JPH01298275A - Method for treating surface of high elastic modulus carbon fiber - Google Patents

Abstract

PURPOSE:To enable the surface treatment of high elastic modulus carbon fibers wherein the surfaces of inactive sites of the carbon fibers are also sufficiently treated and the adhesivity of the carbon fibers to matrix resins is sufficiently improved by subjecting the surfaces of the carbon fibers to an electrolytic oxidation treatment at a specific application voltage and under a specific pulse supplying condition. CONSTITUTION:An electrolytic oxidation treatment is applied to the surfaces of many high elastic modulus carbon fibers (e.g., 1000-24000 fibers) under set conditions where the application voltage is >=10V and wherein electric pulse-feeding intervals comprise electricity-feeding periods of <=0.02sec and feeding-stopping periods >=5 times longer than the electricity-feeding periods. The conditions permit the sufficient treatment of the difficultly oxidized inactive sites of the carbon fibers, the minimized generation of pitching also on the readily oxidized active sites of the carbon fibers and the effective and excellent treatment of the surfaces of the fibers without causing the lowering of the strength of the carbon fibers. The treated fibers exhibit sufficient adhesively to matrix resins as reinforcing fibers for composite materials and do not cause the lowering of the strength of the composite materials.

Description

DETAILED DESCRIPTION OF THE INVENTION L1 Kami Nijo" E1 MI5Z IN+ generally relates to a method for surface treatment of carbon fibers by electrolytic oxidation treatment, and in particular,
Carbon with a high elastic modulus consisting of a large number of filaments such as 24,000, that is, an elastic modulus of over 50 ton/mm'! This invention relates to a method of surface treating a male by electrolytic oxidation treatment using pulsed power supply. As the carbon fiber, carbon ia fibers such as 1-optic type, PAN type, and rayon type can be used.

[Kurachi Ushij f&, near, demand for carbon fiber reinforced composite materials with high strength and high modulus of elasticity is increasing. One of the most important considerations in producing such high strength, high modulus carbon, i- reinforced composites is to improve the adhesion between the matrix resin and the carbon fibers. It has long been known that the adhesion between the matrix resin and )^ element H & male can be dramatically improved by oxidizing the surface of the 14 element fibers, and various surface treatment methods have been proposed. There is.

There is a surface treatment method based on electrolytic oxidation treatment that can continuously and efficiently surface-treat carbon fibers.
In Japanese Patent Application No. 60-182618, the present applicant proposed a surface treatment method for carbon fibers in which the surface of carbon fibers is treated by electrolytic oxidation treatment by pulsed power supply.

According to this method, OH- ions can be supplied to the center of carbon fibers consisting of, for example, 1,000 to 24,000 filaments, and the OH- ions release electrons and are oxidized by the nascent oxygen produced together with water. Carbon #&male was uniformly oxidized to the center, and good carbon fiber surface treatment could be achieved.

As a result of continued research by the present inventors on a surface treatment method for carbon fibers using electrolytic oxidation treatment using the above-mentioned pulsed power supply method, the elastic modulus was found to be 50t.

Carbon fibers with high elasticity such as n/mrn' or less cannot be uniformly surface treated by electrolytic oxidation treatment under the same pulse power supply conditions as normal carbon fibers with an elastic modulus of 50 ton/mrn' or less, and the matrix It has been found that sufficient adhesion to the resin cannot be achieved and, in some cases, strength may be reduced.

The present inventors conducted many research experiments to investigate the cause of this problem, and found that the surface of highly elastic carbon fibers is not necessarily uniform due to differences in graphite orientation angles, disturbances, etc. This is the same pulsed power supply used to process carbon fibers, which have inert sites that are difficult to process (oxidize) and active sites that are easily oxidized, and which have a relatively uniform surface with a normal elastic modulus of 50 ton/mm' or less. Depending on the conditions: If electrolytic oxidation treatment is performed, only the active sites that are easily oxidized will be intensively oxidized, and if the surface is treated until it shows sufficient adhesion, the active sites that are easy to oxidize will be rapidly oxidized. As pitching progresses, pitching occurs,
It was found that surface defects occur, resulting in a decrease in the strength of the carbon fiber. At this time, if the power supply stop time is increased compared to the power supply time in order to prevent pitting, sufficient surface treatment is not performed particularly at inert sites, and sufficient adhesion to the matrix resin cannot be obtained. A problem arose.

As a result of many research experiments, the present inventors have found that this problem can be solved by setting the applied voltage to 10 V or more, setting the pulse feeding interval to 0.02 seconds or less, and setting the power feeding stop time to 50% of the feeding time. If the electrolytic oxidation treatment is performed by setting the amount to be more than double, the inert sites that are difficult to oxidize will be sufficiently treated.
In addition, the active sites that are easily oxidized can minimize the occurrence of pitting, suppress the decrease in the strength of carbon la, and achieve good surface treatment. It has been found that sufficient adhesion is imparted to the film.

The present invention is based on this new knowledge.

Therefore, an object of the present invention is to perform electrolytic oxidation treatment to sufficiently treat the surface of inert sites that are difficult to oxidize, and to minimize the occurrence of pitting on active sites that are easily oxidized, thereby achieving good surface treatment. , a high modulus carbon fiber that has sufficient adhesion with a matrix resin when used as a reinforced am of a carbon fiber composite material, and can obtain a high modulus carbon fiber that suppresses a decrease in the strength of the carbon fiber. An object of the present invention is to provide a surface treatment method.

j - The above object is achieved by the method for surface treatment of high modulus carbon m#I according to the present invention. In summary, the present invention reduces the applied voltage to 10
7 or more, the electrolytic oxidation treatment is performed by setting the pulse power feeding interval so that the power feeding time is 0.02 seconds or less, and the M current stop time is 5 times or more the power feeding time -L. This is a surface treatment method for high modulus carbon fibers made of filaments.

More specifically, according to the present invention, a plurality of, e.g.
The carbon fiber, which consists of 24,000 filaments, is intermittently supplied with pulse power. That is, in the method of the present invention,
Replenishment of OH- ions to the center of the carbon fiber (no current applied) and electrolytic oxidation (continuous Tr1) are performed at alternating voltages, and OH- ions are supplied to the center of the carbon fiber during the non-current application between pulses. Ions are diffused and replenished, and then electricity is applied for a certain period of time to perform electrolytic oxidation. As a result, OH- ions are sufficiently present in the center of the carbon fiber, so that an oxidation reaction occurs also in the center of the carbon fiber, making it possible to obtain a uniform surface treatment.

When the OH- ions inside the carbon fibers are consumed, the current supply is stopped and the OH- ions are diffused and replenished again. By continuously performing such cycles, it becomes possible to uniformly and efficiently surface treat the carbon fibers.

In particular, according to the present invention, the pulse power supply conditions during electrolytic oxidation treatment are such that the applied voltage is 107 or more, the pulse supply interval is 0.02 seconds or less for the power supply time, and the power supply stop time is at least 5 times the power supply time. The 0 surface, which is assumed to be Elastic modulus is 50t
Even if carbon fiber has a high elasticity of on/mrrr',
By performing electrolytic oxidation treatment under such pulsed power supply conditions, inert sites that are difficult to oxidize are sufficiently treated, active sites that are often easily oxidized are also minimized from pitting, and the strength of carbon am is reduced. It is possible to suppress this and achieve a good surface treatment, and therefore, even when used as a reinforced 1m male of a composite material, sufficient adhesion with the matrix resin is imparted.

In other words, according to the results of research experiments conducted by the present inventors, in order to oxidize inactive sites that are difficult to oxidize in carbon fibers with a high elastic modulus, the applied voltage (load pressure) is generally 1Ov or more. 1OV to 1ooV is required; below IOV, active sites are oxidized but inactive sites are not oxidized, and the surface treatment of carbon fibers is incomplete;
When used in composite materials, sufficient adhesion with matrix resin cannot be obtained.

It is important that the pulse feeding interval is such that the feeding time is 0.02 seconds or less, preferably 0.01 seconds or less. That is, as mentioned above, in the present invention, the severe conditions such as an applied voltage of 107 or more are adopted, so if the voltage is continuously applied for more than 0.02 seconds, oxidation occurs at the active sites of the carbon uA fibers. If the carbon fiber surface [m] advances too much, pitching will occur on the carbon fiber surface [m], causing a strong decrease in tλ of the carbon m male.

In addition, the power supply stop time is 0.0 as described above.
If it is 2 seconds or less, it must be at least 5 times the power supply time, and by providing such a power supply stop time, the effect of surface treatment by pulse power supply, that is, the center of the carbon fiber. It is possible to more efficiently exhibit the effect of being able to sufficiently replenish OH- ions and oxidize even the center of the carbon fiber to obtain a uniform surface treatment.

The pulse waveform used in the present invention is not particularly limited, and rectangular waves, triangular waves, sine waves, etc. can be used.

Also, known methods of power supply, electrolyte, etc. can be used.

For example, as a power supply method, a method of supplying power to carbon fibers through a roll electrode or a mercury electrode is generally adopted as shown in British Patent No. 1326736, but the method disclosed in Japanese Patent Publication No. 47-29942 or U.S. Patent No. 423439B is adopted. A non-contact power supply that does not use rolls can also be used to reduce damage to carbon fibers, as shown in Figure 3.

The electrolyte is primary chlorite, concentrated sulfuric acid, concentrated sulfuric acid + Cr
Aqueous or strongly acidic solutions of oxidizing agents such as ions, permanganate; Strongly basic solutions such as sodium hydroxide;
Aqueous solutions of neutral salts such as sulfates and nitrates; weakly basic aqueous solutions such as carboxylates and cationic salts; or weakly basic aqueous solutions such as sodium carbonate may be used. In the present invention, in addition to the common electrolytic solutions such as sodium hydroxide aqueous solution and sodium nitrate aqueous solution, the above-mentioned sodium carbonate aqueous solution and sodium sulfate aqueous solution can also be suitably used.

Next, an embodiment of an electrolytic oxidation surface treatment apparatus that can suitably carry out the surface treatment method according to the present invention will be described with reference to FIG.

In a non-embodiment, the electrolytic oxidation surface treatment apparatus 1 has an electrolytic bath 4 containing an electrolytic solution 2. Two lower rolls 6.8 are rotatably arranged in the electrolytic cell 4 parallel to each other and spaced apart from each other by a predetermined distance. An inlet anode roll lO is rotatably disposed at one end of the L portion of the electrolytic cell 4 so as not to be immersed in the electrolytic solution 2, and an outlet anode roll 12 is rotatably disposed at the other end.

In the above configuration, the 14 element fibers are taken out by a reel (not shown) and are taken out from the inlet anode roll IO to the lower roll 6.8.
The electrolytic solution 2 is stretched over the membrane and immersed in the electrolytic solution 2, and then led out of the electrolytic cell through the outlet anode roll 12, subjected to a cleaning and drying process, and then wound up on a take-up reel (not shown). At this time, a cathode plate 14 is disposed in the electrolytic cell 4 so as to oppose the carbon fiber stretched by the lower roll 6.8, and the cathode plate 14 and the inlet and outlet anode rolls 10.12 The positive side (+) and negative side (-
) are connected respectively.

More specifically, the inlet and outlet anode rolls 10.
12 can be a 40 mm diameter roll made of graphite, for example, and the lower roll 6.8 can be a 40 mm diameter roll made of Teflon, for example. The lower rolls 6.8 are spaced apart from each other by 800 mm and are separated by more than 140 mm ha for the inlet and outlet anode rolls 10.12. Further, the cathode plate 14 is arranged at a distance of about 50 mm from the carbon fiber stretched between the lower rolls 6.8. The cathode plate 14 is usually made of stainless steel plate.

Next, examples will be described in which high modulus carbon fibers were surface treated according to the present invention using the continuous threading electrolytic oxidation surface treated bag 1 shown in FIG. 1 above.

The carbon fiber used is pitch-based carbon fiber with a thread diameter of 1077 m (6000 filaments), and has an elastic modulus of 50 ton/mm' and tensile strength without surface treatment. was 328 kg/mm', and ILSS (interlaminar shear strength) was 3.5 kg/mrn'.

Carbon ta fibers were prepared using a 5% NaOH aqueous solution (temperature 25°C).
The thread was threaded through the electrolytic cell 4 containing the material at a speed of in/min, and the residence time in the immersion section was 60 seconds.

The applied voltage and pulse power supply conditions for each example are as shown in Table 1, and the pulse waveform was a rectangular wave.

The elastic modulus and tensile strength of the carbon fibers after electrolytic oxidation treatment were as shown in Table 1.

A carbon fiber reinforced composite material test piece for ILSS determination was prepared using the surface-treated carbon fibers, and ILSS@l was determined by the short beam method. The results are shown in Table 1.

A carbon fiber reinforced composite material test piece was prepared as follows.

The matrix resin was 100 parts by volume of epoxy resin (trade name, Epicron 850; manufactured by Dainippon Ink and Chemicals, Ltd.), curing agent (trade name, IN-5500, manufactured by Hitachi Chemical Co., Ltd.) 84
It was prepared by mixing 1 tonne part of a heavy base and a curing accelerator (ethylmethylimidazole, manufactured by Shikoku Kasei Co., Ltd.).

The matrix resin made in this way is 7A.

The carbon fiber set in the mold has a carbon fiber volume ratio of 6.
It was injected so that it was 0% and molded by hot pressing.

The molded product is! A carbon fiber-reinforced composite specimen was prepared, having a length of 14 mm in the male force direction and a rectangular cross section of 6 mm x 2 mm.

Wataru Sarahi ↓: Using the same carbon fibers and equipment as in Examples 1 to 6, surface treatment was performed under the applied voltage and pulse power supply conditions shown in Table 1. However, in Comparative Example 1, continuous power supply was used instead of pulse power supply.

The elastic modulus, tensile strength, and ILSS were measured in the same manner as in Examples 1 to 6. The results are shown in Table 1.

From Table 1, in Examples 1 to 6 showing the present invention, there was no decrease in elastic modulus and tensile strength even after one surface treatment, and ILSS was improved, and in Comparative Examples 1 to 6, I
It can be seen that when the LSS is higher than before the surface treatment, the tensile strength is decreased, and when the tensile strength is about the same as before the surface treatment, the ILSS is decreased.

The carbon fiber used has a thread diameter of 1077 m (number of filaments: 6).
000 pieces) of pitch-based carbon fibers without surface treatment, the elastic modulus is 70 ton/m m', the tensile strength is 345 kg/mrn', and the ILSS (interlaminar shear strength) is 2.5 kg/mrn'. there were.

The carbon fiber was threaded through an electrolytic bath 4 containing a 5-layer abrasive % NaOH aqueous solution (temperature 25°C) at a speed of 1-2 in/min.
The residence time in the bond section was 60 seconds.

The applied voltage and pulse power supply conditions for each example are as shown in Table 2, and the pulse waveform was a rectangular wave.

The elastic modulus and tensile strength of the carbon TA fibers after electrolytic oxidation treatment were as shown in Table 2.

Using the surface-treated carbon fibers, ILSS was measured in the same manner as in Examples 1 to 6. The results are shown in Table 2.

±m × 22 LA Using the same carbon fibers and equipment as Examples 7 to 12, Table 2
Surface treatment was performed under the applied voltage and pulse power supply conditions shown below. However, in Comparative Example 6, continuous power supply was used instead of pulse power supply.

In the same manner as Examples 7 to 12, elastic modulus and tensile strength,
Furthermore, ILSS was measured. The results are shown in Table 2.

From Table 2, in Examples 7 to 12 showing the present invention, there was no decrease in elastic modulus and tensile strength even after surface treatment, and ILSS was improved, and in Comparative Examples 6 to 10, ILSS was It will be understood that although it is improved compared to before the treatment, it is still inferior when compared to the present invention, and the tensile strength is lower than before the surface treatment.

Table 1 Table 2 "Example" L As explained above, in the surface treatment method of high elastic carbon ma according to the present invention, electrolytic oxidation treatment is performed by specifying the applied voltage and pulse power supply conditions. The inert sites that are difficult to oxidize are also sufficiently surface-treated, and the active sites that are easily oxidized are able to have a good surface treatment, perhaps because the occurrence of pitting is kept to a minimum. When used as fibers, it has the advantage of providing sufficient adhesion with matrix resin and suppressing a decrease in the strength of carbon fibers.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of an apparatus for carrying out the surface treatment method according to the present invention. 22 Electrolyte 4: Electrolytic cell 6.8: Lower roll 1O112: Anode roll 14+r! i-electrode plate 16, pulse power generator

Claims (1)

[Claims] 1) A large number of methods characterized in that the electrolytic oxidation treatment is performed by setting the applied voltage to 10 V or more, the pulse feeding interval to the feeding time of 0.02 seconds or less, and the feeding stop time to 5 times or more of the feeding time. Surface treatment method for high modulus carbon fibers made of book filaments.