JPS62263375A - Surface 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 surface treatment of carbon fibers,
The object of the present invention is to provide carbon fibers with excellent surface properties that give composites with good impact resistance.

[Conventional technology]

In recent years, as prices have declined, the use of carbon and fiber composites as primary structural materials has been extensively developed to reduce the weight of structures. However, since carbon fiber composites have inferior impact resistance compared to gold and yam, there is currently a strong desire for improvement. In particular, the residual compressive strength after impact of composites (Compression Aft
er Impact (CAI) is important as a measure of tolerance when impact is applied to a structure, and improvement of this CAI is required as an important characteristic value when using a carbon fiber composite for a second structure. ing. However, in the past, most surface treatments were simply aimed at improving the interlaminar shear strength (ILSS) of the composite.
Even if a satisfactory value is obtained with engineering LSS, the peel strength may be extremely low, and evaluation of interfacial adhesion strength using ILSS alone will not result in a composite with better peel resistance and higher performance. We have previously made it clear that this is not possible (Japanese Patent Application No. 59-237770).

On the other hand, fired carbon fibers have a weak adhesive strength with the matrix, and many surface treatment methods have been proposed to improve this adhesive strength. Among these surface treatment methods, 1! Deoxidation treatment is common, but gas phase oxidation treatment can be performed in a short time and has advantages in terms of equipment. Gas-phase oxidation methods using ozone are well known, but because of the thermal decomposition nature of ozone, they are processed at a relatively low temperature range where ozone does not substantially decompose. Although the properties of the composite L8S were good, the peel strength was low and the interfacial adhesion strength was insufficient, and the processing time was too long, making it impossible to implement industrially. Those who started from zero,
Previously, we proposed a method of heat treatment at 160 to 250°C in an oxidizing atmosphere containing ozone (Japanese Patent Application No. 59-23777).
No. 0). That is, instead of the oxidation reaction using osinide, by surface-treating the carbon fibers in the decomposed state of ozone, the oxidation reaction can be completed in a short time, and the peeling resistance of the composite can be improved. Furthermore, the present inventors have proposed a method of immersing the surface in an alkaline aqueous solution after surface treatment (Japanese Patent Application No. 59-272542), which removes oxides of impurities such as silica compounds adhering to the surface layer, and performs post-treatment. We proposed a method to stabilize the sizing process in the process. This method was advantageous in removing silica compounds remaining on the surface layer and was effective in improving the properties of the composite, but it required neutralization and washing steps after immersion in alkali, making the process long and complicated. In addition, there are problems such as trace amounts of alkali metals remaining in the carbon fibers.

[Problem that the invention seeks to solve]

The purpose of the present invention is to improve the peeling resistance of composites upon impact and to improve the so-called CAI value. The object of the present invention is to provide a surface treatment method with excellent feasibility.

[Means for solving problems]

The present inventors studied to improve the peeling resistance of composites, and found that
The present invention was achieved by discovering that oxidation treatment and immersion treatment in hot water of 40° C. or higher or boiling water are essential.

That is, the gist of the present invention is that after carbon fibers are subjected to vapor phase oxidation treatment in air containing ozone at an ambient temperature of 160 to 250°C, the vaginal carbon fibers are immersed and washed in hot water or boiling water at 40°C or higher.

By performing the treatment of the present invention, it was possible to significantly improve the CAI of the composite without adversely affecting the C'AI. That is, the carbon fiber surface layer forms a fragile layer or portion due to low molecular weight carbides decomposed and generated during the firing process and thermal and mechanical damage. This fragile portion generally has a weak bond with the fiber matrix and is easily peeled off. In order to improve CAI, it is important to minimize the peeling inside the composite that occurs due to impact, and to this end, we recognize that it is essential to remove the weak parts of the carbon fiber surface layer. Based on this 9
As a result of studying methods for effectively removing such fragile parts, it was found that the present invention is very effective. Before oxidation treatment, the fragile parts of the surface layer are difficult to remove because they are inelastic and lack hydrophilicity, but by oxidation treatment in an ozone atmosphere, they are decomposed into lower molecular weight and the polarity of the fragile parts is improved. As a result, it was discovered that it was easily eluted in warm water, and this led to the present invention.

When carrying out the present invention, the ozone concentration should be within a range where the oxidation reaction can proceed industrially efficiently (although there is no limit to the ozone concentration, it is usually treated within a range of 1 to 2v01ch).

In addition, in order to effectively remove the fragile layer according to the present invention, the oxygen concentration 01B /
C+a is 0.1 to 0.3, more preferably α15 to α2
It is desirable that the surface be treated in advance so as to have a particle size of 5. The surface oxygen concentration measured by ESCA was measured by a gsCA device BSCALAB MKI [type] manufactured by VG. M! The intensities of the C10 and 018 signals when JKa mound was used as the X-ray source were converted to the 01s/cts atomic ratio according to their respective ASF values (0,205 mounds, 63).

When performing immersion cleaning with water after surface treatment according to the present invention, the higher the treatment temperature, the more effective it is, and the immersion cleaning is preferably carried out at 40° C. or higher, preferably 70° C. or higher, and more preferably using water conveyance. If the temperature is lower than 40°C, the cleaning effect will decrease and the cleaning time will become longer, which is industrially disadvantageous.

There is no particular limit to the cleaning time in the present invention, but from the purpose of the present invention, the carbon fibers are washed until the U, V, and absorbance of the extract with distilled water reach a range that satisfies the following formula (1). It is more preferable to do so.

Q, 01≦Abs, 250℃m-0,027Abs, 2
30℃m≦0.85-(1) Abs, 250℃m: 2
Abs Abs at 50℃m, 230nm: Absorbance at 230℃m The absorbance here refers to the absorbance of 1 to 5g of carbon fiber with an inner diameter of 8 to 5g.
Put it in a 16crn beaker, add distilled water that is 11 times the weight of carbon fiber, and add this to a tank with an internal volume of 298 (width) x 155.
(Depth) x 152 (depth, cod) Ultrasonic cleaner with water temperature in the tank 50 ± 5℃ (oscillation frequency 43 KHz, high frequency output 9
0W) and extracted for 10 minutes, then the upper 71-1+
The absorbance at the corresponding wavelength was measured using a U'V spectrophotometer using distilled water as a reference solution.

Furthermore, the cleaning method may be either a continuous cleaning method following the ozone oxidation treatment, or a method in which the carbon fibers are once wound up after the ozone oxidation treatment and then washed again continuously or in batches. To further improve the cleaning effect, it is also possible to forcibly flow hot water, bubble with inert gas, or apply vibrations using ultrasonic waves.

As mentioned above, immersion treatment with an alkaline water injection solution is effective for removing phosphoric acid on carbon fibers, but in order to improve CAI by removing fragile parts, which is the objective of the present invention, hot water is the first method. It is effective in cleaning and industrially advantageous.

The carbon fiber used in the present invention is a general term for carbon fiber and graphite fiber manufactured from polyacrylonitrile polymer, pitch, etc.

〔Effect of the invention〕

After oxidizing the carbon fiber matrix and fragile parts through the above oxidation treatment, the carbon fibers are subsequently immersed in hot water of 40°C or higher or in water to effectively remove the weakened parts that have been oxidized and become more hydrophilic. Strong peeling resistance, i.e. CAI
It became possible to obtain carbon fiber with high carbon fiber.

〔Example〕

The present invention will be specifically explained below using Examples.

Residual compressive strength (CAI) of carbon fiber composite
) was measured by the following method.

Carbon fiber was mixed with bis(2,3-epoxycyclobenzene) similar to that described in Example 4 of JP-A No. 59-215314.
V) 60 parts of 4,4' bis(3-aminophenoxy) diphenyl sulfone was blended with 477 parts by weight of ether zo, 9 parts and a: A unidirectional prepreg was created using the obtained epoxy resin and C+4510/-45/
90'l.

were laminated in a quasi-isotropic manner and cured at 180° C. for 2 hours to prepare a test piece.

Compliant with NASA RP109Z.

Dimensions 4 x 6 x O, 3 x 5 25 inch test pieces
After fixing it on a steel A/made table with an inch hole, attach a 0.5 inch radius nose in the center of the 'tf 4-9.
- A weight of 15001b per inch of plate thickness is dropped.
After applying an impact of -in, the CAI was determined by compression testing the plate.

Example 1 Carbon fibers with a strand modulus of elasticity of 28 t/m2 were continuously fed into a chamber equipped with an external heater under the conditions shown in Table 1 while supplying ozone-containing air at a rate of 0.5@2/hr V]. The oxidation treatment was carried out by running the specimen under different conditions and changing the treatment temperature and time.

After the carbon fibers oxidized as described above were once wound up in a winder, the carbon fibers were further immersed and run in a cleaning tank overflowing with 11% water for cleaning treatment. At this time, the treatment was carried out by changing the temperature and time of the washing water.

The surface of the carbon fiber obtained as described above was analyzed by ESCA to measure 018/C8s, and the absorbance of the extract was measured by the method described in the text.

Furthermore, the CAI of the obtained carbon fibers was measured and the results are shown in Table 1.

It is clear that carbon fibers with high CAI can be obtained with industrial efficiency by the method of the present invention.

Claims (1)

[Claims] After firing the carbon fibers, the carbon fibers are subjected to gas phase oxidation treatment at 160 to 250°C in air containing ozone, and then immersed in hot water or boiling water at 40°C or higher to be washed. A method for surface treatment of carbon fiber.