JPS6175820A - Manufacturing method of pitch carbon fiber - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION 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 a fiber cross section that exhibits improved strength. It is.

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. Among them, pitch-based carbon fiber has various advantages over polyacrylonitrile-based carbon fiber, such as abundant raw materials, high yield in the carbonization process, and high fiber elastic modulus.

By the way, instead of the isotropic pitch conventionally used as the spinning pitch, by heat-treating the carbonaceous raw material to develop anisotropy and forming molecular species that are easy to orient. Since it was reported that pitch-based carbon fiber with high properties could be obtained (Tokukosho+79-g43'1),
Various studies have been made regarding the preparation of spinning pitch with good orientation.

As is well known, when carbonaceous raw materials such as heavy oil, tar, pitch, etc. are heated to 350 to 00°C, optical anisotropy occurs under polarized light, with particle sizes ranging from several microns to several hundred microns. A small sphere is generated. Then, when heated further,
These spherules grow and coalesce, until the entire structure exhibits optical anisotropy. This anisotropic structure is composed of planar polymeric aromatic hydrocarbons produced by thermal polycondensation reaction of carbonaceous raw materials, stacked and oriented in layers, and is considered to be a precursor of a graphite crystal structure.

A heat-treated product containing such an anisotropic structure is generally called mesophase pitch.

As a method of using a mesophase pitch that hardens as a spinning pitch, for example, &0-qO obtained by heat-treating petroleum-based pitch at about 3so-<xro℃ under stationary conditions.
A method has been proposed in which a pitch containing a weight-related mesophase is used as a spinning pitch (Japanese Patent Application Laid-Open No. 9-9727).

However, since it takes a long time to mentate an isotropic carbonaceous raw material by such a method, the carbonaceous raw material is treated in advance with a sufficient amount of solvent to obtain its insoluble matter, and the
Heat treatment for a short time of 10 minutes or less at a temperature of 0°C to form so-called neomesophase pitch, which is highly oriented, has an optically anisotropic portion of 75% by weight or more, and has a quinoline solubility of 23% by weight or less. However, a method has been proposed in which this is used as the spinning pitch (Japanese Patent Application Laid-Open No. 11-11-1.O'A, No. 2.7).

In addition, as spinning pitch with good orientation for producing high-performance carbon fibers, for example, coal tar pitch is hydrogenated in the presence of a medium such as tetrahydroquinoline, and then approximately t
A pitch that is optically isotropic, obtained by short-time heat treatment at tso°C, and has the property of becoming anisotropic by heating above 0°C, the so-called pre-mesophase pitch (
JP-A-3G-/gtI2/), or a pitch obtained by hydrogenating mesophase pitch by Birch reduction method etc., which is optically isotropic and shows orientation in that direction when an external force is applied. , dormant mesophase (JP-A-57-100/gl, No.), etc. have been proposed.

However, when spinning using a spinning pitch with good orientation as described above, the layered structure of planar polymeric hydrocarbons in the resulting pitch fiber tends to be radially oriented within the fiber cross section, resulting in subsequent failure. During melting and carbonization, tensile stress caused by carbonization shrinkage acts in the circumferential direction of the fiber cross section, so wedge-shaped cracks extending in the fiber axis direction occur in the cross section of the resulting carbon fiber, which reduces the commercial value of the carbon fiber. It will damage the.

The inventors of the present invention have kept these points in mind and as a result of intensive study, the above drawbacks can be reliably and stably overcome by making the nozzle hole of the spinning nozzle into a specific shape and realizing that shape using a specific construction method. This discovery led to the completion of the present invention. That is, an object of the present invention is to stably and industrially advantageously produce pitch-based carbon fibers whose fiber cross-sectional structure is not substantially radially oriented. , a spinning nozzle having a wake section and an intermediate section whose diameter is larger than both the inflow section and the wake section, and in which a spinneret section separated at the intermediate section is integrally constituted. This is achieved by spinning a pitch fiber from a spinning nozzle, subjecting it to infusibility and carbonization treatment, and further subjecting it to graphitization treatment if necessary.

To explain the present invention in more detail below, the spinning pitch used in the present invention is particularly limited as long as it forms molecular species that are easily oriented and provides optically anisotropic carbon fibers. Instead, various conventional ones such as those mentioned above can be used. Examples of the carbonaceous raw material for obtaining spinning pitch include coal-based coal tar, coal tar pitch, coal liquefied products, petroleum-based heavy oil, tar, pitch, and the like. These carbonaceous raw materials usually contain impurities such as free carbon, undissolved coal, and ash, but these impurities can be removed by well-known methods such as filtration, centrifugation, or static sedimentation using solvents. It is preferable to remove it in advance using the following method.

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 heated at a temperature of usually 350 to 500°C, preferably 30 to 0°C for - minutes to 50 hours, preferably S minutes to 5 hours. Mesophase pitch containing an optically anisotropic structure of 90% or more, especially 70% or more, obtained by heat treatment under an inert gas atmosphere such as nitrogen or argon or while being blown into the atmosphere, can be preferably used. The optically anisotropic structure ratio of mesophase pitch is determined by the area ratio of a portion exhibiting optical anisotropy in a mesophase pitch sample under a polarizing microscope at room temperature.

Specifically, - For example, a mesophase pitch sample is crushed into pieces of several meters square, and the sample piece is embedded into almost the entire surface of a resin with a diameter of approximately 100 mm using a conventional method. After polishing the surface, the entire surface is thoroughly inspected using a polarizing microscope. It is determined by observing the sample under a magnification of 100 and measuring the ratio of the area of the optically anisotropic portion to the total surface area of the sample.

In the present invention, the spinning pitch as described above is obtained by using a spinning nozzle having a shape having a middle part with an enlarged nozzle hole, and comprising at least two spinneret parts separated at the middle part, Spinning is performed using a spinning nozzle configured such that the nozzle hole has the above-described shape by joining the two parts at the cut plane. Here, the nozzle hole means a small diameter hole through which molten pitch flows just before spinning to form yarn, but the nozzle hole of a normal spinning nozzle has a constant diameter over its entire length. , or has a structure in which the diameter gradually decreases toward the outlet, but in the present invention, it is important that the nozzle hole is first enlarged in the middle part.

To explain in more detail about the spinning nozzle used in the present invention, the nozzle hole of the spinning nozzle consists of a spinning pitch inlet section, an intermediate section, and a trailing section. This means that the diameter of the spinning pitch is larger than that of the inlet and downstream parts of the spinning pitch. For example, FIG. 1 shows seven typical examples of spinning nozzles used in the present invention.
The figure is a schematic vertical cross-sectional view showing an enlarged view of the nozzle hole. In both figures, / is the introduction hole of the spinning pitch, λ is the inflow part, 3 is the enlarged intermediate part, and q is the downstream part. , y is the spinneret portion A, n is the spinneret portion B, 7 is the end surface on the spinning side of the spinneret portion B, and g is the sectioned surface at the intermediate portion, respectively.

That is, the nozzle hole is a straight pipe with a circular cross section, and consists of a spinning pitch inlet part and a trailing part having the same diameter, and a straight pipe with a circular cross section located in the middle and having a larger diameter than these. It has a shape composed of an intermediate portion 3.

When such a nozzle is used, the spinning pitch first forms a primary yarn at the spinning pitch inlet, and then forms a flow component that expands in the radial direction with respect to the flow of the spinning pitch in the spinning axis direction at the expanded intermediate section. It is thought that by adding this, the mesophase molecules are oriented in that direction, and finally, they are discharged while ensuring spinnability at the trailing part where the diameter is reduced again.

Here, the intermediate part is usually cylindrical as shown in FIG. 2, but it is important and preferable to obtain a component that expands in the radial direction in the flow of the primary yarn formed at the spinning pitch inlet part. It is sufficient to have a shape that has a small area where the spinning pitch remains, and various shapes such as a spherical shape, a spheroidal shape, a modified shape of these shapes, and a gourd-like shape in which multiple enlarged parts are connected are suitable. It is possible to use a straight nozzle, or a normal straight nozzle with orifices installed at the upper and lower ends. Note that the connecting portions between the spinning pitch inflow portion and the intermediate portion, and between the intermediate portion and the trailing portion may be formed smoothly.

The diameter (D2) of the middle part is usually 0. / ~ evening familiarity, preferably 0
．． 7S ~ 3 order, and its length L2) is usually 0.02
~/Omm, preferably 0.7! i~! rtMR. Also, the ratio of length to diameter (L2/D2) is usually 0.
2-S1 preferably 0.5-3. In addition, if the intermediate part is not cylindrical as shown in Fig. 2, the diameter of the intermediate part (D2
) refers to the diameter of the widest part of the middle part.

Next, the spinning pitch inflow section and the downstream section will be explained.

These cross-sectional shapes are usually circular as shown in FIG. 2, but if desired, they can be shaped other than circularly, such as an ellipse. The diameter of the spinning pitch inlet and trailing portion is usually 0.
0/~2 gourds. Preferably, the diameter (Dl) of the spinning pitch inflow section is 0.05 to 1/2, and the diameter (D3) of the downstream section
is 0.0-~/kun.

Note that if the spinning pitch inlet and trailing portions are not uniform in thickness, the diameter of the spinning pitch inlet is the diameter of the narrowest part of the spinning pitch inlet, and the diameter of the trailing portion is the diameter of the spinning pitch inlet. means the diameter of the discharge part. The length of the spinning pitch inlet (Ll) is usually 2 or less, and the length of the trailing portion (Ll) is usually 3 or less. In addition, the ratio of the length and diameter of the trailing section (3/D3) is usually io or less, preferably 3 or less.If the lengths of the spinning pitch inflow section and trailing section are longer than the above ranges, the radial It is estimated that the orientation is more likely to be reproduced or remain.

In the spinning nozzle used in the present invention, the intermediate section gives a component that expands in the radial direction to the flow of the primary yarn formed at the spinning pitch inflow section, so the diameter ratio (D2/
D, ) must be greater than l. Normal (D2/
D,) is in the range of 7.5-10. In addition, the trailing part is to restrict the flow expanded in the radial direction in the intermediate part again to regulate the yarn diameter and discharge it while ensuring spinnability, so the diameter ratio of both (D, /D2) Must be smaller than /.

Furthermore, the diameter of the spinning pitch inlet section (Dl) and the diameter of the downstream section (D
, ) (D3/D,) is desirably equal to or less than HaS. By selecting this ratio to an appropriate value, spinnability can be improved and carbon fibers with good physical properties can be obtained. Within the above range, CDs, /
When D, )≦l, the diameter of the trailing portion becomes relatively small, and the spinnability tends to further improve. Also (D, /D,
)≧/, the diameter of the trailing portion becomes relatively large, which tends to provide carbon fibers with improved physical properties.

Other aspects of the nozzle hole shape in the spinning nozzle used in the present invention are shown in FIGS. 3 to 7 as schematic vertical cross-sectional views showing only the shape of the nozzle hole. (Dl) and (D3) may be different from each other, or the spinning pitch inlet may have no substantially straight tubular portion as shown in FIG.

Still, FIG. 6 conceptually illustrates only the shape of the enlarged middle portion of the nozzle hole. However, the diameters D1 and D3 of the spinning pitch inflow section and the downstream section may be equal as shown in the figure,
Also, either one may be larger as shown in FIG. 3 or FIG. 9.

Furthermore, although FIG. 7 conceptually illustrates the deformation of the inflow section and the wake section, as shown in FIG. The spinning pitch inflow section or trailing section may not have a substantially straight tubular section as long as the gist of the non-explosion surface is not exceeded in the hole. In addition to the nozzle hole shape detailed above, other important requirements for the present invention As shown in FIG. 1, the nozzle hole is composed of at least two spinneret parts A and B. All of these two mouth portions are parts of the spinneret that are separated in the intermediate portion 3 by a cutting plane g, which is a plane parallel to the spinning end surface 7 of the spinneret portion B. And all these parts of both mouths are the section plane g
, they are joined together by a removable mechanism to form a nozzle hole and a spinning nozzle, and are used for a spinning operation. By configuring the spinning nozzle from at least two spindle parts, it becomes possible to manufacture the above-mentioned shapes of the inlet, intermediate, and downstream parts of the nozzle hole with great precision and ease as designed. Therefore, it is possible to further ensure the occurrence of a tendency to provide carbon IR fibers with a random or onion-like structure based on the nozzle shape.

Note that the mouthpiece portion may be divided into three or more parts; for example, FIG. The nozzle part A(5) is further separated from the nozzle part A'(!1) at the cutting surface 7 at the inflow side end of the inlet part, and during the spinning operation, nozzle part A'
and B are joined together at the cutting surface g, and the nozzle parts A' and A' are joined together at the cutting surface 9, thereby forming a nozzle hole and a spinning nozzle.

In this way, it is desirable to determine the number of divisions of the nozzle part as necessary so that each nozzle part does not have the narrowest hole in its internal middle depending on the nozzle hole shape and the relationship between it and the introduction hole of the spinning pitch. .

Therefore, as long as this condition is satisfied, the present invention can be modified in many ways, examples of which are shown in FIGS. That is, in the gist of the present invention, the expression "divided at the middle part of the vagina" includes the case where it is divided at the edge of the middle part, and FIG. Fig. 1O shows a basic cap at the inlet side end edge 3' of the intermediate portion 3, and a cap which is an annular member. Further, the method of fitting the part/S is shown in FIG. 1, which is a cylindrical member whose lower surface is open to the basic cap 26 at the downstream end edge 3 of the intermediate section 3, and whose upper surface center is perforated. The method of fitting the base portion Ω5 is illustrated respectively. In this way, in the present invention, the shape and manufacture of the specific nozzle hole, the method of stacking each divided nozzle part, the method of fitting one or more nozzle parts into one basic nozzle, the combination of both methods, etc.
Various methods can be selected depending on convenience of use.

The spun pitch is spun using the above-mentioned spinning nozzle to become a pitch-based fiber, which is then made infusible and carbonized by a conventional method, and further graphitized if necessary, resulting in a randomly oriented or onion-like fiber. It is possible to obtain a high-performance pitch-based carbon fiber that has a cross-sectional structure completely different from the conventional radial-oriented cross-sectional structure in terms of orientation, and has no wedge-shaped crank extending in the fiber axis direction.

Here, the onion-like orientation means that the main portion of the fiber cross section has a concentric molecular orientation, and a portion, particularly the outer peripheral portion, may have a radial orientation to the extent that no cranking occurs.

Note that these fiber cross-sectional structures were observed using a polarizing microscope or a scanning electron microscope.

Generally, in the case of synthetic fibers, spinning nozzles of various shapes have been proposed for the production of composite yarns, irregular cross-section yarns, etc., and for other purposes. Although it is thought that this is caused by the following, there is no known example in which molecular orientation is influenced by the nozzle shape.

The present inventors have made the surprising finding that, unlike such synthetic fibers, the orientation of the cross-sectional structure of pitch fibers, at least when configured as carbon fibers, can be influenced by the nozzle shape. The present invention was arrived at based on this finding. The reason for this difference is not clear, but there is no doubt that it is basically due to the difference in the spinning raw materials of the synthetic polymer and the pitch.

Based on this knowledge, the present invention further constructs a nozzle having the shape described above from at least two mouth parts separated by a specific part, thereby making it possible to easily manufacture a nozzle shape as designed, thereby making it possible to easily produce a nozzle shape as designed. Random or onion-like orientation can be generated more reliably, and if the nozzle hole becomes clogged for some reason, it can be cleaned very easily and completely by disassembling each nozzle part, so it can be put back into use within a short time. It is possible to realize a great industrial advantage in that it can be recovered. In addition, although the entire portions of the divided openings are basically tightly joined over the entire surface of the divided surface, a partially designed gap may be provided in a portion other than the nozzle hole for some purpose.

The present invention will be specifically explained below with reference to Examples. Example/ A nozzle having the shape shown in FIG. 2 was formed as follows.

That is, at the center of the inflow section 3 (midpoint of length L2) in the figure, there is a section g that is a plane parallel to the spinning end surface 7 of the spinneret.
The nozzle part A and the nozzle part B, which are separated at Created. The dimensions of each nozzle hole are D:0. Jmm,
L: 0. /s mm, D2: 2. Omm,
L2: 2. / w, D3: 0. ．． 3wn, L3
:θ, / familiar.

Coal tarp f2 7 and hydrogenated aromatic oil 2Kq were added to a 5t autoclave, and heat treated at 4'25°C for 7 hours. This treated product was distilled under reduced pressure to obtain pitch residue. Next, this residual pitch 7009 was heat-treated at ≠50° C. for po minutes while bubbling nitrogen gas.

The anisotropy ratio of the obtained mesophase pitch was approximately 99%.

This mesophase pitch was melt-spun at 336° C. using the above-mentioned spinning nozzle, and the resulting pitch fibers had a cross-sectional structure with an onion-like orientation in which a portion of the outer periphery was radially oriented. Then, the obtained pitch fibers were placed in air for 3
Infusible at 70℃ and further under argon atmosphere/q00℃
Carbonization was performed to obtain carbon fibers. This carbon fiber also had a cross-sectional structure with an onion-like orientation in which part of the outer periphery was radially oriented, similar to the pitch fiber.

The mesophase pitch obtained in Comparative Example/Example/ has a diameter of 0.3,
Length is 0. 33A' using a spinning nozzle with small pores.
It was melt spun at C.

The obtained pitch fibers were then infusible and carbonized under the same conditions as in Example/1 to obtain carbon fibers, which had a radially oriented cross-sectional structure and a wedge-shaped structure extending in the fiber axis direction. It had a crank, and there was no change in the fiber cross-sectional structure before and after the infusibility and carbonization treatments.

Embodiment A spinning nozzle having a nozzle hole shaped as shown in FIG. 3 was constructed by separately drilling three nozzle parts as shown in FIG. , and the cap parts A' and B are respectively sectioned plane 7 and sectioned plane g.
A multi-spinning nozzle was manufactured by joining them together and integrally constructing them by tightening screws (not shown). The dimensions of each nozzle hole are: D: 0.3rmnXL: 0.6
Pus, D: 2.0, L2: 2.1. Coral, D3:
0.2 eyebrows, L3: 0, /Kun.

Coal tar pitch/7 and hydrogenated aromatic oil 0. Add left Kq, 200Kg/cr4
The mixture was heat-treated at 3 gO 0 C for 7 hours using a catalyst under a hydrogen pressure of . This treated product was distilled under reduced pressure to obtain pitch residue.

Next, nitrogen gas was blown into the residue pitch filter 0&, and heat treatment was performed at 20°C for 735 minutes to achieve 2/! A mesophase pitch of i was obtained.

The anisotropy ratio of the obtained mesophase pitch was about 60%.

This mesophase pitch was spun using the above-mentioned spinning nozzle.
Melt spinning was carried out at 33°C.

Next, the obtained pitch fibers were made infusible and carbonized under the same conditions as in Example/1 to obtain carbon fibers, but these carbon fibers had a cross-sectional structure with an intermediate orientation between onion-like orientation and random orientation. There was no change in the fiber cross-sectional structure before and after the melting and carbonization treatments.

[Brief explanation of drawings]

FIG. 1 is a partially vertical cross-sectional schematic diagram of the spinneret of the present invention, and FIG. 2 is an enlarged view of the nozzle hole of the spinning nozzle shown in FIG. FIG. 3, FIG. 9, and FIG. S are vertical cross-sectional schematic diagrams conceptually showing only the shape of the nozzle hole, showing examples of deformation of the nozzle hole. FIG. 6.7 is a model conceptually showing another specific example of the shape of the nozzle hole of the spinning nozzle of the present invention. Figures g, 9.10 and 77 are schematic vertical cross-sectional views showing the nozzle hole of the spinning nozzle of the present invention.
Spinning pitch inlet part 3; intermediate part 3'; edge part on the inflow part side of the intermediate part 3'; edge part on the downstream side of the intermediate part q; trailing part 5; spinning metal part A5'; spinning metal Part A'S''; Spinneret part A''Ro; Spinning rod part B7; Spinning side end surface of spinneret part B; Cutting surface in the middle part; Cutting surface at the end of the inlet part / B; Basic rod Part 15; Annular metal part Yuro; Basic mouth part 2 left; Cylindrical mouth part 1; Diameter of the spinning pitch inlet D; Diameter of the intermediate part D3; Diameter of the trailing part L
,; Length of spinning pitch inlet part L2; Length of intermediate part L
31 Length of downstream part Applicant: Mitsubishi Chemical Industries, Ltd. Representative: Patent Attorney Nagakagawa - (and 7 others) Figure 1 Figure 3 Figure 5 Figure 6 (cl) ()) (C )(d)(e)
(f)
(4n(t><7) (4) Figure 17 (a) (b) (ko)
(d) Figure 8 % 9 Figure 10 Figure 11 U

Claims (2)

[Claims] (1) The spinning pitch is determined by a spinning nozzle in which the nozzle hole has an inflow part, a wake part, and an intermediate part whose diameter is larger than both the inlet part and the wake part, and the spinning pitch is divided at the intermediate part. The method is characterized in that pitch fibers are obtained by spinning from a spinning nozzle integrally formed with the spinneret portion, and the pitch fibers are subjected to infusibility and carbonization treatment, and further graphitization treatment as necessary. A method for producing pitch-based carbon fiber. (2) The method for producing a pitch-based carbon fiber according to claim 1, wherein the spinning pitch is a pitch containing mesophase.