JPH0578975A - Method for modifying surface of carbon fiber - Google Patents

Abstract

PURPOSE:To improve wettability on the surface of carbon fiber and enhance adhesion of the carbon fiber to a matrix resin by subjecting the surface of the carbon fiber to fluorinating treatment and then removing the chemically adsorbed fluorine component present on the surface. CONSTITUTION:The surface of carbon fiber is preferably presubjected to oxidizing treatment and then fluorinating treatment in fluorine gas. The fluorine component, produced during the above-mentioned treatment and chemically adsorbed on the surface of the carbon fiber is then washed with water and removed. Thereby, the wettability on the fiber surface is improved to improve the adhesion of the carbon fiber to a matrix resin. The resultant carbon fiber is suitable as carbon reinforcing fiber for composite materials.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for modifying the surface of carbon fiber.

[0002]

2. Description of the Related Art Carbon fiber is a "fibrous carbon material consisting essentially of carbon element", and is a unique material having various characteristics derived from carbon as a substance and fiber as a form. .. That is, it has characteristics peculiar to a carbon material such as heat resistance, chemical stability, electrical conductivity, thermal conductivity, sliding characteristics, and biocompatibility. Further, the first property obtained by shaping into a fibrous shape is flexibility, and when a fibrous structure is given, properties such as high rigidity and dimensional stability are also expressed.

Such carbon fibers are heat resistant, lightweight,
Utilizing many excellent properties such as high rigidity, it is widely used in most industrial and consumer fields, from everyday items such as umbrellas and sports equipment such as rackets to structural materials for aircraft and satellites. Also, unlike synthetic fibers, it is rarely used in the form of yarn or intermediate equipment consisting only of yarn,
Most are used in the form of composite materials.

However, the carbon fibers obtained through carbonization or graphitization have poor surface wettability and poor adhesion to the matrix resin. Therefore, as a method of improving the wettability of the fiber for improving the adhesiveness, a method of chemically treating the fiber to introduce a functional group, a method of fixing a substance having good adhesiveness to the surface, etc. have been studied. .. In the latter case, it has been attempted to grow a silicon carbide whisker, and it is reported to have an improving effect. However, this method has not been put to practical use because it is difficult to grow whiskers uniformly on thousands of single fibers and it takes time to process.

In the former case, an oxidation treatment is usually used. In addition to the formation of hydroxyl groups, carbonyl groups and carboxyl groups on the surface, the dense layer on the surface is removed, the surface area is increased, and the surface is uneven. The change such as occurrence of is effective for improving wettability and adhesiveness. Also, as another chemical method, a method of increasing the affinity between the carbon material and the matrix by using fluorine gas has been reported (Japanese Patent Laid-Open No. 60-191011).

[0006]

In the above oxidation treatment, even if the degree of surface treatment is increased, the amount of active sites does not increase in proportion to the degree of treatment, and surface roughening causes defects. There is no need to improve the wettability by introducing it.

[0007]

Means for Solving the Problems The present inventors have conducted various studies for the purpose of improving the affinity between the carbon fiber and the matrix, and after fluorinating the carbon fiber, a specific fluorine component present on the surface It was found that the wettability can be further improved by removing the above, and the present invention has been accomplished.

That is, the present invention resides in a method for modifying the surface of carbon fiber, which comprises fluorinating the surface of carbon fiber and then removing the chemically adsorbed fluorine component present on the surface. Hereinafter, the present invention will be described in detail. First,
The carbon fiber used in the present invention can be produced from various known raw materials, for example, coal tar pitch, petroleum pitch, polyacrylonitrile, cellulose,
It is also possible to use carbon fibers which are produced from polyvinyl alcohol or the like and which have been carbonized or graphitized fibers which have been graphitized, or whiskers produced by a vapor phase method.

The fluorination treatment in the present invention is carried out with fluorine gas. The temperature is preferably 90 ° C. or lower, preferably 30 ° C. or lower, in a temperature range in which covalent bonds of C—F are not sufficiently formed. Further, the fluorination treatment time is usually 1 to 30 minutes because a short treatment is sufficient if fluorine is uniformly supplied to the carbon fibers, and a corresponding effect cannot be expected even if the time becomes long. , And more preferably 10 minutes or less. The fluorine partial pressure of the fluorine gas is not particularly limited from pressurization to depressurization, but preferably 1 mmHg to 50 mmHg
It is better to process in.

Further, even if fluorine gas is used alone,
It can also be used by mixing with an inert gas such as nitrogen or argon, or air. It is preferable to oxidize the surface of the carbon fiber prior to the above fluorination treatment.
The oxidation treatment may be either liquid-phase oxidation or gas-phase oxidation, as long as it introduces an oxygen-containing functional group or an oxide such as a C—O—C bond to the surface, and increases the surface area or creates unevenness. May be accompanied by.

As the liquid-phase oxidation method, (i) nitric acid, permanganic acid / sulfuric acid, chromate, hypochlorite and other chemical liquid oxidation, and (ii) various electrolytes such as acids, alkalis and salts were used. Electrolytic oxidation can be mentioned. Examples of the gas phase oxidation method include methods using air, oxygen, ozone, nitrogen oxides, halogen gas, plasma, catalytic oxidation and the like.

In the above oxidation, for example, when concentrated nitric acid is used, it is preferable to boil for about 0.5 to 48 hours for chemical solution oxidation. In the case of electrolytic oxidation, the carbon fiber to be treated is used as an anode, voltage 1 to 50 V, current density, 0.1 to 10 mA per 1 cm of carbon fiber length, energization amount, 0.05 to 500 clones per 1 g of carbon fiber, time. ,Few seconds~
The temperature is usually several minutes to room temperature to about 80 ° C.

Further, in the case of vapor phase oxidation, it is generally 400 to 1100 ° C. for several seconds to several minutes, though it depends on the kind of vapor phase. In the method of the present invention, after the above fluorination treatment, the chemically adsorbed fluorine component existing on the surface is removed. That is, although the fluorine component is present in various states on the carbon surface by the above fluorination treatment, it is necessary to substantially remove the fluorine component chemically adsorbed on the surface. For this purpose, for example, a method of washing with water can be adopted.

This washing with water can be carried out at a temperature of usually 50 ° C. or lower, preferably 30 ° C. or lower, for 10 minutes to several days, by dipping or spraying. The type of water is not particularly limited, and may include various salts, but preferably p
H4 ~ 8 is used. After the washing with water is completed, it is usually dried at room temperature to 100 ° C. Further, if it is possible to substantially remove the chemically adsorbed fluorine component, an organic solvent or the like can be used instead of water washing.

By the above method, the chemically adsorbed fluorine component is substantially removed from the surface of the carbon fiber. Since the chemically adsorbed fluorine component is in an atomic state, it has an oxidizing power, and when iodine ion exists in water, they oxidize the iodine ion according to the following formula (I) to produce I ₂ . F ₂ + 3I ⁻ → I ₃ ⁻ + 2F ⁻ (I) This formed I ₃ ⁻ (I ² + I ⁻ ) is quantified by using a starch solution as an indicator by using an aqueous Na ₂ S ₂ O ₃ solution, thereby remaining chemisorption. It is possible to know the presence or absence of the fluorine component.

In the carbon fiber from which the chemisorbed fluorine component is removed from the surface according to the present invention, it is considered that fluorine is in the state of covalent bond or ionic bond or semiionic bond having partial covalent property with carbon on the surface. It is presumed that, in particular, the ionic to semi-ionic bond has polarity and is involved in improving the wettability. The carbon fiber surface-modified according to the present invention has improved wettability with epoxy resin, unsaturated polyester resin, bismaleimide resin, polyimide resin, polysulfone resin, polyether ether ketone resin, etc. ,
It is useful as a fiber reinforcement for composite materials.

[0017]

The present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited to the examples unless it exceeds the gist. Example 1 About 0.7 g of pitch-based carbon fiber (calcined at 1500 ° C.) was placed in a reactor for fluorination treatment, the inside of the container was kept vacuum, and then fluorine gas was introduced to perform fluorination treatment at room temperature (F _Two two
0 mmHg, 30 minutes).

Then, it was immersed in water at room temperature for 24 hours.
After the obtained modified carbon fiber was dried at about 70 ° C. for 24 hours, the receding contact angle was measured as a measure of wettability with water (measuring device: Shimadzu automatic contact angle measuring device “ST-
1S). The measurement was performed 5 times and the average value was calculated. The results are shown in Table 1. Further, the fluorine component having an oxidizing power (chemically adsorbed fluorine component) existing on the surface of the carbon fiber was quantified by iodometry. Iodometry after 1 week soaking carbon fiber about 0.5g in 0.2 N KI solution 200 ml, I ₃ is generated from the following formula (I) ^- (I ₂
+ I ⁻ ) was titrated with a microburet using a 5% starch solution as an indicator using 0.001N Na ₂ S ₂ O ₃ aqueous solution ((II)). F ₂ + 3I ⁻ → I ₃ ⁻ + 2F ⁻ (I) I ₃ ⁻ + 2S ₂ O ₃ ² → → 3I ⁻ + S ₄ O ₆ ²⁻ (II) The results are shown in Table 1.

Further, for comparison, in Example 1 described above, regarding the carbon fiber which was subjected to only the fluorination treatment without immersion in water, the contact angle and the I ₂ were the same as above.
The amount produced was measured. The results are also shown in Table 1 (Comparative Example 1).

[0020]

[Table 1]

[0021]

According to the method of the present invention, it is possible to obtain a modified carbon fiber having improved surface wettability.

Continuation of front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location D06M 101: 40

Claims (2)

[Claims] 1. A method for modifying the surface of a carbon fiber, which comprises fluorinating the surface of the carbon fiber and then removing the chemically adsorbed fluorine component present on the surface. 2. The method according to claim 1, wherein the chemically adsorbed fluorine component is washed with water.