JPS61275468A - 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 [Industrial Application Field] The present invention relates to a method for processing carbon fibers, and particularly to a method for processing carbon fibers to provide reinforcing carbon fibers having excellent composite tensile strength.

[Prior Art] Conventionally, in order to improve the adhesion of carbon fibers to matrix resin, methods of electrolytically treating carbon fibers using carbon fibers as anodes have been described, for example, in Japanese Patent Publications No. 47-26999 and Japanese Patent Publication No. 5
6-17468, JP-A-56-128362, JP-A-59-116469N, etc., in these electrolytic treatments, functional groups are formed on the surface of the carbon fiber, and matrix resin It is not intended to improve or improve the strength of the carbon fiber itself or the tensile strength of the composite, and it is known that strengthening the electric vN treatment conditions will actually reduce the strength of the carbon fiber. was.

In addition, JP-A-47-32195 proposes a method of electrolytically treating carbon fibers using an aqueous solution of chromate or manganate as an electrolyte in order to shorten the electrolytic treatment time. Although it had the effect of shortening the processing time, it did not particularly improve the strength of the carbon fiber itself.

Furthermore, JP-A-54-59497@publication, JP-A-52-3
No. 5796 and Japanese Patent Application Laid-open No. 58-214527, etc., disclose a treatment method for improving and increasing the tensile strength of a composite using carbon fibers or carbon i&li fibers as reinforcing fibers, in which carbon fibers are treated with a concentrated aqueous solution of an inorganic acid. It is known that the carbon fiber surface is removed by immersion, that is, etched, and then heated in a high-temperature inert atmosphere to remove the functional groups on the fiber surface generated by the acid treatment. In order to carry out long-term treatment in a high-temperature, high-concentration inorganic acid aqueous solution, 9. The productivity of carbon fibers decreases, making it impractical from an industrial perspective, and the treatment itself is harsh, which may result in the processed carbon fiber bundles becoming irregularly shaped, broken, or fluffed. In addition, since the structure of carbon fiber is particularly oxidized not only to the surface layer of the fiber but also to the inner layer of the fiber, it is difficult to sufficiently remove functional groups to the inner layer of the fiber even with inactivation treatment. This did not significantly improve the tensile strength of the carbon fibers themselves or of composites using the carbon fibers as reinforcing fibers.

Furthermore, the carbon fibers subjected to the inactivation treatment after being etched with acetic acid are
Alternatively, the improvement in tensile strength of composites using carbon fibers as reinforcing fibers tends to be small, and the tensile strength of composites of treated carbon fibers differs depending on the type of matrix resin, that is, resin dependence Even if the tensile strength of the carbon fiber itself is improved, the tensile strength varies greatly depending on the matrix resin and is not reflected sufficiently in the composite material. The strength was not improved or improved.

[Problems to be Solved by the Invention] An object of the present invention is to solve the problems of the above-mentioned prior art, to shorten the processing time, and to enable continuous processing.

A method for surface modification of carbon fibers, which has excellent industrial feasibility, does not substantially damage the internal structure of carbon fibers, and inactivates the surface layer, especially reinforcing carbon fibers themselves or the fibers. The present invention provides a processing method that can significantly improve the tensile strength of composites made into fibers.

Another object of the present invention is to provide a treatment method that is safer in operation than the conventional acid-free treatment method used in the treatment of carbon fibers.

[Means for Solving the Problems] The above-mentioned object of the present invention is to perform two-strong electrolytic treatment using an aqueous solution of an organic acid or its salt as an electrolyte, and then to make the surface of the carbon fiber inert. This can be achieved by chemical treatment.

Hereinafter, the configuration of the present invention will be specifically explained.

Organic acids or salts thereof as electrolytes in the present invention include aliphatic and alicyclic carboxylic acids or salts thereof, such as formic acid, oxalic acid, tartaric acid, malic acid, malonic acid, maleic acid, itaconic acid, and hexahydrobenzoic acid. acid,
Ammonium formate.

Examples include ammonium oxalate, but among these, formic acid, oxalic acid, tartaric acid, etc. are particularly strongly acidic.

A relatively lower acid having about 10 carbon atoms or less is more preferable.

In addition, when using a metal salt of an organic acid, after strong electrolytic treatment,
It is more preferable to use an organic acid or a salt thereof that does not contain metal ions, since metals tend to remain in the treated carbon fibers that have been subjected to water washing, drying, and deactivation treatment.

The organic acid or its salt is not particularly limited by the temperature of the electrolyte, but it usually ranges from 0.1% to several tens of%.
used as an aqueous solution. If the electrolyte concentration of the organic acid or its salt is extremely low, it becomes difficult to effectively oxidize the carbon fiber surface under the electrolytic treatment conditions described below.

On the other hand, the upper limit of the concentration of an aqueous solution of an organic acid or its salt varies depending on the type of electrolyte, but if the upper limit of the solubility of the electrolyte is exceeded, the electrolyte may precipitate from the aqueous solution.
Since the process becomes unstable, the concentration is preferably lower than the upper limit of solubility.

Further, the temperature of the aqueous solution of the organic acid or its salt is preferably at least 30°C, preferably 40 to 100°C. When the temperature is lower than 30℃, the treatment effect is small,
On the other hand, a high temperature higher than the boiling point is not preferable because the electrolyte becomes unstable and processability deteriorates.

Such an organic acid or its salt has the function of oxidizing or etching the surface of carbon W4 fibers when subjected to strong electrolytic treatment using carbon fibers as an anode, and can be easily made into an aqueous solution of any concentration. Compared to organic acids or inorganic acids such as sulfuric acid, it is less dangerous even in S stock solution.

It is advantageous in that it is relatively inexpensive and has low corrosiveness as an aqueous solution, so treatment equipment can be simplified.

The conditions for the strong electrolytic treatment using the aqueous solution of the Fj1 acid or its salt include an amount of electricity of at least 50 coulombs, preferably 100 to 700 coulombs per gram of carbon fiber,
Processing time 0.05-10 minutes.

Preferably, the treatment is carried out for 0.1 to 3 minutes. If the amount of electricity is less than 50 coulombs/1Q carbon fiber, the treatment will be insufficient, and if the amount of electricity is greater than 700 coulombs/IC carbon fiber, the treatment will be too strong and the strength of the carbon fiber will be reduced. This is not desirable.

The current density of the electrolytic treatment is per 1 m2 of the surface area of the carbon fiber in the aqueous solution of the organic acid or its salt.

It is preferred to operate at least 1.5 amps, preferably between 3 and 1000 amps. If the current density is less than 1.5 amperes/m2, it is difficult to effectively oxidize the carbon fiber surface and the treatment takes a long time, which is not preferable. -The upper limit of the lightning current density varies depending on the type of organic acid or its salt or carbon fiber, but if the voltage between the carbon fiber applied to the anode and the cathode placed in an aqueous solution of the organic acid or its salt is extremely It is necessary to set the current density within a range that does not impair safety.
000 A/m2 or less is preferable.

These electrolytic treatment conditions are not set individually, and are set appropriately within the above range so long as the surface of the carbon fiber, which is the object of the present invention, is oxidized, but the internal structure of the carbon fiber is not substantially oxidized. should be combined within

The carbon fibers oxidized by the above electrolytic treatment are then subjected to a deactivation treatment, i.e. at a temperature of at least 400°C, preferably from 600 to 900°C, in an inert gas such as nitrogen, helium or argon. It is necessary to perform a heat treatment for about 0.1 to 10 minutes, preferably 0.2 to 5 minutes, to remove the functional groups generated on the fiber surface by the electrolytic treatment.

That is, if the functional groups on the surface of the fibers formed by the strong electrolytic treatment remain as they are, a composite using the resulting fibers as reinforcing fibers will have low tensile strength and will substantially lose its practical performance. Therefore, in the present invention, the above-mentioned inactivation treatment is indispensable for the carbon fibers after the strong electrolytic treatment, and it is only through this that the high strength of the carbon fibers, which is the objective of the present invention, can be achieved.

If the deactivation treatment temperature is lower than 400° C., it is not preferable because the functional groups generated on the fiber surface by the two-strong electrolytic treatment cannot be sufficiently removed. On the other hand, if the treatment temperature is higher than 900°C, the strength of the carbon fibers will decrease, which is not preferable.

The carbon fiber in the present invention is not particularly limited, and various carbon fibers can be used. Preferably, an acryloni-1-lyl fiber is used as a precursor, and this fiber is heated in an oxidizing atmosphere. , after oxidation,
Carbon fibers or graphite fibers obtained by carbonization by heating at higher temperatures in an inert atmosphere.

[Effects of the Invention] As is clear from the processing conditions of the present invention described above, according to the present invention, the surface of carbon fibers is oxidized via electricity in an aqueous solution of an organic acid or its salt. Because the uniform treatment and selective oxidation or removal of defects on the fiber surface are carried out, and the treatment time is extremely short, the internal structure of the fiber is substantially retained. Therefore, according to the present invention, not only the strength characteristics of carbon fibers, particularly the composite tensile strength, are significantly improved, but also the strength of the composite is not influenced by the type of matrix resin constituting it. Moreover, the method for treating carbon fibers is different from the previously known treatment methods using inorganic acids.

It has high productivity and can be processed continuously, and since the electrolyte is an aqueous solution of an organic acid or its salt, it is safe to handle even at high concentrations, making it extremely industrially effective. It has a remarkable effect.

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

Example 1 Carbon lli fiber obtained using acrylonitrile fiber as a precursor [Trading Card] T-300-3K manufactured by Toshiku Co., Ltd.
] in dimethylformamide (DMF) heated to 80°C.
After soaking in acetone for 2 hours, the sizing agent was removed by drying.

The desized carbon fibers were immersed in a formic acid aqueous solution with a temperature of 0°C and 5.0%, which was filled into the tank through the guide rollers in a treatment tank equipped with a Teflon guide roller. , yarn speed 1. While running the carbon fiber continuously at a speed of 0m/min, a positive voltage was applied to the carbon fiber via a metal guide roller placed just before the treatment tank, and a platinum cathode plate placed in the treatment solution and the carbon fiber were placed in the treatment solution. A current of 1.65A was passed between the two. The immersion length of the carbon fibers in the treatment tank was approximately 0.5 m, the oxidation electrolytic treatment time was approximately 0.5 minutes, the voltage was 15° OV, the current density was 50 A#, and the amount of electricity per 10 carbon fibers was 500 coulombs. .

Next, the oxidized electrolytically treated carbon fibers were thoroughly washed with water, dried in heated air at about 200° C., and then heated for about 2 minutes in a nitrogen atmosphere at 700° C. to be inactivated.

Regarding the obtained treated carbon fiber, JIS-R-7601
The tensile properties of the resin-impregnated strands were measured by the test method specified in . The results are shown in Table 1.

Here, the resin-impregnated strand test was measured for the following two levels, method A and method B, which have different resin formulations.

Resin formulation A: “'Chissonox” 221/Boron trifluoride monoethylamine (BF3・MEA)/Acetone=
100/3/4 parts were thoroughly mixed, this liquid mixture was impregnated into carbon fibers, and the obtained impregnated strand was heated at 130° C. for 30 minutes to cure it.

Resin formulation B: ``Epicoat'' 82B/N, N.

N-,N--tetraglycidylaminodiphenonylmethane: manufactured by Sumitomo Chemical Co., Ltd. "ELM"434/"'Eviclon'152/4.4'-diaminodiphenylsulfone/BF3・MEA=35/35 /30/3210
．． The carbon fibers were impregnated with 5 parts of a 565% methyl ethyl ketone solution, and the resulting impregnated strands were desolvated in a vacuum dryer at 60° C. for about 6 hours and then heated at 180° C. for 2 hours to cure.

Examples 2 to 10, Comparative Examples 1 to 8 Desizing “Trading Card” T-300- used in Example 1
Example 3 was treated in the same manner as in Example 1 except that carbon fibers were used and formic acid was used as the electrolyte, and the conditions of the oxidation electrolytic treatment/inactivation treatment were changed as shown in Table 2. The results are shown in Table 2.

Examples 11 to 13 Desizing “Toraycatt T-30” used in Example 1
Carbon fiber was used for 0-3, and the electrolytic solution and electrolytic treatment/inactivation treatment conditions shown in Table 3 were used.

It was treated in the same manner as in Example 1. The results are shown in Table 3.

(Hereinafter, blank space) Example 14. Comparative Example 9 Desizing “Trading Card” T-300- used in Example 1
3, the carbon fibers were immersed in the same treatment solution as in Example 1,
The yarn was run continuously at a speed of 0.075 m/min and 0°025 m/min, and a voltage of 4.5 V was applied between the carbon fiber and the cathode.
At a current of 0.124 A and a voltage of 2.5 V, the current is 0.124 A and a voltage of 2.5 V.
041A was flown. Here, the amount of electricity per gram of carbon fiber was set at 500 coulombs.

The immersion length of the carbon fiber in the treatment tank was 0.5 m, and the yarn speed was 0.
．． At 0.075 m/min, the electrolytic treatment time was about 6.7 minutes, and the current density was 3.75 A/m2. on the other hand.

At a yarn speed of 0.025 m/min, the electrolytic treatment time was approximately 20 minutes, and the current density was 1.25 A/m2.

Then, in the same manner as in Example 1, it was washed with water, dried, and inactivated.

The tensile strength of the resin-impregnated strands was measured for the resin formulation A shown in Example 1 for the iq treated carbon fibers, and as a result, the tensile strength of the resin-impregnated strands treated at a current density of 3.75 A/m'' was 365 kc+/mm''. While the strength improvement was large, those treated with a current density of 1.25 A/m2 had a small strength improvement of 350 kO/mm2, and the processing time was long at about 20 minutes, resulting in low productivity. .

Comparative Example 12 Ising 'Trading Card' T-300- used in Example 1
3. About 20 m of carbon fiber was wound around a Pyrex glass frame, immersed in 68% nitric acid, treated at 120°C for 45 minutes, washed with water for about 60 minutes, and dried in an oven at 120°C for about 30 minutes.

The obtained treated carbon fibers were heated for about 2 minutes in an electric furnace at 700° C. under a nitrogen atmosphere to undergo a defunctionalization treatment.

Regarding the obtained treated carbon fibers, the tensile physical properties of the resin-impregnated strands were measured for two levels of resin formulations A and B in the same manner as in Example 1. The results are shown in Table 4.

(Hereafter, margin)

Claims (4)

[Claims] (1) A method for treating carbon fibers, which comprises using an aqueous solution of an organic acid or its salt as an electrolytic solution, subjecting carbon fibers to strong electrolytic treatment using them as anodes, and then inactivating the surface of the carbon fibers. (2) The method for treating carbon fibers according to claim 1, wherein the temperature of the aqueous solution of an organic acid or its salt is at least 30° C., and the amount of electricity in the electrolytic treatment is at least 50 coulombs per gram of carbon fibers. (3) A method for treating carbon fibers according to claims 1 and 2, wherein the current density of the electrolytic treatment is at least 1.5 amperes per 1 m^2 of surface area of the carbon fibers in an aqueous solution of an organic acid or its salt. (4) A method for treating carbon fibers according to claims 1 to 3, wherein the inactivation treatment is a heat treatment in an inert atmosphere maintained at a temperature of at least 400°C.