JPS63548B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for electrolytic surface treatment of carbon fibers. [Prior art] Composite materials using carbon fiber are lightweight, highly strong,
Because it has outstanding properties such as high elasticity, it is widely used in aerospace structural materials, automobile and industrial machinery parts, sporting goods, etc. However, when carbon fibers are used for these composite materials, it is important not only to maintain the strength of the carbon fibers themselves, but also to improve their adhesion to matrices such as resins, thereby increasing the strength of the composite materials.
In practice, it is extremely important to improve interlaminar shear strength. Carbon fibers are usually surface treated to improve their adhesion to these matrices.
As a method for this purpose, methods are known in which the surface of carbon fibers is treated by gas phase oxidation, liquid phase oxidation, electrolytic oxidation, or the like. Among these, a method in which electrolytic oxidation treatment is performed in an electrolyte aqueous solution using carbon fiber as an anode is considered to be particularly useful industrially from the viewpoint of workability, quality, etc. In this electrolytic surface treatment method for carbon fibers, if the electrolyte remains attached to the carbon fibers after treatment, it will adversely affect the post-processing steps for composite material production.
Since the properties of carbon fibers and composite materials deteriorate, the electrolytic step is usually followed by a cleaning step to clean and remove the deposited electrolyte. However, in general, it is difficult to completely remove electrolyte ions attached to carbon fibers by washing with water for a short time, and the reality is that a long and multi-stage washing process is required, especially when the process is continuous. be. In order to solve the above problems, for example,
50-40891 and JP-A-50-157697 disclose a method of using a decomposable electrolyte as an electrolyte, heating carbon fibers after electrolytic treatment, and decomposing and removing adhering electrolyte. In such a method, deterioration of carbon fibers and adhesion of decomposition product residues during decomposition of the electrolyte are unavoidable, and in some cases,
There are disadvantages in that exhaust gas treatment of the decomposed gas is required, or it is disadvantageous in terms of energy because it is heated to a high temperature. Another method is to electrically remove the deposited electrolyte in a cleaning bath, as disclosed, for example, in Japanese Patent Publication No. 49-29906. In order to carry out such a method, it is necessary to separately provide a power source, electrodes, etc. in the cleaning bath, which makes the equipment complicated and process control difficult. [Problems to be Solved by the Invention] The present inventors have discovered that in an electrolytic treatment method for carbon fibers, the adhered electrolyte can be completely removed in a simplified process, and the composite material exhibits excellent properties. As a result of extensive research into surface treatment methods that can industrially advantageously obtain carbon fibers, the method of the present invention was discovered. [Means for Solving the Problems] The present invention provides the steps of applying electricity to the carbon fibers through a non-contact anode when performing electrolytic surface treatment using carbon fibers as anodes in an electrolyte solution, and at least one of the non-contact anodes. Install one on the exit side of the electrolytic bath,
The method of surface treatment of carbon fibers is characterized in that water substantially containing no electrolyte is used as the current-carrying medium of the non-contact type anode on the exit side of the electrolytic bath. In the present invention, electricity is applied to the carbon fibers through a non-contact anode. Here, the non-contact anode refers to an anode that is connected to the anode side of an electrolysis power source and supplies current to the carbon fibers in a non-contact manner via a current-carrying medium. A non-contact type anode consists of an electrode connected to the anode side of an electrolytic power source and a space containing a liquid, which is a current-carrying medium, and has a structure such that carbon fibers can pass through the current-carrying medium. Such a non-contact anode is disclosed in Japanese Patent Publication No. 47-29942,
For example, an electrode having grooves or holes for passing carbon fibers as shown in FIG. 2-A, B, and C,
The electrode may be combined with a current-carrying medium supply section, or the electrode may be immersed in a current-carrying medium bath as shown in FIG. The number of non-contact anodes may be one or more, but at least one of them is installed on the exit side of the electrolytic bath. Generally, one is installed at the inlet and one at the outlet of the electrolytic bath, but in some cases, one, or three or more can be installed. In the present invention, water substantially containing no electrolyte is used as the current-carrying medium for the non-contact type anode installed on the exit side of the electrolytic bath. Such water includes, for example,
Examples include general river water with low suspended solids, well water, industrial water, soft water that has been partially treated with industrial water, and tap water. The main ions contained in such water are NH ₄ ⁺ , Na ⁺ , K ⁺ , Mg ²⁺ , HCO ₃ ^- , Cl ^- ,
It is preferable that the total amount of SO ₄ ^2- , etc. is 500 mg/l or less. The residence time of the carbon fiber in the above-mentioned non-contact anode is determined as appropriate depending on the type of carbon fiber, electrolysis conditions, type of non-contact anode, etc., but is generally between 1 and 120 seconds. . FIG. 1 shows a typical example of an apparatus used to carry out the method of the present invention. In the figure, a carbon fiber 1 is energized by non-contact type anodes 3 and 4 provided at the inlet and outlet sides of an electrolytic bath 2, respectively. The current-carrying medium of the non-contact type anode 3 on the inlet side is not particularly limited as long as it is a conductive liquid, but from the viewpoint of controlling the electrolyte concentration in the electrolytic bath, it is preferable to use the electrolyte itself as the current-carrying medium. In the electrolytic bath, the carbon fiber acts as an anode, and electrolysis occurs between it and the cathode 5. The carbon fibers coming out of the electrolytic bath pass through the non-contact type anode 4 on the exit side. Water is used as the current-carrying medium for the non-contact anode 4. Here too, as described above, an electric current is applied to the carbon fibers, the carbon fibers acting as a cathode, with the result that the electrolytes, in particular the anions, adhering to the carbon fibers are removed. In the non-contact type anode 4, it is preferable in order to enhance the cleaning effect that water, which is a current-carrying medium, is flowed sufficiently so that the removed electrolyte is quickly removed from the system. Preferred examples of the electrolyte used in the present invention include acids such as sulfuric acid, nitric acid, and phosphoric acid, and salts such as ammonium nitrate, ammonium carbonate, and ammonium sulfate. Electrolytic conditions such as electrolyte concentration, current during electrolysis, voltage, temperature, and processing speed are selected appropriately depending on the type of carbon fiber, number of processed carbon fibers, type of electrolyte, electrolytic bath, shape and dimensions of the non-contact anode, etc. be done. Normally, the electrolyte concentration is about 0.1 to 10%, the current is about 10 mA to 5 A per thread, and the voltage is about
Preferably, the voltage is 500mV to 10V, and the temperature is from room temperature to about 80°C. As the electrode material constituting the cathode and non-contact anode, known conductive materials that are resistant to corrosion against electrolytes and current-carrying media, such as graphite, nickel, stainless steel, titanium, tantalum, platinum, etc., are used. . [Effects of the Invention] According to the method of the present invention, at the non-contact anode on the electrolytic bath outlet side, electric current is applied to the carbon fibers, and adhering electrolyte is electrically and physically removed and cleaned at the same time. Compared to conventional methods, carbon fibers with extremely low residual adhering electrolyte and excellent composite properties can be obtained industrially with a simplified cleaning process. In addition, non-contact energization reduces fuzz, thread breakage, and the like, making it possible to realize an industrially advantageous process. [Example] Hereinafter, the present invention will be specifically explained based on Examples. Example 1 Carbon fibers prepared by finally firing acrylic long fibers with a single filament fineness of 1.2 denier and 12,000 filaments in a nitrogen atmosphere at 1,300°C were
Electrolytic surface treatment was performed using the apparatus shown in the figure.
The effective length of the electrolytic cell and non-contact anode is 1 each.
m and 30 cm. 1% nitric acid was used as the electrolyte. Also, as a current-carrying medium for non-contact anodes,
1% nitric acid was used for the anode on the electrolytic bath inlet side, and soft water was used for the anode on the electrolytic bath outlet side. The carbon fiber was run at a speed of 2 m/min, electrolytically treated with a current of 150 mA and a treatment time of 30 seconds, and then washed with water in a 1 m long washing tank.
After sizing and drying, it was wound onto a bobbin. The strand strength of the obtained carbon fiber was measured using a resin according to JIS-R7601, Explanation Example 2. In addition, 100 parts of epoxy resin (Ciba Geigy, MY720),
A prepreg was prepared by impregnating carbon fiber with a methyl ethyl ketone solution containing 30 parts of diaminodiphenylsulfone and 1.5 parts of boron trifluoride monoethylamine, and heat-cured at 130°C for 60 minutes and then at 180°C for 120 minutes to form a flat test piece. was prepared and subjected to measurement of interlaminar shear strength (hereinafter referred to as "ILSS") by the three-point bending shot beam method (L/D=4). On the other hand, about 10 m of carbon fiber before applying the sizing agent
The carbon fibers were collected, extracted with a mixed aqueous solution of anhydrous sodium carbonate and sodium chloride, and the amount of nitrate ions in the carbon fibers was measured by brucine spectrophotometry. The results are shown in Table 1. Comparative Example 1 For comparison, the strand strength, ILSS, The amount of residual nitrate ions was measured. The results are shown in Table 1. Comparative Example 2 The method of Comparative Example 1 was repeated. However, in order to remove the residual electrolyte, the treatment was carried out by increasing the number of 1 m water washing tanks to three stages, but the amount of nitrate ions was still large. The results are shown in Table 1.

[Table] Example 2 The carbon fiber used in Example 1 was subjected to electrolytic surface treatment with a 0.5 mol/aqueous sulfuric acid solution. Using the same device as in Example 1, an electrolytic solution was used as the non-contact type anode on the electrolytic bath inlet side, and industrial water was used as the current-carrying medium in the non-contact type anode on the electrolytic bath outlet side. Processing speed 3m/min, current
After electrolysis at 300mA, rinse with water in a 1m long washing tank.
After sizing and drying, wind it onto a bobbin. When the pH of the adhering water on the carbon fibers after leaving the washing tank was measured using litmus paper, it was found to be almost neutral. In addition, the strand strength and
ILSS was 410Kg/mm ² and 12.8Kg/mm ² , respectively. Comparative Example 3 Electrolytic treatment was carried out under the same conditions as in Example 2, with graphite rolls placed before and after the electrolytic bath instead of the non-contact type anode. The treated fibers were washed with water through three stages of washing tanks each having a length of 1 m, sized and dried, and then wound onto a bobbin. When the pH of the adhering water on the carbon fibers after washing was measured using litmus paper, it was found to be slightly acidic.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of an apparatus used for carrying out the method of the present invention. FIGS. 2A, 2B, and 2C are perspective views showing examples of non-contact electrodes used in the method of the present invention. FIG. 3 is a sectional view showing another example of the non-contact type electrode used in the method of the present invention. 1: carbon fiber, 2: electrolytic bath, 3, 4: non-contact anode, 5: cathode, 6: DC power supply, 7: bath, 8: electrode, 9: current-carrying medium.

Claims (1)

[Claims] 1. When performing electrolytic surface treatment using carbon fibers as anodes in an electrolyte solution, applying electricity to the carbon fibers through a non-contact anode, and installing at least one of the non-contact anodes on the exit side of the electrolytic bath, and A method for surface treatment of carbon fibers, characterized in that water substantially containing no electrolyte is used as the current-carrying medium of the non-contact type anode at the exit side of the electrolytic bath.