JPS61179319A - Production of high performance carbon yarn - Google Patents

Abstract

PURPOSE:In making pitch yarn infusible by oxidation, to obtain the titled yarn having uniform characteristics of product, showing the characteristics of precursor pitch at its maximum, by controlling the reaction using a novel infusibility degree evaluation index and as elemental analysis values of oxidized yarn, etc. CONSTITUTION:Firstly, pertroleum or coal pitch showing optical anisotropy is subjected to melt spinning to give pitch yarn, which is heat-treated in an oxidizing atmosphere such as air, etc. at 300-400 deg.C, made infusible, anc converted into oxidized yarn having elemental analysis values in 0.025<=0/C<=0.05 and H/C<=0.45, quinoline insoluble content of QI value in 75<=QI(%)<=05. Then, the oxidized yarn is carbonized graphitized in an inert atmosphere such as argon, etc., to give the aimed yarn.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention provides a method for producing pitch-based carbon fibers using petroleum-based and coal-based pitches as raw materials. , relates to a method for producing carbon fibers with high elasticity and high quality.

(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 250 to 400°C. After converting this fiber into a so-called infusible fiber, carbonize it by heating in an inert atmosphere such as nitrogen at 300 to 1600°C, and if necessary, further heat it in an inert atmosphere at a high temperature. Since pitch is originally a substance that softens and melts when heated, it is necessary to oxidize the pitch fiber in advance to prevent intermolecular cross-linking and inclusion in side chains or aromatic rings. By introducing oxygen functional groups, a three-dimensional molecular structure is developed, and the fiber shape is maintained even during the subsequent carbonization process.

In the above-mentioned infusibility process, if the pitch fibers are insufficiently oxidized, the fibers will fuse together and the elastic modulus will decrease during subsequent carbonization, and if the oxidation progresses excessively, crystal growth of carbon planes will occur during carbonization. is inhibited by three-dimensional crosslinking,
The formation of intrafiber voids due to the degassing reaction becomes significant, and furthermore, the meso-7Aze type precursor pitch disturbs the orientation of crystals in the fiber axis direction that was achieved during spinning. For this reason, in any case, it is difficult to obtain carbon fibers with satisfactory physical properties. Therefore, in order to produce good carbon fibers, it is essential to control the progress of the infusibility reaction within a certain range.

However, in the case of a pitch system for which there are few indexes showing the degree of progress of the infusibility reaction, that is, the degree of infusibility, JP-A-59-1! ! 6525 specifies that the weight increase in the infusibility step is 8 to 7% by weight, preferably 4 to 6% by weight, and JP-A-58-6525, which is characterized by petroleum-based pitch,
In Publication No. 48a4, the amount of α resin in the infusible fiber is 80
It is stated that the oxygen content in the infusible fiber should be adjusted to 18 to 22% by weight in JP-A-51-119885, which uses mesophase pitch as a precursor. specified to be controlled. In the case of PAN system, slightly JP-A-5y-+
FF19PA5 and other documents only describe controlling the equilibrium moisture content of flame-resistant fibers to about 10 to 11%, and no clear and logical evaluation index for the degree of infusibility has been found. Therefore, in the case of pitch-based materials, it is necessary to determine processing conditions such as heat pattern, oxidizing gas used, bulk density, etc., considering both production efficiency and fiber properties for each precursor pitch and equipment used. Ta.

However, there are very few control items for the fibers after the infusibility process, and the final check of the product is essentially just based on the fiber properties after carbonization. It is also difficult to take measures in subsequent processes, which may lead to a decrease in production efficiency. Furthermore, it is difficult to keep variations in product characteristics to a small level, which poses a major problem in quality control.

Taking the weight increase rate as an index, the average molecular structure lII &
The optimal value will be different depending on the pitch, and the optimum value will be different for different pitches. Even if it shows, the degree of infusibility may differ, and it is difficult to say that it is suitable as an indicator of the degree of infusibility. On the other hand, although equilibrium moisture content is effective for PAN-based flame-resistant fibers, it has the disadvantage that it is difficult to apply to pitch-based infusible fibers that have a low equilibrium moisture content.

(Problems to be Solved by the Invention) The present invention focuses on the above-mentioned problems and aims to optimally control the infusibility reaction of pitch fibers, thereby maximizing the characteristics of precursor pitch. The purpose of the present invention is to achieve a method for manufacturing pitch-based high-performance carbon fibers that can reduce the variation in product properties.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the present inventors have conducted extensive research, and as a result, have controlled the infusibility reaction so as to maximize the performance of the precursor pitch, thereby increasing the productivity of the product. The present invention was achieved by developing a method for manufacturing high-performance carbon fibers that have excellent physical properties that can improve the properties of carbon fibers.

In the method for producing high-performance carbon fibers of the present invention, when petroleum-based and coal-based pitches exhibiting optical anisotropy are used as precursor pitches, the infusibility reaction is determined based on the elemental analysis value of the oxidized fibers and the quinoline insolubility. (QI) values are 0.025 <Q10 <0.050, respectively.

By controlling the infusibility reaction so that Ilo<0.45 and 75 x QI (%) x 95, and performing graphitization treatment in an inert atmosphere such as argon, high performance with high strength and high elastic modulus is achieved. Carbon fiber can be obtained. especially,
When BI (%) > 90% and QI (%) > 20% and a pitch with an anisotropy fraction exceeding 90% is used as a precursor, the analytical value and QI value of the oxidized fiber are 85 and QI (%) 98.0.085 <Olo <
0.045 and Ilo <0.42, and carbonization and graphitization treatments are carried out by conventional methods to obtain high-quality and high-performance carbon fibers.

In general, pitch is a mixture of various condensed aromatic compounds, and by heat-treating pitch fibers after melt-spinning in an oxidizing atmosphere, three-dimensional crosslinks are formed between structural unit molecules, and side chains or aromatic rings are formed. This promotes the introduction of oxygen-containing functional groups into the pitch and causes the pitch to lose its heat-melting properties. However, if more three-dimensional crosslinks are formed than necessary, the growth of crystallites in the subsequent carbonization process will be suppressed, and if the introduction of oxygen-containing functional groups is excessive, OO and C
The elimination reaction of O8 causes voids to be generated within the fiber, leading to a decrease in the physical properties of the carbonized fiber in either case.

Therefore, the progress of the infusibility reaction must be controlled within a certain range.

Figure 1 shows the quinoline insoluble content (Q
I) and benzene insoluble content (BI) (Meso 7Aze pitch, BI=92.5% and Q
I=88.1%), Figure 3 shows FT-IH of infusible fibers.
This shows the measurement results (mesoface pitch) by (
The spectral intensity shown on the vertical axis of FIG. 2 is the relative ratio between the intensity of each absorption wavelength and the 0=0 coupling intensity (d). From these drawings, it can be seen that QI
It can be seen that as the components increase, the formation of carbonyl groups and ether groups becomes noticeable, and on the contrary, the strength of the O-H bond decreases. Therefore, we evaluated the degree of polymerization of pitch fibers, that is, the generation of three-dimensional intermolecular crosslinks, using quinoline insoluble content, and evaluated the degree of introduction of oxygen-containing functional groups into the fibers using VO and V based on elemental analysis. The relationship between carbon fiber strength and fiber strength after carbonization was evaluated, and these optimal values were determined.
An example of this is shown in FIG. From FIG. 8, it can be seen that when the quinoline insoluble content is about 75% or less and about 95% or more, the W fiber strength decreases rapidly. From the above results,
When the validity of values such as QI Olo , Hlo and carbonized fiber strength was confirmed for various mesophase type precursor pitches, it was found that extremely high probability can maximize the raw material properties. Furthermore, we have confirmed that by selecting processing conditions that achieve these maximum values, product variations can be suppressed compared to conventional methods.

In the case of optically anisotropic pitch, orientation is expressed at the stage of pitch fibers after melt-spinning, and attention must be paid to disturbance of orientation due to infusibility.

That is, infusibilization is insufficient for QI (%) 75 and Sho<o, o2g, and QI (%)> 98 and Sho> 0.0.
45 results in a decrease in fiber physical properties and orientation. Therefore, ε, in the present invention, is 0.0!5 <Q10
<0.045, Hlo <0-45 and F5Q
It is necessary to control it within a range of 98%. Oxidized α fibers satisfying these values can be easily obtained by heat-treating pitch fibers obtained by melt spinning in a fermentation atmosphere in the temperature range of 300-400"C, and then By carbonizing the obtained oxidized fibers by a conventional method and, if necessary, graphitizing them, high-quality, high-performance carbon fibers can be obtained.

(Effects of the Invention) As described above, the method of the present invention exhibits excellent mechanical properties, suppresses variation in fiber properties to a smaller level than conventional methods, and maximizes precursor pitch performance. It is possible to produce carbon fibers that can In addition, the evaluation index of the degree of infusibility makes it possible to optimally control the infusibility reaction of pitch fibers, and even if an abnormality occurs in the infusibility process, it can be dealt with in the subsequent process, and the product as a whole can be improved. Productivity can be improved.

Furthermore, the above-mentioned infusibility index in the present invention is highly reliable and reliable for various precursor pitches.

(Examples 1 to 4), (Comparative Examples 1 to 8) It has a softening point of 300°C and a benzene insoluble content (Bl) of 91.
An optically anisotropic pitch with an anisotropic fraction of 92.1%, including 4% and 28.7% quinoline insoluble content (Q I ), yl, 0.2 fin diameter and L/D = 8 nozzle 2
A pitch fiber bundle having a fiber diameter of 7 to 10 μm was obtained by melt spinning using a melt extrusion spinning machine having a diameter of 7 to 10 μm.

This pitch fiber bundle was pretreated with HBr and then heat treated in air without pretreatment to make it infusible. In this case, the temperature increase rate was appropriately set in the range of 2 to 300 to 400°C, and these were combined to change the processing conditions.

As described above, oxidized fibers with different degrees of infusibility were prepared by varying the presence or absence of the pre-treatment, the treatment temperature, and the temperature increase rate. Next, each of the prepared fused carbon fibers was heat-treated at a heating rate of 100°C/min in a nitrogen atmosphere having a temperature profile with a maximum temperature of 1400°C to convert it into various carbon fibers. Table 1 shows the relationship between the physical properties and the degree of infusibility of each of the obtained carbon fibers.

Table 1 shows that when the degree of infusibility is low, that is, when Q = 5 or O/0 < 0.025, the carbide properties decrease.

On the other hand, it can be seen that in Example 1N4, the strength is also a satisfactory value and the variation is small.

(Example 5-ri) Eight types of optical anisotropic pitches shown in Table 2 were prepared with a diameter of 0.2#.
From a melt extrusion spinning machine having 200 nozzles with R and I, /D = 8, a 0.1 weight: tit % aqueous solution of higher alcohol ethylene oxide adduct as a sizing agent was added at a rate of 2 weight % per l#a weight. Winding speed 400m while coating
The fibers are wound onto a bobbin at a speed of 1/min, and then unwound using an unwinding device ψ to double the yarn.The bundled fibers of 3000 filaments are fired by passing through a continuous infusibility/carbonization furnace at a maximum temperature of 1200℃, and then wound onto a bobbin. I took it. After that, the fibers were heated to 2600℃.
Graphitization treatment was performed to obtain graphite fibers. The results are shown in Table 2.

From Table 2, it can be seen that the index for determining the degree of infusibility is useful for the precursor pitch of the three persimmons, and has high reliability and film properties.

[Brief explanation of the drawing]

Figure 1 is a graph showing changes in the benzene-insoluble content and quinoline-insoluble content of oxidized fibers with respect to the infusible temperature, Figure 2 is a graph showing the FT-IR measurement results of the infusible fibers, and Figure 3 is the graph at the time of infusibility. It is a graph showing the relationship between quinoline insoluble content and carbonization strength. Fig. 1: Kobei Dangai ('C) Fig. 2: Fukakuranai and force 6 no 艷 (-〇)

Claims (1)

[Claims] 1. A method for producing carbon fiber in which petroleum-based and coal-based pitch exhibiting optical anisotropy is melt-spun, made infusible, and further carbonized, wherein the pitch is obtained by melt-spinning the pitch. 0.025≦O/C≦0.050, H/C≦0 by heat-treating the pitch fibers in an oxidizing atmosphere at 300 to 400°C.
．． 45 and 75≦quinoline insoluble content (QI)%≦95 % quinoline insoluble matter (QI)% . 2. Contains benzene insoluble content (BI) of 90% or more and quinoline insoluble content (QI) of 20% or more, and has an anisotropic fraction of 9
When mesophase type petroleum and coal-based pitches exhibiting optical anisotropy of more than 0% are used as precursors, the pitch fibers should be 0.035≦O/C≦0.
045, H/C≦0.42 and 85≦quinoline insoluble content %≦93.