JPH0718057B2 - Pitch-based fiber manufacturing method - Google Patents

Description

The present invention relates to a method for producing pitch-based fibers,
More specifically, it relates to a method for stably producing pitch-based fibers having a fiber cross section that exhibits improved strength.

(Prior Art) As is well known, when carbonaceous raw materials such as heavy oil, tar, pitch, etc. are heated to 350 to 500 ° C, they are optically polarized under the polarized light of several microns to several hundreds of microns. Globules that exhibit asymmetric anisotropy are generated. Then, upon further heating, these small spheres grow and coalesce, and finally the whole becomes a state exhibiting optical anisotropy. This anisotropic structure is formed by stacking and orienting planar polymeric aromatic hydrocarbons produced by a thermal polycondensation reaction of a carbonaceous raw material in layers, and is regarded as a precursor of a graphite crystal structure.

A heat-treated product containing such an anisotropic structure is generally called a mesophase pitch, and a pitch fiber can be obtained by melt spinning the mesophase pitch through a nozzle.

Carbon fiber is a material with a high specific strength and a high specific elastic modulus, and has received the most attention as a filler fiber for high-performance composite materials. Among them, pitch-based carbon fibers are abundant in raw materials, and the yield in the carbonization process is large. It has various advantages over polyacrylonitrile-based carbon fiber, which has a high elastic modulus.

(Problems to be Solved by the Invention) Although the pitch-based carbon fiber has the above-mentioned characteristics, conventionally, when the mesophase pitch is spun as the raw material, the laminated structure of the planar polymer hydrocarbon in the obtained pitch fiber is obtained. Tend to be radially oriented within the fiber cross section, resulting in
Subsequent infusibilization, because tensile stress due to carbonization shrinkage during carbonization acts in the circumferential direction of the fiber cross section, a wedge-shaped crack extending in the fiber axis direction occurs in the cross section of the obtained carbon fiber, and the carbon fiber It is to impair the commercial value of.

(Means for Solving Problems) The present inventors have paid attention to such points, and as a result of diligent studies, they found that the above drawbacks can be overcome by spinning using a spinning nozzle having a specific structure. The invention was completed. That is, an object of the present invention is to stably produce pitch-based fibers whose fiber cross-sectional structure is not substantially radial-oriented.

However, such an object is, in a method for producing a pitch-based fiber by spinning a pitch containing mesophase from a spinning nozzle having an intermediate portion in which a nozzle hole is enlarged, in a case where the diameter of the intermediate portion of the nozzle is small. The diameter of the hole,
It is enlarged from the diameter (D ₃ ) of the pore part directly below the middle part,
There ratio of the diameter of the pores of the immediately above the middle portion and (D ₁₎ and the diameter of the intermediate portion _{(D 2) (D 2 /} D 1) is in the range of 1.5 to 10, the middle portion diameter and the intermediate portion the length (L ₂₎ the ratio of (L ₂ / D ₂₎ is shaped as in the range of 0.5 to 3, and the diameter of D ₁ is 0.1 to 1 mm, the diameter of D ₂ is 1 to 3 mm, D The diameter of ₃ is 0.1 to 0.5 mm, the length of L ₂ is 1 to 5 mm
Therefore, when obtained as carbon fibers, such spun fibers can be easily achieved by infusibilizing, carbonizing, and, if necessary, graphitizing. In the present invention, the pitch-based fiber includes the pitch fiber after spinning and the carbon fiber obtained therefrom in a superordinate conception.

The present invention will be described in more detail below.

Examples of the carbonaceous raw material for obtaining the pitch containing the mesophase of the present invention include coal-based coal tar, coal tar pitch, coal liquefaction, petroleum-based heavy oil, tar and pitch. These carbonaceous raw materials include:
Usually, impurities such as free carbon, undissolved coal, and ash are contained, but these impurities can be removed in advance by a known method such as filtration, centrifugation, or static sedimentation using a solvent. preferable.

In addition, the carbonaceous raw material is pretreated by, for example, a method of extracting the soluble matter with a specific solvent after heat treatment, or a method of hydrogenating in the presence of a hydrogen donating solvent or hydrogen gas. You can keep it.

The carbonaceous raw material or the pretreated carbonaceous raw material is then generally 350 to 500 ° C, preferably 380 to 450 ° C.
By heating for 2 minutes to 50 hours, preferably 5 minutes to 5 hours in an atmosphere of an inert gas such as nitrogen or argon, or by heat treatment for blowing, usually 70% or more of the optically anisotropic structure is obtained. A mesophase pitch containing can be obtained.

The ratio of the optically anisotropic structure of mesophase pitch in the present invention is a value obtained as a ratio of the area of a portion showing optical anisotropy in a mesophase pitch sample under a polarization microscope at room temperature.

Specifically, for example, a mesophase pitch sample crushed into a few mm square is embedded with a sample piece on almost the entire surface of a resin having a diameter of about 2 cm according to a conventional method, and after polishing the surface, the entire surface is covered with a polarizing microscope ( It is obtained by observing under 100 magnification) 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 above mesophase pitch is spun from a spinning nozzle having an intermediate portion in which nozzle holes are enlarged.
Here, the nozzle hole means a pore diameter that is circulated immediately before the melt pitch is spun and should regulate the yarn diameter. For example, as shown in FIG. 1, the intermediate portion 3 of the spinning nozzle 5 is a pore. The spinning nozzle is characterized in that it is expanded from a portion 2 (hereinafter referred to as "first pore portion") and a pore portion 4 (hereinafter referred to as "second pore portion"). The diameters of the first and second fine pores may be the same, or may have some differences as long as the enlarged intermediate portion can be formed.

The expanded shape of the intermediate portion gives the mesophase molecules in the pitch flowing out from the first fine pore portion in the axial direction, a flow that expands in the radial direction with respect to the spinning axis direction, and desirably within the intermediate portion. The shape is not particularly limited as long as the portion where the pitch stays is small, for example, a columnar shape,
Spherical shape, spheroidal shape, etc., in the inflow part from the first pore part to the middle part, and in the outflow part from the middle part to the second pore part
A shape having an angle of 90 degrees or less, that is, a shape in which the inflow portion and the outflow portion are conical, and the like can be mentioned.

The effect of the expanding flow of mesophase pitch in the middle part is
Mainly, the diameter of the first pore portion: D ₁ and the diameter of the middle portion: D ₂ , and the ratio D ₂ / D ₁ , the length of the middle portion: L _2, and the ratio of the diameter: D ₂ L ₂ / It is affected by D ₂ , and the diameter of the second pore part: D ₃ and the length: L ₃ , and the ratio L ₃ / D ₃ (see FIG. 2).

And D ₁ is 0.1 to ₁ mm, D ₂ is 1 to 3 mm, and the ratio D ₂ / D ₁ is 1.5.
The range of -10 is preferred.

L ₂ is 1 to 5 mm, L ₂ / D ₂ is 0.5 to 3, and D ₃ is 0.1 to 1
The mm range is preferred.

Regarding L ₃ , the value of L ₃ / D ₃ is more preferably 10 or less, and most preferably 3 or less.

When spinning is performed using the spinning nozzle of the present invention, the spinning safety does not decrease, melt spinning can be performed in the same manner as in a normal spinning nozzle, and pitch-based fibers having improved strength can be stably supplied.

The pitch-based fibers obtained by melt-spinning have an improved fiber cross-sectional structure, that is, random orientation, onion-like orientation, or an intermediate orientation thereof, and such orientation is the subsequent infusibilization, carbonization, and further Does not change even after graphitization.

Here, the onion-like orientation means that the main portion of the fiber cross-sectional area has concentric molecular orientation, and
In particular, the outer peripheral portion includes those which are radially oriented to such an extent that cracking is less likely to occur in the subsequent carbonization or graphitization treatment. Moreover, these fiber cross-sectional structures were measured by a polarization microscope.

The pitch-based fibers thus obtained are infusibilized, carbonized by graphitizing as necessary, and have a fiber cross-sectional structure of random orientation or onion-like orientation, without wedge-shaped cracks extending in the fiber axis direction, high characteristics The pitch-based carbon fiber can be obtained.

The present invention will be specifically described below with reference to examples, but the present invention is not limited to the examples as long as the gist thereof is not exceeded.

(Example) (Example 1) 2 kg of coal tar pitch and 2 kg of hydrogenated aromatic oil were added to a 5 l autoclave, and heat-treated at 425 ° C for 1 hour. This treated product was distilled under reduced pressure to obtain the residual pitch. Next, 700 g of this residual pitch was heated at 450 ° C. for 40 minutes while bubbling nitrogen gas.

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

The mesophase pitch is first discharged as shown in FIG. 2, an intermediate portion having a larger diameter than the first and second fine pores, which is continuous thereunder, and the mesophase pitch is actually discharged. Using a nozzle with a shape consisting of the second pores 33
Melt-spun at 6 ° C.

This nozzle has a diameter D ₁ of the first fine hole portion of 0.3 mm and a length L ₁ of 0.6
mm, the diameter D _{2 of the} intermediate portion is 2 mm, the length L ₂ is 2.1 mm, the diameter D ₃ of the second pore portion is 0.3 mm, and the length L ₃ is 0.1 mm. At this time, D ₂ / D ₁
≈6.6, L ₂ / D ₂ ≈1.

The obtained pitch-based fiber had a cross-sectional structure with an onion-like orientation in which a part of the outer circumference was radial orientation. Next, the obtained pitch-based fiber was made infusible in air at 310 ° C., and further carbonized at 1400 ° C. in an argon atmosphere to obtain a carbon fiber. This carbon fiber also had a cross-sectional structure of onion-like orientation in which a part of the outer circumference was radial orientation similar to the pitch-based fiber described above. The shape of the obtained fiber is shown in FIG. 3 as a scanning electron micrograph at 7500 times.

Comparative Example 1 The mesophase pitch obtained in Example 1 was melt-spun at 336 ° C. using a spinning nozzle having pores with a diameter of 0.3 mm and a length of 0.1 mm.

Infusibilizing the obtained pitch fiber under the same conditions as in Example 1,
Carbon fiber was obtained by carbonization, and this carbon fiber had a radial-oriented cross-sectional structure and had a wedge-shaped crack extending in the fiber axis direction. The shape of the obtained fiber is shown in FIG. 7 as a scanning electron micrograph at 5500 times.

(Example 2) 63 g of residue pitch obtained in the same manner as in Example 1 was subjected to heat treatment while blowing nitrogen gas to obtain 21 g of mesophase pitch. The optical anisotropy ratio of the obtained mesophase pitch was about 75%.

This mesophase pitch was melt-spun at 327 ° C. using the same nozzle as in Example 1. The obtained pitch fiber was infusibilized and carbonized under the same conditions as in Example 1 to obtain a carbon fiber. This carbon fiber had a cross-sectional structure with an intermediate orientation between onion-like orientation and random orientation.

(Example 3) As the nozzle, the diameter D ₁ of the first fine hole portion was 0.1 mm, and the diameter D of the intermediate portion was
Carbon fiber was obtained by spinning, infusibilizing and carbonizing under the same conditions as in Example 1 except that ₂ was 1 mm, length L ₂ was 1 mm, and the diameter D ₃ of the second pores was 0.1 mm. . At this time, D ₂ / D ₁ = 10, L ₂ / D ₂ =
It is 1.

The obtained carbon fiber had a cross-sectional structure of onion-like orientation in which a part of the outer circumference was radial orientation. The shape of the obtained fiber is shown in FIG. 4 as a scanning electron micrograph of 5000 times.

(Example 4) As a nozzle, the diameter D ₁ of the first fine hole portion was 1 mm, and the length L ₁ was 2 mm.
Diameter D _{2 of the} middle portion is 2 mm, length L ₂ is 5 mm, diameter D ₃ of the second fine pore portion
Was spun, infusibilized and carbonized under the same conditions as in Example 1 except that the carbon fiber was 0.5 mm to obtain a carbon fiber. At this time, D ₂ / D ₁ =
2, L ₂ / D ₂ = 2.5.

The obtained carbon fiber had a cross-sectional structure of onion-like orientation in which a part of the outer circumference was radial orientation.

(Example 5) As a nozzle, the diameter D ₁ of the first fine hole portion was 1 mm, and the length L ₁ was 2 mm.
Spinning, infusibilization, and carbonization were carried out under the same conditions as in Example 1 except that the diameter D _{2 of the} intermediate portion was 1.5 mm, the length L ₂ was 4.5 mm, and the diameter D ₃ of the second pore portion was 0.5 mm. Then, a carbon fiber was obtained. At this time D ₂
/ D ₁ = 1.5 and L ₂ / D ₂ = 3.

The obtained carbon fiber had a cross-sectional structure of onion-like orientation in which a part of the outer circumference was radial orientation.

(Example 6) As a nozzle, the diameter D ₁ of the first fine hole portion was 1 mm, and the length L ₁ was 2 mm.
Diameter D _{2 of the} middle portion is 2 mm, length L ₂ is 1 mm, diameter D ₃ of the second pore portion
Was spun, infusibilized and carbonized under the same conditions as in Example 1 except that the carbon fiber was 0.5 mm to obtain a carbon fiber. At this time, D ₂ / D ₁ =
2, L ₂ / D ₂ = 0.5.

The obtained carbon fiber had a cross-sectional structure of onion-like orientation in which a part of the outer circumference was radial orientation. The shape of the obtained fiber is shown in FIG. 5 as a scanning electron microscope photograph of 3000 times.

(Example 7) As a nozzle, the diameter D ₁ of the first fine hole portion was 1 mm, and the length L ₁ was 3 mm.
Diameter D _{2 of the} middle portion is 3 mm, length L ₂ is 5 mm, diameter D ₃ of the second fine pore portion
Was spun, infusibilized and carbonized under the same conditions as in Example 1 except that the carbon fiber was 0.5 mm to obtain a carbon fiber. At this time, D ₂ / D ₁ =
3 is L ₂ / D ₂ = 1.67.

The obtained carbon fiber had a cross-sectional structure of onion-like orientation in which a part of the outer circumference was radial orientation. The shape of the obtained fiber is shown in FIG. 6 as a scanning electron micrograph at 5500 times.

Table 1 shows the shapes of the nozzles used in the above examples.

(Effect of the invention) By the production method of the present invention, since it is possible to reliably obtain a pitch-based fiber having a cross-sectional structure of an onion-like orientation in which a part of the outer circumference is radial orientation, it is difficult for cracks and the like to occur, cracks, etc. Since it is difficult for the strength to decrease due to the above, high-strength carbon fibers can be easily obtained.

[Brief description of drawings]

FIG. 1 shows a partial cross-sectional schematic view of the spinneret of the present invention. FIG. 2 shows an enlarged view of the spinning nozzle section of FIG. FIG. 3 is an electron micrograph showing the shape of the fiber obtained in Example 1. FIG. 4 is an electron micrograph showing the shape of the fiber obtained in Example 3. FIG. 5 is an electron micrograph showing the shape of the fiber obtained in Example 6. FIG. 6 is an electron micrograph showing the shape of the fiber obtained in Example 7. FIG. 7 is an electron micrograph showing the shape of the fiber obtained in Comparative Example 1. 1: introduction hole, 2: first pore portion, 3: intermediate portion, 4: second pore portion 5: spinning nozzle portion, D ₁ : diameter of first pore portion, D ₂ : intermediate portion Diameter D ₃ : diameter of the second pore portion, L ₁ : length of the first pore portion L ₂ : length of the intermediate portion, L ₃ : length of the second pore portion

Claims (2)

[Claims] 1. A method for producing a pitch-based fiber by spinning a pitch containing mesophase from a spinning nozzle having an intermediate portion in which nozzle holes are enlarged, wherein the diameter of the intermediate portion of the nozzle is directly above the fine pores. The diameter of the pores is larger than the diameter of the pores just below the middle part (D ₃ ) and the diameter of the pores just above the middle part (D ₁ ) and the diameter of the middle part (D ₂ ) Ratio (D ₂ /
D ₁ ) is in the range of 1.5 to 10, and the ratio (L ₂ / D ₂ ) of the diameter of the intermediate part to the length of the intermediate part (L ₂ ) is in the range of 0.5 to 3, And the diameter of D ₁ is 0.1-1mm, the diameter of D ₂ is 1-3m
A method for producing a pitch-based fiber, wherein m and D _{3 have} a diameter of 0.1 to 0.5 mm and L _{2 have} a length of 1 to 5 mm. 2. The method for producing a pitch-based fiber according to claim 1, wherein the fiber cross section of the pitch-based fiber is substantially random or onion-like orientation.