JPS6254789A - Production of precursor pitch for carbon fiber - Google Patents

Abstract

PURPOSE:To improve the spinnability, infusibility, and carbonizability, by extracting tar derived from coal with an arom. solvent to remove free carbon, distilling the tar to obtain pitch substantially free from free carbon, and heat- treating the pitch under reduced pressure or while blowing an inert gas therein. CONSTITUTION:Precursor pitch having a softening point of 200 deg.C or above, contg. 45-65wt% benzene-insoluble matter and 0.5wt% or less quinoline-insoluble matter, and comprising an isotropic structure is produced. In order to produce pitch having such properties, an arom, solvent (e.g., benzene, toluene, or xylene) is added to tar derived from coal (preferably high-temp. carbonization tar) to separate and remove free carbon contained in the tar. The tar is distilled to remove the solvent and low-boiling fractions contained in the tar, thereby obtaining pitch substantially free from free carbon. The pitch is heat-treated at a temp. of 350-500 deg.C under reduced pressure or while an inert gas is blown therein.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is directed to GP (General Purpose)
Precursor used to produce grade carbon fiber
The present invention relates to a method for producing pitch, and in particular to a method for producing precursor pitch that uses coal-based high-temperature carbonized tar as a raw material and has excellent spinnability, infusibility, and carbonization properties.

<Prior art and its problems> Methods for producing carbon fiber can be broadly divided into methods using synthetic fibers such as polyacrylonitrile (PAN) as raw materials, and methods using tar pitch such as petroleum pitch and coal tar pitch as raw materials. In addition to being of high rank, the carbonization yield is also low. On the other hand, the latter method generally has the disadvantage that it is difficult to make it infusible if it has good spinnability, and it is difficult to make it spinnable if it has good infusibility.

To obtain coal tar by carbonizing coal, high-temperature carbonization (t
ooo~1300℃) and low-temperature carbonization (500℃).
~900°C).

There is a method for producing precursor pitch for carbon fibers using low-temperature carbonized tar as a starting material (Japanese Unexamined Patent Publication No. 1342/1982), but the precursor pitch obtained by this method is
Since the aromaticity is low and the amount of fixed carbon is low, the yield of carbon fiber from precursor pitch is low and the strength of the carbon fiber is not sufficient.

Ichiriki-mae-temperature carbonization tar has undergone a thermal history at a very high temperature of 1,000 to 1,300°C, so although the tar itself is highly aromatic, it also contains polymer components produced by thermal polymerization and thermal decomposition. Low-molecular-weight components produced by this process still exist in tar.

When preparing precursor pitch for carbon fiber from this high-temperature carbonization tar, it must be heat-treated and polymerized in order to improve its spinnability, infusibility, and carbonization properties. Because it contains a large amount of low molecular weight components, even if this tar is heat-treated to prepare precursor pitch for carbon fibers, the low molecular weight components remain.As a result, a precursor pitch with low viscosity and excellent spinnability is produced. Although pitch can be obtained, the infusibility is poor.

In order to improve the infusibility, when heat treatment is further carried out to form a polymer, a so-called mesophase is easily generated, and this mesophase becomes a factor that impedes spinnability. When the precursor pitch is made into fibers, this mesophase becomes knots in the fibers and causes yarn breakage, and furthermore, when carbonized, it also causes a decrease in fiber strength.

<Object of the Invention> The object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a method for producing precursor pitch for carbon fibers having excellent spinnability, infusibility, and carbonization properties. .

<Structure of the Invention> Among coal-based tars, especially high-temperature carbonized tars, tars with a quinoline insoluble content of 5% by weight or less have few low-molecular components and contain aromatic compounds such as benzene, toluene, and xylene. The present invention was developed based on the knowledge that if the polymer components in tar are separated and removed using light oil, the generation of mesophase can be sufficiently suppressed in the subsequent heat treatment.

In other words, the present invention provides a carbon fiber precursor pitch having a softening point of 200°C or higher, a benzene insoluble content of 45 to 65% by weight, a quinoline insoluble content of 0.5% by weight or less, and an optically isotropic structure. During production, an aromatic solvent is added to coal-based tar to separate and remove the free carbon in the tar, and then a solvent and light components in the tar are added to separate and remove the free carbon in the tar to form a free carbon. A precursor for carbon fiber, characterized in that a pitch substantially free of fr is obtained, and this pitch is heat-treated at a temperature of 350 to 500°C under a certain pressure or under $20F with inert gas blowing. - Provides a method for manufacturing pitch.

The present invention will be explained in more detail below.

The inventors of the present application have developed a carbon fiber precursor with excellent spinnability, infusibility, and carbonization properties using coal-based tar as a raw material.
It has been found that the pitch can be obtained in the following manner.

High-temperature carbonized tar is suitable as a coal-based tar.In particular, among the tars obtained by high-temperature carbonized coal, tar with a free carbon content (same as the quinoline insoluble content) or 5% by weight or less is used as a starting material. Well, this tar,
An aromatic solvent such as benzene, toluene, xylene, or coal-based light oil is added in an amount of 1 to 5 times the amount of tar, and free carbon and free carbon in the tar are removed by centrifugation, static separation, vacuum filtration, pressure filtration, etc. After separating and removing the polymer components,
The free carbon in the tar is separated by adding the solvent, and the light components in the tar are removed to obtain a pitch that does not substantially contain free carbon (free carbon content is 0.01% by weight or less). By heating at 350 to 500°C under reduced pressure or inert gas blowing conditions, it has good thermal stability, excellent spinnability and infusibility,
G P (Gene
ral Purpose) Precursor pitch for carbon fibers can be easily produced.

Tar obtained by carbonizing coal at a high temperature of 1000 to 1300°C is impregnated with solid particles called free carbon in an amount of about 1 to 20% by weight. This free carbon is produced by gas-phase thermal decomposition of tar vapor in a coke oven during the carbonization process, and has a diameter of 1-
It is a solid particle with a spherical shape and a dark color.

It is known that this free carbon does not dissolve in any organic solvent, and this free carbon is usually referred to as the quinoline-insoluble matter in tar. This free carbon is an undesirable component as a carbon fiber precursor pitch. This is because this free carbon can clog the nozzle during melt spinning, and
When pitch is made into fibers, it becomes knots in the fibers, which can cause yarn breakage and reduce the strength of the fibers.

The free carbon content in tar varies greatly depending on many factors, such as the type of coal used, the temperature of the coke oven, the type of coke oven, and the bulk density of the coal in the coke oven. The lower the tar content, the lower the content of high molecular components and low molecular components in the tar.

The high free carbon content in tar means that the tar vapor undergoes a lot of thermal history in the coke oven, and the more thermal history it undergoes, the more deterioration occurs due to thermal polymerization. Tar becomes more polymerized and heavier, and tar becomes lower molecular and lighter due to thermal decomposition.

The present inventors investigated a large number of tars, and found that if the free carbon content in tar is 5% by weight or less, the content of low molecular components is particularly low. It has been found that by doing so, it is possible to finally obtain an excellent precursor pitch.

Methods for obtaining coal tar by carbonizing coal can be roughly divided into two methods: high-temperature carbonization (1000-1300°C);
There is a method using low-temperature carbonization (500-900℃), but the coal tar obtained by high-temperature carbonization has much higher aromaticity, and this coal tar with a high aromatic δ group value is used as a starting material. (Thus, a precursor pitch for carbon fibers with high aromaticity is obtained, and these characteristics greatly contribute to an increase in carbonization yield and development of strength of carbon fibers when made into carbon fibers.

Free carbon in tar is a precursor for carbon fiber.
Since this free carbon is an undesirable component as pitch, it must be separated and removed, but in this separation and removal operation, benzene, toluene, xylene,
The present invention is characterized by the use of an aromatic solvent such as coal-based light oil (a mixture of benzene, toluene, and xylene).

In other words, the free carbon content is +1+- less than 5% by weight.
44-, -t-IJ-(>, pre1*+1<+hI1.M
1uC: A method for separating and removing free carbon. The free carbon content at this time is 0. , otmfd% or less. If this exceeds 0.01% by weight, 1.
This is because this free carbon blocks the nozzle or forms knots in the fibers, significantly reducing the tensile strength of the fibers.

Adding an aromatic solvent to coal tar lowers the viscosity of the solution and makes separation easier.
Two functions can be considered: tPm is removed from the polymer components present in the tar (components that do not dissolve in aromatic solvents) together with free carbon.

Tar, from which free carbon has been removed, is used as a starting material, and when preparing precursor pitch for carbon fibers, heat treatment is performed to remove low molecular weight components and promote polymerization, but the polymer components present in the tar are can become a mesophase component in this heat treatment.

This mesophase component is a so-called quinoline-insoluble solid particle, and is not preferable as a precursor pitch for a general-purpose carbon fiber having an isotropic structure as well as free carbon. In other words, if the nozzle is blocked or fibers are formed during melt spinning, knots may be formed in the fibers, resulting in a significant decrease in fiber strength.

As described above, the present invention is characterized in that in the heat treatment, the polymer components in the tar that easily become mesophase components are separated and removed using an aromatic solvent. If a solvent with a high dissolving power such as pyridine, quinoline, coal-based medium oil, or heavy oil is used, the polymer components in the tar will be dissolved, and mesophase will be easily generated during the subsequent heat treatment process.

When using aliphatic solvents such as n-hexane, cyclohexane, etc., since the high-temperature dry distillation tar has a very high J6 group property, the compatibility between the tar and the aliphatic solvent is weak, and only the polymeric components in the tar are used. In addition, even the effective components that become carbon fiber precursor pitch are removed, resulting in an extremely low yield of precursor pitch.

To add aromatic δ-based light oil to high-temperature carbonized tar and separate and remove free carbon and polymer components in the tar, a temperature below the boiling point of the above-mentioned aromatic solvent is sufficient, and usually 40°C.
It can be operated at relatively low temperatures of ~70°C. Regarding the solvent ratio, 1 to 5 times the amount is optimal, and if the solvent ratio is less than 1,
The viscosity of the solution does not decrease sufficiently, making it extremely difficult to separate and remove free carbon and polymeric components in tar. Furthermore, when the solvent ratio exceeds 5, not only the polymer components in the tar but also
Not only is the effective component, which is the carbon fiber precursor pitch, removed, but there are disadvantages in terms of equipment and cost. From the above results, the optimal solvent ratio is 1 to 5 times the amount.

In this way, aromatic solvents are added to high-temperature carbonized tar.
After separating and removing the free carbon and polymer components in the tar using four-core separation, static separation, and filtration methods, the solvent and light components in the tar are removed to produce pitch (free carbon) that does not contain free carbon. Content is 0.01% by weight
below).

Next, this pitch is heat-treated at 350 to 500°C under reduced pressure or inert gas blowing conditions to remove low molecular components, advance aromatization and polymerization, and create a carbon fiber precursor. - Get the pitch.

The degree of pressure reduction is preferably in the range of 30 mm/11 g or less. The reason for this is that if the degree of vacuum exceeds 30 mm and 11 g, the low molecular weight components in the pitch will not be sufficiently removed. It is also good to carry out the heat treatment while blowing inert gas such as nitrogen, argon, helium, etc. This is because low molecular weight components are distilled out of the yarn together with the inert gas by blowing inert scum in this way. The heat treatment is preferably carried out at a temperature of 350 to 500°C. If the temperature is less than 350°C, polymerization of the pitch will be insufficient, and if it exceeds 500°C, polymerization will proceed too much and mesophase will be generated.

In particular, among coal-based high fA'iZ distilled tars, high-temperature dry distilled tars with a free carbon content of 5% by weight or less
Using tar as a starting material, free carbon and polymer components in the tar are separated using an aromatic solvent.1. Mountain:
Pitch with a free carbon content of 0.01% by weight or less obtained by removing it from P-117 mountains n ridges 1 island Ru l. Even in the heat treatment, the generation of mesophase is sufficiently suppressed, and polymer components represented by benzene-insoluble components can be easily obtained.

The precursor pitch obtained is a pitch consisting of optically equidistant fibers, with a softening point of 200° C. or higher, a benzene insoluble content of 45 to 65 tonne weight %, a quinoline insoluble content of 0.5% by weight or less, Excellent spinnability, infusibility, and carbonization properties.

If the softening point is less than 200°C, infusibility will not proceed sufficiently. If the benzene insoluble content is 45 tonne weight % or less, melt spinnability is excellent, but there is a problem in infusibility, and fibers tend to fuse and melt during the infusibility treatment. If the benzene insoluble content is 65% by weight or more, the viscosity becomes extremely high, making melt spinning difficult. Quinoline insoluble content is 0
．． If it exceeds 5% by weight, this quinoline insoluble content may clog the nozzle or form knots in the fibers, reducing the tensile strength of the fibers.

EXAMPLES Next, the present invention will be specifically described with reference to Examples and Comparative Examples.

<Example 1> Tar obtained by high-temperature carbonization of coal (quinoline insoluble content =
Free carbon content = 2.6% by weight) 1tf (177
Add 3i11 parts of toluene to 1 part, and heat at 60°C.
After stirring and mixing at 60° C., the mixture was allowed to stand for 30 minutes. After that, 70% of the supernatant was removed and the supernatant was heated to 290°C.
The toluene and light oil in the tar were distilled off. The obtained pitch was as follows: Soft weight ratio = 80°C, Benzene insoluble content = lz, 0ffi amount%, Pyricine insoluble content = 3.2
LMW%, quinoline insoluble content = 0. It was less than the old weight%.

50% of this pitch that does not substantially contain free carbon.
Using a 0 ml flask, vacuum level 6 n+a+lI
A precursor pitch for carbon fibers was obtained by heat treatment at 420°C with gabs and an optically isotropic structure with a softening point of 220°C, a benzene insoluble content of 50.2% by weight, and a quinoline insoluble content of 00% by weight or less. .

This precursor pitch was melt-spun at 280°C and subjected to infusibility treatment under the following conditions.
Carbonization treatment was performed at 000°C to obtain carbon fibers. This fiber is
Fiber diameter: 8.2-1, tensile strength: 93 g/nm, elastic modulus: 4
．． It was 1t, /-.

・Infusibility conditions: 30a + 1n at room temperature to 150°C 311r at 150 to 310°C 111 at 310°C Retention air flow rate = 60mi/win <Example 2> High temperature carbonization tar used in Example 1 (quinoline insoluble content = 2
．． 6% by weight) to 1 part by weight, coal-based light oil (benzene = 851fi%, toluene = 10% by weight, xylene-5
To this mixed solution, 3% by weight of diatomaceous filter aid was added and the concentration was adjusted to 3.0 g/cd at a temperature of 75°C. The mixture was filtered under pressure of . The obtained filtrate was distilled at 290°C to remove coal-based light oil and light oil. The obtained pitch is the softening point =
At 85°C, benzene insoluble content was 15.0% by weight, pyridine insoluble content was 5.0% by weight, and quinoline insoluble content was 0.01% by weight or less.

This pitch that does not substantially contain free carbon is 500%
Using a m1 flask, at a vacuum level of 8 mmHg abs,
Heat treated at 430°C, softening point 240°C, benzene insoluble content = 54.2% by weight, quinoline insoluble content = 0.021r
A carbon fiber precursor pitch having an optically isotropic structure of Cζ% was obtained.

This precursor pitch was melt-spun at 295°C, and the actual M
Infusible treatment was performed under the same conditions as in Example 1, followed by carbonization treatment at 1000° C. in argon to obtain carbon fibers. This fiber has a fiber diameter of 9.0-1 and a tensile strength of 102 Kg/m.
Elastic modulus4. It was OL/-.

<Example 3> Tar obtained by high-temperature carbonization of coal (quinoline insoluble content =
4.6% by weight) 2.51 parts by weight of benzene
+Tt and centrifuged at 50°C to remove free carbon and crystal molecules from the tar with the heavy liquid.
I++'>↓l -? 4 1”4^? r-1s5L
The mixture was distilled using a 10-n flow pipe, and benzene and light oil in the tar were distilled off. The obtained pitch had a softening point of 85°C and a benzene insoluble content of t4. Ol amount %, pyridine insoluble content = 5.
The quinoline insoluble content was less than 0, otxi%.

This free carbon-free pitch was heat-treated at 430°C in a 500ml flask at a vacuum level of 61■Hg abs, with a softening point of 230°C and a benzene insoluble content of 51, 1B.
11% by weight, quinoline insoluble content = 0. A carbon fiber precursor pitch consisting of an optically isotropic structure of % by weight was obtained.

This flicker pitch was melt-spun at 285°C, treated to be infusible under the same conditions as in Example 1, and then carbonized at too much°C in argon to obtain carbon fibers. This fiber has a fiber diameter of 8.4-1, a tensile strength of 98 g/-1, and a modulus of elasticity of 4. It was Ot/-.

<Example 4> The free carbon-free pitch shown in Example 3 (softening point: 85°C, benzene insoluble content = 14.0% by weight, pyridine insoluble content = 5.0% by weight, quinoline insoluble content = 0.0% by weight). Put 300g of 500ml flask into a 500ml flask and heat-treat at 450°C under nitrogen gas flow (5It 7ml), softening point 240°C, benzene insoluble content = 54.
A carbon fiber precursor pitch having an optically isotropic structure of 2% by weight and a quinoline insoluble content of 0.2% on the east wall was obtained.

This precursor pitch was melt-spun at 291°C, treated to be infusible under the same conditions as in Example 1, and then carbonized at 1000°C in argon to obtain carbon fibers. This fiber has a fiber diameter of 8.8 μm and a tensile strength of 110 kg/mm.
2. The elastic modulus was 4.5 t/mm2.

Comparative Example 1> Tar obtained by high-temperature carbonization of coal (quinoline insoluble content =
3 parts of benzene was added to 1 part by weight (9.5% by weight) and centrifuged at 60°C to separate and remove the free carphone and polymeric components in the tar as a heavy liquid. The obtained light liquid was distilled at 300°C to remove benzene and light oil in the tar. 11? Softening point = 80
°C, benzene insoluble content = 15% by weight, pyridine insoluble content = 5
．． 2% market weight, quinoline insoluble content==0. It was % of the old tonnage.

The pitch that does not include this free carbon is 500 + Ilt.
Using a flask at a vacuum level of 6 mm and 1 L abs,
As a result of heat treatment at 30°C, the softening point was 190°C, and the benzene insoluble gas was 48. : ] jlI %, quinoline insoluble content = 0.
A pitch consisting of an optically isotropic structure of 5% by weight was obtained.

This pitch was melt-spun at 250°C, subjected to infusibility treatment under the same conditions as in Example 1, and then heated to 1000°C in argon.
When the carbonization treatment was carried out, the fibers were stuck and a satisfactory carbon fiber could not be obtained.

Comparative Example 2> High fA carbonized tar used in Example 1 (quinoline insoluble content =
2.6% by weight) to 1 part by weight, a portion of coal-based medium oil (-180-250℃) was added twice, and 3 small% of this mixed solution was filtered. Diatomaceous earth as an auxiliary agent was added, and the mixture was filtered at a temperature of 80° C. under a pressure of 3.0 g/c to separate and remove free carbon. The obtained pitch had a softening point of 90°C and a benzene insoluble content of 18.
2% by weight, pyridine insolubles 8.2% by weight, quinoline insolubles = 0. The old weight percentage was.

This free carbon-free pitch was heated at 420°C using a 500+D flask at a vacuum level of 6 mmHg abs.
Softening point: 220℃, benzene insoluble content: 48
．． 2%, quinoline insoluble content = 6.21% by weight, and when observed under a polarizing microscope, delicate mesophase spherules (5~
20-) were observed in large numbers.

This pitch was melt-spun, but the nozzle was clogged and spinning could not be performed.

<Effects of the Invention> According to the present invention, pitch is obtained by dissolving particularly high lA dry-distilled tar with an aromatic solvent, and free carbon, low-molecular components, and high-molecular components are suitably removed.
Precursor pitch for carbon fibers with excellent spinnability, infusibility, and carbonization properties can be produced by heat treatment at a temperature of ℃.

Claims (2)

[Claims] (1) Softening point is 200℃ or higher, benzene insoluble content is 45~
65% by weight, quinoline insoluble content is 0.5% by weight or less, and has an optically isotropic structure. When producing carbon fiber precursor pitch, an aromatic solvent is added to coal-based tar. After separating and removing free carbon, the light components in the solvent and tar are removed by distillation to obtain a pitch that does not substantially contain free carbon.
A method for producing precursor pitch for carbon fibers, the method comprising heat treatment at a temperature of °C. (2) Softening point is 200℃ or higher, benzene insoluble content is 45~
65% by weight, quinoline insoluble content is 0.5% by weight or less, and has an optically isotropic structure. When producing carbon fiber precursor pitch, an aromatic solvent is added to coal-based tar. After separating and removing free carbon, the light components in the solvent and tar are removed by distillation to obtain a pitch that does not substantially contain free carbon, and this pitch is heated at 350 to 500°C under conditions of inert gas blowing. 1. A method for producing precursor pitch for carbon fiber, the method comprising heating at a temperature of .