JPH0465572A - Method for carrying out surface oxidation treatment of carbon fiber and treating device therefor - Google Patents

Abstract

PURPOSE:To enable effective surface oxidation treatment of carbon fiber even having high modulus by electrolyzing an electrolytic solution in a state in which part of a cathode is exposed from the electrolytic solution into air when a carbon fiber is subjected to anode oxidation in the electrolytic solution. CONSTITUTION:For example, a carbon fiber bundle 1 is introduced through a current-carrying roll 2 into an electrolyzer 6 in which electrolytic solution consisting of 1N aqueous solution of sulfuric acid is packed and positive charge is applied to the carbon fiber bundle 1 with the current-carrying roll 2 and electricity is continuously applied in a state in which the upper part of cathode 4 is exposed in air. Thereby the surface of a carbon fiber even having high modulus is effectively subjected to oxidation treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method and apparatus for surface oxidation treatment of carbon fibers.

Conventional technology Carbon fiber reinforced plastic (CF RP) takes advantage of its high specific strength and specific stiffness and is used in a variety of fields, including the aerospace field, sports and leisure field, and general industrial field. It is the material.

The properties of this CFRP depend not only on the properties of the carbon fibers that are the reinforcing material, but also on the affinity between the base material and the carbon fibers. Therefore, in general, by surface oxidizing carbon fiber,
Functional groups are introduced to the surface to improve the affinity and adhesion between the base material and the carbon fibers.

Surface oxidation methods include heating in an oxidizing atmosphere such as air, immersion in an oxidizing liquid such as concentrated nitric acid, and electrolytic oxidation in an electrolytic solution using carbon fiber as an anode. It is said that the oxidation method is industrially advantageous in terms of single reaction control and efficiency. For the industrial electrolytic oxidation of carbon fibers, a continuous process is used. An electrolytic solution 3 is put into an electrolytic cell 6, and ml of carbon wire is continuously run through the electrolytic solution while being electrolyzed. A positive charge is applied to the carbon fibers from a current-carrying roll 2 provided outside the electrolytic solution, and the carbon fibers are electrolyzed between the carbon fibers and the cathode, and their surfaces are oxidized.

When electrolytically oxidizing carbon fibers, as the elastic modulus of carbon fibers improves, they become less likely to be oxidized. This is said to be due to the fact that as the elastic modulus improves, the degree of graphitization of the carbon fiber increases. Oxidation reactions occur at the edges of the graphite structure, and it is said that reactions are less likely to occur on the base surface (
J., P., Randinand, E., Yeager, J.
, Electroanal, Chew, 58.3
13 (1975)), that is, the reason why the fiber becomes less susceptible to oxidation as its elastic modulus improves is said to be because there are fewer edges on the fiber surface that are easily oxidized. For this reason, even if high-modulus carbon fibers are subjected to normal electrolytic oxidation treatment, they cannot obtain sufficient affinity with resins when used as composite materials.

In this case, even if the amount of electricity (coulomb amount) applied during electrolysis is increased, sufficient affinity with the resin cannot be obtained.
It is known that the affinity of carbon fibers with resin is closely related to the amount of oxygen on the surface of the carbon fibers. This is because #-containing functional groups are introduced onto the surface by oxidation, and is usually measured as the peak area ratio of oxygen and carbon by ESCA (X-ray photoelectron spectroscopy). In the case of high elastic carbon mJI, the amount of surface oxygen gradually becomes saturated even if the amount of electricity applied is increased, making it difficult to obtain the amount of surface oxygen necessary to obtain sufficient affinity with the resin. In addition, when the amount of coulombs is increased in this way, s#I often deteriorates and the fiber strength decreases.Therefore, in order to effectively oxidize highly elastic carbon fibers, several conventional methods have been developed. has been devised.

For example, there is a method of performing electrolytic oxidation twice by changing the electrolytic solution (Japanese Patent Application Laid-open No. 1992-92470). However, such a treatment method exclusively for high elastic fibers requires complicated steps.
This was disadvantageous from an industrial perspective, as it required new equipment.

Problems to be Solved by the Invention In view of the above-mentioned problems, the present invention provides a method and device that can effectively oxidize high modulus carbon fibers, similar to conventional processes and without using new equipment. It is something to do.

Means for Solving the Problems The present invention is characterized in that when carbon fibers are continuously anodized in an electrolytic solution, electrolysis is performed with a part of the cathode exposed to the air above the electrolytic solution. A method for surface treatment of carbon fibers, a mechanism for supplying electricity to the carbon fibers to become an anodic acid, and an anodizing device for carbon fibers comprising an electrolytic cell and a cathode, wherein the cathode partially removes air from an electrolytic solution. This is a carbon fiber surface oxidation treatment device characterized by being installed so as to be exposed inside the carbon fiber.

When carbon fibers are electrolytically oxidized according to the present invention, even highly elastic carbon fibers can be effectively oxidized. The reason for this is not clear in detail, but it is thought that because the dielectric constants of the electrolytic solution and air are different, charges are concentrated at the interface and the potential becomes high. i.e. 1
In the case of the present invention, since a high-potential current can be effectively applied to the carbon fibers, it is considered that even high-modulus fibers having many parts with a high oxidation potential can be effectively oxidized.

By applying the present invention, there is no need to perform special treatment or add a special process to highly elastic carbon fibers, and there is no need to increase the amount of current applied (coulomb amount). Highly elastic carbon fibers can be effectively oxidized by simply performing the same oxidation treatment as the fibers.

The carbon fiber used in the present invention is not particularly limited, and various carbon mwb can be used. 4. For example, it is manufactured from polyacrylonitrile, pitch, etc., and either carbon fiber or graphite fiber can be used.

The electrolytic solution used in the present invention is not particularly limited, and any electrolytic solution used in normal electrolytic treatment can be used. Specifically, an aqueous solution containing an essential component of an inorganic acid such as sulfuric acid, nitric acid, or phosphoric acid, an organic acid such as benzoic acid, an inorganic base such as sodium hydroxide, or a salt such as sodium hydrogen carbonate can be used.

The concentration of the aqueous solution is not particularly limited as long as it is higher than a concentration that is too low during electrolytic treatment, resulting in large liquid resistance and a significant increase in operating voltage.

The current-carrying mechanism used in the apparatus of the present invention continuously applies a positive charge to the carbon fibers, and a current-carrying roll or the like used in a normal electrolytic oxidation apparatus can be used.

FIG. 1 shows an example of the oxidation treatment apparatus of the present invention.

The carbon fiber bundle 1 passes through an energized roll 2 and is immersed in an electrolytic solution 3. In the electrolytic solution 3, the carbon fiber bundle l is led out of the electrolytic solution via a roll 5 and sent to a cleaning process.In the case of the present invention, the cathode 4 is immersed in the electrolytic solution, but a portion of The carbon fiber bundle l, which must be exposed to the air, is applied with a positive charge from the current-carrying roll 2, and is energized between it and the cathode 4 in an electrolytic solution, and undergoes an electrolytic oxidation reaction at this time.

The position of the cathode 4 may be anywhere as long as a part thereof is exposed to the air and does not come into contact with the carbon fiber bundle 1, but it is preferably near the carbon fiber bundle 1. ,
Further, the shape of the cathode 4 may be any shape such as a plate or a cylinder, and any shape such as being placed on one side of the carbon fiber bundle l, being sandwiched from both sides, or being surrounded is possible. . Further, the number of cathodes 4 may be one or two or more, as long as the cathode 4 can utilize the part where electric charge is concentrated at the interface between the electrolyte and the air. The size is arbitrary, and it is sufficient that a portion of several square meters or more, preferably 10 m1 or more, is immersed in the electrolyte. Also, the size of the portion of the cathode 4 that is exposed to the air is Optional. Cathode 4
Any material can be used as long as it is used in normal electrolytic oxidation, and specifically, copper, lead, etc. can be used.

The cleaning process includes continuous cleaning after electrolytic oxidation treatment,
Alternatively, a continuous method such as a method of winding the carbon fibers and then washing them again continuously or in patches may be used.

Hereinafter, the effects of the present invention will be explained in more detail with reference to Examples.

Example = - The pitch obtained by hot filtration of Luther pitch to remove the quinolinated content is hydrogenated, and the light content is further distilled off to achieve a softening point of 90.
℃, 4% of toluene-insoluble content, and a trace of quinoline-soluble content were obtained.

After heat-treating this, the low-boiling point components were removed to obtain menphase pitch. The mesophase pitch was melt-spun using a spinning nozzle to obtain a pitch am with a yarn diameter of 124 m.

The pitch fibers thus obtained were subjected to infusibility treatment in air, and then heat treated in argon gas for 15 minutes to obtain carbon fibers. Obtained carbon M & who is J engineering 5-R-7
601, the tensile modulus was determined by the resin-impregnated strand tensile test method. Also, ESCA (X-ray photoelectron spectroscopy)
The amount of oxygen on the fiber surface was measured. The specific device used for ESCA measurement is ESCA7 manufactured by Shimadzu Corporation.
50. Using AIKα1.2 as an X-ray source, the surface oxygen atom concentration (
01s/(Cts"0ss)). In this case, the sensitivity correction value was measured with carbon as 1.0 and oxygen as 2.8. Heat treatment temperature, elastic modulus of carbon fiber, and surface of raw carbon fiber were determined. The oxygen content is shown in Table 1.

The raw carbon fiber bundle thus obtained is introduced into the electrolytic cell shown in FIG. 1 filled with an aqueous sulfuric acid solution having a concentration of 1, and a positive charge is applied to the carbon fiber bundle by a current-carrying roll installed in the electrolytic cell. A current was passed between the cathode plate and the cathode plate. Here, the electrolytic cell used had a cylindrical shape with a diameter of 260 layers and a height of 400 layers. The cathode has a thickness of 0.2 am, a height of 50 m, and a diameter of 5
A 0 mm cylindrical copper plate was used and placed so as to surround the carbon fibers. The top 10 layers of this cathode were exposed to air, and the remaining 40 layers were immersed in the electrolyte.

The carbon fiber bundles subjected to such treatment were continuously washed with water in a water washing bath and dried in a heating oven at 120°C.

Regarding the thus obtained carbon fiber bundle, the amount of oxygen on the fiber surface was measured by ESCA. Table 1 shows the amount of surface oxygen when the amount of applied current was varied.

Comparative Example The untreated carbon fiber used in the example was treated in the same manner as in the example except that the apparatus shown in FIG. 2 was used. In the second @ device, the material and shape of the electrolytic cell and the cathode are similar to those in the example. However, the cathode was immersed in the electrolytic solution by 1O■■ from the liquid level. The results are shown in Table 1.

As shown in this ls1 table, by using the processing apparatus of the present invention, it is possible to obtain a sufficient amount of surface oxygen to obtain affinity with the resin even for highly elastic carbon fibers under the same electrolytic treatment conditions as before. can. In the case of low-modulus carbon fibers, there is almost no difference between the example and the comparative example. In other words, in the case of low-modulus fibers, even if the method of the present invention is used, they will not be oxidized more than necessary. Therefore, there is no need to change the equipment when electro-oxidizing low-elastic carbon fibers and high-elastic carbon fibers.

(Left below) Effects of the Invention As described above, the feature of the present invention is that when carbon fibers are continuously anodized in an electrolyte, a part of the cathode is exposed to the air from the electrolyte. Yes, if you follow this,
Even carbon fibers with a high modulus of elasticity of 80 tan/12 can be subjected to surface oxidation treatment in the same manner as carbon fibers with lower modulus. This is thought to be because by exposing the cathode to the air, the high potential portion present at the interface between the air and the electrolyte can be efficiently utilized for the oxidation reaction.

Moreover, as for the device, it is necessary to just slightly change the existing device (-1) and there is no need to introduce a new device.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a specific example of the apparatus of the present invention. FIGS. 2 and 3 are schematic diagrams showing examples of conventionally used devices. 1...Carbon fiber, 2...Electrifying roll, 3...Electrolyte solution, 4...φ cathode, 5...roll, 6φ...electrolytic cell.

Claims (2)

[Claims] (1) A method for surface oxidation treatment of carbon fibers, which is characterized in that when carbon fibers are continuously anodized in an electrolytic solution, the electrolysis is carried out in a state where a part of the cathode is exposed to the air from the electrolytic solution. (2) A carbon fiber anodic oxidation device comprising a mechanism for energizing the carbon fibers serving as the anode side, an electrolytic cell, and a cathode, wherein the cathode is installed with a portion of the cathode exposed to the air from the electrolyte. A carbon fiber surface oxidation treatment device characterized by: