfuric acid solvent is contained less than 20 wt. %; (c) washing, neutralization and drying with a tension between each equipment that satisfies the following relationship: C + A » (0.4 ∩ 1)B « (3 ∩ 7)D (wherein A is the tension between feeding rollers in the coagulating bath, B is the tension between the washing equipment and the neutralization equipment, C is the tension between the neutralization and the drying equipments and D is the tension between the drying equipment and a winder). The wholly aromatic polyamide filaments can have an inherent viscosity of more than 4.5, a tenacity of more than 21 g/d, an initial modulus of more than 550 g/d, a remaining salt content of less than 1.2 % and an NaOH and H2SO4 content of less than 0.05 %, respectively.

Description

A PROCESS FOR PREPARING WHOLLY AROMATIC POLYA I DE F I LAMENTS

TECHNICAL FIELD:

The present invention relates to a process for preparing wholly aromatic polyamide filaments, especially a process for preparing aromatic polyamide filaments having excellent physical properties and both a high tenacity and modulus of elasticity by passing through dry-jet, wet spinning facilities, a washing, neutralization and drying process.

BACKGROUND ART:

Attempts have been made to produce wholly aromatic polyamide filaments.

U.S. Patent No. 4,298,565, U.S. Patent No. 4,070,431, U.S. Patent No. 4,048,279 and U.S. Patent No. 4,455,935 disclose processes in which a spinning solution is obtained by polymerizing poIy(p-p enyIene terephtalamide) according to conventional methods and then heating while it is uniformly mixed with concentrated sulfuric acid. In such methods the polymer and solvent content are controlled within a constant range to reveal a liquid crystal property, and then the spinning soIution(an optical anisotropic spinning solution) is passed through spinning facilities comprising a spinneret, a coagulating bath and an air gap, wet winding equipment provided with a general washing function, and neutralization and drying equipment, to prepare the wholly aromatic polyamide filaments.

However, there have been some problems with these techniques. For example, the density of the fiber structure is affected by the composition and temperature of the coagulating bath, and the drawing ratio of each part of the fibers applied to the fibers in said coagulating bath. Also, the tenacity properties of the fibers are lower than the theoretical tenacity, due to the formation of a skin- core structure. Furthermore, If sulfuric acid remains after the washing or neutralization process of aromatic polyamide synthetic fibers, the light yellow color of the fibers turns into a dark yellow and also mechanical and chemical properties of the fibers are lowered.

Moreover, if too much alkali is used in the neutralization process and salts produced as by-products in that process remain because of insufficient washing, it causes separation between rubber and the fibers when they are used for rubber reinforcing material due to the lowering of adhesion.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide wholly aromatic polyamide filaments wherein the afore-said problems of prior art are avoided. The object of this invention is also to provide wholly aromatic polyamide filaments having a high degree of tenacity and modulus.

According to the invention, the process for preparing wholly aromatic polyamide filaments comprises the following steps: 1) providing a 13-22 wt% anisotropic spinning solution by dissolving an aromatic polyamide polymer having an inherent viscosity of more than 4.5 in a sulfuric acid solvent;

2) preparing filaments by extrusion of said spinning solution through a spinneret into a coagulant in which water or a sulfuric acid solvent is contained in less than 20 wt%;

3) washing, neutralizing and drying with a tension between each equipment that satisfies the following relationship:

C + A ≥ (0.4~1)B ≤ (3~7)D (wherein A is the tension between feeding rollers in the coagul- ating bath, B is the tension between the washing equipment and the neutralization equipment, C is the tension between the neutralization drying equipment and the winder.)

Another object of the present invention is to provide wholly aromatic polyamide filaments in which the inherent viscosity is more than 4.5, the tenacity is more than 21g/d, the initial modulus is more than 550g/d, the content of salt remaining is less than 1.2% and the content of NaOH or H₂S0₄ is less than 0.05%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a spinning facilities for aromatic poly- amide filaments and the process for preparation thereof.

FIG.2 is a graph showing the variation of fiber tenacity according to the concentration and temperature of the coagulant. FIG.3 is a graph showing an effect according to variations in reten¬ tion time in each equipment during the washing and the neutralization processes.

BEST MODE FOR CARRYING OUT THE INVENTIONS

I ) PREPARATION OF THE SPINNING SOLUTION

According to the present invention, aromatic polyamide polymer has repeating units represented by the following formulas(l),(2) and/ or (3), wherein the polymer contains more than 90 mole% of units(1) and (2) in equivalent moles on the basis of mole% of polymer. -NH-R,—NH- ( 1 )

-CO-R₂— CO- ( 2 )

- CO-R,—NH- ( 3 )

(wherein R, , R₂ , R₃ are respectively selected from the aromatic groups of valence 2) The aforementioned aromatic polyamide polymer can be prepared from an aromatic diamine and an aromatic diacid chloride in equivalent moles by conventional methods, such as low temperature solution polymerization, surface polymerization, dissolving polymerization or solid phase polymerization.

An optical anisotropic spinning solution is prepared by dissolving the aromatic polyamide polymer having an inherent viscosity of 4.5 in a sulfuric acid solvent with a concentration of 13~22wt%. When the inherent viscosity of aromatic polyamide polymer is less than 4.5, it is hard to obtain a high tenacity and modulus due to the low degree of polymerization.

The viscosity of the spinning solution is affected by the inherent viscosity and the concentration of the polymer, and the type or concentration of the solvent. It depends greatly on the relative the polymer and solvent, and the concentration of solvent.

The viscosity increases sharply as the content of the polymer relative to sulfuric acid solution is increased, and then as it increases beyond the critical concentration the viscosity sharply decreases. When the concentration reaches its final saturation point, the viscosity increases according to an exponential function and sol idifies.

In view of the variation of viscosity, an anisotropic spinning solution having a liquid crystal property is achieved in the range of 13~22wt% of polymer content, to prepare fibers having excellent physical properties, such as high tenacity and modulus.

When the content of the polymer is less than 13 wt%, the liquid crystal property is poor and tenacity of the fibers falls off. When it exceeds 22 wt%, the spinning property becomes poor due to the high viscosity of the spinning solution.

Spinning solutions of liquid crystal form have a pearly luster due to diffused reflection when they are exposed under a shearing force, and bonding chains of the molecules can be drawn in parallel or in the coaxial direction of each aromatic ring. Generally, if the inherent viscosity of the polymer is more than 1, the liquid crystal property can appear, but in order to obtain fibers having high strength and elasticity which can be used commercially, polymers having an inherent viscosity of more than 4.5 are preferable for preparation of the spinning solution.

The properties of fibers are lowered when the concentration of the polymer is below the critical concentration or the solvent is not highly concentrated. The solvent for preparation of the anisotropic spinning solution is selected from the group consisting of concentrated sulfuric acid, chlorosulfuric acid, fluorosulfuric acid or mixtures thereof having a concentration of 96-100.1%.

When the sulfuric acid concentration is in the range of 96-100.1 %, excellent solubility is achieved and the optical anisotropic spinning solution is prepared in a viscous state which makes it easy to control the process and reveal the required liquid crystal property. When the concentration of sulfuric acid is less than 96%, the solubility of the polymer is lowered and it is difficult to reveal the liquid crystal property of anisotropic solution.

Consequently, it is difficult to produce a spinning solution having a constant viscosity so that it is hard to control the spinning process and also mechanical properties of the final fibers are lowered. On the contrary, when the solubility of the sulfuric acid exceeds 100.1%, it is not preferable because there is too much SO- in fuming sulfuric acid containing surplus S0₃ , and also it is not suitable for the spinning solution since the polymer is partially dissolved. Even though fibers may be obtained by spinning such solutions, the internal structure of the resulting fibers is not compact and they are IusterIess.

Furthermore, mechanical properties of the fibers fall off due to the low diffusion rate of sulfuric acid which is- diffused in the precipitation solution.

II) SPINNING AND COAGULANT With regard to FIG. 1, the optical anisotropic spinning solution (1) of aromatic polyamide, which is prepared according to the afore¬ said method, is spun into the coagulating bath(5) through an air gap(4) via spinneret(3) .

According to the present invention, it is possible to use water or an aqueous sulfuric acid solution of less than 20 wt%, wherein the sulfuric acid acts as a polymer solvent which is also used in prepara¬ tion of the spinning solution. The temperature of the coagulation bath is -5~25°C.

Though fibers having both high elasticity and tenacity can be prepared by means of various methods, it is an accepted principle that the molecular chains forming the fibers should be arranged in the drawing direction to achieve uniform stress in the fibers.

Conventional polymer materials which are composed of flexible molecular chains are used as fibers by rearranging the molecules so that they are extended in the drawing direction to obtain the maximum tenacity.

Though molecular chains in a spinning solution having a liquid crystal property are easily oriented, it is necessary to diffuse and extract the solvent in the spinning solution from the coagulant, wherein the spinning solution is extruded from a spinneret.

In FIG. 1, the spinning solution passes the air gap of dry-jet, wet spinning facilities, and is guided to the coaguIan (5-1) .

Simultaneously, the composition and temperature of the coagulant are selected so that the solvent in the spinning solution may be diffused uniformly, and they are important factors for controlling the structure density.

FIG. 2 shows a graph illustrating the variation of fiber tenacity according to the composition and temperature of the coagulant.

It shows that the tenacity of the fibers is increased when the concentration of the coagulant is 0-10% by weight, and on the contrary, it is decreased after the concentration exceeds 10 wt%. The fiber tenacity gradually decreases as the temperature of the coagulant is increased, but where the temperature of coagulant is less than -5°C, the properties of the fibers fall off and the coagulant solution is frozen over.

IK) WASHING, NEUTRALIZATION AND DRYING In FIG. 1, the fibers (7) prepared by the above process are carried to the washing equipment (11), neutralization equipment (12), and dewaterer (17) to eliminate the solvent, and then carried to the drying equipment (13) to eliminate remaining moisture, yielding the final aromatic polyamide fibers. According to the invention, tension control rollers(δ) and feeding rollers(9) are provided at the inlet of the washing, the neutralization and the drying equipment both to improve the properties of yarn and to control and maintain the pitch of the yarn fed between the respective washing, neutralization and heating rollers in the course of feeding of the filaments.

The tension between each type of equipment is controlled to be more than 0.1g/d(grams/denier) . It is especially necessary to control and maintain the tension to satisfy the following range so that the washing, neutralization and drying steps can be easily achieved. Also the appearance, quality and properties of the fibers can be improved due to the convenient winding and continuous feeding of the fibers.

C +A ≥ (0.4-DB ≤ (3~7)D (wherein A: tension between the feeding rollers in the coagulating bath, B: tension between the washing equipment and neutralization equipment,

C: tension between the neutralization equipment and the drying equipment, D: tension between the drying equipment and winder) The tension is controlled, in general, by using a difference of front and rear rol lers.

In the spinning facilities of the coagulating bath, to ensure compact structure of the fibers, the solvent in the spinning solution is required to be as uniformly dispersed as possible. Consequently, the tension before and after the coagulating bath forming the fibers, and the drying process, have a great influence on the properties of the fibers. The equipment for the washing and neutralization processes according to the present invention may be general equipment used to wash, immerse in a neutralization liquid, or spray.

Water or alkali which can neutralize a solvent such as sulfuric acid may be used in washing or neutralization, and the temperature of the water or alkali is preferably in the range of 20~80°C. When the temperature is less than 20°C, the washing and neutralization are not sufficient, and when it exceeds 80°C, the effect of washing and neutralization barely increases, so it is not economic to do so.

FIG. 3 shows a graph illustrating the relationship of liquid temperature used in the washing and neutralization processes, the content of remaining salt(Na₂S0₄ ) and content of the remaining NaOH or H₂S0₄ as a result of the washing and neutralization processes, wherein the temperatures of water for washing and neutralization are the same. If sulfuric acid remains due to insufficient washing and neutralization, the light yellow color of the fibers turns into a dark yellow, while chemical and mechanical properties of the fibers go down. On the contrary, if the content of alkali used in the neutraliza¬ tion process and salts produced as by-products remains too much over the range, the fibers have a low adhesive property which is needed for rubber reinforcing causing a separation. In such cases, the desirable properties of the fibers are not exhibited sufficiently.

The drying equipment selectively comprises either or both heating rollers (13-1) and a hot heater (13-2) and other conventional drying equipment for drying of fibers.

The fibers are dried at a temperature in the range of 100~250°C so that the remaining moisture regain is less than 12% during the dry¬ ing process. Owing to the drying and heating treatment in the process of preparing fibers, moisture and internal deformation of the fibers can be restricted and also the degree of crystallization increased.

Various properties of the fibers can be increased accordingly.

Time and temperature in the drying equipment are especially important because if the drying process is accomplished too rapidly

(e.g. if the temperature for drying is too high), the surface solidifies too fast, since the evaporation rate of moisture from the surface is much higher than the diffusion rate of moisture from the center to the surface. Furthermore, the drying process is significant not only to eliminate moisture in the fibers but also to reduce the voids which are produced in the precipitation process. Because a plurality of voids are produced immediatly after dry-jet, wet spinning of a rigid polymer solution, the properties of the fibers can be increased by reducing or homogenizing such voids.

A dewaterer(17) is arranged upstream of the neutralization and drying equipment so that the remaining moisture is less than 100%.

This reduces the number of units of equipment and improves the efficiency of treatment simultaneously. If the dewaterer is not used, the fibers commonly contain about 200% of remaining moisture.

Preferably the content of remaining salt in the fibers is less than 1.2% and the content of NaOH and H^SO, is less than 0.05%, respectively.

In order to obtain the aforesaid content, a retention time within 1—5 seconds in each equipment during washing, neutralization and drying process is required and 2-3 seconds is more preferable with respect to appearance, quality, properties of the fibers and economic efficiency.

FIG. 3 shows a graph illustrating the relationship between the retention time in each equipment in the washing and neutralization process, and the content of remaining salt and remaining base(NaOH) or acid(H SO„ ) as a result of the treatment. According to the invention, retention time and temperature for treatment are determined within the range in which both content of remaining salt and NaOH or H_AS0₄ are satisfied.

The rate of winding during the washing, neutralization and drying process, is 1.01-6.0 times as high as the rate of spinning solution extruded from the spinneret so that molecular chains are optically or¬ iented, drawn and crystallized to improve the properties of the fibers. Where the winding rate exceeds the above range, the fibers are incl ined to break.

The aromatic polyamide fibers prepared by the aforesaid process have excellent properties, i.e., the inherent viscosity is preferably more than 5.0, the tenacity is more than 21 g/d and initial modulus is more than 550g/d. Therefore, the aromatic polyamide fibers may be used in various fields such as automobiles, space navigation, general industry and construction materials. This invention is illustrated by the following examples, but should not be construed to be limited thereto.

Example 1

PoIy(p-phenyIene terephthalamide)(PPTA) having an inherent vis- cosity of 6.6 was dissolved in concentrated sulfuric acid of 99.5% at a temperature of 85°C for 30 minutes to prepare an optical anisotropic spinning solution, wherein the content of said PPTA polymer relative to sulfuric acid is 19.5% by weight. The spinning solution had a pearly luster when it was spread onto a plate of glass. Then the spinning solution was extruded into 5wt% of an aqueous sulfuric acid coagulating bath, at a temperature of 10°C, via 10mm of an air gap from the spinneret.

The prepared filaments passed through the washing equipment and the neutralization equipment to eliminate the solvent, and the drying equipment to eliminate the remaining moisture in the filaments to provide the final product of aromatic polyamide filaments.

The control roller for tension and the feeding roller were arranged to control and maintain a uniform pitch of yarn provided between the washing rollers, the neutralization rollers and the heating rollers respectively, when the fibers were fed.

Simultaneously, the tension between each equipment was controlled to be 0.15 g/d, and the ratio of the rate of spinning extruded from the spinneret to the rate of winding during the washing neutralization and drying processd .e. , the drawing ratio) is deter¬ mined as 3.5.

In the washing and the neutralization processes, water was ejected so as to wash the remaining sulfuric acid in the filaments in the first step, and in the second step, an aqueous NaOH solution of 0.7% was ejected to eliminate and neutralize small quantities of remaining sulfuric acid. The retention time in each equipment during the washing, neutralization and drying process was 2.8 seconds, the ejecting temperature of water and aqueous NaOH solution was 45°C and the drying temperature was 180"C.

The thickness of final filament was 1000 denier and the properties are shown in Table 1.

Example 2 and Comparative Examples 1 to 4 The same procedure was carried out as described in Example 1 except for variations of conditions for preparing the spinning solutions, as shown in Table 1.

Example 3 and 4 and Comparative Examples 5 to 8 Aromatic polyamide filaments were prepared in Example 1 except that the composition, the temperature and the drawing ratio (rate of winding / rate of spinning) of the coagulant were varied as shown in Table 1.

The drawing ratio was changed by controlling the winding rate of the washing, neutralization and drying process while the spinning rate was held constant. The results of properties of the prepared filaments are shown in Tabel 1. TABL E 1

inherent concentrat ion polymer coagulant drawing I iquid crystal tenaci ty spinnab- sect ion viscosi ty of concentra¬ content to ratio revelation of i I ity (I.V.) ted sul fur ic sul fur ic composi tion temperature (times) spinning solu¬ (g/d) _* acid (%) acid (wt%) (TC) tion (times) aqueous sulfuric

Example 1 6.6 99.5 19.5 acid solution of 10 3.5 good 23 good 5% aqueous sulfuric

Example 2 6.8 99.6 19.7 acid solution of 10 3.5 good 24 good 5% aqueous sulfuric

ExampIe 3 6.6 99.5 19.5 acid solution of -3 4.5 good 24 good.. 12% ro

Example 4 6.6 99.8 19.8 water 5 4.0 good 22 good I

Comparative aqueous sulfuric Example 1 5.0 94.5 12.0 acid solution of 10 3.5 bad 11 normal 5%

Comparat ive aqueous sulfuric ExampIe 2 4.5 101.5 19.0 acid solution of 10 3.5 bad 8 bad

5%

Comparat ive aqueous sulfuric not impossi¬ Example 3 7.5 100.0 23.5 acid solution of 10 3.5 bad measur¬ ble 5% able

Comparati e aqueous sulfuric not Example 4 5.5 98.2 7.0 acid solution of 10 3.5 bad measur¬ bad 5% able

CONT I NUOUS TABLE 1

Comparative aqueous sulfuric Example 5 6.6 99.5 19.5 acid solution of 12 1.0 good 6 bad 17%

Comparative aqueous sul fur ic not impossi¬ Example 6 6.6 .99.5 19.5 acid solution of 0 7.0 good measur¬ ble 5% able

Comparative aqueous sul fur ic Example 7 6.6 99.5 19.5 acid solution of 7 3.0 good 15 normal 23% O

Comparative 1 Example 8 4.0 99.5 19.5 water 30 2.5 normal 10 bad

sp i nnabi I i ty (%) = (A/N) 100 good : 100-85 the number of success of winding lor 1 hour after the spinning : A normal : below 85-55 the number of fail of winding tor 1 hour after the spinning : B bad : below 55-25 A + B = N ( N≥IO ) impossible : below 25 — 0

Example 5 and 6 and Comparative Examples 9 to 11

Aromatic polyamide filaments were prepared as in Example 1 except the drawing ratio was changed as shown in Table 2.

The results of properties of the prepared filaments are shown in

Table 2.

TABLE 2

tension (g/end) * drawing ratio tenaci ty modulus spinnabi I- section (times) (g/d) (g/d) ity

A B C D (%)

Example 5 200 700 550 750 4.0 24 800 good

Example 6 350 500 350 600 3.5 23 650 good

Comparative cn Example 9 300 800 300 600 1.0 8 200 normal I

Comparative Example 10 450 1500 500 850 7.0 - - impossible

Comparat ive Example 11 600 1200 600 600 1.5 12 250 bad

said values are measured with the consideration of the constant (B: 0.4 1, D: 3-7) in tension end : fiber of a unit in module during the whole process(= 1,000 denier) grams/end A : tension between the feeding rollers in the coagulating bath B : tension between the washing equipment and the neutralization equipment C : tension between the neutralization equipment and the dry equipment D : tension between the dry equipment and the winder

Example 7 and 9 and Comparative Examples 12 to 14

Aromatic polyamide filaments were prepared as in Example 1 except a dehydrator was arranged upstream of the neutralization and drying equipment, and the retention time and treating temperature were varied as shown in Table 3.

The results of properties of the prepared filaments are shown in Table 3.

TABL E 3

washing, neutralization drying moisture content 1) content of remainder(%) Degree rubber of fiber in down¬ of dis¬ adhes¬ section retention temperature retention tempe¬ stream of a sul f- alkali salt mois colora¬ i e¬ t ime(sec) CO t ime(sec) rature dewaterer (%) ric ture tion ness CO acid 2) 3) change-

Example 7 2.8 45 2.8 180 100 0.00 0.05 0.90 7.5 less- 1.0 ness change-

Examp1e 8 3.0 70 3.0 170 85 0.00 0.04 0.80 7.2 less- 1.0 ness change-

Examp1e 9 4.0 30 2.5 150 90 0.00 0.04 0.80 10.2 less- 1.0 I ness dark

Example 12 0.8 25 2.0 280 150 0.15 0.09 1.35 6.2 brown 0.8

dark

Example 13 1.3 15 3.5 150 250 0.10 0.08 1.40 15.5 brown 0.8

dark

Example 14 4.5 10 1.0 95 200 0.02 0.06 1.25 25.0 brown 0.9

1) content of remaining moisture in filaments after dehydration treatment in dehydrator(degree of dehydration)

: remaining rate of moisture in fi laments(%)= Ww/Fwx100 wherein Fw: weight of filaments Ww: weight of water

2) discoloration of fibers : evaluated by weathering test to sun¬ light for 1 year(changelessness: yellow or light yellow)

3) rubber adhesive property : relative values obtained by standardizing the results of 3/8 inch H-test on the basis of Example 7 (a standard value: 1)

< 3/8 inch H-test >

It is a testing method upon JIS, and the results are obtained by measuring the rubber adhesive property after the filament is adhered to rubber under a pressure of 50kg at the temperature of 150°C for 30 min, and then it is maintained at the temperature of 20°C and the humidity of 65% for 24 hrs.

From the results obtained by these examples and comparative examples, we know that the inherent viscosity of the aromatic polyamide filaments is more than 4.5, the tenacity is more than 21 g/d and the initial modulus is more than 550 g/d.

According to the present invention, discoloration of fibers is prevented while mechanical and chemical properties do not go down, owing to the elimination of the problem that sulfuric acid remains partially after the washing and the neutralization processes.

Furthermore, because the alkali used in the neutralization and the salt produced during the neutralization process is rinsed effectively, the present filaments have an excellent adhesive property when used for reinforcing rubber. Further, the physical properties of the final filaments are improved due to minimizing voids in the filaments which results in optimizing of the dry condition.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Claims

WHAT IS CLAIMED IS;

1. A process for the preparation of wholly aromatic polyamide filaments comprising the steps: (a) providing a 13-22 wt% anisotropic spinning solution by dissolving an aromatic polyamide polymer having an inherent viscosity of more than 4.5 in a sulfuric acid solvent;

(b) preparing filaments by extrusion of said spinning solution through a spinneret into a coagulant in which water or a sulfuric acid solvent is contained in less than 20 wt%;

(c) washing, neutralizing and drying with a tension between each equipment that satisfies the following relationship:

C + A ≥ (0.4~1)B ≤ (3~7)D

(wherein A is the tension between feeding rollers in a coagul- ating bath, B is the tension between the washing equipment and the neutralization equipment, C is the tension between the neutralization and the drying equipment and D is the tension between the drying equipment and a winder.)

2. The process according to Claim 1, wherein said aromatic polyamide polymer is polyethylene-terephthaiamide having an inherent viscosity of more than 4.5.

3. The process according to Claim 1, wherein said sulfuric acid solvent is selected from the group consisting of sulfuric acid, chloro-sulfuric acid and fluoro-sulfuric acid. 4. The process according to Claim 2, wherein the con¬ centration of said sulfuric acid solvent is within the range of 96 to 100.1 wt%.

5. The process according to Claim 3, wherein the concentra¬ tion of said sulfuric acid solvent is within the range of 96 to 100.1 wt%.

6. The process according to Claim 1, wherein the temperature of said coagulant is within the range of -5 to 25°C.

7. The process according to claim 1, wherein the tension between each equipment for said washing, neutralization and drying processes is more than 0.1 g/d.

8. The process according to Claim 1, wherein the respective rates of winding during said washing, neutralization and drying processes are 1.01-6,0 times as high as the rate of spinning extruded from the spinneret.

9. The process according to Claim 1, wherein a dewaterer is further installed on the front of said neutralization and drying equipment to maintain the remaining moisture in the filaments to less than 100%.

10. The process according to Claim 1, wherein the retention time of the fibers in each equipment for said washing, neu¬ tralization and drying process is in the range of 1 to 5 seconds. l 1. The process according to Claim 1, wherein the retention time of the fibers in each equipment for said washing, neutralization and drying process is in the range of 1 to 3 seconds.

12. The process according to Claim 1, wherein the temperature for said washing and neutralization is in the range of 20 to 80°C. l 3. The process according to Claim 1, wherein the temperature for said drying step is in the range of 100 to 250°C.

14. The process according to Claim 1, wherein the remaining moisture regain of filaments after said drying process is less than 12%.

15. The process according to Claim 1, wherein the content of remaining salt of filaments after said washing, neutralization and drying process is less than 1.2% and the content of NaOH and H₄S0₄ is less than 0.05%, respecti ely.

16. A wholly aromatic polyamide filament prepared according to the process of Claim 1, which has an inherent viscosity of more than 4.5, a tenacity of more than 21 g/d, an initial modulus of more than 550 g/d, a content of remaining salt of less than 1.2% and a content of NaOH and H^SO, of less than 0.05%, respectively.