JPH07279040A - Carbon fiber and its production - Google Patents

Abstract

PURPOSE:To remarkably improve adhesive strength of a composite and further improve high order processability of carbon fiber and tensile strength of composite. CONSTITUTION:This carbon fiber is constituted by sizing a carbon fiber whose surface oxygen concentration O/C measured by an X ray photoelectric spectroscopy is <=0.20 and whose surface hydroxyl group concentration C-OH/C and surface carboxyl group concentration C-OH/C measured by chemically modified X ray photoelectric spectroscopy and surface nitrogen concentration N/C of carbon fiber measured by X ray photoelectric spectroscopy are each in a specific range with an aliphatic compound having plural epoxy groups or an aromatic compound having plural epoxy groups having >=6 number of atoms between the epoxy group and the aromatic ring. Furthermore, a method for producing this carbon fiber is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon fiber and a method for producing the same, and more particularly to a carbon fiber having excellent adhesiveness with a matrix and excellent composite properties and a method for producing the same.

[0002]

2. Description of the Related Art Carbon fibers are used as a composite reinforcing material composed of various matrices, but in order to take advantage of the characteristics of carbon fibers in a composite material, the adhesiveness with the matrix is important.

Generally, carbon fibers do not have sufficient adhesiveness to a matrix unless surface treatment is performed, and the lateral properties such as peel strength and shear strength of the composite material are low. For this reason, the carbon fiber is usually subjected to an oxidation treatment such as electrolytic oxidation, chemical solution oxidation, and gas phase oxidation after firing to introduce an oxygen-containing functional group on the surface of the carbon fiber to improve the wettability with the matrix.

Regarding the surface characteristics of the carbon fiber obtained by such an oxidation treatment, JP-A-4-361619 discloses that the adhesive strength of the composite is improved by specifying the functional group on the outermost surface of the carbon fiber. There is. Further, a carbon fiber specified by not only the surface oxygen concentration but also the surface nitrogen concentration measured by X-ray photoelectron spectroscopy is disclosed (for example, Japanese Examined Patent Publication No. 4-44016, Japanese Unexamined Patent Publication No. 2-210059). Kaifaira 2-169763, JP-A-63-85167, JP-A-62-27
No. 6075) has not examined the combination with a sizing agent, and there is a problem that the adhesion force to a matrix, particularly a matrix having low reactivity, is low only by specifying the surface functional group.

On the other hand, regarding the sizing agent, carbon fiber or graphite fiber is essentially rigid and brittle, and is poor in convergence, bending resistance and abrasion resistance, so that fluff and yarn breakage are likely to occur in the high-order processing step. Therefore, usually, various sizing agents are added to the carbon fiber to impart a converging property to improve the bending resistance and the abrasion resistance. As described above, the sizing agent has been conventionally developed and used as a so-called sizing agent or sizing agent for the purpose of improving high-order processability, and there has been almost no study to improve the adhesiveness to the matrix by the sizing agent. Further, no study has been made to adapt the sizing agent to the surface characteristics such as functional groups on the surface of the carbon fiber to improve the composite overall characteristics including adhesiveness and tensile strength.

Since the matrix of the carbon fiber reinforced composite material which is most frequently used at present is an epoxy resin, an epoxy represented by bisphenol A diglycidyl ether type epoxy resin which is an aromatic compound having a structure close to that of the matrix is used as a sizing agent. Resins and modified epoxy resins (for example, Japanese Examined Patent Publication No. 4-8542, JP-A-1-
272867, Japanese Patent Publication No. 62-56266,
Japanese Patent Publication No. 57-15229) is mainly used.

Application of a linear epoxy compound having no aromatic ring to a sizing agent is disclosed in JP-B-60-479.
No. 53, Japanese Patent Publication No. 3-67143, etc. Further, Japanese Patent Publication No. 63-14114 discloses that the use of a specific polyol polyglycidyl ether compound as a sizing agent improves the focusing property and the interlaminar shear strength. However, if only such a sizing agent is limited to specific conditions, there is a problem that the adhesive force to the matrix, particularly the matrix having low reactivity, is not sufficient.

Regarding the sizing agent composition, a resin system obtained by incorporating other components such as polyurethane into the above epoxy resin for the purpose of improving higher-order processability such as bundling property (for example, Japanese Patent Publication No. 1-20270, Japanese Patent Publication 59-145
No. 91, Japanese Patent Laid-Open No. 57-47920) and the like are also being studied.

On the other hand, as the oxidation treatment for obtaining the above-mentioned specific surface characteristics, electrolytic oxidation treatment is generally used industrially. As an electrolyte for this electrolytic oxidation treatment, an aqueous solution of various acids, alkalis or salts thereof has been proposed.

As the electrolytic treatment in an alkaline aqueous solution, an inorganic strong alkaline substance such as sodium hydroxide is preferably used from the viewpoints of treatment efficiency and equipment corrosion prevention (Japanese Patent Laid-Open No. 56-53275). JP-A-61-27
5469 publication). An electrolytic treatment using an organic strong alkaline electrolyte containing no metal element is also disclosed (Japanese Patent Publication No. 3-50029).

Further, a method of acid-electrolyzing carbon fiber and then washing with alkali has been disclosed (Japanese Patent Laid-Open No. 61-12).
4674).

As a technique for introducing a nitrogen-containing functional group such as an amino group or an amide group into carbon fiber, a method of using a basic ammonium salt compound or the like as an electrolyte is USP382.
2297, USP 4844781, Japanese Patent Publication No. 2-4294
No. 0 publication. However, since the matrix has different reactivity with carbon fiber depending on its type, it is not always possible to obtain excellent adhesive properties only by specifying the surface treatment.

Further, Japanese Patent Laid-Open No. 63-120741 discloses a carbon fiber having a metal salt as a functional group.
However, while the metal salt activates the reactivity of the epoxy compound, it has a problem of deactivating a specific curing agent and a problem of deteriorating the high temperature characteristics of the composite, which is not preferable.

A method of electrolytically polymerizing an epoxy compound on the surface of carbon fiber (Japanese Patent Publication No. 1-45490 / 1990, Japanese Patent Publication No.
(Japanese Patent No. 45489) and the like, and it is disclosed that the focusing property and the adhesive property are improved. However, during electrolytic polymerization, not only the reaction between the carbon fiber and the epoxy compound but also the polymerization between the epoxy compounds occurs. Therefore, it becomes difficult to control the reaction in the treatment liquid contaminated with this polymer,
Uniform processing cannot be performed. Further, this polymer may adhere to the surface of the carbon fiber as an impurity and hinder the improvement of the adhesiveness, and there is a limit to the improvement of the adhesive force. Further, there is a problem in the stability of the treatment liquid such as ring opening of the epoxy group of the epoxy compound in the treatment liquid showing acidity and alkalinity.

[0015]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a carbon fiber having excellent adhesiveness with a matrix and excellent composite properties, which cannot be achieved by the above-mentioned prior art, and a method for producing the same.

[0016]

In order to achieve the above object, the carbon fiber of the present invention has the following constitution. That is, the surface oxygen concentration O / C of carbon fiber measured by X-ray photoelectron spectroscopy is 0.20 or less, and the surface hydroxyl group concentration C-OH / C measured by chemically modified X-ray photoelectron spectroscopy is 0.5%.
As described above, a carbon fiber having a surface carboxyl group concentration COOH / C measured by chemical modification X-ray photoelectron spectroscopy of 2.0% or less and sized by an aliphatic compound having a plurality of epoxy groups, X-ray photoelectron Carbon fiber surface oxygen concentration O / C measured by spectroscopy is 0.20 or less, surface hydroxyl group concentration C-OH measured by chemically modified X-ray photoelectron spectroscopy
/ C is 0.5% or more, the surface carboxyl group concentration COOH / C measured by chemical modification X-ray photoelectron spectroscopy is 2.0% or less, and the number of atoms between the epoxy group and the aromatic ring is 6%. The surface oxygen concentration O / C of carbon fiber measured by X-ray photoelectron spectroscopy is 0.20 or less, and the surface nitrogen concentration N / C is as follows. The surface oxygen concentration O / C of the carbon fiber which is 0.02 or more and is sized by the aliphatic compound having a plurality of epoxy groups, or the carbon fiber measured by X-ray photoelectron spectroscopy is 0.20 or less, It is a carbon fiber obtained by sizing an aromatic compound having a surface nitrogen concentration N / C of 0.02 or more and a plurality of epoxy groups having 6 or more atoms between an epoxy group and an aromatic ring.

Further, the method for producing carbon fiber of the present invention has the following constitution in order to achieve the above object. That is, carbon fibers characterized by applying an aliphatic compound having a plurality of epoxy groups as a sizing agent after electrolytic treatment in an alkaline aqueous solution or after electrolytic treatment in an acidic aqueous solution followed by washing with an alkaline aqueous solution. The method for producing a plurality of epoxy groups having a number of atoms between the epoxy group and the aromatic ring of 6 or more after electrolytic treatment in an alkaline aqueous solution or electrolytic treatment in an acidic aqueous solution followed by washing with an alkaline aqueous solution. A method for producing a carbon fiber characterized by applying an aromatic compound having as a sizing agent, after electrolytic treatment in an ammonium salt aqueous solution, applying an aliphatic compound having a plurality of epoxy groups as a sizing agent Method for producing a carbon fiber, or after electrolytic treatment in an ammonium salt aqueous solution, an epoxy group and an aromatic ring A method of producing a carbon fiber, wherein the number of atoms between confer aromatic compound having a plurality of epoxy groups is 6 or more as a sizing agent.

The present invention will be described in detail below.

In the carbon fiber of the present invention, a specific functional group capable of binding one end of a specific sizing agent to the surface of the carbon fiber is formed, and the other end of the sizing agent can be bonded to the matrix to form a carbon fiber. The carbon fiber is characterized in that it can be coupled between the matrix and the matrix with a sizing agent. This makes it possible to obtain high adhesion between the carbon fiber and the matrix.

That is, in order to obtain the coupling effect by the sizing agent, it is not sufficient that the surface functional group of the carbon fiber is simply provided with a functional group as has been conventionally said, and O / C or COOH. It is indispensable that COH / C or N / C should be set to a certain value or more rather, by making the value of / C smaller than a certain value.

That is, as the surface functional group of the carbon fiber, a phenolic hydroxyl group or an amino group plays an important role for exhibiting the coupling effect, but a functional group other than the phenolic hydroxyl group, that is, a carboxyl group, a ketone group, etc. The smaller the number, the better. Especially, it is important that the number of carboxyl groups is small.

The reason for this is that the carboxyl group has a higher reactivity with the epoxy group than the hydroxyl group, but when the carboxyl group is formed, it is necessary for the carbon atom to bond with two oxygen atoms. It is considered that the bond of the six-membered ring of the graphite crystal on the surface is broken, and further oxidation to the cut edge portion proceeds, so that the carbon fiber surface layer having the carboxyl group becomes fragile. Therefore, even if the carboxyl group of the carbon fiber surface layer and the sizing agent are firmly adhered, they are peeled off within the brittle carbon fiber surface layer, and as a result, only a low adhesive force between the carbon fiber and the matrix can be obtained. .

On the other hand, it is considered that a hydroxyl group or an amino group can be generated without breaking the bond of the carbon six-membered ring of the graphite crystal on the surface of the carbon fiber, and if such a functional group is bonded to the sizing layer, the carbon fiber is expensive. / Adhesive force between the matrices can be expressed.

Further, as the sizing agent bonded to the surface of the carbon fiber, a highly reactive sizing agent is essential because it reacts with a hydroxyl group or an amino group, which has a lower reactivity than a carboxyl group. For that purpose, a sizing agent having a plurality of highly reactive epoxy rings is indispensable, and an aliphatic compound or an aromatic compound having a large distance between the epoxy group and the aromatic ring, which is less affected by steric hindrance due to the aromatic ring, is effective. Is.

On the other hand, when the adhesive strength between the carbon fiber and the matrix is increased, the tensile fracture of the composite generally becomes more brittle fracture, so that the tensile strength is lowered. A sizing agent having high toughness is effective in improving the trade-off relationship between the adhesive strength and the tensile strength, and for that purpose, an aliphatic or aromatic compound having a long chain length is effective. Therefore, it is preferable to use an aromatic compound or an aromatic compound having a large distance between the epoxy group and the aromatic ring and having a long chain length, which is less affected by steric hindrance due to the aromatic ring.

The carbon fiber of the present invention has a surface oxygen concentration O / C measured by X-ray photoelectron spectroscopy of 0.20 or less, preferably 0.15 or less, more preferably 0.10 or less. When O / C exceeds 0.20, the chemical bond between the functional group of the resin and the outermost surface of the carbon fiber becomes strong, but the oxide layer, which is considerably lower than the original strength of the carbon fiber substrate itself, forms the carbon fiber surface layer. As a result, the resulting composite will have poor lateral properties.

The lower limit of O / C is 0.02 or more, preferably 0.04 or more, more preferably 0.06 or more. If the O / C is less than 0.02, the reactivity and reaction amount with the sizing agent are insufficient, and as a result, improvement in the lateral properties of the composite may not be expected.

One of the carbon fibers of the present invention is that, in addition to setting the O / C of the X-ray photoelectron spectroscopy within a specific range, the surface hydroxyl group concentration C- of the carbon fibers measured by chemically modified X-ray photoelectron spectroscopy. The OH / C is 0.5% or more and the surface carboxyl group concentration COOH / C is 2.0% or less. If C-OH / C is less than 0.5%, the reactivity with the sizing agent and the amount of reaction are insufficient, and improvement in the lateral method properties of the composite cannot be expected.

The upper limit of C-OH / C is 3.0% or less, preferably 2.5% or less, more preferably 2.0% or less. That is, when C-OH / C exceeds 3%, the reactivity with the sizing agent and the amount of reaction are excessive, and further improvement of the adhesive strength properties cannot be expected, and the tensile strength of the composite may decrease. .

When COOH / C exceeds 2.0%, O /
As in the case where C exceeds 0.2, the carbon fiber surface layer is covered with an oxide layer having a strength considerably lower than that of the carbon fiber substrate itself, so that the lateral properties of the resulting composite are improved. Will decrease. Further, there is a problem that the curing speed of the matrix resin is delayed.

The lower limit of COOH / C is 0.2% or more, preferably 0.5% or more. If COOH / C is less than 0.2%, the reactivity and the amount of reaction with the sizing agent may be insufficient, and improvement in the lateral properties of the composite may not be expected.

Another carbon fiber of the present invention is the above O / C.
In a specific range, the surface nitrogen concentration N / C measured by X-ray photoelectron spectroscopy is 0.02 or more, preferably 0.03 or more, and more preferably 0.04 or more. The carbon fiber having N / C of less than 0.02 cannot improve the reactivity with a specific sizing agent described later, and as a result, the effect of improving the lateral properties of the composite by the sizing agent cannot be exhibited.

The upper limit of N / C is 0.30 or less, preferably 0.25 or less, more preferably 0.20 or less. That is, when N / C exceeds 0.3, the reactivity and the amount of reaction with the sizing agent are excessive, and further improvement of the adhesive strength properties cannot be expected, and the tensile strength may decrease.

The nitrogen concentration on the surface of the carbon fiber is particularly important for improving the adhesiveness, and the nitrogen concentration inside the carbon fiber hardly influences the improving of the adhesiveness. Therefore, strictly speaking, the nitrogen concentration obtained by subtracting the average nitrogen concentration of the entire carbon fiber measured by the elemental analysis method from the surface nitrogen concentration is important, and this value is 0 or more, preferably 0.01 or more, more preferably 0. .02
The above is desirable.

The carbon fiber of the present invention has the above surface characteristics,
In addition, the compound having the following specific structure is sized.

First, in the present invention, an aliphatic compound having a plurality of epoxy groups can be used as a sizing agent.

In the present invention, the aliphatic compound means an acyclic straight chain saturated hydrocarbon, a branched saturated hydrocarbon, an acyclic straight chain unsaturated hydrocarbon, a branched unsaturated hydrocarbon, or the above hydrocarbon. Carbon atoms (CH ₃ , CH ₂ , CH, C) of the oxygen atom (O), nitrogen atom (NH, N), sulfur atom (SO
₃ H, SH) and a compound having a chain structure in which a carbonyl atom group (CO) is substituted.

Further, in the present invention, in the aliphatic compound having a plurality of epoxy groups, of the total number of carbon atoms and hetero atoms (oxygen atom, nitrogen atom, etc.) constituting a chain structure connecting two epoxy groups, The largest atomic chain is called the longest atomic chain, and the total number of atoms that make up the longest atomic chain is called the number of atoms in the longest atomic chain. The number of atoms such as hydrogen bonded to the atoms forming the longest atomic chain is not included in the total number.

The structure of the side chain is not particularly limited, but in order to prevent the intermolecular crosslink density of the sizing agent compound from becoming too large, a structure that does not easily form a crosslinking point is preferable.

If the sizing agent compound has less than two epoxy groups, the bridging between the carbon fiber and the matrix resin cannot be effectively performed. Therefore, it is essential that the number of epoxy groups is two or more in order to effectively bridge the carbon fiber and the matrix resin.

On the other hand, if the number of epoxy groups is too large, the density of intermolecular crosslinks of the sizing agent compound becomes high, and a brittle sizing layer is formed, resulting in a decrease in the tensile strength of the composite. It is preferably no more than 4, more preferably no more than 4, and even more preferably two. Further, it is more preferable that the two epoxy groups are located at both ends of the longest atomic chain. That is, the presence of epoxy groups at both ends of the longest atomic chain prevents the local crosslink density from increasing, which is preferable for the composite tensile strength.

The structure of the epoxy group is preferably a highly reactive glycidyl group.

The molecular weight of such an aliphatic compound is 80 or more and 3 or more from the viewpoint of preventing the handling property as a sizing agent from being deteriorated when the resin viscosity is too low or too high.
200 or less is preferable, 100 or more and 1500 or less are more preferable, and 200 or more and 1000 or less are further preferable.

Specific examples of the aliphatic compound having a plurality of epoxy groups in the present invention include, for example, diglycidyl ether compounds such as ethylene glycol diglycidyl ether and polyethylene glycol diglycidyl ethers, propylene glycol diglycidyl ether and polypropylene glycol didiene. Glycidyl ethers,
1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, polytetramethylene glycol diglycidyl ether, polyalkylene glycol diglycidyl ethers and the like can be mentioned.
The polyglycidyl ether compound includes glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ethers, sorbitol polyglycidyl ethers, arabitol polyglycidyl ethers, trimethylolpropane polyglycidyl ethers, pentaerythritol polyglycidyl ethers. Examples thereof include glycidyl ethers and polyglycidyl ethers of aliphatic polyhydric alcohols.

Preferred are aliphatic polyglycidyl ether compounds having a highly reactive glycidyl group.
More preferably, polyethylene glycol diglycidyl ethers, polypropylene glycol diglycidyl ethers, alkanediol diglycidyl ethers and those having the structures shown below are preferable.

[0046]

[Chemical 5]

[Chemical 6]

[Chemical 7] Here, G is a glycidyl group, R ¹ is -CH ₂ CH _2- , -CH
₂ CH ₂ CH _2- , -CH (CH ₃ ) CH _2- , R ² is -CH _2- ,
At least two of R ³ , R ⁴ and R ⁵ are -G, and the others are -H or -G, m is an integer of 1 to 25, n is an integer of 2 to 75, and x, y and z are 0 or a positive integer, x +
y + z is preferably 0 to 25. Moreover, you may use these mixtures.

In the aliphatic compound having plural epoxy groups, it is preferable that the longest atomic chain has 20 or more atoms. That is, when the number of atoms is less than 20, the crosslink density in the sizing layer becomes high, so that a structure having low toughness is likely to be formed, and as a result, composite tensile strength may be difficult to develop. On the other hand, if the number of atoms in the longest atomic chain is large, the sizing layer tends to have a flexible and highly tough structure, and as a result, composite tensile strength is likely to improve, and since it has the characteristic of high tensile strength especially in brittle resins,
The number of atoms in the longest atomic chain is more preferably 25 or more, and further preferably 30 or more.

However, the larger the number of atoms in the longest atomic chain, the more flexible the structure becomes, but if it is too long, it may bend and block the functional group, resulting in a decrease in the adhesive force between the carbon fiber and the resin. Therefore, the number of atoms is preferably 2
00 or less, and more preferably 100 or less.

When the aliphatic compound contains a cyclic aliphatic skeleton, it can be used as long as the epoxy group is sufficiently separated from the cyclic skeleton, specifically, if the number of atoms is 6 or more.

In the present invention, an aromatic compound having a plurality of epoxy groups having 6 or more atoms between the epoxy group and the aromatic ring can also be used as a sizing agent. The number of atoms between the epoxy group and the aromatic ring refers to the total number of carbon atoms, heteroatoms (oxygen atom, nitrogen atom, etc.), and carbonyl atomic groups constituting the chain structure connecting the epoxy group and the aromatic ring. The linear structure in this case is the same as the above-mentioned linear structure.

If the number of atoms between the epoxy group and the aromatic ring is less than 6 as the sizing agent, a rigid and three-dimensionally large compound will be present at the interface between the carbon fiber and the matrix resin, so that the carbon fiber The reactivity with the surface functional groups present on the outermost surface of the composite is not improved, and as a result, improvement in the lateral properties of the composite cannot be expected.

Specific examples thereof include compounds represented by the following formula [I].

[0053]

[Chemical 8] (Here, in the formula [I], R ¹ is

[Chemical 9] , R ² is an alkylene group having 2 to 30 carbon atoms, and R ³ is —H.
Or -CH ₃ , m and n are integers from 2 to 48, m +
n is 4 to 50. In this case, it is preferable that the molecular chain is linear and has flexibility and the molecular weight is small so that a rigid and sterically large compound is not present at the interface between the carbon fiber and the matrix resin. ], Each of m and n is 2 or more, preferably 3 or more, more preferably 5 or more,
m + n is 4 or more, preferably 6 or more, more preferably 10 or more. m and n are each less than 2 or m +
When n is less than 4, the adhesiveness between the matrix resin and the carbon fiber, which is the object of the present invention, may be reduced. On the other hand, when m + n exceeds 50, the compatibility with the matrix resin is lowered, and the adhesion between the matrix resin and the carbon fiber is sometimes lowered. In the formula [I], R ² is
It is preferably —CH ₂ CH ₂ — or —CH (CH ₃ ) CH ₂ —.

Here, the bisphenol A part or F part in the formula [I] has an effect of improving compatibility with the matrix resin and an effect of improving fluff resistance.

In the present invention, the skeleton of the aromatic compound having a plurality of epoxy groups having 6 or more atoms between the epoxy group and the aromatic ring may be a condensed polycyclic aromatic compound.
Examples of the skeleton of the condensed polycyclic aromatic compound include naphthalene, anthracene, phenanthrene, chrysene, pyrene, naphthacene, triphenylene, 1,2-benzanthracene, and benzopyrene. Preferably,
Naphthalene, anthracene, phenanthrene, and pyrene, which have a small skeleton, are good.

The epoxy equivalent of the condensed polycyclic aromatic compound having a plurality of epoxy groups is 150 to 350, more preferably 200 to 3 from the viewpoint of sufficiently improving the adhesiveness.
00 is preferable.

The molecular weight of the condensed polycyclic aromatic compound having a plurality of epoxy groups is 400 to 80 from the viewpoint of preventing the resin viscosity from increasing and the handleability as a sizing agent from deteriorating.
0, more preferably 400 to 600 is preferable.

In the present invention, as the sizing agent, bisphenol type epoxy compounds having a small molecular weight such as Epicoat 828 and Epicoat 834, linear low molecular weight epoxy compounds, polyethylene glycol, polyurethane,
Other components such as polyester emulsifier or surfactant are viscosity adjusted, scratch resistance is improved, fluff resistance is improved, and convergence is improved.
It may be added for the purpose of improving high-order workability.

Further, there is no problem even if a rubber such as butadiene nitrile rubber or an elastomeric linear epoxy modified compound such as epoxy terminated butadiene nitrile rubber is added.

The amount of the sizing agent attached to the carbon fiber is 0.01 weight per unit weight of the carbon fiber from the viewpoint of increasing the degree of improvement in adhesiveness with the resin and preventing the consumption of the sizing agent from becoming excessive. % Or more and 10% by weight or less is preferable, 0.05% by weight or more and 5% by weight or less is more preferable,
It is more preferable to add 0.1% by weight or more and 2% by weight or less.

In the present invention, the sizing agent is preferably uniformly coated and coated.

That is, the thickness of the sizing agent layer is 20 to
It is preferably 200 angstroms and the maximum thickness does not exceed twice the minimum. The coupling effect can be more effectively exhibited by such a uniform sizing layer.

As the mechanical properties of the carbon fiber of the present invention, the strand strength is 350 kgf / mm ² or more, more preferably 4
00kgf / mm ² or more, further preferably 450 kgf / mm ² or more. The elastic modulus of carbon fiber is 22 tf / mm ²
Or more, more preferably 24 tf / mm ² or more, and 2
8 tf / mm ² or more is more preferable. Strand strength or elastic modulus is less than 350 kgf / mm ² or 2 respectively
If the carbon fiber is less than 2 tf / mm ² , it may not be possible to obtain desired properties as a structural material when it is made into a composite.

Next, a method for obtaining the carbon fiber of the present invention will be described. The surface treatment and sizing treatment of the carbon fiber are as described below, but the polymerization, spinning and firing conditions of the carbon fiber are not restricted.

As the raw material carbon fiber used in the method of the present invention, known carbon fibers such as acrylic type, pitch type and rayon type carbon fibers can be applied. Acrylic carbon fibers are preferable because they can easily obtain high-strength carbon fibers. A case of acrylic carbon fiber will be described in detail below as an example.

As a spinning method, a wet type, a dry type, a dry type and the like can be adopted, but a wet type or a dry type which can easily obtain a high strength yarn is preferable, and a dry type is particularly preferable. Although a solution or suspension of a homopolymer or a copolymerization component of polyacrylonitrile can be used as a spinning stock solution, it is important to enhance filtration to remove impurities from the polymer in order to obtain high-performance carbon fiber. Is.

The spinning stock solution is coagulated, washed with water, drawn, and applied with an oil agent to give a precursor stock yarn, which is further flameproofed, carbonized and, if necessary, graphitized to obtain carbon fibers. It is important to obtain high-performance carbon fiber by minimizing impurities such as dust and foreign matter from utility or atmosphere, preventing defect introduction into fiber, and applying tension to increase orientation throughout the yarn making and firing process. Is. As the carbonization or graphitization condition, the maximum heat treatment temperature is 11 to obtain the carbon fiber of the present invention.
The temperature is 00 ° C or higher, preferably 1400 ° C or higher.

In order to obtain a carbon fiber having high strength and elastic modulus, a carbon fiber having a fineness is preferable, and a single fiber diameter of the carbon fiber is 7.5 μm or less, preferably 6 μm or less, more preferably 5.5 μm or less. . The obtained carbon fibers are further surface-treated and sized to be carbon fibers.

O / C in X-ray photoelectron spectroscopy, surface hydroxyl group concentration C-OH / C measured by chemically modified X-ray photoelectron spectroscopy, and surface carboxyl group concentration COOH / measured by chemical modification X-ray photoelectron spectroscopy The carbon fiber having C in the above-mentioned specific range can be produced by the following method.

One is a method of electrolytically treating carbon fibers in an alkaline aqueous solution. The alkaline electrolyte is a strong alkaline aqueous solution having a pH of 7 to 14, preferably 8 to 14, and more preferably 10 to 14.
The electrolyte may be any one that exhibits alkalinity in an aqueous solution, and specifically includes hydroxides such as sodium hydroxide, potassium hydroxide and barium hydroxide, ammonia, or inorganic substances such as sodium carbonate and sodium hydrogen carbonate. Examples include salts, aqueous solutions of organic salts such as sodium acetate and sodium benzoate, and further potassium salts thereof, barium salts or other metal salts, and ammonium salts, and organic compounds such as hydrazine, but preferably resin curing inhibition. It is preferable to use an inorganic alkali such as ammonium carbonate or ammonium hydrogen carbonate that does not contain an alkali metal that causes the above-mentioned phenomenon, or a tetraalkylammonium hydroxide salt having strong alkalinity.

The concentration of the electrolytic solution is 0.01 to 5 mol / liter, preferably 0.1 to 1 mol / liter. That is, the higher the concentration is, the lower the electrolytic treatment voltage is, but the odor becomes stronger and the environment is deteriorated.

The temperature of the electrolytic solution is 0 to 100 ° C, preferably 10 to 40 ° C. That is, when the temperature is high, the odor becomes strong and the environment is deteriorated, so that the temperature is preferably low, and therefore it is preferable to optimize it in consideration of the operating cost.

The amount of electricity is preferably optimized in accordance with the carbonization degree of the carbon fiber to be treated, and a high elastic modulus yarn requires a larger amount of electricity. From the viewpoint of promoting the decrease of the crystallinity of the surface layer and improving the productivity, while preventing the decrease of the strength of the carbon fiber substrate, it is preferable that the electrolytic treatment be repeated a plurality of times with a small amount of electricity. Specifically, the amount of electricity supplied per electrolytic cell is preferably 5 coulomb / g · cell (the number of coulombs per 1 g of carbon fiber) or more and 100 coulomb / g · cell or less, more preferably 10 coulomb / g · More than a tank,
It is preferably 80 coulomb / g · tank or less, more preferably 20 coulomb / g · tank or more and 60 coulomb / g · tank or less.
Further, from the viewpoint of controlling the deterioration of the crystallinity of the surface layer within an appropriate range, it is preferable that the total amount of electricity in the energization treatment is in the range of 5 to 1000 coulombs / g, further preferably 10 to 500 coulombs / g.

The number of tanks is preferably 2 or more, more preferably 4 or more. From the viewpoint of equipment cost, 10 or less tanks are preferable, and it is preferable to optimize the amount of electricity, voltage, current density and the like.

From the viewpoint of effectively oxidizing the surface of the carbon fiber and not impairing the safety, the current density is 1.5 amperes / m ² per 1 m ² of the surface area of the carbon fiber in the electrolytic treatment liquid.
² or more and 1000 amps / m ² or less, preferably 3 amps / m ² or more and 500 amps / m ² or more. The processing time is preferably from a few seconds to a dozen minutes, and further from 10 seconds to 2 minutes.
Minutes are preferable.

From the viewpoint of safety, the electrolysis voltage is 25 V or less,
Furthermore, 0.5-20V is preferable. The electrolytic treatment time should be optimized depending on the amount of electricity and the electrolyte concentration, but from the viewpoint of productivity, it is preferably several seconds to 10 minutes, preferably 10 seconds to 2 minutes. The electrolytic treatment method may be either a batch method or a continuous method, but a continuous method is preferable because it has good productivity and small variations. As the energization method, either direct energization in which the carbon fiber is brought into direct contact with the electrode roller to energize it or indirect energization in which the carbon fiber and the electrode are energized through an electrolytic solution or the like can be adopted, but electrolytic treatment Indirect energization that suppresses fuzzing, electric sparks and the like is preferable.

In the electrolytic treatment method, the required number of electrolytic baths may be arranged and passed once, or the required number of times may be passed through one electrolytic bath. The anode length of the electrolytic cell is preferably 5-100 mm,
Cathode length is 300-1000mm, and further 350-900
mm is preferred.

O / C of X-ray photoelectron spectroscopy, surface hydroxyl group concentration C-OH / C measured by chemically modified X-ray photoelectron spectroscopy and surface carboxyl group concentration COOH / C measured by chemically modified X-ray photoelectron spectroscopy As a method of producing carbon fibers having C in the above-mentioned specific range, a method of subjecting the carbon fibers to be treated to electrolytic treatment in an acidic aqueous solution and subsequently washing with an alkaline aqueous solution can also be used.

In this case, the electrolyte may be any one that exhibits acidity in an aqueous solution, such as sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, boric acid, carbonic acid and other inorganic acids, acetic acid, butyric acid, oxalic acid, acrylic acid, maleic acid. And organic salts such as ammonium sulfate and ammonium hydrogensulfate. Among these, sulfuric acid and nitric acid which show strong acidity are preferable.

Concentration of electrolytic solution, electrolysis temperature, quantity of electricity applied, total quantity of electricity, electrolysis voltage, treatment time, electrolysis treatment method,
As the energizing method, the same method as in the case of the electrolytic treatment in the alkaline aqueous solution described above can be used, but it is also effective to treat at a higher concentration and a higher temperature in order to further increase the oxidizing power.

The electrolytic treatment in the acidic aqueous solution is followed by the cleaning treatment in the alkaline aqueous solution.

The alkaline aqueous solution used as the cleaning liquid is preferably a strong alkaline aqueous solution having a pH of 7 to 14, more preferably 10 to 14. Specifically, hydroxides such as sodium hydroxide, potassium hydroxide and barium hydroxide,
Ammonia or an aqueous solution of an inorganic salt such as sodium carbonate or sodium hydrogen carbonate, an organic salt such as sodium acetate or sodium benzoate, or a potassium salt thereof.
Examples thereof include barium salt or other metal salt, and ammonium salt, and an aqueous solution of an organic compound such as hydrazine, but it is preferable to use an inorganic alkali such as ammonium carbonate or ammonium hydrogen carbonate that does not contain an alkali metal that causes curing inhibition with a resin, or An aqueous solution of tetraalkylammonium hydroxide having strong alkalinity is preferable.

The concentration of the alkaline compound in the alkaline aqueous solution used as the cleaning solution is a pH within the above specified range.
It is preferable to adjust so that
1 to 10 mol / liter, preferably 0.1 to 2 mol / liter
L is good. The temperature of the cleaning liquid is 0 to 100 ° C,
Room temperature to 60 ° C is preferable.

As the cleaning method, there are a dipping method, a spraying method and the like, but a dipping method which is easy to clean is preferable. Further, it is more preferable to vibrate the carbon fiber with ultrasonic waves during cleaning.

After the electrolytic treatment or the washing treatment, it is preferable to wash with water and dry. In this case, if the drying temperature is too high, the functional groups present on the outermost surface of the carbon fiber are likely to disappear by thermal decomposition, so it is desirable to dry at a temperature as low as possible. Specifically, the drying temperature is 250 ° C. or lower,
More preferably, drying at 210 ° C. or lower is desirable.

Carbon fibers whose surface oxygen concentration O / C and surface nitrogen concentration N / C measured by X-ray photoelectron spectroscopy fall within the above-mentioned specific ranges can be obtained by electrolytic treatment in an aqueous ammonium salt solution. .

In this case, the electrolytic solution may be an aqueous solution containing ammonium ions. Specifically, as the electrolyte, for example, ammonium nitrate, ammonium sulfate,
Ammonium persulfate, ammonium chloride, ammonium bromide, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium hydrogen carbonate, ammonium carbonate, and the like, or mixtures thereof can be used, but among them, ammonium sulfate, ammonium nitrate, ammonium chloride, ammonium carbonate. And ammonium hydrogencarbonate are preferable, and ammonium carbonate and ammonium hydrogencarbonate are particularly preferable because they have less residue on the carbon fiber surface after washing with water and drying.

Concentration of electrolytic solution, electrolysis temperature, quantity of electricity applied, total quantity of electricity, electrolysis voltage, treatment time, electrolysis treatment method,
As the preferable conditions for the energization method and the like, the same method as in the case of the electrolytic treatment in the alkaline aqueous solution described above can be used.

The means for applying the sizing agent is not particularly limited. For example, a method of immersing the sizing agent in a sizing solution through a roller, a method of contacting the roller to which the sizing solution is attached, and a method of spraying the sizing solution in a mist form and so on. Further, either a batch system or a continuous system may be used, but a continuous system is preferable because it has good productivity and can reduce variations. At this time, it is preferable to control the concentration of the sizing solution, temperature, yarn tension, etc. so that the amount of the active ingredient of the sizing agent attached to the carbon fibers is uniformly attached within an appropriate range. Further, it is more preferable to vibrate the carbon fiber with ultrasonic waves when applying the sizing agent.

The drying temperature and the drying time should be adjusted according to the amount of the compound deposited, but the time required for the complete removal of the solvent used for applying the sizing agent and the drying is shortened, while
From the viewpoint of preventing the heat deterioration of the sizing agent and preventing the carbon fiber bundles from becoming hard and the spreadability of the bundles from deteriorating, the drying temperature is preferably 150 ° C. or higher and 350 ° C. or lower, and 180 ° C. or higher 250 More preferably, the temperature is not higher than ° C.

Examples of the solvent used for the sizing agent include water, methanol, ethanol, dimethylformamide, dimethylacetamide, and acetone, but water is preferable from the viewpoint of easy handling and disaster prevention. Therefore, when a water-insoluble or slightly water-soluble compound is used as a sizing agent, it is preferable to add an emulsifier, a surfactant or the like to make it water-dispersible. Specifically, the emulsifier, as the surfactant, styrene-maleic anhydride copolymer, olefin-maleic anhydride copolymer, formalin condensate of naphthalene sulfonate, anionic emulsifier such as sodium polyacrylate, Cationic emulsifiers such as polyethyleneimine and polyvinylimidazoline, nonylphenol ethylene oxide adducts, polyvinyl alcohol, polyoxyethylene ether ester copolymers, nonionic emulsifiers such as sorbitan ester ethyl oxide adducts, etc. can be used, but with an epoxy group Nonionic emulsifiers having a small interaction with are preferable.

The carbon fiber of the present invention is used as a composite material in combination with a matrix.

As the target matrix, thermosetting resins such as epoxy and polyester resins, thermoplastic resins such as nylon and polyether ether ketone, and various matrices such as cement can be applied, but the sizing agent compound has an epoxy group. Since it is a compound, a thermosetting resin or a thermoplastic resin having a high affinity is preferable, and an epoxy resin is more preferable.

Specifically, commercially available bisphenol type epoxy can be used. For example, as bisphenol A type, Epicoat 828, 1001, 10 can be used.
04, 1009 (made by Yuka Shell Epoxy Co., Ltd.) and Epotote YD019, YD020, YD7019, YD702
0, Phenototo YP50, YP50P (manufactured by Tohto Kasei Co., Ltd.), Epicron 840, 850, 855, 860, 1
050, 1010, 1030 (manufactured by Dainippon Ink and Chemicals, Inc.) and the like. Examples of bisphenol F type include Epiclon 830 and 831 (manufactured by Dainippon Ink and Chemicals, Inc.).

For the phenol novolac type epoxy resin, Epicoat 152,154 (made by Yuka Shell Epoxy Co., Ltd.), Dow Epoxy DEN431,438,439,4
85 (manufactured by Dow Chemical Co.), Ciba Geigy EPN113
There are 8,1139 (made by Ciba Geigy). As a modified cresol novolac type epoxy, for example, Ciba Geigy ECN 1235, 1273, 1280, 1299
(Manufactured by Ciba Geigy), EOCN102, 103, 1
04 (manufactured by Nippon Kayaku Co., Ltd.), Epicron N660, N66
5, N670, N673, N680, N690, N69
5 (manufactured by Dainippon Ink and Chemicals, Inc.). Alternatively, a modified phenol novolac type epoxy resin may be used. Further, in the polyfunctional epoxy resin, N, N, N ', N'-tetraglycidyl diaminodiphenylmethane is ELM434 (Sumitomo Chemical Co., Ltd.), MY720 (Ciba Geigy Co., Ltd.),
There is YH434 (manufactured by Tohto Kasei Co., Ltd.).

An epoxy resin composition is obtained by combining these epoxy resins according to the purpose. The additives and curing agents are not particularly limited, but polyvinyl acetal resin, polyvinyl butyral resin, polyvinyl formal resin, etc. are used as additives, and diaminodiphenyl sulfone, boron trifluoride / amine complex, imidazole compound, dicyandiamide, urea derivative are used as curing agents. , And multiple curing agents can be used simultaneously.

Further, although the curing temperature is not limited, it is suitable for an epoxy resin composition having a low reactivity with carbon fibers in order to make the effect of improving the lateral properties of the composite remarkable, and the curing temperature is not limited. Is 200 ° C. or lower, preferably 150 ° C. or lower. Specifically, Japanese Patent Publication Sho 63-6
No. 0056, JP-A-63-162732, and other epoxy resin compositions with improved heat resistance at 180 ° C., and epoxy resins at 130 ° C. disclosed in Japanese Patent Publication No. 4-80054. A composition or the like can be preferably used, and is particularly suitable for a 130 ° C.-curable epoxy resin composition having low reactivity.

[0098]

EXAMPLES The present invention will be described in more detail below with reference to examples.

First, a method of measuring individual characteristic values used in the present invention will be described.

Surface oxygen concentration (O / C) of carbon fiber, surface nitrogen concentration (N / C), surface hydroxyl group concentration (C-OH / C), surface carboxyl group concentration (COOH / C), nitrogen concentration by elemental analysis (N / C) and the number of fluffs were determined by the following methods.

The surface oxygen concentration O / C was determined by X-ray photoelectron spectroscopy according to the following procedure. First, a carbon fiber bundle from which a sizing agent and the like has been removed with a solvent is cut and spread on a stainless steel sample support table and arranged, and then a photoelectron escape angle is set to 90 °, and MgKα _1,2 is used as an X-ray source. The inside of the sample chamber is kept at a vacuum of 1 × 10 ⁻⁸ Torr. In order to correct the peak due to charging during measurement, first adjust the binding energy value of the main peak of C _1S to 284.6 eV. The C _1S peak area was determined by drawing a linear baseline in the range of 282 to 296 eV, and the O _1S peak area was determined by drawing a linear baseline in the range of 528 to 540 eV. The surface oxygen concentration O / C was represented by the atomic number ratio calculated by dividing the ratio of the O _1S peak area and the C _1S peak area by the sensitivity correction value specific to the apparatus. In this example, ESCA-750 manufactured by Shimadzu Corporation was used, and the sensitivity correction value peculiar to the above apparatus was 2.85.

The surface oxygen concentration N / C was determined by X-ray photoelectron spectroscopy according to the following procedure. First, a carbon fiber bundle from which a sizing agent and the like has been removed with a solvent is cut and spread on a stainless steel sample support table and arranged, and then a photoelectron escape angle is set to 90 °, and MgKα _1,2 is used as an X-ray source. The inside of the sample chamber is kept at a vacuum of 1 × 10 ⁻⁸ Torr. In order to correct the peak due to charging during measurement, first adjust the binding energy value of the main peak of C _1S to 284.6 eV. The C _1S peak area was obtained by drawing a linear baseline in the range of 282 to 296 eV, and the N _1S peak area was obtained by drawing a linear baseline in the range of 398 to 410 eV. The surface nitrogen concentration N / C is represented by the atomic number ratio calculated by dividing the ratio of the N _1S peak area and the C _1S peak area by the sensitivity correction value specific to the apparatus. In this example, ESCA-750 manufactured by Shimadzu Corporation was used, and the sensitivity correction value peculiar to the above apparatus was 1.7.

The surface hydroxyl group concentration C-OH / C was determined by chemical modification X-ray photoelectron spectroscopy according to the following procedure. First, a carbon fiber bundle from which a sizing agent and the like has been removed with a solvent is cut and spread on a sample support made of platinum to be arranged in a dry nitrogen gas containing 0.04 mol / l anhydrous trifluoroacetic acid gas. After exposure at room temperature for 10 minutes and chemical modification treatment, the sample was mounted on an X-ray photoelectron spectrometer with a photoelectron escape angle of 35 °, AlKα _1,2 was used as the X-ray source, and the inside of the sample chamber was at 1 × 10 ⁻⁸ Torr. Keep vacuum. In order to correct the peak associated with charging during measurement, first adjust the binding energy value of the main peak of C _1S to 284.6 eV. The C _1S peak area [C _1S ] is obtained by drawing a straight base line in the range of 282 to 296 eV, and the F _1S peak area [F _1S ] is 6
It was calculated by drawing a linear baseline in the range of 82 to 695 eV. At the same time, the reaction rate r was determined from the C _1S peak division of polyvinyl alcohol that was chemically modified.

The surface hydroxyl group concentration C-OH / C is represented by the value calculated by the following formula.

COH / C = {[F _1S ] / (3k [C _1S ] -2
[F _1S ]) r} x 100 (%) Note that k is a sensitivity correction value of the F _1S peak area with respect to the C _1S peak area unique to the apparatus.
Using the model SSX-100-206 manufactured by the same company, the sensitivity correction value peculiar to the above apparatus was 3.919.

The surface carboxyl group concentration COOH / C was determined by chemical modification X-ray photoelectron spectroscopy according to the following procedure. First, a carbon fiber bundle from which a sizing agent and the like has been removed with a solvent is cut and spread on a platinum sample support table and arranged,
X-rays after chemical modification treatment were performed by exposing to air containing mol / l trifluoroethanol gas, 0.001 mol / l dicyclohexylcarbodiimide gas and 0.04 mol / l pyridine gas at 60 ° C. for 8 hours. The sample was mounted on a photoelectron spectrometer with a photoelectron escape angle of 35 °, AlKα _1,2 was used as an X-ray source, and the inside of the sample chamber was maintained at a vacuum degree of 1 × 10 ^-8 Torr. In order to correct the peak due to charging during measurement, first adjust the binding energy value of the main peak of C _1S to 284.6 eV. The C _1S peak area [C _1S ] is obtained by drawing a straight base line in the range of 282 to 296 eV, and the F _1S peak area [F _1S ] is 6
It was calculated by drawing a linear baseline in the range of 82 to 695 eV. At the same time, the reaction rate r was obtained from the C _1S peak division of the polyacrylic acid chemically modified, and the residual rate m of the dicyclohexylcarbodiimide derivative was obtained from the O _1S peak division.

The surface carboxyl group concentration COOH / C is represented by the value calculated by the following formula.

COOH / C = {[F _1S ] / (3k [C _1S ]-(
2 + 13 m) [F _1S ]) r} x 100 (%) Note that k is a sensitivity correction value of the F _1S peak area with respect to the C _1S peak area unique to the apparatus.
Using the model SSX-100-206 manufactured by the same company, the sensitivity correction value peculiar to the above apparatus was 3.919.

The average nitrogen concentration by elemental analysis was determined by the following procedure. First, about 2 before the sizing process
CHMG coder manufactured by Yanagimoto Co., Ltd.
It measured on the following conditions using MT-3 type | mold apparatus.

CHN coder sample combustion furnace at 950 ° C.
The oxidizing furnace is heated to 850 ° C. and the reducing furnace is heated to 550 ° C., helium is caused to flow at a rate of 180 ml / min, the washed carbon fibers are precisely weighed, and then put into the sample combustion furnace.

A portion of the decomposed gas in the sample combustion furnace was sucked through the oxidation furnace and the reduction furnace for about 5 minutes using a suction pump, and then the amount of N ₂ was detected by the thermal conductivity type detector of the CHN coder. Was determined and the weight ratio of the amount of nitrogen to the amount of carbon was determined by calibration. The average nitrogen concentration was calculated by converting the obtained weight ratio into an atomic number ratio.

The number of fluffs was determined by the following procedure.
First, five stainless steel rods (chromium plated, surface roughness 1 to 1.5 ^S ) having a diameter of 10 mm are parallel to each other at 50 mm intervals, and while their surfaces are in contact with carbon fiber threads at a contact angle of 120 °. A scraping device was used with the rods arranged in a zigzag so that they could pass through. This device applies a tension of 0.09 g per denier to the carbon fiber yarn on the entry side, and 3
The yarn is passed at a yarn speed of m / min, a laser beam is irradiated from the side face at a right angle to the fiber yarn, and the number of fluffs is detected and counted by a fluff detecting device and displayed in pieces / m.

In the present invention, the tensile strength of the carbon fiber used is the tensile strength of the strand, the elastic modulus, and the tensile strength of the composite. The plate edge peel strength (hereinafter abbreviated as EDS) and the interlaminar shear strength (hereinafter abbreviated as ILSS) were used as an index of the lateral characteristics of the composite, that is, the adhesive force between the carbon fiber and the matrix.

Further, the influence on Charpy impact characteristics was examined.

The strand tensile strength and elastic modulus were determined by the following procedure. It measured according to the resin-impregnated strand test method of JIS-R-7601. Bakelite (registered trademark) ERL422 manufactured by Union Carbide Co. as a resin formulation
1/3 boron fluoride monoethylamine / acetone = 10
Using 0/3/4 (parts by weight), the curing conditions are normal pressure,
130 ° C. and 30 minutes were used. Ten strands were measured and the average value was calculated.

The resins for composite property evaluation are the following A,
B2 types of resins were used.

Resin A was prepared as follows according to Example 1 disclosed in Japanese Examined Patent Publication No. 4-80054. That is, 3.5 kg (35 parts by weight) of Epicoat 1001 manufactured by Yuka Shell Epoxy Co., Ltd. and 2.5 kg of Epicoat 828 manufactured by Yuka Shell Epoxy Co., Ltd.
(25 parts by weight) and Epichron N manufactured by Dainippon Ink and Chemicals, Inc.
3.0 kg (30 parts by weight) of 740, 1.5 kg (15 parts by weight) of Epicoat 152 manufactured by Yuka Shell Epoxy Co., Ltd., 0.8 kg (8 parts by weight) of Denka Formal # 20 manufactured by Denki Kagaku Kogyo Co., Ltd., and 0.5 kg of dichlorophenyldimethylurea. (5 parts by weight) was added and stirred for 30 minutes to obtain a resin composition. A release paper was coated with this to form a resin film.

Curing was carried out under a pressure of 3 kgf / cm ² · G at 135 ° C.
It took 2 hours.

Resin B was prepared as follows according to Example 1 disclosed in JP-B-63-60056. That is,
Sumitomo Chemical Co., Ltd. ELM434 6.0 kg (60 parts by weight), Yuka Shell Epoxy Co., Ltd. Epicoat 825 3.0 kg (30 parts by weight), Dainippon Ink and Chemicals Co., Ltd. Epicron 830 1.0
kg (10 parts by weight) and polyether sulfone 1.75 kg
(17.5 parts by weight) was heated and stirred at 150 ° C. for 30 minutes to obtain a transparent viscous liquid. This composition was cooled to 60 ° C. and 4.6 kg (46 parts by weight) of diaminodiphenyl sulfone was uniformly dispersed to obtain a resin composition. A release paper was coated with this to form a resin film.

Curing was carried out under pressure of 6 kgf / cm ² · G, 180 ° C.,
It took 2 hours.

A composite test piece was prepared as follows. First, wind a resin film coated on a silicon-coated paper with a resin to be combined with carbon fibers on a steel drum having a circumference of about 2.7 m, and then wind the carbon fibers drawn from the creel onto the resin film via a traverse. After arranging and further covering the fibers with the resin film again, the resin is impregnated by rotating and pressing with a pressure roll to impregnate the resin into a unidirectional prepreg having a width of 300 mm and a length of 2.7 m. To do.

At this time, the drum is heated to 60 to 70 ° C. in order to improve the resin impregnation between the fibers, and the fiber areal weight of the prepreg is adjusted by adjusting the rotational speed of the drum and the traverse feeding speed. A prepreg having 200 g / m ² and a resin amount of about 35% by weight was prepared.

The prepreg thus produced was cut,
For EDS (+ 25 / -25 / + 25 / -25 / 9
0) _s were laminated and heat-cured under predetermined curing conditions using an autoclave to produce a cured plate having a thickness of about 2 mm. For ILSS and tensile strength, prepregs were laminated in one direction to make unidirectional laminated plates having a thickness of about 2 mm and about 1 mm, respectively.

The EDS test piece had a width of 25.4 mm and a length of 23.
The test length was set to 0 mm and the test length was set to 127 mm using a normal tensile test jig, and the measurement was performed at a crosshead speed of 1 mm / min. The peel strength was obtained from the load at the time when delamination started on the side surface of the test piece. Five pieces were measured and the average value was calculated.

The ILSS test piece had a width of 12.7 mm and a length of 2
The measurement was carried out at a crosshead speed of 2.5 mm / min by setting the supporting span to 4 times the wall thickness of the test piece using an ordinary 3-point bending test jig. Eight pieces were measured and the average value was calculated.

The test piece for tensile strength had a width of 12.7 mm and a length of 2
30 mm, the thickness of each test piece is 1.2 mm and the length is 5 mm.
A 0 mm GFRP tab was adhered (if necessary, a strain gauge for measuring elastic modulus and breaking strain was attached to the center of the test piece), and the crosshead speed was measured at 1 mm / min.
Five pieces were measured and the average value was calculated.

A unidirectionally hardened plate having a thickness of about 6 mm was prepared for the Charpy impact test by the same method as that for ILSS and tensile strength. The test piece has a width of 10 mm and a length of 6 without a notch.
It was set to 0 mm.

The Charpy impact tester weighs 30 kgf.
We used a standard type m (Yonekura Seisakusho) equipped with a load sensor at the rear of the striking part and instrumented. Therefore, the output from the amplifier of the load sensor was transferred to the personal computer via the waveform digital memory, and the maximum load and the absorbed energy until the maximum load was reached were obtained as measurement items. The impact direction of the test piece was flatwise, and the distance between fulcrums was 40 mm. Ten points were measured and the average value was calculated.

Example 1 Using a copolymer of 99.4 mol% acrylonitrile and 0.6 mol% methacrylic acid, an acrylic fiber having a single fiber fineness of 1 denier and a filament number of 12000 was prepared by a dry-wet spinning method. Obtained. The obtained fiber bundle was stretched at a draw ratio of 1.40 in air at 240 to 280 ° C.
It is heated at 05 to convert into flameproof fiber, and then the temperature rising rate in a temperature range of 300 to 900 ° C in a nitrogen atmosphere is 200 ° C.
/ Min, 10% stretching was performed, and then firing was performed up to 1300 ° C.

Tetraethylammonium hydroxide (hereinafter abbreviated as TEAH) aqueous solution having a concentration of 0.1 mol / liter was used as an electrolytic solution, and the amount of electricity supplied per tank was 10 coulomb / g · tank. The carbon fiber was treated with a total electricity of 40 coulomb / g. The voltage was 12 V and the current density was 9.5 A / m ² . At that time, the electrolytic solution became cloudy. The electrolytically treated carbon fiber was subsequently washed with water and dried in heated air at 150 ° C.

Subsequently, glycerol triglycidyl ether was diluted with dimethylformamide (hereinafter abbreviated as DMF) so that the resin component was 1% by weight to prepare a sizing agent mother liquor, and a sizing agent was added to the carbon fiber by a dipping method. It was applied and dried at 230 ° C. The amount deposited was 0.4% by weight.

The strand strength and elastic modulus of the carbon fiber thus obtained were 484 kgf / mm ² and 23.8 tf / mm ² . Surface functional group amount, tensile strength with resin A and EDS
The measurement results of are shown in Table 1.

(Embodiments 2, 3, 4) The total amount of electricity is 5,1.
A carbon fiber was obtained by the same treatment as in Example 1 except that the number of treatment tanks and the amount of electricity per tank were changed so as to be 0,20 coulomb / g. The results are also shown in Table 1.

(Embodiment 5) The concentration of the electrolytic solution is 0.25 mol /
A carbon fiber was obtained by treating in the same manner as in Example 1 except that the aqueous solution of ammonium hydrogen carbonate was changed. The results are also shown in Table 1.

(Comparative Example 1) The concentration of the electrolytic solution was 0.05 mol /
Carbon fiber was obtained by treating in the same manner as in Example 1 except that the sulfuric acid aqueous solution was changed to liter and the number of treatment tanks and the electricity quantity per tank were changed so that the total electricity quantity was 100 coulomb / g. . The results are also shown in Table 1.

[0136]

[Table 1] (Examples 6 to 9) Resin components of the sizing agent were glycerol diglycidyl ether and polyethylene glycol diglycidyl ether (in the formula [II], R ¹ is -CH ₂ CH _2.
2− , m = 9), diglycerol polyglycidyl ether and diethylene glycol diglycidyl ether were used, and carbon fibers were obtained in the same manner as in Example 1. Table 2 shows the measurement results of the amount of surface functional groups of the obtained carbon fiber, the tensile strength of Resin A and EDS.

(Examples 10 and 11) The resin component of the sizing agent was changed to glycerol diglycidyl ether and polyethylene glycol diglycidyl ether (in the formula [II], R ¹ was -CH ₂ CH _2- , m = 9). except,
A carbon fiber was obtained by treating in the same manner as in Example 5. Surface functional group amount of the obtained carbon fiber, tensile strength with Resin A and ED
The measurement results of S are shown in Table 2.

[0138]

[Table 2] (Comparative Example 2) A carbon fiber was obtained in the same manner as in Example 1, except that the sizing agent was immersed in a DMF solution containing no sizing component. The results are shown in Table 3.

(Comparative Examples 3 and 4) The resin component of the sizing agent was a bisphenol A type diglycidyl ether having an aromatic ring, Yuka Shell Epoxy Co., Ltd. Epicoat 828 (the number of atoms between the epoxy ring and the aromatic ring = 2). A carbon fiber was obtained in the same manner as in Example 1 except that the phenol novolac type glycidyl ether and Epicoat 154 manufactured by Yuka Shell Epoxy Co., Ltd. (the number of atoms between the epoxy ring and the aromatic ring = 2) were used. The results are shown in Table 3.

[0140]

[Table 3] (Example 12) An acrylic fiber having a single fiber fineness of 1 denier and a filament number of 12000 was obtained by a dry-wet spinning method using a copolymer of 99.4 mol% acrylonitrile and 0.6 mol% methacrylic acid. The obtained fiber bundle is heated in air at 240 to 280 ° C. at a draw ratio of 1.05 to be converted into flame-resistant fiber, and then 300 to 300 in a nitrogen atmosphere.
The rate of temperature increase in the temperature range of 900 ° C is set to 200 ° C / min. 1
After 0% stretching, it was fired to 1800 ° C.

Tetraethylammonium hydroxide (TEAH) aqueous solution having a concentration of 0.1 mol / liter was used as an electrolytic solution, and the amount of electricity supplied per tank was set at 40 coulomb / g · tank. Electricity 20
Treated with 0 coulomb / g. Voltage 16V, current density is 3
It was 0 A / m ² . At that time, the electrolytic solution became cloudy. The electrolytically treated carbon fiber was subsequently washed with water and dried in heated air at 150 ° C. Then, glycerol triglycidyl ether was diluted with dimethylformamide (DMF) to adjust the resin component to 1% by weight to prepare a sizing agent mother liquor, and a sizing agent was applied to the carbon fiber by a dipping method, and dried at 230 ° C. Was done. The amount deposited was 0.5% by weight.

Table 4 shows the amounts of surface functional groups of the carbon fibers thus obtained, the tensile strength of the resin A and the EDS measurement results.

(Comparative Example 5) The concentration of the electrolytic solution was 0.05 mol /
A carbon fiber was obtained by the same procedure as in Example 12 except that the sulfuric acid aqueous solution was changed to liter and the sizing agent was immersed in a DMF solution containing no sizing component. The results are shown in Table 4.

(Example 13) Carbon fibers, which had been electrolyzed in a sulfuric acid aqueous solution in Comparative Example 5, subsequently washed with water and dried in heated air at 150 ° C, were continuously treated with a TEAH aqueous solution having a concentration of 0.1 mol / liter. It was stirred and dipped in it for 10 minutes. At that time, the cleaning liquid turned black. Then wash with water, 1
A carbon fiber was obtained by the same treatment as in Comparative Example 5 except that the carbon fiber was dried at 50 ° C. The results are shown in Table 4.

[0145]

[Table 4] (Example 14) A carbon fiber was obtained in the same manner as in Example 13 except that the resin component of the sizing agent was changed to glycerol diglycidyl ether. Table 4 shows the measurement results of the amount of the surface functional groups of the obtained carbon fiber and the EDS of the resin A.

(Example 15) Acrylonitrile 99.4
An acrylic fiber having a monofilament fineness of 0.7 denier and a filament number of 12,000 was obtained by a dry-wet spinning method using a copolymer composed of mol% and methacrylic acid 0.6 mol%. The obtained fiber bundle is heated in the air of 240 to 280 ° C. at a draw ratio of 1.05 to be converted into flame resistant fiber, and then the temperature rising rate in a temperature range of 300 to 900 ° C. in a nitrogen atmosphere is 200 ° C. / Min and 10% stretching, then 1800
Bake to ℃.

An aqueous solution of ammonium hydrogen carbonate having a concentration of 0.25 mol / liter was used as an electrolytic solution, and the amount of electricity supplied per tank was set to 20 coulomb / g · tank. By repeating 5 tanks, the total electric quantity of the carbon fiber was 100 coulombs. / G. The voltage was 13 V and the current density was 15 A / m ² . The electrolytically treated carbon fiber is subsequently washed with water and heated to 180 ° C.
Dried in heated air.

Subsequently, a sizing agent prepared by adding 5% by weight of a nonionic emulsifier to glycerol triglycidyl ether was diluted with water so that the components would be 1% by weight to prepare a sizing agent mother liquor. A sizing agent was applied to the fibers and dried at 180 ° C. The amount deposited was 0.4% by weight.

Table 5 shows the measurement results of surface functional groups, strand strength, strand elastic modulus, composite tensile strength with Resin A and EDS of the carbon fiber thus obtained.
It was shown to. The composite tensile modulus is 17.1 t.
It was f / mm ² .

The absorbed energy up to the maximum load obtained by the instrumented Charpy impact test was 55 kJ / m ² , and the maximum load was 5.2 kN.

(Example 16) The amount of electricity per tank was 20
A carbon fiber was obtained in the same manner as in Example 15, except that the carbon fiber was treated at a coulomb / g · tank of 10 times and the total amount of electricity was 200 coulomb / g. The results are also shown in Table 5.

(Examples 17 to 19) The electrolytic solution was concentrated to 0.2
Aqueous ammonium carbonate solution of 5 mol / liter, concentration of 0.
Carbon fibers were obtained in the same manner as in Example 15 except that the aqueous solution of ammonium sulfate was 10 mol / liter and the aqueous solution of ammonium nitrate was 0.10 mol / liter. The results are also shown in Table 5.

(Comparative Example 6) A carbon fiber was obtained in the same manner as in Example 15 except that the electrolytic treatment was not performed. The results are also shown in Table 5.

(Comparative Example 7) The concentration of the electrolytic solution was 0.05 mol /
A carbon fiber was obtained in the same manner as in Example 15 except that the sulfuric acid aqueous solution was changed to 1 liter. The results are also shown in Table 5.
Further, the composite tensile elastic modulus was 17.2 tf / mm ² .

The absorbed energy up to the maximum load obtained by the instrumented Charpy impact test was 46 kJ / m ² , and the maximum load was 4.6 kN.

(Comparative Example 8) An electrolytic solution having a concentration of 0.10 mol /
A carbon fiber was obtained by treating in the same manner as in Example 15 except that the aqueous sodium hydroxide solution was changed to 1 liter. The results are shown in Table 5.
Are also shown.

[Table 5] (Examples 20 to 31) Resin components of the sizing agent were glycerol diglycidyl ether, diethylene oxide diglycidyl ether, polyethylene oxide diglycidyl ether (in the formula [II], R ¹ is -CH ₂ CH _2-).
, M = 9 and 30), polypropylene oxide diglycidyl ether (in the formula [II], R ¹ is —CH (C
H ₃ ) CH _2- , m = 7, 9, 17 and 69), 1,6
-Hexanediol diglycidyl ether, alkanediol diglycidyl ether (in the formula [III], n
= 12) and a compound of the formula [IV] (R ¹ is —CH ₂ CH ₂ —
, R ³ , R ⁴ and R ⁵ are glycidyl groups, x + y + z = 2
0 and 30), except that the carbon fiber was treated in the same manner as in Example 15. The results are shown in Table 6 or Table 7.

(Comparative Example 9) A carbon fiber was obtained in which the step of applying the sizing agent was omitted. The results are shown in Table 7.

(Comparative Example 10) Except that the resin component of the sizing agent was changed to lauryl monodiglycidyl ether,
A carbon fiber was obtained by treating in the same manner as in Example 15. The results are also shown in Table 7.

(Comparative Examples 11 and 12) Resin components of the sizing agent were bisphenol A type diglycidyl ether, Epicoat 828 (number of atoms between epoxy ring and aromatic ring = 2) manufactured by Yuka Shell Epoxy Co., Ltd. and phenol novolac type. A carbon fiber was obtained in the same manner as in Example 15, except that glycidyl ether, Epicoat 154 manufactured by Yuka Shell Epoxy Co., Ltd. (the number of atoms between the epoxy ring and the aromatic ring = 2) was used. The results are also shown in Table 7.

[0160]

[Table 6]

[Table 7] (Example 32) A 1800 ° C fired yarn prepared by spinning and firing in the same manner as in Example 12 was used with an aqueous ammonium hydrogen carbonate solution having a concentration of 0.25 mol / liter as an electrolytic solution, and the energization amount per tank was 20 coulombs. / G · tank, and the total electric quantity of the carbon fiber is 100 coulomb by repeating 5 tanks /
Treated with g. The electrolytically treated carbon fibers were subsequently washed with water and dried in heated air at 180 ° C.

Then, in the formula [I], R ² is replaced with —CH ₂ CH
_2- , R ³ is -CH ₃ , m is 15, and n is 15 and the resin component of the sizing agent is 1% by weight of a water emulsion.
And dried. The attached amount was 0.8% by weight. Table 8 shows the measurement results of the functional group concentration of the carbon fiber thus obtained, the number of scratched fluffs, the strand strength, the composite tensile strength of the resin A and the EDS. The strand elastic modulus is 30.5 tf / mm ² , and ILSS is 11.
It was 8 kgf / mm ² . The average nitrogen concentration determined by elemental analysis was 0.019.

(Examples 33, 34, 35) The electrolytic solution was an aqueous solution of ammonium carbonate having a concentration of 0.25 mol / liter, an aqueous solution of ammonium sulfate having a concentration of 0.10 mol / liter,
A carbon fiber was obtained in the same manner as in Example 32 except that the ammonium nitrate aqueous solution had a concentration of 0.10 mol / liter. The results are also shown in Table 8.

(Comparative Example 13) A carbon fiber was obtained in the same manner as in Example 32 except that the electrolytic solution was changed to an aqueous solution of sulfuric acid having a concentration of 0.05 mol / liter. The results are also shown in Table 8. The strand tensile modulus is 30.5 tf / mm ² ,
ILSS was 10.8 kgf / mm ² .

(Comparative Example 14) A carbon fiber was obtained in the same manner as in Example 32 except that the electrolytic solution was changed to an aqueous sodium hydroxide solution having a concentration of 0.10 mol / liter. The results are also shown in Table 8.

[Table 8] (Example 36) In the formula [I], R ² is -CH ₂ CH _2- ,
A carbon fiber was obtained by the same procedure as in Example 32 except that a water emulsion in which R ³ was —CH ₃ , m was 2, and n was 2 and the resin component of the sizing agent was 1% by weight. The results are shown in Table 9
It was shown to. O / C was 0.10 and N / C was 0.02.

(Examples 37 to 40) R in the formula [I]
² is -CH ₂ CH _2- , R ³ is -CH ₃ , m is 5, n is 5, a sizing agent having [I] of R ² is -CH ₂ CH _2-.
, R ³ is -CH ₃ , m is 10 and n is 10, and in the formula [I], R ² is -CH ₂ CH _2- , R ³ is-.
A sizing agent in which H and m are 15 and n is 15, and in the formula [I], R ² is -CH ₂ CH _2- , R ³ is -CH ₃ , and m is 3
A carbon fiber was obtained in the same manner as in Example 32 except that a sizing agent having 0 and n of 30 was used. The results are shown in Table 9 or Table 10. O / C is 0.10, N / C is 0.
It was 02.

Comparative Example 15 In the formula [I], R ¹ is -O
H, R ² is -CH ₂ CH _2- , R ³ is -CH ₃ , m is 15, n
The carbon fiber was obtained in the same manner as in Example 32 except that a water emulsion having a sizing agent resin component of 15 was used. The results are also shown in Table 10. O / C
Was 0.10 and N / C was 0.02. The strand tensile elastic modulus is 30.5 tf / mm ² , and ILSS is 10.9.
It was kgf / mm ² .

(Comparative Example 16) In the formula [I], R ² is
CH ₂ CH _2- , R ³ is -CH ₃ , m is 1 and n is 1, and a carbon fiber is treated in the same manner as in Example 32 except that a water emulsion containing 1% by weight of a resin component is used. Obtained.
The results are also shown in Table 10. O / C is 0.10, N /
C was 0.02.

[0168]

[Table 9]

[Table 10] In Tables 9 and 10, the number of epoxy / aromatic ring atoms means the number of atoms between the epoxy group and the aromatic ring.

(Example 41) 1,6-naphthalene polyethylene oxide (6
Molar adduct) diglycidyl ether is diluted with dimethylformamide (DMF) to prepare a sizing agent mother liquor,
A carbon fiber was obtained in the same manner as in Example 32 except that the sizing agent was added to the carbon fiber by the dipping method and the carbon fiber was dried at 230 ° C. The results are shown in Table 11. O / C is 0.1
0 and N / C were 0.03.

(Comparative Example 17) A carbon fiber was obtained in the same manner as in Example 41 except that the electrolytic solution was changed to an aqueous solution of sulfuric acid having a concentration of 0.05 mol / liter. The results are also shown in Table 11. O / C was 0.15 and N / C was 0.01.

[0171]

[Table 11] (Example 42) In the formula [I], R ² is -CH ₂ CH _2- ,
A carbon fiber was obtained by the same treatment as in Example 1 except that the resin component of the sizing agent in which R ³ was —CH ₃ , m was 15 and n was 15 was used. Table 12 shows the composite tensile strength of Resin A and the results of EDS.

[0172]

[Table 12] (Example 43) The composite tensile strength and EDS of the carbon fiber obtained in Example 1 were measured with Resin B. The results are also shown in Table 13.

(Examples 44 to 46) Examples 6, 7, and 42
The composite tensile strength and EDS of the carbon fiber obtained in (1) were measured with Resin B. The results are also shown in Table 13.

(Comparative Example 18) Composite tensile strength and EDS of the carbon fiber obtained in Comparative Example 2 were measured with Resin B. The results are also shown in Table 13.

[0175]

[Table 13]

[0176]

INDUSTRIAL APPLICABILITY The carbon fiber of the present invention has a specific surface functional group on the surface and is provided with a highly reactive aliphatic compound or aromatic compound having a specific structure as a sizing agent. The adhesive strength can be remarkably improved. When the aromatic compound having the specific structure is added as a sizing agent, in addition to the above effects,
For example, it is possible to prevent generation of scratched fluff and yarn breakage during high-order processing of carbon fiber such as prepreg and drum wind.
Workability can be further improved. Furthermore, in a preferred embodiment in which the length of the main chain of the compound having the above-mentioned specific structure is specified, in addition to the remarkable improvement of the adhesive strength of the composite, the tensile strength of the composite often decreases due to the improvement of the adhesive strength. It has a very remarkable effect of suppressing the decrease of

Since the carbon fiber of the present invention has the above-mentioned excellent characteristics, it can be used for a structural member which has been difficult to use due to lack of adhesive strength with a conventional matrix resin.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location D01F 11/16 D06M 10/00 // D06M 101: 40 (72) Inventor Kazuharu Shimizu Iyo Ehime Prefecture 1515 Tsutsui, Matsumae-machi, Kori Toray Industries, Inc. Ehime factory

Claims (27)

[Claims] 1. The surface oxygen concentration O / C of carbon fiber measured by X-ray photoelectron spectroscopy is 0.20 or less, and the surface hydroxyl group concentration C-OH / C measured by chemically modified X-ray photoelectron spectroscopy is 0. Carbon fiber having a surface carboxyl group concentration COOH / C measured by chemical modification X-ray photoelectron spectroscopy of 2.0% or less and a sizing of an aliphatic compound having a plurality of epoxy groups. 2. The surface oxygen concentration O / C of carbon fiber measured by X-ray photoelectron spectroscopy is 0.20 or less, and the surface hydroxyl group concentration C-OH / C measured by chemically modified X-ray photoelectron spectroscopy is 0. Epoxy having a surface carboxyl group concentration COOH / C measured by chemical modification X-ray photoelectron spectroscopy of 2.0% or less and an atom number between the epoxy group and the aromatic ring of 6 or more. A carbon fiber obtained by sizing an aromatic compound having a plurality of groups. 3. The carbon fiber has a surface oxygen concentration O / C of 0.20 or less, a surface nitrogen concentration N / C of 0.02 or more, and a plurality of epoxy groups as measured by X-ray photoelectron spectroscopy. Carbon fiber obtained by sizing an aliphatic compound. 4. The carbon fiber has a surface oxygen concentration O / C of 0.20 or less and a surface nitrogen concentration N / C of 0.02 or more as measured by X-ray photoelectron spectroscopy, and has an epoxy group and an aromatic ring. A carbon fiber obtained by sizing an aromatic compound having a plurality of epoxy groups having 6 or more atoms between. 5. The carbon fiber according to claim 1, which is a compound having epoxy groups at both ends of the longest atomic chain. 6. The carbon fiber according to claim 1, which is a compound having epoxy groups only at both ends of the longest atomic chain. 7. The epoxy group is a glycidyl group.
The carbon fiber according to any one of to 6. 8. The number of atoms in the longest atomic chain of the aliphatic compound having a plurality of epoxy groups is 20 to 200, and any one of claim 1, claim 3, claim 5, claim 6, and claim 7. The described carbon fiber. 9. The aliphatic compound having a plurality of epoxy groups is at least one compound selected from glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyethylene glycol diglycidyl ethers and polypropylene glycol diglycidyl ethers. The carbon fiber according to claim 1, claim 3, claim 5, claim 6, or claim 7. 10. The number of atoms between the epoxy group and the aromatic ring is 6
The carbon fiber according to claim 2 or 4, wherein the aromatic compound having a plurality of epoxy groups as described above is a compound represented by the following formula. [Chemical 1] (Here, in the formula [I], R ¹ is , R ² is an alkylene group having 2 to 30 carbon atoms, and R ³ is —H.
Or -CH ₃ , m and n are integers from 2 to 48, m +
n is 4 to 50. ) 11. R ² is —CH ₂ CH ₂ — or —CH (CH ₃ ).
The carbon fiber according to claim 10, which is CH _2- . 12. The carbon fiber according to claim 2 or 4, wherein the aromatic compound is a condensed polycyclic aromatic compound. 13. The carbon fiber according to claim 12, wherein the skeleton of the condensed polycyclic aromatic compound is naphthalene, anthracene, phenanthrene, or pyrene. 14. After electrolytic treatment in an alkaline aqueous solution,
Alternatively, a method for producing carbon fiber, which comprises electrolytically treating in an acidic aqueous solution and subsequently washing with an alkaline aqueous solution, and then applying an aliphatic compound having a plurality of epoxy groups as a sizing agent. 15. After electrolytic treatment in an alkaline aqueous solution,
Alternatively, after electrolytic treatment in an acidic aqueous solution and subsequent washing with an alkaline aqueous solution, an aromatic compound having a plurality of epoxy groups having 6 or more atoms between an epoxy group and an aromatic ring is added as a sizing agent. And a method for producing a carbon fiber. 16. A method for producing carbon fiber, which comprises applying an aliphatic compound having a plurality of epoxy groups as a sizing agent after electrolytic treatment in an aqueous solution. 17. A sizing agent, characterized by applying an aromatic compound having a plurality of epoxy groups having 6 or more atoms between an epoxy group and an aromatic ring as a sizing agent after electrolytic treatment in an aqueous ammonium salt solution. Carbon fiber manufacturing method. 18. The method for producing a carbon fiber according to claim 14, which is a compound having epoxy groups at both ends of the longest atomic chain. 19. The method for producing a carbon fiber according to claim 14, which is a compound having an epoxy group only at both ends of the longest atomic chain. 20. The method for producing carbon fiber according to claim 14, wherein the epoxy group is a glycidyl ether group. 21. The number of atoms in the longest atomic chain of the aliphatic compound having a plurality of epoxy groups is 20 to 200.
4. The method for producing a carbon fiber according to claim 16, claim 18, or claim 19. 22. The aliphatic compound having a plurality of epoxy groups is at least one compound selected from glycerol polyglycidyl ether, diglycerol diglycidyl ether, polyethylene glycol diglycidyl ethers and polypropylene glycol diglycidyl ethers. A method for producing a carbon fiber according to claim 14, claim 16, claim 18, or claim 19. 23. The number of atoms between the epoxy group and the aromatic ring is 6
The method for producing a carbon fiber according to claim 15 or 17, wherein the aromatic compound having a plurality of epoxy groups as described above is a compound represented by the following formula [I]. [Chemical 3] (Here, in the formula [I], R ¹ is , R ² is an alkylene group having 2 to 30 carbon atoms, and R ³ is —H.
Or -CH ₃ , m and n are 2 to 48, and m + n is 4
~ 50. ) 24. R ² is —CH ₂ CH ₂ — or —CH (CH ₃ ).
The method for producing a carbon fiber according to claim 23, which is CH _2- . 25. The method for producing carbon fiber according to claim 15 or 17, wherein the aromatic compound is a condensed polycyclic aromatic compound. 26. The method for producing a carbon fiber according to claim 25, wherein the skeleton of the condensed polycyclic aromatic compound is naphthalene, anthracene, phenanthrene, or pyrene. 27. The method for producing a carbon fiber according to any one of claims 14 to 26, wherein sizing is performed with a water solvent system.