JP2604866B2 - Acrylic carbon fiber and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an acrylic carbon fiber and a method for producing the same, particularly an acrylic carbon fiber excellent in compressive strength and a method for producing the same.

[Prior art] In recent years, as the application development of carbon fiber has expanded, the required performance for carbon fiber has been increasingly higher. Conventionally, the demand for improvement in tensile properties has been the main focus, and the tensile strength of carbon fibers has been greatly improved in recent years in response to the demand. However, since the compressive strength has hardly improved, the problem that practical characteristics such as bending strength have reached a plateau due to the compressive strength has become apparent. Furthermore, the graphitized yarn having a high firing temperature, that is, a crystal size Lc and a modulus of elasticity of 390 GPa or more, has a single fiber compressive strength level of about 3.5 GPa, which is about 3.5 GPa, which is about half that of a carbonized yarn with a modulus of elasticity of about 245 GPa Therefore, in fields where bending strength is required, such as primary structural materials for aircraft, it has become a bigger problem.

Conventionally, many proposals have been made on techniques for improving the tensile properties, but at present there are few proposals on techniques for improving the compressive strength. High compressive strength modulus by slightly specifying the spinning and firing conditions
Graphitized fibers of 340 GPa or more have been proposed (Japanese Patent Application Laid-Open
No. 211326), the inventors of the present invention have conducted intensive studies on a technique which has a remarkable effect even on a carbon fiber having a higher compressive strength and an elastic modulus of less than 340 GPa.

In other words, we are diligently studying a technique for improving the compressive strength of carbon fiber, which is an important factor that controls the compressive strength of carbon fiber reinforced composite materials, and reduce the crystallinity of the surface layer. The inventors have found that by adopting a structure close to isotropic, the single fiber compressive strength is greatly improved, and the present invention has been achieved.

As a technique for reducing the crystallinity of the surface layer of a single fiber, the present inventors previously conducted a chemical oxidation treatment in a heated concentrated inorganic acid such as sulfuric acid, nitric acid, phosphoric acid, or an aqueous electrolyte solution containing nitrate ions. A method has been proposed in which an electrochemical oxidation treatment is performed followed by an inactivation treatment (Japanese Patent Application Laid-Open Nos. 58-214527 and 61-225330). However, all of these are effective for improving the tensile strength, but are insufficient for improving the compressive strength, and in these treatments, the oxygen-containing functional groups are excessively generated in the surface layer portion of the carbon fiber. Therefore, it is necessary to perform an inactivation treatment for removing the functional group after the treatment, which is disadvantageous in cost. Therefore, the present inventors have further studied a technique which further remarkably lowers the crystallinity and does not require an inactivation treatment, and has arrived at the present invention.

The so-called ion implantation method, in which ionized atoms or molecules are accelerated and implanted from the surface of a material, is being studied as a technique for modifying the surface layer of various materials mainly for semiconductor applications (Japanese Patent Application Laid-Open No. 58-87818). JP, JP-A-58-87894). The present inventors have previously proposed applying it to a carbon material (Japanese Patent Application Laid-Open No. 62-235280). It has been reached.

Regarding ion implantation into carbon fiber, there is a report on vapor-grown carbon fiber (carbon, 1984, No. 104, p2), but highly anisotropic carbon fiber such as vapor-grown carbon fiber. Thus, even if ion implantation is performed, no remarkable improvement in compression characteristics is observed as in the case of acrylic carbon fibers.

[Problem to be Solved by the Invention] An object of the present invention is to provide a carbon fiber having a large crystal size Lc, that is, a carbon fiber having a high compressive strength, which cannot be achieved by the above-described conventional technology, in a region of so-called graphitized fiber, and a method for producing the same Is to provide.

[Means for Solving the Problems] The problems of the present invention are as follows: (1) The carbon content determined by elemental analysis is 98% or more, and the crystal size Lc of the carbon network plane determined by wide-angle X-ray diffraction
Is 22 to 65 °, the degree of orientation in the fiber axis direction π ₀₀₂ is 85% or more, in the acrylic carbon fiber, substantially contains a heterogeneous element, substantially no heterogeneous element in the central portion of the single fiber,
The single fiber surface layer has a maximum concentration portion of a different element, and has a region with low crystallinity compared to the central portion of the fiber, and a laser Raman spectrum of the low crystallinity region of 1320 to 1380 cm ^−1. Width of the scattering peak at νa and 1320-1380 cm of the laser Raman spectrum at the center of the single fiber
The ratio νa / νb of the scattering peak at ^{−1 to} the half width νb is 1.
5 or more, and the single fiber compression strength σcf (GP
Acrylic carbon fiber, wherein a) satisfies the formula (I).

σcf ≧ 10.78−0.1176 × Lc (I) or (2) an acrylic carbon fiber bundle obtained by firing an acrylic fiber having a brightness difference ΔL of 45 or less by an iodine adsorption method, and a bundle having a single fiber thickness The fiber is opened so as to have a diameter of 1 to 5 times the diameter, and atoms or molecules that are solid or gaseous at room temperature are ionized under vacuum, accelerated by an electric field, and applied to the carbon fiber surface at least twice from different directions. The above problem can be solved by a method for producing an acrylic carbon fiber, wherein ions are implanted in an amount of 10 ¹⁵ (ions) / cm ² or more to obtain the acrylic carbon fiber.

First, the acrylic carbon fiber of the present invention will be described.
That is, in the acrylic carbon fiber of the present invention, the fiber center portion is a region within 0.3 μm from the fiber center, and the surface layer portion is a region which is 半径 or less of the fiber radius from the surface and 2.0 μm or less. Further, the crystallinity of the surface layer portion is lower than that of the fiber center portion means that at least a part of the region of the single fiber surface layer portion is 1320 by laser Raman spectroscopy of a single fiber cross section described later.
The ratio νa / νb of the half width νa of the scattering peak at 〜1380 cm ⁻¹ (hereinafter simply referred to as 1350 cm ⁻¹ ) and the half width νb of the peak near 1350 cm ^{−1 in the} center of the single fiber exceeds 1.0. means.

Here, the crystallinity is a characteristic determined by the size of the crystal constituting the carbon fiber and the order of the carbon network plane arrangement,
It is said that the higher the crystal size and the greater the order of the carbon network arrangement, the higher the crystallinity.

With such a high-performance acrylic carbon fiber, a high-performance acrylic carbon fiber having a high compressive strength, which cannot be achieved by the conventional technology, is obtained, and a region having a large crystal size Lc, that is, a graphitized yarn having a high elastic modulus is obtained. In the region, the compression strength level of the single fiber was about 7 GPa and the compression strength was about the same as that of carbonized yarn with an elastic modulus of about 245 GPa, and carbon fibers having both high elastic modulus and high compression strength were made possible.

Such a carbon fiber having a high compressive strength can expand the application to applications requiring bending strength such as an aircraft primary structural material.

Next, an example of a method for producing the acrylic carbon fiber of the present invention will be described.

That is, the acrylic polymer constituting the acrylic fiber (precursor) as the raw material fiber of the acrylic carbon fiber includes at least 90 mol% or more of acrylonitrile and 10 mol% or less of a copolymerizable vinyl monomer such as acrylic acid. And copolymers with methacrylic acid, itaconic acid and their alkali metal salts, ammonium salts and lower alkyl esters, acrylamide and its derivatives, allylsulfonic acid, methallylsulfonic acid and their salts or alkyl esters be able to.

As for the polymerization method, conventionally known solution polymerization, suspension polymerization,
Emulsion polymerization and the like can be applied, but the degree of polymerization is preferably at least 1.2, more preferably at least 1.7 in terms of intrinsic viscosity ([η]). In addition, it is general that [η] is limited to 5.0 or less from the viewpoint of spinning stability.

As the spinning method, a wet spinning method, a dry-wet spinning method, a dry spinning method, or the like can be employed, but a dry-wet spinning method which can obtain a dense precursor is preferable.

In order to obtain carbon fibers having high compression properties, a precursor having high density is effective. As the denseness, a dense precursor having a value of a lightness difference ΔL by an iodine adsorption method of preferably 45 or less, more preferably 30 or less, and further preferably 5 to 10 is good. Means for obtaining a dense precursor having a value of ΔL of 45 or less include lowering the degree of swelling of the coagulated yarn by increasing the concentration of the spinning dope polymer, lowering the temperature of the spinning dope and the coagulation bath solution, and lowering the tension during coagulation. It is effective to suppress the swelling degree of the bath drawn yarn by suppressing the number of drawing steps, drawing ratio and drawing temperature during bath drawing.

Preferably, the single fiber denier of the precursor is 2.
0d or less, more preferably 1.5d or less, still more preferably 0.
It is fine denier of 1-1.0d.

As the flame-proofing conditions for firing such a precursor, the density is preferably 1.25 g / cm ³ or more, more preferably 1.30 g / cm ³ or more under tension or stretching conditions in an oxidizing atmosphere at 240 to 300 ° C. It is good to heat until reaching. It is to be noted that the density is generally limited to 1.60 g / cm ³ or less, and if it is more than this, physical properties may be deteriorated, which is not preferable. Generally, the atmosphere is known air, oxygen,
An oxidizing atmosphere such as nitrogen dioxide or hydrogen chloride can be employed, but air is preferred from the viewpoint of economy.

The obtained oxidized fiber is placed in an inert atmosphere at 1000 ° C or higher for 20
It can be carbonized at a temperature of less than 00 ° C. and, if necessary, graphitized at a temperature of 2000 ° C. or more. At this time, 350 ~ 500
C. and the rate of temperature rise in the region of 1000-1200 ° C.
A temperature of 0 ° C./min or less, more preferably 300 ° C./min or less, and still more preferably 150 ° C./min or less is effective for obtaining a dense carbon fiber having few internal defects such as voids.
If the heating rate is 10 ° C./min or less, the productivity is too low. The stretching may be performed in the range of 350 to 500 ° C. or 2300 ° C. or more, preferably 1% or more, more preferably 5% or more, and still more preferably 10% to 40%.
It is effective in improving the denseness. Stretching exceeding 40% is not preferable because fluff is likely to occur.

Regarding the firing atmosphere, in the region of 300 ~ 1500 ℃,
It is also possible to fire in a mixed atmosphere with an active atmosphere such as hydrogen chloride.

The acrylic carbon fiber of the present invention can be obtained by irradiating the surface of the carbon fiber obtained as described above with higher-speed atoms or molecules and injecting it.

The most preferable method of producing high-speed atoms or molecules and injecting them from the surface of the carbon fiber is the so-called ion implantation method in which atoms and molecules are ionized under vacuum and accelerated by an electric field. That is, in this method, atoms and molecules having energy proportional to the electric field can be obtained by increasing the electric field, so that the atoms and molecules can be implanted to a target depth.
The fast atoms or molecules collide with the carbon atoms forming the carbon fiber and create radiation damage in the carbon fiber by imparting its kinetic energy to the carbon atoms. As a result of accumulation of such irradiation damage, a layer having low crystallinity, that is, a layer closer to isotropic, is formed on the surface layer of the carbon fiber.

In particular, when the graphitized carbon fiber is subjected to the ion implantation treatment, the graphite in the surface layer of the single fiber is modified, and a layer close to an isotropic material similar to a diamond-like carbon film is formed.

That is, the acrylic carbon fiber of the present invention is characterized in that the surface layer portion is close to isotropic, and as a means, a method of damaging the highly crystalline surface layer portion to make it isotropic. And / or a method of modifying the surface layer into a crystal structure close to diamond to make it isotropic.

When conventional carbon fibers are observed by laser Raman spectroscopy, two peaks are observed at 1550 to 1610 cm ^-1 (hereinafter, simply referred to as near 1580 cm ^-1 ) and at the above-mentioned vicinity of 1350 cm ^-1 .

The peak near 1580 cm ^-1 corresponds to perfect graphite crystals, and the relative intensity and half width of the peak near 1350 cm ^-1 tend to increase as the proportion of graphite having a disordered structure increases. Accordingly, the half-value width νa of the peak near 1350 cm ^{−1 in} at least a part of the surface layer portion of the single fiber and the 13
The larger the ratio νa / νb to the half-value width νb of the peak near 50 cm ⁻¹ indicates that the surface layer portion is closer to isotropic, and the ratio is 1.5 or more in order to obtain high compressive strength in the present invention. , More preferably, 2.0 or more.

Graphitized fibers having an elastic modulus of 340 GPa or more have a carbon content of 98% or more determined by elemental analysis, a crystal size Lc of the carbon network plane determined by wide-angle X-ray diffraction of 22 to 65 °, and a degree of orientation in the fiber axis direction. Can be obtained by graphitizing a structure of 85% or more.

The present inventors, by implanting ions such as boron under high vacuum at a high accelerating voltage into the above-mentioned conventionally known graphitized fiber, the single fiber compressive strength and single fiber tensile strength of the graphitized fiber are significantly increased. I found something that could be improved. Furthermore, as a result of analyzing the ion-implanted graphitized fiber by laser Raman spectroscopy, it was found that a spectrum similar to that of the diamond-like carbon film was observed.

The present inventors have conducted detailed studies on the relationship between the change in the Raman spectrum and the improvement in the single-fiber compressive strength and the single-fiber tensile strength, and as a result, have reached the present invention.

When the graphitized fiber before the ion implantation is analyzed by laser Raman spectroscopy, two relatively sharp peaks are observed around 1580 cm ^-1 and around 1350 cm ^-1 (Fig. 2,
6) The spectrum changes as follows by implanting ions. That is, when the obtained Raman spectrum is divided into peaks by curve fitting using a Gaussian function form, for example, FIGS. 4 and 5, that is, FIG. 4 shows the Raman spectrum of the surface of the modified graphitized fiber into which boron ions are implanted at 10 ¹⁶ / cm ^2. Divided by Gaussian function form,
Figure 5 As shown in those divided by three Gaussian functions form a Raman spectrum of the boron ions 10 ¹⁵ / cm ² injected modified graphitized fiber surface, the peak of 1580 cm ^-1 vicinity 1350
cm ^-1 in addition to the peak in the vicinity of the peak is observed in 1400～1500Cm ^-1, approximate to a diamond-like carbon film larger the peak intensity ratio with respect to the peak of 1580 cm ^-1 vicinity of the peak of this 1400～1500Cm ^-1 It is considered that the proportion of the structure is large. In the present invention, in order to improve the single fiber compression strength and the single fiber tensile strength, the peak strength ratio is preferably set to 0.3 or more, more preferably 0.5 to 1.5. It is generally difficult to make the peak intensity ratio 1.5 or more.

The larger the peak strength ratio is, the larger the increase in single fiber tensile strength and single fiber compressive strength is, and when the peak strength ratio is preferably 0.3 or more, the single fiber tensile elastic modulus is 340 GPa or more, and the single fiber tensile strength is 3.9 GPa or more. , Single fiber compression strength is 4.
High performance acrylic carbon fiber of 9 GPa or more can be obtained.

Incidentally, the laser Raman spectrum of the diamond-like carbon film is generally centered at 1500 to 1600 cm ^-1 and 1350 to
This is an asymmetric spectrum having a shoulder at 1450 cm ^-1 .

In the case of the ion implantation method, examples of ion species to be implanted include beryllium, boron, carbon, silicon, phosphorus, titanium, chromium, iron, nickel, cobalt, copper, zinc, germanium, silver, tin, molybdenum, tellurium, and tantalum. Normal temperature solid elements such as, tungsten, gold, platinum, etc. and gaseous elements at normal temperature such as hydrogen, nitrogen, neon, argon, krypton, fluorine, chlorine, oxygen, etc. However, nitrogen, boron, argon, carbon, silicon, titanium, chromium, nickel, and copper are preferable, and nitrogen, boron, carbon, titanium, and chromium are more preferable from the viewpoint of economy and the effect of improving the compression characteristics by injection. Simultaneous or continuous implantation of two or more ion species is also effective for improving the processing effect.

The implantation conditions should be selected according to the relationship with the carbon fiber as the target to be implanted, from the viewpoint of the ion species, acceleration voltage, and implantation amount most suitable for obtaining a desired structure.

The degree of vacuum at the time of injection should be 10 ⁻³ Torr or less,
Preferably, the pressure is 10 ^-4 Torr or less, more preferably 10 ^-5 Torr or less, for effective ion implantation.

The ion accelerating voltage is preferably 50 kV or more, more preferably 100 kV or more, and further preferably 150 kV or more. Since the implantation depth is determined by the combination of the ion species and the acceleration voltage, it is preferable to optimize the combination to obtain a desired implantation depth.

The implantation amount is 10 ¹⁵ (ions) / cm ² or more, more preferably 10 ¹⁶ / cm ² or more, and still more preferably 10 ¹⁷ / cm ² or more. The implantation amount is optimized by a combination of ion species and acceleration voltage. Good to do.

Although the injection time is determined by the beam intensity of the injected volume and the injection device, 10 ¹⁵ / cm ² or more injection volume to produce good injection 0.1 .mu.A / cm ² or more, preferably 1 .mu.A / cm ² or more, more preferably Has a beam intensity of 5 μA / cm ² or more. 1
The injection can be performed with a processing time of 10 minutes or less, preferably 1 minute or less, with a beam intensity of μA / cm ² or more.

As a method of supplying the carbon fiber bundle at the time of implantation, the thickness of the carbon fiber bundle in the ion implantation direction is 1 to 5 of the single fiber diameter.
The fiber is opened in a state in which the single fibers are dispersed so as to be twice, more preferably one to three times, and still more preferably one to two times.

As an opening method, a single fiber may be cut out and fixed to a metal frame or the like, but it is preferable to open the carbon fiber bundle by a widening guide to which a low frequency or mechanical vibration such as ultrasonic vibration is applied. Is good. At this time, it is preferable to use a combination of the flat guide and the convex guide. This method also enables continuous supply of carbon fibers, which is preferable from the viewpoint of productivity.

Furthermore, since it is difficult to inject into the back side even in the state of being dispersed in a single fiber, it is injected at least twice from different directions such as front and back. As a method of injecting at least two times from different directions, the injection may be performed simultaneously from two directions, or may be performed from one direction and then performed again from another direction. At that time, the ion species can be changed.

The crystal structure of the carbon fiber obtained by ion implantation shows that the crystallinity of the surface layer into which the ions are implanted is lower than that of the fiber center, but the central part not implanted is the same as before the ion implantation. It is characterized by a clear step-like structure.

When injecting solid atoms or molecules at room temperature,
The surface of the carbon fiber has a structure in which the injected elements are distributed in an atomic or molecular state, and the distribution state can be measured by secondary ion mass spectrometry (SIMS). The distribution state does not substantially exist in the central portion of the single fiber, but has the maximum concentration portion in the surface layer portion. The distribution shows a distribution close to the normal distribution, and the element concentration on the surface of the carbon fiber is generally 1/2 or less, preferably 1 or less with respect to the maximum concentration of the surface layer. As described above, there is an excellent feature that the structure of the surface layer portion can be modified without inhibiting the adhesion to the resin due to the low concentration of the different elements on the surface. The term "heterogeneous element" used herein means an element other than carbon, and the phrase "heterogeneous element is not substantially present in the central portion of the single fiber" means that the element concentration is less than 0.05% in atomic ratio. Say. However, for elements such as nitrogen contained in the carbon fiber substrate itself, there is a content determined by the firing temperature, which means that the element concentration does not change before and after the ion implantation treatment.

In the present invention, the crystallinity, single fiber tensile strength, elastic modulus, single fiber compressive strength, crystal size, orientation degree, torsional elasticity, ΔL, element distribution according to SIMS and composite 0 ° compressive strength by laser Raman spectroscopy are as follows: Each value is obtained by the analysis method described below.

Crystallinity distribution in the depth direction of carbon fiber cross section by laser Raman spectroscopy The single fiber is electrolessly plated with copper and then embedded in epoxy resin, and the angle of the single fiber is about 5 ° with respect to the fiber axis. The cross section was polished and provided for analysis. When the inclination angle is 10 ° or more, the polished surface of the single fiber cross section becomes smaller, and the number of measurement points in the radial direction decreases in the analysis with a beam diameter of 1 μm,
It is not preferable because accuracy is lowered.

As an evaluation device, Ramanor U-1000 manufactured by Jobin-Yvon, France
A microscopic Raman system was used. Using an argon ion laser (beam diameter: 1 μm) with an excitation wavelength of 5145 °, a Raman spectrum was measured at intervals of about 1 μm from the carbon fiber surface to the center. For each Raman spectrum, peak division was performed by curve fitting using a Gaussian function form, and the change in half-value width of the peak near 1350 cm ⁻¹ was determined in the depth direction. Note that a peak that cannot be divided by the Gaussian function was divided into peaks using the Lorentz function form.

Crystallineity of Carbon Fiber Surface by Laser Raman Spectroscopy One single fiber was collected from a sample fiber bundle and analyzed. As an evaluation device, Ramanor U-10 manufactured by Jobin-Yvon of France
A microscopic Raman system was used. Using an argon ion laser (beam diameter: 1 μm) with an excitation wavelength of 5145 °, the Raman spectrum of the carbon fiber surface was measured. For each Raman spectrum, peak division was performed by curve fitting using the Gaussian function form, and the peak intensity (peak height) observed in the range of 1400 to 1500 cm −1 and the peak
The ratio of the peak intensity (peak height) observed near cm-1 was determined.

Single fiber tensile strength and elastic modulus The single fiber test was performed according to the single fiber test method in JIS-R7601. In addition, the test length of the single fiber was set to 25 mm, and 50 samples were measured for each sample at one level, and the average value was obtained. As the cross-sectional area of the single fiber, the average single-fiber cross-sectional area obtained from the fiber and density of the sample fiber bundle and the number of constituent single fibers was used.

A single fiber having a compressive strength of single fiber σcf of about 10 cm is placed on a slide glass, and one or two drops of glycerin are dropped at the center to form a loop while twisting the single fiber, and a preparation is placed thereon. Put this under the microscope, project it on a monitor (CRT) with a video camera connected to the microscope, observe it, always hold the loop in the field of view, hold down both ends of the loop with your fingers, pull at a constant speed, Apply distortion. Then, the behavior until the break is recorded on a video, and the minor axis (D) and major axis (φ) of the loop shown in FIG. 7 are measured on the CRT while stopping the playback screen. The strain (ε) at point A in FIG. 4 is calculated from the single fiber diameter (d) and D according to the following equation, and ε is plotted on the horizontal axis, and the ratio of the major axis to the minor axis (φ / D) is plotted on the vertical axis. Plot (FIG. 8).

ε = 1.07 × d / D φ / D shows a constant value (approximately 1.34) in a region where compression buckling does not occur, but increases sharply when compression buckling occurs. Therefore,
The strain at which φ / D starts to increase suddenly is determined as the compression yield strain (εcf). This was measured for about 10 single fibers, and the average value was determined. The value obtained by multiplying the obtained average value by the tensile modulus was defined as the single fiber compressive strength.

The tensile modulus of the carbon fiber bundle was measured using "Bakelite" ERL.
-4221 / boron trifluoride monoethylamine (BF ₃ · MEA)
/ Acetone = 100/3/4 parts, and the obtained resin-impregnated strand is cured by heating at 130 ° C. for 30 minutes, JIS-R-
It was measured according to the resin impregnated strand test method specified in 7601.

Elemental analysis The carbon content was determined using Yanagimoto Seisakusho CHN Corder Model MT-3, and the carbon content relative to the sample weight was calculated.
The moisture content of the sample was measured to correct the weight of the sample.

Crystal size Lc Cut the fiber bundle into 40 mm lengths, precisely weigh out 20 mg, align the sample fiber axes exactly parallel, and then use a sample adjustment jig to have a uniform thickness of 1 mm in width. The sample fiber bundle was prepared. After being impregnated with a thin collodion solution and fixed so as not to lose its shape, it was fixed to a sample table for wide-angle X-ray diffraction measurement.
As the X-ray source, using an X-ray generator manufactured by Rigaku Denki Co., Ltd., CuKα ray with 35kV-15mA output (using Ni filter)
Was used. Using a goniometer manufactured by Rigaku Denki KK, 2θ equivalent to the surface index (002) of graphite by a transmission method.
A diffraction peak near = 26 ° was detected by a scintillation counter.

Using the above formula from the half width at the diffraction peak,
The crystal size Lc was determined.

Lc = λ (β ₀ cos θ) where λ is the wavelength of the used X-ray (here, CuKα ray is used, 1.5418 °), and θ is the Bragg diffraction angle. Β ₀ is the true half-value width, and was determined by the following equation.

_{^{β 0 2 = β E 2 -β}} 1 2 (β E is the half-value width of the apparent, beta ₁ is an apparatus constant, where 1.05 × 10 ^-2 rad is) in the fiber axis direction of orientation [pi ₀₀₂ crystal size Lc The sample was prepared in the same manner as in the above case, and the degree of crystal orientation π was obtained from the half width (H ゜) of the profile expansion in the meridian direction including the highest intensity of the (002) diffraction obtained by the same analysis method using the following equation. ₀₀₂ (%) was determined.

π ₀₀₂ = [(180−H) / 180] × 100 Torsional elastic modulus Gf An instant adhesive is obtained by inserting one end of a single fiber with a length of about 10 cm into the pore provided in the center of a glass weight of about 0.5 g. The other end is bonded to the cushion paper with an instant adhesive, fixed with clips and suspended (FIG. 9). Turn the weight about +10 turns to twist the fiber, release it and turn it counterclockwise about -10 turns to stop, and then turn it to return to the original +10 turns and stop for 1 time. Five consecutive periods are obtained as a period T (sec), and the average thereof is obtained. This was measured for about 5 single fibers, the average thereof was determined, and the torsional elastic modulus Gf (GPa) was determined by the following equation.

Gf = 125πlI / (d ⁴ T ² ) × 10 ^-5 I = MD ² / (8g) (l: fiber length (mm), d: single yarn diameter (mm), M: weight of weight (g) , D: Weight diameter (mm), g: Gravitational acceleration (m / se
c ² ), I: torsional moment) ΔL by iodine adsorption method About 0.5 g of a dry sample having a fiber length of 5 to 7 cm was precisely weighed and placed in a 200 ml Erlenmeyer flask with a stopper, and the iodine solution (I ₂ : 51) was added thereto.
g, 2,4-dichlorophenol 10 g, acetic acid 90 g and potassium iodide 100 g are weighed, transferred to a volumetric flask and dissolved in water to a constant volume), and 100 ml is added thereto. An adsorption process is performed. After washing the sample adsorbing iodine in running water for 30 minutes, centrifugal dehydration (2000 rpm x 1)
Minutes) and air-dry quickly. After the sample is opened, the lightness (L value) is measured with a Hunter-type color difference meter (CM-25, manufactured by Color Machine Co., Ltd.) (L ₁ ).

On the other hand, the corresponding sample not subjected to the iodine adsorption treatment was opened, the lightness (L ₀ ) was measured in the same manner with the hunter type color difference meter, and the lightness difference ΔL was obtained from L ₀ −L ₁ .

A-DIDA 3000 manufactured by ATOMIKA West Germany was used as an element distribution evaluation device by SIMS. Under a high vacuum of 10 ^-9 Torr, oxygen ions (O ₂ ⁺ ) were applied to the carbon fiber surface at an acceleration voltage of 12 kV and an ion current of 70 μA, and secondary ions generated by sputtering were subjected to mass spectrometry. Specimens were arranged with carbon fiber bundles aligned and 120 μm × 120
It was measured in the analysis area of μm. The depth is 15
Using glassy carbon fired at 00 ° C., the relationship between the sputtering time and the depth was measured in advance by a surface roughness meter, and was determined from the sputtering rate and the sputtering time determined thereby.

Composit 0 ° Compressive strength Carbon fibers were aligned in one direction, prepregs impregnated with # 3620 resin manufactured by Toray Co., Ltd. were laminated, and measured in accordance with the test specimen and test method specified in ASTM-D695.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples.

Example 1, Comparative Example 1 99.4 mol% of acrylonitrile (AN) and methacrylic acid 0.
Using a copolymer consisting of 6 mol%, a dimethyl sulfoxide (DMSO) solution having a concentration of 20% by weight was prepared. This solution was adjusted to a temperature of 35 ° C, discharged into the air through a spinneret with a hole diameter of 0.12 mm and a number of holes of 3,000 and ran through a space of about 4 mm, and then coagulated in a DMSO aqueous solution at a temperature of 5 ° C and a concentration of 30%. I let it. After washing the coagulated yarn with water, drawing it 3.5 times in a three-stage drawing bath, applying a silicone oil agent, and then bringing it into contact with the roller surface heated to 130 to 160 ° C. to dry and densify it.
Single fiber fineness after drawing 3 times in 7kg / cm ² pressurized steam
A fiber bundle with 0.8d and total denier of 2400D was obtained. The ΔL of the fiber bundle was 28.

The obtained fiber bundle is drawn at a draw ratio of 1.05 in air at 240 to 280 ° C.
To convert the fiber into a flame-resistant fiber having a density of 1.38 g / cm ³ . Next, the heating rate in a temperature range of 350 to 500 ° C in a nitrogen atmosphere is
200 ° C./min., After 8% stretching, 1400
Fired to ° C. The crystal size Lc of the obtained carbon fiber is 18
Was Å.

The obtained carbon fiber was further graphitized to 2400 ° C. to obtain a graphitized fiber.

Approximately 100 single fibers are separated from the graphitized fibers, and the single fibers are aligned and fixed in a 10 cm square aluminum frame so as to be arranged in parallel. The degree of vacuum is 3 × 10 ⁻⁶ Torr, the acceleration voltage is 150 kV, and the boron ion is Was injected at 1 × 10 ¹⁶ / cm ² . This treatment was performed from both the front and back sides. The beam intensity was 0.2 μA / cm ² and the processing time was about 20 minutes per side. Table 1 shows the single-fiber compressive strength, the crystallinity of the surface layer by laser Raman spectroscopy, and the single-fiber tensile properties of the graphitized fibers before and after ion implantation.

As can be seen from Table 1, the ion implantation into the graphitized fibers drastically reduced the crystallinity of the surface layer from νa / νb from 1.0 to 4.8. Single fiber compression strength σcf is 3.53GPa to 7.45G
Pa to about 2 times and torsional elasticity from 14.7 GPa to 27.
It almost doubled to 4GPa. 3.23 GPa tensile strength
To 4.21 GPa, a remarkable effect was observed.

From the crystallinity distribution analysis in the cross-sectional depth direction by laser Raman spectroscopy, the ion-implanted graphitized fiber has a layer with low crystallinity formed from the surface to a depth of about 0.8 μm, and the νa is measured from the surface. This is a value obtained by averaging Raman spectrum data at seven points in a region up to a depth of about 0.8 μm. This distribution is shown in FIG. When the distribution of boron atoms in the graphitized fiber after ion implantation was analyzed by SIMS, it showed a distribution where the concentration became maximum near 0.5 μm from the surface. This distribution is shown in FIG.

Further, with respect to the graphitized fibers before and after the ion implantation, the carbon content, the crystal size Lc, the degree of orientation π ₀₀₂ and the peak analysis crystals by laser Raman spectroscopy are also shown in Table 3.
By ion implantation, the peak of 1400~1500cm ^-1 1580cm ^-1
It can be seen that the peak intensity ratio with respect to the nearby peak was greatly improved from 0.05 to 0.55, and the ratio of the structure similar to the diamond-like carbon film was increased.

Examples 2 to 3 When the ion implantation is performed in the same manner as in Example 1 by using the graphitized fiber before ion implantation used in Example 1, the kind of ion and the injection amount are changed to prototype a modified graphitized fiber. did. The properties of the resulting modified graphitized fibers were evaluated, and the results are shown in Table 1.

Examples 4 and 5 Using the same oxidized fiber as in Example 1 in a nitrogen atmosphere
Set the heating rate in the temperature range of 350 to 500 ° C to 200 ° C / min.
%, And then the maximum temperature is raised to 1800 ° C and
Each was fired at 2000 ° C. to produce two levels of carbon fibers or graphitized fibers. The above fibers were subjected to ion implantation under the same conditions as in Example 1. Table 2 shows the fiber properties of the obtained carbon fibers or graphitized fibers.

Examples 6 to 9 The procedure of Example 1 was repeated, except that the ion implantation conditions were changed as shown in Table 3, to obtain graphitized fibers. Table 3 shows the properties of the obtained graphitized fibers.

Example 10, Comparative Example 2 The fired yarn at 1400 ° C. used in Example 1 was further graphitized to 2850 ° C. to obtain a graphitized fiber having a crystal size Lc of 57 °.

Using the graphitized fiber, boron ions were implanted in the same manner as in Example 1 except that the injection amount was 5 × 10 ¹⁶ / cm ² . The crystal size Lc of the graphitized fiber after ion implantation was 54 °.

As a result of measuring the single fiber compressive strength before and after ion implantation, 3.
The effect of greatly improving from 63 GPa to 5.78 GPa was recognized.

Example 11 and Comparative Example 3 The thickness of the graphitized fiber bundle before ion implantation used in Example 1 becomes three times or less the diameter of a single fiber by low-frequency vibration using a convex and a flat vibration guide. And the aluminum foil was wound up on a bobbin together with the lead paper as lead paper. The obtained winding bobbin was set in a vacuum system, the carbon fiber bundle was pulled out together with the lead paper, and wound on another bobbin at a speed of 1 cm / min. Boron ions were continuously injected into the traveling carbon fiber bundle from a direction perpendicular to the traveling direction.

The degree of vacuum was 1 × 10 ⁻⁶ Torr, the acceleration voltage was 150 kV, and the injection amount was 1 × 10 ¹⁶ / cm ² per side. Once wound, the carbon fiber was unwound from the opposite direction and processed again to inject from both the back and the front.

As a result of measuring the composite 0 ° compression strength of the obtained graphitized fiber before and after ion implantation, the graphitized fiber after ion implantation (Example 11) was 1.35 GPa, and the graphitized yarn before ion implantation (Comparative Example 3) It was greatly improved compared to 1.05GPa.
The crystal size Lc of the graphitized fiber before and after ion implantation was 43 ° (Example 11) and 41 ° (Comparative Example 3), respectively.

Comparative Example 4 The graphitized fiber bundle before ion implantation used in Example 1 was wound around a Pyrex glass frame, and had a concentration of 60% and a temperature of 120.
After heat treatment in hot concentrated nitric acid at 45 ° C. for 45 minutes, washing with water for about 60 minutes, drying in an oven at 120 ° C., and further heat treatment in a nitrogen atmosphere at 700 ° C. for about 1 minute. Table 5 shows the properties of the obtained graphitized fibers.

The graphitized fiber obtained by the treatment has νa / νb of 1.
0 and the same level as the untreated yarn, and the crystallinity analysis by the laser Raman spectroscopy described above did not find any difference from the untreated yarn.
The single fiber compressive strength and the torsional elasticity hardly changed before and after the treatment.

Comparative Example 7 The graphitized fiber bundle before ion implantation used in Example 1 was introduced into a tank filled with nitric acid at a concentration of 30% and a temperature of 50 ° C. through a ceramic guide, and the yarn speed was 0.4 m / min. The carbon fiber was continuously run, and an electric current was applied to the carbon fiber by a metal roller provided immediately before the tank, and an electric quantity of 200 coulombs per 1 g of the carbon fiber was applied. After the obtained carbon fiber was washed with water and dried, it was further heat-treated in a nitrogen atmosphere at 700 ° C. for about 1 minute. Table 7 shows the properties of the obtained graphitized fibers.

In the carbon fibers obtained by the treatment, the single fiber compressive strength and the torsional elasticity hardly changed before and after the treatment.

[Effects of the Invention] According to the present invention, in the region of carbon fibers having a large crystal size Lc, which are low in compressive strength in the related art, so-called graphitized fibers, they have high compressive strength, specifically, compressive strength comparable to that of carbonized yarn. An acrylic carbon fiber can be provided. Further, the acrylic carbon fiber of the present invention is excellent in torsional elasticity and tensile strength. As a result, it is possible to expand the development of graphitized fibers in the field of primary structural materials for aircraft, where both high compressive strength and high tensile modulus are required.

[Brief description of the drawings]

FIG. 1 shows the Raman spectrum of the surface layer of the cross section of the ion-implanted graphitized fiber of the present invention divided by three Gaussian functions. FIG. 2 shows the Raman spectrum of the fiber center of the cross section of the ion-implanted graphitized fiber of the present invention. FIG. 3 is a graph in which the half-value width of the peak near 1350 cm ⁻¹ of the ion-implanted graphitized fiber of the present invention is plotted with respect to the depth from the surface. 4 and 5 show the results of measuring the crystallinity of the surface of the ion-implanted graphitized fiber by laser Raman spectroscopy (FIG. 4 shows the result of boron ion implantation at 10 ¹⁶ / cm ² , and FIG. 5 shows the result of boron ion implantation of 10 ¹⁶ / cm ²⁾ . ¹⁵ / cm ² injected ones), 6 4 Raman spectrum of the graphite fibers surface before boron ions implantation
Divided by two Gaussian function forms. 7 and 8 are schematic diagrams of a method for measuring the single fiber compressive strength by the loop method (FIG. 7 shows a method for measuring the short diameter (D) and the long diameter (φ) of the loop, and FIG. And plotting the ratio of the major axis to the minor axis (φ / D) on the vertical axis), FIG.
Is a schematic diagram of the measurement method of the torsional modulus, FIG. 10 shows the relationship between the crystal size and single fiber compressive strength of Examples and Comparative Examples, together with the measurement results of conventional commercial carbon fibers as reference data Indicated. FIG. 11 shows the carbon fibers obtained in Example 6,
The distribution of implanted elements in the depth direction measured by secondary ion mass spectrometry (SIMS) (the horizontal axis is the depth from the carbon fiber surface, and the vertical axis is the secondary ion intensity of boron ions)
It shows.

Continuing from the front page (72) Inventor Kazuo Yoshida 1-1-1 Sonoyama, Otsu-shi, Shiga Prefecture Toray Research Center Shiga Research Institute Joint Panel Referee Chief Harumi Miyamoto Referee Atsushi Kawai Referee Takuko Funakoshi (56) Reference Document JP-A-63-120112 (JP, A) JP-A-63-211326 (JP, A) JP-A-2-259118 (JP, A) JP-B-62-60476 (JP, B2)

Claims (4)

(57) [Claims] 1. The carbon content determined by elemental analysis is 98% or more, the crystal size Lc of the carbon network plane determined by wide-angle X-ray diffraction is 22 to 65 °, and the degree of orientation π _{002 in the} fiber axis direction is 85%. In the above-mentioned acrylic carbon fiber, substantially containing a different element, the core portion of the single fiber does not substantially contain the different element, and the surface layer portion of the single fiber has a maximum concentration part of the different element, It has a region with low crystallinity as compared to the fiber center, and the half-value width ν of the scattering peak at 1320 to 1380 cm ⁻¹ of the laser Raman spectrum of the region with low crystallinity.
a and 1320 of the laser Raman spectrum at the center of the single fiber
The ratio of the scattering peak at 1380 cm ^{-1 to} the half-value width νb νa / ν
b is 1.5 or more, and the single fiber compression strength σc by the loop method
An acrylic carbon fiber, wherein f (GPa) satisfies the formula (I). σcf ≧ 10.78−0.1176 × Lc (I) 2. The laser Raman spectrum of the surface of a single fiber
Modified graphitized peak is observed in the range of 1400~1500cm ^-1, Claims first (1, characterized in that the peak intensity is not less than 0.3 times the graphite peak intensity existing in 1550～1610Cm ^-1 Acrylic carbon fibers according to the above item. 3. The method according to claim 1, wherein the single fiber tensile modulus is 340 GPa or more, the single fiber tensile strength is 3.9 GPa or more, and the single fiber compressive strength is 4.9 GPa or more. Acrylic carbon fiber according to the above 2). 4. An acrylic carbon fiber bundle obtained by firing an acrylic fiber having a lightness difference ΔL of 45 or less by an iodine adsorption method so that the thickness of the bundle is 1 to 5 times the diameter of a single fiber. Open the fiber, ionize atoms or molecules that are solid or gaseous at room temperature under vacuum, accelerate by an electric field and apply ions to the carbon fiber surface at least twice from different directions at least 10 ¹⁵ (ions) / cm ² A method for producing an acrylic carbon fiber, comprising injecting to obtain the acrylic carbon fiber according to any one of claims (1) to (3).