JPS6253422A - Carbon fiber manufacturing method - 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 (Industrial Application Field) The present invention is a carbon fiber manufacturing process using petroleum-based or coal-based pitch as a raw material. The present invention relates to a method for producing carbon fibers having excellent material properties.

(Prior art) Generally, as a method for manufacturing carbon fiber using petroleum-based or coal-based pitch as a raw material, pitch fibers obtained by melt-spinning raw material pitch are placed in an oxidizing atmosphere such as air at a temperature of 250 to 400°C. After heat treatment to convert into infusible fiber, 80
The method used is to carbonize by heating in an inert atmosphere such as nitrogen at 0 to 1600"C, and if necessary, further heat in a high temperature inert atmosphere to form graphite fibers. After infusibility. It is known that the physical properties of carbon fibers obtained can be improved by applying tension during the heat treatment process. JP-A-59-144
Publication No. 624 describes that the strength and elastic modulus of carbon fibers are significantly improved by infusibility treatment while applying tension to pitch fibers. In addition, it has been reported that physical properties can be improved by applying a load of 7~/denier or more during the treatment process up to 1000 °C after the infusibility treatment (S, Tan, et al. App
Lied Polymer Symposia J & 9
, P 255 (1969)).

Furthermore, U.S. Patent No. 3,454,862 describes high strength,
When making carbon fiber yarn with a high elastic modulus, it stipulates a method in which the carbonaceous yarn is stretched in the longitudinal direction and fired until the elongation reaches at least 1 inch. Tokuko Sho 47-10
No. 254 discloses 5 as a method for producing highly elastic carbon fiber.
It is described that stress is applied at a temperature of 50-850°C and/or 1350-2800°C. Also,
By applying stress graphitization treatment that causes plastic deformation in the graphitization temperature range of 1800°C or higher, the selective orientation of the polymer and the characteristics of crystal growth are clearly changed, and the physical properties are also improved (Kindai Editorial Publishing, Okama・“Carbon Fiber” by Kimura
(See pages 147-150).

On the other hand, a stretching operation is essential in order to impart orientation to the PAN-based carbon fibers.

Either increase the orientation by stretching the raw yarn during the spinning process, or if the orientation is not completely imparted during the spinning process, apply excessive tension in the stabilization process to bring the orientation to completion, or if necessary, perform a high-temperature treatment process. In reality, these various elements are appropriately combined to create a product. Since it is a polymer with a uniform molecular size compared to pitch-based yarn, the tensile strength of the yarn from the original yarn to the intermediate process is considerably high, and the stretching operation is easy. The strength of pitch fibers and infusible fibers is at most 5 kg/tj,
The elongation is less than 1 inch, making it extremely fragile. Therefore, tension processing at this stage requires extremely accurate tension control.
It is industrially disadvantageous and has not been put to practical use.

It is believed that the crystal orientation and crystallinity of the fiber axis directly reflect the elastic modulus. In fact, 2500-8000℃
The elastic modulus of graphitized fibers treated with
It shows a value of about 70chi.

It is known that the elastic modulus increases as the La and Lc orientation angles of graphite get closer, and from this point of view, tension treatment of the fibers is advantageous because it can improve the orientation.

On the other hand, the tensile strength of fibers is at most 5 GPa, which is only about 3% of the theoretical strength of graphite, 180 GPa. The fact that the difference between the expected tensile strength and the actual value is so large means that rather than a microstructural problem, it is more likely that macroscopic defects such as surface and internal flaws and defects weaken the strength of the a-fibers. It is thought that there is a strong possibility that Therefore, tension during the heat treatment process is advantageous in terms of improving the orientation of the fibers, but care must be taken because if the setting conditions are incorrect, it will encourage the occurrence of defects and cause a decrease in strength. No.

As mentioned above, the tension in the infusibility process makes the treated fibers extremely brittle, making it difficult to put it into practical use. Also,
9. If the treatment temperature exceeds 600°C during the carbonization process. The fibers carbonize as they contract, forming a dense structure, but applying tension inhibits the development of a dense structure, making it impossible to sufficiently fill in macroscopic defects, which tends to result in a decrease in strength. Similarly, graphitization involves shrinkage of the fibers, so graphitization under tension does not increase strength enough compared to the increase in elastic modulus, and the elongation at break decreases, making it impossible to obtain satisfactory physical properties. .

(Problems to be Solved by the Invention) The present invention focuses on the above-mentioned problems, and provides easy tension control.
Moreover, it is an object of the present invention to achieve a method for producing pitch-based carbon fibers that can be processed without losing strength and have versatile material properties such as high elongation and medium strength.

(Means for Solving the Problems) In order to achieve the above object, the present inventors conducted extensive research on the carbonization behavior of fibers, and found that a carbonization method that improves the orientation of fibers and improves both strength and elongation properties. found the following conclusion: Pitch fibers spun using optically isotropic petroleum- and coal-based pitches as raw materials were made infusible by a known method, and then heated to 650°C under tension in an inert atmosphere. 900-11 without applying any tension in an inert atmosphere after heat treatment.
By performing heat treatment to 00''C, carbon fibers with high elongation and medium strength could be obtained.

In this case, the appropriate temperature range for applying tension is 300 to 650°C, preferably 500 to 650°C. The tension applied to the fibers is preferably 60 g/- or more, and the infusible fibers used in the carbonization treatment are o, o a o ≦ 010 (atomic ratio) < 0.100, and 40 ≦ QI (quinoline insoluble content, ≦70 is desirable.

In general, pitch is a mixture consisting of various types of condensed aromatic compounds, and pitch fibers after melt spinning are heat-treated in an oxidizing atmosphere to generate three-dimensional crosslinking reactions between structural unit molecules and to form side chains or aromatic rings. The introduction of oxygen-containing functional groups is promoted, and pitch loses its heat-melting properties. In the subsequent carbonization process, the oxygen-containing functional group introduced in the infusibility process becomes co.

Polymerization between unit molecules progresses while desorbing as Co2, and 6
When the temperature reaches 00° C. or higher, a condensation reaction accompanied by demethanization and dehydrogenation progresses, carbon planes grow, and physical properties specific to carbon fibers are developed. As a result of extensive research into the carbonization behavior of fibers, we discovered that the carbonization region can be broadly divided into two.

That is, as shown in Fig. 1, when the carbonization temperature is changed, the elastic modulus hardly changes up to 600°C and increases rapidly above 600°C, while the tensile strength increases from around 1500°C and reaches 900°C. At temperatures above ℃, the value remains almost constant. For this reason, the elongation at break has a sharp peak at 600'C.

Figure 2 shows the change in fiber diameter, and it can be seen that the fiber shrinks rapidly at temperatures above 700°C.

In addition, from the analysis results of the gas generated during carbonization treatment, it was found that
It can be seen that the oxygen-containing functional groups introduced by infusibilization are eliminated as CO and CO2 up to 650''C, and a condensation reaction accompanied by dehydrogenation and demethanization proceeds from 700 to 900°C (see Figure 3). Also, 500~600℃
It was confirmed that an orange tar-like substance was produced.

In other words, in the low-temperature region based on 600°C, a polymerization reaction accompanied by the elimination of bromine-containing groups and a depolymerization reaction accompanied by the generation of tar-like substances due to thermal decomposition proceed, and the homogenization of the system progresses. The condensation reaction that involves dehydrogenation and demethanization progresses, filling the defects in the fibers and forming a dense structure, while the crystals themselves grow, resulting in the fibers shrinking and creating a uniquely custom-made structure. It will emerge.

Therefore, if tension is applied in a temperature range where the fibers contract and form a dense structure, the orientation will be improved, but this will encourage the occurrence of defects and there is a strong possibility that the strength will decrease instead.

On the other hand, in the pre-carbonized region where polymerization and depolymerization reactions are progressing and the system is becoming more homogeneous, orientation can be improved without forming defects even when tension is applied, and strength and elongation can be improved. becomes.

From the above, it has been found that fibers that have been de-intensified by a known method are heat-treated under tension up to 650°C, and then further heat-treated at 900-1100"C in an inert atmosphere without applying tension to achieve high elongation and medium-strength. Strong carbon fiber can be obtained.

The appropriate temperature range for applying tension is 300 to 650°C, and considering the tensile strength and handling properties of the fibers, the temperature range is 10 to 650°C.
Preferably, it is strained at 500-650°C with a strength of 20 mm/-. At temperatures below 800℃, the fibers themselves become brittle.
The carbonization reaction does not proceed, and the effect of applying tension becomes low. On the other hand, temperatures of 650° C. or higher promote the occurrence of defects in the fibers, increasing the possibility of deterioration of properties.

When the tension applied to fRul is 609 g/- or more, it is possible to reach the breaking strength at the processing temperature of the fiber, but it is practically preferable to suppress the elongation to within 20%, and the effectiveness decreases at a tension of 60 g/- or less.

Infusible #J! If the degree of infusibility of the fiber is controlled within the range of 0.060≦0/C (atomic ratio)≦0.100 and within the range of 40×QI (quinoline insoluble content, Q)≦70, the obtained carbonization properties can be improved. Although it is described that a product with little variation, high performance, and high quality can be obtained, the properties can be further improved by using infusible fibers that satisfy the above requirements in the tension carbonization treatment of the present invention.

(Effects of the Invention) As described above, the present invention can produce carbon fibers with high elongation and medium strength by heat treatment at a temperature range of up to 650°C under a specific tension, and the resulting high elongation The degree of carbon fiber has increased flexibility when processed into various shapes, and has sufficient strength, so it is extremely versatile for use as structural materials, sliding members, insulation materials, conductive materials, etc., and its industrial value is high. Extremely high and useful.

(Examples 1 to 8) (Comparative Examples 1 to 8) Softening point 217°C 1 fixed carbon 85.8%, benzene insoluble content (BI) 57.2% and trace amount of quinoline insoluble content (QI
) was wound onto a bobbin at a winding speed of 400 m/min from a melt extrusion spinning machine with 200 nozzles of diameter 0.2 and L/D-3, and then unwound. While unwinding with a device, it is continuously passed through an infusibility furnace, and then heat treated at 280°C for 90 minutes in air containing 3 volumes of NO to make it infusible, and then wound onto a bobbin again through a gold thread device. Ta. Next, in a nitrogen atmosphere, the carbon fibers were heat-treated to 1000°C under the carbonization conditions shown in Table 1 while adjusting the tension. The results are shown in Table 1. In addition to Examples 1, 2, and 8, in which heat treatment was performed within the range of treatment conditions in the present invention, Table 1 also shows Comparative Examples 1, 2, and 8, in which tests were conducted outside the range of these conditions for the purpose of comparison.
2 and 3 are shown.

From the above table, the fibers are heated under a tension of 60 g/mm2 or more at 300~
Carbon fibers with excellent material properties such as high elongation and medium strength can be obtained by heat treatment in the temperature range of 650°C.
It can be seen that under conditions other than the above, the elongation and strength are inferior.

[Brief explanation of drawings]

Figure 1 is a graph showing the change in carbonization temperature and fiber properties obtained by performing a tensile test on fibers at varying treatment temperatures in a nitrogen atmosphere. Figure 2 is a graph showing changes in fiber properties as a result of varying treatment temperatures in a nitrogen atmosphere. A graph showing the weight loss rate and change in fiber diameter with respect to the infusible fiber, and Figure 3 shows the gas (
0, Co , OH,, H,) is a graph showing the analysis results. Figure 1 300400 50t) 600 77) 0 800
900 1000 degrees psychologically 61 degrees ζ 2

Claims (1)

[Claims] 1. A method for producing carbon fibers using petroleum-based and coal-based pitches that exhibit optical isotropy as raw materials, in which infusible fibers are heat-treated to 650°C under tension in an inert atmosphere. , further at 900-1100℃ in an inert atmosphere without adding tension.
A method for producing carbon fiber, which is characterized by performing heat treatment up to 2. The method according to claim 1, wherein the temperature at which the tension is applied is 300 to 650°C, preferably 500 to 650°C. 3. The method according to claim 1, wherein a tension of 60 g/mm^2 or more is applied to the fiber. 4. Infusible fiber is 0.060≦O/C (atomic ratio)≦0
．． 100, and 40≦QI (quinoline insoluble matter)≦70
The method according to claim 1.