JP2016210925A - Raw material pitch for producing carbon fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a raw material pitch for producing a carbon fiber, enabling the carbon fiber excellent in tensile strength to be produced relatively inexpensively .SOLUTION: The raw material pitch for producing a carbon fiber of the present invention is a pitch which is obtained from coal and is used for producing a carbon fiber by melt spinning and has a content percentage of oxygen of 1.0 mass% or more and a content percentage of toluene soluble component of 20 mass% or more. The coal is preferably bituminous coal or sub-bituminous coal. The raw material pitch for producing a carbon fiber is preferably one obtained by heat treatment of a soluble component at a temperature of 150°C or more, the soluble component being separated from a thermal decomposition of coal in a solvent by a solvent extraction treatment at a temperature less than 300°C.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a raw material pitch for producing carbon fibers.

  Carbon fiber is widely used as a reinforcing material for structural materials such as resin, concrete, and ceramic. In addition, carbon fiber is also used as, for example, a heat insulating material, activated carbon raw material, conductive material, heat transfer material, and the like.

  The carbon fiber is generally produced by forming a synthetic resin such as polyacrylonitrile or a pitch obtained from petroleum or coal into a fiber shape by spinning, and making the yarn infusible (air oxidation) and carbonized. Among the above raw materials, coal pitch is a residue after removing volatile components such as naphthalene by distillation from coal tar, which is a liquid material by-produced when carbon is produced by carbonization to produce coke. Black material. Such a coal pitch is a mixture of many compounds containing many aromatic compounds containing many benzene rings in their skeletons.

  More specifically, since the coal pitch is heated to about 1000 ° C. during coke production, the main component is a polycyclic aromatic compound having a high degree of ring condensation, such as a methyl group, an ethyl group, or a propyl group. The content of chains and oxygen-containing structures such as ether bonds and phenol groups is extremely small. Although the oxygen content can be used as an index of the content of these structures, the oxygen content of the coal pitch is generally 1% by mass or less, and in many cases 0.5% by mass or less. is there.

  Such a coal pitch melts and becomes a viscous liquid when heated from about 100 ° C. to about 200 ° C., and can be spun by extruding it from a nozzle. However, as described above, coal pitch is a by-product during coke production and is recovered as a residue. For example, spinning of metal impurities and solid carbon, and subsequent infusibilization and carbonization are performed. It contains various ingredients that inhibit it. For this reason, it is difficult to produce carbon fiber stably and efficiently from coal pitch. Moreover, since these impurities can cause the defect of the carbon fiber manufactured, the tensile strength of the carbon fiber obtained is reduced.

  Moreover, it is preferable that the raw material pitch used for manufacture of carbon fiber melts uniformly at a constant temperature during spinning. Further, the softening point of the raw material pitch is preferably 150 ° C. or higher so that the temperature of the infusibilization treatment for fixing the shape of the fiber on which the raw material pitch is spun can be increased, and the temperature at which no thermal decomposition reaction occurs during spinning. 350 ° C. or lower is preferable so that spinning can be performed at

  In order to satisfy these requirements, it has been proposed to modify the pitch of the coal obtained by, for example, adjusting the components and removing impurities from the pitch obtained by the solvent extraction treatment of the coal (for example, Tokuhei) No. 7-15099).

  However, the coal pitch reforming process as described above is a factor that increases the production cost of carbon fibers.

Japanese Patent Publication No. 7-15099

  In view of the above disadvantages, an object of the present invention is to provide a raw material pitch for producing carbon fibers that can produce carbon fibers having excellent tensile strength at a relatively low cost.

  The invention made to solve the above-mentioned problems is a pitch for producing carbon fiber obtained from coal and melt-spun, and has an oxygen content of 1.0% by mass or more and a toluene-soluble component. It is a raw material pitch for carbon fiber production characterized by having a content of 20% by mass or more.

  The carbon fiber production raw material pitch has an oxygen content of 1.0% by mass or more, so that oxygen forms crosslinks between molecules in the carbonization step. For this reason, the said raw material pitch for carbon fiber manufacture can inhibit the lamination | stacking formation of an aromatic ring, and can suppress the development of a crystal | crystallization. Thereby, since stress concentration between the microcrystals when stress acts on the carbon fiber can be relaxed, the tensile strength of the obtained carbon fiber is improved. The carbon fiber raw material pitch is excellent in meltability and spinnability in the melt spinning process because the content of toluene-soluble component composed of a compound having a relatively small molecular weight is 20% by mass or more. . Therefore, by using the raw material pitch for producing carbon fibers, carbon fibers having excellent tensile strength can be produced at a relatively low cost.

  The coal may be bituminous coal or subbituminous coal. Thus, since the above-mentioned coal is bituminous coal or subbituminous coal, the yield of the raw material pitch for carbon fiber production becomes relatively high. As a result, the raw material pitch for carbon fiber production, and consequently the carbon fiber, It can be manufactured at low cost.

  The carbon fiber-producing raw material pitch may be obtained by heat-treating a soluble component separated from a thermal decomposition product in a coal solvent by a solvent extraction process at a temperature of less than 300 ° C. at a temperature of 150 ° C. or more. As described above, the raw material pitch for carbon fiber production is obtained by heat-treating a soluble component separated from a thermal decomposition product in a solvent of coal by a solvent extraction treatment at a temperature of less than 300 ° C. at a temperature of 150 ° C. or more. Thus, the oxygen content and the toluene soluble content can be easily and reliably within the above ranges. As a result, the carbon fiber production raw material pitch, and hence the carbon fiber excellent in tensile strength, can be produced at a relatively low cost.

  Here, the “content ratio of oxygen” means the content ratio of oxygen atoms including not only oxygen molecules but also atoms bonded to other atoms, and specifically conforms to JIS-M8813 (2004). Means the measured value. The “content of toluene-soluble content” is a value measured according to JIS-K2207 (1996). Further, “bituminous coal” and “subbituminous coal” refer to coal having a coal quality defined in JIS-M1002 (1978).

  As described above, carbon fiber can be produced at low cost by using the raw material pitch for producing carbon fiber of the present invention.

It is a flowchart which shows the procedure of the manufacturing method of the raw material pitch for carbon fiber manufacture of one Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

[Raw material pitch for carbon fiber production]
The raw material pitch for producing carbon fibers according to an embodiment of the present invention is a raw material pitch obtained from coal and for producing carbon fibers by melt spinning.

  It is preferable that the said raw material pitch for carbon fiber manufacture is a thing obtained from the thermal decomposition thing in the solvent of coal. Coal contains more oxygen-containing structures such as alkyl side chains and more toluene-soluble matter than coal tar and petroleum production residues processed at relatively high temperatures. For this reason, the said raw material pitch for carbon fiber manufacture obtained from the thermal decomposition thing in the solvent of coal can be equipped with the characteristic which is demonstrated below.

  As a minimum of the content rate of oxygen in the raw material pitch for carbon fiber manufacture, it is 1.0 mass%, 1.5 mass% is preferred, and 1.7 mass% is more preferred. On the other hand, the upper limit of the oxygen content is preferably 5.0% by mass, more preferably 4.0% by mass, and even more preferably 3.0% by mass. When the oxygen content is less than the above lower limit, crystal growth during carbonization cannot be sufficiently suppressed, and the resulting carbon fiber may be easily broken by stress concentration. Conversely, if the oxygen content exceeds the above upper limit, the mass reduction rate during carbonization is large, and the carbon fiber production cost may increase due to a decrease in the yield of carbon fibers.

  The lower limit of the content of toluene-soluble components in the raw material pitch for producing carbon fibers is 20% by mass, preferably 30% by mass, and more preferably 35% by mass. On the other hand, as an upper limit of the content rate of toluene soluble part, 80 mass% is preferable, 60 mass% is more preferable, and 50 mass% is further more preferable. When the content of toluene-soluble components is less than the lower limit, the meltability and spinnability during melt spinning may be insufficient. On the other hand, when the content of the toluene-soluble component exceeds the above upper limit, the carbon fiber production cost may increase due to a decrease in the yield of the carbon fiber.

  Examples of the coal used as the raw material pitch for carbon fiber production include anthracite coal, bituminous coal, subbituminous coal, lignite, etc., in descending order of coalification degree. preferable. Bituminous coal and sub-bituminous coal have a relatively high content of toluene-soluble components and have an appropriate oxygen content. Therefore, by using bituminous coal and sub-bituminous coal as raw material coal, The yield of the raw material pitch for producing carbon fibers within the above range can be increased. In addition, the brown coal whose coalification degree is lower than subbituminous coal has the fault that the yield of carbon fiber from a raw material pitch becomes low because oxygen content rate is too large. In addition, anthracite coal having a degree of coalification higher than that of bituminous coal has a drawback that it becomes difficult to melt-spin the raw material pitch because the oxygen content and the toluene soluble content are small.

[Production method of raw material pitch for carbon fiber production]
Then, the manufacturing method of the said raw material pitch for carbon fiber manufacture is demonstrated.

  The raw material pitch for producing carbon fiber can be produced by the production method shown in FIG. Fig. 1 A method for producing a raw material pitch for carbon fiber production includes a step of forming ashless coal which is a pyrolyzate of coal by pyrolysis and extraction in a solvent of coal (pyrolysate formation step: step S1); The step of separating the ashless coal obtained in this pyrolyzate formation step into a soluble component and an insoluble component by a low-temperature solvent extraction process (separation step: step S2), and the soluble component obtained in this separation step A heat treatment step (heat treatment step: step S3).

<Thermal decomposition product formation process>
In the pyrolysate forming step of step S1, the slurry obtained by mixing the raw coal and the solvent is heated to a temperature equal to or higher than the thermal decomposition temperature of the raw coal, and the soluble component of the pyrolyzed raw coal is extracted into the solvent. Ashless coal is obtained by separating insoluble components at the decomposition temperature. The “ashless coal” is a modified coal obtained by reforming coal and has an ash content of 5% or less, preferably 3% or less, more preferably 1% or less. In addition, "ash content" means the value measured based on JIS-M8812 (2004).

  The solvent is not particularly limited as long as it has a property of dissolving the raw material coal. For example, monocyclic aromatic compounds such as benzene, toluene and xylene, bicyclic rings such as naphthalene, methylnaphthalene, dimethylnaphthalene and trimethylnaphthalene. Aromatic compounds, tricyclic aromatic compounds such as anthracene, and the like can be used. The bicyclic aromatic compound includes naphthalene having an aliphatic chain and biphenyl having a long aliphatic chain.

  Among the above solvents, a bicyclic to tricyclic aromatic compound which is a coal derivative purified from a coal carbonization product is preferable. The bicyclic aromatic compound of the coal derivative is stable even in a heated state and has an excellent affinity with coal. Therefore, by using such a bicyclic aromatic compound as a solvent, the ratio of coal components extracted into the solvent can be increased, and the solvent can be easily recovered and reused by a method such as distillation. .

  As a minimum of heating temperature (pyrolysis extraction temperature) of a slurry, 300 ° C is preferred, 350 ° C is more preferred, and 380 ° C is still more preferred. On the other hand, the upper limit of the heating temperature of the slurry is preferably 450 ° C, more preferably 420 ° C. If the heating temperature of the slurry is less than the above lower limit, the bonds between the molecules constituting the coal cannot be sufficiently weakened. For example, when low grade coal is used as the raw coal, There is a possibility that the solidification temperature cannot be increased, and the yield may be low and uneconomical. On the contrary, when the heating temperature of the slurry exceeds the above upper limit, the pyrolysis reaction of coal becomes very active, so that the oxygen content of ashless coal may become insufficient, and recombination of generated pyrolysis radicals As a result, the extraction rate of ashless coal may be reduced.

  The extraction rate from coal in the pyrolysate formation step (the yield of ashless coal) depends on the quality of the coal used as a raw material, but in the case of bituminous coal or sub-bituminous coal, for example, 20% by mass to 60% by mass It is as follows.

<Separation process>
In the separation step of Step S2, the ashless coal obtained in the pyrolyzate formation step of Step S1 is subjected to a low temperature solvent extraction treatment, whereby a relatively low molecular weight soluble component and a solvent extraction are extracted at low temperature. Separated into relatively high molecular weight insoluble components that are not. Thereby, the soluble component which can be melt-spun is obtained.

  More specifically, a slurry in which pulverized ashless coal is dispersed in a solvent is prepared, and this slurry is held within a predetermined temperature range for a certain period of time. Separate the solvent from which the dissolved components have been eluted.

  The lower limit of the average particle size of the ashless coal dispersed in the solvent is preferably 50 μm, and more preferably 100 μm. On the other hand, the upper limit of the average particle size of the ashless coal dispersed in the solvent is preferably 3 mm, and more preferably 1 mm. When the average particle diameter of the ashless coal dispersed in the solvent is less than the above lower limit, it may be difficult to separate the liquid containing the extracted soluble component from the solid component that is an insoluble component. On the other hand, when the average particle size of ashless coal dispersed in the solvent exceeds the above upper limit, the extraction efficiency of soluble components may be reduced. The “average particle size” means a particle size at which the volume integrated value is 50% in the particle size distribution measured by the laser diffraction scattering method.

  The lower limit of the mixing ratio of ashless coal with respect to the solvent of the slurry is preferably 3% by mass, and more preferably 5% by mass. On the other hand, the upper limit of the mixing ratio of ashless coal to the solvent is preferably 40% by mass, and more preferably 30% by mass. If the mixing ratio of ashless coal to the solvent is less than the above lower limit, the production efficiency is low, which may be uneconomical. Conversely, when the mixing ratio of ashless coal with respect to the solvent exceeds the above upper limit, handling of the slurry and separation of insoluble components may be difficult.

  There is no particular limitation on the method for separating the solvent from which soluble components are eluted and the insoluble components, and a known separation method such as a filtration method, a centrifugal separation method, a gravity sedimentation method, or a combination of these two methods is employed. it can. Among these, a combination of a centrifugal separation method and a filtration method that can continuously operate a fluid, is suitable for a large amount of processing at low cost, and can reliably remove insoluble components is preferable.

  By removing the solvent from the liquid (supernatant liquid) from which the insoluble components have been separated in this way, the soluble components of ashless coal are separated and recovered, and by removing the solvent from the solids concentrate, Insoluble components are separated and recovered. It does not specifically limit as a method of removing a solvent from the said supernatant liquid and solid concentration liquid, A general distillation method, an evaporation method, etc. can be used. In particular, the removal of the solvent from the insoluble component is preferably performed by distillation in order to recover and reuse the solvent.

  The solvent used in the separation step may be any solvent that can elute low molecular weight components of ashless coal, and the same solvents as those used in the thermal decomposition product forming step can be used. As the solvent for the separation step, a solvent capable of obtaining a sufficient extraction rate at a low temperature, preferably room temperature is preferable, and examples of such a preferable solvent include pyridine, methylnaphthalene, tetrahydrofuran, anthracene and the like.

  The solvent extraction processing temperature in the separation process varies depending on the type of solvent. However, generally, the solvent extraction treatment temperature is preferably less than 300 ° C, more preferably 200 ° C or less, and further preferably 150 ° C or less. On the other hand, the lower limit of the solvent extraction treatment temperature is not particularly limited, but normal temperature, for example, 20 ° C. is preferable. When the solvent extraction treatment temperature exceeds the above upper limit, the molecular weight of the soluble component to be extracted increases, so that the softening temperature becomes too high, and the spinning efficiency may be lowered during melt spinning. Conversely, when the solvent extraction treatment temperature is less than the above lower limit, cooling is required, and the cost may increase unnecessarily.

  The lower limit of the extraction time in the separation step, that is, the time maintained at the solvent extraction treatment temperature is preferably 10 minutes, and more preferably 15 minutes. On the other hand, the upper limit of the extraction time is preferably 120 minutes, more preferably 90 minutes. When extraction time is less than the said minimum, there exists a possibility that the low molecular weight component of ashless coal may not fully be eluted. Conversely, when the extraction time exceeds the above upper limit, the manufacturing cost may increase unnecessarily.

  As a minimum of the extraction rate of the soluble component from ashless coal in a separation process, 10 mass% is preferred, 20 mass% is more preferred, and 30 mass% is still more preferred. On the other hand, as an upper limit of the extraction rate of the soluble component from ashless coal, 90 mass% is preferable, 70 mass% is more preferable, and 50 mass% is further more preferable. When the extraction rate of soluble components from ashless coal in the separation step is less than the lower limit, the yield is low, and the production cost of the raw material pitch for producing carbon fibers may increase. On the contrary, when the extraction rate of the soluble component from the ashless coal in the separation step exceeds the upper limit, the softening temperature of the soluble component is increased, and the spinning efficiency may be decreased.

<Heat treatment process>
In the heat treatment step of step S3, the soluble component obtained in the separation step of step S2 is heated to volatilize the low molecular weight component, and the carbon fiber is decomposed and removed in advance at a low temperature. A raw material pitch for production is obtained. Thus, by previously removing volatile components and decomposable components that may hinder melt spinning, the raw material pitch for producing carbon fibers can be easily melt-spun and has excellent tensile strength at a relatively low cost. Carbon fiber can be manufactured.

  The heat treatment is preferably performed in a non-oxidizing gas atmosphere. Thus, by heating in a non-oxidizing gas atmosphere to prevent oxidative crosslinking, inconveniences such as an increase in softening temperature can be prevented. The non-oxidizing gas is not particularly limited as long as the oxidation of pitch can be suppressed, but nitrogen gas is more preferable from the economical viewpoint.

  The heat treatment is preferably performed in a reduced pressure state. Thus, by heat-processing in a pressure-reduced state, the vapor | steam of a volatile component and the gas of a thermal decomposition product can be efficiently removed from pitch.

  As a minimum of heat processing temperature in the above-mentioned heat processing process, 150 ° C is preferred, 170 ° C is more preferred, and 200 ° C is still more preferred. On the other hand, the upper limit of the heat treatment temperature is preferably 350 ° C, more preferably 320 ° C, and even more preferably 280 ° C. When the heat treatment temperature is less than the lower limit, volatile components in the insoluble component cannot be sufficiently removed, and the spinnability of the carbon fiber production raw material pitch becomes insufficient, and the spinning efficiency may decrease. There is. Conversely, if the heat treatment temperature exceeds the upper limit, the energy cost may increase unnecessarily, the useful components may be thermally decomposed and the production efficiency of the carbon fiber may decrease, and the carbonization may proceed and spinning. May decrease.

  Moreover, it is preferable that the heat processing temperature in a heat processing process is higher than the solvent extraction processing temperature in the isolation | separation process of step S2. Thus, when the heat treatment temperature is higher than the solvent extraction treatment temperature, volatile components having a boiling point higher than the solvent extraction treatment temperature can be removed from the pitch. Thereby, it can prevent that a void | hole is formed or a filament breaks because a volatile component escapes from the said raw material pitch for carbon fiber manufacture at the time of spinning.

  The heat treatment temperature in the heat treatment step is more preferably higher than the melt spinning temperature. In this way, when the heat treatment temperature is higher than the melt spinning temperature, components that can be thermally decomposed during melt spinning can be previously thermally decomposed and removed in this heat treatment step. As a result, it is possible to prevent the pyrolyzate generated during spinning from breaking the filaments obtained by spinning the pitch, and the formation of defects in the carbon fiber from which these pyrolysates are finally obtained.

  As a minimum of the heat processing time in the said heat processing process (time hold | maintained at the said heat processing temperature), 10 minutes are preferable and 15 minutes are more preferable. On the other hand, the upper limit of the heat treatment time in the heat treatment step is preferably 120 minutes, more preferably 90 minutes. When the heat treatment time in the heat treatment step is less than the lower limit, the low molecular weight component may not be sufficiently removed. Conversely, when the heat treatment time in the heat treatment step exceeds the upper limit, the treatment cost may be unnecessarily increased.

  As a minimum of the softening temperature of the raw material pitch for carbon fiber production obtained by heat-treating the soluble component, 150 ° C is preferable, and 170 ° C is more preferable. On the other hand, the upper limit of the softening temperature of the raw material pitch for carbon fiber production is preferably 280 ° C, and more preferably 250 ° C. When the softening temperature of the raw material pitch for carbon fiber production is less than the lower limit, the infusibilization temperature cannot be increased, and the infusibilization treatment may be inefficient. On the contrary, when the softening temperature of the raw material pitch for carbon fiber production exceeds the above upper limit, it is necessary to increase the melt spinning temperature, which may cause unstable spinning and increase the cost. The “softening temperature” is a value measured by a ring and ball method in accordance with ASTM-D36.

  As a minimum of the yield of the said raw material pitch for carbon fiber manufacture from the soluble component obtained at the said isolation | separation process in this heat processing process, 80 mass% is preferable and 85 mass% is more preferable. On the other hand, the upper limit of the yield of the raw material pitch for producing carbon fibers from the soluble component in the heat treatment step is preferably 98% by mass, and more preferably 96% by mass. When the yield of the carbon fiber production raw material pitch from the soluble component in the heat treatment step is less than the lower limit, the yield of the carbon fiber production raw material pitch may be unnecessarily lowered. Conversely, if the yield of the carbon fiber production raw material pitch from the soluble component in the heat treatment process exceeds the above upper limit, residual volatile components or components thermally decomposed at a low temperature in the carbon fiber production raw material pitch As a result, the spinnability of the pitch becomes insufficient, and the spinning efficiency may be reduced.

[Method for producing carbon fiber]
Furthermore, the method of manufacturing carbon fiber using the said raw material pitch for carbon fiber manufacture is demonstrated.

  The carbon fiber production method using the carbon fiber production raw material pitch includes a step of melt spinning the carbon fiber production raw material pitch, a step of infusibilizing the filament obtained by the melt spinning, and an infusible yarn shape. And carbonizing the body.

<Melt spinning process>
In the melt spinning step, the carbon fiber production raw material pitch is melt-spun using a known spinning device. That is, the raw material pitch in a molten state is formed into a thread by passing through a nozzle (die), and the shape of the raw material pitch is fixed to the thread by cooling.

  As the nozzle used for the melt spinning, a known nozzle may be used. For example, a nozzle having a diameter of 0.1 mm to 0.5 mm and a length of 0.2 mm to 1 mm can be used. The filamentous material obtained by melt spinning the raw material pitch is wound, for example, by a drum having a diameter of about 100 mm to 300 mm.

  As a minimum of melt spinning temperature, 180 ° C is preferred and 200 ° C is more preferred. On the other hand, the upper limit of the melt spinning temperature is preferably 350 ° C, more preferably 300 ° C. When the melt spinning temperature is less than the above lower limit, the raw material pitch may not be sufficiently melted and stable spinning may not be possible. On the other hand, when the melt spinning temperature exceeds the above upper limit, the spun filaments may be disconnected due to thermal decomposition of components in the raw material pitch.

  Although it does not specifically limit as a minimum of the linear velocity of melt spinning, 100 m / min is preferable and 150 m / min is more preferable. On the other hand, the upper limit of the melt spinning linear velocity is preferably 500 m / min, and more preferably 400 m / min. When the line speed of melt spinning is less than the lower limit, the production efficiency is low and the carbon fiber may be expensive. On the other hand, when the linear speed of melt spinning exceeds the above upper limit, the spinning becomes unstable, so that the production efficiency is lowered, and the carbon fiber may still be expensive.

  The lower limit of the average diameter of the filaments spun in melt spinning is preferably 5 μm, more preferably 7 μm. On the other hand, the upper limit of the average diameter of the filaments spun in melt spinning is preferably 20 μm and more preferably 15 μm. When the average diameter of the filamentous body is less than the lower limit, there is a possibility that spinning cannot be stably performed. On the other hand, when the average diameter of the filamentous body exceeds the above upper limit, the flexibility of the filamentous body may be insufficient.

<Infusibilization process>
In the infusibilization process, the filament obtained in the melt spinning process is crosslinked and infusible by heating in an atmosphere containing oxygen. As an atmosphere containing oxygen, air is generally used.

  The lower limit of the infusibilization treatment temperature is preferably 150 ° C, more preferably 200 ° C. On the other hand, the upper limit of the infusibilization treatment temperature is preferably 300 ° C, and more preferably 280 ° C. When the infusibilization treatment temperature is less than the lower limit, infusibilization may be insufficient, or the infusibilization treatment time may be increased, resulting in inefficiency. Conversely, when the infusibilization temperature exceeds the above upper limit, the filamentous body may be melted before oxygen crosslinking.

  The lower limit of the infusibilization time is preferably 10 minutes, and more preferably 20 minutes. On the other hand, the upper limit of the infusibilization time is preferably 120 minutes, more preferably 90 minutes. If the infusibilization time is less than the lower limit, infusibilization may be insufficient. Conversely, when the infusibilization treatment time exceeds the above upper limit, the production cost of the carbon fiber may be unnecessarily increased.

<Carbonization process>
In the carbonization step, carbon fibers are obtained by heating and carbonizing the filaments infusible in the infusibilization step.

  Specifically, the filamentous body is charged into an arbitrary heating device such as an electric furnace, the inside is replaced with a non-oxidizing gas, and then heated while blowing the non-oxidizing gas into the heating device.

  As a minimum of heat processing temperature in a carbonization process, 700 ° C is preferred and 800 ° C is more preferred. On the other hand, as an upper limit of heat processing temperature, 3000 degreeC is preferable and 2800 degreeC is more preferable. If the heat treatment temperature is less than the lower limit, carbonization may be insufficient. Conversely, when the heat treatment temperature exceeds the above upper limit, the production cost may increase from the viewpoint of improving the heat resistance of the equipment and fuel consumption.

  The heating time in the carbonization step may be appropriately set depending on the characteristics required of the carbon material, and is not particularly limited, but the heating time is preferably 15 minutes or longer and 10 hours or shorter. If the heating time is less than the lower limit, carbonization may be insufficient. Conversely, when the heating time exceeds the above upper limit, the production efficiency of the carbon material may be reduced.

  The non-oxidizing gas is not particularly limited as long as it can suppress the oxidation of the carbon material, but nitrogen gas is preferable from an economical viewpoint.

[Other Embodiments]
The said embodiment does not limit the structure of this invention. Therefore, in the above-described embodiment, the components of each part of the above-described embodiment can be omitted, replaced, or added based on the description and common general knowledge of the present specification, and they are all interpreted as belonging to the scope of the present invention. Should.

  As an example, in the method for producing the raw material pitch for carbon fiber production, ash and the like in the slurry are not separated from the ashless coal in the thermal decomposition product forming step, and the ash and the like in the ashless coal in the next separation step. You may isolate | separate with an insoluble component.

  Moreover, in the manufacturing method of the said raw material pitch for carbon fiber manufacture, you may abbreviate | omit a heat treatment process.

  EXAMPLES Hereinafter, although this invention is explained in full detail based on an Example, this invention is not interpreted limitedly based on description of this Example.

<Raw material pitch for carbon fiber production>
As will be described below, Examples 1 to 6 and Comparative Examples 1 and 2 of raw material pitches for carbon fiber production with different production conditions were made as prototypes. Carbon fibers were prototyped by melt spinning, infusibilization and carbonization under the same conditions.

Example 1
As raw coal, an Australian bituminous coal with an oxygen content of 6.5% by mass on an anhydrous ashless basis was used. First, 1 kg of the above bituminous coal pulverized to 1 mm or less was mixed with 5 kg of methylnaphthalene, charged in an autoclave, held at 400 ° C. for 1 hour in a nitrogen atmosphere, and then cooled to obtain a thermal decomposition product. Next, 5 kg of methylnaphthalene is further added to this pyrolyzate, and the soluble component is extracted by stirring at an extraction temperature of 60 ° C. for 1 hour, followed by filtration. The obtained filtrate is distilled under reduced pressure to dissolve the soluble component. Separated. The soluble component was heat-treated in a nitrogen atmosphere at a heat treatment temperature of 230 ° C. for 1 hour to obtain a raw material pitch for carbon fiber production of Example 1.

(Examples 2 to 6)
Example 2 was experimentally manufactured under the same conditions as in Example 1 except that the extraction temperature was 80 ° C. Example 3 was experimentally manufactured under the same conditions as in Example 1 except that the extraction temperature was 100 ° C. Example 4 was experimentally manufactured under the same conditions as in Example 1 except that the heat treatment temperature was 250 ° C. Example 5 was manufactured on the same conditions as Example 1 except that the extraction temperature was 80 ° C. and the heat treatment temperature was 250 ° C. Example 6 was made on the same conditions as Example 1 except that the extraction temperature was 100 ° C. and the heat treatment temperature was 250 ° C.

(Comparative Example 1)
1 kg of the same bituminous coal crushed to 1 mm or less as in Example 1 was mixed with 5 kg of methylnaphthalene and charged in an autoclave. The raw material pitch for carbon fiber manufacture of the comparative example 1 was obtained by heat-treating for 1 hour under nitrogen atmosphere.

(Comparative Example 2)
A commercially available hard pitch having an oxygen content of 0.9% by mass and a toluene soluble content of 64% by mass was prepared as a raw material pitch for carbon fiber production in Comparative Example 2, and this was prepared in a nitrogen atmosphere at a heat treatment temperature of 350 ° C. The raw material pitch for carbon fiber manufacture of the comparative example 2 was obtained by heat-processing for 20 hours.

<Component analysis>
The oxygen content rate of the raw material pitch for producing carbon fibers of Examples 1 to 6 and Comparative Examples 1 and 2 was measured according to JIS-M8813 (2004). Moreover, the toluene soluble content rate of the raw material pitch for carbon fiber manufacture of Examples 1-6 and Comparative Examples 1 and 2 was measured based on JIS-K2207 (1996).

<Carbon fiber>
The trial production of carbon fibers using the raw material pitch for carbon fiber production in Examples 1 to 6 and Comparative Examples 1 and 2 was performed by first applying a spinning pitch to a spinning machine having a nozzle having a diameter of 0.2 mm and a length of 0.4 mm. Filled and melt spun at 250 ° C. At this time, the spun filament was wound on a drum having a diameter of 100 mm rotating at 600 rpm (linear speed: about 190 m / min). Subsequently, the filament was infusibilized by heating in air at 250 ° C. for 1 hour. Further, the insolubilized fiber was carbonized at 800 ° C. In addition, since the raw material pitch for carbon fiber production of Comparative Example 1 could not be stably melt-spun even when heated to 350 ° C., no carbon fiber was obtained.

<Tensile strength>
The tensile strength of each carbon fiber manufactured using the carbon fiber production raw material pitches of Examples 1 to 6 and Comparative Examples 1 and 2 was measured according to JIS-L1013 (2010).

  On the anhydrous ashless base from the oxygen content of the raw material pitch for carbon fiber production of Examples 1 to 6 and Comparative Examples 1 and 2, the toluene soluble content, and the raw material coal (hard pitch for Comparative Example 2). Table 1 below shows the yield and the tensile strength of the carbon fiber prototyped using these.

  Thus, the carbon fiber which is comparatively excellent in tensile strength by making the oxygen content rate of the raw material pitch for carbon fiber production 1.0% by mass or more and the content rate of the toluene soluble content 20% by mass or more. It was confirmed that can be manufactured stably.

  The raw material pitch for producing carbon fibers of the present invention is suitably used for producing carbon fibers.

S1 Thermal decomposition product formation process S2 Separation process S3 Heat treatment process

Claims (3)

A pitch obtained from coal and for producing carbon fiber by melt spinning,
A raw material pitch for producing carbon fibers, wherein the oxygen content is 1.0 mass% or more and the content of toluene-soluble components is 20 mass% or more.   The raw material pitch for carbon fiber production according to claim 1, wherein the coal is bituminous coal or subbituminous coal.   The carbon fiber according to claim 1 or 2, wherein a soluble component separated from a pyrolyzate in a solvent of coal by a solvent extraction treatment at a temperature of less than 300 ° C is heat-treated at a temperature of 150 ° C or more. Raw material pitch for manufacturing.

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