KR102148752B1 - Method of manufacturing carbon fiber with thick denier - Google Patents

Abstract

The present invention is a spinning solution containing a polyacrylonitrile-based polymer and a conductive carbon material to prepare a high-fineness polyacrylonitrile-based precursor fiber for carbon fibers having a single yarn fineness of 2 to 4 denier, and then, it is flame-resistant and carbonized. By processing, a single yarn fineness of 1 to 2 denier carbon fiber is prepared.
The present invention has an effect of greatly improving the productivity of carbon fibers because the single yarn fineness constituting the carbon fiber is 1 to 2 denier, and the single yarn fineness is relatively high compared to the conventional single yarn fineness of the carbon fiber.
In addition, the present invention is a polyacrylonitrile-based precursor fiber for carbon fiber has a single yarn fineness of 2 to 4 denier, but contains a conductive carbon material, so that the inside and outside of the precursor fiber The difference in heat stabilization (difference in flame resistance) is minimized, in other words, uniform heat stabilization (salt resistance) occurs both inside and outside of the precursor fiber, causing a number of pores on the carbon fiber when manufacturing the carbon fiber. It is possible to effectively prevent problems in which the rate is increased or mechanical properties are deteriorated.

Description

Method of manufacturing carbon fiber with thick denier

The present invention relates to a method of manufacturing a carbon fiber having a high single yarn, and specifically, a high single yarn fineness can greatly improve the productivity of carbon fibers, and a polyacrylonitrile-based precursor fiber for carbon fibers in a flame-resistant process even if the single yarn fineness is high The outside and inside of the fiber are relatively uniformly heat-stabilized (salt-resistance), and a large number of pores are generated on the carbon fiber, thereby reducing mechanical properties or increasing the cutting rate during the process. About.

In general, carbon fibers are cyclized and thermally stabilized acrylonitrile oxidized fibers (Oxi-PAN fibers) through a flame-resistant process in which polyacrylonitrile-based precursor fibers are heat-treated at a temperature of about 200 to 300°C. It is produced by finally forming a hexagonal structure of only carbon through a carbonization process of heat treatment at a high temperature of about 800°C or higher.

The conventional flame-resistant process of carbon fiber is performed by heat treatment of a polyacrylonitrile-based (PAN)-based carbon fiber precursor (Precursor) in 3 to 4 steps. At this time, the individual polyacrylonitrile-based (PAN)-based precursor fibers are thermally stabilized from the surface toward the inner surface due to the heat treatment effect.

Depending on the heat transfer rate and time, thermal stabilization and chlorination resistance proceeds through contact and diffusion of oxygen in the surface layer. In this way, it is divided into a thermal stabilization and chlorination-resistant region in contact with oxygen, and a thermal stabilization region in which oxygen does not penetrate during the chlorination-resistant process because it is mad inside the precursor fiber and only thermal stabilization is performed.

In this case, when thermal stabilization is excessive during the chlorination process, pores are formed or fractured in the precursor. When this phenomenon occurs, the mechanical properties of the carbon fiber deteriorate. On the other hand, if thermal stabilization is insufficient, it may ignite and be cut off. At this time, the lower the chlorination temperature is, the easier it is for heat stabilization, but it takes a lot of time. The higher the heat stabilization temperature, the more severe the difference in the degree of heat stabilization between the surface layer and the inner layer occurs, and pores are likely to occur. Therefore, even in the case of using the same precursor fiber that is conventionally prepared, mechanical strength is formed in a wide range of properties from 1.0 GPa to 3.0 GPa due to the difference in salt resistance.

In order to solve the above problem, a method of performing flame resistance within 10 minutes using a microwave such as plasma has been proposed instead of the flame resistance process using hot air. There are many problems, so it has not been commercialized.

In order to solve the above problems, Korean Patent Laid-Open No. 10-2014-0148343 discloses a polyacrylonitrile-based precursor for carbon fibers containing 0.03 to 3.0% by weight of conductive carbon materials such as carbon black and having a single yarn fineness of 0.8 to 2.0 denier. To produce a carbon fiber through a carbonization process of heat treatment of the oxidized acrylonitrile fiber at a high temperature of 800° C. or higher after producing acrylonitrile oxide fiber through a flame resistance process of heat-treating the fiber at a temperature of 200 to 300°C. How to publish.

The conventional method can solve the problem that the difference in heat stabilization inside and outside the fiber becomes severe during the flame resistance process because the polyacrylonitrile-based precursor fiber for carbon fiber contains a conductive carbon material that increases internal heat transfer during flame resistance. However, since the single yarn fineness of the precursor fiber is as thin as 2 denier or less, there is a problem that the productivity of the carbon fiber is deteriorated.

An object of the present invention is to provide a method for manufacturing carbon fibers capable of improving the productivity of carbon fibers by up to four times compared to conventional methods.

Another object of the present invention is when heat treatment of a polyacrylonitrile-based precursor fiber for carbon fiber (hereinafter abbreviated as "precursor fiber") in a flame resistance process, the single fiber fineness of the precursor fiber is the conventional single fiber fineness (2.0 Provides a carbon fiber manufacturing method capable of preventing pores from being generated in the precursor fiber by evenly causing heat stabilization (saltization) inside and outside the precursor fiber even if it is relatively thicker than denier). will be.

In order to achieve such a problem, the present invention prepares a polyacrylonitrile-based precursor fiber for carbon fibers having a single yarn fineness of 2 to 4 denier with a spinning solution containing a polyacrylonitrile-based polymer and a conductive carbon material. , To produce a carbon fiber having a single yarn fineness of 1 to 2 denier by treatment with flame resistance and carbonization.

The present invention has an effect of greatly improving the productivity of carbon fibers because the single yarn fineness constituting the carbon fiber is 1 to 2 denier, and the single yarn fineness is relatively high compared to the conventional single yarn fineness of the carbon fiber.

In addition, the present invention is a polyacrylonitrile-based precursor fiber for carbon fiber has a single yarn fineness of 2 to 4 denier, but contains a conductive carbon material, so that the inside and outside of the precursor fiber The difference in heat stabilization (difference in flame resistance) is minimized, in other words, uniform heat stabilization (salt resistance) occurs both inside and outside of the precursor fiber, causing a number of pores on the carbon fiber when manufacturing the carbon fiber. It is possible to effectively prevent problems in which the rate is increased or mechanical properties are deteriorated.

1 is a cross-sectional photograph of a carbon fiber prepared in Example 1.
Figure 2 is a cross-sectional photograph of a carbon fiber prepared in Comparative Example 2.

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

The method for producing a high-fidelity carbon fiber according to the present invention comprises: (i) a spinning solution for preparing a spinning solution containing a polyacrylonitrile-based polymer and a conductive carbon material by adding a conductive carbon material to a polyacrylonitrile-based polymer solution Manufacture process; (Ii) a spinning process of spinning, coagulating, washing, drawing, tanning, and drying the spinning solution to prepare a high-fidelity polyacrylonitrile-based precursor fiber for carbon fibers having a single yarn fineness of 2 to 4 denier; (Iii) a flame-resistant process of heat-treating the polyacrylonitrile-based precursor fiber for carbon fiber at a temperature of 200 to 300°C to produce an oxidized acrylonitrile-based fiber; And (iv) a carbonization process of heat-treating the oxidized acrylonitrile-based fiber at a temperature of 800° C. or higher to produce carbon fiber having a single yarn fineness of 1 to 2 denier.

Specifically, in the present invention, a spinning solution including a polyacrylonitrile-based polymer and a conductive carbon material is prepared by first adding a conductive carbon material to a polyacrylonitrile-based polymer solution.

At this time, it is preferable to adjust the content of the conductive carbon material in the spinning solution to 0.0011 to 0.09% by weight.

When the content of the conductive carbon material in the spinning solution is less than 0.0011% by weight, the effect of uniformizing thermal stabilization by improving the heat transfer rate during heat treatment of the precursor fiber becomes insignificant, and when it exceeds 0.09% by weight, thermal stabilization occurs uniformly. The effect is no longer improved, only radioactivity can be reduced.

The conductive carbon material is carbon black, carbon nanotubes (CNT), graphene, graphene oxide, or a mixture thereof.

In the present invention, the conductive carbon material is a carbon material that does not volatilize in a carbonization process while having lower thermal conductivity and specific resistance than a precursor for organic carbon fibers such as polyacrylonitrile (PAN), by using the conductive carbon material, By improving the heat transfer rate into the precursor, heat stabilization can be achieved quickly, and carbon fibers can be economically manufactured by shortening the flame resistance time.

In addition, the conductive carbon material is its electrical resistivity is 3.5 × 10 ^- means to be ⁵ Ω-cm to 10 ³ Ω-cm. At this time, the conductivity, the lower the electrical resistivity of carbon material thermal conductivity is excellent, but the electrical resistivity of the electrically conductive carbon material is 3.5 × 10 ^- can not be less than ⁵ Ω-cm, is 10 ³ Ω-cm greater than the actual conductive carbon material The increase in the input amount of the chlorine is offset by the increase in the cost of producing the precursor.

For the conductive carbon material used in the present invention, the specific resistance is 3.5 × 10 ^- has a very high heat transfer performance at a level of ⁵ Ω-cm. On the other hand, in the case of conductive metals, thermal conductivity is expected to be high due to a much lower resistivity value, but due to its nature, metals are easily ionized and act as an unstable factor in the chlorination process through a catalytic reaction, and process stability is very weak. have.

Accordingly, in the present invention, it is preferable to use a conductive carbon material having an electrical resistivity of 3.5×10 ^-5 Ω-cm to 10 ³ Ω-cm, which exhibits stable properties even in the chlorination resistance process.

In addition, the conductive carbon material may have a purity of 95 to 99.9%. At this time, if the purity of the conductive carbon material is less than 95%, the impurities inhibit the covalent bonding of carbon in the chlorination and carbonization processes, resulting in poor mechanical properties and poor final yield. In particular, if a metal component other than a conductive carbon material remains, it may be preferable not to use it because the possibility of ignition is high.

In addition, the conductive carbon material may have a particle diameter of 200 nm or less, and preferably, 0.1 to 200 nm. At this time, if the particle diameter of the conductive carbon material is less than 0.1 nm, the dispersion stability becomes weak and the price of the conductive carbon material increases rapidly.If the particle diameter of the conductive carbon material is more than 200 nm, it is basically impossible to fiberize by putting it inside the polymer forming the precursor. there is a problem.

The polyacrylonitrile-based polymer can be obtained by solution polymerization by introducing a polymerization initiator into a solution containing a monomer containing acrylonitrile (some abbreviated as AN) as a main component and a conductive carbon material. It goes without saying that a suspension polymerization method or an emulsion polymerization method can be applied in addition to the solution polymerization method.

At this time, it is preferable to use the conductive carbon material by dispersing it in the solvent before polymerization. The reason for introducing the conductive carbon material before polymerization is that the viscosity of the solvent is very low, so it is uniformly dispersed and the amount of the conductive carbon material added can be improved. . When a conductive carbon material is added after polymerization, the spinning dope maintains a high viscosity of 400 poise or more, so it is difficult to achieve a uniform spinning dope no matter how much additional reactors for dispersion are attached to the conductive carbon material. A large number of agglomeration points due to non-uniformity are found inside, and high-magnification stretching required to secure the strength of the precursor of 6 g/denier or more becomes difficult.

Among the monomers, in addition to acrylonitrile, a monomer copolymerizable with acrylonitrile may be included, which may serve to promote salt resistance, and examples thereof include acrylic acid, methacrylic acid, or itaconic acid. It is preferable that such a copolymerizable monomer is 5% by weight or less of the total polymer component.

After polymerization, it usually involves a process of neutralization using a polymerization terminating agent, which serves to prevent rapid coagulation in the coagulation bath when spinning the spinning dope containing the obtained polyacrylonitrile-based polymer. In general, ammonia may be used as the polymerization terminator, but there is no limitation thereto.

A polymer is obtained from a monomer containing acrylonitrile as a main component, and then neutralized using the polymerization terminator to prepare a solution containing a polyacrylonitrile-based polymer in the form of a salt with ammonium ions.

On the other hand, the polymerization initiator used for polymerization is not specifically limited, and oil-soluble azo compounds, water-soluble azo compounds, peroxides, etc. are preferable, and from the viewpoint of handling properties in terms of safety and industrially efficient polymerization. An azo-based compound that does not cause generation of oxygen that inhibits polymerization during decomposition is preferably used, and in the case of polymerization by solution polymerization, an oil-soluble azo compound is preferably used from the viewpoint of solubility. As specific examples of the polymerization initiator, 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis (2,4'-dimethylvaleronitrile), and 2 , 2'-azobisisobutyronitrile, etc. are mentioned.

Next, the spinning solution is spun, coagulated, washed with water, stretched, treated with an emulsion, and dried to prepare a polyacrylonitrile-based precursor fiber for carbon fibers having a single yarn fineness of 2 to 4 denier.

The polyacrylonitrile-based precursor fiber for carbon fiber is made of a polymer containing a polyacrylonitrile-based polymer (which may be abbreviated as a PAN-based polymer), wherein the polyacrylonitrile-based polymer is mainly composed of acrylonitrile. It means a polymer made into. Specifically, it is preferable to contain acrylonitrile in 95 mol% or more of all monomers.

At this time, the superfineness polyacrylonitrile precursor for carbon fiber is manufactured with a single yarn fineness of 2 to 4 denier, and when the single yarn fineness is less than 2 denier, the productivity of the carbon fiber decreases, and when it exceeds 4 denier, The productivity of the carbon fiber is improved, but there is a problem that a difference in heat stabilization between the inside and the outside of the precursor fiber occurs in the flame-resistant process of the precursor fiber.

In addition, it is preferable to adjust the content of the conductive carbon material in the polyacrylonitrile-based precursor fiber to be 0.05 to 0.1% by weight. If the content is less than 0.05% by weight, a difference in thermal stabilization between the inside and the outside of the precursor fiber occurs in the chlorination process of the precursor fiber, and when the content exceeds 0.1% by weight, the dispersibility of the conductive carbon material in the precursor fiber This may deteriorate.

A polymerization solvent may also be included in the spinning solution.

Examples of the organic solvent include dimethyl sulfoxide, dimethyl formamide, dimethyl acetamide, and the like.

The spinning method is preferably a wet spinning method or a dry wet spinning method. Among them, the wet spinning method is a method in which the spinning solution is discharged from the detention hole into the coagulation solution of the coagulation bath. Even if it is raised, the spinning draft does not increase significantly, but there is a problem that thread breakage may occur in the detention surface as the actual draft rate rapidly increases, and there may be a limit to setting the winding speed high.

In addition, in the dry-wet spinning method, since the spinning solution is once discharged into the air (air gap) and then surface crystallization proceeds, it is induced in the coagulation bath, so the actual spinning draft rate is absorbed from the raw liquid in the air gap, enabling high-speed spinning. can do.

The solidification rate and stretching method can be appropriately set according to the purpose of the target refractory fiber or carbon fiber.

The coagulation solution of the coagulation bath may contain a so-called coagulation accelerating component in addition to solvents such as dimethyl sulfoxide, dimethylformamide, dimethyl acetamide, zinc chloride (ZnCl ₂ ) aqueous solution, and sodium rodan oxide (NaSCN) aqueous solution. As the coagulation promoting component, it may be preferable that the polyacrylonitrile-based polymer is not dissolved and has usability and a solvent used in the spinning dope, an example of which may be water. At this time, the concentration of the solvent contained in the coagulation solution is preferably 15 to 75% of the concentration of the solvent contained in the spinning solution. That is, when the concentration is 15% or more, the extraction rate of the solvent from the spun fiber can be prevented from becoming too fast, and when the concentration is 75% or less, the concentration of the solvent more than the minimum amount can be extracted from the spun fiber. .

In addition, the temperature of the coagulation solution is set to -35°C to +15°C based on the temperature of the spinning solution, so that the extraction rate of the solvent from the spun fiber is moderately slowed to improve the surface crystallinity, thereby improving the strength of the yarn. It can be. At this time, when the temperature of the coagulating solution is low, it is preferable that the solvent concentration of the coagulating solution is also lowered, and when the temperature is increased, it is advantageous to increase the solvent concentration of the coagulating solution. This is all to properly control the extraction rate of the solvent.

After discharging the spun polymer into a coagulation bath to solidify the yarn, it is possible to obtain a precursor fiber for carbon fiber through water washing, stretching, oiling (oiling), and drying.

At this time, the solidified fibers may be drawn directly in a drawing bath without washing with water, or may be drawn in a separate drawing bath after washing and removing the solvent. In addition, in order to manufacture a strong precursor fiber for carbon fibers after applying an emulsion, multistage stretching may be performed at a low magnification or high magnification stretching may be performed with high temperature steam. At this time, it is possible to improve the strength of the precursor fiber by increasing the draw ratio of 4 to 20 times, and in particular, it is preferable to set the single fiber strength of the precursor fiber to 6 g/denier or more. In order to improve the strength of the carbon fiber, it is even more preferable that it is 8.0 g/denier or more, and the single fiber strength of the precursor fiber may be 6 g/denier to 15 g/denier.

The application of an oil agent to the fibers is to prevent adhesion between monofilaments, and for example, it is preferable to provide an oil agent made of silicone or the like. It is preferable that such a silicone emulsion is a modified silicone, and it may be desirable to contain a reticulated modified silicone having high heat resistance.

Next, the high-fineness polyacrylonitrile precursor fiber for carbon fiber is heat-treated at a temperature of 200 to 300°C to prepare an oxidized acrylonitrile fiber, and then, the oxidized acrylonitrile fiber is subjected to a temperature of 800°C or higher. By heat treatment, carbon fibers with a single yarn fineness of 1 to 2 denier are prepared.

The present invention has an effect of greatly improving the productivity of carbon fibers because the single yarn fineness constituting the carbon fiber is 1 to 2 denier, and the single yarn fineness is relatively high compared to the conventional single yarn fineness of the carbon fiber.

In addition, the present invention is a polyacrylonitrile-based precursor fiber for carbon fiber has a single yarn fineness of 2 to 4 denier, but contains a conductive carbon material, so that the inside and outside of the precursor fiber The difference in heat stabilization (difference in flame resistance) is minimized, in other words, uniform heat stabilization (salt resistance) occurs both inside and outside of the precursor fiber, causing a number of pores on the carbon fiber when manufacturing the carbon fiber. It is possible to effectively prevent problems in which the rate is increased or mechanical properties are deteriorated.

Hereinafter, the present invention will be described in more detail through examples. These examples are for illustrative purposes only, and it will be apparent to those of ordinary skill in the art that the scope of the present invention is not limited by these examples.

Example One

A copolymer comprising 95 mol% of acrylonitrile, 3 mol% of methacrylic acid, and 2 mol% of itaconic acid was used as a solvent using dimethyl sulfoxide, and a carbon nanotube (CNT), a carbon material before polymerization, was 0.06 wt% based on the content of acrylonitrile. % Is added and polymerized by solution polymerization, and ammonia is added in the same amount as itaconic acid to neutralize it to prepare a polyacrylonitrile-based copolymer in the form of an ammonium salt, and the content of the copolymer component is 20% by weight. A spinning solution was prepared.

Next, the spinning solution prepared as described above was spun through a spinneret, coagulated in a coagulation solution, which is an aqueous solution of 40% dimethyl sulfoxide, and stretched at a draw ratio of 5 after washing with water, and treated with emulsion and dried to achieve a single yarn fineness of 2.5 A polyacrylic precursor fiber for carbon fiber in which 3,000 denier monofilaments are bundled was prepared.

The polyacrylonitrile-based fiber bundle prepared as described above is not substantially twisted and is flame-resistant in a 4-stage hot air oven having a temperature distribution of 220 to 270°C in an air atmosphere at equal time intervals (with stretching ).

Then, after preliminary carbonization in an inert atmosphere of 400 ~ 700 ℃ to remove off-gas (Off-gas), and then finally carbonization treatment (with stretching) at a temperature of 1,350 ℃ to improve the strength, thereby producing a carbon fiber.

The carbon fiber produced as described above had low cutoff rate during the process and excellent mechanical properties such as strength because pores were not formed in the cross-sectional photograph as shown in FIG. 1.

The carbon fiber prepared as described above has the strength, pore occurrence, and productivity measured by ASTM D 4018 as shown in Table 1.

Example 2

Carbon fibers were prepared in the same manner as in Example 1, except that the single yarn fineness of the polyacrylic precursor fiber for carbon fiber was changed to 3.0 denier.

The carbon fiber prepared as described above has the strength, pore occurrence, and productivity measured by ASTM D 4018 as shown in Table 1.

Example 3

Carbon fibers were prepared in the same manner as in Example 1, except that the single yarn fineness of the polyacrylic precursor fiber for carbon fiber was changed to 3.5 denier.

The carbon fiber prepared as described above has the strength, pore occurrence, and productivity measured by ASTM D 4018 as shown in Table 1.

Example 4

Carbon fibers were prepared in the same manner as in Example 1, except that the single yarn fineness of the polyacrylic precursor fiber for carbon fiber was changed to 4.0 denier.

The carbon fiber prepared as described above has the strength, pore occurrence, and productivity measured by ASTM D 4018 as shown in Table 1.

Comparative Example One

Carbon fiber was prepared in the same manner as in Example 1, except that the single yarn fineness of the polyacrylic precursor fiber for carbon fiber was changed to 1.0 denier.

The carbon fiber prepared as described above has the strength, pore occurrence, and productivity measured by ASTM D 4018 as shown in Table 1.

Comparative Example 2

Carbon fibers were prepared in the same manner as in Comparative Example 1, except that carbon nanotubes (conductive carbon material) were not added to the spinning solution.

The carbon fiber prepared as described above has the strength, pore occurrence, and productivity measured by ASTM D 4018 as shown in Table 1.

Carbon fiber properties division Strength (Gpa) Pore occurrence productivity Example 1 3.45 No occurrence 2.5 times Example 2 3.75 No occurrence 3.0 times Example 3 3.20 No occurrence 3.5 times Example 4 3.60 No occurrence 4.0 times Comparative Example 1 3.40 No occurrence 1 times Comparative Example 2 3.28 Occurred 1 times

Various physical properties of carbon fiber were evaluated by the following method.

burglar( Gpa )

It was evaluated by the ASTM D 4018 method.

Pore occurrence

A cross-sectional picture of the carbon fiber was taken to visually observe whether pores occurred.

productivity

The productivity of Examples 1 to 4 and the productivity of Comparative Example 2 were compared relative to each other using the productivity of Comparative Example 1 as a standard (1 times).

Claims (5)

(I) a spinning solution manufacturing process of preparing a spinning solution including a polyacrylonitrile polymer and a conductive carbon material by adding a conductive carbon material to the polyacrylonitrile polymer solution;
(Ii) a spinning process of spinning, coagulating, washing, drawing, tanning, and drying the spinning solution to prepare a high-fidelity polyacrylonitrile-based precursor fiber for carbon fibers having a single yarn fineness of 2 to 4 denier;
(Iii) a flame-resistant process of heat-treating the polyacrylonitrile-based precursor fiber for carbon fiber at a temperature of 200 to 300°C to produce an oxidized acrylonitrile-based fiber; And
(Iv) a carbonization process of heat-treating the oxidized acrylonitrile-based fiber at a temperature of 800° C. or higher to produce carbon fiber having a single yarn fineness of 1 to 2 denier; including,
Controlling the content of the conductive carbon material in the spinning solution to 0.0011 ~ 0.09% by weight, a method of producing a high-fidelity carbon fiber. The method of claim 1, wherein the conductive carbon material is at least one selected from carbon black, carbon nanotubes (CNT), graphene, and graphene oxide. The method of claim 1, wherein the conductive carbon material has an electrical resistivity of 3.5×10 ^-5 Ω·cm to 3.5×10 ³ Ω·cm, a purity of 95% or more, and a particle diameter of 0.1 to 200 nm. Method for producing high fineness carbon fiber. delete The method of claim 1, wherein the content of the conductive carbon material in the polyacrylonitrile-based precursor fiber for carbon fiber is adjusted to 0.05 to 0.1% by weight.

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