WO2022145940A1 - Method for producing para-aramid fibers, and para-aramid produced therefrom - Google Patents

Abstract

The present invention relates to a method for producing para-aramid fibers, and a para-aramid produced therefrom. The method for producing para-aramid fibers involves: spinning, into filament form, a spinning dope including a particulate additive, and then performing a series of coagulation and washing steps to remove the particulate additive from the spinning dope and thereby form recesses and protrusions on the surface thereof; and inducing crosslinking by treating with a crosslinking agent. Thus, the present invention can provide para-aramid fibers that exhibit improved rubber adhesion while maintaining, at an excellent level, or further improving the intrinsic properties, such as the mechanical properties, of para-aramid fibers.

Description

Method for producing para-aramid fiber and para-aramid prepared therefrom

Cross-Citation with Related Application(s)

This application claims the benefit of priority based on Korean Patent Application No. 10-2020-0186067 on December 29, 2020, and all contents disclosed in the literature of the Korean patent application are incorporated as a part of this specification.

The present invention relates to a method for producing para-aramid fibers and to para-aramid produced therefrom.

Aramid is an amide-based synthetic polymer in which 85% or more of amide bonds are directly linked to two aromatic groups, and is well known as an aromatic polyamide.

Aramid is classified into meta-aramid with flexible flexibility and para-aramid with rigid rod structure according to the structural characteristics of molecular chains. In particular, a poly(para-phenylene terephthalamide) fiber, which is one of the para-aramid fibers, has excellent mechanical properties, heat resistance, and flame retardancy while having a low density. Para-aramid fibers are mainly applied as reinforcing materials for various base materials such as rubber and resin in industrial fields requiring high performance.

In order to apply para-aramid fibers as reinforcing materials, appropriate pretreatment for para-aramid fibers is required in order to increase compatibility with the base material. For example, para-aramid fibers pretreated with a solution such as epoxy or isocyanate may be applied as a rubber reinforcing material.

However, there is a problem in that the interfacial adhesion with the pretreatment solution decreases due to the structural characteristics of the para-aramid fibers. In order to solve the above problem, a method of introducing a functional group to the surface of the para-aramid fiber through plasma treatment or generating irregularities on the surface of the para-aramid fiber through sand blasting has been attempted.

However, previously tried methods have resulted in a problem of lowering the mechanical strength, which is the strength of para-aramid fibers.

The present invention provides a method for producing para-aramid fibers.

The present invention also provides a para-aramid fiber prepared from the above manufacturing method.

Hereinafter, a method for producing a para-aramid fiber according to a specific embodiment of the present invention and a para-aramid fiber prepared through the manufacturing method will be described.

According to one embodiment of the present invention, there is provided a method for manufacturing a spinning dope comprising: preparing a spinning dope comprising at least one particulate additive selected from the group consisting of water-soluble polymer particles and metal salt particles and an aromatic polyamide polymer; spinning the spinning dope in the form of a filament; coagulating and washing the spun dope to obtain a filament having surface irregularities due to detachment of the particulate additive from the surface of the spun dope; and treating the filaments having the surface unevenness with a crosslinking agent.

On the other hand, according to another embodiment of the present invention, it comprises a monofilament formed of an aromatic polyamide polymer, wherein the monofilament has a surface roughness of greater than 0.1 μm, and the at least two or more monofilaments are linked through a cross-linked para- Aramid fibers are provided.

Para-aramid fiber has excellent mechanical properties, heat resistance and flame retardancy while having a low density, so it is useful as a reinforcing material for various base materials such as rubber and resin, but has a disadvantage in that compatibility with the base material is not good.

As a result of continuous research to solve this problem, the present inventors have spun a spun dope including a particulate additive and an aromatic polyamide polymer in the form of a filament, and then coagulated and washed with water through a series of processes to remove the particulate additive from the spun dope. The para-aramid fibers exhibiting improved rubber adhesion while maintaining or further improving the intrinsic properties such as mechanical properties of para-aramid fibers at an excellent level by removing them to form irregularities on the surface, and treating them with a cross-linking agent to introduce cross-linking. It was confirmed through an experiment that it can be provided, and the present invention was completed.

Hereinafter, the method for producing the para-aramid fiber and the para-aramid fiber prepared therefrom will be described in detail.

In the method for producing para-aramid fibers according to the embodiment, first, a spinning dope is prepared.

The spinning dope comprises an aromatic polyamide polymer and a particulate additive.

The aromatic polyamide polymer may be obtained by polymerizing an aromatic diamine and an aromatic diecide halide. Alternatively, an appropriate commercial product may be used as the aromatic polyamide polymer.

As a non-limiting example, the aromatic diamine includes p-phenylenediamine, 4,4'-oxydianiline, 4,4'-diaminobiphenyl, 2,6-naphthalenediamine, 1,5-naphthalenediamine and 4 At least one selected from the group consisting of ,4'-diaminobenzanilide and the like may be used.

As a non-limiting example, the aromatic diecide halide includes terephthaloyl dichloride, [1,1'-biphenyl]-4,4'-dicarbonyl dichloride, 4,4'-oxybis(benzoyl chloride) , at least one selected from the group consisting of naphthalene-2,6-dicarbonyl dichloride and naphthalene-1,5-dicarbonyl dichloride may be used.

A polymerization solvent in which an inorganic salt is added to an organic solvent may be used for polymerization of the aromatic diamine and the aromatic diecide halide.

Examples of the organic solvent include N-methyl-2-pyrrolidone (NMP), N,N'-dimethylacetamide (DMAc), hexamethylphosphoamide (HMPA), N,N,N',N'-tetra At least one selected from the group consisting of methyl urea (TMU), N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) may be used.

The inorganic salt may be added for the purpose of increasing the degree of polymerization of the aromatic polyamide. As the inorganic salt, a halogenated alkali metal salt or a halogenated alkaline earth metal salt may be used. For example, the inorganic salt may include at least one selected from the group consisting of CaCl ₂ , LiCl, NaCl, KCl, LiBr, and KBr.

As the amount of the inorganic salt added increases, the degree of polymerization of the aromatic polyamide polymer increases. However, when the inorganic salt is added in excess, an inorganic salt not dissolved in the organic solvent may exist to inhibit polymerization. Therefore, the inorganic salt is preferably added within 0.01 to 10% by weight based on the total weight of the polymerization solvent.

For polymerization of the aromatic diamine and the aromatic diecide halide, a mixed solution may be prepared by dissolving the aromatic diamine in a polymerization solvent. In addition, a predetermined amount of the aromatic diecide halide may be added to the mixed solution while stirring the mixed solution to perform preliminary polymerization.

The polymerization reaction of the aromatic diamine and the aromatic diecide halide proceeds rapidly with exotherm. If the polymerization rate is too fast, the degree of polymerization difference between the finally obtained polymers may become large. Accordingly, by pre-forming a polymer having a molecular chain of a predetermined length through the preliminary polymerization and then performing a polymerization process, a difference in polymerization degree between finally obtained polymers can be minimized.

The prepolymerization may be performed by stirring at a temperature of 0° C. to 45° C. for 1 minute to 30 minutes or 5 minutes to 15 minutes. Then, the residual amount of the aromatic diecide halide is added to the obtained prepolymer solution and further polymerization is performed to prepare an aromatic polyamide polymer. The additional polymerization may be performed by stirring at a temperature of 0° C. to 45° C. for 5 minutes to 1 hour or 10 minutes to 40 minutes.

Since the aromatic diecide halide reacts with the aromatic diamine in a molar ratio of 1:1, the molar ratio of the aromatic diecide halide to the aromatic diamine may be about 0.9 to 1.1.

The aromatic polyamide polymer included in the spinning dope is poly(para-phenylene terephthalamide), poly(4,4'-benzanilide terephthalamide), poly(paraphenylene-4,4'-biphenylene-dica). carbonyl amide), poly(paraphenylene-2,6-naphthalenedicarbonyl amide), or a copolymer thereof. For example, the aromatic polyamide polymer included in the spinning dope may be poly(para-phenylene terephthalamide).

The particulate additive included in the spinning dope is at least one particle selected from the group consisting of water-soluble polymer particles and metal salt particles.

Specifically, the water-soluble polymer particles may be polyvinyl alcohol resin particles.

In addition, the metal salt particles may be one or more particles selected from the group consisting of iron sulfate (Fe ₂ (SO ₄ ) ₃ ) particles and aluminum sulfate (Al ₂ (SO ₄ ) ₃ ).

The particulate additive preferably has an average particle diameter of 0.01 to 1 μm. Specifically, the particulate additive may have an average particle diameter of 0.01 to 1 μm or 0.1 to 1 μm.

If the particle diameter of the particulate additive is too large, the surface unevenness due to the drop-off of the particulate additive in the coagulation and water washing process may deepen, thereby reducing mechanical properties of the filament. However, if the particle diameter of the particulate additive is too small, it is difficult to remove the particulate additive in the coagulation and water washing process, so that the target surface unevenness may not be formed.

*36The spinning dope may be prepared by dissolving the aromatic polyamide polymer in a solvent and then mixing the particulate additive.

As a solvent for the spinning dope, 97 to 102 wt% of sulfuric acid may be used. Alternatively, chlorosulfuric acid or fluorosulfuric acid may be used instead of sulfuric acid as the solvent.

As the concentration of the aromatic polyamide polymer in the spinning dope increases, the viscosity of the spinning dope also increases, but beyond the critical concentration, the viscosity of the spinning dope rapidly decreases. At this time, the radiation dope changes from optically isotropic to optically anisotropic without forming a solid phase. Due to the structural and functional properties of the anisotropic spun dope, high-strength para-aramid fibers can be prepared without a separate stretching process. Therefore, it is preferable that the concentration of the aromatic polyamide polymer in the spinning dope exceeds the critical concentration, but if the concentration is too high, the viscosity of the spinning dope may become too low. Accordingly, the spinning dope may include the aromatic polyamide polymer in an amount of 10 to 25 wt% based on the total weight of the spinning dope.

The particulate additive is preferably included in the spinning dope in an amount of 0.01 wt % or more based on the weight of the aromatic polyamide polymer so that the effect of forming surface irregularities by the particulate additive can be expressed.

However, when the particulate additive is included in an excessive amount, the spinnability of the dope may be inhibited and mechanical properties of the filament may be deteriorated. Therefore, the particulate additive is preferably included in the dope in an amount of 5.0 wt% or less based on the weight of the aromatic polyamide polymer.

Specifically, the particulate additive is present in an amount of 0.01 to 5.0% by weight, or 0.1 to 3.0% by weight, or 0.1 to 2.0% by weight, or 0.1 to 1.5% by weight, or 0.5 to 1.0% by weight based on the weight of the aromatic polyamide polymer. It may be included in the spinning dope as a content.

Subsequently, spinning the spinning dope in the form of a filament; and coagulating and washing the spun dope to obtain a filament having surface irregularities due to detachment of the particulate additive from the surface of the spun dope.

The spinning step may be performed under conventional conditions using a spinning apparatus having a conventional configuration except for using the spinning dope.

For example, in the spinning, the spinning dope may be spun in the form of a filament through grit wet spinning.

The air-gap wet spinning involves placing an air-gap between the spinneret and the coagulation bath surface. According to such a wet spinning method, the spinning dope may be spun into a coagulation tank containing a coagulating liquid through an air gap through a spinneret. The air gap may be mainly an air layer or an inert gas layer. The length of the air gap may be adjusted to 0.1 to 15 cm.

The spinneret may have a plurality of capillaries having a diameter of 0.1 mm or less. When the diameter of the capillary formed in the spinneret exceeds 0.1 mm, the molecular orientation of the produced filament is deteriorated, and as a result, the strength of the filament may be lowered.

Through the spinning step, an unsolidified filament in which the particulate additive and sulfuric acid are distributed on a matrix that is an aromatic polyamide polymer is obtained.

The dope spun in the spinning step may be coagulated by passing through the air gap and sequentially passing through the coagulation tank containing the coagulation solution and the coagulation tube under the coagulation tank.

The coagulation tank is located in the lower portion of the spinneret, the coagulation liquid is stored therein, and a coagulation tube is formed in the lower portion of the coagulation tank. Accordingly, the spinning dope passing through the capillary tube of the spinneret is solidified while passing through the air gap, the coagulation tank and the coagulation tube to form a filament, which is discharged while passing through the coagulation tube.

The coagulation solution is water; monohydric alcohols such as methanol, ethanol or propanol; dihydric alcohols such as ethylene glycol or propylene glycol; triols such as glycerol; Or it may be a sulfuric acid solution in which sulfuric acid is added to a mixture thereof. The dope passing through the spinneret forms filaments while the sulfuric acid therein is removed while passing through the coagulating solution. At this time, if the sulfuric acid is rapidly removed from the filament surface, the filament surface may be solidified before the sulfuric acid contained therein goes crazy, and the uniformity of the filament may be deteriorated. Accordingly, the coagulating solution preferably contains 5 to 15% by weight of sulfuric acid. And, the temperature of the coagulating solution is preferably 1 to 10 ℃. If the temperature of the coagulating solution is too low, it may be difficult for the sulfuric acid to escape from the filament. If the temperature of the coagulating solution is too high, sulfuric acid may be rapidly escaped from the filament, thereby reducing the uniformity of the filament.

The coagulation tube is connected to the coagulation tank, and a plurality of injection holes may be formed in the coagulation tube. In this case, the injection hole is connected to a predetermined jet device (jet device), the coagulation liquid injected from the injection device is injected into the filament passing through the coagulation tube through the injection hole. The plurality of injection holes are preferably arranged so that the coagulating liquid can be symmetrically injected with respect to the filament. The injection angle of the coagulating liquid is preferably 0 to 85° with respect to the axial direction of the filament, and in particular, an injection angle of 20 to 40° is suitable in a commercial production process.

In the coagulation process, at least a portion of the particulate additive present in the filament may be removed from the surface of the filament.

After the coagulation process, a water washing process is performed. The washing process is a process for removing at least a portion of the sulfuric acid remaining in the solidified filament and the particulate additive present on the surface of the filament. The water washing process may be performed by spraying water or a mixed solution of water and an alkali solution onto the coagulated filament.

The water washing process may be performed in multiple steps. For example, the coagulated filament may be first washed with 0.1 to 1.5% by weight of an aqueous caustic solution, followed by secondary washing with a thinner aqueous caustic solution.

At least a portion of the particulate additive present in the filament is removed from the surface of the filament during the coagulation and washing process. Then, irregularities are formed on the surface of the filament by the drop-off.

As an example, the filament has a surface roughness exceeding 0.1 μm, thereby exhibiting excellent rubber adhesion while exhibiting various intrinsic physical properties of the para-aramid fiber. More specifically, the filaments have a surface roughness of more than 0.1 μm, 0.15 μm or more, 0.20 μm or more, and 1.0 μm or less, 0.8 μm or less, or 0.60 μm or less, thereby exhibiting excellent intrinsic physical properties and excellent rubber adhesion at the same time. .

The surface roughness was measured using Atomic Force Microscopy (AFM). Specifically, the para-aramid fiber was fixed well in the V-groove of the substrate having the V-groove, and then the surface roughness was measured using a Nanoscope III a Multimode manufactured by Digital Instruments, UK.

The filaments that have undergone the coagulation and water washing process do not have sufficient crystal orientation, and since the crosslinking agent can smoothly penetrate into the filaments due to the particulate additive dropped in the water washing process, the treatment with the crosslinking agent is the spun dope. It is preferably carried out between the water washing process and the drying process. However, after treating the filament with the crosslinking agent, a water washing process may be additionally performed to remove the unnecessary crosslinking agent remaining on the surface of the filament. In addition, optionally, a crosslinking agent treatment process may be performed after the washing and drying processes. The filaments that have undergone the drying process have sufficient crystal orientation so that the crosslinking agent treatment effect is insignificant compared to the case where the crosslinking agent treatment is performed before the drying process, but shows good results compared to the case where the crosslinker treatment is not performed.

As an example, following the coagulation and washing process, a process of treating the filaments having surface irregularities formed by the dropping of the particulate additive with a crosslinking agent may be performed.

The crosslinking agent is one capable of forming a crosslink between the ends of the aromatic polyamide polymer constituting the filament, and may be an aromatic dianhydride, an aromatic diamine, an aromatic diecide halide, or a mixture thereof.

Specifically, as the aromatic dianhydride, pyromellitic dianhydride (PMDA), benzophenone tetracarboxylic dianhydride (CDPA), 3,3'4,4'-ratio Phenyltetracarboxylic dianhydride (3,3'4,4'-biphenyltetracarboxylic dianhydride (BPDA)), 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (4,4'-(hexafluoroisopropylidene) ) diphthalic anhydride (6FDA)), 4,4'-oxydiphthalic anhydride (ODPA)), 2,3,6,7-naphthalene tetracarboxylic dianhydride (2, 3,6,7-naphthalene tetracarboxylic dianhydride (NDA)) and 3,3',4,4'-diphenylsulfonetetracarboxylic acid dianhydride (3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride) One or more selected from may be used. Examples of the aromatic diamine include p-phenylenediamine, 4,4'-oxydianiline, 4,4'-diaminobiphenyl, 2,6-naphthalenediamine, 1,5-naphthalenediamine and 4,4'-dia At least one selected from the group consisting of minobenzanilide may be used. Examples of the aromatic diecide halide include terephthaloyl dichloride, [1,1'-biphenyl]-4,4'-dicarbonyl dichloride, 4,4'-oxybis(benzoyl chloride), naphthalene-2, At least one selected from the group consisting of 6-dicarbonyl dichloride and naphthalene-1,5-dicarbonyl dichloride may be used.

For example, aromatic dianhydride may be used as the crosslinking agent, and more specifically, benzophenone tetracarboxylic acid dianhydride, 3,3'4,4'-biphenyltetracarboxylic acid dianhydride, and 4,4'- At least one selected from the group consisting of oxydiphthalic anhydride may be used.

The treatment with the crosslinking agent may be performed by a dipping method or a spraying method.

Specifically, in the crosslinking agent treatment process, a solution in which the crosslinking agent is dissolved in an appropriate solvent may be prepared. Water may be used as the solvent, and when the crosslinking agent is not soluble in water, a polar solvent may be used or a polar solvent may be mixed with water to dissolve the crosslinking agent. As a non-limiting example, the polar solvent includes N-methyl-2-pyrrolidone (NMP), N,N'-dimethylacetamide (DMAc), hexamethylphosphoamide (HMPA), N,N,N' At least one selected from the group consisting of ,N'-tetramethyl urea (TMU), N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) may be used.

The crosslinking agent may be dissolved in a solvent in an amount of 1 to 20% by weight based on the total weight of the crosslinking agent solution. A sufficient strength improvement effect may be obtained by forming an appropriate cross-linkage between the aromatic polyamide polymers while minimizing the content of the remaining cross-linking agent within this range.

The crosslinking agent treatment process may be performed by a dipping method in which a filament having surface unevenness is immersed in the crosslinking agent solution and then taken out, or a spray method in which the crosslinking agent solution is sprayed onto the filament having surface unevenness.

At this time, the crosslinking agent solution may be maintained at a temperature higher than room temperature, for example, 30 to 70 ℃, 40 to 60 ℃ or 45 to 55 ℃ so that the crosslinking agent can penetrate smoothly into the filament.

A drying process may be performed after the crosslinking agent treatment process. In this drying process, cross-linking between aromatic polyamide polymers forming monofilaments may be formed by the cross-linking agent. The cross-linking may be formed within one filament or between two or more monofilaments.

However, if the same kind of monomer as the monomer used in the preparation of the aromatic polyamide polymer is employed as the crosslinking agent, the crosslinking structure is the same as the polymer chain structure forming the aromatic polyamide polymer. For this reason, in the finally prepared para-aramid fiber, it is difficult to ascertain whether the bonding structure in one filament was formed in the polymerization process of the aromatic polyamide polymer or in the crosslinking agent treatment process performed after the formation of surface irregularities of the monofilament. . Accordingly, the para-aramid fiber according to the other embodiment may be defined as having cross-linking between monofilaments, which is a characteristic structure introduced by treatment with a cross-linking agent after filament formation.

The drying process causing the crosslinking reaction may be performed by controlling the time the filament is in contact with the heated drying roll or by controlling the temperature of the drying roll.

In the drying process, the temperature of the drying roll may be adjusted to about 150 to 250 °C or 150 to 200 °C. In addition, in the drying process, the contact time between the filament and the drying roll may be adjusted to about 0.5 to 15 seconds or 1 to 10 seconds. Within this range, a crosslinking reaction between the aromatic polyamide polymers may sufficiently occur, and the moisture content remaining in the filament may be adjusted to an appropriate level.

Para-aramid fiber manufacturing method according to the embodiment may further include the step of heat-treating the dried filament after the drying step.

The heat treatment process may be performed at about 250 to 500 °C. In addition, in the heat treatment process, the dried filament may be hot drawn by applying a predetermined tension. For example, in the heat treatment process, the filament may be hot-drawn by applying a tension of about 2000 to 4000 cN to the filament. Through such hot stretching, the mechanical properties of the para-aramid fibers can be further improved.

The monofilament constituting the para-aramid fiber finally obtained is formed of an aromatic polyamide polymer and may have a surface roughness of greater than 0.1 μm. In particular, as described above, the para-aramid fiber has a structure in which at least two monofilaments among the monofilaments constituting the fiber are connected through cross-linking by being treated with a crosslinking agent after surface irregularities are formed by dropping the particulate additive. can have

The monofilament constituting the para-aramid fiber may have a fineness of 1.0 to 2.5 de (denier).

And, the para-aramid fiber according to another embodiment may include a plurality of the monofilaments, and may have a total fineness of 600 to 10,000 de.

The para-aramid fiber prepared by the above-described method may exhibit excellent adhesion performance to various pretreatment solutions or base materials through the surface unevenness while having excellent tensile strength.

Para-aramid fiber manufacturing method according to an embodiment of the present invention, the particulate additive is removed from the spun dope through a series of processes of coagulating and washing with water after spinning a spinning dope including a particulate additive in the form of a filament, thereby forming irregularities on the surface By forming and treating with a crosslinking agent to introduce crosslinking, it is possible to provide para-aramid fibers exhibiting improved rubber adhesion while maintaining or further improving intrinsic properties such as mechanical properties of para-aramid fibers at an excellent level.

Hereinafter, the action and effect of the invention will be described in more detail through specific examples of the invention. However, this is presented as an example of the invention and the scope of the invention is not limited in any way by this.

Synthesis Example 1: Preparation of aromatic polyamide polymer

A polymerization solvent was prepared by adding CaCl ₂ to N-methyl-2-pyrrolidone (NMP). A mixed solution was prepared by dissolving p-phenylenediamine (PPD) in the polymerization solvent.

While stirring the mixed solution, terephthaloyl chloride (TPC) of the same mole as PPD was added to the mixed solution in two portions to prepare poly(para-phenylene terephthalamide) (PPTA).

The acid was neutralized by adding water and NaOH to the solution containing PPTA. Then, after pulverizing the PPTA, the polymerization solvent contained in the PPTA was extracted using water, dehydrated and dried to finally obtain PPTA.

Example 1: Preparation of para-aramid fibers

The PPTA obtained in Synthesis Example 1 was dissolved in 99 wt% sulfuric acid in an amount of 20 wt% based on the total weight of the spinning dope, and 1.0 wt% of iron sulfate particles (Fe ₂ (SO ₄ ) ₃ , average particle diameter of 0.8 μm based on the weight of PPTA) ) was mixed with the solution to prepare a spinning dope.

The spinning dope was spun using a spinneret, and then passed through an air gap through a coagulation tank containing 10 wt% sulfuric acid solution at 5 °C. Subsequently, while passing the coagulation tube under the coagulation bath, coagulated filaments were obtained.

The coagulated filaments were washed with water to remove sulfuric acid remaining on the filaments and iron sulfate particles present on the surface of the filaments.

On the other hand, 4,4'-oxydiphthalic anhydride was dissolved in a mixed solvent of water and N-methyl-2-pyrrolidone (NMP) in a volume ratio of 8:2 in an amount of 5% by weight based on the total weight of the crosslinking agent. A solution containing

Then, the washed filaments were dipped in a solution containing the crosslinking agent at about 50° C. for about 0.5 seconds, and then dried at 180° C. for 5 seconds. Then, by winding the dried filament on a bobbin, the monofilament had a surface roughness of 0.4 μm, a fineness of 1.5 de, and a total fineness of 1,500 de to obtain para-aramid fibers.

Comparative Example 1: Preparation of para-aramid fibers

A spinning dope was prepared by dissolving the PPTA obtained in Synthesis Example 1 in 99% by weight of sulfuric acid at 20% by weight based on the total weight.

The spinning dope was spun using a spinneret, and then passed through an air gap through a coagulation tank containing 10 wt% sulfuric acid solution at 5 °C. Subsequently, while passing the coagulation tube under the coagulation bath, coagulated filaments were obtained.

The coagulated filaments were washed with water to remove sulfuric acid remaining on the filaments, and dried at 180° C. for 5 seconds. Then, by winding the dried filament on a bobbin, the monofilament had a surface roughness of 0.09 μm, a fineness of 1.5 de, and a total fineness of 1,500 de to obtain para-aramid fibers.

Comparative Example 2: Preparation of para-aramid fibers

The surface roughness of the monofilament was 0.6 μm in the same manner as in Comparative Example 1, except that 1.0% by weight of silica particles (average particle diameter 0.8 μm) based on the weight of PPTA was added to the spinning dope of Comparative Example 1, and fineness A para-aramid fiber of 1.5 de and a total fineness of 1,500 de was obtained.

Test Example: Evaluation of physical properties of para-aramid fibers

The physical properties of the para-aramid fibers obtained in Examples and Comparative Examples were measured according to the method described below, and the results are shown in Table 1.

(1) fineness (denier, de)

Fineness was measured according to ASTM D 1577 as denier (de) expressed in grams (g) by weight of 9000 m yarn.

(2) Tensile strength (g/d)

Para-aramid fibers prepared in Examples and Comparative Examples were cut to a length of 250 mm to prepare a sample, and the sample was stored at a relative humidity of 55% and a temperature of 23° C. for 14 hours.

Then, according to the ASTM D885 standard test method, the sample was mounted on INSTRON's testing machine (Instron Engineering Corp, Canton, Mass), one side of the fiber was fixed, and a superload was applied to 1/30 g of the fineness (fineness X 1/30) g), the other side was tensioned at a speed of 25 mm/min, and the tensile load (g) when the fiber was broken was measured. The strength (g/d) was obtained by dividing the measured tensile load by the fineness.

(3) Rubber adhesion (kgf)

The para-aramid fibers obtained in Examples and Comparative Examples were respectively dipped in an epoxy solution in the same manner and dried to prepare samples. H-Test based on the standard test method of ASTM D 4776-98 was performed on the samples to measure rubber adhesion (kgf).

	Example 1	Comparative Example 1	Comparative Example 2
Tensile strength (g/d)	28	26	23
Rubber adhesion (kgf)	18	14	13

Referring to Table 1, it was confirmed that the para-aramid fibers according to the examples exhibited superior tensile strength compared to the fibers according to Comparative Examples 1 and 2 and had improved rubber adhesion.

Claims (17)

1. preparing a spinning dope comprising at least one particulate additive selected from the group consisting of water-soluble polymer particles and metal salt particles and an aromatic polyamide polymer;

   spinning the spinning dope in the form of a filament;

   coagulating and washing the spun dope to obtain a filament having surface irregularities due to detachment of the particulate additive from the surface of the spun dope; and

   A method for producing a para-aramid fiber, comprising the step of treating the filament having the surface asperity with a crosslinking agent.
2. The method for producing para-aramid fibers according to claim 1, wherein the aromatic polyamide polymer contained in the spinning dope is poly(para-phenylene terephthalamide).
3. The method of claim 1, wherein the water-soluble polymer particles are polyvinyl alcohol resin particles.
4. The para-aramid fiber according to claim 1, wherein the metal salt particles are at least one particle selected from the group consisting of iron sulfate (Fe ₂ (SO ₄ ) ₃ ) particles and aluminum sulfate (Al ₂ (SO ₄ ) ₃ ). manufacturing method.
5. The method of claim 1 , wherein the particulate additive has an average particle diameter of 0.01 to 1 μm.
6. The method according to claim 1, wherein the particulate additive is included in the spinning dope in an amount of 0.01 to 5.0% by weight based on the weight of the aromatic polyamide polymer included in the spinning dope.
7. The method according to claim 1, wherein the crosslinking agent is an aromatic dianhydride, an aromatic diamine, an aromatic diecide halide, or a mixture thereof.
8. 8. The method according to claim 7, wherein the aromatic dianhydride includes pyromellitic dianhydride, benzophenone tetracarboxylic acid dianhydride, 3,3'4,4'-biphenyltetracarboxylic acid dianhydride, 4,4' - (hexafluoroisopropylidene) diphthalic anhydride, 4,4'-oxydiphthalic anhydride, 2,3,6,7-naphthalene tetracarboxylic dianhydride and 3,3',4; A method for producing para-aramid fibers using at least one selected from the group consisting of 4'-diphenylsulfonetetracarboxylic acid dianhydride.
9. The method of claim 7, wherein the aromatic diamine is p-phenylenediamine, 4,4'-oxydianiline, 4,4'-diaminobiphenyl, 2,6-naphthalenediamine, 1,5-naphthalenediamine and A method of producing para-aramid fibers using at least one selected from the group consisting of 4,4'-diaminobenzanilide.
10. 8. The method according to claim 7, wherein the aromatic diecide halide is terephthaloyl dichloride, [1,1'-biphenyl]-4,4'-dicarbonyl dichloride, 4,4'-oxybis(benzoyl chloride) ), using at least one selected from the group consisting of naphthalene-2,6-dicarbonyl dichloride and naphthalene-1,5-dicarbonyl dichloride, para-aramid fiber manufacturing method.
11. According to claim 1, wherein the treating with the crosslinking agent is a dipping method in which a filament having surface irregularities is immersed in a solution containing a crosslinking agent and then taken out, or a spray method in which a solution containing a crosslinking agent is sprayed on the filament having surface unevenness. A method for producing para-aramid fibers, which is carried out by
12. The method of claim 11 , wherein the solution containing the crosslinking agent contains 1 to 20% by weight of the crosslinking agent based on the total weight of the crosslinking agent solution.
13. 12. The method of claim 11, wherein in the step of treating with the crosslinking agent, the solution containing the crosslinking agent is maintained at a temperature of 30 to 70 °C.
14. a monofilament formed of an aromatic polyamide polymer;

    wherein the monofilament has a surface roughness of greater than 0.1 μm;

    Para-aramid fiber, wherein said at least two or more monofilaments are connected via cross-linking.
15. 15. The para-aramid fiber according to claim 14, wherein the monofilament has a surface roughness of greater than 0.1 μm and less than or equal to 1.0 μm.
16. 15. The para-aramid fiber of claim 14, wherein the monofilament has a fineness of 1.0 to 2.5 de.
17. 15. The para-aramid fiber of claim 14, wherein the para-aramid fiber comprises a plurality of monofilaments and has a total fineness of 600 to 10,000 de.