KR101417217B1 - Method for preparing carbon fiber precursor - Google Patents

Abstract

The present invention relates to a method for producing precursor fibers for carbon fibers, and more particularly, to a method for producing precursor fibers for producing carbon fibers having excellent tensile strength and compressive strength, using a superdrawing process, To a method of producing precursor fibers of fine denier by a single component spinneret to obtain a high strength and high-elasticity carbon fiber together with shortening of a stabilization time .

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a precursor fiber for carbon fiber,

The present invention relates to a method for producing precursor fibers for carbon fibers, and more particularly, to a method for producing precursor fibers for producing carbon fibers having excellent tensile strength and compressive strength, using a superdrawing process, To a method of producing precursor fibers of fine denier by a single component spinneret to obtain a high strength and high-elasticity carbon fiber together with shortening of a stabilization time .

Carbon fiber can be produced by high-temperature (700 ~ 7 GPa) and high-elasticity (150 ~ 950 GPa) fibers with carbon content of more than 92% and high precursor materials with high carbon yield. Among these precursor materials, acrylonitrile fibers having excellent tensile strength and compressive strength and good tensile elastic modulus are most widely used when making carbon fibers. Acrylonitrile polymer has a lower decomposition temperature than melting temperature and is difficult to melt spinning. Some textile fibers are mass produced by melt spinning using a plasticizer such as water, but most of acrylonitrile fibers for carbon fiber Radiation. The solution-irradiated acrylonitrile fibers are subjected to stretching in hot water (~100 ° C) or multi-step stretching in order to produce high-performance carbon fibers (see also the process diagram in FIG. 1). Generally, when acrylonitrile undrawn yarn is stretched, orientation of molecules occurs and crystallinity increases accordingly.

The acrylonitrile stretch as the precursor fiber is made of carbon fiber through the stabilization process (250 ~ 350 ℃) and the carbonization process (800 ~ 1500 ℃) in the inert atmosphere in the oxidizing atmosphere and optionally the graphitization process (~ 2500 ℃) It is also said. In the stabilization process, cyclization of the PAN molecular structure and binding of oxygen are involved. At this time, oxygen diffusion requires oxygen diffusion into the stabilized PAN fiber, so that the stabilization time increases dramatically depending on the fiber thickness. In the carbonization process, the ladder-like molecular structures formed in the stabilization process are bonded to each other to be deformed into a structure similar to graphite, and the volatilization of elements other than carbon proceeds. The longitudinal shrinkage of the fiber occurs due to physical or chemical causes during the stabilization process and the carbonization process, which causes the molecular orientation of the finally obtained carbon fiber to deteriorate. Therefore, a well-developed carbon fiber longitudinal direction crystal structure can be expected by improving the molecular orientation by applying a tensile force during the stabilization and carbonization process. According to Griffith's flaw theory, as the fiber diameter decreases in the same material, the surface area per unit length becomes smaller and the probability of the defect is lowered and the tensile strength is increased. Therefore, as the diameter of the acrylonitrile precursor fiber is decreased, the tensile per unit area can be increased during the stabilization and carbonization process, so that it is possible to produce carbon fibers of high strength. In order to produce small-diameter precursor fibers, a spinneret having a corresponding fine discharge port is required. In order to produce microfine fibers, two or more polymer polymers are spun together to form a fiber of a desired component in a divided yarn or chemical It is necessary to use an expensive composite radiation facility for separating by a sea shore method.

International patent (WO 2009/049174) manufactures high strength (~ 4.5 GPa) microfine carbon fibers through composite radiation in the form of core-shell or sheath-core or islands-in-a-sea However, there is a problem of cost increase in the process of dissolving or incinerating auxiliary components after spinning as well as expensive spinning equipment.

In addition, U.S. Patent No. 6,428,891 discloses a method for producing carbon fibers in which an acrylonitrile precursor is wet-spun, stretched in a bath drawing and secondarily drawn in a steam drawing, and U.S. Patent No. 6,641,915 discloses an acrylonitrile polymer in a solution A method for producing acrylonitrile fibers for spinning and stretching in a first coagulation bath and for stretching in a second coagulation bath has been proposed in Japanese Patent Application Laid-open No. 64-52811, in which acrylonitrile polymer is spun in solution a method for producing acrylonitrile fiber for a carbon fiber precursor which is stretched in a coagulation bath has been proposed, but it is difficult to control the free fiber cross-sectional area freely while satisfying the mechanical properties as a carbon fiber precursor.

On the other hand, Korean Patent Laid-Open No. 1991-2966 discloses an ultra-stretched polyethylene fiber reinforced composite material composed of an ultra-stretched polyethylene fiber and an elastomer-modified epoxy resin, Patent No. 2006-265788 proposes a method for producing a composite fiber in which fibers prepared by melt spinning have a fiber diameter of 1-10 μm so as to have a fiber diameter of 1 to 10 μm, There is a problem that carbon yield is low for use as a fiber precursor.

As a result of research to solve the problems of the prior art as described above, it has been found out that it is possible to produce precursor fibers for carbon fibers having excellent physical properties when microfine fiber is produced by spinning the fiber and then using the ultra- .

The present invention can produce a carbon fiber having an excellent tensile strength and a tensile elastic modulus by thinning the fiber diameter of As-spun acrylonitrile fiber discharged from a conventional spinneret using a super-stretch process to meet the application The present invention provides a method for producing a precursor fiber for a carbon fiber.

It is another object of the present invention to provide a precursor fiber for carbon fibers capable of producing precursor fibers having excellent molecular orientation and small diameter through pre-stretching and producing high strength and high rigidity carbon fibers.

In order to solve the problems of the present invention,

The present invention provides a method for producing acrylonitrile fibers, comprising: a first step of irradiating acrylonitrile fibers from a spinning solution containing an acrylonitrile polymer;

A second step of ultra-stretching the fibers radiated in the first step to adjust fiber diameter; And

A third step of stretching the fibers prepared in the second step to produce precursor fibers;

And a method for producing the precursor fiber for high strength carbon fibers.

According to the method for producing a precursor fiber for a carbon fiber of the present invention, it is possible to produce a carbon fiber whose superfactor is shortened in the cross-sectional area of the fiber to shorten the stabilization time and increase the strength. The carbon fiber thus produced can be used for manufacturing automobile chassis and body parts, aircraft structural members, wind turbine blades, sporting goods, and construction structural materials. When used in automobile and aircraft structural materials, And the safety is improved due to high rigidity.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view showing a general manufacturing process of a carbon fiber manufacturing method according to the fine fineness described in International Patent (WO 2009/049174).
2 is a process diagram briefly showing a manufacturing process of the method for producing precursor fibers for carbon fibers according to the present invention.

Hereinafter, the present invention will be described in more detail as an embodiment.

The present invention is characterized in that precursor fibers for high-strength carbon fibers are produced by a process such as spinning, superdrawing, stretching, etc. of acrylonitrile fibers from an acrylonitrile polymer spinning solution. Such a manufacturing process can be typically represented by a process as shown in FIG.

The precursor fibers for carbon fibers produced according to the present invention are preferably obtained from acrylonitrile polymers. The acrylonitrile polymer used as one embodiment of the present invention is copolymerized with other copolymerizable monomers using acrylonitrile monomer as a main component, and the content of acrylonitrile units is preferably 90 to 99% by weight, Is 95 to 99% by weight. If the content of the acrylonitrile is less than 90% by weight, the crystal structure of the carbon fiber precursor and the carbon fiber may not be well developed and the strength and rigidity of the carbon fiber may be deteriorated. The acrylonitrile polymer is preferably used in copolymerization with other copolymerizable monomers in order to shorten the stabilization time and to improve the final carbon fiber quality, and to make the total amount of acrylonitrile monomer to be 100% by weight. At this time, the copolymerizable monomer may be selected from one or more of acrylic acid (AA), methacrylic acid (MA), itaconic acid (IA), methacrylate (MA) and acrylamide (AM).

In order to prepare a carbon fiber precursor from the acrylonitrile polymer, the present invention includes preparing a dope by dissolving the acrylonitrile polymer in a solvent or by solution polymerization. Among them, a method of dissolving the acrylonitrile polymer in a solvent is more preferable. When the solution polymerized solution is directly spun, low molecular weight components, initiators, catalysts, etc. may affect the mechanical properties of the carbon fiber precursor and the carbon fiber. Examples of the solvent used in the spinning solution include dimethylsulfoxide (DMSO), N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), nitric acid Selected ones can be used. The content of the acrylonitrile polymer in the acrylonitrile polymer spinning solution (hereinafter referred to as 'spinning solution') is 5 to 25% by weight, preferably 10 to 20% by weight. If the content of the polymer is too small, the viscosity is low and spinning becomes difficult. If the content is too high, the mechanical properties of the carbon fiber precursor and the carbon fiber may be deteriorated due to intermolecular or intramolecular entanglement of acrylonitrile. The spinning solution is stored for at least 24 hours to remove bubbles and remove impurities using a filter having a pore size of 10 microns or less during spinning.

In the first step of spinning the acrylonitrile fibers from the acrylonitrile polymer spinning solution, the spinning solution may be spun in a conventional solution spinning process and processed into the form of fibers. The spinneret and the coagulation bath may be disposed by conventional wet spinning, striking (dry spinning wet spinning) methods, preferably by striking spinning methods to improve the orientation of the acrylonitrile molecules in the precursor fibers It is possible to make carbon fiber.

When this spinning solution is radiated, the distance between the spinneret and the coagulating solution should be maintained at 1 to 100 mm, more preferably 5 to 25 mm. The coagulating solution used is a mixture of solvent and non-solvent. The higher the ratio of non-solvent, the faster the solidification rate becomes. Water or alcohols can be selectively used.

According to the present invention, in the second step of superfolding the fibers radiated in the first step and controlling the fiber diameter, the as-spun fiber immediately after the spinning produced through the above process is preliminarily stretched. At this time, the super-stretching temperature is higher than the glass transition temperature of acrylonitrile, preferably 100 to 180 占 폚, more preferably 150 to 170 占 폚. The strain rate is set in the range of 0.4 to 400 sec ^-1, preferably 150 to 250 sec ^-1 . If the elongation is too high, the orientation of the molecules will occur quickly. If the elongation is too low, the productivity will decrease. Also, the thickness of the superextracted fiber may be preferably 0.05 to 0.5 denier.

In the third step of preparing the precursor fibers by stretching the fibers prepared in the second step, stretching is performed when the fiber diameter reaches the target range through the preliminary stretching. The stretching is carried out at a temperature of 150 to 180 DEG C by a conventional method.

As described above, when the crystallization polymer is subjected to stretching without increasing the orientation crystallization, the preliminary stretching can exhibit desirable characteristics when the stretching speed at a temperature higher than the glass transition temperature of the polymer is satisfied. According to the present invention, by utilizing the super-stretching process as described above, the acrylonitrile precursor fiber produced in one spinneret can be made as thin as possible by suppressing orientation crystallization as desired, and then stretched to finally achieve the desired thickness and physical properties .

The thus prepared precursor fibers according to the present invention can improve the molecular orientation and can produce carbon fibers having a shortened stabilization time and increased strength due to a small cross-sectional area of the fibers by super-stretching.

The precursor fibers prepared according to the present invention are used for producing carbon fibers. The carbon fibers can be prepared through ordinary stabilization and carbonization conditions, but the stabilization time is set in inverse proportion to the fiber cross-sectional area.

The carbon fiber thus produced can be made into a fiber diameter as narrow as that of an as-spun acrylonitrile fiber discharged from a conventional spinneret, and can produce carbon fibers having excellent tensile strength and tensile elastic modulus .

In addition, the carbon fiber produced by using the precursor fiber according to the present invention can be used for manufacturing automobile chassis and body parts, aircraft structural members, wind turbine blades, sports goods, and structural members And when it is used for automobile and aircraft structural materials, the fuel efficiency can be improved by lighter weight, and the safety can be improved due to high rigidity.

Hereinafter, the present invention will be described in more detail by way of examples. The following examples are provided to aid understanding of the present invention, and the present invention is not limited by the following examples.

Example 1: Preparation of precursor fibers using pre-stretch

10% by weight of acrylonitrile copolymer copolymerized with 2% by weight of itaconic acid was dissolved in 10% by weight of dimethylsulfoxide, and the resultant was placed in a vacuum oven to remove air bubbles. The air bubbles were removed by vacuum, Immediately after the production of the fibers. The primary coagulation bath is mixed with dimethyl sulfoxide and water at a ratio of 60:40, and the secondary coagulation bath is mixed with a solvent and water at a ratio of 40:60. The spinneret is a circle having a diameter of 120 탆.

Immediately after spinning through the above conditions, the fibers are super-stretched at a drawing speed of 200 sec ^-1 using a heating plate or a Godet roller at a temperature of 150 ° C. The initial draft ratio is set to be 90 times as the ratio of the primary rolled fiber winding speed to the fiber feeding speed immediately after spinning.

The above-mentioned pre-drawn ^sheet is stretched at a stretching speed of 450 sec ^-1 at a temperature of 170 ° C. The stretching ratio was expressed by the ratio of the winding speed of the drawn yarn and the feeding speed of the primary yarn, and the stretching ratio was extended to 15 times.

Comparative Example 1

In Example 1, precursor fibers were prepared by setting the super-stretching temperature at 70 占 폚.

Comparative Example 2

In Example 1, the precoat speed was set at 380 sec ^-1 to produce precursor fibers.

Comparative Example 3

The precursor fibers are prepared without the preliminary stretching in Example 1.

Comparative Example 4

According to the international patent (WO 2009/049174), fibers were prepared immediately after radiation of a diameter of 150 탆 including islands-in-a-sea composite radiation at an angle of 64 degrees, At a stretching speed of 450 sec < ^{-1 &} gt ;, and then the precursor fibers are prepared by dissolving only the sea component.

Experimental Example: Physical property measurement test

The tensile strength and tensile elastic modulus of the precursor fibers were measured by a method of ASTM D3822 with a gage length of 25.4 mm and a crosshead speed of 0.254 mm / min. The crystallinity was determined by the ratio of the area of the crystalline region [(200, 110), (201), (310, 020), (003)] to the area sum of the crystalline region and the amorphous region of the two-dimensional X-ray diffraction graph using XRD. The Herman's orientation factor of the acrylonitrile polymer molecules can be determined by the method of Wilchinsky, ZW, MEASUREMENT OF ORIENTATION IN POLYPROPYLENE FILM, Journal of Applied Physics, 1960. 31 (11): p. 1969-1972) . The fiber diameter was measured by measuring the density of the fiber using a hydrometer and then measuring the weight of the fiber of the unit length and converting the diameter of the circular cross-section yarn into the following formula.

Where m is the weight (g) of the fiber, ρ is the density (g / cm ³ ), and l is the fiber length (cm).

The results of the experiment are shown in Table 1 below.

As can be seen from Table 1, the fiber diameter is significantly larger than that of Example 1 when the super-stretching temperature is low as in Comparative Example 1. It can be seen from the comparison example 2 that the effect of decreasing the fiber diameter is smaller than that of the example 1 when the drawing speed is somewhat high.

It was confirmed that the precursor fibers having a larger fiber diameter and lower mechanical properties were produced than those of the Examples in the case where the preliminary stretching was not performed as in Comparative Example 3. In Comparative Example 4, 1, it was confirmed that it is possible to produce a precursor fiber having a small fiber diameter and excellent mechanical strength.

Therefore, when the precursor fiber is prepared by using the pre-stretch, precursor fibers having excellent mechanical properties can be produced by controlling the fiber diameter according to the super-stretching condition. The precursor fibers prepared in this manner can stabilize and shorten the carbonization time in the process of carbon fiber production, thereby reducing the production cost. Further, it is possible to produce carbon fibers having a more developed crystal structure, thereby improving the mechanical properties of carbon fibers .

Claims (10)

A first step of irradiating acrylonitrile fiber from a spinning solution containing an acrylonitrile polymer;
A second step of subjecting the fibers radiated in the first step to ultra-stretching at a stretching rate of 150 to 250 sec ^-1 and a stretching temperature of 150 to 170 ° C to control the fiber diameter; And
A third step of stretching the fibers prepared in the second step at a temperature of 150 to 180 DEG C to produce precursor fibers;
Wherein the carbon fiber precursor fiber is a carbon fiber precursor fiber.
The method of claim 1 wherein the acrylonitrile polymer is selected from the group consisting of acrylonitrile monomers and one or both of acrylic acid (AA), methacrylic acid (MA), itaconic acid (IA), methacrylate (MA) and acrylamide Of the copolymerizable monomer.
The method according to claim 1, wherein the acrylonitrile polymer has an acrylonitrile content of 90 to 99 wt%.
The spinning solution according to claim 1, wherein the spinning solution is a mixture of acrylonitrile polymer content of 5 to 25% by weight and a solvent selected from dimethylsulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc) .
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