JPS5953717A - Pitch-based carbon fiber having high strength and modulus and its manufacture - Google Patents

Abstract

PURPOSE:To obtain the titled fiber free from cracks and having specific orientation angle, crystal size, laminar spacing, strength and modulus, by melting a spinning-grade pitch, heating the molten pitch to a temperature higher than the viscosity-change temperature, spinning the pitch, making the filament infusible, and baking the product. CONSTITUTION:In the melt spinning of a raw pitch for spinning, the molten pitch is heated to a temperature higher than the viscosity-change temperature of the pitch, and spun to obtain a pitch fiber. The fiber is made infusible and baked to obtain the objective carbon fiber composed of the skin layer 1 having crystals oriented along the circumferential direction and the core part 2 containing radially or mosaically oriented crystals, and having a micro-structure characterized by an orientation angle (OA) of 30-50 deg., crystal size (Lc) of 12-80Angstrom and laminar spacing (d002) of 3.4-3.6Angstrom (measured by X-ray diffraction), and having a tensile strength of >=200kg/mm.<2> and a modulus of >=10t/mm.<2>.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel pitch-based carbon fiber and a method for producing the same. More specifically, the present invention provides a novel carbon fiber made from pinch as a raw material and which exhibits properties comparable to carbon fiber obtained from polyacrylonitrile fiber.
The present invention relates to a manufacturing method for industrially manufacturing the same with excellent productivity.

Carbon fiber was initially manufactured using rayon as a raw material, but as a result of research and development of various raw materials and processes, in terms of its characteristics and economic efficiency, carbon fiber is now mostly manufactured using polyacryloni, ], and lyl as raw materials. These are dominated by PAN-based carbon fibers and pitch-based carbon fibers made from coal- or petroleum-based pitches.

By the way, pitch-based carbon fibers generally have low strength and low monularity, so they are usually used for general-purpose grade purposes.Until now, PAN-based carbon fibers have been used as high-performance grade carbon fibers that require particularly high strength and high modulus. Carbon fibers have been the mainstream, but recently there has been an increase in interest in the economical technology of producing high-performance grade carbon fibers using pitch as a raw material. Several techniques have already been proposed, including a method of obtaining high-strength, high-modulus carbon fibers by melting and firing.

However, even though the pinch type carbon fibers obtained by these methods show some improvement in tensile strength and monylus, they are still considerably inferior to PA'N type carbon fibers. It is inevitable that the usage will be limited.

The present inventors have determined that in terms of performance such as strength and modulus,
As a result of intensive research to develop pitch-based carbon fibers that are comparable to or better than PAN-based carbon fibers, we have found that specific improvements should be made to the conditions when melt-spinning pitch raw materials for spinning. It was unexpectedly discovered that a new pitch-based carbon fiber with a microstructure completely different from that of conventional pitch-based carbon fibers and a performance comparable to that of PAN-based carbon fibers could be obtained. The present invention has been made based on this.

That is, the present invention provides orientation angles (OA
) is 30~50°, crystal size (Lc) is 12~80A
, a microstructure with a dooz of 3.4-3.6 A, and a tensile strength of at least 200 kg/t
The present invention provides a pinch type carbon fiber characterized by exhibiting a modulus of at least 10 t/mm.

High-performance grade carbon fibers obtained from conventional membrane pitch are polycrystalline fibers consisting of crystals with an orientation angle (OA) smaller than 30° and highly oriented in the fiber axis direction, and a size (Lc) larger than 8OA. It has a three-dimensional structure of graphite. In terms of physical properties, this material exhibits high thermal conductivity and electrical conductivity as graphitization properties, but its mechanical properties as a fiber, especially its strength and elongation, are inferior to that of PAN-based carbon fibers. There is. This is because the graphitized structure is highly oriented and highly oriented, which causes non-uniformity of the microstructure inside the fiber, and the inside of the fiber becomes a radial structure, which makes cracks more likely to occur. This is considered to be due to a positive decrease in physical properties.

On the other hand, the carbon fiber of the present invention has an orientation angle (OA) of 30 to 50 degrees, preferably 35 degrees, as determined by X-ray diffraction.
~45°, not very highly oriented, and crystal size (Lc) of 12-80A, preferably 20-75A
It has a dense crystal structure with a interlayer spacing (dooz) in the range of 3.4 to 3.6 A, and it also has giant lobed domains extending in the fiber length direction, as seen in carbon fibers made from menface pitch. Since the structure is relatively homogeneous and does not contain carbon, its strength and modulus are high.

In general, crystal size (Lc) and interlayer spacing (dooz)
has a correlation with the above-mentioned orientation angle (OA), and as the orientation angle becomes smaller, the crystal size tends to increase and the interlayer spacing tends to decrease. If the crystal size becomes too large and the interlayer spacing becomes too small, high strength cannot be obtained, and if the crystal size becomes too small and the interlayer spacing becomes too large, the monylus will deteriorate.

The carbon fiber of the present invention has the three structural parameters mentioned above, namely orientation angle, crystal size, and interlayer spacing, which are appropriately balanced, and has excellent mechanical strength that is completely different from that of conventional pitch-based carbon fiber. This shows that.

The carbon fiber of the present invention has the specific microstructure described above, but if the crystals in the surface layer of the fiber are arranged in the circumferential direction, especially in the cross section of the fiber, cranking will not occur and the carbon fiber will have a higher This is advantageous because it is a strong fiber.

The cross-sectional structure of such fibers can be observed using a scanning electron microscope. Figure 1 of the attached drawings, (B)
is a schematic diagram showing an example of such a cross-sectional structure. 1 in the diagram is the surface layer where crystals are arranged in the circumferential direction, and here, the plate-like carbon layer surface is parallel to the fiber surface. It takes an array. 2 is the center where the crystals are arranged in a radial or mosaic pattern. At this time, if the thickness of the surface layer 1 is extremely small, the effect of preventing cranking will be small, so it is preferable that the thickness of the surface layer 1 is at least a factor of 10 of the fiber radius, particularly from 10 to 60 inches. The center part 2 may have any structure as long as it is dense, and may have a concentric structure similar to the surface part 1, but the center part 2 may have a structure different from the surface part 1, especially if it has a structure shown in FIG.
) or a mosaic structure as shown in FIG. 1(B) are preferable because they have a high modulus.

The diameter of the fiber is preferably in the range of 5 to 50μ,
The fiber length can be selected arbitrarily.

The carbon fiber of the present invention having the above-mentioned special structure is
Those that have a strength of at least 200 ky/mA and a modulus of at least 10t/IIl+lI, and have a strength of 25o kg/mA or more and a modulus of xst/- or more are particularly useful as reinforcing materials for resins. It is.

The carbon fiber of the present invention having such excellent performance,
It can be easily produced by melting a spinning pitch material for spinning 1 containing a Brimethoface pinch, subjecting it to heating and melt spinning under specific temperature conditions, and then firing it to make it infusible.

Next, this manufacturing method will be explained in detail.

As the raw material, a pitch raw material for spinning, at least a part of which is brimenface pinch, is used. This burimesoface pitch is optically isotropic, but when heated above 600°C, it changes to an optically anisotropic memphispitch, and when an external force is applied, it becomes optically anisotropic. It is clearly different from the so-called dormant mesophase pitch.

As a raw material for producing the carbon fiber of the present invention, among the pitch raw materials for spinning containing such Brimenface, a material containing a quinoline soluble component in an amount of 30% by weight or more, preferably in the range of 30 to 70% by weight, and the number average molecular weight of the quinoline soluble component determined by vapor osmotic pressure method is 70.
0-1700, specific gravity at 20℃ in a pinch is 1.29
-1.35 and the degree of aromatization is particularly preferably in the range of 0.45-0.8.

Then, the quinoline-soluble component was removed from the solvent in proton NMR (tetramethylsilane relative to all detected hydrogen).
TMS) standard chemical shift 5-7 hydrogen HA ratio is 4.5-10%, same chemical shift 3-4 ppm
It is preferable to use a polycyclic condensed compound whose core is partially hydrogenated, such that the proportion of hydrogen HB is 2.5 to 7.5%.

The H/C value of this material is within a very limited range of 0.5 to 0.65.

Such pitch raw material for spinning contains a considerable amount of a component in which about 2 to 10 structural units consisting of a partially hydrogenated polycyclic condensed compound having 2 to 6 rings are bonded to the core via side chains. Since the planarity of the molecules of the component is distorted by nuclear partial hydrogenation, it has good fluidity in the spinning pinch, and is also excellent in compatibility with membrane pitch, resulting in good melt spinnability.

Such spinning pitch raw materials include, for example, coal tar,
Coal tar pitch, coal-based heavy oil such as coal liquefied oil, normal pressure residual oil of petroleum, tar and pitch by-produced by vacuum distillation and heat treatment of these residual oils, oil sand,
After refining heavy petroleum oil such as beemen,
It can be produced by subjecting it to a first stage treatment of heating in the presence of a specific hydrogenation solvent and a second stage treatment of heating to a high temperature after or while removing the solvent.

As the raw material pinch in this case, coal tar pitch is particularly advantageous in that it is easy to process and provides a suitable pinch raw material for spinning.

As the hydrogenation solvent used in the first stage treatment, tetrahydroquinoline (hereinafter abbreviated as rTHQJ) is most suitable, but a mixture of quinoline and THQ may also be used.
Also, quinoline can be used with hydrogen in the presence of a catalyst (cobalt-molybdenum type, iron oxide type, etc.), and naphthalene oil, anthracene oil, creonate oil, pitch oil, absorption oil, etc. can also be used with hydrogen gas. It is possible.

When T I-I Q is used as a hydrogenation solvent, 'l' per 100 parts by weight of raw material pitch (Q 30-1000
Add parts by weight to 300-500°C1, preferably 340-500°C
Heat to a temperature of 450°C for 10-60 minutes. The product thus treated is subjected to the next second stage treatment.

In the second stage treatment, the THQ treated pinch is maintained at a temperature of 450° C. or higher, preferably 450 to 550° C., for 5 to 60 minutes under reduced pressure, for example, at a pressure of s Omm 11 g, abs or less. In this case, instead of the decompression treatment as described above,
After removing THQ, it may be held at a temperature of 450 to 550°C for 5 to 60 minutes under normal pressure, or after removing THQ, the temperature may be raised to a temperature higher than 450°C under normal pressure, and then to 400 to 430°C. Reduce to this temperature 15-1
It may be held for 80 minutes.

In such a two-stage treatment, a preferable pitch raw material for spinning can be obtained by appropriately selecting the treatment conditions within the above range depending on the composition and properties of the raw material pinch.

The pitch raw material for spinning obtained in this manner, ie, the pinch containing premethophase, has a singularity in its viscosity behavior with respect to temperature.

The viscosity of pitch can be summarized by Andrade's equation, which is known as a relational equation between viscosity and temperature. This formula is: ηa=Aexp(B/T)=Aexp(△Ha/R
T). (Here, ηa is the viscosity, A is the constant, B
-ΔHa/RT, where ΔHa is the apparent activation energy of the flow, R is the gas constant, and T is the absolute temperature) Take the logarithm of both sides of this equation. And, log ηa = IogA + B/T ・1/2.3
03, and log ηa and 1/T are a straight line.

At this time, ηa of the pitch raw material for spinning that can be preferably used in the present invention is shown by two straight lines with respect to 1/T. This means that the flow state of the pinch changes at the intersection temperature of these two straight lines. Figure 2 shows an example of this situation. The relationship between log ηa and 1/T is shown by the straight line II on the high temperature side and the straight line ■ on the low temperature side.
Ts is the temperature at the intersection of both the straight lines.

According to observation using a reflective polarizing microscope equipped with a hot plate, it is recognized that the optical characteristics of the pitch change at the intersection temperature (Ts) of straight lines I and II. In other words, it is recognized that the optical anisotropy disappears on the higher temperature side than the intersection temperature (Ts) in the pitch containing membranes.

In the present invention, the intersection point temperature (Ts) is set to 1 viscosity change source degree.
It is called.

In the present invention, the pinch raw material for spinning is once heated to a temperature higher than the viscosity change temperature (Ts) and then spun. If the pitch is spun without being heated to a higher temperature than this temperature during spinning, the fiber crystals will always have a radial structure, making cranks more likely to occur. On the other hand, when heated to a higher temperature than this temperature, the plate-like carbon layer surfaces from the fiber surface portion are arranged parallel to the fiber surface, and the vicinity of the center becomes radial or mosaic-like.

It was confirmed that the higher this heating temperature was raised, the more the plate-like layer planes aligned parallel to the fiber surface spread into the interior, and finally the entire fiber became a concentric structure (so-called onion structure) with the entire fiber aligned parallel to the fiber surface. It was done.

This phenomenon is also observed when the pitch is heated to a temperature (TA) higher than the viscosity change temperature (Ts) and then rapidly cooled down for spinning. Therefore, if pitch heated to a temperature higher than the viscosity change temperature has a low viscosity and smooth spinning is difficult, the pitch heated to a temperature higher than the viscosity change temperature can be heated to a temperature where the viscosity becomes suitable for spinning rapidly, that is, the appropriate viscosity. It is preferable to perform spinning after cooling down to temperature (TB).

Further, the fibers discharged from the spinneret are preferably cooled and solidified as quickly as possible, and for this reason, it is preferable to set the draft rate during spinning to 30 or more to rapidly cool the fibers.

This is probably due to the fact that at high temperatures above the viscosity change temperature, the lamination of the non-face is broken down due to molecular thermal motion, allowing the molecules constituting the membrane to move in a disjointed state, and are removed from the spinneret while maintaining this state. When the fiber is discharged, the shear at the mouthpiece prevents the memphatic lamella from arranging in the radial direction of the cross section of the fiber, and when the fiber discharged in this state is rapidly cooled, the surface layer of the fiber becomes concentric. It is thought that a structure is formed.

In addition, the pinch heated to a higher temperature than the viscosity change temperature maintains the above state even if it is rapidly cooled. Once heated to a temperature (TA) higher than the viscosity change temperature (Ts), it is possible to quickly (preferably within about a few minutes) cool down to the appropriate viscosity temperature (TB) and then perform spinning. Spinning can be carried out.

The relationship between pinch viscosity and temperature varies depending on the type of pitch and pitch preparation conditions, but the viscosity change temperature (Ts
) can be easily determined experimentally. Generally, the temperature (Ts) is related to the softening point of the pitch, and the viscosity change temperature (Ts) of most pinches is 70 to 90°C below the softening point.
The temperature is high. In the present invention, it is appropriate to heat the pitch to a temperature (TA) 30 to 40°C higher than this viscosity change temperature, and by raising the temperature of the pitch to this temperature (TA), at least the fiber surface layer becomes concentric. Fibers having a structure arranged in a shape can be formed. The heating temperature (TA) of pitch for spinning is 1 below the softening point of pitch.
It is possible to raise the temperature to about 00 to 130°C, but if the temperature is too high, spherical membranes that will not disappear even if heated to a higher temperature will be generated during the melting pinch, which is undesirable.

- When spinning pitch by rapidly lowering the temperature after the pitch has been heated to the above temperature (TA), the range of temperature reduction varies depending on the type of pitch and preparation conditions, but is generally preferably about 40 to 80°C, and , the temperature at the time of discharge from the spinneret (TB
) varies depending on the pinch, but is usually 30° below the softening point.
It is preferable to set the temperature to ~80°C higher.

The fiber discharged from the spinneret has a draft rate of 30 or more,
Preferably, it is suitable to take over at 50 or more. Here, the draft rate is a value defined by the following formula, and a large value means a high deformation speed during spinning, and if other conditions are the same, the larger the draft rate, the faster the quenching effect will be. Become.

When drawn at a draft rate of 30 or more, especially 50 or more, the spun pinch is rapidly cooled and solidified, forming pitch fibers with a large orientation angle and suppressed crystal growth.

As for the take-up speed of the spinning yarn, although spinning can be carried out very smoothly even at a high speed of 1000 m/min or higher under the above-mentioned spinning conditions, a range of 300 to xsoom/min is usually preferably used.

The pitch fiber obtained by employing the special spinning conditions described above is then subjected to an infusible treatment by heating it in the presence of oxygen to 0.5-b and maintaining it for 5-30 minutes. As mentioned above, fibers made from pitch raw materials for spinning, which are mainly composed of polycyclic condensed compounds with partially hydrogenated aromatic nuclei, can be infusible quickly and are more durable than conventional pitch fibers. It is possible to shorten processing time.

This is thought to be because in a polycyclic condensed compound in which the aromatic nucleus is partially hydrogenated, it is difficult for oxygen to enter the hydrogenated region.

The fibers thus infusible are then heated in an inert gas to a temperature of usually 1,000 to 1,500°C, maintained at this temperature for 10 to 30 minutes, and fired. Carbon fiber can be obtained.

The crystal size (Lc) of the carbon fiber produced in this manner changes depending on the firing temperature during the manufacturing process, and the higher the firing temperature, the larger the crystal size (Lc) tends to be. Therefore, a large I-crystalline chair can be obtained by firing at a temperature exceeding 1500°C, but such a firing temperature may be used if the size is 80A or less.

The carbon fibers of the present invention may be used as they are (although they may be further heated to about 3000° C. to graphitize before use).

Next, each index representing the characteristics of fiber and pitch in the present invention will be explained.

(1) X-ray structural parameters orientation angle (OA), crystal size (Lc) and layer spacing (
dooz) is a parameter representing the fine structure of the fiber determined by wide-angle X-ray diffraction. The orientation angle (OA) indicates the degree of orientation of the crystal with respect to the fiber axis direction, and the smaller this angle is, the more advanced the orientation is. The crystal size (Lc) represents the apparent stacking height of carbon microcrystals, and the interlayer spacing (dooz) represents the interlayer spacing of microcrystals.

For X-ray diffraction, a bundle of fibers is attached perpendicular to the X-ray beam, the azimuth angle 2θ is scanned from 0 to 90°, and 1/1 of the maximum value of the intensity distribution in the (002) band (approximately 26°) is used. From the full width (half width) B at position 2 and the azimuth 2θ, Lc is calculated using the following formula.

dooz is calculated.

(Here K = 0.9, b-0,0017ra
d,,λ=1.5418A) dooz−−・−−m− 2s+n θ Also, if the fiber bundle is placed in the vertical plane of the X-ray beam at the azimuth position where the intensity distribution of the (002) band has the maximum value, 1
By rotating it by 80°, the intensity distribution of the (002) band is obtained, and the half-value width at the point of 1/2 of the maximum intensity value is taken as the orientation angle (OA).

(2) Parameters that indicate pitch characteristics a) Number average molecular weight Pyridine is used as a solvent, and a vapor pressure osmometer (VPO) is used.
Measured using. VPOs include Knauner, Dumpdorsk, and Osmometer.
fdruck, Oamo-meter), using pyridine as a solvent and benzyl as a standard substance.

b) Degree of aromatization Calculated using the following formula from the IR measured by the KBr tablet method.

The IR measuring device is manufactured by Shimadzu Corporation. Uses IR-27G type.

C) Proton NMR i1+11 Using a PS-100 spectrometer manufactured by JEOL Ltd., the chemical shift is expressed in r-type with tetramethylsilane (TMS) as the internal standard. For NMR spectra, deuterium chloride was used as the solvent.

d) H/C Calculated according to the following formula from elemental analysis measured according to JISM-ss13.

e) Viscosity Measured using a double cylindrical rotational viscometer manufactured by Oiki Seisakusho.

f) Softening point Using a PerkinElmer HP S C-I D type, put 10 m9 of fine pitch powder crushed to 100 mesh or less into an aluminum cell (inner diameter 5Wlll+), press lightly from above, and heat at a rate of 10°C/ The temperature is measured while increasing the temperature to nearly 400° C. in minutes, and the temperature at the inflection point to the endothermic peak indicating the melting point on the DSC chart is defined as the softening point.

(3) Physical properties of carbon fiber Fiber diameter (single yarn diameter) and tensile strength of carbon fiber.

Elongation and modulus were measured according to JIS R-7601f-Carbon Fiber Test Method. In addition, a laser measurement method was used to measure the fiber diameter.

Hereinafter, the present invention will be explained in further detail by giving experimental examples.

In addition, "Reference example" shows the preparation method of pinch raw material for spinning and the properties of the obtained pitch, and "Comparative example"
This is an example of manufacturing carbon fiber that does not have the structure and physical properties specified in the present invention.

It should be noted that all numbers in the examples represent weight % unless otherwise specified.

Reference Example A pitch raw material for spinning containing brimethoface or brimethoface and memface was prepared.

Five types of coal-based pitch and petroleum-based pitch (
One type of naphtha cool pitch was used. The properties of each pitch were as shown in Table 1.

Approximately 400 g of these pitches were placed in a 24 autoclave, and a mixture of quinoline and quinoline containing 80.3% of tetrahydroquinoline (hereinafter referred to as T) (hereinafter referred to as Q) was added to the autoclave.
00.9, about 209 red mud was added as a catalyst, and heated to a predetermined temperature of 410 to 470°C at an average heating rate of 2.5'C/min while stirring under hydrogen pressure (initial pressure cuff 5kg/crl). Hold for 10-60 minutes. Immediately after the time elapsed, the autoclave was removed from the furnace and cooled to room temperature. The contents were washed out using quinoline and then centrifuged, and the supernatant was filtered under reduced pressure using qualitative filter paper.

The precipitate was removed by adding fresh quinoline, dried and weighed. The amount of quinoline dissolved was determined by subtracting the amount of red mud used as a catalyst from the amount of this precipitate. The filtered supernatant liquid was reduced to 101ml under reduced pressure of 11g/abs, and the content was reduced to 29.
Distill under reduced pressure and THQ until reaching a temperature of 0 °C.

Light oils of quinoline and pitch were removed. The distillation residue is the amount of quinoline soluble content, and the value obtained by subtracting the amount of quinoline soluble content and the amount of quinoline soluble content from the amount of raw pitch is (oil + gas).
Quantity. These are summarized in Table 2.

Pinch raw materials for spinning were prepared using the phosphorus soluble components in Table 1 and Table 2. In other words, put about 100g of the soluble compound into a glass cylindrical container with 3 nozzles attached, and add about 49g of
It was placed on top of a 0°C heated furnace and preheated to about 300°C. A glass tube was inserted into this and high purity nitrogen gas was blown into it. Next, it was placed in a furnace, and after the internal temperature reached 470°C, it was held for a predetermined time of 8 to 22 minutes. In addition, 47
It took about 4 minutes to reach 0°C. moreover,
To prevent the reflux of light oil generated during this process as much as possible,
In addition, to facilitate distillation, the amount of nitrogen gas blown was 1 to 1.
The speed was adjusted within the range of 31/min. Immediately after the time elapsed, the container was removed from the oven and cooled to room temperature. The residue thus obtained was used as pitch for spinning. The yield and properties of this spinning pitch are summarized in Table 3.

In addition, these pinches have a specific gravity of 1 or 2 at 20°C.
It is within the range of 9 to 1.35, and the degree of aromatization is 0.45 to 0.
．． 8, I(/Co) was 5 to 0.65.

In addition, the number average molecular weight of the -quinoline soluble portion is 700 to 17
It was within the range of 00.

3rd year old 1) Yields are values based on the quinoline soluble content in Table 2.

Example 1 The viscosity of the pitch raw material for spinning prepared in Reference Example was measured using a double cylinder viscometer to determine the temperature at which the viscosity of the pitch changes. At this time, the pitch was placed in a container, heated to about 400°C, and the viscosity was measured at a predetermined temperature while gradually lowering the temperature. .

However, in the straight line (2), t shows almost the same value for all pitches, and it can be said that the viscosity behavior depending on temperature is substantially the same for all pitches. Table 4 shows the Ts of the spinning pinch, the viscosity at that temperature, and the Bxlo-3 value.

Table 4 (1) The value of Ts - SP is the difference between Ts and the softening point in Table 3.

Spinning of the spinning pitch was carried out using a brass spinning machine with a nozzle diameter of 0.3 or 0.5 m. A pinch was placed in the spinning machine and heated by an external heater. The molten pitch was A thermocouple was placed inside, and this temperature was set as the melting temperature.When the predetermined temperature was reached, nitrogen gas was applied from above the pitch to extrude the pitch from the nozzle, and the diameter of the fibrous pitch was reduced to about 10 μm using a drum. Naroyo ni 45
It was wound up at a winding speed of 00 to 1000 m/min.

This fibrous pitch was placed in an infusibility furnace and heated to 200°C in air.
The sample was heated at a temperature increase rate of 5° C./min up to 300° C., then heated to 300° C. at a temperature increasing rate of 2° C./min, and held at this temperature for 30 minutes. This infusible fibrous pinch was heated to 1000°C at a temperature increase rate of 25°C/min in a nitrogen stream.
This was held for 5 minutes to form carbon fibers.

Among these carbon fibers, wide-angle
Perform X-ray diffraction to determine orientation angle (OA), crystal size (Lc),
The layer spacing (doo2) was measured.

Further, the obtained carbon fibers were heated to 2800° C. in a Tammann furnace in an argon stream and held for 30 minutes to undergo graphitization treatment. A cross section of this graphitized fiber was observed using a scanning electron microscope to examine the arrangement of carbon layer planes.

FIGS. 3 to 7 are scanning electron micrographs showing typical arrangements of carbon layer surfaces in graphitized fibers. Figure 3 shows a fiber with a radial arrangement but with cracks, Figure 4 shows a radial arrangement but without cracks, Figure 5 shows a fiber in which the surface layer is concentric and the area near the center is radial. Run □Dam arrangement, Figure 7 is completely concentric arrangement □
belongs to. No matter which spinning pitch of experiment numbers 1 to 10 is used, any of the arrangements shown in FIGS. 3 to 7 will be obtained by changing the melting temperature during spinning.

Table 5 shows the melting temperature, viscosity and 10
The physical properties of carbon fibers fired at 00°C and the arrangement of carbon layer planes in cross section are shown. Further, Table 6 summarizes the results of observing the cross section of graphitized fibers obtained from the spinning pitches listed in Table 4.

Table 5 Example 2 Commercially available coal tar pitch 402g and THQ1206
．． 9 is SUS 31 equipped with an electromagnetic induction rotation stirring device.
After the autoclave was charged into an autoclave manufactured by No. 6, the autoclave was sufficiently purged with nitrogen, the internal pressure was set to Okfi'/iG, the temperature was raised to 450° C. while stirring after sealing, and after reaching 450° C., the temperature was maintained for an additional 15 minutes. Then, the mixture was cooled to room temperature and the contents were filtered through a 04 glass filter to remove insoluble materials.

The filtrate was distilled under reduced pressure at a final temperature of 290° C. to 10 mm m 1 j·abs to remove volatile components mainly consisting of unreacted THQ and quinoline produced by the reaction, to obtain quinoline-soluble optically isotropic pitch.

Analyzing this pitch, the average molecular weight of the structural unit is 2.
The specific gravity of the pitch at 20° C. was within the range of 1.25 to 1.31. Also, from the results of nuclear magnetic resonance analysis, etc., this pitch has a condensed ring number of 2 to 2.
It was found that it is a polycyclic aromatic condensation product of No. 6 and is mainly composed of a compound whose nucleus is partially hydrogenated.

Next, change this pitch to 465℃, 10 +Il+xl1g
- Pitch for spinning was prepared by heat treatment with ABS in a nitrogen atmosphere for 15 minutes. The specific gravity of this pitch at 20℃ is 1
．． 330, quinoline solubility is 45.0%.

The toluene insoluble content was 85%, and the number average molecular weight of the quinoline soluble content, pitch H/C, etc. also satisfied the preferred range of the present invention.

Furthermore, when the viscosity change temperature (Ts) of this pitch was measured, it was found to be Ts = 330°C.

The spinning pitch was set using a 1600 mesh filter and L
/ D = 0.1 / 0.1 (mm/mm)
, using an extruded cylinder equipped with a cap with one hole (the cylinder has a structure in which the temperature of the holder part of the melting pinch and the cap part can be controlled independently), -
After heating to 445°C, the temperature was adjusted to 370°C just before the spinneret, and the carbon fiber was spun into room temperature air at a linear discharge speed of 8.4 m/min, and the formed fiber was wound onto a bobbin at a speed of soom/min. A precursor pitch fiber was obtained.

The orientation angle (OA) of this pinch fiber was 37.2°, the crystal size (Lc) was 34.4A, and the interlayer spacing was 3.47X.

The same pitch fibers were placed in an infusibility furnace and heated under no tension in an air atmosphere at a rate of 2°C/min from 200°C to 300°C, and then heat treated at 300°C for 30 minutes. Next, it is placed in a firing furnace and heated to 15°C from 200°C in a nitrogen atmosphere.
The temperature was raised to 00'C at a rate of 15°C/min, and then maintained at 150.0'C for 15 minutes to obtain carbon fibers.

The orientation angle (OA) of the obtained carbon fibers was 3665°.

Crystal size (Lc) is 28.3X, layer spacing (dooz
) was 3.5 OA. In addition, the fiber properties are a single yarn diameter of 10.2 μ, a tensile strength of 2 s 2 kg/m4 + an elongation of 1.40, and a modulus of zot/-, which shows significantly superior performance compared to conventional pitch-based carbon fibers. Ta.

In addition, the fractured surface of the obtained carbon fiber was observed using a scanning electron microscope. FIG. 8 is a microscopic photograph thereof. As is clear from Fig. 8, in the surface layer of this carbon fiber,
The crystals are arranged in the circumferential direction, and the crystals are arranged in a radial manner in the center, forming a skin onion structure. In addition,
The thickness of the surface layer of the fiber was 48.7% of the fiber radius.

Example 3 351 g of commercially available coal tar pinch and THQ1053
．． 9 was placed in the same autoclave as in Example 2, and after being sufficiently purged with nitrogen, the internal pressure was set to Okg/cnIG, and the temperature was raised to 410°C with stirring after sealing.
After reaching 0°C, it was maintained for 60 minutes. Thereafter, the mixture was cooled to room temperature and the contents were filtered using a 04 glass filter to remove insoluble materials. The filtrate was treated in the same manner as in Example 2 to obtain quinoline-soluble optically isotropic pitch.

The pitch was heat treated in a nitrogen atmosphere at 470°C and 1ogl1gabs for 15 minutes to form a spinning pitch.
prepared. The quinoline solution of this spinning pitch is 43.5%, and the viscosity change temperature (Ts) is 331°C.
Met.

This pitch is also similar to Example 1.2, specific gravity, H/C
The number average molecular weight of the quinoline soluble fraction was also within the range of 700 to 1,700.

The spinning pitch was heated to 440°C using the same cylinder as in Example 2, and then heated to 380°C just before the spinneret.
The temperature was rapidly lowered to 100 mL, and the sample was discharged into room temperature air at a discharge linear velocity S of 4 m/min. At this time, various precursor pitch fibers were obtained by changing the winding speed as shown in Table 7.

Each pitch fiber was placed in an infusibility furnace and heated at 2°C/200°C under its own weight in an air atmosphere from 200'C to 300°C.
The temperature was raised at a rate of 1 minute, and then heat treatment was performed at 300° C. for 30 minutes.

Next, the infusible fibers were placed in a firing furnace and heated at a rate of 15°C/min from 200°C to 1000°C under a nitrogen atmosphere, followed by heat treatment at 15°C for 15 minutes to obtain carbon fibers. .

When the X-ray parameters and mechanical properties of the obtained carbon fiber were measured, the results shown in Table 7 were obtained.

85 Comparative Example 1 Commercially available coal tar pitch 134g and THQ402I
was charged into a 5US316 11 autoclave equipped with an electromagnetic stirring device, and after being sufficiently replaced with nitrogen, the internal pressure was reduced to O.
kl? /dG, and after sealing, the temperature was raised to 430° C. while stirring, and after reaching 430° C., the temperature was maintained for an additional 15 minutes. Thereafter, the mixture was cooled to room temperature, and the contents were filtered using a G4 glass filter to remove insoluble matter.

Next, the P solution was heated to a final temperature of 290°C, 1011g abs
Volatile components, mainly consisting of unreacted T H, Q and quinoline produced by the reaction, were distilled off to obtain quinoline-soluble and optically isotropic pitch.

This pitch was heat-treated for 15 minutes in a nitrogen atmosphere at 465°C and 1o IIg·abs to prepare pitch for spinning. This spinning pitch has a quinoline solubility of 40
．． It contained 3%, and the viscosity change temperature (Ts) was 325°C.

This was spun using the same cylinder as in Example 2, with both the temperature of the holder part of the cylinder and the temperature of the spinning rod set at 350°C, and a linear discharge speed of 8.4 m/min and a winding speed of 5 oon/min. At this time, a spinning tube with a length of 60 m was attached directly below the spinneret, the atmosphere temperature inside the tube was maintained at 320° C., and the spun fibers were passed through the tube and then cooled and solidified.

The orientation angle (OA) of the pinched fibers thus obtained was 27°. This pitch fiber was subjected to infusibility and firing treatment under the same conditions as in Example 2 to obtain carbon fiber.

The orientation angle (OA) of the obtained carbon fibers was 24.0°.

Crystal size (Lc) is 70x1 layer spacing (doo2) is 3
．． 45 K, the tensile strength was 39/mrl, the elongation was 0.65, and the modulus was 12.8 tly!.

When the fractured surface of this fiber was observed with a scanning electron microscope, as shown in the micrograph in Figure 9, the crystal alignment was radial, and a large rank reaching the center of the fiber was observed. Admitted.

[Brief explanation of the drawing]

FIGS. 1(5) and 1(B) are schematic diagrams each showing an example of a cross section of the carbon fiber of the present invention. FIG. 2 is a graph showing the relationship between the viscosity and temperature of spinning pitch, and Ts in the figure is the viscosity change temperature of the pitch. Figures 3 to 7 are several examples of scanning electron micrographs of fractured surfaces of graphitized fibers, and Figures 8 to 9 are scanning electron micrographs of fractured surfaces of carbon fibers. FIG. 9 is about the carbon fiber according to the present invention, and FIG. 9 is about the carbon fiber other than the present invention. In FIG. 1, reference numeral 1 indicates the surface layer portion of the carbon fiber, and 2 indicates the center portion. Patent Applicant: Director of the Agency of Industrial Science and Technology Teijin Ltd. Figure 1 (8) Figure 1 (8) Figure 3 Figure 4 Figure 5;

Claims (1)

[Claims] I Orientation angle (OA) determined by X-ray diffraction is 30 to 500
, crystal size (Lc) is 12~80A, layer spacing (do
oz) of 3.4 to 3.6 A and a tensile strength of at least 200 kl? /rrnl. A pitch-based carbon fiber exhibiting a modulus of at least 1 ot/mA. 2. The pitch-based carbon fiber according to claim 1, which has a structure in which crystals are arranged in a circumferential direction in the surface layer of the fiber and arranged in a radial or mosaic pattern in the center in a cross section of the fiber. 3. The pinch carbon fiber according to claim 2, wherein the thickness of the surface portion where the crystals are arranged in the circumferential direction is at least 10 times the radius of the fiber. 4. When producing carbon fiber by melt-spinning the pitch raw material for spinning, infusible treatment of the obtained pinch fibers, and further firing treatment, the molten pitch raw material is once heated to a temperature higher than the viscosity change temperature of the pitch raw material. A method for producing high-strength, high-modulus pitch-based carbon fiber, which comprises raising the temperature to a certain temperature and then spinning the fiber. 5. The manufacturing method according to claim 4, wherein the pitch raw material is heated to a temperature higher than the viscosity change temperature, and then the pitch material is quickly cooled down to the appropriate viscosity temperature and then spun. 6. The manufacturing method according to claim 4 or 5, wherein spinning is performed at a draft rate of 30 or more. 7. The manufacturing method according to claim 4, 5 or 6, wherein the spinning is carried out at a take-up speed of 300 to xsoo@/min. 8. Claims 4, 5, and 6, wherein at least a part of the pinch raw material for spinning is burimesoface pinch.
or 7.