JPH0735609B2 - Infusibilizing method for pitch fibers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for infusibilizing pitch fibers.

(Prior Art) Conventionally, a method for producing carbon fiber using pitch as a raw material has been known. A generally employed method for producing carbon fibers using pitch as a raw material is a method in which the pitch is melt-spun, the obtained pitch fiber is oxidized to infusibilize, and then carbonized or further graphitized. The reason for performing oxidation treatment after melt spinning is that the pitch fiber obtained by melt spinning is
Since melting occurs at a temperature above the softening point of the pitch, it is not possible to maintain the fiber shape and heat it to the carbonization temperature as it is, so oxidation at a temperature below the softening point does not melt the pitch fiber. Because it is necessary to However, since the oxidation rate of Pitch is extremely slow at temperatures below the softening point, it is usually within the range where melting of Pitch fibers does not occur, while the oxidation treatment temperature is increased in accordance with the increase in the softening point accompanying the progress of oxidation. A method of performing infusibilizing treatment is adopted. However, even when performing infusibilizing treatment by such a method, in order to carry out infusibilization to an extent sufficient for heating to the carbonization temperature, the temperature of the pitch fiber is always kept at a temperature equal to or lower than the softening point of the pitch fiber. Since it needs to be raised, there is a problem that it takes a long time to infusibilize and the economy is low. Furthermore, since the oxidation of Pitch fibers is an exothermic reaction, if the filling rate per unit volume of Pitch fibers is large, heat removal will be insufficient and fusion of fibers will easily occur, which will cause a problem that the physical properties of yarn will be deteriorated. . Further, there is also a problem that the graphitization property is remarkably lowered because the fiber contains oxygen due to the oxidation.

(Problems to be Solved by the Invention) An object of the present invention is to solve the above-mentioned problems of the prior art. Particularly, heat fusion is prevented, and the Pitch fibers are efficiently infusibilized to obtain high quality. To enable the production of carbon fiber.

(Means for Solving Problems) The present invention uses a step of eluting at least one part of a meltable component from the fiber as at least part of the step of obtaining the infusible fiber from the pitch fiber obtained by spinning. Is characterized by.

The pitch fiber in the present invention can be obtained by preparing petroleum-based or coal-based heavy oil, tar, pitch or the like as a spinning raw material by a conventionally known method and melt spinning.

Several methods have already been known as methods for producing such pitch fibers. For example, it is described in JP-B-41-15728 and JP-A-49-19127.
In the present invention, when the pitch is composed of a plurality of components having different solubilities regardless of whether the pitch is optically isotropic or anisotropic, the pitch fiber produced by any of the melt spinning methods Can also be applied to.

Furthermore, the present invention is a method of producing pitch fibers by spinning a method other than melt spinning by adding a component having an effect of lowering the softening point of pitch or solubilizing pitch to improve the fluidity of pitch. Can also be applied to.

In the present invention, it is essential to elute at least a part of the meltable component from the pitch fiber obtained by spinning.

In this elution treatment, the pitch fiber is treated with an organic solvent to elute a part or substantially all of the fusible components which are soluble in an organic solvent having a solubility in pitch equal to or higher than that of benzene.

At that time, as the solvent, a solvent having a dissolving power for pitch equal to or larger than that of benzene is used.
When treated with a solvent having a lower solubility in pitch than that of benzene, the low softening point component that causes fusion of fibers remains by heating during carbonization performed after this elution treatment, which is not preferable. In addition, removal of fusible components with a solvent
It suffices that the fibers do not fuse together during carbonization, and at least the surface layer of the fibers must be partially removed. Exemplarily explaining the removal rate of the benzene-soluble component, 10% by weight or more of the benzene-soluble component (that is, the elution amount in the case of almost completely eluting with benzene),
Particularly, it is preferable to elute the soluble component corresponding to 50% by weight or more. There is no particular upper limit. It is preferably removed over substantially the entire fiber. The elution treatment method is not particularly limited, and various methods can be adopted. Specifically, a method in which a continuous thread is passed through a solvent bath, a method in which the thread is laminated on a container such as a wire mesh, and the whole container is immersed in the solvent can be employed. The solvent is preferably heated as needed. It is also possible to draw the fibers during elution and reduce the voids after the elution components have been removed to increase the density.

The mesophase pitch having an optically anisotropic component is composed of a hot melt component and a heat infusible component, and can be easily made infusible by removing the heat melt component with a solvent. It is therefore particularly preferred to apply the method of the invention to mesophase pitches. When using the mesophase pitch, the amount of the optically anisotropic component is preferably 60% or more. In order to increase the elution effect of the present invention, this amount is preferably 80% or more, particularly 90%.
The above is more preferable. Incidentally, since the mesophase can be developed by removing the soluble component, if the fiber yield is taken into consideration, an isotropic phase pitch can also be used.

The solvent used in the present invention may be essentially any solvent having a solubility in pitch equal to or greater than that of benzene, such as benzene, toluene, aromatic hydrocarbons such as tetralin, and cyclic hydrocarbons such as tetrahydrofuran. Oxygen-containing compounds, cyclic nitrogen-containing compounds such as pyridine and quinoline, and mixtures thereof can be used.

In the present invention, the fusible components are removed by a solvent only in the vicinity of the fiber surface to partially infusibilize the pitch fiber, and the partially infusible pitch fiber is subjected to a known oxidation treatment and / or an inert atmosphere. It is also possible to apply a heating and firing treatment. As the solvent used at that time, it is sufficient that partial infusibility can be achieved, and in addition to the above-mentioned solvent, methanol, n-hexane, or the like having a smaller dissolving power than benzene can also be used. In that case, there is an advantage that the infusibilization by the oxidation can be efficiently performed in a short time, as compared with the pitch fiber not subjected to the elution treatment.

(Examples) Hereinafter, the present invention will be described in more detail with reference to Examples.
The measuring method in the examples is as follows.

[Optical Anisotropy] A sample was embedded in an epoxy resin and then polished by a conventional method. The polished surface was observed by a reflection polarization method using an ORTHOPLAN microscope manufactured by Leitz. The abundance of the optically anisotropic component is
It was determined from the area ratio of the isotropic portion and the anisotropic portion when observed under the above-mentioned polarized light. The measurement was performed 10 times and the average value was shown.

[Quinoline insoluble matter (QI), quinoline soluble / pyridine insoluble matter (QS / PI), pyridine soluble / benzene insoluble matter (PS / B)
I), Benzene solubles (BS)] Add 100 g of solvent to 1 g of the sample and perform Soxhlet extraction at boiling point for 24 hours. The extraction procedure is benzene, pyridine, and quinoline in this order, and the insoluble matter in each solvent is 0.45 μm in pore size.
Filter off with a membrane filter at 75 ℃ and weigh insoluble matter.

Example 1. A petroleum-based pitch was heated to 440 ° C. at a heating rate of 5 ° C./min, and then heat-treated at 440 ° C. for 5 hours while bubbling 6 ml / min of nitrogen per 1 g of the pitch from the bottom of the container. During the heat treatment, the pitch was agitated at 600 rpm. After heat treatment for a predetermined time, it was cooled at 3 ° C./min to obtain a mesophase pitch. The amount of optical anisotropy of the obtained mesophase pitch is 95%, QI = 41%, PI-QS = 28.
%, BI-PS = 23%, BS = 8%. The mesophase pitch
It was pressurized with nitrogen at 370 ° C., extruded from a nozzle having a diameter of 0.5 mm, melt-spun, and wound at 600 m / min to obtain a green fiber. The resulting green fiber was placed in benzene at 60 ° C.
Soaking was carried out for 30 minutes to remove soluble matter. The benzene-treated green fiber was placed in a carbonization furnace and carbonized at 1000 ° C in nitrogen while heating at 4 ° C / min. The carbonized yarn obtained was carbonized without fusion between the fibers, and good carbon fibers were obtained.

Comparative Example 1. The green fiber used in Example 1 was carbonized in the same manner as in Example 1 in the carbonization furnace without benzene treatment. The result was that only fibers with extremely low tensile properties could be obtained due to fusion between fibers.

Example 2. After treating the green fiber used in Example 1 in benzene at 60 ° C. for 10 minutes, the temperature was raised from room temperature at 5 ° C./min to 25
It heat-treated at 0 degreeC for a fixed time, and performed the oxidation process in the air.
Green fiber without benzene treatment is infusible. 2
Although it took time, the benzene-treated yarn could be infusibilized after 0.5 hour treatment.

Example 3. The mesophase pitch used in Example 1 was pressurized with nitrogen at 370 ° C.
It was melt-spun by extrusion from a 0.3 mm diameter nozzle. A bath of anthracene oil at 200 ° C is installed 5 mm below the nozzle,
Immediately after discharging, the Pitch fiber was treated with anthracene oil to remove soluble components and was collected at a speed of 50 m / min. The surface of the obtained Pitch fiber is infusibilized.
It was possible to perform air oxidation by putting it in an atmosphere of ° C. By performing the solvent treatment, the infusibilization treatment by air oxidation can be started at a temperature equal to or higher than the softening point of the pitch fiber, and thus the infusibilization can be easily performed.

Claims (2)

[Claims] 1. A step of eluting at least a part of a component soluble in an organic solvent having a dissolving power for pitch equal to or greater than benzene from a pitch fiber obtained by melt spinning. Method for infusibilizing pitch fibers. 2. The method according to claim 1, wherein the fiber subjected to the elution treatment is further subjected to an oxidation treatment.