JPH0477597A - Pitch and production of carbon fiber using the same pitch - Google Patents

Abstract

PURPOSE:To obtain a new pitch capable of providing a carbon fiber having specific properties, suitable as a raw material for airplane component, sport goods, etc., and having excellent high-strength, etc., by adding optical anisotropic phase to pitch at a specific amount. CONSTITUTION:Heavy oil [preferably having >=350 deg.C initial distillation point and <=2wt.% hetero element content e.g. S or O] such as petroleum-based heavy oil is heat-treated and a heat decomposed material is removed to provide the objective pitch containing >=90% (preferably >=95%) optical anisotropic phase, being <=20% in weight decrease at 800 deg.C by thermobalance, having exothermic peak existing between 250 deg.C and 520 deg.C by differential thermal analysis, but never existing in temperature region exceeding 520 deg.C. Furthermore, the resultant pitch 1 is subjected to melt spinning, preferably at <=360 deg.C, and subjected to infusibilization treatment, preferably in 0.5-15vol.% nitrogen dioxide and further subjected to carbonization treatment under an inert atmosphere to provide the carbon fiber.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a new pitch and a method for manufacturing carbon fiber using the same, and more specifically, it relates to a new pitch and a method for manufacturing carbon fiber using the same. The present invention relates to a pitch capable of producing carbon fibers having a tensile strength of 2 or more, and a method for producing the high-performance carbon fibers using this pitch.

[Prior art and problems to be solved by the invention] Carbon fiber has excellent characteristics such as high strength, high modulus of elasticity, and light weight, so it is used for example in aircraft parts, automobile parts, In recent years, demand has increased significantly for use as a material and resin reinforcing material in various fields such as sports equipment.

This carbon fiber can be roughly classified into PAN-based carbon fiber and pitch-based carbon fiber.

The former PAN-based carbon fiber is made from polyacrylonitrile and usually has high strength and medium elastic modulus, or has the disadvantage of high manufacturing cost. .

On the other hand, the latter pitch-based carbon fiber uses carbonaceous pitch as a raw material, so its production cost is low and it is economically viable, but it has the disadvantage of lower tensile strength compared to PAN-based carbon fiber. .

By the way, due to recent improvements in technology, some pitch-based carbon fibers have appeared that have a tensile strength of up to 350 kg/mm2. However, in order to compete with PAN-based carbon fibers, pitch-based carbon fibers with even higher tensile strength are required.

As one such technique, a method of spinning using a irregularly shaped nozzle has been proposed (Japanese Unexamined Patent Publication Nos. 61-47826 and 61-113828).

According to this method, pitch-based carbon fibers having a tensile strength of 450 kg/mm2 or more can be obtained, but the resulting carbon fibers also have irregular shapes, so that the handling properties during winding are extremely poor. Further, there are problems such as the spinnability is somewhat poor and it becomes difficult to set the infusibility conditions.

[Means to solve the problem]

Therefore, as a result of intensive research to solve these conventional problems, the present inventors discovered a new pitch with specific properties. When carbon fiber was manufactured using this pitch, the cross-sectional shape It was discovered that a pitch-based carbon fiber having a tensile strength of 450 kg/mm2 or more can be obtained without maintaining a perfect circle, and based on the second finding, the present invention was completed.

That is, the present invention is characterized in that the content of the optically anisotropic phase is 90% by weight or more, the weight loss at a temperature of 800°C measured by thermobalance (TG) is 20% by weight or less, and differential thermal analysis ( DTA) exothermic peak is 250-5
Provided is a pitch that is between 20°C and does not exist in a temperature range exceeding 520°C, and is characterized by subjecting this pitch to infusibility treatment and carbonization treatment after melt spinning. A method for manufacturing carbon fiber is also provided.

As described above, the pitch of the present invention is a mesophase pitch containing 90% by weight or more, preferably 95% by weight or more of an optically anisotropic phase (mesophase). Here, the meso phase is 90% by weight.
If it is less than that, the strength of the obtained carbon fiber will decrease, which is not preferable.

Furthermore, as mentioned above, the pitch of the present invention is determined by thermobalance (TO).
The weight loss at a temperature of 800°C (under an inert gas atmosphere) according to ) is 250-52
It exists between 0'C and does not exist in a temperature range exceeding 520C.

Here, if the weight loss at a temperature of 800''C on a thermobalance exceeds 20% by weight, the strength of the carbon fiber will decrease.

Furthermore, if the exothermic peak determined by differential thermal analysis exists in a temperature range exceeding 520''C, the strength of the obtained carbon fiber will decrease, which is not preferable.

Furthermore, the pitch of the present invention preferably has the properties shown below. That is, the quinoline solubility is 5 to 5
0% by weight, more preferably 15-40% by weight, and a softening point of 250-380''C1, more preferably 265-3
40"C. If the quinolinated content is less than 5% by weight, the strength of the carbon fiber will decrease, while if it exceeds 50% by weight, the spinnability will decrease.
If the temperature is less than 0°C, the strength of the carbon fiber will decrease, while if it exceeds 380°C, the spinnability will decrease.

In addition, the content of the optically anisotropic phase, which is a mesophase, is determined by observing the content under a polarizing microscope under crossed Nicols, taking a photograph, and determining the proportion occupied by the optically anisotropic phase or the optically isotropic phase. be able to.

The pitch of the present invention having the above characteristics is, for example,
It can be manufactured by the following method.

First, as the heavy oil that is the raw material for pitch, any of the petroleum and nine coal-based heavy oils can be used, but in the case of coal-based heavy oil, it is necessary to use one that has been hydrogenated under known conditions. . In addition to this, the heavy oil that is used as a raw material for pitch does not contain mesophase or quinoline-soluble components that cause a decrease in the strength of carbon fibers, and it also does not substantially contain catalyst ash. In order to facilitate the removal of thermal decomposition products during heat treatment, the initial boiling point is 300°C or higher, preferably 350°C or higher, and the content of hetero elements such as sulfur, nitrogen, and oxygen is 5. It is necessary to use less than 2% by weight, preferably less than 2% by weight.

Next, such raw material heavy oil is subjected to heat treatment.

Heat treatment is used to efficiently remove thermal decomposition products.
It is preferable to perform a two-stage reduced pressure heat treatment.

First stage is temperature 360~450℃ 1 pressure 1~20℃
Heavy-duty treatment is performed for 0.5 to 5 hours under torrO heat treatment conditions. The pitch obtained here is isotropic on the entire surface, and has a toluene insoluble content (TI) of 5 to 30% by weight.
The quinoline soluble content (QI) is 0 to 5% by weight.

Next, the second stage is a temperature of 450 to 550℃, a pressure of 0.1 to
The heat treatment is performed under 20 torrO heat treatment conditions. In addition, it is preferable to use inert gas blowing together in the latter stage of the reaction in this second stage heat treatment, since thermal decomposition products can be efficiently removed. This second heat treatment reduces the mesophase content to 90% by weight.
It is possible to obtain mesoface pitches above. If the mesophase content is less than 90% by weight, the isotropic phase will be mixed in when it is made into fibers, making it impossible to obtain sufficient tensile strength and knot strength, making it impossible to fully achieve the purpose of the present invention. I can't.

In this way, the pitch of the present invention (mesophase pitch) having the properties described above can be obtained. Note that the measured values in thermal balance analysis (TGA) and differential thermal analysis (DTA) are measured under an inert gas atmosphere such as nitrogen or argon.
This value was obtained by raising the temperature from room temperature to 800°C at a heating rate of 0°C/min.

The pitch of the present invention, such as No. 2, has few volatile components at high temperatures and is therefore stable at high temperatures. Furthermore, since the mesophase content is high, the pitch homogeneity and orientation properties are good, and the resulting carbon fibers can exhibit high tensile strength by firing at high temperatures. In addition, there is little light content or quinolinated content, so it has good fluidity.
Good spinnability.

Next, the pitch obtained in this manner is melt-spun and then subjected to infusibility treatment and carbonization treatment, thereby producing the desired carbon fiber.

Here, the melt spinning method may be a known method and is not particularly limited, but the spinning temperature is preferably 400'C or less, more preferably 360'C or less.Here, the spinning temperature is 400'C or less. If it exceeds this, spinnability will decrease.

Usually, pitch fibers are created by melt spinning using a nozzle with a diameter of 0.1 to 0.5 mm.

Next, the pitch fibers created as described above are subjected to an infusible treatment. The infusibility treatment may be carried out in air, or in particular may be carried out using air containing nitrogen dioxide in a proportion of 0.1 to 30% by volume, preferably 0.5 to 15% by volume. This is preferable because carbon fibers with high carbon fibers can be obtained. In addition, this infusibility treatment is performed at a temperature of 150 to 400
``C1'' Preferably, the temperature range is from 180 to 320°C for about 10 to 600 minutes.

Furthermore, the fibers thus infusible are subjected to a carbonization treatment, or if necessary, are pre-carbonized at a temperature in the range of 350 to 800°C under an inert gas atmosphere such as nitrogen or argon. Processing may be performed.

In the carbonization treatment, the infusible fibers or the fibers that have been pre-carbonized if necessary are fired at a temperature in the range of 1000 to 3000° C. in an atmosphere of an inert gas such as nitrogen or argon.

In this way, carbon fibers having a high tensile strength of 450 kg/Iu12 or more can be efficiently obtained.

In addition, in the present invention, the reason why the tensile strength of carbon fibers was significantly improved is presumed to be due to the following cause.

That is, in the pitch of the present invention, 800
The fact that the weight loss at a temperature of 20.degree. C. or less is less than 20.degree. C. means that the weight loss during the carbonization process during the production of carbon fibers is small. Therefore, it is thought that the strength of the carbon fiber is improved because the amount of voids generated in the carbonization process is reduced compared to the conventional method.

Moreover, the pitch of the present invention does not exist in the temperature range exceeding 520° C., which is the exothermic peak determined by differential thermal analysis. 520
The exothermic peak that occurs in the temperature range exceeding ℃ is also 250 to 52℃.
It is possible that both the exothermic peak between 0℃ and 0℃ are due to thermal decomposition of the pitch, or pitches that have exothermic peaks in the temperature range above 520℃ are more likely to heat up to high temperatures than pitches that do not have this peak. It is presumed that the strength of the carbon fiber decreases because decomposition occurs and a large amount of thermal decomposition products are produced.

〔Example〕

Next, the present invention will be explained in detail with reference to examples.

Example 1 (1) As a petroleum-based heavy oil used as a raw material for producing mesophase pitch, the residual oil obtained by conjugated cracking of vacuum gas oil was further distilled under reduced pressure to obtain a light oil content of 90%.
2000g of the residual oil obtained by cutting the
A weighting treatment was performed for 60 minutes at a pressure of 5 Torr, and an isotropic pitch with a quinoline soluble content of 09 (f+, t); an ene insoluble content of 12.0% by weight, and a softening point (Koka flow tester method) of 202°C. 948g was obtained.

20 g of this isotropic pitch was meso-ized at 460°C and I Tarr for 6 minutes, then at 460°C and under nitrogen gas flow for 2 minutes, resulting in a quinoline solution of 30.8% by weight.
, 9.8 g of mesophase pitch having a softening point of 328° C. and 100% mesophase was obtained.

The results of thermal balance analysis (TGA) and differential thermal analysis (DTA) of the obtained pitch are shown in FIG.

From FIG. 1, it can be seen that the weight loss at 800°C measured by thermobalance was 18.6% by weight, and that no exothermic peak was found in the temperature range exceeding 520°C as determined by differential thermal analysis. This measurement was carried out under the conditions of a temperature increase rate of 10° C./min, a nitrogen aeration rate of 500 ml for 11 minutes, a sample weight of 4.51 cm, and a reference material of alumina of 11.220 mg.

(2) Manufacture of carbon fiber The mesophase pitch thus obtained was spun at a temperature of 348°C to a spinneret diameter of 0.2 mm.

Melt spinning was performed using a nozzle with L/D = 3.5 to obtain a pitch yarn with a yarn diameter of 11.8 μm.

Next, this pitch yarn was subjected to infusibility treatment at 220° C. for 3 hours using air containing 2.5% by volume of nitrogen dioxide.

Further, the thus obtained infusible yarn was fired at a temperature of 1550'C in a nitrogen gas atmosphere to obtain carbon fibers with a fiber diameter of 9.2 μm.

The tensile strength of this carbon fiber is 477.6 kg/mm
2. The tensile modulus is 34. Ot/mm2. The elongation is 1.
It was 41%.

Comparative Example 1 (1) Production of mesophase pitch 20 g of isotropic pitch obtained in the first stage heat treatment of Example 1 (1) was subjected to mesophase treatment for 8 minutes at 460''C, I Torr, Quinoline solubility 30.5% by weight.

9.9 g of mesophase pitch having a softening point of 327° C. and 100% mesophase was obtained.

The results of thermogravimetric analysis (TGA) and thermogravimetric analysis (DTA) of the obtained pitch are shown in FIG.

According to Figure 2, the weight loss at 800°C determined by thermobalance is 18.9% by weight, or the exothermic peak determined by thermogravimetric analysis exists in the temperature range exceeding 520°C. I understand. In addition, in this measurement, the sample was 4.55■, and
The test was carried out under the same conditions as in Example 1 (FIG. 1).

(2) Production of carbon fibers Carbon fibers were obtained by melt spinning, infusibility, and firing in the same manner as in Example 1 (2) except that the mesophase pitch obtained in (1) above was used.

The tensile strength of this carbon fiber is 415.2 kg/n+m
The tensile modulus was 33.2t/2, the elongation was 1.25%, and the fiber diameter was 9.2 μm.

Comparative Example 2 (1) Production of mesophase pitch 2000 g of the same petroleum heavy oil used in Example 1 (1)
was subjected to a heavy treatment at a temperature of 400°C and a pressure of 10 Torr for 60 minutes, resulting in a quinoline-soluble content of 0% and a toluene-insoluble content of 6%.
．． 5% by weight, 1218g of isotropic pitch with a softening point of 170°C
I got it.

30 g of this isotropic pitch was meso-ized for 10 minutes at 460° C. and I Torr to obtain 9.9 g of mesophase pitch, which has a quinoline soluble content of 29.8% by weight, a softening point of 328° C., and a meso phase of 100%. I got it.

The results of thermogravimetric analysis (TGA) and thermogravimetric analysis (DTA) of the obtained pitch are shown in FIG.

According to FIG. 3, the weight loss at 800°C measured by thermobalance was 22.4% by weight, and furthermore, the exothermic peak by thermogravimetric analysis was found to exist in a temperature range exceeding 520°C. In addition, in this measurement, the sample was 4.53■, and
The test was carried out under the same conditions as in Example 1 (FIG. 1).

(2) Production of carbon fibers Carbon fibers were obtained by melt spinning, infusibility, and firing in the same manner as in Example 1 (2) except that the mesophase pitch obtained in (1) above was used.

The tensile strength of this carbon fiber is 383.0 kg/mm2
Tensile modulus is 31.1 t/mm2 Elongation is 1.2
39t; and the fiber diameter was 9.2 μm.

〔Effect of the invention〕

By using the new pitch of the present invention, it is possible to produce carbon fibers having a high tensile strength of 450 kg/ma2 or more.

Furthermore, the novel pitch of the present invention allows carbon fibers with a cross-sectional shape or a perfect circle to be produced without the need to use irregularly shaped nozzles when producing carbon fibers, compared to when using conventional irregularly shaped nozzles. Compared to this, handling has been significantly improved.

[Brief explanation of drawings]

Figure 1 shows the thermobalance analysis (T) of the pitch obtained in Example 1.
2 is a chart showing the results of GA) and the results of differential thermal analysis (DTA). Figure 2 shows the thermobalance analysis (T) of the pitch obtained in Comparative Example 1.
2 is a chart showing the results of GA) and the results of differential thermal analysis (DTA). Figure 3 shows the thermobalance analysis (T) of the pitch obtained in Comparative Example 2.
2 is a chart showing the results of GA) and the results of differential thermal analysis (DTA).

Claims (2)

[Claims] (1) The content of the optically anisotropic phase is 90% by weight or more, the weight loss at a temperature of 800°C by thermobalance is 20% by weight or less, and the exothermic peak by differential thermal analysis is 250 to 520%. ℃, and does not exist in a temperature range exceeding 520℃. (2) The content of the optically anisotropic phase is 90% by weight or more, the weight loss at a temperature of 800°C by thermobalance is 20% by weight or less, and the exothermic peak by differential thermal analysis is 250 to 520%. After melt spinning the pitch which is between 520°C and not present in the temperature range above 520°C,
A method for producing carbon fiber, characterized by subjecting it to infusible treatment and carbonization treatment.