HIGHLY ELASTIC COPOLYMERIZED ARAMID FIBERS

TECHNICAL FIELD

The preset invention relates to a highly elastic copolymerized aramid fiber, and more particularly, to a highly elastic copolymerized aramid fiber which includes aramid copolymers containing an aromatic group substituted with a cyano group (—CN), so as ensure appropriately controlled crystallinity, crystal size and orientation angle of fibers by heat treatment, thereby accomplishing high elastic modulus even without a reduction of strength.

BACKGROUND ART

Aramid fibers generally include para-aramid fibers and meta-aramid fibers. Among those, the para-aramid fiber has excellent characteristics such as high strength, high elasticity and low shrinkage. In particular, even a very fine thread having a thickness of about 5 mm has a remarkable strength enough to lift a 2-ton vehicle, therefore, is widely used for bullet-proofing, as well as in a variety of applications in advanced industries of an aerospace field.

As shown in FIG. 1, the aramid fiber is generally produced by a process including: (i) spinning an aramid spinning dope through a spinneret 20; (ii) passing the spun aramid fiber through a coagulation tank 30 and a coagulation tube 40 into which a coagulant solution is injected in this order to coagulate the fiber; (iii) passing the coagulated aramid fiber through at least one washing roller 50 in this order, as shown in FIG. 4, while injecting a washing solution to the aramid fiber that passes over the washing roller 50 through washing solution injection nozzles 90 provided on an outside of top ends of the washing rollers 50, so as to wash the aramid fiber; and (iv) drying the washed aramid by means of a dryer 70 and then winding the same around a winding roller 80 in this order.

Herein, an example of a process for preparing the aramid spinning dope described above has been disclosed in Korean Patent Registration No. 10-0910537, wherein a mixture solution is prepared by dissolving aromatic diamine such as para-phenylenediamine in an organic solvent including an inorganic salt added thereto, aromatic diacid halide such as terephthaloyl dichloride is added to the mixture solution, followed by reacting the same to prepare an aramid polymer, and then, the prepared aramid polymer is dissolved in sulfuric acid to prepare a spinning dope.

The organic solvent described above may include, for example, N-methyl-2-pyrrolidone (NMP), N,N′-dimethylacetamide (DMAc), hexamethylphosphoamide (HMPA), N,N,N′,N′-tetramethylurea (TMU), N,N-dimethylformamide (DMF) or a mixture thereof. The inorganic salt described above may include, for example, CaCl₂, LiCl, NaCl, KCl, LiBr, KBr, or a mixture thereof.

The aromatic diamine may include, for example, para-phenylenediamine, 4,4′-diaminobiphenyl, 2,6-naphthalenediamine, 1,5-naphthalenediamine, or 4,4′-diaminobenzanilide.

The aromatic diacid halide may include, for example, terephthaloyl dichloride, 4,4′-benzoyldichloride, 2,6-naphthalene dicarboxylic acid dichloride or 1,5-naphthalene dicarboxylic acid dichloride.

The aramid polymer may include, for example, para-phenylene terephthalamide, poly(4,4′-benzanilide terephthalamide), poly(para-phenylene-4,4′-biphenylene-dicarboxylic acid amide) or poly(para-phenylene-2,6-naphthalene dicarboxylic acid amide), according to types of the used aromatic diamine and aromatic diacid halide.

Another example of the method for preparing the aramid spinning dope has been disclosed in Korean Patent Registration No. 10-171994, wherein a spinning dope including a copolymerized aramid polymer containing an aromatic group substituted with a cyano group (—CN) is prepared by adding terephthaloyl dichloride to an organic solvent in which paraphenylenediamine and cyano-para-phenylenediamine are dissolved, followed by reacting the same. In such a case, even without a process of dissolving the copolymerized aramid polymer in sulfuric acid, the spinning dope could be advantageously prepared.

The aramid fibers produced by the above processes entailed some problems such as low aramid fiber elastic modulus of less than 1,100 g/D and significant decrease in strength and elongation at heat treatment, since the organic solvent remaining in the fibers has a concentration exceeding 100 ppm or a crystallinity, crystal size and orientation angle of the fiber are not properly controlled by the heat treatment.

DISCLOSURE
Technical Problem

An object of the present invention is to provide a highly elastic copolymerized aramid fiber, which includes aramid copolymers containing an aromatic group substituted with a cyano group (—CN), so as to have excellent elastic modulus of 1,100 to 1,300 g/d and elongation of 1 to 4% while maintaining a strength of 17 to 30 g/d.

Technical Solution

In order to accomplish the above object, the present invention includes characteristics of: more uniformly and effectively washing aramid fibers to allow a content of organic solvent remaining in the aramid fibers to be less than 100 ppm; and improving elasticity of the aramid fiber even without decreasing a strength thereof while properly controlling a crystallinity, crystal size and orientation of the aramid fiber through heat treatment.

Advantageous Effects

According to the present invention, the content of the solvent remaining in the fiber is small in a range of less than 100 ppm, and the crystallinity, crystal size and orientation angle of the fiber are properly controlled by the heat treatment. Therefore, the elastic modulus is greatly improved even without a decrease in the strength, as compared to the conventional aramid fibers.

The present invention is useful as a raw material for various products requiring high elasticity as well as high strength of the aramid fiber.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of a process for preparing aramid fibers.

FIG. 2 is a cross-sectional view of a washing roller used in an embodiment of the present invention.

FIG. 3 is a process schematic view illustrating a washing process of the aramid fibers using the washing roller shown in FIG. 2 according to the present invention.

FIG. 4 is a schematic view illustrating a washing process of aramid fibers according to a conventional method.

BEST MODE

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

A highly elastic copolymerized aramid fiber according to the present invention includes aramid copolymers which contain an aromatic group substituted with a cyano group (—CN), so as to have an elastic modulus of 1,100 to 1,300 g/d, a strength of 17 to 30 g/d and an elongation of 1 to 4%.

The present invention provides a highly elastic copolymerized aramid fiber, which includes aramid copolymers containing an aromatic group substituted with a cyano group (—CN), so as to have an elastic modulus of 1,100 to 1,300 g/d, a strength of 17 to 30 g/d, a crystallinity of 60 to 80%, a crystal size of 100 to 200 Å (200 faces) and 100 to 170 Å (110 faces), an orientation angle (200 faces) of 2 to 9°.

The aramid copolymer containing the aromatic group substituted with a cyano group (—CN) has a repeat unit represented by Formula I below:

—(NH-A-NH CO—Ar—CO)— [Formula I]

(wherein Ar is an aromatic group represented by Formula II below, and A is an aromatic group represented by Formula III below or an aromatic group having a ratio of the aromatic group of Formula II below to the aromatic group of Formula III below in a range of 1:9 to 9:1)

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Different physical properties of the highly elastic copolymerized aramid fiber according to the present invention have been assessed by means of the following methods.

Crystallinity (%)

Using a diffraction pattern obtained by X-ray analysis, a ratio of crystal peaks to amorphous peaks was estimated to thus determine the crystallinity.

Crystal size (Å)

Using a diffraction pattern obtained by X-ray analysis, a full width at half maximum (FWHM) to thus calculate the crystal size using Scherrer equation.

Strength (g/d), Elongation (%) and Elastic Modulus (g/d)

Elongation physical properties of the aramid fiber were determined according to ASTM D885 test method. In particular, the physical properties of the fiber were determined by stretching a copolymerized aramid fiber having a length of 25 cm by means of Instron tester (Instron Engineering Corp., Canton, Mass.) until it is broken.

Herein, an elongation velocity was set to be 300 mm/min and an initial load was set to be fineness×1/30 g. After testing five samples, an average of the tested results was estimated. The elastic modulus, strength and elongation were estimated from a gradient on a strength-stretch curve (S-S curve), a maximum load at breaking and a length at breaking, respectively.

Orientation Angle

After azimuthal scanning at a site of each face of the diffraction pattern obtained by X-ray analysis, the full width at half maximum (FWHM) of each peak was measured to determine the orientation angle.

Next, an example of the method for fabricating a highly elastic copolymerized aramid fiber of the present invention will be described.

However, the following example of the above method is proposed as a preferred embodiment to fabricate the highly elastic copolymerized aramid fiber of the present invention, and it is duly not construed that the scope of the present invention is particularly limited to this example.

First, the present invention conducts a process of preparing a spinning dope for fabrication of aramid fibers. More particularly, after adding inorganic salt to an organic solvent to prepare a polymerization solvent, para-phenylenediamine and cyano-para-phenylenediamine may be dissolved together or cyano-para-phenylenediamine may be dissolved alone in the organic solvent to prepare a mixture solution. After then, a small amount of terephthaloyl dichloride is added to the mixture solution while stirring the same to conduct primary polymerization, thereby forming a prepolymer.

Then, terephthaloyl dichloride is further added to the polymerization solvent to conduct secondary polymerization, so as to prepare a spinning dope for preparing aramid, in which the copolymerized aramid copolymers which contain an aromatic group substituted with a cyano group (—CN) is dissolved in an organic solvent.

In this regard, the organic solvent used herein may include, for example, N-methyl-2-pyrrolidone (NMP), N,N′-dimethylacetamide (DMAc), hexamethylphosphoamide (HMPA), N,N,N′,N′-tetramethylurea (TMU), N,N-dimethylformamide (DMF) or a mixture thereof. The inorganic salt used herein may include, for example, CaCl₂, LiCl, NaCl, KCl, LiBr, KBr, or a mixture thereof.

Next, as shown in FIG. 1, after spinning the spinning dope prepared as described above through a spinneret 20, the spun aramid fiber passes through a coagulation tank 30 and a coagulation tube 40 into which a coagulant solution is injected in this order, the coagulated aramid fiber passes over washing rollers 50 and 60 in this order to wash the fiber, and is subjected to heat treatment in a heater 70 to properly control a crystallinity, crystal size and orientation angle, then the fiber is wound around a winding roller 80, thereby fabricating highly elastic copolymerized aramid fibers.

In this regard, according to an embodiment of the present invention, as shown in FIG. 2, the washing roller 50 includes washing solution injection holes 51 formed in the surface thereof to inject the washing solution by a centrifugal force generated during rotation of the washing roller 50. Further, the washing roller 50 includes a hollow washing solution feeding pipe 52 formed in a form of concentric circle to an outer circumference of the washing roller 50 therein. The washing solution injection holes 51 allow the washing roller 50 communicating with the washing solution feeding pipe 52 to wash the aramid fiber Y so that a content of organic solvent remaining in the aramid fiber Y becomes less than 100 ppm.

In particular, as shown in FIG. 3, when the aramid fiber passes over the washing roller 50, the washing solution contained in the washing solution feeding pipe 52 formed in the washing roller 50 is injected toward the aramid fiber Y by a centrifugal force generated during rotation of the washing roller 50 through the washing solution injection holes 51 formed in the surface of the washing roller 50.

As a result, the injected washing solution may be smoothly penetrated into the aramid fiber Y passing over the washing roller 50, so as to decrease a content of the organic solvent remaining in the aramid fiber Y to less than 100 ppm.

Further, according to an embodiment of the present invention, the washed aramid fiber is heated at a temperature of 250 to 500° C. under a tensile strength of 0.01 to 5 g/d for 0.5 to 20 seconds and a water content during heat treatment is controlled to be 5 to 100%.

Hereinafter, the present invention will be described in more detail by the following examples and comparative examples. However, these examples are proposed for concretely explaining the present invention, while not limiting the scope of the present invention to be protected.

EXAMPLE 1

N-methyl-2-pyrrolidone (NMP) organic solvent including 3 wt. % of CaCl₂was fed in a reactor under a nitrogen atmosphere, and 50 mol % of para-phenylenediamine and 50 mol % of cyano-p-phenylenediamine were dissolved therein to prepare a mixture solution.

Then, 100 mol % of terephthaloyl dichloride was added to the reactor containing the mixture solution, thereby preparing a spinning dope including a copolymerized aramid polymer.

Thereafter, as shown in FIG. 1, after spinning the spinning dope through a spinneret 20, the spun copolymerized aramid fiber was coagulated while passing through a coagulation tank 30 containing water (coagulant solution) at 40° C. and a coagulation tube 40 into which the water (coagulant solution) is injected at 40° C. Next, as shown in FIGS. 2 and 3, a washing process was performed twice in a washing roller 50 wherein: washing solution injection holes 51 are formed in the surface thereof to inject a washing solution by a centrifugal force generated during rotation of the washing roller 50; and a washing solution feeding pipe 52 is formed in a form of concentric circle to an outer circumference of the washing roller 50 in the washing roller 50, and wherein the injection holes 51 communicate with the washing solution feeding pipe 52. Herein, the washing process was conducted such that, while passing the copolymerized aramid fiber, which passed through the coagulation tube 40, over the washing roller 50, water at 50° C. as the washing solution contained in the feeding pipe 52 in the washing roller 50 was injected toward the copolymerized aramid fiber, which passed over the washing roller 50, through the washing solution injection holes 51 formed in the surface of the washing roller 50 by a centrifugal force generated during rotation of the washing roller 50. After then, heat treatment was conducted at 400° C. using a heater 70 under conditions of 10% water content and non-tensile strength for 10 seconds, followed by winding the heated fiber around a winding roller 80 to completely fabricate the copolymerized aramid fiber. Different physical properties of the fabricated copolymerized aramid fiber were measured, and results thereof are shown in Table 1 below.

EXAMPLE 2

N-methyl-2-pyrrolidone (NMP) organic solvent including 3 wt. % of CaCl₂was fed in a reactor under a nitrogen atmosphere, and 100 mol % of cyano-p-phenylenediamine was dissolved therein to prepare a mixture solution.

Then, 100 mol % of terephthaloyl dichloride was added to the reactor containing the mixture solution, thereby preparing a spinning dope including a copolymerized aramid polymer.

Thereafter, as shown in FIG. 1, after spinning the spinning dope through a spinneret 20, the spun copolymerized aramid fiber was coagulated while passing through a coagulation tank 30 containing water (coagulant solution) at 50° C. and a coagulation tube 40 into which the water (coagulant solution) is injected at 50° C. Next, as shown in FIGS. 2 and 3, a washing process was performed twice in a washing roller 50 wherein: washing solution injection holes 51 are formed in the surface thereof to inject a washing solution by a centrifugal force generated during rotation of the washing roller 50; and a washing solution feeding pipe 52 is formed in a form of concentric circle to an outer circumference of the washing roller 50 inside the washing roller 50, and wherein the injection holes 51 communicate with the washing solution feeding pipe 52. Herein, the washing process was conducted such that, while passing the copolymerized aramid fiber, which passed through the coagulation tube 40, over the washing roller 50, water at 60° C. as the washing solution contained in the feeding pipe 52 in the washing roller 50 was injected toward the copolymerized aramid fiber, which passed over the washing roller 50, through the washing solution injection holes 51 formed in the surface of the washing roller 50 by a centrifugal force generated during rotation of the washing roller 50. After then, heat treatment was conducted at 400° C. using a heater 70 under conditions of 10% water content and 0.5 g/d tensile strength for 10 seconds, followed by winding the heated fiber around a winding roller 80 to completely fabricate the copolymerized aramid fiber. Different physical properties of the fabricated copolymerized aramid fiber were measured, and results thereof are shown in Table 1 below.

EXAMPLE 3

Then, 100 mol % of terephthaloyl dichloride was added to the reactor containing the mixture solution, thereby preparing a spinning dope including a copolymerized aramid polymer.

Thereafter, as shown in FIG. 1, after spinning the spinning dope through a spinneret 20, the spun copolymerized aramid fiber was coagulated while passing through a coagulation tank 30 containing water (coagulant solution) at 40° C. and a coagulation tube 40 into which the water (coagulant solution) is injected at 40° C. Next, as shown in FIGS. 2 and 3, a washing process was performed twice in a washing roller 50 wherein: washing solution injection holes 51 are formed in the surface thereof to inject a washing solution by a centrifugal force generated during rotation of the washing roller 50; and a washing solution feeding pipe 52 is formed in a form of concentric circle to an outer circumference of the washing roller 50 inside the washing roller 50, and wherein the injection holes 51 communicate with the washing solution feeding pipe 52. Herein, the washing process was conducted such that, while passing the copolymerized aramid fiber, which passed through the coagulation tube 40, over the washing roller 50, water at 50° C. as the washing solution contained in the feeding pipe 52 in the washing roller 50 was injected toward the copolymerized aramid fiber, which passed over the washing roller 50, through the washing solution injection holes 51 formed in the surface of the washing roller 50 by a centrifugal force generated during rotation of the washing roller 50. After then, heat treatment was conducted at 450° C. using a heater 70 under conditions of 20% water content and non-tensile strength for 15 seconds, followed by winding the heated fiber around a winding roller 80 to completely prepare the copolymerized aramid fiber. Different physical properties of the fabricated copolymerized aramid fiber were measured, and results thereof are shown in Table 1 below.

EXAMPLE 4

Then, 100 mol % of terephthaloyl dichloride was added to the reactor containing the mixture solution, thereby preparing a spinning dope including a copolymerized aramid polymer.

Thereafter, as shown in FIG. 1, after spinning the spinning dope through a spinneret 20, the spun copolymerized aramid fiber was coagulated while passing through a coagulation tank 30 containing water (coagulant solution) at 40° C. and a coagulation tube 40 into which the water (coagulant solution) is injected at 40° C. Next, as shown in FIGS. 2 and 3, a washing process was performed twice in a washing roller 50 wherein: washing solution injection holes 51 are formed in the surface thereof to inject a washing solution by a centrifugal force generated during rotation of the washing roller 50; and a washing solution feeding pipe 52 is formed in a form of concentric circle to an outer circumference of the washing roller 50 inside the washing roller 50, and wherein the injection holes 51 communicate with the washing solution feeding pipe 52. Herein, the washing process was conducted such that, while passing the copolymerized aramid fiber, which passed through the coagulation tube 40, over the washing roller 50, water at 50° C. as the washing solution contained in the feeding pipe 52 in the washing roller 50 was injected toward the copolymerized aramid fiber, which passed over the washing roller 50, through the washing solution injection holes 51 formed in the surface of the washing roller 50 by a centrifugal force generated during rotation of the washing roller 50. After then, heat treatment was conducted at 450° C. using a heater 70 under conditions of 20% water content and non-tensile strength for 15 seconds, followed by winding the heated fiber around a winding roller 80 to completely fabricate the copolymerized aramid fiber. Different physical properties of the fabricated copolymerized aramid fiber were measured, and results thereof are shown in Table 1 below.

COMPARATIVE EXAMPLE 1

Then, 100 mol % of terephthaloyl dichloride was added to the reactor containing the mixture solution, thereby preparing a spinning dope including a copolymerized aramid polymer.

Thereafter, as shown in FIG. 1, after spinning the spinning dope through a spinneret 20, the spun copolymerized aramid fiber was coagulated while passing through a coagulation tank 30 containing a water-soluble solution of 10% N-methyl-2-pyrrolidone (NMP) (coagulant solution) and a coagulation tube 40 into which the 10% N-methyl-2-pyrrolidone (NMP) solution (coagulant solution) is injected. Next, as shown in FIG. 4, a washing process was performed twice in a washing roller 50 such that, while passing the copolymerized aramid fiber, which passed through the coagulation tube 40, over the washing roller 50, water at 15° C. as the washing solution was injected toward the copolymerized aramid fiber, which passed over the washing roller 50, through washing solution injection nozzles 90 provided at the outside of top ends of the washing rollers 50. After then, heat treatment was conducted at 300° C. using a heater 70 under conditions of 50% water content and 10 g/d tensile strength for 30 seconds, followed by winding the heated fiber around a winding roller 80 to completely fabricate the copolymerized aramid fiber. Different physical properties of the fabricated copolymerized aramid fiber were measured, and results thereof are shown in Table 1 below.

COMPARATIVE EXAMPLE 2

Then, 100 mol % of terephthaloyl dichloride was added to the reactor containing the mixture solution, thereby preparing a spinning dope including a copolymerized aramid polymer.

Thereafter, as shown in FIG. 1, after spinning the spinning dope through a spinneret 20, the spun copolymerized aramid fiber was coagulated while passing through a coagulation tank 30 containing a water-soluble solution of 10% N-methyl-2-pyrrolidone (NMP) (coagulant solution) and a coagulation tube 40 into which the 10% N-methyl-2-pyrrolidone (NMP) solution (coagulant solution) is injected. Next, as shown in FIG. 4, a washing process was performed twice in a washing roller 50 such that, while passing the copolymerized aramid fiber, which passed through the coagulation tube 40, over the washing roller 50, water at 15° C. as the washing solution was injected toward the copolymerized aramid fiber, which passed over the washing roller 50, through washing solution injection nozzles 90 provided at the outside of top ends of the washing rollers 50. After then, heat treatment was conducted at 500° C. using a heater 70 under conditions of 50% water content and 10 g/d tensile strength for 30 seconds, followed by winding the heated fiber around a winding roller 80 to completely fabricate the copolymerized aramid fiber. Different physical properties of the fabricated copolymerized aramid fiber were measured, and results thereof are shown in Table 1 below.

TABLE 1

Comparative
Comparative

Section
Example 1
Example 2
Example 3
Example 4
Example 1
Example 2

Elastic modulus
1,200
1,250
1,110
1,300
900
1,250

Strength (g/d)
24
22
18
30
20
15

Elongation (%)
2.2
3.4
1.2
3.9
4.8
4.5

Orientation angle
4°
6°
2°
9°
10°
5°

(200 faces)

Crystallinity (%)
65
78
68
75
57
75

Crystal
(200
130
190
110
160
90
180

size
faces)

(Å)
(110
125
165
100
155
82
160

faces)

DESCRIPTION OF REFERENCE NUMERALS

10: Extruder, 20: Spinneret

30: Coagulation tank, 40: Coagulation tube

41: Coagulant solution injection hole, Y: Aramid fiber

50: Washing roller, 70: Heater

80: Winding roller, 90: Washing solution injection nozzle

J: Washing solution injected toward aramid fiber

51: Washing solution injection hole, 52: Washing solution feeding pipe

INDUSTRIAL APPLICABILITY

The present invention is useful as a material for various products requiring high elasticity as well as high strength of aramid fibers such as bulletproof materials.

HIGHLY ELASTIC COPOLYMERIZED ARAMID FIBERS

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