JPH0413396B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pitch composition useful as a dope for spinning carbon fibers. More specifically, by going through a series of steps of melt spinning - infusibility treatment - carbonization treatment, it is possible to form carbon fibers with high strength and high modulus that could not be achieved with conventional pitch-based carbon fibers. However, the present invention relates to a new pitch composition.

Currently, carbon fibers mainly produced include PAN-based carbon fibers made from polyacrylonitrile (PAN) fibers and pitch-based carbon fibers made from coal-based or petroleum-based pitch. but,
High-strength, high-modulus, high-performance carbon fiber is mainly used as a reinforcing material for resins in composite materials.
PAN type is the mainstream, and Pitch type has a strength of 200Kg/mm ²
Only the following relatively low-strength products have been manufactured.

Attempts have been made to produce higher performance fibers among such pitch-based carbon fibers.
Up to now, the following proposals have been made regarding the production of pitches for producing carbon fibers.

(a) A method of hydrogen-treating or heat-treating a specific condensed polycyclic aromatic compound to produce pitch for carbon fiber (Japanese Patent Publication No. 45-28013, Japanese Patent Publication No. 49-3634).

(b) A method in which petroleum-based tar or pitch is subjected to a first heat treatment in the presence of a Lewis acid catalyst, and then the catalyst is removed and a second heat treatment is performed to produce mesophase pitch (Japanese Patent Publication No. 53 −7533).

(c) A method of heating pitch under an inert gas flow or under reduced pressure to produce mesophase pitch with a predetermined mesophase content (Japanese Patent Application Laid-open No. 86717/1983,
(Japanese Patent Publication No. 53-36718).

(d) A method of treating optically isotropic pitch with a solvent (benzene, toluene, peptane, etc.) and heating the insoluble part to form a neomesophase (Japanese Patent Application Laid-open No.
No. 54-160427, JP-A No. 55-58287, JP-A-55
−130809).

However, even with these methods,
Since it is not possible to obtain carbon fibers with advanced performance comparable to PAN-based carbon fibers, Pitu-based carbon fibers have until now been used in fields where low strength is required, such as asbestos substitutes. The reality is that In addition, among the above methods, the method using Mesophace pitch has a very high viscosity as a spinning dope, resulting in poor spinnability and difficulty in melt spinning at an economical spinning speed. It also has the above problem.

In view of the above-mentioned current situation in the production of pitch-based carbon fibers, the present inventors have conducted research to develop a method for producing carbon fibers with excellent quality using pitch-based carbon fibers as raw materials. Infusibility/
We have proposed a new method for producing carbon fibers using a unique Primesophase pitch that converts into an optically anisotropic Mesophace during the carbonization process (Japanese Patent Application Laid-open No. 18421-1983), and furthermore, We have proposed a method suitable for industrially producing pitchi (Japanese Patent Application Laid-open No. 196292/1983).

The present inventors further investigated the pitch composition for spinning that can form high-performance pitch carbon fibers, and found that the properties of the pitch composition, the properties and chemical structure of the quinoline-soluble component therein, In particular, the degree of aromatization and specific gravity of pitch and the number average molecular weight of the quinoline-soluble component are important for obtaining high-performance carbon fibers, and pitch compositions with these within specific ranges have good melt spinnability. , and by performing infusibility treatment and carbonization treatment after spinning,
The present invention was achieved by discovering the fact that it is possible to form carbon fibers with performance comparable to that of PAN-based carbon fibers.

That is, in the present invention, after hydrogenating an optically isotropic pitch with a hydrogenation solvent or hydrogen gas,
30% of quinoline soluble components heat treated at 450-550℃
Pitch containing ~70% by weight, with a specific gravity of 1.29-1.40 at 20°C and a degree of aromatization of 0.45-0.9
and the number average molecular weight of the quinoline soluble component is 700 to 1700, and in its ¹ H-NMR,
The proportions of hydrogen H _A with a mechanical shift of 5 to 7 ppm and hydrogen H _B of 3 to 4 ppm based on tetramethylsilane (TMS) relative to all detected hydrogen excluding the solvent are H _A = 4.4 to 10% and H _B = 2.5 to 2.5 ppm, respectively. This is a pitch composition for producing carbon fibers with excellent melt spinnability, characterized by a concentration of 7.5%.

Generally, when producing high-performance carbon fibers, the spinning pitch needs to have both molecular orientation to the extent that it can be oriented during the spinning stage, as well as yarn properties and fluidity that can be formed into filaments. Conventional mesophase pitches are made into polymers through heat treatment from the viewpoint of molecular orientation, but as mentioned above, this has problems with fluidity and dirtiness during spinning, and even with careful spinning, The spinning speed is about 400
m/min is the limit. Furthermore, when such mesophasic pitch is melt-spun, due to its highly oriented properties, giant leaf-like domains tend to be prepared in the carbon fiber precursor pitch fibers, leading to radialization of the final fiber structure after carbonization. Performance is likely to deteriorate due to vertical cracking of the fibers, etc.

As a result of research on this problem, the inventors found that
The internal structure and performance of the final carbon fiber are greatly influenced by the chemical structure and properties of the pitch used for spinning, and it is effective to reduce the molecular orientation to a certain degree compared to conventional mesophase pitch. I found out. However, in this case, the molecular orientation of the pitch can be recovered to some extent during the spinning stage, and the spinning stage is capable of forming a latent orientation ability that allows a highly oriented structure to appear in the subsequent carbonization process. It has to be something.

The pitch composition of the present invention satisfies these requirements, has good spinnability (fluidity, threadability) during melt spinning, allows smooth spinning even at high speeds of 1000 m/min or more, and In the carbonization step after spinning, the ideal structure as described above can be developed.

The pitch composition of the present invention contains 30 to 70% by weight of quinoline soluble components. quinoline soluble component
If it is less than 30% by weight, the softening point is high and spinnability is poor.
Further, the structure of the carbon fibers produced tends to have a radial shape.

Furthermore, the pitch composition of the present invention has the following properties (a) to (c). That is, (a) the number average molecular weight of the quinoline-soluble component in the pitchi composition is 700 to 1,700, preferably 800 to 1,500, and (b) the specific gravity (at 20°C) of the pitchi is 1.29 to 1.40, preferably 1.30 to 1.35, and (iii) the degree of aromatization must be within the range of 0.45 to 0.9.

Conventional mesophase pitch is a mixture of a quinoline-soluble component and a quinoline-insoluble component, and therefore, the two tend to undergo phase separation, making it difficult to maintain good spinnability. On the other hand, those that meet the above conditions have good compatibility between the quinoline-insoluble component and the quinoline-soluble component that may be contained in the composition, and exhibit good spinnability even in compositions containing a considerable amount of quinoline-insoluble component. maintain. Moreover, since the pitch composition of the present invention has a structure in which the polycyclic condensed compound maintains high aromatic properties and has a partially hydrogenated nucleus, the planarity of the compound is moderately distorted, and it has large foliate domains. At the same time, it imparts latent orientation to at least the spun fibers after spinning, and in the subsequent carbonization treatment, flatness is restored by dehydrogenation and excellent orientation and crystallinity can be developed. . In addition, the above-mentioned distortion of planarity leads to increased molecular mobility and provides excellent fluidity during spinning.

However, if the number average molecular weight of the quinoline-soluble component is less than 700, phase separation from the quinoline-insoluble component tends to occur, and the fibers tend to melt and break during the infusibility treatment of spun pitch fibers, or the fibers tend to be easily cut during the carbonization treatment. However, there are problems such as the tendency for defects to occur due to shedding of low molecular weight substances. On the other hand, the number average molecular weight
If it exceeds 1700, the softening point of the pitch composition as a whole becomes too high, making smooth spinning difficult. Furthermore, if either the specific gravity or the degree of aromatization of the pitch composition is outside the above range, huge leaf-like domains tend to occur in the carbon fiber, making it impossible to obtain a high-performance carbon fiber. There are also liquidity issues.

The pitch composition of the present invention is further required to satisfy the following condition (d), and preferably satisfies the condition (e).

(d) In ¹ H-NMR, the quinoline soluble component is
Chemical shift based on tetramethylsilane (TMS) relative to all detected hydrogen excluding solvent: 5 to 7 ppm
The proportions of hydrogen _HA of 3 to 4 ppm and hydrogen _HB of 3 to 4 ppm are _HA = 4.5 to 10% and _HB = 2.5 to 7.5%, respectively. The fact that H _A and H _B are within the above range means that the aromatic nucleus in the polycyclic condensed compound is partially hydrogenated, and the planarity of the compound is distorted.

(e) H/C (hydrogen/carbon ratio) of the pituti composition is 0.5
Must be within the range of ~0.65. This indicates that it exhibits the above-mentioned hydrogenated structure and maintains high aromaticity.

That is, a product that satisfies these conditions has about 2 to 10 structural units with 4 to 6 condensed rings connected by side chains, and the aromatic nucleus of each structural unit is partially hydrogenated.
The planar structure of molecules is distorted.

Next, the number average molecular weight, aromatization degree, as used in the present invention,
¹ Explain measurement methods such as H-NMR and H/C.

(1) Number average molecular weight Measured using VPO with pyridine as solvent.

VPO as vapor pressure osmometer
Using a Knauner Dempfdruck Ostomer, pyridine was used as the solvent and pendyl was used as the standard.

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

Aromatization degree = 3050cm ^-1 intensity / (3050cm ^-1 intensity +
2925cm ^-1 intensity) The IR measurement device is an IR-1 manufactured by Shimadzu Corporation.
Uses 27G type.

(3) A JEOL PS-100 spectrometer was used as ^{the 1} H-NMR measurement device, and the chemical shift was measured using TMS.
is expressed as a δ value using as an internal standard.

NMR spectra were measured using deuterated pyridine as a solvent.

(4) H/C Calculated according to the following formula from elemental analysis measured according to TIS M-3813.

H/C=(H analysis value/1) (C analysis value/12) Next, a method for producing the pitch composition of the present invention as described above will be explained.

Raw material pitches include coal tar, coal tar pitch, coal-based heavy oil such as coal liquefied products, atmospheric residual oil of coal, vacuum distillation residual oil, and tar and pitch by-produced by heat treatment of these residual oils. Although petroleum-based heavy oils such as , oil sand, and bitumen can be used, corn tar pitch is preferred because it facilitates the production of the pitch composition of the present invention.

The pitch composition of the present invention comprises a first stage treatment in which the commercially available raw material pitch is purified and then heated in a specific hydrogenation solvent, and a second stage treatment in which the pitch is heated to a high temperature after or while removing the solvent. It is manufactured by applying

Tetrahydroquinoline (hereinafter abbreviated as THQ) is optimal as the hydrogenation solvent used in the first stage treatment, but a mixture of quinoline and THQ may also be used. It is also possible to use quinoline with hydrogen in the presence of iron oxides, and it is also possible to use naphthalene oil, anthracene oil, creosote oil, absorption oil, etc. with hydrogen gas. When THQ is used as the hydrogenation solvent, 30 to 100 parts by weight of THQ is added per 100 parts by weight of the raw material pitch and heated at 300 to 500°C, preferably 340 to 450°C for 10 to 60 minutes. The product thus treated is subjected to the next second stage treatment.

In the second stage treatment, the THQ treatment pitch is under reduced pressure.
For example, 5 to 60 at 450 to 550℃ at a pressure of 50 mmHg or less
Hold for a minute. In this case, instead of such a vacuum treatment, THQ is removed and then heated at 450 to 550℃ under normal pressure.
In this two-stage treatment, the pitch composition of the present invention can be treated by appropriately selecting the treatment conditions within the above range depending on the composition and properties of the raw pitch. can do.

According to the research conducted by the present inventors, in order to produce a good spinning pitch composition of the present invention, the pitch before the heat treatment (second stage treatment) must be substantially
It is 100% quinoline soluble, its specific gravity at 20℃ is 1.25-1.31, and the average molecular weight of the structural unit measured by mass spectrometry (MS) is
It is preferable to use a polycyclic aromatic condensate having 2 to 6 condensed rings, which is 200 to 400. In this pitch, the aromatic nucleus is partially hydrogenated in the first stage treatment (hydrogenated solvent treatment), forming a structure in which the planarity of the molecule is distorted, but this basic structure is maintained even in the second stage treatment (heat treatment). The addition of side chains during the second stage treatment results in pitch compositions of the invention having the various features and advantages described above.

The pitch composition of the present invention as described above has appropriate viscoelastic properties at the spinning temperature and has extremely good melt spinnability.

Melt spinning can be carried out by methods known per se. For example, the pitch composition of the present invention has a pore size of 0.1
~50~ from the softening point from a spinneret with a 0.8mm spinning hole
The filament is extruded at a temperature 100℃ higher and discharged from the spinneret at a spinning (winding) speed of 300 to 1500 m/s.
It can be easily made into fibers by winding it up in minutes. The obtained pitch fibers are then heated to 250 to 350°C in the presence of oxygen at a heating rate of 0.5 to 3°C/min and maintained for 5 to 30 minutes to make them infusible. , 2-5℃/in inert gas
Carbonization treatment is carried out by heating to 1000-1500°C at a temperature increase rate of 10 minutes and maintaining this temperature for 10-30 minutes.

The pitch composition of the present invention becomes a complete mesophase during this carbonization process, forming carbon fibers with a dense structure that is fully oriented and does not contain large domains.

The obtained carbon fiber has a high strength of 200Kg/mm2 ^or more.
It has a modulus of 10 ton/mm ² or more, and has extremely high performance.

Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples.

In addition, the fiber diameter (thread diameter) of the carbon fiber in each example,
Tensile strength, elongation, and modulus were measured according to JIS R7601 "Carbon Fiber Test Method."

Note that the fiber diameter was measured using a helium-neon laser.

Example 1 134 g of pitch in commercially available coal tar and 402 g of tetrahydroquinoline (referred to as THQ) were placed in a 1-liter autoclave made of SUS316 equipped with an electromagnetic induction rotary stirring device, and after being sufficiently purged with nitrogen, the internal pressure was reduced to 0 kg/cm ²
G, and after sealing, raise the temperature to 430℃ while stirring,
After reaching 430°C, it was maintained for an additional 15 minutes. Thereafter, the mixture was cooled to room temperature, stirring was stopped, and the contents were taken out. The mixture was passed through a water aspirator under reduced pressure.
Insoluble matter was removed by suctioning through No. 4 qualitative paper and then through a G-4 glass filter. The mother liquor thus obtained was distilled under reduced pressure at 290° C. and 10 mmTorr to remove a solvent mainly consisting of unreacted THQ and quinoline produced by the reaction, to obtain THQ-treated pits. After that, the pitch was placed in a 300 ml heat-resistant glass three-necked flask and heated to 10 Torr in a _N2 gas flow.
and heated to 465°C. The internal temperature rose rapidly with the distillation of low-boiling substances. After the internal temperature became constant, heating was continued for 15 minutes and then cooled.

The resulting spinning pitch was analyzed and placed in a cylinder with a constant-speed descending plunger.
The yarn was spun and wound at 370° C. at a speed of 1000 m/min to obtain pitch fiber. The pitch fiber is placed in an air stream.
After heat treatment at a heating rate of 2°C/min between 200°C and 300°C, the fibers are made infusible by further heat treatment at 300°C for 15 minutes, and then at 1500°C in a _N2 stream for 15 minutes.
After carbonization (firing) treatment was performed for a minute to form carbon fibers, mechanical properties were measured using conventional methods.

The content of the quinoline-soluble component in the spinning pitch according to JIS K-2425 was 58.0% by weight, and the number average molecular weight of the quinoline-soluble component was 950 as measured using VPO with pyridine as a solvent. or,
The specific gravity of the pitch at 20°C is 13.22,
The degree of aromatization was determined to be 0.60 from the IR measured by the KBr tablet method using the following formula: degree of aromatization = 3050 cm ^-1 intensity/[(3050 cm ^-1 intensity) + (2925 cm ^-1 intensity)]. In addition, H _A and H _B determined by ¹ H-NMR of quinoline-soluble components using deuterated pyridine as a solvent were each 6.2%,
It was 5.8%. In addition, from the elemental analysis measured in accordance with JIS M-8813, H/C was determined to be 0.54 according to the following formula: H/C = (H analysis value/1)/(C analysis value/12). . These data indicate that the pitch has a highly developed polycyclic condensed skeleton and aromatic properties, yet hydrogen is effectively introduced and the molecular planarity is moderately distorted. Therefore, it is believed that the pitch has excellent flow properties, forms at least an orientation base during the spinning process, and prevents the formation of giant lobed domains that lead to longitudinal cracking during firing.
In addition, the distortion of the molecular planarity of the pitch is caused by carbonization (calcination).
It is easily repaired by dehydrogenation occurring during the process.

In addition, the obtained carbon fiber has a thread diameter of 10μ and a strength of
245Kg/mm ² and modulus 17Ton/mm ² .

Comparative Example 1 100 g of the same commercially available coal tar pitch used in Example 1 was placed in a glass three-necked flask equipped with a stirrer, heat treated in a nitrogen stream at normal pressure at 400°C for 24 hours with stirring, and then taken out. After reduction at 80 to 90° C. with metal lithium in an amount equal to the weight of the pitch in 65 ml of dehydrated ethylene diamine per 1 part by weight, hydrogenated coal tar pitch was obtained by neutralizing in a conventional manner and washing with water repeatedly. The hydrogenated pitch is _N2
A spinning pitch was prepared by heat treatment at 400° C. for 1 hour under stirring in an air stream at normal pressure. The spinning pitch was analyzed according to Example 1, and the mechanical properties were measured using carbon fiber.

As a result, the spinning pitch contained 99% of quinoline soluble components, and when pyridine was used as a solvent,
The number average molecular weight of the quinoline soluble component measured by VPO was 1300. Also, the specific gravity of the pitch is
1.280, and the degree of aromatization was 0.43. In addition, H _A and H _B determined by ¹ H-NMR of quinoline-soluble components using deuterated pyridine as a solvent are respectively
3.7% and 11.2%, and β and γ hydrogen are also 18.3% and
It was present in a fairly large amount at 10.5%. Also, H/C is
It was 0.75.

These data indicate that the pitches are composed of highly developed aromatic polycyclic condensates, but also contain significant side chains. (Moreover, the molecular planarity is considered to be good.) Such pitches are thought to be likely to cause side chains to be cut and detached during firing, and there is a high possibility that defects in the carbon fibers will increase.

The obtained carbon fiber has a thread diameter of 9.5μ and a viscosity of 148Kg/mm ² .
The modulus was 10Ton/ ^mm2 .

Comparative Example 2 400 g of petroleum pitch obtained from FCC decant oil was placed in a three-neck glass flask equipped with a stirrer, heat treated in a nitrogen stream at normal pressure, 400°C, and stirred for 1 hour, then taken out, crushed, and mixed with the heat treated pitch. in equal weight of tetrahydrofuran (THF),
The mixture was stirred for 1 hour at room temperature under a nitrogen stream. After that,
The solution was filtered through a N ₂ pressurizer using No. 4 qualitative paper and a metal cloth to remove insoluble matter. To the thus obtained solution, toluene in an amount four times the amount of THF was added under stirring in a nitrogen stream, and the stirring was continued for 1 hour. The formed precipitate was collected by passing through a G-4 glass filter, and then dried by a conventional method. The solvent fractionation pitch was placed in a three-necked flask and heat-treated at 440° C. under nitrogen flow at normal pressure for 15 minutes with stirring to prepare a spinning pitch. The spinning pitch was analyzed according to Example 1, and the mechanical properties were measured using carbon fiber.

As a result, the spinning pit contains 50% quinoline soluble components and uses pyridine as a solvent.
The number average molecular weight of the quinoline soluble component measured by VPO was 650. The pitch had a specific gravity of 1.309 and a degree of aromatization of 0.51. In addition, H _A and H _B determined by ¹ H-NMR of quinoline-soluble components using deuterated pyridine as a solvent were 4.1% and 7.6, respectively.
%, and H/C was 0.61.

These data indicate that the pitch is composed of a highly developed aromatic polycyclic condensate and has an excellent molecular plane.

It is thought that such pitches tend to prepare huge leaf-like domains in the carbon fiber due to the highly developed mesophase, and tend to cause longitudinal cracks in the yarn.

The obtained carbon fiber has a thread diameter of 9.8μ and a strength of 150 to 100.
Kg/mm ² and modulus in the range of 8 to 15 Ton/mm ² , and some yarns were observed to have longitudinal cracks.

Comparative Example 3 200g of the same petroleum-based pitch used in Comparative Example 2
The mixture was placed in a glass three-necked flask equipped with a stirrer, and heated under stirring at 400°C under nitrogen for 24 hours at normal pressure to prepare a spinning pitch.

The spinning pitch was analyzed in accordance with Example 1, and an attempt was made to measure the mechanical properties using carbon fiber.

As a result, the spinning pitch contained 38% quinoline soluble components and
The number average molecular weight of the quinoline soluble component was 600 as measured by VPO. The specific gravity of the pitch is 1.345
The degree of aromatization was 0.65. In addition, H _A and H _B determined by ¹ H-NMR of quinoline-soluble components using deuterated pyridine as a solvent were each 1.8%,
It was 3.4%, and H/C was 0.51.

These data indicate that the pitch is composed of a highly developed aromatic polycyclic condensate and has excellent molecular planarity.

It is thought that such pitches tend to prepare huge leaf-like domains in the carbon fiber due to the highly developed mesophase, and tend to cause longitudinal cracks in the yarn.

When spinning was carried out according to Example 1, the spinnability of the pitch was poor and winding at 600 m/min was impossible. It was found that winding was barely possible by reducing the winding speed to 300 m/min. For this reason, in order to maintain the fiber diameter,
After adjusting the descending speed of the plunger, carbon fibers were produced in the same manner as in Example 1.

The obtained carbon fiber has a thread diameter of 10.3μ and a strength of 80 to 145.
Kg/mm ² and modulus lath varied in the range of 7 to 14Ton/mm ² , and some yarns were observed to have longitudinal cracks.

Claims (1)

[Scope of Claims] 1 Pitch containing 30 to 70% by weight of a quinoline-soluble component, which is obtained by hydrogenating an optically isotropic pitch using a hydrogenation solvent or hydrogen gas and then heat treating it at 450 to 550°C. The specific gravity at 20°C is 1.29 to 1.40, the degree of aromatization is 0.45 to 0.9, the number average molecular weight of the quinoline-soluble component is 700 to 1700, and the ¹ H-NMR shows that the solvent is excluded. Hydrogen H and 3 with a chemical shift of 5 to 7 ppm based on tetramethylsilane (TMS) relative to all detected hydrogen
The proportion of hydrogen H of ~4ppm is H _A =4.4~
10%, and H _B =2.5 to 7.5%. A pitch composition for producing carbon fibers with excellent melt spinnability. 2. The pitch composition according to claim 1, wherein the H/C value of the entire composition is 0.5 to 0.65. 3. The pitch composition according to claim 1 or 2, which contains 50 to 70% by weight of a quinoline-soluble component.