JPH06108316A - Production of pitch-based carbon fiber - Google Patents

Abstract

PURPOSE:To obtain a method for producing optically isotropic pitch-based carbon fiber having a high strength, elastic modulus, heat and electric conductivities and good in sliding property. CONSTITUTION:This method for producing optically isotropic pitch-based carbon fiber is to melt and mix (B) 10-50 pts.wt. optically isotropic pitch obtained by polymerizing naphthalene in the presence of a Lewis acid catalyst and having 200-270 deg.C softening point with (A) 100 pts.wt. optically isotropic pitch prepared by heat-treating pitch while blowing an oxygen-containing gas, then to spin the resultant mixed pitch, to infusibilize the formed fiber and to carbonize the infusibilized fiber. This carbon fiber contains an optically anisotropic component.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved method for producing an optically isotropic pitch-based carbon fiber containing an optically anisotropic component. More specifically, the present invention has excellent spinnability, has an optically isotropic surface layer portion, and contains an optically anisotropic component inside thereof, and therefore has excellent slidability or conductivity. The present invention relates to a method for producing an isotropic pitch-based carbon fiber.

[0002]

2. Description of the Related Art The mechanical performance of pitch-based carbon fibers is greatly influenced by the performance of spinning pitch, and optical isotropic pitch provides general-purpose (GP) carbon fibers having low strength and elastic modulus, while It is known that high-performance (HP) carbon fibers having high strength and elastic modulus can be obtained from mesophase (liquid crystal) pitch containing a mechanically anisotropic phase.

However, when carbon fibers are produced by using mesophase pitch, when the mesophase pitch is spun,
Since the fibers are arranged in the fiber axis direction, cleavage is likely to occur on the fiber surface during carbonization and graphitization. In order to improve this problem, various studies have hitherto been made. Therefore, in JP-A-62-170528, in the pitch adjusting step, an optically isotropic pitch is added to the optically anisotropic pitch,
By mixing, the surface layer is an optically isotropic component,
And a method in which the central portion of the carbon fiber has a two-layer structure composed of an optically anisotropic component and does not cause cleavage on the fiber surface of the carbon fiber.

However, in this method, since the optically isotropic pitch is simply melt-mixed with the optically anisotropic pitch to obtain the spinning pitch, it is difficult to uniformly disperse the optically anisotropic component. As a result, there is a problem that the spinnability is poor and that the fully satisfactory activated carbon fiber having the above double structure cannot be obtained.

[0005]

Under these circumstances, the present invention efficiently uses general-purpose carbon fibers that are inexpensive and have abundant pitch as raw materials, have excellent spinnability, and have good fiber physical properties. It is made for the purpose of providing a manufacturing method.

[0006]

Means for Solving the Problems As a result of intensive studies to achieve the above-mentioned object, the inventors of the present invention have found that the optical anisotropy pitch and the optical anisotropy during spinning do not easily cause optical anisotropy. After mixing with a substantially optically isotropic pitch to be isotropic at a predetermined ratio, the mixture is spun at a predetermined temperature, whereby the surface layer shows optical isotropy and the inside is optically different. It has been found that a carbon fiber having a dual structure, which exhibits a directionality, can be obtained. The present invention has been made based on such findings.

That is, according to the present invention, (A) the softening point 2 obtained by heat treatment while blowing an oxygen-containing gas into the pitch.
With respect to 100 parts by weight of a substantially optically isotropic pitch of 30 to 300 ° C., (B) a substantially soft optical property at a softening point of 200 to 270 ° C., which has a property of being converted into optical anisotropy by stress during spinning. Softening point 200-270 ° C. obtained by polymerizing isotropic pitch, for example, naphthalene in the presence of Lewis acid catalyst.
The present invention provides a method for producing pitch-based carbon fibers, which comprises melt-mixing 10 to 50 parts by weight of the substantially optically isotropic pitch, and then melt-spinning the mixture by a conventional method.

In the spinning pitch of the present invention, the substantially optically isotropic pitch used as the component (A) has a softening point of 230 to 300 ° C. obtained by heat treatment while blowing an oxygen-containing gas into the raw material pitch. belongs to. The type of the raw material pitch is not particularly limited as long as it gives a pitch having the above-mentioned softening point by being heat-treated while blowing an oxygen-containing gas, but it is not particularly limited, for example, crude oil distillation residue Oil, fluid catalytic cracking (FC
C) Filtration, distillation, hydrogenation and contact of petroleum pitch (heavy oil) such as heavy oil, naphtha cracked residual oil, ethylene bottom oil, coal tar and coal liquefied oil (coal heavy pitch) Examples thereof include those prepared through a treatment step such as cracking, and among these, fluid catalytic cracking heavy oil is preferable in terms of reactivity to oxygen, high softening point and the like.

The raw material pitch may be treated by any method as long as it is a method of giving a pitch having substantially the above-mentioned softening point while being substantially optically isotropic by performing a heat treatment while blowing an oxygen-containing gas. However, the following treatment methods are preferably used. That is, first, while blowing the oxygen-containing gas into the raw material pitch, at normal pressure or
Under a slight pressure of about 0.3 kg / cm ² · G, preferably 300 to 3
Heat treatment is performed at a temperature in the range of 70 ° C., and the heat treatment is stopped immediately before the generation of the optically anisotropic component. In this case, the heat treatment time is usually about 5 to 12 hours. By this heat treatment, quinoline insoluble matter (hereinafter referred to as QI)
Content is as low as 0 to 15% by weight, and the degree of polymerization / crosslinking is 210 to the extent that it does not contain an optically anisotropic component.
An optically isotropic pitch having a softening point of about 280 ° C. can be obtained. Next, if necessary, the substantially optically isotropic pitch thus obtained is blown with an oxygen-containing gas, and usually 100 Torr or less, preferably 5 to 3
Heat treatment is performed under a reduced pressure of 0 Torr at a temperature of about 300 to 370 ° C. for 10 minutes to 3 hours, preferably for 20 minutes to 1 hour to set the softening point of the pitch to 230 to 30.
You may raise to 0 degreeC. Examples of the oxygen-containing gas used in the above heat treatment include air and oxygen-rich gas, but air is preferable from the viewpoint of easy availability. The amount of oxygen used is usually 1 kg of pitch,
It is 0.2 to 5 NL / min, preferably 0.5 to 2 NL / min, and in the case of air, it is about 4 times the amount of oxygen. When an inert gas such as nitrogen is used instead of an oxygen-containing gas, it is difficult to maintain the optically isotropic structure, the amount of optically anisotropic components increases, and the object of the present invention cannot be achieved.

This treatment may be carried out by either a batch type or a continuous type, but when the heat treatment is continuously carried out, the apparatus is not particularly limited as long as it is an extruder with a deaeration hole. Examples thereof include a pelletizer for producing molded particles, a mixing / kneading machine and the like, and a self-cleaning type extruder which also serves to deaerate and remove various by-products associated with polycondensation.

The substantially optically isotropic pitch of the component (A) thus obtained has a QI content of 0 to 25% by weight.
Degree, generally as low as 5% by weight or less, and 230 to 3
It has a high softening point of 00 ° C. (measured by the Mettler method).
If the softening point is less than 230 ° C, the strength of the obtained fiber will be poor, and if it exceeds 300 ° C, the viscosity will be too high and spinning will be difficult, and an optically anisotropic component will be easily mixed. In the spinning pitch of the present invention, as the component (B), a substantially optically isotropic pitch having a softening point of 200 to 270 ° C. having a property of being converted into optical anisotropy by a stress during spinning, for example, naphthalene. In the presence of a Lewis acid catalyst, a substantially optically isotropic pitch having a softening point of 200 to 270 ° C. obtained by polymerization is used.

In the polymerization of naphthalene, naphthalene is heat-treated at a temperature of 230 to 300 ° C. in the presence of a Lewis acid catalyst. The treatment time depends on the temperature and the type and amount of the catalyst, and cannot be unconditionally determined, but the polymer is a substantially optically isotropic pitch,
And it heat-processes until it becomes a softening point of 200-270 degreeC. The treatment time is generally about 10 minutes to 5 hours. Examples of the Lewis acid catalyst used at this time include hydrogen fluoride, boron trifluoride, anhydrous aluminum chloride, anhydrous ferric chloride, etc. These may be used alone or in combination of two or more. May be. or,
In order to facilitate mixing with the component (A) and to carry out spinning smoothly, the softening point of the component (B) is close to that of the component (A).
It is preferably in the range of 0 to 270 ° C.

In the present invention, the pitch of the component (B) is 10 to 100 parts by weight of the pitch of the component (A).
The mixture is melt mixed at a ratio of 50 parts by weight to obtain an optically isotropic pitch for spinning.

The softening point of the spinning pitch thus obtained is usually in the range of 210 to 290 ° C., and the QI
The content is usually in the range of 0 to 15% by weight.

The above spinning pitch is spun by a conventionally known melt spinning method. Since this pitch is an optically isotropic pitch, it has good spinnability, and since the pitch of the component (B) is converted to optical anisotropy during spinning, the spun fiber shows isotropic surface layers, The inside has a double structure showing anisotropy. This double structure can be confirmed by observing the cross section of the fiber with a polarization microscope. The reason why the optically anisotropic portion concentrates inside the fiber is unknown, but the influence of the stress distribution in the spinning nozzle is considered.

By infusibilizing and carbonizing this spun fiber by a conventionally known method, the spun fiber has a higher strength, a higher elastic modulus, a higher thermal conductivity and a higher electric conductivity than the conventional optically isotropic pitch carbon fiber. An optically isotropic pitch-based carbon fiber having high conductivity and good slidability can be obtained.

[0017]

EXAMPLES The present invention will be described in more detail by way of examples, which should not be construed as limiting the invention thereto.

Example 1 (1) Preparation of (A) Component Pitch FCC decant oil was flash distilled to give 495-5.
FCC heavy oil (softening point 70 ° C.) obtained by cutting a fraction of 00 ° C./normal pressure was used as a raw material pitch and
By heat-treating for 9 hours while blowing 1 NL / kg · min of air at 0 ° C, an optical isotropic pitch with a softening point of 250 ° C (Mettler softening point) and a QI content of 3% by weight is obtained with a yield of 70%. Was obtained. Observation of this pitch with a polarization microscope revealed that it contained no optically anisotropic component. (2) Preparation of Component (B) Pitch Mixing was carried out at a ratio of 2 mol of hydrogen fluoride and 0.5 mol of boron trifluoride to 1 mol of naphthalene, and polymerization was carried out at 240 ° C. for 30 minutes. After the polymerization, the Lewis acid catalyst was removed to obtain an optically isotropic pitch having a softening point of 230 ° C. (Mettler softening point). Observation of this pitch with a polarization microscope revealed that it contained no optically anisotropic component. (3) Preparation of spinning pitch Optically isotropic pitch 100 obtained in the above (1)
30 parts by weight of the optically isotropic pitch obtained in (2) above was added to parts by weight, and the mixture was melt-mixed and stirred at 280 ° C. for 30 minutes to prepare a spinning pitch. When this pitch was observed with a polarization microscope, it was an optically isotropic pitch. The spinning pitch had a softening point of 245 ° C. (Mettler softening point) and a QI content of 3% by weight.

This spinning pitch was spun at a spinning temperature of 270 ° C.
Then, a 18 μm pitch fiber was obtained by spinning from a nozzle having an inner diameter of 0.3 mm by a melt spinning method at a winding speed of 500 m / min. As a result of observing the cross section with a polarization microscope, it was confirmed that the surface layer had a double structure in which the surface layer was isotropic and the inside was anisotropic. This pitch fiber was infusibilized by heating from 120 ° C to 300 ° C at an infusibilizing rate of 3 ° C / min. After that, 1500 in an inert gas atmosphere
Carbonized at ℃ and 2000 ℃, the physical properties are shown in the following table.

[0020]

[Table 1]

Comparative Example 1 80 parts by weight of an optically isotropic pitch having a softening point of 265 ° C. and 20 parts by weight of an optically anisotropic pitch having a softening point of 265 ° C. were obtained in the same manner as in Example 1 (1). After finely pulverizing and mixing, the mixture was melted and stirred at 350 ° C. to obtain a spinning pitch. This pitch was spun at a spinning temperature of 290 ° C., but many yarn breakages prevented spinning.

[0022]

EFFECTS OF THE INVENTION According to the present invention, it is possible to easily obtain a spinning pitch, which has an optically isotropic pitch but is partially converted into an optically anisotropic pitch during spinning. This spinning pitch has good spinnability, high strength, high elastic modulus,
It is possible to provide an optically isotropic pitch-based carbon fiber having excellent thermal conductivity and electrical conductivity and having good slidability.

Claims (2)

[Claims] 1. The stress during spinning is (B) to 100 parts by weight of (A) a substantially optically isotropic pitch having a softening point of 230 to 300 ° C. obtained by heat treating while blowing an oxygen-containing gas into the pitch. 10 to 50 parts by weight of a substantially optically isotropic pitch having a softening point of 200 to 270 ° C., which has a property of converting to optical anisotropy, is melt-mixed, and this mixture is then mixed.
A method for producing an optically isotropic pitch-based carbon fiber containing an optically anisotropic component, characterized by spinning. 2. (B) A substantially optically isotropic pitch having a softening point of 200 to 270 ° C., which has a property of being converted into optical anisotropy by a stress during spinning, has naphthalene in the presence of a Lewis acid catalyst. The method for producing an optically isotropic pitch-based carbon fiber according to claim 1, wherein the pitch is obtained by polymerization.