JP2932582B2 - Surface modification method for carbon fiber - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for modifying the surface of carbon fibers.

(Prior art) Carbon fiber is a "fibrous carbon material consisting essentially of carbon element" and is a unique material having various properties derived from carbon as a substance and fiber as a form. . That is, it has characteristics inherent to carbon materials such as heat resistance, chemical stability, conductivity, heat conductivity, sliding characteristics, and biocompatibility. The first property obtained by shaping into a fibrous form is flexibility, and when a fiber structure is given, properties such as high rigidity and dimensional stability are also exhibited.

Such carbon fibers utilize many excellent properties such as heat resistance, light weight and high rigidity, and are used in most industrial and consumer products, from daily necessities such as umbrellas and sports equipment such as rackets to structural materials for aircraft and satellites. Widely used in the field. Also, unlike synthetic fibers, they are rarely used in the form of yarn or an intermediate substrate consisting of only yarn, and are mostly used in the form of composite materials.

However, carbon fibers obtained through carbonization or graphitization have poor surface wettability and low adhesion to matrix resins. 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, and the like are being studied. .

In the latter case, attempts have been made to grow whiskers of silicon carbide, and it has been reported that there is an improvement effect. However, this method has not been practically used because it is difficult to uniformly grow whiskers on thousands of single fibers and it takes time for the treatment.

In the former, oxidation treatment is usually used, and in addition to the formation of hydroxyl groups, carbonyl groups, and carboxyl groups on the surface, a dense layer on the surface is removed, the surface area is increased, and irregularities are generated on the surface. Changes have an effect on improving wettability and adhesiveness.

As another chemical method, a method of increasing the affinity between a carbon material and a matrix using fluorine gas has been reported (Japanese Patent Application Laid-Open No. 60-191011).

(Problems to be Solved by the Invention) In the above-mentioned 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 does not increase defects. In addition to the introduction, further improvement in wettability is required.

(Means for Solving the Problems) The present inventors have conducted various studies with the aim of improving the affinity between the carbon fiber and the matrix, and by using a combination of fluorination and alkali treatment of the carbon fiber, the wettability has been significantly improved. Was found to be improved, and the present invention was reached.

That is, the gist of the present invention is a method of modifying the surface of a carbon fiber, which comprises fluorinating the surface of the carbon fiber and then treating the surface with an alkali.

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, carbon fiber produced from coal tar pitch, petroleum pitch, polyacrylonitrile, cellulose, polyvinyl alcohol, etc., and carbonized Fibers, graphitized graphitized fibers, or whiskers by a gas phase method can also be used.

The fluorination treatment in the present invention is performed using fluorine gas. The temperature is preferably 90 ° C. or lower, more preferably 30 ° C. or lower, in a temperature range in which a sufficient amount of C—F covalent bond is not formed. In addition, the fluorination treatment time may be a short treatment if the fluorine is uniformly supplied to the carbon material, and the treatment time is usually 1 to 30 minutes since a corresponding effect cannot be expected even if the time is long. , More preferably 10 minutes or less.

The fluorine partial pressure of the fluorine gas is not particularly limited from pressurized to depressurized, but it is preferable to perform the treatment at 1 mmHg to 50 mmHg.

The fluorine gas may be used alone, or may be used by mixing an inert gas such as nitrogen or argon. Furthermore, it can be used even if it contains a gas such as oxygen.

In the present invention, after the fluorination treatment, the surface of the carbon fiber is subjected to an alkali treatment.

Examples of the alkali include hydroxides of alkali metals such as potassium and sodium, carbonates, hydroxides of alkaline earth metals such as barium and the like, which form hydroxyl ions in a solution.

The concentration of these alkalis is usually 1 N or less, preferably 0.1
Used at ~ 0.001N.

The alkali treatment varies depending on the degree of the fluorination treatment in the former stage and the alkali concentration, but is usually selected from the conditions of room temperature to about 100 ° C. for several seconds to several days.

In the method of the present invention, before and after the fluorination treatment,
It is also possible to perform liquid phase oxidation such as various chemical liquid oxidations or electrolytic oxidations or gas phase oxidations, and then perform the above alkali treatment.

The carbon fiber surface-modified according to the present invention has improved adhesiveness with a thermosetting and thermoplastic resin such as an epoxy resin, an unsaturated polyester resin, a bismaleimide resin, a polyimide resin, a polysulfone resin, and a polyetheretherketone resin. Useful as a fiber reinforcement for composite materials.

(Examples) Hereinafter, the present invention will be described in more detail with reference to Examples.
The scope of the present invention is not limited to the examples unless it exceeds the gist.

Examples 1 to 4 and Comparative Examples 1 to 3 About 0.1 g of pitch-based carbon fiber (sintered at 1500 ° C.) was placed in a reactor for fluorination treatment, and after maintaining the inside of the vessel at a vacuum, fluorine gas was introduced. The treatment was performed under the fluorination conditions shown in Table 1.
Next, the obtained fluorinated carbon fiber was treated with an alkali under the conditions shown in Table 1 to obtain a modified carbon fiber.

As a measure of the wettability of these modified carbon fibers with water, the receding contact angle was measured by the Wilhelmy method (measuring device: Shimadzu automatic contact angle measuring device "ST-1S"). The measurement was performed five times, and the average value is shown in Table 1.

(Effect of the Invention) According to the method of the present invention, the wettability of the surface is improved, and a carbon fiber that is stable over time can be obtained.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-1911011 (JP, A) JP-A-62-149968 (JP, A) JP-B-49-38954 (JP, B1) (58) Field (Int.Cl. ⁶ , DB name) D06M 11/00-11/84

Claims (3)

(57) [Claims] 1. A method for modifying the surface of a carbon fiber, wherein the surface of the carbon fiber is fluorinated and then treated with an alkali. 2. The method according to claim 1, wherein the fluorination treatment is performed at a temperature of about 90 ° C. or less. 3. The method according to claim 1, wherein the concentration of the alkali is 1 N or less.