JPS6347823B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for surface treatment of carbon fibers.

Composite materials made of carbon fiber and various resin matrices are used in aerospace structural materials, automobiles, industrial machinery parts, sporting goods, etc. due to their outstanding properties such as light weight, high strength, and high elasticity. However, when using carbon fiber as these composite materials,
In addition to the importance of the strength of carbon fiber itself, it is extremely important to improve its adhesion to matrices such as other resins, and to improve its strength as a composite material and interlaminar shear strength.

In order to improve this adhesion, methods such as vapor phase oxidation, liquid phase oxidation, and electrolytic oxidation of the carbon fiber surface have been proposed. Among these, in electrolyte aqueous solutions such as sodium hydroxide, sulfuric acid, and phosphoric acid,
An electrolytic treatment method in which carbon fibers are energized is considered to be useful;
It is disclosed in Publication No. 12444. However, the disadvantage of electrolytic surface treatment is that the electrolyte adheres to the carbon fibers, which adversely affects subsequent processing steps. In other words, it is not possible to remove adhering ions almost completely with water washing for a short time, and recently, for example,
A method using a decomposable electrolyte has been proposed as seen in Japanese Patent Application Laid-open No. 40891 or Japanese Patent Application Laid-Open No. 157697/1983. However, this method also requires a washing process, and it is necessary to treat the washing wastewater and, in some cases, to treat the decomposed gas during drying, and decomposition at high temperatures requires extra energy. The current situation is that this method is not necessarily satisfactory in terms of product quality and economic efficiency.

Under such circumstances, the present inventors have conducted intensive studies on a surface treatment method that has excellent adhesion of carbon fibers to matrix resin, and is also economical and productive, and as a result, has arrived at the present invention.

That is, the present invention uses carbon fiber as an anode,
NH ₄ ⁺ , Na ⁺ , K ⁺ , Ca ⁺⁺ , Mg ⁺⁺ , HCO ₃ ^- , Cl ^- ,
A method for surface treatment of carbon fibers characterized by continuously supplying SO ₄ ^--- ions in water with a total of 500 mg or less and conducting electricity between the water and a cathode.

According to the method of the present invention, carbon fibers having high strength and interlaminar shear strength with excellent adhesion to matrix resins can be obtained, and can be usefully used in applications such as aerospace structural materials and automobile parts. Furthermore, since the method of the present invention does not substantially use electrolytes, there is no need for a washing process, no need to treat washing wastewater, and no harmful gases are emitted during drying, resulting in an extremely simple process that improves productivity and economy. It is an extremely useful process and has great industrial value.

The method of the present invention only requires a tank containing water (current-carrying tank) equipped with a copper plate, graphite plate, etc. as a cathode.
This is an extremely simple method in which electricity is applied to the carbon fiber as an anode through rollers, etc. before and after that, and the carbon fiber that comes out of this current-carrying layer passes through a water squeezing roller and is immediately coated with a sizing agent and made into a product. .

In the present invention, the water used in the energized tank is water that does not substantially contain electrolytes, such as general river water with few suspended solids, well water, industrial water, soft water partially treated with industrial water, and tap water. etc. are included.

Furthermore, in order to fully achieve the purpose of the present invention, NH ₄ ⁺ , which is the main ion contained in the water,
Na ⁺ , K ⁺ , Ca ²⁺ , Mg ²⁺ , HCO ₃ ^- , Cl ^- , SO ₄ ^2- ,
The total amount is 500mg/or less.

In the method of the present invention, the method of energizing the continuously running carbon fiber as an anode may be carried out in a contact manner via a carbon roller or the like, or may be a conventionally known method such as non-contact energization. Further, this energization may be carried out at two places before and after the energizing tank, but depending on the case, it may be carried out at one place or three or more places.

In the method of the present invention, the amount of electricity to be applied varies depending on the type of carbon fiber, processing speed, degree of processing, etc., but is usually from about 10 mA as a current.
The current is about 5A, and the voltage is about 1.5V to 200V. If it is less than this, no improvement in adhesion to the matrix resin will be observed and the object of the present invention will not be met. Further, if the amount is more than this, excess energy is simply added to the carbon fibers, which may cause damage to the carbon fibers, which is not practical.

Next, the present invention will be explained by examples, but the present invention is not limited thereto.

Example 1 Carbon fiber obtained by finally firing acrylic fiber at 1350°C (strength 385 Kg/mm ² , elastic modulus 23.5 T/mm ² ,
A bundle of 12,000 filaments with a single fiber diameter of 7.5 μm was used for continuous surface treatment at a yarn speed of 1.5 m/min. Industrial water was placed in a 1 m long energizing tank equipped with a graphite electrode plate, and a current of 5 V and 100 mA was applied via carbon rollers before and after the energizing tank, using the carbon fiber as an anode and the graphite in the energizing tank as a cathode. This industrial water
NH ₄ ⁺ (0.mg/), Na ⁺ (7mg/), K ⁺ (1mg/
), Ca ⁺⁺ (12 mg/), Mg ⁺⁺ (2 mg/),
HCO ₃ ^- (40mg/), Cl ^- (0.mg/), SO ₄ ^-- (9
mg/) ion total was 71 mg/. The carbon fibers were squeezed with water, immediately coated with a conventional sizing agent, and dried. The tensile strength of the carbon fiber thus obtained is 383Kg/ ^mm2 , and the elastic modulus is 23.5T/mm2.
It was warm in ^mm2 . Furthermore, in order to check the adhesion with the resin, a unidirectional prepreg was prepared by impregnating an epoxy resin (Epicoat 828 100 parts by weight) and boron trifluoride monomethylamine (3 parts by weight) in a methyl ethyl ketone solution. This unidirectional prepreg was laminated in one direction and thermally cured at 130°C for 10 minutes and at 175°C for 2 hours to create a tabular composite material with a fiber content of 60%. Next, using an Instron, the interlaminar shear strength (ILSS) was measured using the three-point bending shot beam method.
Measurement was performed under the condition of =4. The resulting composite had no voids, cured satisfactorily, and had an ILSS of 8.6.
Kg/mm ² , the value of 6.1 when a similar experiment was conducted using carbon fiber without surface treatment for comparison.
A clear improvement in adhesion was observed compared to Kg/mm ² .

Example 2 An experiment was carried out in the same manner as in Example 1, using carbon fibers having a tensile strength of 392 Kg/mm ² and an elastic modulus of 26.5 T/mm ² and using soft water in the energizing bath. NH ₄ ⁺ (0.mg/), Na ⁺ (30mg/), K ⁺ (4
mg/), Ca ⁺⁺ (0.mg/), Mg ⁺⁺ (0.mg/l),
HCO ₃ ^- (0.mg/l), Cl ^- (0.mg/l), SO ₄ ^-- (0.
mg/) ion total was 34 mg/. The tensile strength of the surface-treated carbon fiber is 395Kg/mm ² , the elastic modulus is 26.4T/mm ² , and the ILSS is 8.4Kg/mm ² , which is clearly superior to the value of 5.9Kg/mm ² without surface treatment. Ta.

Comparative Example For comparison, the carbon fiber of Example 1 was electrolytically treated with a 5% aqueous solution using caustic soda and ammonium carbonate as electrolytes in an energized tank in the same manner. A unidirectional prepreg and a composite material were created using the method of Example 1 using the two types of carbon fibers obtained. Those treated with caustic soda solution had poor curing and could not produce good molded products. In addition, samples using ammonium carbonate tend to have voids in the molded product, and ILSS was measured, but reliable data was not obtained at 6.5 to 7.6 Kg/mm ² . It is thought that all of these are caused by the adhesion of electrolytes. In addition, ammonium carbonate was used as the electrolyte, and the surface was treated by applying a current of 4.7V and 100mA according to Example 1, and then washed with water to remove the electrolyte.
The ILSS measured was 8.0Kg/ ^mm2 . From this fact, the present invention has almost the same processing efficiency as the treatment using conventionally known electrolytes, and achieves the desired ILSS.
This method is equivalent to or superior to the conventionally known method (washing with water after electrolytic treatment).

From the above examples, it can be seen that the present invention is an excellent method that improves the adhesion to the matrix resin and is simple and economical, requiring no water washing step.

Claims (1)

[Claims] 1 Using carbon fiber as an anode, NH ₄ ⁺ , Na ⁺ , K ⁺ ,
Ca ⁺⁺ , Mg ⁺⁺ , HCO ₃ ^- , Cl ^- , SO ₄ ^--- ions are continuously supplied into water with a total of 500 mg/less or less, and electricity is conducted between them and the cathode in the water. Carbon fiber surface treatment method.