KR101617891B1 - Manufacturing method of carbon fiber - Google Patents

Abstract

The present invention discloses a method for producing carbon fiber capable of improving heat treatment efficiency and a heat-resistant lead fiber usable therefor.

Description

[0001] The present invention relates to a manufacturing method of carbon fiber,

The present invention relates to a method for producing carbon fibers and a lead fiber used therefor.

Since carbon fibers have a high specific strength and a high modulus of elasticity as compared with other fibers, they are widely used as reinforcing fibers for composite materials, in addition to conventional sports applications, aerospace applications, automobiles, civil engineering and construction, pressure vessels and wind turbine blades It is widely deployed in general industrial applications, and there is a high demand for further productivity improvement and stabilization of production.

The polyacrylonitrile (hereinafter may be abbreviated as PAN) carbon fiber, which is most widely used among carbon fibers, is produced by wet spinning, dry spinning or dry wet spinning of a spinning solution containing a PAN-based polymer as a precursor thereof Carbon fiber precursor fibers are obtained by heating them in an oxidizing atmosphere to convert them into chlorinated fibers and heating them in an inert atmosphere to carbonize them.

These carbon fibers have been continuously applied to a wide range of applications and require high performance. Efficiency is also required from the manufacturing method aspect.

The present invention provides a method for producing carbon fiber which can reduce the time required for a stable temperature rise of a heat treatment furnace and can reduce the amount of fibers to be heat-treated which is consumed for raising the temperature to a stable temperature.

The present invention includes, as a preferred embodiment, a step of converting polyacrylonitrile-based precursor fibers for producing carbon fibers into air-chlorinated fibers while being stretched in air at a temperature of 200 to 300 ° C, and a step of carbonizing by heating in an inert atmosphere And the conversion into chlorinated fibers is carried out by placing at least one kind of fiber selected from para-aromatic wholly aromatic polyamide fiber, wholly aromatic polyester fiber and polyparaphenylene bis oxazole fiber in a heat treatment furnace with lead fibers and heating Thereafter, when the temperature of the heat treatment furnace reaches a target temperature, lead fibers and polyacrylonitrile-based precursor fibers for producing carbon fibers are connected and the lead fibers are replaced with polyacrylonitrile-based precursor fibers for producing carbon fibers and heat-treated To provide a method for producing carbon fibers.

In the method for producing carbon fiber according to an embodiment of the present invention, the heat treatment furnace may be composed of three to six individual heat treatment furnaces, each of which has a different temperature raising target temperature.

In the method for producing a carbon fiber according to an embodiment of the present invention, a polyacrylonitrile-based precursor fiber for producing carbon fibers is produced by spinning a spinning solution containing a polyacrylonitrile-based polymer and discharging the spinning solution into a coagulating bath, Followed by washing, stretching, emulsion application, and dry densification.

In the method for producing carbon fibers according to an embodiment of the present invention, the step of carbonizing may be preliminarily carbonized in an inert atmosphere at a temperature of 300 to 800 ° C, subjected to carbonization treatment while being stretched in an inert atmosphere at a temperature of 1,000 to 3,000 ° C .

Another embodiment of the present invention provides a lead fiber for a high temperature heat treatment furnace selected from para-aromatic wholly aromatic polyamide fibers, wholly aromatic polyester fibers, and polyparaphenylene bis oxazole fibers. At this time, the high temperature heat treatment furnace may be used for producing carbon fibers.

According to the method for producing carbon fiber according to one embodiment of the present invention, the time required for the stable temperature rise of the heat treatment furnace can be reduced by applying the high heat-resistant lead fibers to the chloride- The amount of the target fiber can be reduced, and efficient heat treatment is possible.

Hereinafter, the present invention will be described in detail.

The carbon fiber precursor fiber is composed of a polymer comprising a polyacrylonitrile-based polymer (sometimes referred to as PAN-based polymer), wherein the polyacrylonitrile-based polymer means a polymer containing acrylonitrile as a main component. Specifically, it means a polymer containing acrylonitrile in an amount of 85 mol% or more of the entire monomers.

The polyacrylonitrile-based polymer can be obtained by solution polymerization by introducing a polymerization initiator into a solution containing a monomer mainly composed of acrylonitrile (sometimes referred to as AN) as a main component. It is needless to say that suspension polymerization or emulsion polymerization may be applied in addition to solution polymerization.

In addition to acrylonitrile, the monomer may include a monomer capable of copolymerizing with acrylonitrile, which may serve to accelerate the chloride attack. Examples thereof include acrylic acid, methacrylic acid, itaconic acid, and the like.

After the polymerization, it usually involves a step of neutralizing by using a polymerization terminator. This serves to prevent rapid coagulation in the coagulating bath when the spinning stock solution containing the polyacrylonitrile polymer to be obtained is spun.

As the polymerization terminator, ammonia can be used, but it is not limited thereto.

A polymer is obtained from a monomer containing acrylonitrile as a main component and then neutralized by using the above polymerization terminator to prepare a solution containing a polyacrylonitrile polymer in a salt form with ammonium ion.

On the other hand, the polymerization initiator used in the polymerization is not specifically limited, and an oil-soluble azo compound, a water-soluble azo compound, a peroxide and the like are preferable, and from the viewpoint of safety in terms of handling and industrially efficient polymerization An azo compound which does not cause the generation of oxygen which inhibits polymerization during decomposition is preferably used, and in the case of polymerizing by solution polymerization, an azo compound in the aspect of solubility is preferably used. Specific examples of the polymerization initiator include 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis (2,4'-dimethylvaleronitrile) , 2'-azobisisobutyronitrile, and the like.

The preferred range of the polymerization temperature varies depending on the type and amount of the polymerization initiator, but may be preferably 30 占 폚 or higher and 90 占 폚 or lower.

The solution containing the polyacrylonitrile polymer to be obtained has a solids content of 10 to 25% by weight. When applied as a spinning solution for producing carbon fiber precursor fibers, it is easy to remove the solvent during spinning, It may be advantageous in terms of preventing generation of tar or impurities generated in the chlorination step and maintaining the uniform density of filaments.

The solution containing the polyacrylonitrile polymer thus obtained can be used as a spinning stock solution in the process of producing the carbon fiber precursor fiber, and the spinning stock solution can be spun to obtain the carbon fiber precursor fibers. The spinning solution may contain an organic or inorganic solvent as a solvent together with a polyacrylonitrile copolymer. Examples of the organic solvent include dimethylsulfoxide, dimethylformamide, dimethylacetamide and the like.

The spinning method may be dry spinning, wet spinning or dry-wet spinning.

Among them, the dry spinning method is a method of concentrating and solidifying a spinning liquid by discharging it from a spinning hole into a hot gas atmosphere to evaporate the solvent. This is because the spinning speed becomes the evaporation rate of the solvent, There is a drawback that the chamber becomes very long.

The wet spinning method is a method in which a spinning solution is discharged from a spinning bath through a spinning bath. Since solidification progresses while swelling of 3 times or more occurs immediately after the spinning solution is discharged from the spinning holes, Even if the winding speed is increased, the radiation draft does not increase greatly. However, there is a problem that yarn breakage occurs on the claw surface as the actual draft rate increases sharply.

In addition, since the spinning solution is once introduced into the air (air gap) and then introduced into the coagulation bath after surface crystallization, the actual spinning draft rate is absorbed in the raw solution in the air gap, .

In addition, melt spinning and other known methods can be used.

Preferably, the above-mentioned spinning solution is discharged from the spinneret by wet spinning or dry-wet spinning, and the spinning solution is introduced into a coagulating bath to solidify the fibers.

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

The coagulating bath may contain a so-called coagulation promoting component in addition to a solvent such as dimethyl sulfoxide, dimethylformamide and dimethylacetamide. As the coagulation promoting component, it may be preferable that the polyacrylonitrile-based polymer is not dissolved, but is usable with a solvent used in the spinning solution. For example, water may be mentioned.

The temperature of the coagulating bath and the amount of the coagulation promoting component can be appropriately set according to the purpose of the refractory fiber or the carbon fiber.

The radiated polymer is discharged into a coagulating bath to coagulate the yarn, and then the carbon fiber precursor fibers can be obtained by washing, extending, emulsifying (oiling), and drying and densifying. At this time, the yarn may be coagulated and then drawn in a direct drawing bath without water washing, or the solvent may be removed by water washing and then stretched in a separate drawing bath. Further, in order to produce a strong carbon fiber precursor after emulsion application, it is possible to perform multi-stage stretching at low magnification or high-rate stretching at high temperature.

The application of an emulsion to the yarn is to prevent adhesion of the short fibers, and it is preferable to provide an emulsion of silicone or the like for example. Such a silicone emulsion is preferably a modified silicone, and it may be preferable that the silicone emulsion contains a network-modified silicone with high heat resistance.

The single fiber fineness of the carbon fiber precursor fiber thus obtained is preferably 0.01 to 3.0 dtex, more preferably 0.05 to 1.8 dtex, and still more preferably 0.8 to 1.5 dtex. If the single fiber fineness is too small, the process stability of the sacrificial process and the firing process of the carbon fiber may be deteriorated due to occurrence of thread breakage due to contact with the roller or the guide. On the other hand, if the single fiber fineness is too large, the difference in sectional inner and outer delamination structure between the short fibers after the chlorination becomes large, the processability in the subsequent carbonization process may be lowered, and the tensile strength and tensile elastic modulus of the resulting carbon fiber may be lowered. That is, if the temperature is outside the above range, the firing efficiency may be abruptly lowered. In the present invention, the monofilament fineness (dtex) is the weight (g) per 10,000 m of monofilament.

The degree of crystal orientation of the carbon fiber precursor fiber of the present invention is preferably 85% or more, and more preferably 90% or more. If the crystal orientation degree is less than 85%, the strength of the resulting precursor fiber may be lowered.

In the dry densification process, the heat treatment may be performed at a temperature of 100 to 180 ° C to increase the heat treatment speed, or to heat the surface of the carbon fiber precursor fiber by using a far-infrared heater or the like.

A process for producing a carbon fiber by using the carbon fiber precursor fiber comprising the polyacrylonitrile polymer thus obtained will be described.

The carbon fiber precursor fibers are used to produce carbon fibers.

In the chlorination treatment, the carbon fiber precursor fibers are heat-treated while stretching them in air at a temperature of 200 to 300 캜.

In the case of heat-treating a fiber or film (hereinafter abbreviated as "object") which is usually difficult to handle, a method of disposing a fibrous material (usually referred to as "lead fiber") that is easy to handle in a heat treatment furnace have. However, if the heat resistance of the lead fiber is worse than the desired heat treatment temperature, the lead fiber is set in the heat treatment furnace below the heat-resistant temperature of the lead fiber, and then the lead fiber is connected to the object and the lead fiber is replaced with the object. A method of raising the temperature is used. When the heat treatment furnace is a large facility, the time required for replacing the lead fiber with the object and the time required for the temperature of the heat treatment furnace are increased. Further, as the amount of the object to be consumed increases while the temperature of the heat treatment furnace is raised to the predetermined temperature, the loss is economically large.

In this regard, in the present invention, a method of applying lead fibers having higher heat resistance than a heat treatment furnace temperature to lead heat-resistant lead fibers into a heat treatment furnace, then raising the heat treatment furnace to a prescribed temperature and replacing the lead fibers with an object To be applied.

Specifically, in carrying out the step of converting into chlorinated fibers, at least one kind of fiber selected from para-aromatic wholly aromatic polyamide fibers, wholly aromatic polyester fibers and polyparaphenylene bis oxazole fibers is used as a lead fiber , And after the temperature of the heat treatment furnace reaches the target temperature, the lead fibers and the polyacrylonitrile-based precursor fibers for producing carbon fibers are connected and the lead fibers are replaced with the polyacrylonitrile-based precursor fibers for producing carbon fibers Heat treatment.

As described above, the step of converting the carbon fiber precursor fibers into the chlorinated fibers is carried out in air at 200 to 300 ° C. The fiber having the higher heat-resistant temperature is applied to the heat treatment furnace and heated to a heat treatment furnace. When the temperature reaches a target temperature, lead fibers and polyacrylonitrile-based precursor fibers for producing carbon fibers are connected and the lead fibers are replaced with polyacrylonitrile-based precursor fibers for carbon fiber fabrication.

As lead fibers having a high heat-resistant temperature, parabolic wholly aromatic polyamide fibers (heat resistance temperature of 250 ° C or higher, usually called "aramid fibers"), wholly aromatic polyester fibers (heat resistance temperature of 200 ° C or higher) And a bisoxazole fiber (heat-resistant temperature of 400 DEG C or higher) is preferable.

The thickness of the lead fiber is not particularly limited, but an initial thickness of about 3,000 dtex is used for easy connection with the carbon fiber precursor fiber, and a rope of 10,000 dtex or more is taken as an initial lead fiber Is preferable in terms of continuous reuse rather than disposable.

The connection between the heat-resistant lead fiber and the carbon fiber precursor fiber can be performed by a simple knot or interlacing method.

In the heat treatment using the heat-resistant lead fibers, the heat treatment furnace is composed of 3 to 6 individual heat treatment furnaces, each of which has a different temperature raising target temperature, so that the heating heat treatment is performed to uniformly heat the carbon fiber precursor and shorten the heat treatment time Lt; / RTI > In particular, when the target temperature is set to 250 ° C or higher in the individual heat treatment furnace, a high heat-resistant lead fiber is necessarily required.

 When the heat-resistant lead fiber is heat-treated, it is possible to shorten or eliminate the time required for replacing the lead fiber with the object, and moving the object to a temperature aimed at the heat treatment furnace. In addition, since the amount of waste objects consumed while the temperature of the heat treatment furnace is raised to the predetermined temperature can be reduced, it is economically advantageous. That is, when the lead fiber having low heat resistance is applied, the carbon fiber precursor fiber is raised to the heat-resistant temperature of the lead fiber, and then the carbon fiber precursor fiber is substituted with the carbon fiber precursor fiber. The fibers are generated, which can be reduced by applying heat-resistant lead fibers.

The elongation at the time of the chlorination treatment is -15 to 5%.

Then, preliminary carbonization treatment is carried out in an inert atmosphere at a temperature of 300 to 800 DEG C while being stretched according to the purpose, and carbonization is carried out while stretching in an inert atmosphere at a maximum temperature of 1,000 to 3,000 DEG C, depending on the intended use, Fiber.

The preliminary carbonization treatment and the carbonization treatment are performed in an inert atmosphere. Examples of the gas used in the inert atmosphere include nitrogen, argon, and xenon, and nitrogen is preferably used from an economical viewpoint. The maximum temperature in the carbonization treatment may be 1,000 to 3,000 DEG C depending on the mechanical properties of the desired carbon fiber. Generally, the higher the maximum temperature of the carbonization treatment, the higher the tensile elastic modulus of the resulting carbon fiber becomes. The maximum temperature of the carbonization treatment is preferably 1,200 to 1,700 ° C, and more preferably 1,300 to 1,600 ° C, for the purpose of increasing both the tensile strength and the tensile elastic modulus.

In addition, weight reduction is important when considering the use of aircraft, and it is also preferable that the maximum temperature of the carbonization treatment is 1,700 to 2,300 DEG C in terms of increasing the tensile elastic modulus. Although the tensile modulus increases with the maximum temperature of the carbonization treatment, the graphitization progresses and the carbon nanotube surface tends to buckle due to the growth and lamination of the carbon nanotube surface, resulting in a decrease in compressive strength Therefore, the temperature in the carbonization process is set in consideration of the balance between the two.

On the other hand, the degree of elongation upon carbonization treatment after oxidation stabilization may be -10 to 5%, preferably -5 to 5%.

The obtained carbon fiber can be electrolytically treated for surface modification thereof. As the electrolytic solution used for the electrolytic treatment, an acidic solution such as sulfuric acid, nitric acid and hydrochloric acid, or an alkali such as sodium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, ammonium carbonate and ammonium bicarbonate or salts thereof may be used as an aqueous solution. Here, the amount of electricity required for the electrolytic treatment can be appropriately selected in accordance with the degree of carbonization of the carbon fiber to be applied.

It is possible to optimize the adhesiveness with the carbon fiber matrix in the obtained fiber-reinforced composite material by the electrolytic treatment, and there is a problem that the composite material is excessively strong and the tensile strength in the fiber direction is lowered , The problem that the tensile strength in the fiber direction is high but the adhesiveness with the resin is low and the strength characteristic in the non-fiber direction is not developed is solved. In the obtained fiber-reinforced composite material, So that a balanced strength characteristic is exhibited.

After the electrolytic treatment, a sizing treatment may be carried out to give the carbon fiber an aggregate property. As the sizing agent, a sizing agent having good compatibility with a matrix resin or the like can be appropriately selected depending on the type of resin used.

The carbon fiber obtained by the present invention can be applied to a variety of molding methods such as autoclave molding as a prepreg, molding by resin transfer molding as a preform such as a woven fabric, and molding by filament winding, And can be preferably used as a sports member such as a golf shaft.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the scope of the present invention is not limited to these Examples.

≪ Example 1 >

A copolymer consisting of 95 mol% of acrylonitrile, 3 mol% of methacrylic acid and 2 mol% of itaconic acid was polymerized by a solution polymerization method using dimethylsulfoxide as a solvent, ammonia was added thereto in the same amount as itaconic acid And neutralized to prepare a polyacrylonitrile copolymer in the form of an ammonium salt to obtain a spinning solution having a copolymer component content of 22% by weight.

This spinning solution was discharged through a spinneret (temperature: 45 ° C, diameter: 0.08 mm, two holes of 6,000 holes) and introduced into a coagulation bath to be an aqueous solution of 40% dimethyl sulfoxide controlled at 45 ° C The test was made.

After washing the test piece, the test piece was stretched 5 times in hot water, and a silicone-modified silicone emulsion was added to give an intermediate stretched yarn.

This intermediate stretched yarn was subjected to drying treatment using a heating roller and stretched in a pressurized steam to obtain a polyacrylonitrile type fiber bundle having a total draw ratio of winding 10 times, a single fiber fineness of 1.5 dtex and a filament count of 12,000. This is called carbon fiber precursor fiber.

The resulting polyacrylonitrile-based fiber bundle was subjected to chlorination (stretching) for 80 minutes in a four-stage hot air oven having a temperature distribution of 220 to 270 DEG C in an air atmosphere without imparting a substantial twist at a speed of 4 m / Respectively.

Specifically, the dechlorinating treatment was carried out in the following manner.

And two para-type wholly aromatic polyamide fibers (aramid fiber, manufactured by Kolon Co., Ltd., product name: Heraclon) having 3,300 dtex as lead fibers were twisted together. 100 turns / m in the S direction as the lower edge, and 70 turns / m in the Z direction as the upper edge.

The lead wire was connected to the automatic sagger device, and the threading device was operated to set the lead fiber in each heat treatment furnace. After the setting, the temperature of each heat treatment furnace was raised to 220, 230, 255 and 270 DEG C, respectively, which are the specified temperatures.

The lead fiber and the polyacrylonitrile-based fiber bundle were connected during the temperature rise of the heat treatment furnace. Each of the heat treatment furnaces was raised to a specified temperature and then driven at a speed of 3 m / min to replace the lead fibers in the heat treatment with polyacrylonitrile fibers for 80 minutes. Upon completion of the replacement, the target heat-treated polyacrylonitrile-based fibers were continuously wound and transferred to a subsequent process.

Table 1 below shows the time required to raise the lead fiber thread, the temperature rise time, the substitution time, and the total time required for performing the chlorination treatment.

The fiber subjected to the chlorination treatment was subjected to pre-carbonization in an inert atmosphere at 400 to 700 ° C to remove off-gas, followed by carbonization (stretching) at 1,350 ° C to improve the strength.

≪ Example 2 >

Carbon fibers were prepared in the same manner as in Example 1 except that the chlorinated fibers were treated with wholly aromatic polyester fibers (Vectran, manufactured by Kuraray Co., Ltd.) as lead fibers.

Table 1 below shows the time required to raise the lead fiber thread, the temperature rise time, the substitution time, and the total time required for performing the chlorination treatment.

≪ Example 3 >

Carbon fiber was prepared in the same manner as in Example 1 except that polychloroprene was used as the lead fiber, and polychloroprene bisoxazole fiber (product of Toyo Bosch Co., Ltd .;

Table 1 below shows the time required to raise the lead fiber thread, the temperature rise time, the substitution time, and the total time required for performing the chlorination treatment.

≪ Comparative Example 1 &

Carbon fibers were prepared in the same manner as in Example 1 except that polyester fiber lead fibers having the same structure as the aramid fibers were used as the lead fibers in the chlorination treatment. After the installation, the temperature of each heat treatment furnace was raised to 150 캜 (primary heating).

During the temperature rise of the heat treatment furnace, lead fibers and polyacrylonitrile fibers were connected. After the heat treatment furnace was heated to 150 캜, the lead fibers in the heat treatment were driven at a speed of 3 m / min to replace the lead fibers in the heat treatment for 80 minutes (primary replacement).

After completing the replacement of each of the heat treatment furnaces, the temperature was sequentially raised to 220 ° C, 230 ° C, 255 ° C, and 270 ° C (hereinafter, referred to as the present temperature elevation). After the temperature rise was completed and the residence time (hereinafter referred to as " replacement ") was terminated, the heat-treated object was continuously wound.

Table 1 shows the time required for each process.

Lead fiber thread hook
Time (minutes) The primary heating-up time
(minute) Primary replacement time
(minute) example
Heating time
(minute) example
Substitution time
(minute) Total time required
(minute) PAN Fiber loss time (minutes) Example 1 80 0 0 120 80 280 0 Example 2 80 0 0 120 80 280 0 Example 3 80 0 0 120 80 28 0 Comparative Example 1 80 60 80 90 80 390 110

Claims (6)

A step of converting polyacrylonitrile-based precursor fibers for producing carbon fibers into air-chlorinated fibers while being stretched in air at a temperature of 200 to 300 캜, and a step of carbonizing by heating in an inert atmosphere,
In the step of converting into chlorinated fibers, at least one kind of fiber selected from para-aromatic wholly aromatic polyamide fibers, wholly aromatic polyester fibers and polyparaphenylene bisoxazole fibers is placed in a heat treatment furnace, When the temperature of the heat treatment furnace reaches the target temperature, the lead fiber is connected to the polyacrylonitrile-based precursor fiber for producing carbon fibers, and the lead fiber is replaced with a polyacrylonitrile-based precursor fiber for producing carbon fibers, A method for producing a carbon fiber. The method of manufacturing a carbon fiber according to claim 1, wherein the heat treatment furnace is composed of 3 to 6 individual heat treatment furnaces with different target temperatures for temperature rise. The polyacrylonitrile-based precursor fiber for producing carbon fiber according to claim 1, wherein the polyacrylonitrile-based precursor fiber for spinning the spinning solution is discharged into a coagulating bath to coagulate the yarn, and then washed, drawn, Wherein the carbon fiber is obtained from a method including a densification step. The method of producing a carbon fiber according to claim 1, wherein carbonization is carried out by preliminary carbonization treatment in an inert atmosphere at a temperature of 300 to 800 캜 and carbonization treatment while stretching in an inert atmosphere at a temperature of 1,000 to 3,000 캜. delete delete