JPS596950B2 - Tansoseniohiyoumenshiorisurhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for surface treatment of carbon fibers necessary for obtaining carbon fiber reinforced composite materials with excellent performance.

Carbon fiber surface treatment methods for improving the adhesion between carbon fibers and matrix and improving the performance of carbon fiber reinforced composite materials include air oxidation, ozone oxidation, concentrated nitric acid oxidation, hypochlorous acid oxidation, and whisker. Power methods such as rising,
It has been known for a long time.

However, among these surface treatment methods, gas phase oxidation such as air oxidation and ozone oxidation is difficult to control the reaction and not only poses problems in terms of quality control, but also forms excessive etch pits on the carbon fiber surface. Therefore, there is a problem that the carbon fibers are damaged, resulting in a non-negligible decrease in strength.

On the other hand, liquid phase oxidation methods such as concentrated nitric acid oxidation method and hypochlorous acid oxidation method have the advantage of being easy to control the reaction, but they often require a long time for the reaction. There is a problem of lack of selectivity.

Furthermore, carbon fibers treated with these gas-phase and liquid-phase oxidation methods certainly exhibit superior composite physical properties compared to untreated carbon fibers, but they do not provide the most important properties for carbon fiber reinforced composite materials. Interlaminar shear strength (I
inter Lam inar ShearS tr
ength (hereinafter abbreviated as ILSS),
The performance level required for practical use has not yet been reached, and improvement is strongly desired.

Further, although the whiskering method is somehow possible to implement in the laboratory, it is currently impossible to implement it industrially.

The inventors of the present invention have conducted extensive research into surface treatment methods for carbon fibers in order to overcome the above-mentioned deficiencies of the prior art, and as a result, have completed the present invention and achieved the intended purpose.

The carbon fibers treated by the method of the present invention show excellent ILSS when composited, and the method of the present invention is easy to control the reaction, and is also highly effective in effectively oxidizing the surface of carbon fibers in a relatively short period of time. play.

The gist of the present invention is to combine carbon fiber with amidosulfuric acid, I b,
It is characterized by immersing it in a mixed solution of one or more compounds selected from water-soluble inorganic compounds of metal elements belonging to groups lIb1IVb, V, ■, ■a1 and ■, and oxidizing its surface. There is a method for surface treatment of carbon fiber.

The performance of composite materials is highly dependent on the adhesion between the reinforcing fibers and the matsox, and in order to produce composite materials with excellent performance, it is first necessary to improve the interfacial adhesion between the two.
It becomes an essential requirement.

This interfacial adhesion is determined by the surface properties of the reinforcing fibers, the resin system of the matrix, and the method of molding the composite material.
Primarily determined.

However, the surface properties of carbon fibers are mainly determined by the specific surface area, the type and concentration of surface functional groups, the surface shape, and the type and amount of surface adsorbed components, leading to the production of carbon fiber reinforced composite materials with excellent performance. In order to achieve this, it is important to first optimize these surface factors from the carbon fiber side.

As a result of our research, the present inventors have found that in order to improve ILSS, which is one of the most important properties of carbon fiber reinforced composite materials, it is necessary to introduce polar functional groups onto the carbon fiber surface and at the same time etch the surface to some extent. It was confirmed that this is effective.

However, excessive etching accompanied by a significant increase in surface area not only substantially reduces the concentration of effective functional groups attached to the backbone of the carbon fiber, but also destroys the surface layer of the carbon fiber and, in turn, the fiber itself. This type of etching must be avoided since it causes a decrease in the strength of the metal.

According to the method of the present invention, compared to the conventional concentrated nitric acid oxidation method, unnecessary increase in surface area is suppressed, so that a carbon fiber surface with a high distribution density of functional groups can be obtained.

That is, the method of the present invention has high surface selectivity for oxidation reaction.

Furthermore, the carbon fibers oxidized by the method of the present invention are
It has the great feature of exhibiting excellent ILSS when made into a composite.

Furthermore, the method of the present invention is characterized by good reaction reproducibility and easy control of the reaction.

Note that amide sulfuric acid alone has extremely weak oxidizing power on carbon fibers, and it is virtually impossible to introduce acidic functional groups onto the surface of carbon fibers. However, according to the method of the present invention, carboxyl It becomes possible to introduce acidic functional groups such as hydroxyl groups and phenolic hydroxyl groups.

In the present invention, amidosulfuric acid is a compound represented by the chemical formula HSO3NH2, and is also called sulfamino acid, sulfamic acid, or aminosulfonic acid.

As the solvent for amidosulfuric acid, an aqueous solvent is usually used.

This aqueous solvent can contain water-soluble substances such as inorganic acids in addition to water.

There are no particular restrictions on the concentration of amidosulfuric acid in the solution, but in order to effectively carry out the oxidation reaction, it is usually 5.
~50%.

On the other hand, as reaction catalysts, Ib, IIb, IVb, ■,
One or more inorganic compounds selected from water-soluble inorganic compounds of metal elements belonging to groups ①, ②a, and vm can be used, but in view of the promoting effect on the oxidation reaction of carbon fibers, Particularly preferred are water-soluble inorganic compounds of copper, silver, zinc, cadmium, tin, lead, vanadium, antimony, bismuth, chromium, molybdenum, tungsten, selenium, manganese, iron, cobalt, palladium, and platinum.

The water-soluble inorganic compound referred to here refers to 8 of the above elements.
It means an inorganic compound with a solubility in water of 1% or more at 0°C, and typical examples include chlorides, nitrates, and sulfates of these elements, and metal acids containing these metal elements as constituents and their salts. be able to.

Specific examples of these water-soluble inorganic compounds include copper nitrate,
Silver nitrate, zinc nitrate, zinc sulfate, cadmium nitrate, tin chloride, lead nitrate, ammonium vanadate, ammonium metavanadate, antimony nitrate, bismuth nitrate, chromium nitrate, ammonium molybdate, ammonium tungstate, ammonium selenate, manganese nitrate, manganese Examples include ammonium acid, iron nitrate, iron sulfate, cobalt nitrate, cobalt sulfate, palladium chloride, and chloroplatinic acid.

There are no particular restrictions on the amount of these catalysts used, but
Usually, it is 0.1 to 20% by weight based on carbon fibers (the percentages below refer to the weight fraction unless otherwise specified).

) is used within the range.

Further, there is no particular restriction on the concentration of carbon fibers in the reaction solution, but from the viewpoint of reaction operation, about 0.1 to 20% is appropriate.

The oxidation treatment temperature is preferably 80° C. to 110° C., and practically preferably around 100° C.

Further, the oxidation reaction time depends on the composition of the reaction liquid, the reaction temperature, etc., but is usually within the range of 10 minutes to 20 hours.

Carbon fibers treated in this way are made of epoxy resin,
When composited with polyimide resin or the like as a matrix, the composite exhibits excellent physical properties.

The method of the present invention is applicable to carbon fibers, graphite fibers, and graphite whiskers, regardless of the starting material (precursor) thereof.

Furthermore, the method of the present invention can be implemented in either a batch or continuous process.

Examples of the present invention will be described below.

, Example 1 Polyacrylinolenitrile fiber was finally heated to 1350°C.
Carbon fiber (high strength yarn, tensile strength 300 kg/crA, tensile modulus 23
50 g of tow (consisting of 10,000 single yarns with a diameter of about 8 μm) of
500ml of a solution consisting of 45 parts of amide sulfuric acid and 55 parts of water
The sample was immersed in a reaction solution prepared by dissolving 5 g of ammonium metavanadate in 1 liter of water, and the reaction was carried out at 100° C. for 9 hours.

After the reaction was completed, the carbon fibers were thoroughly washed with pure water and then dried.

The acidic functional group concentration of the obtained carbon fiber was measured by conductivity titration, and it was found that 23×10” mol/I? of acidic functional groups were introduced onto the carbon fiber surface.

In addition, the specific surface area of the same fiber was measured using the nitrogen gas adsorption method, and the specific surface area was 2 m/L? It turned out to be.

Next, the carbon fibers obtained in this manner were impregnated with a resin composition consisting of 86 parts of "Epicoat (8828)" (an epoxy resin manufactured by Shell), 4 parts of boron trifluoride monoethylamine, and 10 parts of methyl ethyl ketone. A prepreg was prepared by aligning this on a silicone-treated release paper and then heating it at 130°C for 25 minutes.

Note that this prepreg was created using a drum winder.

The prepreg obtained in this way has a length of 280 m7
IL, cut to a width of 30 mm, stacked 9 sheets, put them in a mold of the same size, and then inserted between the hot plates of a hydraulic press heated to 130 ° C, 7 kg. /c
yst for 30 minutes at 130°C and further at 170°C.
Heated at °C for 1 hour.

Then, the obtained molded product was placed in an oven at 170°C.
I did the post-cure for 2 hours.

The resulting composite contained 58% by volume of carbon fiber, and its ILSS was measured according to the method of ASTM D-2344, and was found to be 8.08 kg/1.

Example 2 As a reaction solution, bismuth nitrate [molecular formula = B i
(NO3) s・5H20, 120.7g (4.27
Carbon fibers were oxidized in the same manner as in Example 1, except that a solution containing X10-2 mol) was used, and the physical properties of the obtained product were evaluated.

The acidic functional group concentration of the obtained carbon fiber was 25×10 −5 mol/V.

Further, the ILSS of the composite 1 produced using the carbon fiber obtained here was 8.24k9/1.

Note that the volume content of carbon fiber in this composite was 58%.

Comparative Example 1 Carbon fibers were surface-treated in the same manner as in Example 1, except that 500 ml of a solution consisting of 45 parts of amide sulfuric acid and 55 parts of water (no catalyst) was used as the reaction solution. Physical properties were evaluated.

The specific surface area of the obtained carbon fiber is 0. 6 ml? Met.

On the other hand, it was found that almost no functional groups were introduced on the surface of the fiber.

Moreover, the ILSS of the composite made using the carbon fiber obtained here was 5.94 kg. /It was one.

Note that the volume content of carbon fiber in this composite was 60%.

Examples 3 to 6 and Comparative Example 2 Ammonium metavanadate 5g (4
．． Carbon fibers were oxidized in the same manner as in Example 1 except that 4.27X10-2 gram equivalents of the catalyst shown in Table 1 were used on the basis of the metal element instead of 27X10''.mol). The physical properties of the product were evaluated.

The obtained results are shown in Table 1 together with the results for the untreated carbon fiber used as a comparison sample.

Note that the volume content of carbon fiber in the composites prepared here was all 56 to 60%.

Claims (1)

[Claims] 1 Carbon fiber, amidosulfuric acid, Ib, nb1rvb,
A carbon fiber characterized by immersing it in a mixed solution of one or more compounds selected from water-soluble inorganic compounds of metal elements belonging to Groups V, VI, ■a, and ■, and oxidizing its surface. How to treat the surface.