KR20180087924A - Method of preparing carbon fiber having an excellent dimensional stability and carbon fiber by the same - Google Patents

Abstract

The present invention relates to a method for producing a carbon fiber, comprising the following steps: coating a surface of the carbon fiber primarily with an epoxy compound having at least two epoxy functional groups to enhance shape stability of the carbon fiber; and secondarily coating the same with a modified epoxy compound having at least two urethane-modified functional groups. The present invention further relates to a carbon fiber produced thereby. The carbon fiber produced by the present invention has a good running state of carbon fiber bundles in a prepreg process, and the warp of the wound carbon fiber is not changed with no twisting. In addition, urethane-modified epoxy on the surface of the carbon fiber was changed to a semi-solid state by heating at an inlet of an opening machine, thereby improving the processability of the opening process. Thus, it is possible to produce a carbon fiber prepreg with excellent quality without cracks and unevenness.

Description

[0001] The present invention relates to a method of producing a carbon fiber having excellent shape stability,

The present invention relates to a method of producing carbon fiber having excellent shape stability and a carbon fiber produced by the method. More particularly, the present invention relates to a carbon fiber produced by coating a surface of a carbon fiber with an epoxy compound having two or more epoxy functional groups, And then coated with a modified epoxy compound having at least two urethane-denatured functional groups having a large molecular weight, the running state of the carbon fiber bundle in the prepreg step is favorable, the warp of the wound carbon fiber is not deformed, To a carbon fiber produced by the method and a carbon fiber produced by the method.

Carbon fibers produced from acrylonitrile (PAN) polymers are very strong and widely used as raw materials for carbon fibers. More recently, more than 90% of the total carbon fibers are PAN-based carbon fibers. As is well known, as a method of producing carbon fibers, precursor fibers (precursors) such as polyacrylonitrile are subjected to chlorination treatment at 200 to 310 占 폚 in an oxidizing atmosphere to obtain raw chlorinated fibers And then carbonizing the carbon fiber at 350 to 2000 ° C in an inert gas atmosphere to obtain carbon fibers.

Carbon fiber has been widely used in the fields of sports / leisure, aerospace, automobile, secondary battery, carbon film, and the like as the industrial use of composite materials such as carbon fiber composite material (CFRP) Researches and developments have been actively conducted on high performance (high strength and high elasticity), light weight (reduction of fiber weight and fiber content) and improvement of physical properties of composites (improvement of carbon fiber surface / interfacial characteristics).

On the other hand, prepreg refers to a sheet-shaped intermediate material for a carbon fiber composite material impregnated with a resin and carbon fibers at a predetermined ratio in advance. The use of prepreg can precisely control the ratio of resin and carbon fiber, and can increase the fiber volume ratio of the molded product rather than applying the direct molding method, so that high-quality composite parts with high reliability can be produced. Further, there is also an advantage that a sheet-like prepreg can be cut and used as needed in the desired fiber direction. Recently, industrial heat resistant prepregs, high strength prepregs for automobiles, and functional prepregs with CNTs have been developed and are in commercial production. Unidirectional carbon fiber prepregs and woven carbon fiber prepregs are being produced.

A carbon fiber for producing a unidirectional carbon fiber prepreg, wherein a sizing agent is attached in an amount of 0.1 to 0.5 wt% based on the weight of the carbon fiber bundle, and a bundle of carbon fibers having a bundle width of 15 to 322 Japanese Patent Laid-Open No. 2003-003376. In the above document, the sizing agent does not contain an epoxy group and has excellent openability, but there is a problem that adhesiveness is poor in a composite property of a composite material comprising an epoxy resin as a matrix. In addition, the amount of the sizing agent adhered to the carbon fibers is small and the size of the sizing agent is likely to be uneven in the Rajit carbon fibers having a large number of filaments of the fibers. In the portion where the sizing agent is small, the coefficient of friction is high, There is a problem that it can not be obtained. As a result, the quality of the prepreg is deteriorated due to unevenness caused by yarn twisting during manufacture of a low-weight prepreg, and occurrence of gaps due to poor carding.

It is an object of the present invention to provide a method for producing carbon fibers which can improve defects in quality due to warping, twisting and the like when the carbon fiber passes through the guide during the prepreg process.

Another object of the present invention is to provide a carbon fiber which is produced by the above-mentioned method for producing a carbon fiber and which is capable of producing a low-weight, low-weight prepreg of excellent quality by significantly reducing warpage and yarn twist at the opening of the can opener.

According to one aspect of the present invention for achieving the above object,

Subjecting a precursor fiber bundle containing a polyacrylonitrile polymer to a chlorination process, a preliminary carbonization process, and a carbonization process to obtain a carbon fiber bundle; Impregnating the carbon fiber bundle with a first sizing bath in which a first sizing agent containing an epoxy compound having at least two epoxy functional groups is dispersed in water to coat the first sizing agent on the surface of the carbon fiber; And

The carbon fiber bundle coated with the epoxy compound is passed through a second sizing bath in which a second sizing agent containing a modified epoxy compound having two or more urethane-modified functional groups is dispersed in water, And coating a sizing agent on the carbon fiber.

According to another aspect of the present invention for achieving the above object,

A sizing agent-coated carbon fiber bundle coated with a sizing agent on a carbon fiber bundle, wherein a first sizing agent comprising an epoxy compound having at least two epoxy functional groups is coated on the surface of the carbon fiber bundle, To a sizing agent-coated carbon fiber bundle coated with a second sizing agent comprising a modified epoxy compound having two or more urethane-modified functional groups on the surface of a fiber bundle.

According to another aspect of the present invention for achieving the above object,

A thermoplastic resin containing the sizing agent-coated carbon fiber bundle, and a thermosetting resin containing an epoxy compound and an aromatic amine curing agent.

In the carbon fiber produced by the present invention, a hard sizing agent is coated on the surface of the carbon fiber so that the running state of the carbon fiber bundle in the prepreg process is good, and the warp of the wound carbon fiber is not deformed, . In addition, the urethane-modified epoxy on the surface of the carbon fiber is changed to a semi-solid state by heating at the opening of the can opener, and the processability of the carding process is improved, so that a carbon fiber prepreg of excellent quality without cracks and unevenness can be manufactured.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view showing a step of providing a first sizing agent containing an epoxy compound having two or more epoxy functional groups on a surface of a bundle of carbon fibers passing through a first sizing bath according to the present invention. FIG.
2 is a schematic view showing a step of providing a second sizing agent containing a modified epoxy compound having two or more urethane-modified functional groups on the surface of the carbon fiber bundle passing through the second sizing bath according to the present invention.

According to the present invention, a surface of a carbon fiber is first coated with an epoxy compound having two or more functional groups to concentrate the carbon fibers, and then the surface of the carbon fiber is coated with a modified epoxy compound having two or more urethane-modified functional groups A carbon fiber for preparing a prepreg having excellent shape stability and improved interfacial properties of a composite material is produced.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, with reference to the accompanying drawings and examples, a method for producing carbon fibers produced by the present invention will be described. Although the terms used in the present invention have been selected as general terms that are widely used at present, there are some terms selected arbitrarily by the applicant in a specific case. In this case, the meaning described or used in the detailed description part of the invention The meaning must be grasped. Like reference numerals refer to like elements throughout the specification. The use of the terms " lower " and " upper " herein is based on the direction of the gravitational direction.

A precursor fiber comprising a polyacrylonitrile polymer is prepared and subjected to a chlorination process, a preliminary carbonization process, and a carbonization process on the precursor fiber to obtain a carbon fiber bundle.

At this time, the carbon fiber precursor fibers are obtained from the acrylonitrile-based polymer, and the properties of the carbon fiber precursor basically vary depending on the composition of the acrylonitrile-based polymer. The main component of the acrylonitrile-based polymer used in the present invention is an acrylonitrile unit, and the content of the acrylonitrile unit is preferably 90% by weight or more, more preferably 95% by weight or more based on the total acrylonitrile- %, For example, 95 to 99 wt%. Here, if the content of the acrylonitrile unit is too small, the strength of the carbon fiber obtained by the firing process is lowered, and the mechanical properties of the carbon fiber may be deteriorated.

The acrylonitrile-based polymer may contain, if necessary, one or more copolymerizable components (auxiliary components other than acrylonitrile), and the content thereof is preferably 10% by weight or more, , More preferably less than 5 wt%, for example, 1 to 5 wt%. Examples of the copolymerization component include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, maleic acid, alkyl esters (such as methyl acrylate), diamine compounds and triamine compounds.

In order to prepare a carbon fiber precursor from such an acrylonitrile-based polymer, the acrylonitrile-based polymer is dissolved in an organic solvent to prepare a dope stock solution, the dope stock solution is spun, the coagulated fiber formed by spinning the dope stock solution Washing, stretching, drying, emulsion and winding steps. Generally, the process for producing carbon fiber precursor fibers is roughly classified into wet and dry wet spinning processes. Examples of the solvent for preparing the dope solution include dimethyl sulfoxide (DMSO), dimethyl acetate, zinc chloride An organic solvent and an inorganic solvent capable of dissolving an acrylonitrile polymer such as an aqueous solution, nitric acid, and the like can be used. The amount of the solvent to be used is usually 10 to 30 parts by weight based on 100 parts by weight of the acrylonitrile-based polymer. Here, if the amount of the organic solvent used is too small or too large, it may be difficult to spin the polymer, or void removal may be performed inefficiently.

As a non-solvent for the coagulation bath, a solvent compatible with the organic solvent of the polymer solution but capable of solidifying the polymer without dissolving the polymer can be used without limitation. The non-solvent may be water, preferably a mixture of water and an organic solvent, and if necessary, a solution of three or more components may be used. When an organic solvent is used for the non-solvent, it is preferable that the content thereof is uniformly maintained at about 35 to 85% by weight. The temperature of the non-solvent of the coagulating bath can be adjusted, for example, in the range of 5 to 85 ° C, preferably in the range of 30 to 33 ° C. If the temperature setting is out of the above range, the spinning of the polymer solution is not performed smoothly, the efficiency of the spinning process is lowered and the operation is uneconomical.

The coagulated fiber that has passed through the coagulation bath is washed with water through a washing bath. Further, a squeezing roller can be used to compress the spun solidified fibers, and the pressure of the compression roller is usually 1 to 5 kgf / cm2, preferably 2 to 3 kgf / cm2. When the step of washing and stretching and drying the coagulated fiber is completed, an emulsion is provided. After the emulsion is treated with an aqueous solution containing 0.01 to 5.0% by weight of an emulsion containing an amino-modified silicone emulsion, fine particles and an ammonium compound, Lt; RTI ID = 0.0 > high-temperature < / RTI > The total draw ratio of the prepared precursor fibers is generally 7 to 35 times, and the single fiber fineness is 0.5 to 2.0 dtex. The spun carbon fiber precursor is subjected to a chlorination treatment in an oxygen atmosphere and at a temperature of 200 to 310 占 폚 in an ordinary atmosphere and then carbonized at 350 to 2000 占 폚 in an inert atmosphere to obtain a carbon fiber having uniform physical properties have.

In the carbon fiber bundle according to the present invention, the produced carbon fiber short fibers are bundled into a bundle of fibers. The number of the staple fibers is preferably 3000 to 43500, more preferably 10000 to 20,000. The total fineness of the sizing agent-coated carbon fiber bundle according to the present invention is preferably 310 to 3000 tex. The number of filaments of the carbon fiber is preferably 10,000 to 30,000.

Hereinafter, a step of providing a sizing agent containing an epoxy compound having two or more functional groups in a carbon fiber bundle and a modified epoxy compound having two or more urethane-modified functional groups will be described.

1 is a schematic view showing a step of providing a first sizing agent containing an epoxy compound having two or more epoxy functional groups on the surface of a bundle of carbon fibers passing through a first sizing bath according to the present invention, And a second sizing agent comprising a modified epoxy compound having at least two urethane-modified functional groups on the surface of the carbon fiber bundle passing through the second sizing bath by the second sizing bath.

Referring to FIGS. 1 and 2, a carbon fiber bundle 20 having passed through a first turn-guide 30 which concentrates a carbonized bundle of carbon fibers 20 has a structure having two or more functional groups Is impregnated in a first sizing bath (10) containing a first sizing agent (11) dispersed in water-dispersed epoxy compound. A second turn-guide 31 is provided in the first sizing bath 10 so that the carbon fiber bundle 20 passing through the first turn-guide 30 passes through the second turn- The surface of the carbon fiber bundle 20 is coated with an epoxy compound. The carbon fiber bundle 20 having passed through the second turn-guide 31 in the first sizing bath 10 passes through the third turn-guide 32 provided at the rear end of the first sizing bath 10, And travels toward the bathtub 40.

The second sizing bath 40 is spaced apart at regular intervals in the running direction of the carbon fiber bundle 20 and includes a lower bath 41 and a lower bath 42 positioned opposite to each other with the carbon fiber bundle 20 as a center, ). In the lower bath 41 and the upper bath 42, a second sizing agent 43 in which a modified epoxy compound having two or more urethane-modified functional groups is dispersed is placed.

A modified epoxy compound having two or more urethane-denatured functional groups is coated on one surface of the carbon fiber bundle 20 in the lower bath 41 and a urethane-denatured epoxy compound is coated on the other surface of the carbon fiber bundle 20 in the upper bath 42, Is coated with a modified epoxy compound having at least two functional groups. Specifically, a fourth turn-guide 33 is provided in the lower bath 41 so that when the carbon fiber bundle 20 passes through the fourth turn-guide 33, A modified epoxy compound having two or more urethane-modified functional groups is coated. The carbon fiber bundle 20 is then spaced apart from the upper portion of the lower tub 41 and passes through the upper tub 42 located opposite the lower tub 41 about the carbon fiber bundle 20, A turn-guide 34 is installed in the upper bath 42 to allow the carbon fiber bundle 20 to pass through the fifth turn-guide 34 to form two urethane- Modified epoxy compound having a functional group of at least one of the above is coated.

Since the fourth turn-guide 33 is partially submerged in the lower tub 41, when the carbon fiber bundle 20 contacts the fourth turn-guide 33 while passing through the fourth turn-guide 33, A second sizing agent 43 applied to the surface of the fourth turn-guide 33 is coated on one surface of the carbon fiber bundle 20 and similarly a fifth turn-guide 34 is coated on the surface of the upper tub 42 The carbon fiber bundle 20 is applied to the surface of the fifth turn-guide 34 when it contacts the fifth turn-guide 34 while passing through the fifth turn-guide 34 A modified epoxy compound having two or more urethane-modified functional groups on both surfaces of the carbon fiber is coated with a so-called kissing type in which the second sizing agent 43 is coated on the other surface of the carbon fiber bundle 20. [

The carbon fiber bundle 20 having passed through the upper bath 42 passes through the sixth turn-guide 35 and is dried in a drier (not shown) provided at the rear end of the second sizing bath 40, A carbon fiber bundle is obtained. In this case, the drying temperature is preferably 110 to 250 ° C, more preferably 210 ° C or less. If the drying temperature is lower than 110 deg. C, drying may not be performed properly. If the drying temperature is higher than 250 deg. C, the functional groups existing on the outermost surface of the carbon fiber tend to disappear due to thermal decomposition. .

In addition, the carbon fiber bundle 20 may be dried in a dryer (not shown) before passing through the first sizing bath 10 and then through the second sizing bath 10. The drying temperature is preferably 110 to 250 ° C, more preferably 210 ° C or less. If the drying temperature is lower than 110 deg. C, drying may not be performed properly. If the drying temperature is higher than 250 deg. C, the functional groups existing on the outermost surface of the carbon fiber tend to disappear due to thermal decomposition. .

In the present invention, the vertical length between the lower bath 41 and the upper bath 42 is preferably set to 10 cm to 1000 cm. When the vertical length is less than 10 cm, the length from the lower bath 41 to the upper bath 42 is too short, so that the modified epoxy compound having two or more urethane-modified functional groups is formed on the surface of the carbon fiber bundle 20 sufficiently It can not be coated. When the vertical length exceeds 1000 cm, vibration occurs in the carbon fiber bundle 20 and the tension of the carbon fiber bundle 20 becomes unstable, making it impossible to express the carbon fiber of high quality / high uniformity.

In the present invention, the epoxy compound having two or more epoxy functional groups in the molecule is semi-solid at room temperature, and includes bisphenol A epoxy resin, bisphenol F epoxy resin, phenol novolac epoxy resin, cresol novolak epoxy resin, Epoxy resin, and naphthalene type epoxy resin, but is not limited thereto.

In the present invention, the modified epoxy compound having two or more urethane-modified functional groups is solid at room temperature and has at least one ring structure. The modified epoxy compound having two or more urethane-modified functional groups can be obtained by reacting a polyepoxy compound and a polyurethane having an isocyanate content of 0.1 to 10 mass% obtained from a polyhydroxy compound and an excess polyisocyanate compound. Examples of the polyisocyanate used herein include, but are not necessarily limited to, hexamethylene diisocyanate, isophorone diisocyanate, norbornadiisocyanate, and the like.

The first sizing agent and the second sizing agent further include an epoxy compound having two or more epoxy functional groups and an accelerator for enhancing the adhesion of the carbon fiber and the sizing agent in addition to the modified epoxy compound having two or more urethane- . Thus, convergence or flexibility is imparted to the sizing agent-coated carbon fiber bundle, whereby the handling property, the scratch resistance and the resistance to infiltration can be enhanced, and the impregnation property of the matrix resin can be improved. Further, for the purpose of stability of the sizing agent, an auxiliary component such as a dispersant and a surfactant may be further included.

The sizing pick-up (SPU) of the first sizing agent is 0.3 to 2.8 wt%, and the SPU of the second sizing agent is 0.2 to 2.7 wt%. If the size sizing pick-up of the first sizing agent is less than 0.3 wt%, the thickness of the carbon fiber can be increased due to friction during the process. If the size sizing pick-up of the second sizing agent is less than 0.2 wt% it's difficult.

The epoxy compound having two or more epoxy functional groups is preferably contained in an amount of 40 to 80 mass% with respect to the total amount of the sizing agent applied to the surface of the carbon fiber bundle 20. [ When the content of the epoxy compound having two or more epoxy functional groups is less than 40 mass%, the adhesiveness is deteriorated. When the content exceeds 80 mass%, the properties of the prepreg prepared using the sizing agent-

According to the sizing agent imparting method of the present invention, the carbon fiber bundle is impregnated in a bath in which the epoxy compound having two or more epoxy functional groups in the molecule is dispersed in the molecule to increase the frictional resistance during focusing and processing, Of a modified epoxy compound having two or more urethane-modified functional groups is dispersed in water to form a coating on both surfaces of a carbon fiber running in a kissing type, and thus the morphology stability of the carbon fiber bundles is excellent.

Hereinafter, a process for producing a prepreg using a carbon fiber bundle coated with a sizing agent according to the present invention will be described.

The prepreg of the present invention is a matrix resin impregnated with a carbon fiber bundle coated with a sizing agent according to the present invention. The prepreg can be produced, for example, by a wet method in which a matrix resin is dissolved in a solvent such as methyl ethyl ketone or methanol to effect impregnation with a low viscosity or by a hot melt method in which the matrix resin is impregnated with a low viscosity by heating can do.

In the wet method, a prepreg can be obtained by immersing a sizing agent-coated carbon fiber bundle in a liquid containing a matrix resin, taking out the solution, and evaporating the solvent using an oven or the like. In the hot melt method, a method of directly impregnating a matrix resin that has been made into a low viscosity by heating with a sizing agent-coated carbon fiber bundle, or a method in which a film coated with a matrix resin on a release paper or the like is prepared first, The prepreg can be manufactured by a method in which the film is stacked on both sides or one side of the bundle and heated and pressed to impregnate the matrix resin with the sizing agent-coated carbon fiber bundle. The hot melt method is preferred because there is no solvent remaining in the prepreg.

The prepreg of the present invention is a prepreg comprising the sizing agent-coated carbon fiber and the thermosetting resin of the present invention. The thermosetting resin contains an epoxy compound and an aromatic amine curing agent.

The epoxy compound used in the preparation of the prepreg is not particularly limited and examples thereof include bisphenol type epoxy compounds, amine type epoxy compounds, phenol novolak type epoxy compounds, cresol novolak type epoxy compounds, resorcinol type epoxy compounds, glycidyl aniline Type epoxy compound, a phenol aralkyl type epoxy compound, a naphthol aralkyl type epoxy compound, a dicyclopentadiene type epoxy compound, an epoxy compound having a biphenyl skeleton, an isocyanate modified epoxy compound, a tetraphenylethane type epoxy compound, a triphenylmethane type Epoxy compounds and the like can be selected and used.

The aromatic amine curing agent is not particularly limited as long as it is an aromatic amine used as an epoxy resin curing agent, and specific examples thereof include 3,3'-diaminodiphenylsulfone (3,3'-DDS), 4,4'-diamino Diphenyl sulfone (4,4'-DDS), diaminodiphenylmethane (DDM), 3,3'-diisopropyl-4,4'-diaminodiphenylmethane, 3,3'- Butyl-4,4'-diaminodiphenylmethane, 3,3'-diethyl-5,5'-dimethyl-4,4'-diaminodiphenylmethane, 3,3'-diisopropyl- Dimethyl-4,4'-diaminodiphenylmethane, 3,3'-di-t-butyl-5,5'-dimethyl- 5,5'-tetraethyl-4,4'-diaminodiphenylmethane, 3,3'-diisopropyl-5,5'-diethyl-4,4'-diaminodiphenylmethane, 3,3 Di-t-butyl-5,5'-diethyl-4,4'-diaminodiphenylmethane, 3,3 ', 5,5'-tetraisopropyl-4,4'-diaminodiphenyl Methane, 3,3'-di-t-butyl-5,5'-diisopropyl-4,4'-diaminodiphenyl methane, 3,3 ', 5,5'-tetra- , 4'-diaminodiphenyl (DAMPE), bisaniline, benzyldimethylaniline, 2- (dimethylaminomethyl) phenol (DMP-10), 2,4,6-tris (dimethylaminomethyl) phenol (DMP- , 2-ethylhexanoic acid esters of 2,4,6-tris (dimethylaminomethyl) phenol, and the like. These may be used alone or in combination of two or more.

In order to form the carbon fiber-reinforced composite material using the prepreg of the present invention, a method of thermally curing the matrix resin while laminating the prepreg and applying pressure to the laminate may be used. According to the present invention, it is possible to stably travel at a variation of main yarn width of 6% or less compared to the fiber width at the time of passing through the prepreg process. In addition, it is possible to stably travel to the opening of the dog gate by suppressing the occurrence of twist by hard sizing agent coating at the time of driving, and the width and twist of the dog gate are significantly reduced, thereby producing a low- can do.

The thus prepared prepreg of the present invention is suitably used in sports applications such as golf shafts and fishing rods as well as other general industrial applications, including aircraft members, spacecraft members, automobile members and ship members.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, The facts will be apparent to those skilled in the art. Therefore, the scope of protection of the present invention should be defined in the appended claims and their equivalents.

10: first sizing bath 11: first sizing agent
20: carbon fiber bundle 30: first turn-guide
31: second turn-guide 32: third turn-guide
33: fourth turn-guide 34: fifth turn-guide
35: Sixth turn - Guide 40: Second sizing bath
41: lower bathtub 42: upper bathtub

Claims (13)

Subjecting a precursor fiber bundle containing a polyacrylonitrile polymer to a chlorination process, a preliminary carbonization process, and a carbonization process to obtain a carbon fiber bundle;
Impregnating the carbon fiber bundle with a first sizing bath in which a first sizing agent containing an epoxy compound having at least two epoxy functional groups is dispersed in water to coat the first sizing agent on the surface of the carbon fiber; And
The carbon fiber bundle coated with the epoxy compound is passed through a second sizing bath in which a second sizing agent containing a modified epoxy compound having at least two urethane-modified functional groups is dispersed in water to coat the second sizing agent on the carbon fiber surface Wherein the step of forming the prepreg comprises the steps of:
The apparatus according to claim 1, wherein the second sizing bath is composed of an upper bathtub and a lower bathtub facing each other with respect to a traveling path of the carbon fiber bundle, the bathtub being spaced apart at regular intervals in the running direction of the carbon fiber bundle, , The second sizing agent is coated on one surface of the carbon fiber, and the second sizing agent is coated on the other surface of the carbon fiber in the upper bathtub.
The method of claim 1, wherein a fixed turn-guide is provided in the first sizing bath, and the first sizing agent is coated on the surface of the carbon fiber bundle while the carbon fiber bundle passes through the fixed turn- Gt;
3. The carbon fiber bundle according to claim 2, wherein the carbon fiber bundle passes through a turn-guide partially immersed in the lower tub, while the second sizing agent applied to the surface of the turn- And the second sizing agent coated on the surface of the turn-guide in the upper bath while the carbon fiber bundle passes through the turn-guide partially immersed in the upper bath is coated on the other surface of the carbon fiber bundle By weight based on the total weight of the prepreg.
The method of claim 1, wherein the carbon fiber bundle is further dried at a temperature of 110 to 250 DEG C in a drier before passing through the first sizing bath and the second sizing bath By weight based on the total weight of the prepreg.
3. The method of claim 2, wherein the vertical length between the lower bath and the upper bath is 10 cm to 1000 cm.
2. The prepreg according to claim 1, characterized in that the sizing pick-up (SPU) of the first sizing agent is 0.3 to 2.8 wt% and the SPU of the second sizing agent is 0.2 to 2.7 wt% Gt;
The method for producing a carbon fiber for prepreg according to claim 1, wherein the epoxy compound having two or more epoxy functional groups is contained in an amount of 40 to 80 mass% based on the total amount of the sizing agent applied to the surface of the carbon fiber bundle.
A sizing agent-coated carbon fiber bundle coated with a sizing agent on a carbon fiber bundle, wherein a first sizing agent comprising an epoxy compound having at least two epoxy functional groups is coated on the surface of the carbon fiber bundle, A sizing agent-coated carbon fiber bundle coated with a second sizing agent comprising a modified epoxy compound having two or more urethane-modified functional groups on the surface of a fiber bundle.
The sizing agent-coated carbon fiber bundle according to claim 9, wherein the SPU of the first sizing agent is 0.3 to 2.8 wt% and the SPU of the second sizing agent is 0.2 to 2.7 wt%.
The sizing agent-coated carbon fiber bundle according to claim 9, wherein the epoxy compound having two or more epoxy functional groups is contained in an amount of 40 to 80 mass% with respect to the total amount of the sizing agent applied to the surface of the carbon fiber bundle.
The sizing agent-coated carbon fiber bundle according to claim 9, wherein the number of the staple fibers constituting the carbon fiber bundle is 3000 to 43500, and the total fineness of the carbon fiber bundle is 310 to 3000 tex.
A prepreg comprising a sizing agent-coated carbon fiber bundle according to any one of claims 9 to 12, and a thermosetting resin containing an epoxy compound and an aromatic amine curing agent.

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