JPS6065178A - Surface treatment of carbon fiber - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for electrolytically treating carbon fibers, and more particularly to a method for electrolytically oxidizing the surface of carbon fibers uniformly and with high efficiency. In recent years, carbon fiber has been used as a composite material by combining various resin materials, and its usefulness has been increased by reflecting its excellent strength and elastic modulus in structural materials. However, carbon fiber surfaces are inherently extremely chemically stable, have poor wettability and adhesion to resin matrices, and have low mechanical strength, especially interlaminar shear strength, even when molded as a composite material, so they cannot be used as structural materials. However, the practical performance was not satisfied.

In order to solve these essential drawbacks of carbon fibers, various oxidation treatment methods have been studied as surface treatment methods for carbon fibers. Among these surface oxidation treatment methods, the method of electrolytic surface oxidation treatment using carbon fiber as an anode has a high workability and
Although it is said to be industrially advantageous in terms of environmental protection and quality, this surface electrolytic treatment method has the following drawbacks. When manufacturing carbon fiber industrially, electrolytically treating multiple yarns in parallel is advantageous in terms of production efficiency, but it is difficult to produce carbon fiber bundles, which is an important matter for quality control. It is difficult to perform electrolytic treatment evenly and uniformly between yarns.

That is, in the conventional electrolytic treatment method described above, it is observed that adjacent yarns come close to each other in the electrolytic cell and run in close contact with each other, but such closeness of adjacent yarns causes disturbances in the voltage distribution in each yarn. This results in uneven electrolytic treatment not only within the fiber bundle but also between the fiber bundles. Therefore, as mentioned above, in recent years, carbon fiber composite materials, which have become widely used as structural materials for aviation materials,9 heavy electrical materials, etc., are being used for long periods of time. Although improving the strength of the material is an important issue, even if the unevenness of electrolytic treatment does not clearly appear as a difference in strength as a result of material testing, it may be difficult to It reduces the mechanical properties of the material.

Note that Japanese Patent Application Laid-Open No. 47-35396 proposes a method of treating carbon fibers with an aqueous surfactant solution.
The surfactant in this case is used as a fiber treatment agent and is intended to form a thin film on the fiber surface, and its purpose is clearly different from the electrolytic oxidation treatment of carbon fibers, which is the object of the present invention.

As a result of intensive research to solve the problems with the prior art, the present inventors discovered that the cause of the sticking in the electrolytic cell is the surface tension of the electrolyte solution that wets the carbon fibers, and the present invention has been made based on this finding. It has come to this.

That is, the object of the present invention is to reduce the crowding of fiber threads running in parallel in surface electrolytic treatment of carbon fibers, and to perform uniform surface electrolytic treatment within and between fiber bundles. The purpose is to provide a method.

This object of the present invention can be achieved by electrolytically treating carbon fibers in an electrolyte solution containing a surfactant.

The invention will be explained in more detail below.

A feature of the present invention is that a surfactant is added to the electrolyte solution to reduce the surface tension of the electrolyte solution. Therefore, the surfactant used in the present invention is preferably a compound that dissolves in an electrolyte solution and has the property of lowering the surface tension of the electrolyte solution, either alone or in a mixture of two or more. Specific examples of such surfactants include hydrophobic groups such as hydrocarbon groups, polydimethylsiloxane groups, or fluorinated hydrocarbon groups, and carboxylates, sulfonates, ammonium salts, or ethylene oxide adducts. Compounds having hydrophilic groups may be mentioned, but surfactants which, when added to the electrolyte solution, can reduce the surface tension of the electrolyte solution to about 40 dynes/a11 or less are preferably used.

Furthermore, by adding a surfactant above the critical micelle concentration, it is possible to stably lower the surface tension of the electrolyte solution; This is undesirable from the viewpoint of environmental conservation or operation.

The carbon fibers subjected to surface electrolytic treatment in the present invention include:
Various known carbon fibers may be mentioned, but the material is not particularly limited. The electrolyte solution is usually an aqueous solution of sulfuric acid, nitric acid, boric acid, caustic alkali, or an ammonium compound, and its concentration is not particularly limited due to the transference number, but it is usually in the range of several percent by weight. ten percent
used within the range of Further, the temperature of the electrolyte solution is not particularly limited, but it is usually carried out in the range of room temperature to about 80°C.

Since the present invention has the above configuration, it has the following effects. That is, since the surface tension of the electrolyte solution is lowered, the tendency of adjacent yarns to come together in electrolytic treatment of multiple yarns is reduced, so that the unevenness of electrolytic treatment within a fiber bundle and between fiber bundles is significantly reduced. Furthermore, as the surface tension of the electrolyte solution decreases, when the carbon fiber bundle enters the electrolyte solution, the electrolyte solution sufficiently penetrates into the inside of the carbon fiber bundle and wets it, so that electrolytic treatment within the fiber bundle is performed. It is possible to reduce unevenness.

In carrying out the present invention, the electrolytic cell is preferably a cell equipped with a non-contact electrode as described in Japanese Patent Publication No. 47-29942, and more preferably a portion of the electrolytic cell near the surface of the electrolyte solution is treated. is even more effective.

A further useful point of the present invention is that carbon fibers can be uniformly electrolyzed simply and efficiently without any need for modification of electrolytic treatment tanks known in the prior art.

Hereinafter, the present invention will be specifically explained with reference to Examples.

Example 1 Carbon fiber obtained by firing acrylic fiber was
10 yarns were run continuously in parallel at intervals of 0.1 wt.
Electrolytic treatment was performed at a current of 0.8 A/tube using a non-contact electrode type electrolytic cell filled with a 5% by weight aqueous sulfuric acid solution in which the molar adduct had been dissolved. The surface tension of the sulfuric acid aqueous solution can be increased from 71 dynes/Lff11 to 18 by adding a surfactant.
the law of nature.

The force of the fibers decreased to 1/am, and the force of adjacent yarns coming together in the electrolytic cell was not observed during the electrolytic treatment.

The carbon fibers subjected to surface electrolytic treatment were thoroughly washed with water, dried by heating, and wound up. The obtained carbon fiber bundle was molded into a unidirectionally strengthened (gamma) composite material using an epoxy resin (trade name Koko Pico 828° manufactured by Shell Co., Ltd.) containing boron trifluoride monoethylamine as a resin matrix. In the past, the average value of 10 specimens of composite material with 1 tensile strength in the 0 direction was 192 kg/'m"
The range of variation in r measurements was 5 kg/m”.

In addition, the average value of the interlaminar shear strength of 10 specimens was 9.2
kg/kaku2, variation range is 0.3 kg/t
It was "m".

Comparative Example 1 Carbon fibers were electrolytically treated in the same manner as in Example 1 without adding a surfactant to the electrolyte solution. It was observed that four of the ten carbon fiber threads running in parallel were coming together two at a time.

Unidirectional reinforcement molded from the resulting carbon fiber.

The average value of the tensile strength in the 0° direction of the composite material (number of samples = lO) is 185 kg/wa", and the range of variation is 12
kg/m”. Also, the interlaminar shear strength (number of samples =
The average value of lO) was 9.1 kg/ms'', and the range of variation was 0.8 kg/m''.

Patent application Daitoshi Co., Ltd. (8 complete)

Claims (1)

[Claims] A method for surface treatment of carbon edges, which comprises electrolytically treating carbon fibers in an electrolyte solution containing a surfactant.