JPS62268873A - 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 Field of Application] The present invention relates to a method for surface treatment of carbon fibers, and relates to a method for surface treatment of carbon fibers, including composites having good impact resistance. Carbon M1. has excellent surface properties. Maintenance? It is about providing.

[Conventional technology]

In recent years, as prices have declined, the use of carbon fiber composites as primary structural materials has been actively developed to reduce the weight of structures. However, since carbon fiber composites have inferior impact resistance compared to metals, there is currently a strong desire for improvement. In particular, the residual compressive strength after impact of composites (Compression After
OA work) is important as a measure of tolerance when impact is applied to a structure, and is an important characteristic value when using carbon fiber composite for the primary structure. Enter. However, in the past, most surface treatments were simply aimed at improving the interlaminar shear strength (L8S) of the composite;
Even if a satisfactory value is obtained for S, the peel strength may be extremely low, and as an evaluation of interfacial adhesion strength, engineering LSB is used.
We have previously clarified that it is not possible to obtain a composite with higher performance and good peeling resistance by just evaluating it.
No. 9-257770).

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, electrolytic oxidation treatment is common industrially;
Various compounds have been proposed for the electrolyte used, and it is known that surface properties can be improved by electrolytic treatment in a dialkaline aqueous solution.

For example, Japanese Patent Publication No. 5B-24554 proposes using ammonium carbonates as an electrolyte and then decomposing and removing the electrolyte by heating without washing.

However, these electrolytic oxidation methods are not suitable for composite engineering LSS.
The cleaning of the carbon fibers after oxidation was merely intended to remove the electrolyte. The present inventors have revealed that cleaning with an alkaline aqueous solution after electrolytic treatment is effective in improving the peel strength of composite properties (Japanese Patent Application No. 59-2723
No. 42, No. 59-247s91).

However, when electrolytic treatment is performed in an acidic aqueous solution, the oxygen concentration increases and although the peel strength in lateral tension improves, the impact peel strength typified by CA processing actually decreases.

[Problems to be Solved by the Invention] The purpose of the present invention is to improve the peeling resistance of composites upon impact and to improve the so-called CAI value, and to shorten the heating and processing time to be solved. The object of the present invention is to provide a surface treatment method with simplified steps and excellent industrial feasibility.

[Means for Solving the Problems] As a result of our study to improve the overall CA process of composites, we found that electrolytic oxidation in an alkaline aqueous solution? The present inventors have discovered that the steps of applying and then washing in warm water or an alkaline aqueous solution are essential, leading to the present invention.

That is, the gist of the present invention is that after firing carbon fibers, electrolytically oxidizing the carbon fibers in an alkaline aqueous solution using the carbon fibers as an anode,
The carbon fiber is washed with water or immersed in an alkaline aqueous solution.

The carbon fiber surface layer forms a fragile layer or part due to low molecular weight carbides decomposed during the firing process and thermal and mechanical defects, and this fragile part is generally in a state where the bond with the fiber matrix is weak and it is easy to peel off. It has become. In order to improve the OA process of composites, it is important to minimize the peeling inside the composite that occurs due to impact.To do this, it is necessary to oxidize the carbon fiber surface layer and at the same time remove the weak parts. Recognizing that it is essential to remove such weak parts, the present invention has discovered a method for effectively removing such weak parts.

The fragile parts of the carbon fiber surface layer are not removed at all as long as electrolytic oxidation is carried out in an acidic aqueous solution, and only by electrolytic oxidation in an alkaline aqueous solution are they oxidized and decomposed into low-molecular substances and at the same time polarized by the introduction of functional groups. The increased brittle portion becomes easily eluted into the alkaline aqueous solution.

When electrolytic oxidation is performed in an alkaline aqueous solution, the electrolyte becomes noticeably colored, which suggests that oxidation may also have a negative effect on OA work. It is possible to remove the weakened parts of the carbon fibers by combining the carbon fiber matrix with subsequent thorough washing in water or an alkaline aqueous solution. It can be strongly bonded and the impact peel strength can be greatly improved.

In the present invention, when washing with water after electrolytic oxidation treatment, the higher the treatment temperature is, the more effective it is;
It is preferable to perform the cleaning treatment at a temperature higher than 0.degree. C., more preferably using a flood. If the temperature is lower than 40°C, the cleaning effect will decrease and the cleaning time will become long, which is industrially disadvantageous.

Furthermore, depending on the treatment conditions for electrolytic oxidation, using an alkaline aqueous solution with a pH of more than 7 can be used for more effective cleaning. Cleaning in an alkaline aqueous solution is more effective when increasing the current density to increase the electrolytic oxidation level, or when reducing the electrolytic solution concentration to suppress elution of soluble materials. In this case, the alkaline aqueous solution for cleaning does not need to be the same as the alkaline aqueous solution for electrolysis, and a completely different alkali type, concentration, and pH can be used, but from an industrial perspective, it is advantageous to use the same solution. Of course.

The alkaline compound used in the present invention is usually dissolved in water by 0.02%, more preferably α05% or more, and has a pE of
is greater than 7 and less than or equal to 14, such as hydroxides such as sodium hydroxide, potassium hydroxide, and barium hydroxide, ammonia, disodium phosphate, tripotassium phosphate, sodium carbonate, and sodium hydrogen carbonate. Inorganic salts such as ammonium carbonate, ammonium hydrogen carbonate, nitrate), organic salts such as sodium acetate, potassium acetate, sodium benzoate, ammonium benzoate, etc. may be used alone or in a mixture of two or more. Can be done. In order to avoid residual alkali metals and alkaline earth metals in carbon fibers, it is preferable to use ammonium salts such as ammonium phosphate, ammonium benzoate, ammonium carbonate, etc. Sonium and the like are more preferable because they can be removed by thermal decomposition.

In addition, when cleaning with an alkaline aqueous solution, 30 to 8
It is more effective and desirable to carry out heating to 0°C. However, like ammonium carbonate and ammonium hydrogen carbonate,
For compounds that are easily decomposed by heating, it is appropriate to treat them at room temperature.

The cleaning time in the present invention is not particularly limited, but for the purpose of the present invention, the extraction liquid of carbon fibers with distilled water is
It is more preferable to wash until the absorbance falls within a range that satisfies the following formula ().

α01≦Abs, 250nm-α027 Abs, 2
30nm≦ α85 ・1llAbs, 250nm
: 250nm absorbance Abs, 250nm :
Absorbance at 230 nm The absorbance here is carbon fiber 1~
51 into a beaker with an inner diameter of 8 to 16 crR, add distilled water that is 11 times the weight of carbon fiber, and do this? Tank internal volume 298
(Width) x 155 (Depth) x 152 (Depth, W) Ultrasonic cleaner with tank water temperature 50±5℃ (oscillation frequency 43 KHz)
, high-frequency power of 90 W) for 10 minutes, and then the supernatant was collected and placed in a quartz MUv cell with a cell length of one leap. It is absorbance.

The cleaning step of the present invention may be carried out by any method, such as a continuous cleaning method after electrolytic oxidation treatment, or a method in which carbon filth fibers are once rolled up and then washed again continuously or batchwise.
To further improve the cleaning effect, it is also possible to forcibly flow hot water, use bubbling with an inert gas, or apply vibrations using ultrasonic waves.

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 electrolytic oxidation treatment in an alkaline aqueous solution, washing in warm water or an alkaline aqueous solution oxidizes the carbon fiber surface layer and simultaneously completely removes the brittle layer, resulting in strong impact peeling resistance. That is, it becomes possible to obtain carbon fiber for composites with high CA quality.

〔Example〕

The present invention will be specifically explained below using Examples.

The residual compressive strength (ch) of the carbon fiber composite after impact was measured by the following method.

The carbon fibers were mixed with 20.9 M bis(2,3-dipoxycyclopentyl)ether similar to that described in Example 4 of JP-A-59-215314.

A unidirectional prepreg is made using an epoxy resin obtained by blending 47.7 parts by weight of N, Nzr tetraglycidyl 4.4'diamino diphenylmethane with 60 parts by weight of 4.4'bis(3-aminophenoxy)diphenylsulfone. A test piece was prepared by laminating C+a 5101-45/90-+4s in a quasi-isotropic manner and curing at 180° C. for 2 hours.

Compliant with NASA RP 1092.

After fixing a test piece with dimensions 14 x 6 x α 25 inches on a steel stand with a 3 x 5 inch hole,
A 4.9 kg weight with an inch radius nose? After dropping the plate and applying a Vr blow of υ15001b-1n per inch of plate thickness, the plate was subjected to a compression test to determine the OA work.

Implementation u11 Each aqueous solution of 2% sulfuric acid, 5% ammonium phosphate, 5% sodium nitrate, 5% disodium phosphate and 5% potassium hydroxide was applied to 12 with a modulus of elasticity of 24 t/m'' using carbon fiber tow 1002 as an anode. 1 t as electrolyte, 1.
Electrolytic oxidation treatment was performed for 1 minute at a current density of 5 A/m2. When the transmittance at 400 nm of the treated progeny electrolyte was measured, the results shown in Table 1 were obtained. pH of electrolyte is 7
As the size increases, it can be seen that oxidation products from the surface treatment are eluted into the electrolyte.

Table 1 Example 2 1, OA /
After electrolytic oxidation treatment at a current density of m'', water washing was performed under each condition shown in Table 2, and the absorbance of the extract of the obtained carbon fibers was calculated using the method described in the text.

In addition, the results shown in Table 2 were obtained when the entire ♂A process of the obtained carbon fiber was measured.

Table 2, Column 3: Elastic modulus: 30 t/w'', carbon fiber tow used as an anode, t a b/m in 10 m of ammonium bicarbonate aqueous solution
After electrolytic oxidation treatment at a current density of 2, the treated system was washed with a 15% aqueous sodium hydroxide solution at room temperature, and then washed with water at room temperature to obtain a treated system. Sodium hydroxide solution and subsequent water washing time? On the contrary, when absorbance and OA were measured, the results shown in Table 3 were obtained.

Table 3 Example 4 After surface treatment was performed on 12' of elastic modulus 28 t/w2 using carbon fiber tow as an anode under the conditions shown in Table 4 (A) 70
(B) When washed with warm water at 20°C for 3 minutes and (B) after washing with a sodium hydroxide aqueous solution of Section 15 for 4 minutes,
A comparison is shown for the case of washing for 1 minute. The superiority of cleaning with an alkaline aqueous solution is clear.

Table 4 Example 5 After surface treatment for 1 minute at a current density of 1.8 h/m'' in a 5% sodium hydroxide aqueous solution using a carbon fiber tow as an anode with an elastic modulus of 33 t/m'', A treatment system was obtained by cleaning with the alkali species and concentration shown in the table and the liquid temperature. Washing with water after washing with the Hikoo alkaline aqueous solution was carried out at room temperature for 2 minutes. The absorbance and CAI of the obtained carbon fibers are shown in Table 5.

Table 5

Claims (1)

[Claims] 1. A carbon fiber characterized in that after firing the carbon fiber, the carbon fiber is electrolytically oxidized in an alkaline aqueous solution using the carbon fiber as an anode, and then the carbon fiber is washed with water or immersed in an alkaline aqueous solution. surface treatment method. 2. The treatment method according to claim 1, wherein the washing is carried out in hot water of 40° C. or higher or in boiling water. 3. The treatment method according to claim 1, wherein the alkaline aqueous solution is an aqueous solution of ammonium carbonate, ammonium hydrogen carbonate, or ammonium carbamate.