JPH03816A - High-performance pitch-based carbon fiber and production thereof - Google Patents

Abstract

PURPOSE:To obtain the title high-performance fiber useful for a primary structural material of airplane, etc., having high compression strength by specific modulus in tension and compression strength of single fiber. CONSTITUTION:A pitch-based carbon fiber bundle is opened by an enlarging guide provided with mechanical vibration, preferably low-frequency vibration and made into a state wherein single fibers are dispersed so that bundle thickness in the direction of ion impregnation is <=5 times diameter of single fiber. Then atoms are molecules (nitrogen, boron, etc.) which are solid or gas at normal temperature and ionized are accelerated by an electric field at >=50KV under <=10<-3>Torr vacuum and impregnated into the surface of the opened fiber bundle in at least two directions to give the aimed fiber having >=35t/mm<2> (preferably 35-60t/mm<2>) modulus in tension and >=300kg/mm<2> (preferably >=350kg/mm<2>) compression strength of single fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to high-performance pitch-based carbon fibers, particularly pitch-based carbon fibers with excellent compressive strength, and a method for producing the same.

[Prior Art] In recent years, carbon fibers have been used in various composite materials due to their excellent mechanical properties, and demand is rapidly increasing. Along with this, the performance requirements for carbon fibers are becoming higher and higher. Conventionally, the focus has been on improving the tensile properties, and in response to these demands, the tensile strength of carbon fibers has been significantly improved. However, since there has been little improvement in compressive strength, the problem has emerged that practical properties such as bending strength are dominated by compressive strength and reach a plateau.

In order to make effective use of the stiffness of carbon fiber and further reduce the weight of composite materials, it is important to create a thinner structural material, which requires carbon fiber with a high modulus of elasticity. Pitch-based carbon fibers with high graphite crystallinity are seen as promising, but since pitch-based carbon fibers use easily graphitized raw materials, shear buckling is likely to occur. ) type carbon fiber has a problem that its compressive strength is about 1/2 lower than that of carbon fiber.

In the past, many proposals have been made regarding techniques for improving tensile properties, but at present there have been almost no proposals regarding techniques for improving compressive strength. Only a few graphitized fibers with high compressive strength and an elastic modulus of 35 to 712 or more have been proposed by specifying spinning and firing conditions for PAN-based carbon fibers (Japanese Patent Laid-Open No. 63-2113).
No. 26), pitch-based carbon fibers are not proposed.

Therefore, the present inventors have intensively investigated techniques for improving the compressive strength of pitch-based carbon fibers, and found that it is important to improve the single fiber compressive strength of carbon fibers, which is the dominant factor in the compressive strength of carbon fiber reinforced composite materials. To this end, we have discovered that the single fiber compressive strength can be significantly improved by reducing the crystallinity of the surface layer of the fiber, that is, by making the N-surface part more nearly isotropic in structure, which led to the present invention. It is something.

Note that ionized atoms or molecules are accelerated and implanted from the surface of the material. The so-called ion implantation method 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, Japanese Patent Application Laid-Open No. 58-87,
No. 87894) is not known to have applied this type of technology to pitch-based carbon fibers.

[Problems to be Solved by the Invention] An object of the present invention is to provide a high-performance pitch-based carbon fiber with high compressive strength that could not be achieved with the above-mentioned conventional techniques.

[Means for Solving the Problems] The above-mentioned problems of the present invention are as follows: (1) A high-performance pitch characterized by having a tensile modulus of elasticity of 35 J/mm2 or more and a single fiber compressive strength of 300 kg/mm2 or more. carbon fiber.

(2) Spread the pitch-based carbon fiber bundle so that the bundle thickness in the ion implantation direction is 5 times or less the single fiber diameter, and
- High-performance pitch-based carbon fiber characterized by ionizing atoms or molecules that are solid or gaseous at room temperature under a vacuum of 3 Torr or less, accelerating them in a field, and injecting them from at least two directions on the surface of the carbon fiber bundle. manufacturing method.

It can be solved by

First, the fiber of the present invention will be explained below.

The pitch-based carbon fiber of the present invention has a tensile modulus of 35 t/
It is essential that it is at least mm2. As mentioned above, in order to make the structural material thinner, a high elastic modulus, especially 35
This is because a tensile modulus of elasticity of t/mm2 or more is required. The higher the tensile modulus, the more the structural material can be made into four-walled material, but as the tensile modulus increases, the compressive strength tends to decrease, so it is preferably 35 to 60 t/mm2.
．． More preferably, it can be said that about 35 to 55 t/mm2 is good in terms of balance.

Single fiber compressive strength σ is an important factor for the compressive strength of composite materials. f is 300 kg/mm2 or more, preferably 350
kg/mm2 or more, more preferably 400 kg/mm2 or more
Mu2 or higher is better. That is, there is a good correlation between the single fiber compressive strength and the compressive strength of the composite material, and the pitch-based carbon fiber of the present invention has a single fiber compressive strength σcT of 300.
It is possible to obtain a composite material compressive strength equivalent to that of PAN-based carbon fiber, which is at least kg/mn+2. This has made it possible to use pitch-based carbon fibers in applications where conventionally only PAN-based carbon fibers could be used because of compressive strength rate limiting.

Here, the tensile modulus and single fiber compressive strength (
σ. ``) are values obtained using the following methods.

■Zhang Jiao Production Carbon fiber bundle is impregnated with "Bakelite" ERL-4221/Boron Trifluoride Monoethylamine (BF3/MEA)/Acetone = 100/3/4 parts, and the resulting resin-impregnated strand is heated to 130°C. Heat for 30 minutes to harden,
The tensile modulus was determined by measuring according to the resin-impregnated strand test method specified in J I5-R-7601.

t σr Place a single fiber of about 10 cm on a slide glass, add 1 to 2 drops of glycerin to the center, twist the single fiber to make a loop, and place the preparation on top of it. This is placed under a microscope and projected onto a monitor (CRT) using a video camera connected to the microscope, so that the loop is always visible while observing this. Then, while holding both ends of the loop with your fingers, pull it at a constant speed to apply strain. The behavior up to the point of failure is recorded on video, and the short axis (D) and long axis (φ) of the loop are measured on a CRT while the playback screen is stopped. The strain (ε) at point A in Figure 1 is calculated from the single fiber diameter (d) and D using the following formula, where ε is the horizontal axis and the ratio of the major axis to the minor axis (
φ/D) is plotted on a graph with the vertical axis (FIG. 2).

s=1.07Xd/D φ/D is a constant value (approximately 1.34
), but it suddenly increases when compressive buckling occurs, so φ/
The strain at which D suddenly begins to increase is determined as the compressive yield strain (i cf). 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.

Next, an example of manufacturing the fiber of the present invention will be explained.

That is, as the pitch-based carbon fiber that is the raw material fiber for the fiber of the present invention, mesophase pitch-based carbon fiber is preferable because it is easily graphitized and can easily obtain a high modulus of elasticity through graphitization treatment. The raw material for mesophase pitch can be either coal-based or petroleum-based, and after performing conventionally known solvent fractionation, hydrogenation, heat treatment, etc., and melt-spinning to make pitch fibers, it is made infusible in an oxidizing atmosphere, and then in an inert atmosphere. , by carbonization under tension or further graphitization. In order to obtain pitch-based carbon wA fibers with high compressive strength, carbon fibers with few defects such as voids are preferable.For example, in terms of tensile strength level, preferably 300 kg/mu2 or more, more preferably 400 kg/mcn2 or more. be. Further, the tensile modulus level of the raw carbon fiber is preferably 35t.
/Ill! It is 112 or more.

Using such pitch-based carbon fibers, atoms or molecules that are solid or gaseous at room temperature are ionized under vacuum.
It is accelerated by an electric field and injected into the carbon fiber surface.

The most preferred method for creating high-speed atoms or molecules and injecting them from the surface of carbon and other materials is to ionize two molecules of atoms under vacuum and accelerate them using an electric field. This is a so-called ion implantation method. That is, in this method, by increasing the electric field, it is possible to obtain nine molecules of atoms having energy proportional to the electric field, so that nine molecules of atoms can be implanted to a desired depth.

The high-velocity atoms or molecules collide with the carbon atoms forming the carbon fibers and impart their kinetic energy to the carbon atoms, thereby creating radiation damage in the carbon fibers. As a result of such irradiation damage resulting in M loss, a layer with low crystallinity, that is, a layer that is more isomorphous, is formed on the surface layer of the carbon fiber, and the compressive strength of the fiber is improved.

An example of the ion species to be implanted is beryllium.

Boron, carbon, silicon, phosphorus, titanium, chromium, iron, nickel, cobalt, copper, zinc, germanium,
Elements that are solid at room temperature such as silver, tin, molybdenum, tellurium, tantalum, tungsten, gold, and platinum, as well as hydrogen, nitrogen, neon, and argon.

Elements that are gaseous at room temperature, such as krypton, fluorine, and chlorine, or molecular ions, such as boron fluoride, which are composites of these elements, can be applied, but nitrogen, boron, argon, carbon, and silicon can be used due to economic efficiency and the effect of improving compressive properties by injection. , titanium, chromium.

Nickel and copper are preferred, and nitrogen is more preferred.

Boron, carbon, titanium, and chromium are good.

Furthermore, it is also effective to implant two or more types of ion species simultaneously or successively to improve the processing effect.

The implantation conditions are determined from the viewpoint of the most suitable ion species, accelerating voltage, and implantation amount to obtain a structure with a large effect of improving compressive properties.
It should be selected depending on the relationship with the carbon fiber that is the target to be injected.

The degree of vacuum during injection is 10-3 Torr or less, preferably 10-'Torr or less, more preferably 10-5 Torr.
It is effective for the ion implantation to be less than or equal to r.

The ion accelerating voltage is preferably 50 kV or higher, more preferably 100 kV or higher, even more preferably 150 kV or higher. Since the implantation depth is determined by the combination of ion species and accelerating voltage, it is preferable to optimize the combination in order to obtain a desired implantation depth that is highly effective in improving compressive properties.

The injection amount is preferably 10” (ions)/
cm2 or more, more preferably 10"/cm2 or more, even more preferably 1017/cm2 or more, and the implantation amount is preferably optimized by combining the ion species and acceleration voltage.

The implantation time is determined by the implantation amount and the beam intensity of the implantation device, but for example, in order to implant an implantation amount of 10"/cm2 or more with good productivity, the injection time is O,lμA/cm2 or more, preferably 1μA/crn2 or more, more preferably 1μA/crn2 or more. 5μA/cm
A beam intensity of 2 or more is good. With a beam intensity of 1 μA/crn2 or more, it is possible to perform the implantation in a processing time of 10 minutes or less, preferably 1 minute or less.

As described above, it is important to implant ions into the spread fiber bundle, but since it is difficult to implant ions into the back side, it is important to implant ions from at least two directions, the front and back sides. As for the method of injecting from two directions, it is possible to inject from two directions at the same time, or to inject from one direction and then inject again from the other direction. At this time, it is also possible to change the ion species.

The method for supplying carbon fiber bundles during injection is such that the single fibers are dispersed so that the bundle thickness in the ion implantation direction is 5 times or less, preferably 3 times or less, and more preferably 2 times or less the single fiber diameter. It is important to spread the fibers. In other words, ions traveling in a straight line in a vacuum can only be injected to a depth of about 0.1 to 2 μm from the surface layer of pitch-based carbon fibers, and are not injected into the overlapping shadow areas, so that ions can be injected uniformly throughout the fiber. In order to do so, the above-mentioned opening is necessary. If this fiber opening is insufficient, some parts are implanted with ions and some parts are not implanted, which is not preferable because the compressive strength of the single fiber mentioned above cannot be sufficiently improved.

As for the opening method, single fibers may be cut out and fixed to a metal frame, etc., but it is preferable to open the carbon fiber bundle using a widening guide that applies mechanical vibration such as low frequency or ultra-frequency vibration. good. At this time, it is preferable to use a combination of flat and convex guides. With this method,
This is a preferred method because it enables continuous supply of carbon fibers and improves productivity.

oral example Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 Approximately 100 single fibers were separated from a mesophase pitch-based carbon fiber bundle with an elastic modulus of 38 t/mm2 made from coal-based pitch as a raw material, and arranged so that the single fibers were lined up in parallel on an IQcm square aluminum frame. and fix it, vacuum degree 3 x 10 =
Torr, boron ions at an acceleration voltage of 150 kV
016/0m2 injected. This treatment was performed from both the front and back sides. The beam intensity is 0°2μA/cm2,
Processing time was approximately 20 minutes per side.

As a result of evaluating the single fiber compressive strength of carbon fibers before and after ion implantation, the single fiber compressive strength σ was found. r is 350kg/mu
”, which was significantly improved compared to the non-injected yarn (σc+: 170 kg/mm2).Furthermore, the single fiber tensile properties were 380 kg/m in strength [lI22 modulus of 38 sh/mm2,
Uninjected yarn (strength 340 kg#nm2. elastic modulus 38 j
/mm2), the effect of maintaining the elastic modulus and improving the tensile strength was observed.

Example 2 The carbon fiber bundle used in Example 1 before ion implantation was opened using convex and flat excitation guides with low frequency vibration so that the thickness was three times or less the single fiber diameter. , aluminum foil was wound onto a bobbin as lead paper. The obtained winding bobbin was set in a vacuum system, and the carbon fiber bundle was pulled out together with the lead paper and wound onto another bobbin at a speed of 1 cm/min. Boron ions were continuously injected into this running carbon fiber bundle from a direction perpendicular to the running direction.

Vacuum degree is IXI 0-6 Torr, acceleration voltage is 15
0kV.

The injection volume was 1×1016/cm2. The carbon fiber bundle that had been wound up twice was unwound from the opposite direction and treated once again to inject it from both the back and front sides.

As a result of evaluating the single fiber compressive strength of the obtained carbon fiber, it was found to be 340 kg/mm2, which was significantly improved compared to the non-injected yarn. In addition, the single fiber tensile properties have a strength of 370 k
g/mm2. The elastic modulus was 38 t/mm2, which showed a tendency to maintain the tensile elastic modulus and improve the tensile strength compared to before injection.

Comparative Example 1 In Example 2, a pitch-based carbon fiber bundle was opened by low-frequency vibration so that the thickness of the fiber bundle was 10 times the single fiber diameter, and then wound around a bobbin using aluminum foil as a lead paper. The obtained winding bobbin was set in a vacuum system, and boron ions were continuously injected into the carbon fiber from both the back and front sides under the same conditions.

As a result of evaluating the single fiber compressive strength of the obtained carbon fiber, 2
The result was 10 kF/lllll12, which was almost no improvement compared to the non-injected thread.

Comparative Example 2 In Example 1, after the single fibers were aligned and fixed in parallel to a 10 cm square aluminum frame, boron ions were implanted only on one side under the same conditions.

As a result of evaluating the compressive properties of the obtained carbon fibers, the single fiber compressive strength σ was determined. was 225 kg/mm2, which was almost no difference compared to the non-implanted yarn, and when ions were implanted from only one direction, almost no improvement in compressive properties was obtained.

[Effects of the Invention] As stated above, the tensile modulus of the present invention is 35t/mm.
Pitch-based carbon fibers with a single fiber compressive strength of 2 or more and 300 kg/mm2 or more can be used in applications that require high bending strength, particularly as primary structural materials for aircraft.

[Brief explanation of drawings]

Figures 1 and 2 are schematic diagrams of a method for measuring single fiber compressive strength using the loop method (illustration: loose short axis (D) and long axis (
φ) measurement method. Figure 2: Strain ε on the horizontal axis. A graph plotted with the ratio of the major axis to the minor axis (φ/D) on the vertical axis. ).

Claims (2)

[Claims] (1) A high-performance pitch-based carbon fiber characterized by having a tensile modulus of 35 t/mm^2 or more and a single fiber compressive strength of 300 kg/mm^2 or more. (2) Spread the pitch-based carbon fiber bundle so that the bundle thickness in the ion implantation direction is 5 times or less the single fiber diameter, and
^-^ A high-performance pitch characterized by ionizing atoms or molecules that are solid or gaseous at room temperature under a vacuum of 3 Torr or less, accelerating them with an electric field, and injecting them from at least two directions on the surface of the carbon fiber bundle. A method for manufacturing carbon fiber.