JPS6262916A - Production of pitch carbon yarn - Google Patents

Abstract

PURPOSE:To suppress heat dissipation and to stably obtain the titled yarn providing carbon yarn having high characteristics since an extrusion face can be kept at high temperature, by equipping the extrusion face of yarn of a spinneret to subject pitch to melt spinning with a heat insulating layer. CONSTITUTION:Firstly, the extrusion face of yarn of the spinneret 1 having the spinning nozzles 2 is equipped with the heat insulating layer 5 made of glass fibers, etc., the spinning pitch 3 is subjected to melt spinning from the spinneret 1 to give the pitch yarn 6. Then, the yarn is subjected to infusible treatment, carbonized and optionally graphitized, to give the aimed yarn. A sheet having <=3mm thickness is preferable as the shape of the heat insulating material and the heat insulating layer is set preferably in contact with the extrusion face of yarn in order to suppress heat dissipation. Further the spinning pitch has preferably >=70wt% optically anisotropic texture.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for producing pitch-based carbon fibers, and more particularly, to a method for stably producing pitch-based carbon fibers having high properties. It is.

[Conventional technology]

Carbon fiber is a material with high specific strength and specific modulus, and is attracting the most attention as a filler fiber for high-performance composite materials, especially pitch-based carbon FI! It has various advantages over polyacrylonitrile carbon fibers, such as abundant fiber material, high yield in the carbonization process, and high fiber elastic modulus.

Incidentally, various types of spinning pitch, which is a raw material for pitch-based carbon fibers having such advantages, have been studied.

In other words, instead of isotropic pitch, which has conventionally been used as spinning pitch, carbonaceous raw material is heat-treated to develop anisotropy and form molecular species that are easily oriented. Since it was reported (Special Publication No. 1979-4AJ'1) that pitch-based carbon fibers with high properties could be obtained,
Various studies have been made regarding the preparation of spinning pitch with good orientation.

As is well known, carbonaceous raw materials such as heavy oil, turf, pitch, etc. ! 0-j 00''CK When heated, small spherules with particle sizes ranging from several microns to several hundred microns and exhibiting optical anisotropy under polarized light are formed in these materials.When heated further, these spherules They grow, coalesce, and finally exhibit optical anisotropy as a whole.This anisotropic structure is composed of layers of planar polymeric aromatic hydrocarbons produced by thermal polycondensation reaction of carbonaceous raw materials. It is stacked and oriented, and is considered a precursor of graphite crystal structure.

A heat-treated product containing such an anisotropic structure is generally called Nihameso 7A's Pitch.

Various methods have been proposed for using such meso-7Aze pitch as a spinning pitch. A pitch that is optically isotropic and becomes anisotropic when heated to 100° C. or higher, so-called pre-mesophase pitch (Japanese Patent Application Laid-open No. 5R-IS: Tico No. 1), has been proposed.

Pitch fibers can be obtained by melt-spinning such spinning pitch into a gas phase through a nozzle. Next, by infusibleizing, carbonizing, and optionally graphitizing this pitch fiber, a pitch-based high-performance carbon fiber can be obtained.

[Problem that the invention seeks to solve]

However, when melt-spinning using the above-mentioned spinning pitch according to the conventional method, the entire spinning apparatus is heated so that the temperature of the spinneret section having the spinning nozzle that forms the fiber threads is higher than the temperature at which the spinning pitch can be maintained in a molten state. Rarely needed heating.

In such a heating method, since the spinneret part is in direct contact with the outside air, the spinning temperature decreases due to heat dissipation from the fiber discharge surface of the spinneret part, which adversely affects the properties of the resulting pinch fibers, or conversely, the spinneret part If the heating temperature of the heating device outside the spinning spinback is increased in order to ensure an appropriate spinning temperature, problems such as thermal decomposition of the spinning pitch and changes in its physical properties, and generation of bubbles and scaling may occur. This tends to occur, and temperature distribution in the radial direction of the spinneret on the fiber discharge surface of the spinneret also tends to occur, which is also a cause of poor spinning.

[Means for solving problems]

Therefore, the present inventors conducted intensive studies to solve the problems of the conventional technology, and as a result, they discovered that the above problems could be solved by maintaining the fiber discharge surface of the spinneret at a predetermined high temperature. invention has been achieved.

That is, an object of the present invention is to provide a method for stably producing pitch fibers that provide carbon fibers with high properties.

The purpose is to melt-spun the spinning pitch from a spinneret with a spinning nozzle, perform infusibility treatment, then carbonization treatment, and further graphitization treatment as necessary to produce sibitsu-based carbon fiber. This can be easily achieved by melt spinning using a spinneret provided with a heat insulating layer on the fiber discharge surface of the spinneret.

In the following, the present invention will be described in detail.The spinning pitch of the present invention is not particularly limited as long as it forms a molecular species that is easily oriented and provides an optically anisotropic pitch. A variety of conventional ones can be used, such as.

However, if high specific strength and specific modulus are not required, amorphous pitch can also be used. Examples of carbonaceous raw materials for obtaining these spinning pitches include coal-based coal tar, coal tar pitch, coal liquefied products, petroleum-based heavy oil, tar, and pitch. These carbonaceous feedstocks usually contain impurities such as free carbon, undissolved coal, and ash, and these impurities can be removed by well-known methods such as filtration, centrifugation, or static sedimentation using solvents. It is desirable to remove it in advance.

Further, the carbonaceous raw material is pre-treated by, for example, heat-treated and then extracted with a specific solvent, or hydrogenated in the presence of a hydrogen-donating solvent or hydrogen gas. You can leave it there.

In the present invention, the carbonaceous raw material or the pretreated carbonaceous raw material is usually heated at 3jθ to SOO°C, preferably 3g0 to 50°C, for -min to SO hours, preferably S minutes to S hours, under nitrogen. A pitch containing an optically anisotropic structure with a diameter of 70 or more, particularly 70 or more obtained by heat treatment under an inert gas atmosphere such as argon or while being blown can be suitably used as the spinning pitch.

The optically anisotropic texture ratio of a spinning pitch as used in the present invention is a value determined as the area ratio of a portion exhibiting optical anisotropy in a spinning pitch sample under a polarizing microscope at room temperature.◇ Specifically, For example, a pitch sample is crushed into several n square pieces, and the sample piece is embedded into almost the entire surface of a resin with a diameter of about 2 CIA using a conventional method. After polishing the surface, the entire surface is thoroughly examined under a polarizing microscope (IOO magnification). Observe and measure the ratio of the area of the optically anisotropic portion to the total surface area of the sample.

In the present invention, when melt-spinning the above-mentioned spinning pitch, the N of the spinneret! , melt spinning is performed using a spinneret with a heat insulating material layer on the ia discharge surface.

Here, the spinneret is a flat plate made of porous maple that has a large number of pores, that is, spinning nozzles, through which the spinning pitch flows just before spinning and that defines the yarn diameter, and is used to discharge the spinning pitch of the spinning device. It forms part of the

The heat insulating material layer is not particularly limited as long as it can be used as a heat insulating material, such as phenol resin fibers, glass fibers, ceramic fibers, asbestos,
A layered material made of rock wool or the like in the form of a woven fabric or non-woven fabric (felt), or a ceramic molded body is used.

As the ceramic molded body, heat-resistant ceramic coating is used.

Further, the shape is not particularly limited, but it may be one that covers the entire fiber discharge surface of the spinneret, or if the diameter of the spinneret is large, only the center part where there is no spinning nozzle. It is preferable to use a flat layered material, sheet, etc., which usually has a thickness of less than 3 mm, preferably 3 mm or less.

The heat insulating layer used is preferably installed in contact with the fiber discharge surface of the spinneret so as to suppress heat dissipation from the fiber discharge surface, but as long as the object of the present invention is not impaired, the discharge surface and the heat insulating layer may be A slight space may be provided between them. Such a space also has a heat insulating effect.

In addition, when forming a heat insulating material layer on the entire fiber discharge surface of the spinneret, it is of course necessary to have pores corresponding to the numerous spinning nozzles provided in the spinneret so that the spun pitch fibers can pass through without hindrance. That's true.

Here, FIG. 1 is an example showing an embodiment of the present invention,
/ indicates a spinneret, U indicates a spinning nozzle, 3 indicates a spinning pitch, Hiro indicates a device for heating the spinning pitch, S indicates a heat insulating layer, 6 indicates a pitch fiber, and 7 indicates a winding roller.

Here, the spinning pitch 3 is spun through the spinning nozzle while being pressurized by a pump (not shown) K, and is formed into pitch fibers 6, which are wound up by a winding roller 7 and transferred to the next process. .

At this time, the spinning pitch 3 is introduced into the spinning nozzle while being maintained in a molten state by the spinning pitch heating device. Since the spinneret l is in contact with the gas phase portion from which the pitch fibers 6 are discharged via the heat insulating material layer S, the spinning pitch 3 is spun while maintaining the molten state within the spinning spin puncture.

Since pitch fibers are very fragile immediately after spinning, it is preferable to provide a cylindrical or other protective cylinder at the bottom of the spinning device to prevent yarn breakage due to air currents.

The pitch fibers obtained as described above are cine-melted, carbonized, and optionally graphitized by known methods to obtain pitch-based carbon fibers with higher properties.

〔effect〕

According to the present invention, by providing a heat insulating layer on the fiber discharge surface of the spinneret, heat radiation from the fiber discharge surface of the spinneret is suppressed, and the discharge surface is almost uniformly heated over its entire surface. Since the temperature is maintained, there is no temperature distribution in the radial direction of the discharge surface, and pitch fibers can be stably spun evenly from each spinning nozzle. In addition, since the amount of heat dissipated from the fiber discharge surface of the spinneret is reduced, the temperature difference between the heating temperature in the external heating device and the pitch temperature in the spinning spinback can be reduced, thereby preventing thermal decomposition of the spinning pitch, changes in physical properties, and air bubbles. Problems such as generation and scaling can be solved, and power costs for external heating devices can also be reduced.

Furthermore, since the fiber discharge surface of the spinneret can be maintained at a higher mK, the spinning temperature can be set higher, so-called high-temperature spinning is facilitated, and the properties of the resulting pitch fibers can be improved.

The present invention will be specifically explained below with reference to Examples, but the present invention is not limited to the embodiments described below unless it goes beyond the gist of the present invention.

Example 1 Coal tar pitch was hydrogenated and then heat treated while blowing nitrogen gas to obtain spinning men pitch with 100% optical anisotropy. The spinning pitch is set to 0.2 mm in nozzle hole diameter and 0.2 mm in nozzle length.
Melt spinning was performed using a spinneret with a nozzle hole number of λjo10 and a gold diameter of 2.01EII.

The spinneret (diameter 2!; Ofl) was provided with a nozzle hole as shown in Figure 1, and a heat insulating material layer S with a diameter of 100 mm was provided on the spinneret surface without the nozzle hole.

A ceramic molded body having a thickness of jn was used as the heat insulating material layer.

Also, below the nozzle is the diameter -jOIIIg, and the length! r 0
A 0 mN spinning tube was provided, and hot gas at 230° C. was fed into the spinning tube to cool it. The spinning pitch was melt-spun at a spinning temperature of 34 AO°C and wound around a bobbin at a speed of 100 y% to obtain a pitch fiber tow with a single yarn diameter of 10 μm and a bundled number of SO pieces.

During this time, the spinning was extremely stable and there were no troubles for an hour. The resulting pitch fiber tow was placed in the air for 3
Infusible at 10℃ and further under argon atmosphere/e00℃
Carbonization was performed to obtain carbon fibers. Thirty single yarns were arbitrarily sampled from among the obtained carbon fibers, and the strength and elastic modulus of each single yarn were measured, and the following results were obtained.

Tensile strength average value abOK9/m Standard deviation 30 kfi/11-d Elastic modulus average value Coj torpid Standard deviation 3 to 4/mI Comparative example 1 Example/ except that a spinneret without a heat insulating layer was used in Example/ Pitch was melt-spun in the same manner as described above. Pitch spinnability is unstable, medium, 70-2 after starting spinning
At 0 minutes, a problem of thread breakage occurred and spinning was interrupted. The spinning operation was repeated each time the yarn broke, and the pitch fiber tows obtained while the spinnability was relatively stable were collected.

Hereinafter, 30 single yarns of the carbon fibers obtained by infusibility and carbonization were treated in the same manner as in Example 1, and the strength and elastic modulus were determined in the same manner as in Example 1. The following results were obtained.

Tensile strength average value -33 to 9/- Standard deviation 55 kg/mri Elastic modulus average value 3 ton/+iJ Standard deviation A ton/ad It can be seen that there is a large variation (standard deviation) in the physical property values of the examples.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a schematic view of the spinning apparatus of the present invention, and FIG. 1 is a schematic view of the fiber discharge surface of the spinneret used in Examples.

/: Spinneret - 2 spinning nozzles J: Spinning pitch 4 t: Spinning pitch heating device S: Heat insulating layer 6: Pitch fiber 7 2 winding roller Applicant: Mitsubishi Chemical Industries, Ltd. Representative: For Hase - (7 others) ) 2nd concave

Claims (5)

[Claims] (1) When producing pitch-based carbon fiber by melt-spinning spinning pitch from a spinneret having a spinning nozzle, performing infusibility treatment, then carbonization treatment, and further graphitization treatment as necessary, the spinneret 1. A method for producing pitch-based carbon fiber, which comprises performing melt spinning using a spinneret provided with a heat insulating layer on the fiber discharge surface. (2) The method according to claim 1, wherein the heat insulating layer is made of phenolic resin fiber, glass fiber or ceramic fiber. (3) The method according to claim 1, wherein the heat insulating layer is made of asbestos or rock wool. (4) The method according to claim 1, wherein the heat insulating material layer is a ceramic molded body. (5) The method according to claim 2, wherein the heat insulating material layer is a woven or nonwoven fabric of fibers.