JPS6215329A - Carbon fiber - Google Patents

Abstract

PURPOSE:Carbon fibers, obtained by spinning an aqueous solution of acrylamide polymer, drying the resultant filament yarn at a specific temperature and heat- treating the dried filament yarn at a specific temperature and firing the resultant filament yarn in an inert gas stream. CONSTITUTION:An aqueous solution of a polymer consisting of 70-100wt% acrylamide and 0-30wt% acrylonitrile is spun into a solvent, e.g. methanol, and wound. The resultant filament yarn is dried and heat-treated at <=300 deg.C, fired at 1,000-2,000 deg.C in an inert gas stream while heating normally for 2-10min and then carbonized and partially graphitized to afford the aimed carbon fibers. Preferably, the above-mentioned drying and heat treatment are carried out by first removing adsorbed moisture at 80-120 deg.C, slowly increasing the temperature and finally heating the yarn at 250-300 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to carbon fibers suitable for use in fiber-reinforced resin composite materials, conductive composite materials, fiber-reinforced concrete, and the like.

[Prior art and its problems]

Carbon fiber, which has high strength and high modulus of elasticity, has recently attracted attention as a composite material that can be combined with resin, concrete, metal, etc. In particular, carbon fiber composite materials with a resin matrix are being applied to aviation and space materials because they are lightweight and have strength and elastic modulus that exceed those of metals. Carbon fiber is made from polyacrylonitrile or pitch, which is spun and then fired and graphitized.

Although these carbon fibers have extremely high strength and elastic modulus, their interfacial adhesion with the matrix resin is weak (for this reason, when shear force is applied to the composite material, the bond between the carbon fiber and the resin is weak). There is a drawback that fractures easily occur at the interface, and the inherent properties of carbon fiber cannot be fully imparted to the composite material. Various surface treatments have been carried out on carbon fiber, but the results are not always satisfactory.

The present invention aims to improve the adhesion between the conventional carbon fiber and resin interface described above, and to provide a novel carbon fiber suitable for a resin composite material having excellent interlaminar shear strength.

[Means for solving problems]

In the present invention, an aqueous polymer solution containing 70 to 100% by weight of acrylamide and 30 to 0% by weight of acrylonitrile is spun, dried and heat treated at 300'C or less, and then heated at 1000 to 2000°C in an inert gas stream. It is a carbon fiber that is obtained by firing, carbonizing, and partially graphitizing, and surprisingly, compared to conventional carbon fibers made from polyacrylonitrile and pitch as starting materials, the interlayer in resin composite materials is It was obvious that the shear strength was significantly superior and the adhesive force at the interface between the carbon fiber and the resin was improved.

The acrylamide and acrylonitrile polymers mentioned above are
It is a homopolymer of acrylamide or a copolymer of acrylamide and acrylonitrile. Acrylamide and acrylonitrile are mixed in an aqueous solution with persulfates such as potassium persulfate and ammonium persulfate, azobis(4-cyanopentanoic acid), and azobis(2-cyanopentanoic acid). The polymer can be easily obtained in the presence of a radical initiator such as a water-soluble azonitrile such as (aminopropane) hydrochloride or a water-soluble peroxide such as hydrogen peroxide. In this case, a reducing agent may also be used in order to control the reaction rate and polymerization sound. If the content of acrylonitrile exceeds 30% by weight of the total monomers, it will be difficult to obtain a uniform polymer, and this is inappropriate for the present invention. The content of acrylonitrile (IJ) is particularly preferably 0 to 20% by weight.

The molecular weight of the above polymer depends on the polymerization temperature, the amount of water, and the type and amount of the polymerization initiator, but the weight average molecular weight of the polymer used in the present invention is preferably 50,000 to 2,000,000. desirable.

When the monomers are polymerized at a high concentration, the polymer exhibits a gel-like appearance, but by adding the necessary water, it can be made into an aqueous solution that can be spun.

Spinning is usually accomplished by extruding an aqueous solution through a nozzle with a diameter of 50 to 1000 μ to remove moisture, and the method is not particularly limited, but examples include methanol, ethanol, isopropanol, tetrahydrofuran, dimethylformamide, This can be easily carried out by forcing an aqueous polymer solution out of a nozzle into a water-soluble solvent such as dimethylacetamide or acetone, which does not dissolve the polymer, and drawing it out. At this time, do you incorporate electrolytes such as salt or sodium sulfate into the aqueous polymer solution or phase separate?
There is no problem even if the solvent is contained to such an extent that it does not occur.

The spun polymer is dried to remove water and solvent until it can be handled, wound onto a bobbin, and then heated at 300° C. or lower. In this heating step, adsorbed water is removed and cyclization is performed by a dehydration reaction. The cyclization reaction proceeds in air, in an inert gas, or under vacuum.

It is preferable that this heating is carried out at 80 to 120°C to remove the sound of adsorbed water, gradually raising the temperature, and finally heating to 250 to 600°C. The time of this treatment step is monitored by the decrease in the infrared absorption spectrum of the carbonyl of the amide group,
It is desirable that the absorption amount of amide groups is 30% or less of the initial value (before heating).

After the above heating step, firing is performed at 1000 to 2000°C in an inert gas stream. If the above heating step is not performed or is insufficient, the fibers will be burned or only fibers with extremely low strength will be obtained. It is thought that carbonization progresses and some graphitization occurs during the main firing process. Usually, the heating time during this period is 2 to 10 minutes,
Furthermore, in order to advance graphitization, heating may be performed in an inert gas at 2000 to 3000°C. As graphitization progresses, the elastic modulus improves, but the strength tends to decrease slightly, and the firing temperature and firing time can be appropriately selected depending on the purpose of use.

The resulting fibers are usually filaments with a diameter of 5 to 20 μm, and in practical use, they are produced as a bundle of filaments (referred to as rovings) by simultaneously spinning from 1000 or more nozzles, heating them, and firing them. In order to prevent the filament from coming apart, it is common to bundle it with a small amount of epoxy resin and then wind it.

The above-mentioned carbon fibers of the present invention can be in a roving state or woven into a woven fabric by weaving rovings, and can be made from thermosetting resins such as epoxy resins and imide resins, polycarbonate resins, polyamide resins, polyester resins, thermoplastic polyimide resins, and polyphenylene/sulfide resins. It is used as a resin composite material by impregnating it with a thermoplastic resin such as polysulfone resin, polyether sulfone resin, polyether ether ketone resin, etc., and thermoforming it.

In the above-mentioned resin composite material, the carbon fiber of the present invention has improved adhesion with the resin, shows excellent results in interlaminar shear strength, and can significantly improve the reliability of the resin composite material.

Further, the carbon fiber of the present invention can also be used by mixing the chopped strand with a resin and injection molding.

Examples of the present invention will be specifically described below.

〔Example〕

Example 1 100 parts by weight of acrylamide, 1000 parts by weight of ion-exchanged water, and 0.1 part by weight of ammonium persulfate were charged into a reactor, heated and mixed at 60°C for 5 hours while passing nitrogen gas through the liquid, and further ion-exchanged. The mixture was diluted by adding 1,400 parts by weight of water to obtain an aqueous polyacrylamide polymer solution.

The above polyacrylamide polymer aqueous solution Y was extruded into methanol through a nozzle with a diameter of 0.5 m, and while being drawn out from the methanol at a linear speed of 10 m/min, it was passed through a drying zone at 80 °C and wound up onto a bobbin to perform spinning. .

Next, take out the above yarn from the bobbin and
The sample was passed through drying zones of 120°C in the second zone, 200°C in the third zone, and 270°C in the fourth zone.

The residence time in each zone was 3 minutes in the first zone, 5 minutes in the second zone, 6 minutes in the third zone, and 3 minutes in the fourth zone.

Next, the heat-treated yarn was heated in an argon gas stream for 1 hour.
The carbon fibers (1) of the present invention having a diameter of 11 μm were obtained by firing at 500° C. for 3 minutes and at 2000° C. for 5 minutes.

Example 2 80 parts by weight of acrylamide, 20 parts by weight of acrylonitrile, 1000 parts by weight of ion-exchanged water, and 0.2 parts by weight of azobis (4-cyanopentanoic acid) were charged into a reactor and nitrogen gas was passed through the liquid. While heating and mixing at 60° C. for 7 hours, the mixture was further diluted by adding 1400F4 ion-exchanged water to obtain an aqueous solution of acrylamide acrylonitrile copolymer.

Spinning the above copolymer aqueous solution in the same manner as in Example 1,
The carbon fiber (n) of the present invention was obtained by heat treatment and firing.

Evaluation Example 1 Carbon fibers (I) and (I) of the present invention obtained in Examples 1 and 2
6,000 filaments of each were immersed in a 1% by weight solution of phenoxy resin in methyl ethyl ketone and dried to obtain rovings.

Next, epoxy resin Ebiko) 1001 (trade name manufactured by Shell Chemical Co., Ltd.) 100 parts by weight, methylene dianiline 200
The roving was immersed in a solution of 10 parts by weight, 10 parts by weight of dimethylaminophenol, and 800 parts by weight of acetone, rolled up on a Teflon drum with a diameter of 100 u while traversing, dried under reduced pressure at 60°C, and then cut open. A unidirectional prepreg with a width of 150 m and a length of 31411 m was obtained. The carbon fiber content of each prepreg ranged between 61% and 59% by volume.

8 sheets of the above unidirectional prepreg were laminated, sealed in a vacuum bag, and then autoclaved at 170°C under a pressure of 8 to 4/-.
Each unidirectional composite material test piece (1
) and (11) were obtained.

Comparative evaluation example 1 Polyacrylonitrile carbon fiber (filament diameter 11
μ) was obtained in the same manner as in Evaluation Example 1. Next, a unidirectional prepreg was manufactured and laminated in the same manner as in Evaluation Example 1 to obtain a unidirectional composite material test piece (III) for comparative evaluation. Note that the carbon fiber content of the prepreg was 61% by volume.

Evaluation Example 2 Each roving using the carbon fibers (Il and (I[) of the present invention obtained in Evaluation Example 1) was mixed with 10% of polycarbonate resin.
A unidirectional prepreg was obtained by immersing it in a methylene chloride solution in the same manner as in Evaluation Example 1. Next, 8 sheets of the above-mentioned unidirectional prepreg and 9 sheets of 50 μm polycarbonate film were alternately laminated and inserted into a flat plate mold heated to 500°C.
The specimens were pressurized at a pressure of 9/- for 5 minutes, cooled to 130°C, and then molded to obtain unidirectional composite material specimens (IV) and (Vl').

The carbon fiber content of each specimen was 58% by volume and 57% by volume.
Met.

Comparative Evaluation Example 2 Using the polyacrylonitrile-based carbon fiber roving prepared in Comparative Evaluation Example, a unidirectional composite material for comparison evaluation was prepared using the same method as Evaluation Example 2 to manufacture unidirectional pre-pulg and laminated molding. A test piece was obtained. The carbon fiber content of the test piece was 58% by volume.

Evaluation of each test piece Using each unidirectional composite material test piece (11-(Vo), the bending strength, bending elastic modulus, and interlaminar shear intensity sound at room temperature were measured. The results are shown in Table 1.

Table 1 [Effect of the invention] Regarding bending strength and bending elastic modulus, no difference is observed between the water side of the present invention and the comparative example, but in terms of interlaminar shear strength, it is clear that the carbon fibers of the present invention Test piece (I) ~ (
) showed excellent results.

Claims (1)

[Claims] (1) An aqueous solution of a polymer consisting of 70 to 100% by weight of acrylamide and 30 to 0% by weight of acrylonitrile is spun, dried and heat treated at a temperature below 300°C, and then heated to 1000 to 2000°C in an inert gas stream. A carbon fiber characterized by being obtained by firing, carbonizing and partially graphitizing.