JPS593567B2 - Graphite fiber and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a carbon fiber having a structure with a three-dimensional arrangement specific to polycrystalline graphite, which has a high elastic Young's modulus and a high tensile strength.

More particularly, the present invention may be partially liquid crystal or so-called [
The present invention relates to carbon fibers as described above having high Young's modulus and high tensile strength produced from pitch transformed into the mesophase J state.

The rapid development and growth of the aircraft, space and missile industries in recent years has created a need for materials that possess a unique and extraordinary combination of physical properties.

Materials characterized by high strength and toughness, and at the same time light weight, for use, for example, in the manufacture of aircraft structures, atmospheric reentry vessels and spacecraft, etc., as well as in the manufacture of deep-sea submersibles and similar structures. is needed.

Current technology cannot supply such materials;
Research to meet this need has focused on manufacturing composite articles.

One of the most promising materials suggested for use in composites is high-strength, high-modulus carbon fabric, which was introduced to the market just as the aircraft, space and missile industries were rapidly growing. It was hot.

Such fabrics, when incorporated into plastic and metal matrices, result in composites with very high strength-to-weight and modulus-to-weight ratios and other special properties.

However, the high strength used in such composites,
The cost of manufacturing high modulus carbon fabrics is high, which is a major impediment to widespread use despite the outstanding properties exhibited by this composite.

Most currently available high strength, high modulus carbon fabrics are derived largely from rayon or acrylic fibers and are inherently expensive due to the high cost of their precursors.

Besides the high cost of the starting materials, the low carbon yields obtained from such precursors (on the order of 25-50%) and the complex processing steps required to produce satisfactory carbon fabrics This also increases the cost of the final product.

For example, carbon fabrics made from rayon fibers at low temperatures are weak, porous, and almost completely disordered;
High modulus and strength can only be obtained by stressing the fibers in the longitudinal direction at elevated temperatures where the fibers become somewhat plastic.

On the other hand, high strength and modulus are obtained by subjecting the acrylic fibers to longitudinal stress during a long heat stabilization treatment, generally in an oxygen-containing atmosphere, before carbonization.
Additionally, carbon fabrics derived from acrylic fibers are generally obtained by continuing to apply stress during subsequent heat treatments if desired.

In both cases, it is necessary to apply stress to the fibers to obtain the desired level of modulus and strength.

In the case of rayon, stress is applied at high temperatures to cause the disordered crystallites present in the fiber to align parallel to the fiber axis, thereby increasing the strength and modulus of the fiber.

In the case of acrylic fibers, such as polyacrylonite T-IJ, the precursor is already highly oriented and stress is generally applied during a heat stabilization process prior to carbonization to maintain this orientation, but during the heat treatment the fiber molecules The cross-linking that occurs between the two makes this orientation more permanent.

In either case, the application of stress often results in fiber breakage during processing, requiring separate processing equipment, and
This causes a substantial increase in the cost of the fiber.

Rayon and acrylic fibers are not only expensive and difficult to process into carbon fabrics, but they are also "non-graphitizable" materials that cannot be substantially converted into the three-dimensional crystalline structure characteristic of polycrystalline graphite through heat treatment. .

Carbon produced from most carbonaceous precursors undergoes further heat treatment to some extent converting the carbonization product from a poorly oriented structure to one that almost approximates the three-dimensional crystalline structure characteristic of polycrystalline graphite. However, only certain so-called "graphitizable" or "graphitizable" materials, such as carbon made from petroleum coke, exhibit sufficient graphitic structure and associated graphite-like properties, such as high density and low electrical resistance. be able to.

Rayon and acrylic fibers are among the materials that cannot form large crystals with a high degree of three-dimensional arrangement, as is characteristic of materials that pyrolyze into charcoal without melting.

Despite this, fibers made by pyrolysis of such materials are commonly classified as "carbonized" or "graphitized" based on their elemental carbon content or the temperature to which they are heated. .

For example, Schmidt and Jones have
Fibers made at temperatures between 0°F and 1,700°F are classified as partially carbide or carbide, while fibers processed at temperatures between 2.704 and 2,982°C (4,900 and 5,400°F) Similarly, fibers with an elemental carbon content of up to 90% by weight are classified as "partially carbonized," while fibers with an elemental carbon content of 91 to 98% by weight are "carbonized."
Fibers with an elemental carbon content of more than 98% by weight are classified as "graphite."

(Schmidt, D.L. and Johns, W.C., [Carbon-Based Fiber Reinforced Plastics"Car
bon-Base F 1berReinforce
d P 1astics ”j, AFML, WPAFB
, Deaton, Ohio ASD-TDR-62-635
゜August, 1962).

However, such classification methods do not take into account the actual crystal structure of the fibers.

Therefore, for example, in this classification method, "graphite (1
, 1 fibers, even though they are made from "non-graphitized" precursors and thus essentially lack the three-dimensional crystalline structure characteristic of polycrystalline graphite, are processed at very high temperatures or This means that the carbon content is very large.

Rayon and acrylic fibers from 2,500 to 3.00
High modulus, high strength carbon fibers made by processing at elevated temperatures of 0°C and above exhibit properties similar to pristine graphite, such as high density, high carbon content, and low electrical resistance as temperature increases. However, as mentioned above, this fiber cannot sufficiently exhibit the three-dimensional array structure of polycrystalline graphite.

When the fiber is heated to a temperature high enough to produce a fiber that is essentially all carbon, e.g. about planes gradually develop within the fiber.

Upon further heating above about 1,000° C., these stacks or crystallites continue to grow and increase in size by coalescing with other crystallites or by incorporating surrounding unorganized carbon atoms, and Upon heating to so-called "graphitization" temperatures, the layer planes within the crystallites begin to rearrange themselves with some mutual rotation and displacement.

However, the growth of microcrystals and the rotation of the layer planes within the crystallites are extremely small, and the resulting microcrystals have a small turbostratic structure (t
urbostratic), i.e. the layer planes within the crystallite are all substantially parallel to each other, but these layers (
In other words, a layer in which carbon atoms are densely arranged in parallel in one plane)
are rotationally offset from each other.

When stress is applied in the longitudinal direction of the fibers (at high temperatures for rayon or during heat stabilization for acrylic fibers), some orientation occurs within the fibers by aligning their crystallites parallel to the longitudinal fiber axis. However, even after heating to high temperatures, each crystallite still has a turbostratic structure and substantially lacks the three-dimensional alignment of polycrystalline graphite.

The preferred orientation of the crystallites parallel to the longitudinal fiber axis endows the fiber with high modulus and strength, but if the carbon faces within each crystallite do not align themselves with each other, the fiber will have true graphitic properties, e.g. Prevents it from exhibiting high thermal and electrical conductivity.

Rayon and acrylic fibers from 2.500 to 3.00
The highly preferred orientation of the fiber microcrystals of high-modulus, high-strength carbon fibers produced by treatment at high temperatures of 0°C and higher indicates that the (001) band in the X-ray diffraction images of these fibers clearly indicated by the short circular arcs that make up the .

The turbostratic structure of these microcrystals, that is, the parallel layers within the microcrystals are mismatched with each other, is due to the absence of 112 cross grating lines [i.e., 112 lines, 112 plane reflection lines] in the diffraction image and the wide 10 diffraction band. are two different lines 100 [100
This becomes clear because it is not resolved into 101 [plane reflection lines] and 101 [101 plane reflection lines].

The lack of three-dimensional alignment within the microcrystals is further explained by the relatively large interlayer spacing d in the layer planes (distance between basal planes of carbon microcrystals, distance between 002 diffraction lines in the X-ray diffraction pattern of the fiber). 3) for fibers made from polyacrylonitrile or rayon.
Indicated by exceeding 4OA.

This measurement was calculated from the distance between the corresponding (oog lines of the X-ray diffraction pattern and was related to the proportion of the non-oriented layer of carbon or the non-oriented parameter P by R. E. Franklin, R. E. Franklin, Acta
Cryst t↓t 253.

1951).

(1) Based on the relationship shown by Franklin,
The non-compounding parameter P for fibers made from either polyacrylonitrile or rayon is greater than 0.7.

After undergoing heat treatment at 3,000°C, the layer spacing d.

Carbons with o2 greater than 3.4 OA or non-orientation parameter P greater than 0.7 are "ketographitized" carbons, while after undergoing heat treatment at 3,000 °C, the interlayer spacing d.

o2 is 3.37A or less or non-orientation parameter is 0.
Carbons below 4 are considered to be "well graphitizing" or "graphitizable" carbons (see for example GB 1220482).

((1) The proportion P of non-oriented layers was calculated from line 112 assuming a random distribution of oriented and non-oriented layers.

We then combined this measurement with 3.354A for the oriented or non-oriented separated between the two orientations, 3.399A for the first orientation on either side of the group of orientations, and 3.399A for all other orientations. Layer spacing d assuming that there are only three layer spacings of .440A.

Related to o2. ) In addition to having a layer spacing greater than about 3.4 OA and a non-orientation parameter greater than about 0.7, rayon and acrylic fibers are
The microcrystals of high modulus and high strength carbon fibers produced by processing at temperatures of 000°C and above have the characteristics of "graphitic carbon", that is, the layer size La of 500A or more and the microcrystal thickness. 5tack hei-gh
t) "Non-graphitic" in that it cannot exhibit Lc (microcrystalline thickness, measured by microdensitometer scanning of the width of the 002 diffraction line in the X-ray diffraction image of the fiber).
It is thought that.

That is, the apparent layer size La of the microcrystals of these substances is 20
0A, while the apparent microcrystalline thickness Lc is 100
Do not exceed A.

Due to their small size, these microcrystals cannot be detected using ordinary polarized light microscopy techniques at 1,000 times magnification [the maximum resolving power of a standard polarized light microscope with magnification i, ooo is 1ζ a few tenths of a micron]. Not too much (1 micron - 10,00
OA).

Therefore, microcrystals with dimensions of 1.0 OOA or less cannot be detected with this technique].

Jackson and Marjoram (Jackson, P.W. and Marjoram, R.W.
, Nature, vol. 218, pp. 83-84, April 6
1E], 1968) used polymer fibers up to 1, . 000
"Carbonized" fibers made by controlled pyrolysis down to 1,000 degrees Celsius and "graphitized" fibers made by further processing up to 2,700 degrees Celsius can be recrystallized by coating them with nickel and heating them to over 1,000 degrees Celsius. Although it is possible to produce graphitized fibers with a wide range of three-dimensional arrangements and a crystallite size of 500 A, it has been reported that such recrystallization is accompanied by a rapid decrease in fiber strength.

Of course, weakened fibers are difficult to separate from the nickel coating, are prohibitively expensive to manufacture, and are unsuitable for making high strength-to-weight and modulus-to-weight composites.

In addition to rayon and acrylic fibers, various natural and synthetic pitches have been suggested as precursors for carbon fabrics.

These materials have a high carbon content and can form spinnable melts, making them suitable for the production of carbon fibers or, due to the thermoplastic nature of the pitch, first thermosetting the fibers during carbonization. It is not possible to carbonize fibers drawn from pitch without causing the fibers to retain their filament shape.

Heat curing is generally accomplished by heating the fiber in air or other oxygen-containing atmosphere for an extended period of time until it becomes infusible.

However, such treatment not only renders the fiber infusible, but also hinders the growth and alignment of crystallites during subsequent heat treatment, thereby preventing the development of the graphitic structure of the fiber.

The resulting carbon fibers are therefore composed of small turbostratic crystallites without the high degree of crystallite orientation along the fiber axis that usually accompanies high fiber modulus.

The first publication on the problem of producing carbon fibers from pitch (Okuni, N., "On carbon fibers from molten pyrolysis products", Carbon, 131-38, 1965)
) does not carry commercially available pitches such as coal tar pitch or petroleum pitch, but instead sells special pitches made by pyrolyzing polyvinyl chloride at approximately 400-415°C for 30 minutes or more in a nitrogen atmosphere. We are handling more.

This method involves melt spinning such pitch into fibers, oxidizing the fibers in ozone below 70°C and/or in air up to 260°C to form infusible fibers, and then 500 to 1,35 in a nitrogen atmosphere.
It is proposed to carbonize at 0°C to create oxygen fibers.

The fibers made in this way are composed of vitreous carbon, and have a maximum weight of approximately 18 x 106 g/C (256,
Tensile strengths of 0,000 psi) have been reported.

However, the highest modulus obtainable with such fibers is 5 x 1085'/era (8X 106 psi), apparently due to the lack of crystallite orientation within the fibers.
It was lower.

It is said that almost identical fibers were obtained when the residual cool material produced as a by-product in the production of benzyl chloride by the reaction of chlorychitoluene was used as the starting material.

Recently, the production and properties of carbon fibers spun from petroleum asphalt and coal tar pitch were discussed by Otani (Otani, Nis, Yamada, Qi, Koikubashi, Qi, and Yokoyama, Nie), Raw Materials for rMP Carbon Fibers. About Matter”, Carbon, ↓2425-432
, 1966).

These materials were first dry distilled (by bubbling nitrogen gas through the pitch) at about 380°C for 60 minutes, then vacuum distilled for 60-80 minutes at 380°C or below, followed by 200°C.
The fibers were spun at temperatures between 370°C and 370°C.

In the case of coal tar pitch, to improve high-speed spinnability, an additional 280 min.
It was necessary to heat at °C.

The spun fibers were oxidized in ozone at 60-70°C, then made infusible by heating to 260°C in air, and then carbonized by heating to i,ooooC in a nitrogen atmosphere.

The properties of fibers drawn from petroleum asphalt were similar to those of fibers made from polyvinyl chloride pitch, but fibers made from coal tar pitch were less strong and more difficult to spin.

Fibers made from a mixture of petroleum asphalt and coal tar pitch were more similar to fibers made from petroleum asphalt than fibers made from coal tar pitch.

More recently, Hawthorn et al. have shown that the tensile strength and Young's modulus of carbon fibers made from petroleum asphalt and other pitches by the same method used by Okuni et al. have been determined by stretching the fibers at temperatures between 2,000 and 2,8000 C. By 250X103psi and one 7X106p
si to 375X10”psi and 70X106 respectively
psi (Hawthorne, H.M., Baker, C., Bentall, R.H., and Ringer, C.R., [high strength, high modulus graphite fibers from pitch] , Nat
uret227.946-947.August 29, 197
0).

The structure of the fibers produced in this way was said to be similar to that previously observed in rayon and polyacrylonyl "graphite" fibers.

However, for fibers derived from these initial precursors, applying longitudinal stress to the fibers results in a high degree of orientation of the fiber crystallites parallel to the longitudinal axis, but each crystallite remains in a turbostratic structure. It substantially lacks the three-dimensional arrangement characteristic of polycrystalline graphite.

In a recent report, Hawthorne more fully discusses the structure of fibers made by hot drawing of vitreous carbon fibers derived from pitch and similar precursors (Hawthorne, H.M.; “Structure and properties of tensile graphitized vitreous carbon fiber”, “Carbon fiber,
``International Conference on Composites and Applications'', Plastics Institute, Paper/I6.13.13/
113/13, London, 1971).

The X-ray diffraction characteristic of these fibers is based on polyacrylonitrile and rayon in that there are no reflections other than the (OO1) line and hk band, which is consistent with the turbostratic nature of these fibers. It is generally said that the fibers are similar to

The fiber crystallites have large d-spacing (≧3.4OA) and small apparent crystallite size (La
≦136 A t L c ≦145 A).

Fibrils with granular areas of widths up to 30 OA and diameters of 800-90 OA have been noted.

Otani et al. further show that carbon fibers with a highly preferred orientation of the carbon crystals parallel to the fiber axis can be obtained by applying stress at high temperatures to fibers drawn from pitch materials as in Hawthorne et al. reported that it can also be obtained from pitch with highly oriented molecules made from tetrabenzophenazine without the application of stress (Okuni, Nis, Kokubo, Y).
, Koitabashi, Chi., "Production of highly oriented carbon fibers from pitch materials", Bulletin of the Chemical Society of Japan, 43°3291-3.
292. October, 1970).

However, a method for manufacturing such fibers is not disclosed.

Fibers made from such pitches have been reported to be highly oriented, but such fibers may have a graphitic structure or the application of stress at high temperatures may cause the pre-pitch
It is not pointed out how this differs from highly oriented carbon fibers previously made from precursor materials.

Therefore, pitch materials change from an isotropic structure to highly oriented molecular domains (domain
) 'A technical term used in physics that refers to a three-dimensional region in which the molecules within that region are more strongly and highly aligned with each other in the same direction than the surrounding molecules. It is well known that Kokichi can be converted into a structure containing [indicating a three-dimensional region] (Brooks, G.D.
, and Tiller, G. H., "Formation of Certain Graphitized Carbons," Chemistry and Physics of Carbon, Volume 4, Marcel Detzker, Inc., New York, 1968, pp. 243-268; White, G.R., Guthrie, G.L., and Gardner, G.O., "Mesophase Microstructure of Carbonized Coal Tar Pitch," Carbon,
5,517°1968; and Chebois, J.
Agache, C. and White, G.L.
"Carbonaceous mesophase formed by pyrolysis of graphitizable organic materials", Metallography, 3, 337-369, 19
70), no method has been reported for converting such materials into carbon fibers having the three-dimensional crystal structure characteristic of polycrystalline graphite.

Carbon fibers with such a structure are still unknown, and to date, carbon fibers derived from pre-pitch precursors have not been produced either by high-temperature drawing or directly from highly oriented pitch precursors without applying stress. All high modulus, high strength carbon fibers differ little in structure from high modulus, high strength carbon fibers made from rayon or acrylic precursors.

All such fibers, regardless of their precursor, are characterized by the presence of carbon microcrystals arranged primarily parallel to the fiber axis, but all fibers exhibit the three-dimensional structure characteristic of polycrystalline graphite. It doesn't have an array.

According to the invention, carbon fibers (as-spun pitch fibers) with a highly preferred orientation of the molecules parallel to the fiber axis are produced in a suitable manner, partially converted into a liquid crystal or so-called "mesophase" state. Carbon fibers that can be spun from carbonaceous pitch, for example by melt-spinning techniques, and which have a high elastic Young's modulus and high tensile strength by further heat-treating such fibers (heating removes hydrogen and other volatiles) It has been found that it can be converted into fibers after being removed and carbonized.

The carbon fibers produced in this way not only have a highly oriented structure, characterized mainly by the presence of carbon microcrystals arranged parallel to the fiber axis, but also produce polycrystalline graphite when heated to graphitization temperatures. exhibits a characteristic three-dimensional arrangement and associated graphite-like properties such as high density and low electrical resistance.

At all stages of development from the drawn state to the graphitized state, the fiber is characterized by large elongated oriented graphitizable domains arranged primarily parallel to the fiber axis.

As is well known, natural pitch is a complex mixture of organic compounds made essentially from molten cyclic aromatic hydrocarbons, with the exception of some rare paraffinic pitches derived from some oils, such as Pennsylvanian crude oil, and thus It is said to be based on aromatics.

Since the molecules constituting these organic compounds are relatively small (average molecular weight of several hundred or less) and have weak interactions, such pitches are isotropic in nature.

When these pitches are heated under static conditions (without agitation) at about 350-450°C, either at a constant temperature or gradually increasing the temperature, small insoluble liquid particles begin to appear in the pitch; If you continue to do so, the dimensions will gradually increase.

Examination by electron diffraction and polarized light microscopy shows that these spheres consist of layers of oriented molecules oriented in the same direction.

As these spheres continue to grow in size as they continue to heat up, the spheres touch each other and gradually coalesce together into a large mass of aligned layers.

As coalescence continues, domains of molecules that are much more dog-shaped than the initial spheres are formed.

These domains come together to form a bulk mesophase, in which the transition from one orientational domain to another occurs smoothly and continuously, sometimes through gradually curved thin layers. and sometimes through more sharply curved laminae.

Differences in orientation between domains form complex arrays in this torque mesophase with extinction contours in polarization corresponding to linear discontinuities of molecular alignment with different alignments.

The ultimate size of the resulting oriented domains depends on the viscosity of the mesophase forming the domain and the rate of increase in viscosity, which in turn depends on the particular pitch and heating rate.

At some pitches, domains from 200 to several hundred microns in size are formed.

For other pitches, the viscosity of the menphase is such that only limited layer coalescence and structural rearrangement occurs such that the final domain size does not exceed 100 microns.

The highly oriented, optically anisotropic, insoluble material produced by treating pitch in this way is called "menphase", and the pitch containing this material is known as "menphase pitch". There is.

Such pitch, when heated above its softening point, becomes a mixture of two immiscible liquids, one optically anisotropically oriented mesophase portion and one isotropic non-mesophase portion.

The word "menphase" comes from the Greek word "mens"
It is derived from the word "intermediate" and refers to the solidified nature of this highly oriented, optically anisotropic material.

Carbonaceous pitch having a menphase content of about 40 to about 90% by weight is suitable for the production of highly oriented carbonaceous fibers capable of developing the three-dimensional alignment characteristic of polycrystalline graphite according to the present invention. be.

However, in order to obtain the desired fibers from such pitches, the mesophase contained in the pitches must form large coalescing domains (coales = ced do
(main), that is, a homogeneous bulk mesophase having aligned molecular domains with a particle size of 200 to several hundred microns must be formed.

Pitches that have small oriented domains rather than large coalescent domains and form fibrous bulk mesophases under static conditions are unsuitable.

Such pitches form highly viscous menphases that undergo only limited coalescence, insufficient to form large coalesced domains of size greater than 200 microns.

Instead, the mesophase of small oriented domains aggregates to form clumps or fibrous masses with a final domain size of no more than 100 microns.

Certain pitches are of this type that polymerize very rapidly.

Similarly, pitches that do not form a homogeneous bulk mesophase are unsuitable.

The latter phenomenon is caused by the presence of infusible solids (present in the original pitch or formed during heating) and between them that are surrounded by the coalescing mesophase and serve to prevent the homogeneity and uniformity of the coalescing domains. is caused by the existence of boundaries.

As mentioned above, the present invention has been explained in relation to menphase, bulk mesophase, domain, etc., but the relationship among them will be further summarized and explained.

When pitch is heated to a temperature of, for example, about 400° C., small spheres of menphase appear, which gradually increase in size over time.

These spheres are in a liquid state at their formation temperature and consist of layered stacks of aromatic molecules.

Each method constitutes an oriented liquid at its formation temperature; the term for the oriented liquid is generally "liquid crystal" and for pitch, "mesophase."

As the concentration of menphase spheres increases, spheres collide with each other, coalesce into larger spheres, and finally produce large areas of coalesced menphase spheres.

The large region of the coalescent mesophase is the "bulk mesophase."

If the bulk mesophase is homogeneous, ie, contains no solid or liquid foreign phases, the bulk mesophase is called a "homogeneous bulk mesophase."

A "domain" is a relatively small region within the bulk mesophase that is separated by all molecules having approximately the same orientation within the bulk mesophase.

The size or size of a domain is technically defined as the straight-line distance between the extinction contours of the object's image under crossed Nicols□.

This distance is essentially measured between the molecular orientation '8H45° rotated contours for the molecules in the domain.

A bulk mesophase containing molecules oriented in the same direction throughout constitutes a single domain.

Therefore, one homogeneous bulk mesophase may also be one domain.

Bulk mesophase usually contains two or more domains.

To summarize more simply, mesophase globules coalesce into a bulk mesophase, and a domain is a region within the bulk mesophase that contains molecules oriented in the same direction.

Therefore, if all the molecules that make up the bulk mesophase are oriented in the same direction, the bulk mesophase is one domain, and among all the molecules that make up the bulk mesophase, a group of molecules in a certain region are oriented in the same direction, and ■) a group of molecules in another region are oriented in the same direction, but if the direction is different from the direction of the group of molecules in the region (5), then two domains becomes.

Therefore, if multiple such states exist among all molecules constituting the bulk mesophase, multiple domains will exist.

Usually, bulk mesophase contains two or more domains.

The size of a domain is technically defined as the straight-line distance of the extinction contour of the object's image under crossed Nicols.

Another requirement is that the pitch be non-thixotropic under the conditions used for spinning into fibers, i.e. the pitch must exhibit Newtonian or plastic flow behavior such that the flow is uniform and well behaved. be.

When such pitch is heated to a temperature at which the viscosity thereof ranges from about 10 poise to about 200 poise, homogeneous fibers can be easily spun.

On the other hand, pitches that do not exhibit Newtonian or plastic flow behavior at the spinning temperature cannot be spun into homogeneous fibers that can be converted by subsequent heat treatment into fibers that can develop the three-dimensional arrangement characteristic of polycrystalline graphite. .

Carbonaceous pitch having a menphase content of about 40 to about 90% by weight can be obtained by heating carbonaceous pitch in an inert atmosphere at a temperature of about 350° C. or higher for a time sufficient to produce the desired amount of menphase using known techniques. It can be manufactured by

By inert atmosphere is meant an atmosphere that does not react with the pitch under the heating conditions used, such as nitrogen, argon, xenon, helium, and the like.

The heating time required to produce the desired mesophase content will vary depending on the particular pitch and temperature used, with longer heating times required at lower humidity than at higher temperatures.

The minimum humidity generally required for mesophase formation is 3.
At 50°C, at least one week of heating is usually required to produce a menphase content of about 40%.

At humidity levels of about 400-450°C, conversion to mesophase is rapid and can typically produce 50% mesophase content within about 1-40 hours at such temperatures.

Therefore, such a temperature is preferable.

Temperatures above about 500°C are undesirable, and heating at this temperature should not be used for more than about 5 minutes to avoid conversion of pitch to coke.

The extent to which pitch is converted to mesophase can be easily determined by polarized light microscopy and solubility testing.

With the exception of certain non-mesophase infusibles present in the initial pitch or, in some cases, formed upon heating, the non-mesophase portion of the pitch is readily soluble in organic solvents such as quinoline and pyridine, while the mesophase The percentage of quinoline solubles (Q·■·) in a given pitch is determined by quinoline extraction at 75°C.

The percentage of pyridine insolubles (P·■·) is determined by Soxhlet extraction in boiling pyridine (115° C.)].

In the case of pitches that do not produce non-mesophase insolubles upon heating, the amount of infusible material in the heat-treated pitch that is greater than or equal to the amount of insoluble anastomoses in the pitch before heat treatment substantially corresponds to the mesophase content [ The insoluble anastomotic content of untreated pitch is generally less than 1% (with the exception of some coal tar pitches) and consists mostly of coke and carbon black found in thick pitches].

In the case of pitches that generate non-mesophase insolubles upon heating, the insoluble anastomotic content of the heat-treated pitch, which is greater than or equal to the insoluble anastomotic content of the pitch before heat treatment, is solely based on the conversion of the pitch to mesophase. It also refers to non-mesophase insoluble substances that are generated together with mesophase during heat treatment.

Pitches containing a sufficient amount of insoluble non-mesophase insolubles (either present in the raw pitch or generated by heating) to inhibit the development of a homogeneous bulky menphase can be used in the present invention as described above. unsuitable for use.

Generally, pitches containing more than about 2% by weight of such insoluble materials are unsuitable.

The presence or absence of insoluble non-mesophase insolubles, as well as the presence or absence of such homogeneous bulk mesophase regions, can actually be observed by polarized light microscopy of pitch [e.g. References Brooks, G.D. and Tiller, G.H., (ibid.) and Du Bois, G.I., Agachessey, and White, G.L., (ibid.)].

The amounts of each of these substances can also be actually measured using this method.

Carbon content of about 92 to about 96% by weight and hydrogen content of about 4
Aromatic carbonaceous pitch ranging from about 8% by weight is generally suitable for making menphasic pitch that can be used to make the fibers of the present invention.

Elements other than carbon and hydrogen, such as oxygen, sulfur and nitrogen, are undesirable and therefore should not be present in excess of about 4% by weight.

Higher amounts of foreign elements inhibit the formation of carbon crystals during subsequent heat treatment and prevent the development of graphitic structures within fibers made from these materials.

Furthermore, the presence of foreign elements reduces the carbon content of the pitch and thus reduces the ultimate strength of the carbon fiber.

When such foreign elements are present in amounts of about 0.5 to about 4% by weight, the pitch generally has a carbon content of about 92-95% by weight, with the balance being hydrogen.

Petroleum pitch, which is a pitch that is highly graphitized, is the preferred starting material for making the menphase pitch used to make the fibers of the present invention.

Petroleum pitch, of course, is a residual carbonaceous material obtained from the distillation of crude oil or the catalytic cracking of petroleum distillates.

Certain pitches, such as fluoranthene pitch, polymerize very rapidly when heated and are therefore not suitable precursors because they are unable to develop large coalescing domains of mesophase.

Pitches with a high content of insoluble non-mesophases which are likewise insoluble in organic solvents such as quinoline or pyridine,
Pitch, which is insoluble and has a high non-mesophase content when heated, is the homogeneous material needed to produce highly oriented carbonaceous fibers that can develop the three-dimensional alignment characteristic of polycrystalline graphite. As mentioned above, it should not be used as a starting material since it cannot produce bulky mesophases.

For this reason, pitches that are quinoline-soluble or pyridine-insoluble and contain more than about 2% by weight (measured as described above) of infusible materials are either not used or are filtered before being heated to form menphase. This material should be removed by

Such pitches are preferably filtered if they contain more than about 1% by weight of the above-mentioned infusible, insoluble materials.

Most petroleum pitches have a low content of infusible and insoluble materials and can be used directly without such filtration.

To generate mesophase, set the pitch to 350~
Heating at 500° C. will of course cause some thermal decomposition of the pitch, and the pitch composition will vary depending on the heating time, composition and structure of the starting materials.

However, generally the carbonaceous pitch is about 40 to about 90
Upon heating for a sufficient period of time to achieve a weight percent menphase content, the resulting pitch has a carbon content of about 94-96 weight percent and a hydrogen content of about 4-6 weight percent.

Such a pitch contains elements other than carbon and hydrogen at about 0.
When containing 5 to about 4% by weight, mesophase pitch generally has a carbon content of about 92-95% by weight, with the balance being hydrogen.

After the desired menphase pitch is created, it is spun into fibers using conventional techniques such as melt spinning, centrifugal spinning, blow spinning, or other known methods.

As mentioned above, in order to obtain highly oriented carbonaceous fibers that can develop the three-dimensional alignment characteristic of polycrystalline graphite, the pitch must form a homogeneous bulk mesophase with large coalescent domains under static conditions. and be non-thixotropic under the conditions used during spinning.

Furthermore, to obtain homogeneous fibers from such pitch,
The pitch must be agitated just before spinning to effectively mix the immiscible mesophase and non-mesophase portions of the pitch.

The temperature at which the pitch is spun will of course depend on the temperature at which the pitch exhibits a suitable viscosity.

Since the softening point of pitch and its viscosity at a given temperature increases as the menphase content of the pitch increases, the menphase content should not increase to the point of raising the softening point of the pitch to excessive levels. There must be.

For this reason, pitches with more than about 90% menphase content are generally not used.

However, the menphase content ranges from about 40 to about 90
Pinch by weight generally exhibits a viscosity of about 10 to about 200 poise at temperatures of about 250 to about 450°C and can be readily spun at such temperatures.

At such viscosities, the fibers can be blown from such pitches from about 10 to about 100 feet/minute, up to 3,000 feet/minute.
It is convenient to spin at a speed of 1 minute.

Preferably, the pitch used has a menphase content of from about 45 to about 65% by weight, most preferably from about 55 to about 65%, and at a humidity of about 340 to about 380°C.
It exhibits a viscosity of 0 to about 60 poise.

At such a viscosity and humidity, homogeneous fibers of about 10 to about 20 microns in diameter can be easily spun.

However, as mentioned above, in order to obtain the desired fibers, it is important that the pitch be non-chitisotropic and exhibit Newtonian flow trJJ or plastic flow during fiber spinning.

The carbonaceous fiber thus produced is a highly oriented graphitizable material in which the molecules are highly preferably oriented parallel to the fiber axis.

"Graphitizable" means that the fibers can be thermally converted into a structure having the three-dimensional arrangement characteristic of polycrystalline graphite (usually at temperatures above about 2,500°C, e.g. from about 2,500°C to about 3°C).
(by heating to a temperature of 000°C).

The fibers produced in this way, of course, have the same chemical composition as the drawn pitch and, like this pitch, about 40%
% to about 90% by weight mesophase.

When examined under magnification with polarized light microscopy techniques, the fibers exhibit textural changes that give them the appearance of "small complexes."

The term "small complex" here refers to a tissue modification that gives the fiber the appearance of a small complex when the fiber is examined under polarized light.

It can be observed that large elongated chemically anisotropic domains with a fine fiber-like appearance are distributed in the fiber.

These optically anisotropic domains are highly oriented;
and are mainly arranged parallel to the fiber axis.

It is believed that these optically anisotropic domains, which are elongated by the shear forces exerted on the pitch during fiber spinning, are not entirely composed of mesophase, but are also composed of non-mesophase.

Apparently the non-mesophase is simultaneously stretched and oriented into the elongated domains due to the shear forces during spinning and the orientation effects exerted by the menphasic domains as they are elongated.

Optically isotropic regions cannot be seen with the naked eye and may exist, although they are difficult to distinguish from optically anisotropic regions that happen to exhibit extinction.

Characteristically, the oriented elongated domain has a diameter of 5,000 mm.
The number of individuals exceeds 0, and generally ranges from about 10,000 to about 40,000, and because of their large size, they can be easily observed using normal polarized light microscopy techniques at 1.000x magnification.

(The maximum resolving power of a standard polarizing microscope with magnification i, ooo is only a few tenths of 1 micron [1 micron = 10,00
0 persons], optically anisotropic domains with dimensions i, ooo persons or less cannot be detected with this technique.

). On the other hand, fibers drawn from non-mesoface pitch do not contain any observable oriented optically anisotropic domains when examined in this manner.

Carbon fibers made from rayon and acrylic precursors similarly do not show the presence of oriented optically anisotropic domains when examined in this manner.

X-ray diffraction images of carbonaceous fibers made from mesophase pitch according to the present invention show that the fibers are characterized by a highly preferred orientation of pitch molecules parallel to the fiber axis.

This is clear from the short circular arcs that constitute the 002 band of the diffraction image.

When scanning the 002 band of exposed X-ray film with a microdensitometer, this preferred orientation is generally about 20° to about 35°, usually about 25° to about 30° (expressed as the full width at half maximum (FWHM) of the azimuthal intensity distribution). It is.

Similarly, the apparent crystallite thickness Lc of the pitch molecule alignment domain measured by microdensitometer scanning of the width of the 002 diffraction arc is generally about 25 to about 60, usually about 30 to about 50. .

The layer spacing of the array domain d calculated from the distance between the 002 diffraction arcs is generally about 3.40 to 3.55 people, usually about 3.55 people.
45 to about 3.55 people.

Typically such fibers are characterized by a density of about 1.25 to about 1.40 g/cc, most commonly about 1.30 to about 1.35 g/cc.

Since most of the carbonaceous fibers produced in accordance with the present invention are thermoplastic, it is usually necessary to thermoset these fibers prior to carbonization.

, fibers spun from pitches containing more than about 85% by weight menphase often retain their shape when carbonized without pre-thermal curing, but fibers spun from pitches containing less than about 85% menphase by weight often retain their shape when carbonized without preheat curing. The fibers require some heat curing before carbonization.

Heat curing of the fibers is readily accomplished by heating the fibers in an oxygen-containing atmosphere for a sufficient period of time to render them infusible.

The oxygen-containing atmosphere used may be pure oxygen or an oxygen-enriched atmosphere.

Most conveniently air is used as the oxidizing atmosphere.

The time required to heat-set the fiber will, of course, vary depending on factors such as the particular oxidizing atmosphere, the temperature used, the diameter of the fiber, the particular pitch from which the fiber was made, and the mesophase content of the pitch.

Generally, however, heat curing of the fibers can be accomplished in a relatively short period of time, typically from about 5 to about 60 minutes.

The temperature used to heat set the fibers must of course not exceed the softening point of the fibers.

The maximum humidity that can be used therefore depends on the particular pitch on which the fiber is spun and the mesophase content of that pitch.

The higher the mesophase content of the fiber, the higher its softening temperature and the higher the humidity that can be used to effect thermal curing.

Of course, fibers of a given diameter can be heat cured at higher temperatures in a shorter time than is possible at lower humidity.

On the other hand, fibers with lower memphase content require longer heat treatments at somewhat lower humidity to render them infusible.

A minimum temperature of at least 250° C. is generally required to effectively heat cure the carbonaceous fibers made according to the present invention.

Temperatures above 400° C. should be avoided as they may cause melting and/or excessive burnout of the fibers.

Preferably, a temperature of about 300 to about 390°C is used.

At such temperatures, heat curing can generally take place in about 5 to about 60 minutes.

Generally, the fibers are not heated for more than about 60 minutes or at temperatures above 400° C., since it is undesirable to oxidize the fibers more than necessary to render them completely infusible.

After thermosetting the fibers, the infusible fibers are carbonized by heating in an inert atmosphere as described above to a temperature high enough to remove hydrogen and other volatiles and to form substantially all of the carbon. Make it into fiber.

Fibers with a carbon content of about 98% by weight or more generally have a carbon content of about 100% by weight or more.
It can be produced by heating to temperatures above 0°C, and the fibers are fully carbonized at temperatures above about 1500°C.

The preferred degree of orientation of the fibrils deteriorates somewhat when the fibers are heated to about 1000°C, but with further heating the preferred degree of orientation improves and at about 1300°C it becomes substantially the same as the fibrils.

Typically, carbonization is carried out at a humidity of about 1000 to about 2000°C, preferably about 1500 to 1700°C.

Generally, residence times of about 0.5 to about 25 minutes are used, preferably about 1 minute to about 5 minutes.

Although longer heating times can be used with good results, such long residence times are uneconomical and as a practical matter there is no advantage to using such long times.

In order to avoid excessive fiber weight loss rates and destruction of the fiber structure, it is preferred to heat the fibers briefly at about 700 to about 900° C. before heating them to the final carbonization temperature.

A residence time of about 30 seconds to about 5 minutes is usually sufficient at these humidities.

Preferably, the fibers are heated to about 700°C for about 30 seconds and then to about 900°C for the same period of time.

In any case, the heating rate must be controlled so that volatilization does not proceed at an excessive rate.

A preferred method of heat treatment involves passing the continuous filament through a series of heated zones maintained at successively higher humidity levels.

If desired, the first of these zones may contain an oxidizing atmosphere to effect thermal curing of the fibers.

Several devices can be used in an array to provide a series of heating zones.

For example, one oven may be used to pass the fiber through the oven several times, increasing the humidity each time.

Alternatively, the fibers may be passed through several ovens only once, with each successive oven being held at a higher temperature than the previous oven.

It is also possible to use a single furnace with several heating zones maintained at successively higher temperatures in the direction of fiber movement.

The carbon fibers produced in this way have a highly oriented structure characterized by the presence of carbon microcrystals arranged mainly parallel to the fiber axis, and when heated to the graphitization temperature, ,
It is a graphitizable material that exhibits the characteristic three-dimensional arrangement of polycrystalline graphite and associated graphitic properties such as high density and low electrical resistance.

When examined under magnification by polarized light microscopy techniques, the oxidized fibers before carbonization exhibit a similar texture appearance to the drawn precursor.

The large oriented elongated graphitizable domains present in drawn fibers are also present in carbonized fibers, and as in drawn fibers, these domains are primarily oriented parallel to the fiber axis.

Fibers carbonized without pre-oxidation, on the other hand, no longer resemble the microstructural appearance of drawn fibers, but rather are characterized by much larger dimensions of their domains.

During the carbonization process, the menphasic domains present in the drawn unoxidized fibers coalesce with each other and with the non-mesophase pitch present to form very large dals that are mainly aligned parallel to the fiber axis, as in the case of drawn fibers. Gives rise to oriented domains.

However, in fibers that are oxidized before carbonization, the development of very large domains, such as is present in fibers that are carbonized without oxidation, is prevented by the oxidation that occurs when the fibers are heated in the presence of oxygen.

As a result, the orientation domains of fibers carbonized without pre-oxidation are much thicker than those of fibers carbonized after oxidation.

The actual width is about 10,000 to about 100,000 λ versus about 5,000 to about 40,000 people).

The short circular arcs constituting the 002 band of the X-ray diffraction image of carbon fibers made according to the present invention indicate that the fibers are characterized by a preferable and highly oriented carbon crystallites parallel to the fiber axis.

Microdensitometer scanning of the 002 band of exposed X-ray film shows that the preferred orientation parameter (FWHM) for fibers heated to about 1000° C. is less than about 45°, usually from about 30 to about 40°. has been done.

Fibers heated to about 2000°C have a high degree of preferred orientation, i.e. about 10° to about 20°; usually about 13° to 17°.
It has a preferred orientation parameter (FWHM) of .

The preferred degree of orientation is further improved by heating the fibers to higher temperatures.

Thus, when the drawn fibers are heated to 1000°C, the preferred degree of orientation deteriorates to some extent, but when further heated to about 2000°C, a much higher degree of preferred orientation is obtained.

The preferred degree of orientation of the fibers heated to about 1300 DEG C. as described above is substantially the same as that of the drawn precursor, such as about 20 DEG to about 35 DEG, usually about 25 DEG to about 30 DEG.

When the width of the 002 diffraction arc of the X-ray diffraction image of the fiber heated to about 1000°C is scanned with a microdensitometer,
It has been shown that the apparent crystallite thickness Lc of the carbon crystallites of the fibers is generally about 15 to about 25, usually about 18 to about 22.

For fibers heated to about 2000°C, the apparent microcrystalline thickness Le generally exceeds about 75 mm, usually from about 80 to about 100 mm.
It's a person.

Furthermore, by heating at a higher temperature, the apparent thickness of the microcrystals can be easily improved to a significantly higher value.

The interlayer spacing of carbon microcrystals in the fiber heated to approximately 1500°C is
002 Calculated from the distance between the diffraction arcs, generally about 3.40
3.43 people.

These fibers have a tensile strength of approximately 100 x 103 psi or more,
For example, about 100XIQ3 to about 200X10”psi
, and an elastic Young's modulus of about 20×10 6 psi or greater, such as about 20×10 6 to about 40×10 6 psi.

Usually, the tensile strength of the fiber is about 140 x 103 to about 160
X103 psi, and Young's modulus is about 25X10' to about 35X106 psi.

Fibers heated to about 1500°C have a very high density, 2
．． 1 g/cc or more, usually about 2.1 to about 2.2 g/cc
Indicates the density of cc.

The electrical resistance of such fibers is generally about 800X10-6
to about 1200×10 −6 ohm CIrL.

The carbonized fibers are heated at about 2500 to about 3300°C, preferably about 2800 to about 3000°C, in an inert atmosphere as described above.
Further heating to even higher temperatures can produce fibers having not only a highly preferred orientation of the carbon crystallites parallel to the fiber axis, but also a structure characteristic of polycrystalline graphite.

A residence time of about 1 minute is sufficient, although shorter or longer times can be used, such as from about 10 seconds to about 5 minutes or more.

Residence times longer than 5 minutes are uneconomical and unnecessary, but can be used if desired.

Fibers made by heating at temperatures above about 2500°C, preferably above about 2800°C, are characterized by a three-dimensional arrangement of polycrystalline graphite.

This three-dimensional arrangement is clearly confirmed in the X-ray diffraction image of the fiber, in particular by the presence of the 112 cross-lattice lines and the resolution of the 10 bands into two different lines 100 and 101.

The short arcs constituting the 001 band of the diffraction image mainly indicate carbon microcrystals of the fibers arranged parallel to the fiber axis.

Microdensitometer scanning of the 002 band of exposed X-ray film shows that this preferred orientation is less than about 10°, usually from about 5 to about 10° (expressed as the half-width of the azimuthal intensity distribution). ing.

The apparent layer size La of the crystallites and the apparent crystallite thickness Lo are greater than 1000 and are therefore too large to be measured by X-ray techniques.

The interlayer spacing d of the microcrystals is calculated from the distance between the corresponding 001 diffraction arcs and is 3.37 Å or less, usually 3.36 to 3.37.
It's a person.

The non-orientation parameter p, which corresponds to a layer spacing of 3.37 people, is approximately 0.4 as determined by the R.E.Franklin relationship discussed above, while p, which corresponds to a layer spacing of 3.36 people.
is approximately 0.25.

When the fibers are examined under magnification using polarized light microscopy techniques, they exhibit the same appearance as the precursor fibers and, like the precursor, large oriented elongated optically anisotropic domains ( It is now characterized by the presence of graphitic (rather than graphitizable) properties.

These domains are created from oriented planes of carbon.

The width or diameter of these domains, measured transverse to the fiber axis, typically ranges from 5,000 to about 40,000, unless the fibers are made from carbonized and graphitized fibers without prior oxidation. people, in which case the width of the domain is typically 10,000 to about 100,000 people.

These domains are highly anisotropic and therefore visible at 1000x magnification in a polarized light microscope.

In addition to having a structure characteristic of polycrystalline graphite structures, the fibers are characterized by graphite-like properties associated with their structure, such as high density and low electrical resistance.

Typically these fibers contain 2.1 to 2.2 g/c
It has a density of c and higher.

The electrical resistance of the fiber is 250 x 10 = ohmcfrL
smaller, usually about 150X10-6 to about 200X1
It was found to be 0-6ohmCrrL.

The fibers are also characterized by high modulus and high tensile strength.

That is, these fibers were found to be characterized by a tensile strength of greater than about 200XIO" psi and an elastic Young's modulus of greater than about 50X10' psi.

Typically, such fibers are greater than about 250 x 103 psi, such as about 250 x 103 to 350 x 103 psi.
si tensile strength and greater than about 75 x 106 psi, such as from about 75 x 106 to about 120 x 106
It has a Young's modulus of psi.

Accordingly, the present invention provides a convenient method for producing high strength, high modulus fibers in high yields from inexpensive and readily available high carbon precursors.

The fibers can be used in the same applications for which high strength, high modulus fibers are traditionally used, such as in the manufacture of composites.

The fibers are particularly useful in applications where electrical and thermal conductivity along the fiber axis is important, and can be used, for example, to make textile graphite heating elements.

Because of their extremely low electrical resistance, these fibers can be used as filler materials in graphite electrode production.

The unique structure of the fiber of the present invention can be easily seen from the accompanying X-ray diffraction image and polarized light micrograph.

X-ray diffraction images were obtained on a sample bundle of approximately 10 single fibers mounted perpendicular to the X-ray beam.

Alpha radiation was used on copper with a nickel filter.

Flat plate or cylindrical film transmission images were taken depending on the fiber heating temperature.

Exposure times of 5 to 16 hours were used.

Photomicrographs were obtained on fibers coated with epoxy resin so that either transverse or longitudinal sections could be examined.

The samples were first milled on a silicon carbide V-tub <1 ap), then successively polished on a diamond paste wrap, and finally polished with a fine cloth saturated with a 0.3% suspension of alumina in water.

The samples were examined with a Ba-usch and Lomb metallurgical microscope under polarized light using a crossed polarizer.

FIG. 1 is an X-ray diffraction image of pitch fiber obtained by heating commercially available petroleum pitch at 400° C. for 10 hours to bring the mesophase content to approximately 50%, and then spinning the resulting product at 350° C.

Despite the fact that the X-rays are of the fiber in the stretched state, there is a highly preferred orientation of the pitch molecules parallel to the fiber axis, as evidenced by the short circular arcs that make up the 002 band of the diffraction image.

The preferred degree of orientation (FWHM) and apparent crystallite thickness Lc were 29° and 47°, respectively.

This preferred orientation is measured by microdensitometer scanning of the 002 band of the exposed X-ray film (expressed as the half-width of the azimuthal intensity distribution (FWHM)), and is determined by the apparent microcrystalline orientation in the pitch molecule alignment region. The thickness Lc was simultaneously measured by scanning the width of the 002 diffraction arc with a microdensitometer.

Figure 2 is an X-ray diffraction image of a pitch fiber spun from the same petroleum pitch as the fiber whose X-ray diffraction image is shown in Figure 1.
However, the pitch was directly heated to a spinning temperature of 158° C. without any preheat treatment to form a menphase.

In this case, the X-ray image also relates to the fibers in the stretched state.

However, while the fiber whose X-ray diffraction image is shown in Figure 1 is characterized by a highly preferred orientation parallel to the fiber axis, no preferred orientation is seen in Figure 2 (002 (as indicated by the wide diffuse halo that constitutes the band).

Figure 3 shows a fiber spun from the same petroleum pitch under the same conditions as the fiber whose X-ray diffraction image is shown in Figure 2, and then spun in oxygen at 10°C.
This is an X-ray diffraction image of carbon fibers carbonized by heating to 350°C at a rate of 100°C and then to 1000°C (5).

FIG. 4 is an X-ray diffraction image of the same carbon fiber whose X-ray image is shown in FIG. 3 after further heating (6) to 3000°C.

A comparison of Figures 3 and 4 with Figure 2 shows that heating to higher temperatures did not impart a preferred orientation to the drawn fibers.

Figure 5 shows the X-ray diffraction image of the one shown in Figure 1, which was spun from the same petroleum pitch under the same conditions, and then spun at 10° in oxygen.
This is an X-ray diffraction image of carbon fiber that was carbonized by heating to 350° C. at a rate of C/min and then to 1000° C. (5).

FIG. 6 is an X-ray diffraction image of the same carbon fiber whose X-ray diffraction image is shown in FIG. 5 after further heating (6) to 3000°C.

Comparing FIG. 6 with FIG. 1, it can be seen that the preferred orientation of the fibers in the drawn state is maintained after heating to 3000°C.

Comparing Figure 5 with Figure 1, it can be seen that some disruption of the preferred orientation of the drawn fibers occurs when heated to 1000°C, but a much higher degree of preferred orientation is obtained on further heating to 3000°C. .

(Preferable degree of orientation of 1000°C heat-treated fibers (FWH)
M) and the apparent crystallite thickness Lc, measured as described above in the discussion of FIG.
It was a person.

) 3000°C heat-treated fiber preferred degree of orientation (FWH
M) was similarly measured and was approximately 8°.

The layer dimensions La and the crystallite thickness Lc were more than 1000λ and were therefore too large to be measured by X-ray techniques.

((5) Carbonization was carried out for about 1 hour in an argon atmosphere.

(6) The fibers were heated for about 1 hour in an argon atmosphere for 3
000°C and held at 3000°C for 10 minutes).

112 The fiber whose X-ray diffraction pattern is shown in FIGS. In contrast to the turbostratic structure of the fibers shown in (produced by heating fibers made of polyacrylonitrile and rayon to 3000°C, respectively), the fibers have a highly three-dimensional arrangement characteristic of polycrystalline graphite. Has characteristics.

Furthermore, compared to the fibers whose X-ray diffraction images are shown in Figures 7 and 8, the graphitic nature of these fibers is due to the layer spacing d and the non-orientation parameter p, whose X-ray diffraction images are shown in Figures 13 and 14. The crystallite size is significantly smaller than the interlayer spacing d and the non-orientation parameter p of the fibers shown in the X-ray diffraction patterns, as shown by the fact that the crystallite size is significantly larger than the crystallite size of the fibers shown in Figures 7 and 8. (See discussion in Figures 7 and 8 below).

The layer spacing d is calculated from the distance between the corresponding 001 lines and is 3.3
There were seven people.

The non-orientation parameter p corresponding to this value was determined from the above-mentioned R.E.Franklin relationship to be about 0.4.

Figure 7 shows that polyacrylonitrile fibers are first oxidized in air at 200-250°C under stress for 12 hours, then the fibers are carbonized to 1000°C, and finally the carbonized fibers are heated to 300°C.
This is an X-ray diffraction image of carbon fiber made by heating (6) to 0°C.

A highly preferred orientation parallel to the fiber axis is evident from the short arcs that make up the 001 band in the diffraction image, or the presence of 112 cross grating lines and the nonresolvability of the 10 band indicate the absence of three-dimensional alignment. ing.

Calculated from the distance between the corresponding 001 lines, the layer spacing d is 3.
There were 41 people.

The non-orientation parameter p corresponding to this value was determined from the above-mentioned R.E.-Franklin relationship and was about 0.8.

002 Thickness of microcrystal from width of arc.

was shown to be quite small. The apparent layer size La and the apparent thickness of microcrystals for polyacrylonitrile fibers treated in the same manner.

are 200 and 90, respectively, according to Nie Shindo's measurements.
(Shindo N., "Research on Graphite Fibers," Report A317, Industrial Research Institute, Osaka, December 1961).

((6) The fibers were heated to 3000°C in an argon atmosphere for about 1 hour and held at 3000°C for 10 minutes).

Figure 8 shows that rayon fibers are first heated in air at 260-280°C.
This is an X-ray diffraction image of a carbon fiber made by heating the carbon fiber for several minutes, then carbonizing it to 1000°C (7), and finally heating the carbonized fiber to 3000°C under stress (8).

((7) Carbonization was performed in a nitrogen atmosphere for less than 1 minute.

(8) The fibers were heated to 3000 °C under stress in a nitrogen atmosphere for less than 1 minute and then reheated at 3000 °C for 10 minutes without stress in an argon atmosphere).

A highly preferred orientation parallel to the fiber axis is evident from the short arcs that make up the 001 band in the diffraction image, whereas the lack of 112 cross grating lines and the non-resolvability of the 10 band indicate a lack of three-dimensional alignment. .

Calculated from the distance between the corresponding 001 lines, the layer spacing d is 3.
It turned out that there were 41 people.

The non-orientation parameter p corresponding to this value was determined from the above-mentioned R.E.-Franklin relationship and was about 0.8.

002 The thickness of the microcrystal from the width of the arc.

I found out that it was smaller than the others. The apparent layer size Iia and apparent crystallite thickness of similarly treated rayon fibers.

were about 100 people each, according to measurements by Leland et al.
Perret, Ro and Ruland, W. [J, A.
ppl, Cryst, J, 3, 525.1970; Fourdeux, Nie (Fourdeux, A.)
, , Pellet, R. and Ruland, D.A.
Ru1and, W'), ``Conference on Carbon Fibers, Their Composites and Applications'', Plastics Institute (Plasti-cs, In5titut).
e), London, February-April, 1971, Shishuya 9
).

FIG. 9 is a polarized light micrograph of a cross section of a pitch fiber prepared by heating commercially available petroleum pitch at 400° C. for 10 hours to reach a menphase content of 50%, and then spinning the fiber at 350° C.

FIG. 10 is a polarized light micrograph of a longitudinal section of the above fiber.

This photomicrograph was taken at a magnification of 500X, and the textural changes seen in the photomicrograph showing the fibers in the stretched state indicate that "small complexes" have formed in the fibers.

It can be seen that large oriented domains are distributed throughout the fiber, and as is clear from the longitudinal photograph in Figure 10, these oriented domains have a microfibrous appearance and are mainly parallel to the fiber axis. Dinner is served at 1 pm.

The width of the domain is approximately Q, 5-2 mm under magnification, indicating an actual width of approximately 1-4 microns.

Figure 11 shows the fibers shown in micrographs or Figures 9 and 10 spun from the same petroleum pitch under the same conditions and then heated to 350°C at a rate of 10°C/min in oxygen; This is a polarized light micrograph of a cross section of carbon fiber that was then heated to 1675° C. (5) and carbonized.

FIG. 12 is a longitudinal photograph of the same fiber.

Figures 13 and 14 are polarized light micrographs of a cross section and a longitudinal section, respectively, of carbon fibers made by the same method except that the fibers were heated to 3000° C. (6).

((5) Carbonization was performed in an argon atmosphere for about 1 hour.

(6) The fibers were heated to 3000°C in an argon atmosphere for about 1 hour and held at 3000°C for 10 minutes).

Micrographs are at 100x magnification.

The fibers shown there are photomicrographs numbered 9 and 1.
It shows the same preferred orientation and fibrillar appearance as for the fibers in the drawn state shown in Figure 0.

A magnified view of the fibers heat treated at 1675 DEG C. and 3000 DEG C. shows that the width of the microfibrous regions is between about 1-4 microns, which indicates an actual width of about 1-4 microns.

FIG. 15 is a polarized light micrograph of a cross section of a pitch fiber spun from the same petroleum pitch as the micrographs of the fibers shown in FIGS. 9 and 10, except that the pitch was preheat treated to form mesophase. Figure 16 is a micrograph of a longitudinal section of the same fiber.

The photomicrograph is at 1000X magnification and shows the fibers in the stretched state.

Although the fibers shown there appear to be substantially homogeneous, there are no texture changes and a "small complex" appearance as in the case of the stretched fibers whose micrographs are shown in Figures 9 and 10. Not shown.

The white spots and lines present in the micrographs are not due to the presence of anisotropic domains, but are caused by the penetration of the abrasive compound into the fiber voids and cracks during sample preparation.

FIG. 17 shows the fibers whose micrographs are shown in FIGS. 15 and 16 spun from the same petroleum pitch under the same conditions and then heated to 340° C. at a rate of 10° C./min in oxygen; This is a polarized light micrograph of a cross section of carbon fiber that was then heated to 1600° C. (11) and carbonized.

((11) Carbonization was performed in an argon atmosphere for about 1 hour and held at 1600° C. for 10 minutes).

FIG. 18 is a longitudinal photograph of the same fiber.

Figures 19 and 20 are polarized light micrographs of the cross-section and longitudinal section, respectively, of carbon fibers made in the same manner except that the fibers were heated to 3000°C (6).

The magnification of each photomicrograph is 100OX.

The fibers heat treated to 1600°C (Figures 17 and 18) appear substantially homogeneous, similar to the stretched fibers whose micrographs are shown in Figures 15 and 16.
The micrographs do not show the tissue changes and fibrillar appearance of the fibers shown in Figures 9-14.

((6) The fibers were heated at 300 °C for about 1 hour in argon.
(heated to 0°C and held at 3000°C for 10 minutes).

(Similar to Figures 15 and 16, the white spots present in the photomicrographs were caused by the abrasive compound penetrating the sample voids during sample preparation).

By comparing Figures 17 and 18 with Figures 15 and 16, it can be seen that heating to higher temperatures does not impart a preferred orientation to the drawn fibers.

On the other hand, one of the fibers whose micrograph is shown in FIG.
Despite the fact that it was made from petroleum pitch that was not heat treated to form a mesophase (heat treated to 3000 °C), some randomly oriented grain structure developed near part 6 of the fiber. (the other fibers shown in Figures 19 and 20 are substantially homogeneous).

This unusual phenomenon occurs during heat treatment of fibers in oxygen.
This is due to incomplete oxidation in 6 parts of the fiber, resulting in some generation of randomly oriented granular crystalline domains in the unoxidized core of the fiber during subsequent heat treatment at higher temperatures.

Under such conditions, some non-menophase pitches present in the unoxidized core of the fibers are heated to 400-500°C.
can transform into mesophase during carbonization, and the resulting fibers contain small crystalline domains (
(about 1 micron or less) but remain unchanged in the rest of the fiber.

However, the domains are randomly oriented and granular rather than elongated, and such fibers do not have oriented domains that are primarily aligned parallel to the fiber axis.

Figure 21 is a polarized light micrograph of a cross-section of a polyacrylonitrile fiber made by first oxidizing it in air under stress at 200-250°C for about 12 hours and then heating to 400°C.

FIG. 22 is a polarized light micrograph of a longitudinal section of the same fiber.

Micrographs are at 1000X magnification.

Fibers are substantially homogeneous or micrographs 9-14
The tissue changes and fibrillar appearance of the fibers shown in the figure do not appear to be shown.

(The white spots present in the micrograph were caused by the infiltration of the abrasive compound into the sample voids during the preparation of the sample)
.

Figure 23 is a polarized light micrograph of a cross section of a carbon fiber made by first oxidizing polyacrylonitrile fibers in air under stress at 200-250°C for about 12 hours and then carbonizing to 1400°C.

FIG. 24 is a longitudinal photograph of the same fiber.

Figures 25 and 26 are polarized light micrographs of a cross-section and a longitudinal section, respectively, of carbon fibers made in the same manner except that the fibers were heated to 2800°C.

Micrographs are at 1000X magnification.

As in the case of the 400°C heat-treated fibers whose micrographs are shown in Figures 21 and 22, the fibers are substantially homogeneous, but the texture changes in the case of the fibers whose micrographs are shown in Figures 9-14. and does not appear to exhibit a microfibrous appearance.

From a comparison of Figures 23-26 with Figures 21 and 22, it is clear that such structure is not imparted to the fibers even when heated to higher temperatures.

(The white spots present in the micrographs were caused by the infiltration of the abrasive compound into the sample voids during sample preparation).

Figure 27 shows that rayon fibers are first placed in the air at a temperature of 260-280.
Heat stabilized at ℃ for several minutes, then heated to 300℃ in a nitrogen atmosphere.
This is a polarized light micrograph of a cross section of a fiber made by heating for less than 1 minute.

FIG. 28 is a polarized light micrograph of a longitudinal section of the same fiber.

The magnification of the photomicrograph is 1 ooox.

Although these fibers appear substantially homogeneous, the micrographs do not show the texture changes and fibrillar appearance as in the fibers shown in Figures 9-14.

Figure 29 is a polarized light micrograph of a cross section of a carbon fiber made by heat stabilizing rayon fibers in air at 260-280°C for several minutes and then carbonizing at 1300°C for less than 1 minute in a nitrogen atmosphere. .

FIG. 30 is a longitudinal photograph of the same fiber.

Figures 31 and 32 are polarized light micrographs of a cross-section and a longitudinal section, respectively, of carbon fibers made in the same manner except that the fibers were heated to 3000°C (8).

((8) The fibers were heated to 3000°C under stress in a nitrogen atmosphere.
(heated for less than a minute and then reheated at 3000° C. in an argon atmosphere for 10 minutes without stress).

Micrographs are at 100x magnification.

300°C, the micrographs of which are shown in Figures 27 and 28.
As with the heat treated fibers, the fibers appear substantially homogeneous, but the micrographs do not show the texture changes and fibrillar appearance as in the fibers shown in Figures 9-14.

From a comparison of Figures 29-32 with Figures 27 and 28, it is clear that such structure is not imparted to the fibers even when heated to higher temperatures.

(The white spots present in the micrograph are caused by abrasive compounds penetrating the sample voids during sample preparation)
.

The following examples are included for illustrative purposes so that those skilled in the art may better understand the invention.

It goes without saying that these examples are merely illustrative and do not limit the invention.

Example A pitch having a menphase content of about 50% by weight was prepared using commercially available petroleum pitch.

Previously, the hard material pitch had a density of 1.233 g/C1, a softening temperature of 120.5°C, and 0.83% by weight of quinoline solubles (Q, 1. determined by quinoline extraction at 75°C).

).

According to chemical analysis, carbon content is 93.3% and hydrogen content is 5.6%.
%, sulfur content 0.94% and ash content 0.044%.

Menphase pitch was made by heating this precursor petroleum pitch at about 400° C. for about 32 hours under a nitrogen atmosphere under static conditions.

After heating, the pitch contained 49.3% by weight of quinoline solubles, indicating that the mesophase content of the pitch was close to 50%.

A portion of this pitch was placed in an extrusion cylinder, and under nitrogen atmosphere and humidity at 372°C, the molten pitch was extruded through a pinhole orifice (0.015 inch diameter) at the bottom of the extruder under pressure with a piston. Fibers were obtained by spinning at a spinning speed of 80 fibers/min.

Fibers of 12-23 microns in diameter were produced in this manner.

In this case, the menphasic pitch forms a homogeneous bulk mesophase with large coalescing domains (domain sands 240 microns) under static conditions, yet the pitch is non-chickentropic at spinning temperatures, and 10 It has a viscosity of 200 to 200 poise.

Fibers made using the same method (same pitch at 400℃ for 10
X-ray diffraction studies revealed that the fibers were with a preferred orientation (FWHM) of 29° (spun at 350°C after heating for
(measured by microphotometer scanning of the 002 band of the line film).

The apparent crystallite thickness Lc of the unidirectional domains of the pitch molecules in the fiber was determined to be 47 by microdensitometer scanning measurements of the width of the 002 diffraction arc.

See FIG. 1 for the X-ray diffraction image of this fiber.

Polarized light microscopy of the same fibers revealed the presence of large elongated optically anisotropic domains with a fibrillar appearance, oriented primarily parallel to the fiber axis.

See Figures 9 and 10. A portion of the drawn fiber thus produced was heated to 300°C for about 30 minutes in oxygen.
and held at this temperature for approximately 15 minutes.

The resulting oxidized fibers were completely infusible and did not sag even when heated at high temperatures.

The infusible fibers were heated to 800° C. for about 80 minutes in a nitrogen atmosphere, held at this temperature for about 10 minutes, and then heated to 1400° C. at a rate of 50-1006 C/min in argon.
Heated to a final temperature of ~1800°C.

In each case the fibers were held at the final temperature for approximately 15 minutes.

Fibers with tensile strengths in excess of 100 x 103 psi and elastic Young's modulus in excess of about 20 x 106 psi were thus produced.

As a further example, a fiber heated to 1600°C has a tensile strength of 201 x 103 psi and an elastic Young's modulus of 32.6 x
It was 10'psi.

Fibers heated to 1800°C have a tensile strength of 149 x 1
03psi, Young's modulus is 53.2 x 106psi
Met.

Fibers made in the same manner (fibers made from the same pitch were heated in oxygen to 350°C at a rate of 10°C/min and then carbonized by heating to 1000°C for about 1 hour in an argon atmosphere). According to X-ray diffraction studies, such fibers have a preferred orientation (FWHM) of 40° and a
The apparent thickness of a person's microcrystals.

It was shown that it has. An X-ray diffraction image of such a fiber is shown in FIG.

Figure 6 shows an X-ray diffraction image of the same fiber after heating to 3000°C.

The 3000°C heat treated fibers have a preferred orientation of about f and 10
The apparent layer dimension La and the thickness of microcrystals exceed 0.00.

had. Polarized light microscopy examination of fibers made in the same manner but heat treated to 1675° C. revealed the presence of large oriented elongated graphitizable regions similar to the stretched fibers.

Fibers made in the same manner but heat-treated at 3000°C also showed largely oriented elongated optically anisotropic domains (no longer graphitizable, but rather graphitic) that were oriented primarily parallel to the fiber axis. ).

See Figures 11-14.

Fibers made in the same manner but heated above 3000°C were found to have tensile strengths in excess of 300 x 103 psi and Young's modulus in excess of 100 x 106 psi.

Although the present invention has been described in detail above, it still includes the following embodiments.

(1) Electrical resistance 150X10”ohmcrrL~200
X10-6ohmcrrL, tensile strength 250X10”p
si or more, and an elastic Young's modulus of 75×10' psi or more.

(2) The fiber of claim 1 containing elongated domains of 10,000 to 40,000 in diameter.

(3) Electrical resistance 250X10-6ohmcfrL or less,
The fiber according to item (2) above, which has a tensile strength of 200×10 3 psi or more and an elastic Young's modulus of 50×10 6 psi or more.

(4) Electrical resistance 150 x 10-6 to 200 x 10
-6ohmCrfL, a tensile strength of 250×10 3 psi or more, and an elastic Young's modulus of 75×10 6 psi or more.

(5) The fiber of claim 1 containing elongated domains of 10,000 to 100,000 in diameter;
3. The method according to claim 2, wherein the method is heated at .

(The method according to item (6) above, wherein the oxygen-containing atmosphere is selected from the group consisting of air and oxygen.

(8) The method according to claim 2, wherein the carbonaceous fiber is spun at a temperature with a pitch viscosity of 30 to 60 poise.

(9) 300 to about 390°C in an oxygen-containing atmosphere
is heated.

The method described in item (8) above. (10) Item (9) above, wherein the oxygen-containing atmosphere is selected from the group consisting of air and oxygen.
The method described in section.

Claims (1)

[Claims] 1. By heating petroleum-based pitch having aromatic molecules at a temperature of about 50 °C to about 450 °C under stationary conditions, a pitch having a mesophase content of about 40 parts to about 90 parts (by weight) and The mesophase produces mesophase pitch, which is a homogeneous bulk mesophase with a domain size of 200 microns or more, and the mesophase pitch is non-Chickentropic and has a viscosity of 10 poise to 200 poise at the spinning temperature. The mesophase pitch is then spun into pitch fibers having a diameter of 30 microns or less at a spinning temperature, and the pitch fibers are sintered in an oxygen-containing atmosphere to form the pitch at a temperature of 50°C to about 400°C. The pitch fibers are heated for a period sufficient to render them infusible, and then the pitch fibers are initially
1. A method for producing graphite fiber having a structure of multiorganic crystalline graphite having a three-dimensional array characteristic, the method comprising heating at a temperature of 0.degree. C. or higher, and then heating to a temperature of about 2,500'C or higher.