US20150376816A1

US20150376816A1 - Apparatus for producing pitch-based chopped carbon fiber and producing method of the chopped fiber

Info

Publication number: US20150376816A1
Application number: US14/736,721
Authority: US
Inventors: Kwang-Eui YOON; Hyun-chul Lee; Hag-Cheon KIM
Original assignee: OCI Co Ltd
Current assignee: OCI Holdings Co Ltd
Priority date: 2014-06-26
Filing date: 2015-06-11
Publication date: 2015-12-31
Also published as: KR101592714B1; CN105274655A; JP2016008372A; KR20160001776A

Abstract

The present invention relates to an apparatus for producing a pitch-based chopped carbon fiber and a producing method for the chopped fiber and, more specifically, to an apparatus and a method for drawing an ejected pitch using melt spinning and producing carbon fibers as chopped fibers in a continuous manner.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No. 10-2014-0078927, filed on Jun. 26, 2014 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

BACKGROUND

In a general manufacturing method of a carbon fiber, polyacrylonitrile, a petroleum- or coal-based pitch (isotropic or anisotropic), a phenol resin, etc., which is a starting material of the carbon fiber, is thermally melted, and then melt spinning or melt blown spinning is performed, or the thermally melted result dissolves in a solvent and then undergoes solution spinning to obtain an organic fiber which is a precursor of the carbon fiber. More particularly, for the pitch-based carbon fiber, a melt spinning method for drawing an ejected pitch using a rotational force, centrifugal spinning for spinning the pitch using a high speed rotational force, or melt blown spinning for spraying a high speed hot blast to draw the pitch is used.
The pitch-based carbon fiber is classified as anisotropic (mesophase) and isotropic according to an optical state of the pitch. It is known to be essential to use an anisotropic pitch in order to product a high-performance (high strength and/or high elasticity) carbon fiber based on a pitch. Although the carbon fiber produced from PAN or the anisotropic pitch has preferable property of matter, however, it is expensive, therefore there have been efforts for developing a method to utilize relatively cheap isotropic pitch.
It is known that the pitch with no anisotropic property, that is, isotropic pitch cannot produce a high-performance carbon fiber, which means that only the carbon fiber at a general grade can be obtained. As described above, the pitch-based carbon fiber can be produced by melt spinning or melt blown spinning, while the anisotropic pitch-based carbon fiber is mainly prepared by using melt spinning. In the meantime, since the isotropic pitch has a brittle property, which makes it hard to form a long fiber from the isotropic pitch, the isotropic pitch is spun by melt blown spinning or centrifugal spinning rather than melt spinning. In particular, in the melt blown spinning, the spun fiber is collected on a non-woven fabric, which simplifies a process and extremely reduces a fiber diameter, and, during a conveying process of the fabric, it is not necessary to wind the pitch fiber, which improves productivity and lowers a production cost, and, therefore, the melt blown spinning is mainly used as a spinning method for the isotropic pitch-based carbon fiber.
However, since, while producing the pitch-based carbon fiber by melt blown spinning, the precursor pitch ejected from a spinning nozzle is drawn into air, the drawing property is not as uniform as the melt spinning which draws using a rotational force of the roll and the diameter control of the carbon fiber produced by melt blown spinning cannot be performed uniformly, and, as a result, the produced carbon fiber has a wide diameter distribution and it is extremely difficult to align the spun carbon fibers to be oriented in one direction.
Meanwhile, a infusibilization process in the carbon fiber producing process needs for transforming a theremoplastic fiber into a thermosetting fiber and the infusibilization process oxidizes the fiber from a surface in order to prevent fusion or melting of the fiber during a subsequent high temperature carbonization or graphitization process, and it requires the longest time and affects the strength of the carbon fiber based on the a infusibilization state.
Here, the pitch fiber produce d by using melt blown spinning has different oxygen contents for respective fibers in the subsequent infusibilization process, and this causes the property of matter of the final carbon fiber to be non-uniform, and, since orientations of molecules are random due to the non-uniform drawing, it is shown that the mechanical property of the final carbon fiber is lower by 20-30% than fiber produced by melt spinning.
A conventional method of producing a high-performance carbon fiber by using a isotropic pitch which has a specific reflectance as a raw material is described in Korean Patent Application No. 10-1984-0002038. However, this method has drawbacks that it has low production yield.
Also, Korean Patent Application No. 10-1987-0011290 discloses a method of producing a carbon fiber whose inner portion has an average size of a particle greater by at least 10% than that of an outer surface portion by spinning a carbonaceous pitch composed of anisotropic components, positioning the carbonaceous pitch fiber in an oxidizing atmosphere oxidizing atmosphere, oxidizing only the outer surface portion, selectively infusibilizing the outer surface portion of the carbonaceous pitch fiber, and then carbonizing and sintering the result. However, this method only focuses on preventing welding and increasing elasticity of a fiber by selectively infusibilizing only the outer surface portion of the carbonaceous pitch fiber.
Although, when producing a high strength and high electricity carbon fiber using a anisotropic pitch, it is possible to increase the strength of the fiber by applying a tension in a infusibilization process to arrange molecular structures in one axial direction, since the isotropic pitch is produced by melt blown spinning, it is difficult to produce a continuous carbon fiber and to apply the tension. Therefore, while infusibilizing the carbon fiber in a chopped fiber state, a temperature gradient incurs partial fusion and melting between fabrics due to an exothermic reaction, which makes it difficult to produce the carbon fiber.

SUMMARY OF THE INVENTION

The isotropic pitch-based carbon fiber which is produced by the prior art has drawbacks that its molecular structures are randomly distributed and it has low strength and is easy to break, which makes it hard to produce a carbon fiber in continuous way. Therefore, the carbon fiber is typically produced using melt blown spinning as a chopped fiber in a non-woven fabric shape. Thus, the carbon fiber produced by the prior art has drawbacks that its application is restricted due to its general purpose grade and it cannot be used for a structure requiring a strength of about 1.5 GPa.
Therefore, the present invention has an objective to provide a method of producing a pitch-based chopped carbon fiber and a producing method for the chopped fiber which adopt melt spinning instead of melt blown spinning in order to solve the problem about non-uniformity occurring when the carbon fiber is produced from an isotropic pitch using melt blown spinning described as above.
That is, an objective of the present invention is to provide an apparatus for drawing an ejected isotropic pitch using melt spinning and continuously producing a high strength carbon fiber as a chopped fiber.
Also, another objective of the present invention is to provide a method for drawing an ejected isotropic pitch using melt spinning and continuously producing a high strength carbon fiber as a chopped fiber.
In order to accomplish the technical problem as above, according to another aspect of the present invention, there can be provided an apparatus for producing a pitch-based chopped carbon fiber comprising: a pitch fiber spinning unit including a pitch injecting unit for injecting a molten pitch into a spinning nozzle and at least one spinning nozzle for ejecting the injected molten pitch in a fiber shape; at least one rotation roll unit which is located under the pitch fiber spinning unit, wherein the pitch fiber, which is ejected from the pitch fiber spinning unit, is wound on the rotation roll unit; at least one cutting unit for cutting the pitch fiber wound on the rotation roll unit; and a conveying unit which transfers the pitch-based chopped carbon fiber, which is formed by being cut by the cutting unit, in one direction.
In one embodiment, the pitch fiber can be spun as a plurality of fibers from the at least one spinning nozzle.
In another embodiment, the apparatus for producing a pitch-based chopped carbon fiber can further comprise a collecting unit which is located between the pitch fiber spinning unit and the rotation roll unit and collects the pitch fiber spun as a plurality of fibers. According to the embodiment, the pitch fiber is supplied to the rotation roll unit in bundles.
In one embodiment, the rotation roll unit is located to move left and right in its parallel direction, and a position where the pitch fiber is wound on the rotation roll unit can be moved left or right by the movement of the rotation roll unit.
In one embodiment, the rotation roll unit is located under the pitch fiber spinning unit and includes a first rotation roll unit on which the pitch fiber ejected from the pitch fiber spinning unit is wound, and a second rotation roll unit which draws the pitch fiber which passed through the first rotation roll unit, wherein the first rotation roll unit is stationary, and the second rotation roll unit can be provided to move left and right in its parallel direction.
In one embodiment, the cutting unit can include a first cutting unit and a second cutting unit which are located at a left side and a right side of the rotation roll unit, respectively.
In one embodiment, the pitch-based chopped carbon fibers which are formed by being cut by the cutting unit can be arranged in the same direction on the conveying unit.
According to another aspect of the present invention, there can be provided a method of producing a pitch-based chopped carbon fiber comprising: (a) injecting a molten pitch to a pitch fiber spinning unit; (b) ejecting the molten pitch from the the pitch fiber spinning unit to spin a pitch fiber; (c) winding the pitch fiber which is spun in step (b) on a rotation roll to draw the pitch fiber; (d) cutting the pitch fiber which is wound on the rotation roll; and (e) infusibilizing the cut pitch fiber.
In one embodiment, the molten pitch can be at least one selected from a petroleum-based pitch, coal-based pitch, and a chemical-based pitch, and can preferably be an isotropic pitch.
In one embodiment, a infusibilization temperature in step (e) can be 150-400° C.
In one embodiment, the method can further comprise a step for infusibilizing the pitch fiber which is wound on the rotation roll before performing the cutting of step (d). the infusibilization temperature according to the embodiment is preferably 150-280° C.
In one embodiment, the non-embodiment can be performed in an atmosphere where an oxidizing gas is mixed.
In one embodiment, the pitch fibers which are cut in step (d) can be arranged in the same direction.
The method of producing the pitch for carbon fiber according to the present invention has the following effects.
According to an embodiment of the present invention, an isotropic isotropic pitch is maximally drawn by a rotation force of the roll, thereby maximizing mechanical strength of a pitch precursor.
Also, according to an embodiment of the present invention, a pitch fiber which is being spun can be cut in a chopped state, thereby resolving a fiber breakage problem.
Furthermore, according to an embodiment of the present invention, the pitch fiber which is being spun can be arranged in one direction without using separate additional processes, and be transformed into a carbon fiber with excellent strength through a non-embodiment process and/or a carbonization process.
By adopting the effects as above, the carbon fiber using an isotropic pitch as a raw material can obtain competitiveness by replacing a high cost PAN or an anisotropic pitch-based carbon fiber.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:

FIG. 1 shows a cross-sectional view of an apparatus for producing a pitch-based chopped carbon fiber according to an embodiment of the present invention;

FIG. 2 shows a perspective view of an apparatus for producing a pitch-based chopped carbon fiber according to an embodiment of the present invention;

FIG. 3 shows a perspective view of the apparatus for producing a pitch-based chopped carbon fiber according to another embodiment of the present invention; and

FIG. 4 schematically shows variation in a position where the pitch fiber is wound on the rotation roll unit and a position where the pitch fiber is cut by the movement of the rotation roll unit.

DETAILED DESCRIPTION OF THE INVENTION

In order to ease understanding of the present invention, specific terms and expediently defined in the present application. Unless defined to the contrary, scientific terms and technical terms used in the present invention have meanings which are generally understood by those of ordinary skill in the art to which the present invention pertains. Also, unless specifically specified in the context, a term in a singular form is to be understood to include its plural forms while a term in a plural form is to be understood to include its singular form.
Although terms including an ordinal number such as first, second, etc. can be used to describe various components, the components are not restricted by those terms. These terms are used only to discriminate one component from another.
Hereinafter, an apparatus for producing a pitch-based chopped carbon fiber according to an embodiment of the present invention is described by referring to the appended drawings.
According to another aspect of the present invention, there can be provided an apparatus for producing a pitch-based chopped carbon fiber comprising: a pitch fiber spinning unit 10 including a pitch injecting unit 11 for injecting a molten pitch into a spinning nozzle and at least one spinning nozzle 12 for ejecting the injected molten pitch in a fiber shape; at least one rotation roll unit 14 which is located under the pitch fiber spinning unit 10 and draws the pitch fiber 13 which is ejected from the pitch fiber spinning unit 10; at least one cutting unit 15 for cutting the pitch fiber 13 wound on the rotation roll unit 14; and a conveying unit 16 which transfers the pitch-based chopped carbon fiber, which is formed by being cut by the cutting unit in one direction (refer to FIG. 1).
The apparatus for producing the pitch-based chopped carbon fiber according to the present invention is an apparatus to which melt spinning is applied, and the ejected pitch is drawn not by high speed hot blast but by a rotational force of the roll, and the apparatus can produce the pitch-based chopped carbon fiber irrespective of optical state (isotropic and/or anisotropic) of the pitch. Preferably, since the spun fiber has a brittle property, which makes it hard to form a long fiber from the spun fiber, the pitch-based chopped carbon fiber can be produced by using the isotropic pitch which is mainly spun by melt blown spinning or centrifugal spinning rather than melt spinning.
Here, the pitch fiber spinning unit known to the field to which the present invention pertains can be applied as the pitch fiber spinning unit 10 including a pitch injecting unit 11 for injecting a molten pitch into a spinning nozzle and at least one spinning nozzle 12 for ejecting the injected molten pitch as a fiber.
Also, when there are a plurality of spinning nozzles 12, the pitch fiber 13 can be spun from the spinning nozzles 12 as a plurality of fibers (refer to FIG. 2).
For example, a spinneret unit disclosed in Korean Patent Registration No. 10-1279890 entitled “APPARATUS FOR MANUFACTURING CURVED ISOTROPIC PITCH-BASED CARBON FIBERS AND METHOD FOR MANUFACTURING FIBER MAT USING THE SAME” can be applied as the spinning pitch fiber spinning unit 10 according to the present invention, and it is reasonable to regard that the configuration corresponding to melt blown spinning is not applied because melt blown spinning is applied for drawing the ejected pitch using a high speed hot blast in the spinneret unit disclosed in No. 10-1279890.
In another embodiment, the apparatus for producing a chopped carbon fiber according to an embodiment of the present invention can further comprise a collecting unit 18 which is located between the pitch fiber spinning unit 10 and the rotation roll unit 14 and collects the pitch fiber 13 spun as a plurality of fibers (refer to FIG. 3).
The pitch fibers which are spun as a plurality of fibers from a plurality of spinning nozzles 12 by the collecting unit 18 can be collected in bundles and wound on the rotation roll unit 14 in bundles. Also, a collecting agent supply unit (not shown) for supplying a collecting agent for collecting the pitch fibers as a plurality of fibers in bundles can be further provided on the collecting unit 18.
The apparatus for producing a pitch-based chopped carbon fiber according to the present invention comprises at least one rotation roll unit 14 which is located under the pitch fiber spinning unit 10 and draws the pitch fiber 13 which is ejected from the pitch fiber spinning unit 10. Here, there can be one or more rotation roll units 14, and rotation speeds of the rotation roll units 14 can be different from one another.
The rotation roll unit 14 can wind the pitch fiber 13 ejected from the the pitch fiber spinning unit 10 at a constant winding speed, and the pitch fiber 13 is characterized in that it is drawn at a constant drawing rate. The rotation speed of the rotation roll unit 14 can be adjusted to enable the pitch fiber to have a desired diameter, and is preferably adjusted such that the pitch fiber can be maximally drawn without causing breakage.
The rotation roll unit 14 winds the pitch fiber 13 ejected from the spinning pitch fiber spinning unit 10 at a constant speed, and a tension (rotational force) applied to the pitch fiber 13 can be adjusted by the rotation speed of the rotation roll unit 14 where the pitch fiber 13 is wound.
In one embodiment, the rotation roll unit 14 is provided to be moved left and right in its horizontal direction, and a position where the pitch fiber 13 spun from the spinning pitch fiber spinning unit 10 is wound on the rotation roll unit 14 can be changed by the movement of the rotation roll unit 14.
That is, the rotation roll unit 14 is located to move left and right in its parallel direction, and a position where the pitch fiber 13 is wound on the rotation roll unit 14 can be moved left or right by the movement of the rotation roll unit 14. More particularly, when the rotation roll unit 14 is moved left, the position where the pitch fiber 13 is wound on the rotation roll unit 14 is moved right while when the rotation roll unit 14 is moved right, the position where the pitch fiber 13 is wound on the rotation roll unit 14 is moved left (refer to FIG. 4).
In another embodiment, the rotation roll unit 14 is located under the pitch fiber spinning unit and includes a first rotation roll unit on which the pitch fiber 13 ejected from the pitch fiber spinning unit 10 is wound, and a second rotation roll unit which draws the pitch fiber which passed through the first rotation roll unit, wherein the first rotation roll unit is stationary (that is, its left-right movement in a horizontal direction is not possible), and the second rotation roll unit can be provided to move left and right in its parallel direction.
When the second rotation roll unit moves, a position where the pitch fiber 13, which has passed the first rotation roll unit, is wound on the second rotation roll unit can be configured to be moved left or right.
It is possible to adjust the left-right movement of the rotation roll unit 14 such that the pitch fibers 13 wound on the rotation roll unit 14 are not excessively overlapped, and it is also possible to enable the pitch fiber 13 wound on the rotation roll unit 14 to be cut in a constant length by the cutting unit 15.
Also, in another embodiment, the rotation roll unit 14 can further comprise a heating means, wherein the heating means is characterized in heating the rotation roll unit 14 to a temperature selected from a range of 150-280° C.
That is, before the pitch fiber 13 is cut to be separated from the rotation roll unit 14, a first non-embodiment step can be performed by the rotation roll unit 14 heated by the heating means under the temperature condition which does not soften or deform the pitch fiber 13 which is melt-spun from the pitch fiber spinning unit 10.
In one embodiment, a constant amount of pitch fiber 13 is wound by the rotation of the rotation roll unit 14, and in the meantime, at least one cutting unit 15 for cutting the pitch fiber 13 can be provided on the rotation roll unit 14.
That is, one cutting unit 15 can be provided on the rotation roll unit 14, or a first cutting unit 21 and a second cutting unit 22 can be provided at a left side and a right side of the rotation roll unit 14, respectively. Here, the first cutting unit 21 and the second cutting unit 22 are preferably provided to be apart from each other.
Also, a plurality of cutting units can be provided on the rotation roll unit 14, and the present invention is not restricted to the number of the cutting units. Similarly to the case with two cutting units, the cutting units are preferably provided to be apart from one another.
The cutting units are provided to be apart from one another in order to prevent the position where the pitch fiber 13 is wound on the rotation roll unit 14 from being cut by the cutting units.
When the position where the pitch fiber 13 is wound on the rotation roll unit 14 moves right as the rotation roll unit 14 moves left, the first cutting unit 21 cuts the pitch fiber 19 from a left end of the rotation roll unit 14 to the position where the pitch fiber 13 is wound on the rotation roll unit 14.
When the position where the pitch fiber 13 is wound on the rotation roll unit 14 moves left as the rotation roll unit 14 moves right, the first cutting unit 22 cuts the pitch fiber 20 from a right end of the rotation roll unit 14 to the position 20 where the pitch fiber 13 is wound on the rotation roll unit 14.
In the meantime, it is preferred that the position where the pitch fiber 13 is wound on the rotation roll unit 14 is not cut by the first cutting unit 21 and the second cutting unit 22.
The cutting unit 15 can be provided to be movable from the rotation roll unit 14. Thus, when the pitch fiber 13 is wound at a constant speed on the rotation roll unit 14, the cutting unit 15 is spaced apart from the rotation roll unit 14, and when the pitch fiber 13 wound on the rotation roll unit 14 is cut into chopped fibers 17 with a constant length, the cutting unit 15 is moved to the rotation roll unit 14.
Since the fiber which is spun by using an isotropic pitch as a raw material is brittle and, thus, is difficult to be made as a long fiber differently from the fiber made by using an anisotropic pitch, the cutting unit 15 can be controlled to cut the pitch fiber 13 before the pitch fiber 13 wound on the rotation roll unit 14 is broken.
After the pitch fiber 13 wound on the rotation roll unit 14 is cut by the cutting unit 15, the chopped fiber 17 which is separated from the rotation roll unit 14 can be collected on a conveying means 16 such as a conveyor belt, and in the meantime, the chopped fibers 17 are characterized in being arranged in the same direction on the conveyor belt 16. The directional property of the chopped fiber as above can increase strength of a carbon complex, for example carbon fiber reinforcement plastic.
The chopped fibers 17 which are separated from the rotation roll unit 14 and arranged in the same direction on the conveyor belt 16 are successively moved in a transfer direction of the conveyor belt 16, and a second non-embodiment process can be performed in a infusibilizing oven providing a infusibilization temperature of 150-400° C., preferably 170-360° C. Also, the chopped fiber which is infusibilized in the infusibilizing oven can be successively carbonized in a carbonization furnace.
According to another aspect of the present invention, there can be provided a method of producing a pitch-based chopped carbon fiber comprising: (a) injecting a molten pitch to a pitch fiber spinning unit; (b) ejecting the molten pitch from the the pitch fiber spinning unit to spin a pitch fiber; (c) winding the pitch fiber which is spun in step (b) on a rotation roll to draw the pitch fiber; (d) cutting the pitch fiber which is wound on the rotation roll; and (e) infusibilizing the cut pitch fiber.
In one embodiment, the molten pitch is preferably an isotropic pitch according to the objective of the present invention. Here, the isotropic pitch can include at least one selected from a petroleum-based pitch, a coal-based pitch and a chemical-based pitch.
In the meantime, the petroleum-based pitch includes various residues of various oil distillates for example atmospheric distillation residues, vacuum distillation residues, and catalytic cracking residues, and the coal-based pitch is coal tar produced by drying distillation on coals and can use, α-bitumen, β-bitumen, and chemical tar. Also, the chemical-based pitch includes residues produced by pyrolysis of polyolefin such as polyethylene and polypropylene and a polymerization material such as polyvinyl chloride.
More preferably, a coal-based coal tar pitch can be used as the isotropic pitch, and even more preferably, a coal-based coal tar pitch with a high softening point, for example a softening point higher than or equal to 250° C. can be used. Also, when the coal-based coal tar pitch is used, content of quinoline insolubles in the pitch is preferably low (substantially no content is favorable).
Typically, a melt spinning temperature is set to be higher than the softening point of a raw material pitch by 30-60° C. The spun pitch fiber can be spun to a tow having a filament bundle consisting of a nanofilament or a plurality of nanofilaments.
The tension (rotational force) applied to the pitch fiber can be adjusted by the rotation speed of the rotation roll where the melt-spun pitch fiber is wound. Also, when there exist a plurality of rotation rolls, rotation speeds of the respective rotation rolls can be different from one another.
In one embodiment, the method can further comprise a step for infusibilizing the pitch fiber which is wound on the rotation roll before performing the cutting of step (d). The infusibilization temperature at this step can be equal to or different from the infusibilization temperature of step (e), but this step is preferably performed under a temperature condition selected from a range of 150-280° C. That is, the non-embodiment step performed before the pitch fiber is cut and separated from the rotation roll is preferably performed under the temperature range where the melt-spun pitch fiber is not softened or deformed.
In one embodiment, the non-embodiment step can be performed by the rotation roll which is heated to the temperature range selected from the aforementioned temperature range. In order the prevent softening or deformation of the pitch fiber wound on the the rotation roll, the infusibilizing time can be adequately selected from a range between 5 minutes and 15 hours, and the non-embodiment step is performed during the infusibilizing time. The infusibilizing time can be adjusted based on the rotation speed of the rotation roll and/or a frequency of the cutting steps.
the pitch fiber which is spun in step (b) is wound on the rotation roll, drawn to a drawing ratio which maintains a maximum drawing state is maintained, cut in a constant chopped shape to have a predicted length by the cutting means (for example, cutter, etc.), and then separated from the rotation roll.
The chopped fiber which is separated from the rotation roll can be collected on the conveying means such as a conveyor belt, and, here, the chopped fibers are characterized in being arranged in the same direction on the conveyor belt. The directional property of the chopped fiber as above can increase strength of a carbon complex, for example carbon fiber reinforcement plastic.
The chopped fibers 17 which are separated from the rotation roll and arranged in the same direction on the conveyor belt are successively moved in a transfer direction of the conveyor belt, and can be infusibilized in a infusibilizing oven providing a infusibilization temperature of 150-400° C., preferably 170-360° C.
In the non-embodiment step according to step (e), a plurality of temperature segments can be set, and the infusibilization temperatures for the respective temperature sections can be controlled to be different from one another.
In one embodiment, the non-embodiment can be performed in an atmosphere where an oxidizing gas is mixed. Here, at least one selected from oxygen, ozone, air, nitrogen oxide, halogen, and sulfurous acid gas can be used as the oxidizing gas, and the non-embodiment process can be performed under a concentration of the oxidizing gas of 20-100 vol %.
The method of producing a pitch-based chopped carbon fiber according to the present invention further comprises a step of carbonizing or, as necessary, graphitizing the pitch fiber, which has been infusibilized before performing the cutting by step (e) or, as necessary, step (d), in an inert gas atmosphere.
The carbonization process can be performed for 1-3 minutes at a temperature of 800-1,500° C. When the carbonization process is performed at a temperature lower than 800° C., it is not possible to obtain a carbon fiber having a carbon structure, while when it is performed at a temperature higher than 1,500° C., the pitch fiber is transformed to a graphite fiber other than the carbon fiber, which results in a rise in production cost.
More preferably, the carbonization process can be performed by heating the infusibilized fiber for 1-30 minutes at a temperature of 1,000-1,200° C. A heating rate in the carbonization process is preferably 5-20° C./min, and more preferably the temperature can rise at 10-20° C./min.
Hereinafter, the present invention will be described in more detail using embodiments. Here, these embodiments are provided only to illustrate the present invention, and the scope of the present invention are not to be deemed to be restricted by these embodiments.
Production of Pitch-Based Chopped Carbon Fiber

Embodiment 1

100 wt % isotropic pitch with a softening point of 280° C. was melt-spun and wound with 500 m/min to produce a pitch fiber. The pitch fiber which was spun (melt spun) while wound on the rotation roll was cut in a constant length of 3 cm. The cut fiber (chopped fiber) was heated to a temperature of 260° C. for 1 hour to perform a first non-embodiment process, and then, the chopped fiber, which had undergone the first infusibilized, was processed in a second infusibilization process in a infusibilizing oven at a speed of 1° C./min within a infusibilization temperature of 280-320° C. The chopped fiber, which had undergone the second infusibilization process, was carbonized at a heating rate of 10˜20° C./min for 10 minutes at 1000° C. and finally transformed into a chopped carbon fiber. An average fiber length of the produced carbon fiber was 3 cm, an average diameter was 8 μm, and tensile strength was 1.5 GPa.

Embodiment 2

All conditions are the same Embodiment 1 except that the speed of the rotation roll is 500 m/min. An average fiber length of the produced carbon fiber was 3 cm, an average diameter was 10 μm, and tensile strength was 1.2 GPa.

Embodiment 3

All conditions are the same Embodiment 1 except that the speed of the rotation roll is 500 m/min. An average fiber length of the produced carbon fiber was 6 cm, an average diameter was 10 μm, and tensile strength was 1.2 GPa.

Comparative Example 1

All conditions (used raw material, infusibilization and carbonization conditions) for performing the method of producing a chopped carbon fiber according to the comparative example were the same as those for the embodiments except for a spinning method. That is, while producing the chopped carbon fiber according to the comparative example, hot air (a spray at spinning temperature +10° C., blown speed 4,000˜5,000 m/min) was used.

Evaluation of Property of Matter of Pitch-Based Chopped Carbon Fiber

Average fiber lengths, fiber shapes, directional properties, and tensile strength of the chopped carbon fibers produced by the embodiments and the comparative example are listed in table 1.

TABLE 1

Average	Average
fiber	fiber		Directional	Tensile
length	diameter	Fiber	property of	strength
(cm)	(μm)	shape	fiber	(GPa)

Embodiment 1	3	8	chopped	Single	1.5
			fiber
			(Chopped)
Embodiment 2	3	10	chopped	Single	1.3
			fiber
			(Chopped)
Embodiment 3	6	10	chopped	Single	1.2
			fiber
			(Chopped)
Comparative	Non-	10	Mat	Non-	0.5
example 1	uniform			uniform

Referring to the results listed in Table 1, the embodiments of the present invention are more advantageous in producing a chopped carbon fiber with a desired length than a conventional chopped carbon fiber producing method using melt blown spinning, and it is possible to enable the chopped carbon fibers to have a uniform directional property while being cut. Also, it is acknowledged that even with the same raw material, tensile strength of the chopped carbon fiber according to the present invention is greater by at least two times.
That is, according to an embodiment of the present invention, an isotropic pitch can be maximally drawn by a rotational force of the roll, thereby maximizing mechanical strength of a pitch precursor. Also, the pitch fiber spun according to an embodiment of the present invention is cut in a chopped shape, thereby solving a problem of fiber breakage. Furthermore, according to an embodiment of the present invention, the pitch fibers which are being spun can be arranged in one direction without using separate additional processes, and be transformed into a carbon fiber with excellent strength through a infusibilization process and/or a carbonization process.
While the present invention has been particularly described with reference to an embodiment of the present invention, those of ordinary skill in the to which the present invention pertains can readily modify and alter the present invention in various ways by appending, changing, deleting, or adding components without departing from the spirit of the present invention as defined by the following claims, which are also deemed to fall in the scope of the present invention.

EXPLANATION ON SYMBOLS

- 10: PITCH FIBER SPINNING UNIT
- 11: PITCH INJECTING UNIT
- 12: SPINNING NOZZLE
- 13: PITCH FIBER OR PITCH FIBER BUNDLE
- 14: ROTATION ROLL UNIT
- 15: CUTTING UNIT
- 16: CONVEYOR BELT
- 17: CHOPPED FIBER
- 18: COLLECTING UNIT
- 21: FIRST CUTTING UNIT
- 22: SECOND CUTTING UNIT

Claims

What is claimed is:

1. An apparatus for producing a pitch-based chopped carbon fiber comprising:

a pitch fiber spinning unit including a pitch injecting unit for injecting a molten pitch into a spinning nozzle and at least one spinning nozzle for ejecting the injected molten pitch as a fiber;

at least one rotation roll unit which is located under the pitch fiber spinning unit, wherein the pitch fiber, which is ejected from the pitch fiber spinning unit, is wound on the rotation roll unit;

at least one cutting unit for cutting the pitch fiber wound on the rotation roll unit; and

a conveying unit which transfers the pitch-based chopped carbon fiber, which is formed by being cut by the cutting unit, in one direction.

2. The apparatus for producing a pitch-based chopped carbon fiber according to claim 1, characterized in that:

the pitch fiber is spun as a plurality of fibers from the at least one spinning nozzle.

3. The apparatus for producing a pitch-based chopped carbon fiber according to claim 1, characterized in further comprising:

a collecting unit which is located between the pitch fiber spinning unit and the rotation roll unit and collects the pitch fiber spun as a plurality of fibers.

4. The apparatus for producing a pitch-based chopped carbon fiber according to claim 1, characterized in that:

the rotation roll unit is located to move left and right in a parallel direction thereof, and a position where the pitch fiber is wound on the rotation roll unit is moved left or right by the movement of the rotation roll unit.

5. The apparatus for producing a pitch-based chopped carbon fiber according to claim 4, characterized in that:

the rotation roll unit is located under the pitch fiber spinning unit and includes a first rotation roll unit on which the pitch fiber ejected from the pitch fiber spinning unit is wound, and a second rotation roll unit which draws the pitch fiber which passed through the first rotation roll unit,

wherein the first rotation roll unit is stationary, and the second rotation roll unit is provided to move left and right in a parallel direction thereof.

6. The apparatus for producing a pitch-based chopped carbon fiber according to claim 1, characterized in that:

the cutting unit includes a first cutting unit and a second cutting unit which are located at a left side and a right side of the rotation roll unit, respectively.

7. The apparatus for producing a pitch-based chopped carbon fiber according to claim 1, characterized in that:

the pitch-based chopped carbon fibers which are formed by being cut by the cutting unit are arranged in the same direction on the conveying unit.

8. A method of producing a pitch-based chopped carbon fiber comprising:

(a) injecting a molten pitch to a pitch fiber spinning unit;

(b) ejecting the molten pitch from the the pitch fiber spinning unit to spin a pitch fiber;

(c) winding the pitch fiber which is spun in step (b) on a rotation roll to draw the pitch fiber;

(d) cutting the pitch fiber which is wound on the rotation roll; and

(e) infusibilizing the cut pitch fiber.

9. The method of producing a pitch-based chopped carbon fiber according to claim 8, characterized in that:

the molten pitch is at least one selected from a petroleum-based pitch, coal-based pitch, and a chemical-based pitch.

10. The method of producing a pitch-based chopped carbon fiber according to claim 8, characterized in that:

a infusibilization temperature in step (e) is 150-400° C.

11. The method of producing a pitch-based chopped carbon fiber according to claim 8, characterized further comprising:

a step for infusibilizing the pitch fiber which is wound on the rotation roll before performing the cutting of step (d).

12. The method of producing a pitch-based chopped carbon fiber according to claim 11, characterized in that:

the infusibilization temperature is 150-280° C.

13. The method of producing a pitch-based chopped carbon fiber according to claim 8, characterized in that:

the infusibilization is performed in an atmosphere in which an oxidizing gas is mixed.

14. The method of producing a pitch-based chopped carbon fiber according to claim 8, characterized in that:

the pitch fibers which are cut in step (d) are arranged in the same direction.