JPH0382822A - Production of pitch-based carbon fiber - Google Patents

Abstract

PURPOSE:To obtain in greatly high efficiency the title fine carbon fiber good in handleability by using, as precursor, pitch-based conjugate fiber produced by conjugate spinning of carbonaceous pitch and a specific thermoplastic organic synthetic polymer. CONSTITUTION:Two components, i.e., (A) carbonaceous pitch for carbon fiber production, a thermoplastic pitch with a softening point of pref. 230-320 deg.C and (B) a thermoplastic organic synthetic polymer good in spinnability, i.e., polystyrene, nylon or a copolyester containing pref. >=60mol% of (poly)ethylene terephthalate component, are spun into pitch-based conjugate fiber, followed by, if needed, condensing and/or doubling, thus obtaining pitch-based conjugate fiber bundle. Thence, the bundle is heated in an oxygen-rich gas atmosphere to remove the component B to form pitch fiber bundle consisting of the component A alone, along with carrying out insolubilization and baking treatment, thus obtaining the objective carbon fiber.

Description

[Detailed Description of the Invention] The present invention relates to a method for producing carbon fiber, and in particular to a method for producing pitch-based carbon fiber, which is characterized in that a pitch-based composite fiber is used as a pitch fiber precursor. This relates to a manufacturing method. In this specification, carbon fiber is meant to include graphite fiber.

Currently, rayon-based and PAN-based carbon fibers as well as pitch-based carbon fibers are widely used in various technical fields.
In particular, pitch-based carbon fibers manufactured from carbonaceous pitches such as petroleum-based pitch and coal-based pitch, rayon-based and PA
It has attracted attention in recent years because it has a higher carbonization yield and better physical properties such as elastic modulus than N-based carbon fibers, and can be manufactured at low cost. There is.

Currently, pitch-based carbon fibers are produced by: (1) preparing carbon pitch suitable for carbon fiber from petroleum-based pitch, coal-based pitch, etc., heating and melting the carbon pitch, spinning it in a spinning machine, converging it, (2) The pitch fiber bundle is heated to 200 to 350°C in an oxidizing gas atmosphere in an infusible furnace to make it infusible; (3) Subsequently, The infusible fiber bundle is pre-carbonized by heating to 500 to 1500°C under an inert gas atmosphere in a pre-carbonization furnace. (4) Next, the pre-carbonized fiber bundle is heated in a carbonization furnace under an inert gas atmosphere. It is manufactured by heating to 1,500 to 2,000°C to carbonize it, and further heating to 3,000°C to graphitize it.

However, carbonaceous bits generally have poor spinnability and have an extremely narrow range of stable spinning. Therefore, it is extremely difficult to heat and melt carbonaceous bits and continuously and stably spin them using a spinning machine. Have difficulty. In particular, in order to obtain carbon fibers with high strength and high elastic modulus, fibers (filaments) of about 5 to 7 μm are used.
In order to produce carbon fibers with a diameter of less than 10 m, it is necessary to spin pitch fibers as carbon fiber precursors to a fiber diameter of 10 m or less, which is practically impossible or extremely difficult. Ta.

Furthermore, the pitch fibers before being pre-carbonized are extremely brittle and must be handled with great care. however,
Even if pitch fibers are bundled and doubled with great care, fuzz may occur due to fibers (filaments) being cut during pitch fiber convergence and doubling prior to preliminary carbonization. .

In order to solve the above problems, it has been proposed to prepare carbonaceous pitch with excellent spinnability by processing petroleum-based pitch, coal-based pitch, etc. in various ways to prepare components and remove inorganic foreign matter. It requires various complicated processing steps and has problems in terms of production efficiency and manufacturing cost.

In addition, various proposals have been made for the structure of spinnerets for pitch fibers and the structure of spinning machines for uniform cooling.
Even if a particular carbonaceous pitch is effective, there is no method that can continuously and stably spin various carbonaceous pitches without yarn breakage.

Further, as described above, even if pitch fibers were spun, the difficulty in handling due to the brittleness of the pitch fibers themselves before pre-carbonization was not improved in any way.

The present inventor conducted many research experiments to solve the above problems, and found that by composite spinning carbonaceous pitch with a thermoplastic organic synthetic polymer compound that can be melt-spun and has good spinnability, We have found that the above problems can be solved.

The present invention is based on this new knowledge.

Therefore, an object of the present invention is to use a pitch-based composite fiber as a pitch fiber precursor to enable continuous and stable spinning of various carbonaceous pitches without thread breakage, and to improve handling properties. It is an object of the present invention to provide a method for producing pitch-based carbon fibers, which can be easily bundled and doubled as desired, and can produce even small-diameter pitch-based carbon fibers extremely efficiently.

The above objects are achieved by the method for producing pitch-based carbon fibers according to the present invention. In summary, the present invention involves spinning a pitch-based composite fiber formed from component A consisting of carbonaceous pitch for producing carbon fibers and component B consisting of a thermoplastic organic synthetic polymer compound with good spinnability. , a step of producing a pitch-based composite fiber bundle by bundling and doubling as necessary; heating the pitch-based composite fiber bundle in an oxygen-rich gas atmosphere to remove the B component to form a pitch fiber bundle; The present invention also provides a method for producing pitch-based carbon fibers, comprising a step of infusibleizing the pitch fiber bundle, and a step of firing the infusible fibers.

That is, the feature of the present invention is that pitch-based composite fibers are used as pitch fiber precursors when producing pitch-based carbon fibers.

Referring to FIG. 1, one embodiment of the pitch-based composite fiber for manufacturing carbon fibers used in the present invention is shown. In this example, the pitch-based composite fiber IA consists of a component A 2 consisting of a carbonaceous bitch for producing carbon fibers, and a thermoplastic organic synthetic polymer with good spinnability formed around the component A 2. It is composed of component B 4 consisting of a compound.

FIG. 4 schematically shows an embodiment of a spinneret for producing such a pitch-based composite fiber 1A for producing carbon fibers. In this embodiment, the spinneret 100 has first, second, and 30th gold plates 102, 104, and 106, and the 10th gold plate 102 and the 20th gold plate 104 are disposed in close contact with each other. The gold plate 106 is the second
0 gold plate 104 at a predetermined distance,
As will be explained later, a supply passage 108 for the B component material is formed.

In addition, the first spinning metal plate 102 is formed with a supply hole 110 for Alli material, and the second spinning metal plate 1
04, a hollow spinning nozzle 11.2 is installed in alignment with the A component material feed hole 110. The spinning nozzle 1
12 extends through the B component material feeding passage 108 and the 30th gold plate 106, and further around the spinning nozzle 1.12 in the third spinning metal plate 106, B from the material supply passage 108 extends. Annular nozzle 1 for component materials
14 is formed.

In the spinneret 100 having the above configuration, the material supply hole 110
When the material for the A component, that is, carbonaceous pitch, is supplied to the spinning nozzle 112, and the material for the B component, that is, the thermoplastic organic synthetic polymer compound, is supplied to the annular nozzle 114 from the material supply passage 108. As shown in FIG. 1, the carbonaceous pitch for producing carbon fiber used in the present invention is A component 2, and a thermoplastic organic synthetic polymer having stringability is arranged around the A component 2. B component 4 formed from a compound
A pitch-based composite fiber IA for producing carbon fibers having the following properties is spun.

FIGS. 2 and 3 show other examples of pitch-based composite fibers for producing carbon fibers.

FIG. 2 shows a so-called multifilamentary pitch-based conjugate fiber IB for producing carbon fibers, in which a large number of A components 2, usually 6 to 100, are dispersed in a B component 4 in a roughly-shaped manner.

FIG. 5 shows an embodiment of a spinneret 100A for producing such a pitch-based composite fiber IB for producing multifilamentary carbon fibers. The spinneret 100A according to this embodiment has the same structure as the spinneret explained in FIG. − ],
, 06 is provided in close contact with the fourth spindle plate 1.16, and the spindle plate 116 is formed with a funnel-shaped gathering nozzle portion 118 for gathering each composite fiber spun from the spinning nozzle. They are different in that they are

Figure 3 shows a pitch-based composite fiber IC for producing carbon fibers in which A component 2 is arranged in a fan shape within a fiber with a circular cross section, and the B component 4 surrounds it, so that the whole has a circular cross section.
shows.

In each of the above embodiments, the pitch-based composite fiber 1 has an A component 2 consisting of carbonaceous pitch for carbon fiber manufacturing, and a B component 4 consisting of a thermoplastic organic synthetic polymer compound having spinnability.
However, the pitch-based carbon fiber used in the present invention is not limited to this.
As shown in Figures to Figure 9, the A component 2 is divided by the B component 4, and a part of the A component 2 is exposed on the yarn surface, so-called split type pitch-based composite fiber 1 ( 1”8~
1° D). The pitch-based conjugate fiber of this example is considered to be a more preferable pitch-based conjugate fiber in the present invention.

Referring to FIG. 6, pitch-based splittable conjugate fiber 1°A for carbon fiber production includes an A component 2 consisting of carbonaceous pitch for carbon fiber production, and is arranged in such a manner that the A component 2 is divided. It is composed of component B 4, which is a thermoplastic organic synthetic polymer compound with good spinnability. At this time, according to this embodiment, the entire outer periphery of component A is not covered with component B, but a portion is exposed to the outside, that is, to the thread surface.

FIGS. 7 to 9 show other embodiments of the splittable composite fiber 1 for producing carbon fibers.

In the embodiment of FIGS. 7 and 8, the radially arranged B
Component 4 provides composite fiber 1'B, 1° C., in which component A 2 is divided into four or eight parts.

Further, in the embodiment shown in FIG. 9, a composite fiber 1"D is provided in which the cross section of the yarn is oval, and the A component 2 is divided into four parts by the B component 4 arranged in parallel. Also in this example, a part of the A component 2 is exposed on the yarn surface.

Fig. 10 to Fig. 13 show the pitch-based splittable conjugate fiber for producing carbon fibers shown in Fig. 8 at 1°C for producing such splittable pitch-based conjugate fibers for producing carbon fibers.
An embodiment of a spinneret that can suitably spin a spinneret is shown schematically.

In this embodiment, the spinneret 200 has first and twentieth gold plates 201 and 202 that are closely attached to each other,
The 20th gold plate 1-202 has an opening 203 opened at the mating surface of the first and 20th gold plates 201 and 202.
A spinning hole 204 communicating with the opening 203 is formed. In addition, the 20th gold plate 202 has an X in FIG.
As shown in FIG. 12, which is a view taken in the direction -X, in this embodiment, eight communication grooves 205 are formed in the radial direction so as to communicate with the opening 203.

On the other hand, the 10th gold plate 201 has the opening 2 of the 10th gold plate.
A component supply passage 206 is formed at a position corresponding to 03, and at the bottom of the supply passage 206, as shown in FIG. 10 and FIG. 11, which is a view taken along Y-Y in FIG.
Four communicating holes 207 communicating with the spinning hole openings 203 are formed at equal intervals in the center and eight in the outer periphery. Also, the first
As understood from FIG. 1, the tenth gold plate 201 has a groove that does not intersect with the communication hole 207 and that
05, eight communication grooves 208 are formed. Some grooves in the communication groove 208 are connected to the spinning hole opening 203.
In this example, the 4
It is formed by connecting two grooves 208. Each communication groove 208 communicates with a B component supply passage 209 formed in the tenth gold plate 201 .

In the spinneret 200 having the above configuration, the material supply hole 206
When the material for component A 2, that is, carbonaceous pitch is supplied from the material supply passage 209, and the material for component B 4, that is, the thermoplastic organic synthetic polymer compound is supplied from the material supply passage 209, the 13th
As can be understood from the figure, component A 2 consisting of carbonaceous pitch for carbon fiber production as shown in FIG. 8 is formed of a thermoplastic organic synthetic polymer compound with good spinnability. Pitch-based splittable conjugate fiber 1°C for producing carbon fibers is spun using component B 4.

In the above-mentioned pitch-based composite fiber for manufacturing carbon fibers which can have various forms, the ratio of A component 2 to the yarn cross-sectional area is 50 to 9.
Therefore, the B component is 50 to 5%.

If the B component 4 is less than 5%, the effect of the B component formed from the thermoplastic organic synthetic polymer compound having spinnability cannot be sufficiently exhibited, and both the spinnability and the composite properties deteriorate. On the other hand, even if B component 4 exceeds 50%, as will be explained later,
Although the spinnability and composite properties are good, component B 4 is not a component that contributes to the physical properties of the carbon fiber as a product and is removed prior to firing, so it should be minimized for economic reasons. Therefore, it is considered undesirable if the B component exceeds 50%.

In addition, in the case of the split type pitch-based composite fiber 1゛ (1°A to 1゛D) shown in Figs. 6 to 9, the ratio of A component 2 to the yarn cross-sectional area is 50 to 90. %, therefore, it is more preferable that component B 4 is 50 to 10%.

As component B 4, a thermoplastic organic synthetic polymer compound is used, particularly polyethylene terephthalate-1-, a copolyester containing at least 60 mol% of ethylene terephthalate, polystyrene, or nylon such as nylon 6 or nylon 66. is preferably used.

In addition, as component A 2, any carbonaceous pitch conventionally used for manufacturing carbon fibers, that is, petroleum-based pitch,
Thermoplastic bits such as coal-based pitch may be used, but
If the softening point of the carbonaceous pitch used exceeds 320° C., thermal decomposition of the thermoplastic organic synthetic polymer compound used as component B 4 will become intense, causing spinning defects, which is not preferable. In addition, the softening point of carbonaceous pitch is 230
If it is lower than 210° C., the melt viscosity balance with component B 4 will be poor, and components A will coalesce, resulting in poor composite properties, which is not preferable.

The pitch-based conjugate fiber for producing carbon fibers produced as described above is bundled and doubled as necessary to form a pitch-based conjugate fiber bundle having a predetermined number of filaments.

According to the present invention, the pitch-based composite fiber bundle has a temperature of 18
It is subjected to a heating process at 0° C. to 350° C. in an oxygen-rich gas atmosphere. In this heat treatment, the vinyl-based composite fiber becomes B
The components are removed to form a pitch fiber bundle as a carbon fiber precursor consisting only of component A, and the pitch fiber bundle is treated to be infusible.

The infusible fiber bundle thus obtained is then
According to the usual method for manufacturing pitch-based carbon fibers, (a) the infusible fiber bundle is pre-carbonized by heating to 500 to 1500°C in an inert girth atmosphere in a pre-carbonization furnace; (b) Next, carbon fibers are produced by heating the pre-carbonized fiber bundle in a carbonization furnace to 1500 to 2000 °C in an inert gas atmosphere to carbonize it, and further heating to 3000 °C to graphitize it. be done.

According to the present invention, it is possible to continuously and stably spin yarn using various carbonaceous pitches without yarn breakage, and moreover,
Carbon fibers (filaments) with a small diameter of ~7 μm can be easily produced.

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

Example 1 Contains approximately 55% optically anisotropic phase and has a softening point of 232°C
A carbonaceous pitch with the following properties was used as the precursor pitch. Using a cylindrical centrifugal separator with an effective volume of 200 mg, this precursor pitch was continuously separated into a pitch with a large amount of optically anisotropic phase and a pitch with a large amount of optically isotropic phase at a temperature of 370°C and a centrifugal force of 30,000 G. It was separated into two parts and each was extracted.

The obtained pitch containing a large amount of optically anisotropic phase contained 98% of the optically anisotropic phase, had a softening point of 265° C., and had a quinoline solubility of 29.5%. This carbonaceous bitch was used as a material for component A. As the material for component B, polyethylene terephthalate having an intrinsic viscosity of 0.65 in an orthochlorophenol solution at 25° C. was used.

A split spinneret with a structure as shown in Figures 10 to 13, with a discharge hole diameter of 0.30 mm and a number of discharge holes of 24, is used, and the temperature of the spinneret portion is maintained at 310°C. Then, spinning was carried out for 60 minutes at a winding speed of 800 m/min. Stable spinning was carried out continuously without any yarn breakage during spinning.

The diameter of each single yarn (filament) obtained was about 19 μm, the number of A components was 8, and the fineness of each A component was about 0.38 denier, and the Δ components did not join together and were completely independent. It had a uniform morphology and showed a good composite state. Further, the ratio of component A/component B was 85/15 in terms of the cross-sectional area of the yarn. Furthermore, the obtained pitch-based composite fiber bundle was free of fuzz and had excellent handling properties.

The pitch-based composite fiber bundle is made by applying dimylphenylbolysiloxane (phenyl group content: 25 mol%) with a viscosity of 40 centistokes at 25° C. to the yarn using an oiling roller in order to impart lubricity and cohesiveness to the yarn. Approximately 0.8% was added to the total amount.

Subsequently, after doubling 10 of these pitch-based composite fiber bundles, the threads were passed through a continuous infusibility furnace in an oxygen-rich gas atmosphere (oxygen/nitrogen = 40/60) with a furnace entrance temperature of 180°C and a maximum temperature of 298°C at a speed of 1 m. It was introduced continuously at 1/min. temperature 180
The temperature was raised at a rate of 6°C/min from °C to 260°C, held at 260°C for 3 minutes, and then raised at a rate of 5°C/min to a maximum temperature of 298°C, and held at 298°C for 2 minutes.

By this heat treatment, the B component in the pitch-based composite fibers was decomposed, a pitch-based fiber bundle was formed, and the pitch-based fiber bundle was made infusible.

The infusible yarn was continuously threaded through a continuous carbonization furnace having a nitrogen gas atmosphere with a furnace entrance temperature of 300°C and a maximum temperature of 1500°C at a threading speed of 1 m/min for carbonization. Further, the carbonized yarn was placed in a continuous graphitization furnace having an argon gas atmosphere, and graphitized at 2500''C for 15 minutes.

The carbon fiber thus obtained has almost no fuzz, a filament fineness of approximately 0.32 denier, a tensile modulus of 67 t/mm, and a tensile strength of 320.
K, g/mm'', and the fiber had extremely excellent properties.

Example 2 Contains about 55% optically anisotropic phase and has a softening point of 232°C
A carbonaceous pitch with the following properties was used as the precursor pitch. This precursor pitch was collected using a cylindrical centrifugal separator with an effective volume of 200 m42 at a temperature of 370°C and a centrifugal force of 30,000 G.
As a result, the bitge containing many optically anisotropic phases and the pitch containing many optically isotropic phases were continuously separated and extracted.

The obtained pitch containing a large amount of optically anisotropic phase contained 98% of the optically anisotropic phase, had a softening point of 265° C., and had a quinoline solubility of 29.5%. This carbonaceous pitch was used as the material for the A component. As the material for component B, polystyrene having an intrinsic viscosity of 0.73 in a toluene solution at 30° C. was used.

Using a spinneret with a structure as shown in Fig. 5, in which the number of spinning nozzles per filament is 36, the diameter of the discharge hole is 10 mm, and the number of discharge holes is 30, Maintaining the temperature at 310℃, winding speed 1000m
/min for 60 minutes. Stable spinning was carried out continuously without any yarn breakage during spinning.

An oil in water type oil agent consisting of a smoothing agent, an antistatic agent, and an emulsifier was applied to the spun pitch-based composite fiber bundle (yarn) by roller contact. The adhesion amount was 0.7% by weight based on the yarn.

The diameter of each single yarn (filament) obtained was approximately 41 μm, the number of A components was 30, and the diameter of each A component was approximately 6.2 μm.
m, there was no merging of the A components, and the A components had a completely independent and uniform morphology, showing a good composite state. Also, A component/B
The ratio of the components was 85/15 based on the cross-sectional area of the yarn. Furthermore, the obtained pitch-based composite fiber bundle was free of fuzz and had excellent handling properties.

Subsequently, this pitch-based composite fiber bundle is unwound from the pitch-based composite fiber bundle package, and the pitch-based composite fiber bundle is adjusted to 0.0% with respect to the A component.
A tension of 0.2g/denier was applied, and the furnace entrance temperature was 1.80.
℃, the thread was threaded through a continuous infusibility furnace in an oxygen-rich gas atmosphere (oxygen/nitrogen = 4.0/60) with a maximum temperature of 298℃ at a speed of 1.
Continuous introduction was carried out at m/min. Temperature 180℃ to 250℃
The temperature was raised at a rate of 5°C/min to 250°C, held at 250°C for 3 minutes, and then raised at a rate of 5°C/min to a maximum temperature of 298°C.
It was held at C for 2 minutes.

Through this heat treatment, the B component in the pitch-based composite fibers is dissolved and removed, forming a pitch-based fiber bundle, and
The pitch-based fiber bundle was made infusible.

The infusible yarn was continuously threaded through a continuous carbonization furnace having a nitrogen gas atmosphere with a furnace entrance temperature of 300°C and a maximum temperature of 1500°C at a threading speed of 1 m/min for carbonization. Further, the carbonized thread was placed in a continuous graphitization furnace having an argon gas atmosphere, and graphitized at 2500° C. for 15 minutes.

The carbon fiber thus obtained has almost no fluff, a single filament diameter of about 5.0 LLm, and a tensile modulus of 71 t/mm2. Tensile strength is 320 Kg
/ mm 2 and was a fiber with extremely excellent properties.

As described above, according to the present invention, by using a pitch-based composite fiber as a pitch fiber precursor, various carbonaceous pitches can be continuously and stably spun without thread breakage. In addition, it is easy to handle, can be easily bundled and doubled as desired, and can produce small-diameter, high-performance pitch-based carbon fibers extremely efficiently.

[Brief explanation of drawings]

1 to 3 are cross-sectional views of examples of pitch-based composite fibers for producing carbon fibers. FIGS. 4 and 5 are cross-sectional views showing the structure of a spinneret for producing pitch-based composite fibers for producing carbon fibers. 6 to 9 are cross-sectional views of other examples of pitch-based composite fibers for producing carbon fibers. FIG. 10 is a sectional view showing the structure of a spinneret for producing pitch-based splittable composite fibers for producing carbon fibers according to the present invention. FIG. 11 is a plan view taken along line XX in FIG. 10. FIG. 12 is a plan view taken at 41 Y-Y in FIG. 10. FIG. 13 is an explanatory diagram showing the manner in which each material is supplied to the spinneret of FIG. 10. l, 1°: Pitch-based composite fiber for carbon fiber production 2: A component 4: B component

Claims (1)

[Claims] 1) Component A consisting of carbonaceous pitch for producing carbon fibers and B consisting of a thermoplastic organic synthetic polymer compound with good spinnability.
A step of spinning a pitch-based composite fiber formed from the components and, if necessary, converging and doubling to produce a pitch-based composite fiber bundle, heating the pitch-based composite fiber bundle in an oxygen-rich gas atmosphere. Production of pitch-based carbon fibers, which comprises the steps of: removing the B component to form a pitch fiber bundle, and making the pitch fiber bundle infusible; and further firing the infusible fiber. Method. 2) The method for producing a pitch-based carbon fiber according to claim 1, wherein the ratio of the A component to the yarn cross-sectional area of the pitch-based composite fiber is 50 to 95%, and the B component is 50 to 5%. 3) The carbonaceous pitch for producing carbon fibers forming component A is a thermoplastic pitch with a softening point of 230°C to 320°C;
The thermoplastic organic synthetic polymer compound forming the component is polyethylene terephthalate, a copolyester containing at least 60 mol% of ethylene terephthalate component,
The method for producing pitch-based carbon fiber according to claim 1, wherein the pitch-based carbon fiber is polystyrene or nylon. 4) The step of removing component B and making the pitch fiber bundle infusible is 18
Claim 1: The method is carried out by heating at 0°C to 350°C.
The method for producing pitch-based carbon fiber described above.