JPH0551686B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical field] The present invention relates to a method for producing high-performance carbon fibers in which acrylonitrile polymer fibers are subjected to flame-retardant treatment under specific conditions and then carbonized. [Prior art] Generally, carbon fibers are produced from acrylic fibers. To do this, heat treatment is performed in an oxidizing atmosphere at 200 to 400°C to form a flame-resistant structure, and then heat treatment is performed at 400°C.
The above method of carbonization in an inert atmosphere is used. At that time, applying tension or elongation in the flameproofing process is effective in producing carbon fibers with excellent strength and elastic modulus. for example,
JP-A No. 49-54632 discloses a method of producing high-performance carbon fibers by distributing the elongation during flameproofing treatment between an early region and a late region. However, in the case of acrylic fibers, carbon fibers with superior performance can be obtained by shrinking the acrylic fibers rather than elongating them during the flame-retardant treatment process due to differences in the initial degree of molecular orientation or molecular cohesion. There is. Therefore, in the above method, excessive elongation may promote fuzzing and structural defects. As described above, the optimum elongation or shrinkage rate for flame resistance differs depending on the breaker and is also affected by the ambient temperature, so it is currently extremely difficult to optimize it. . [Purpose of the Invention] Therefore, the present inventors provided a plurality of drive rollers in the flameproofing process, and determined the expansion/contraction ratio between each roller by performing a batch experiment on the fibers at the supply roller point between them. The inventors have discovered that carbon fibers with extremely excellent performance can be obtained by setting the carbon fiber to a certain value, and have completed the present invention. [Structure of the Invention] The gist of the present invention is to apply a multi-stage flame-retardant treatment by stretching PAN-based polymer fibers in multiple stages in an oxidizing atmosphere at 200 to 400°C using a flame-retardant furnace having a plurality of driving rollers. , for each stage of flame-retardant treatment, first perform batch flame-retardant treatment to reduce the flame-retardant treatment time of each stage.
The load-elongation rate curve corresponding to Tn (n indicates the n-th flame retardant treatment inspection process. The same applies hereinafter), the load Pn and the elongation rate En at the inflection point of the curve are sequentially determined, and the measured values are This is a method for producing carbon fiber, which is characterized in that the elongation rate of the nth stage in multi-stage flameproofing treatment is set within En±3% based on the flameproofing process, and then carbonized. The time the fibers stay between each drive roller of multi-stage stretching is 20 minutes or less. An example of a flameproofing furnace having a plurality of driving rollers according to the present invention is shown in FIG. Figure 2 shows an example of the expansion/contraction behavior of the starting acrylic fiber at 240°C in air under various constant loads over time. The manufacturing method in the present invention will be described below. In FIG. 1, it is assumed that the time T ₁ that the fiber stays in the furnace from rollers R ₀ to R ₁ is 10 minutes, and the ambient temperature is 240°C. Next, when the expansion/contraction rate and its load at the same time T ₁ 10 minutes are plotted from FIG. 2, a linear relationship with an inflection point approximately at P ₁ is obtained as shown in FIG. 3. However, in general, even if the ambient temperature is the same in the flameproofing furnace and the batch furnace used in the firing process, the temperature-time dependence of changes in the physical properties of the fibers usually differs due to differences in the equipment characteristics. Therefore, rather than making the stay time in the furnace the same as described above, it may be better to make the physical property parameters, especially the fiber density, which is one measure of the progress of flame resistance, the same. Thus the inflection point
Find the elongation rate E ₁ corresponding to P ₁ . According to the degree of orientation determined by wide-angle X-ray diffraction, the degree of orientation increases as the elongation increases up to an elongation rate of E ₁ , but the increase reaches a plateau at E ₁ or higher, and fuzz is also observed. That is, this elongation rate E ₁ becomes the optimum elongation between rollers R ₀ and R ₁ . Next is the setting of the elongation rate between rollers R ₁ and R _2. In this case, the fibers at supply roller R ₁ ,
In other words, in the same manner as mentioned above, the fibers which were given elongation E ₁ by treatment at 240°C for 10 minutes (T ₁ ) were subjected to the fourth batch experiment corresponding to the second flame-retardant treatment time (T ₂ ).
Plot the relationship between load and elongation rate as shown in the figure to find the elongation rate _E2 . Hereinafter, the elongation rate between each roller is determined in the same manner. Determined in this way, the elongation rate En (n=1.2...)
In some cases, the optimum point appears on the contraction side depending on the acrylic fiber. At this time, it is desirable that the time the fibers stay between each roller is within 20 minutes, preferably 2 to 15 minutes. If it is longer than 20 minutes, the length of the stretching region will increase and the stretching rate between the rollers will increase accordingly, resulting in uneven stretching and the tension difference between the next roller will increase. Slips may also occur on the border rollers, increasing the frequency of fluff. When the time is less than 2 minutes, the number of times of contact with the rollers increases, which also causes the generation of fuzz, and the number of rollers becomes extremely large, so there is no benefit in the apparatus. [Example] Hereinafter, the present invention will be specifically explained with reference to Examples. Strand strength and strand elastic modulus are
Measured according to the method of JISR7601. Example 1 Acrylonitrile 98wt%, methyl acrylate
Acrylic fiber (total denier 4360, 3000 filament,
Single fiber strength 5.0g/d, elongation 13.0%) 220−240−
When performing heat treatment in a hot air circulation flame retardant furnace having a three-stage temperature profile of 260°C, drive rollers are provided at the borders of each of the first, second and third flame retardant zones, and between the drive rollers, i.e. Since the time that the fibers stayed between each zone was 20 minutes, the elongation ratios E ₁ , E ₂ and E ₃ were determined using the method according to the present invention in a batch furnace. As a result, the elongation rate of the first zone was 15.0±1.0% or less, the second zone,
The elongation rate of the third zone is 5.2±0.6% and 0.0±1.2, respectively.
It was %. After flame-retardant treatment under the above conditions, the flame-retardant fibers were then passed through a first carbonization furnace at 600°C in a _N2 stream for 3 minutes.
, and then heat-treated under a tension of 400 mg/denier in a second carbonization furnace at 1200° C. in the same atmosphere. Table 1 shows the strand strength and strand elastic modulus of the obtained carbon fibers. Example 2 In the same flameproofing furnace as in Example 1, the free roller located at the center was changed to a driving roller between each driving roller, and the time the fibers stayed between each driving roller was set to 10 minutes. The elongation ratios E ₁ , E ₂ ...E ₆ were calculated in the same way, and the results were 12.0 in order from E ₁ .
±1.2%, 5.4±0.6%, 3.4±0.9%, 2.0±1.0%,
They were 0.8±1.0% and -0.8±0.8%. Carbon fibers were obtained under the same conditions as in Example 1 except for this flame-resistant elongation condition. Its performance is shown in Table 1. Comparative Example 1 In Example 1, the elongation rates E ₁ , E ₂ and E ₃ were set to 10.0.
%, 2.0% and 0%, and all other conditions were the same as in Example 1 to obtain carbon fibers. Its performance is shown in Table 1. Comparative Example 2 In Example 1, all drive rollers during the flameproofing process were changed to free rollers, and 20% elongation was applied only to the godet rollers at the entrance and exit of the flameproofing furnace. Its performance is shown in Table 1.

〔Effect of the invention〕

By employing the method of the present invention, products with significantly improved strength and elastic modulus can be obtained.

[Brief explanation of the drawing]

FIG. 1 is an example of a flameproofing furnace used to carry out the present invention. Figure 2 shows the expansion and contraction of acrylic fibers in air at 240°C under various loads, with the horizontal axis representing time and
The vertical axis shows the shrinkage rate. The denier is
I used breaker denier. Figure 3 shows
The expansion/contraction rate at 10 minutes in Figure 2 is plotted against each load. FIG. 4 shows a plot similar to FIG. 3 for the fibers at supply roller _R1 .

Claims (1)

[Claims] 1. When PAN-based polymer fibers are stretched in multiple stages and subjected to flame-retardant treatment in an oxidizing atmosphere at 200 to 400°C using a flame-retardant furnace having a plurality of driving rollers, each stage is For each flame-retardant treatment, first, the load-extension rate curve corresponding to the flame-retardant treatment time Tn (n indicates the nth stage flame-retardant treatment step; the same applies hereinafter) of each stage by batch flame retardant treatment and its The load Pn and the elongation rate En at the inflection point of the curve are sequentially determined, and based on these measured values, the elongation rate of the nth stage in the multi-stage flameproofing treatment is set within En ± 3%, and the flameproofing process is performed.
A method for producing carbon fiber, which comprises carbonizing the fiber thereafter. 2. The method for producing carbon fibers according to claim 1, wherein the time the fibers stay between each drive roller of the multi-stage stretching is 20 minutes or less.