JPS633972B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an acrylonitrile fiber bundle (tow)
This invention relates to a method for producing a flame-resistant fiber bundle (tow) using as a starting material, which has high strength without sticking, excellent spinnability, and is suitable for obtaining high-strength carbon fibers and fibrous activated carbon. . Starting material is acrylonitrile fiber bundle (tow), which is oxidized at 200 to 400°C in an oxidizing atmosphere to produce flame-resistant fibers, which can be used as textiles,
It is known to be used as knitted fabrics, nonwoven fabrics, etc., or as intermediate raw materials for fibrous activated carbon, carbon fibers, etc. When obtaining such flame-resistant fiber bundles economically,
The raw material acrylonitrile fiber is a fiber bundle (tow)
It is preferable to carry out the oxidation treatment under these conditions. However, when acrylonitrile fibers are oxidized in the form of tow, a characteristic of acrylonitrile polymers is that the fiber surfaces may become softer and the surfaces of the fibers may stick together. Furthermore, acrylonitrile-based polymers generate approximately 50 to 100 Kcal/g of reaction heat during oxidation treatment, and this reaction heat accumulates inside the fiber bundle, causing the temperature inside the fiber bundle to become abnormally high and causing fibers to stick together. Phenomena such as cutting and stiffening of the fiber bundle occur, which impairs the stability of operation, reduces the spinnability of the fiber bundle, and further reduces the quality (spinnability, strength, activation) of fibrous activated carbon and carbon fiber. (yield, processability) decreases, and quality irregularities occur. As a result of studies on these problems, the present inventors found that (1) stiction during oxidation of acrylonitrile fiber bundles occurs at the early stage of the oxidation reaction, especially when the amount of oxygen bonded is 8% by weight.
(2) Adhesion rarely occurs in the following steps; (3) Adhesion easily peels off (separates) in the initial stage;
It has been found that separation is difficult at an advanced stage of oxidation treatment. For example, a 450,000 denier acrylonitrile fiber bundle (92% acrylonitrile, methyl acrylate)
4.5% acrylamide, 3.5% acrylamide, copolymer single fiber fineness 3 denier was oxidized in air at 245°C, and the sticking occurrence rate was determined from each oxidized fiber with an oxygen bond amount in the range of 2 to 21% by weight. The results are shown in curve A in Figure 1.
When an acrylonitrile fiber bundle is oxidized in this way, most of the adhesion occurs up to about 8% by weight of oxygen bonding, and there is no increase in adhesion after that point. Moreover, this sticking can be easily separated by forcibly opening the fibers at an early stage. Based on this knowledge, the present inventors conducted studies and arrived at the present invention. That is, in the present invention, when an acrylonitrile fiber bundle (tow) is oxidized in an oxidizing atmosphere to produce a flame-resistant fiber bundle, when the oxidation treatment is applied to an oxygen bond amount of 4.5 to 8% by weight, This is a method for producing a flame-resistant fiber bundle, which comprises opening the fiber bundle and continuing the oxidation treatment until the amount of oxygen bonded becomes 15% by weight or more. According to the present invention, it is possible to obtain a high quality acrylonitrile-based flame-resistant fiber bundle that is free from sticking. Here, the amount of oxygen bond is determined by Yanagimoto high-speed CHN coder.
CHN was measured using Model MT-2 and calculated using the following formula. Oxygen binding amount (%) = Sample weight - Ash content - (CHN) total amount / Sample weight - Ash content x 100
(%) In addition, the incidence of sticking of fiber bundles is determined by the following formula by observing cross-sectional photographs of fibers at 500x magnification. Incidence of sticking (%) = Number of stuck fibers / Number of fibers in the photo × 100 (%) In the present invention, an acrylonitrile fiber bundle is a fiber made of a polymer mainly composed of acrylonitrile, and usually contains at least 75% by weight of acrylonitrile. In fibers made of copolymers or polymers containing the above, unsaturated compounds copolymerizable with acrylonitrile, such as acids such as acrylic acid, methacrylic acid, and methyl acrylate, and derivatives thereof, are used as comonomers. Fibers made by mixing these polymers or copolymers with other acrylonitrile copolymers or polymers may also be used. Comonomer content is 25% by weight
If the temperature exceeds that level, the surface will be significantly softened during the oxidation treatment, and sticking will occur easily, and separation of stuck fibers will also become difficult. The acrylonitrile fiber bundle used has a total denier of about 60,000 to 1,700,000 deniers, but usually has a total denier of 140,000 to 600,000 deniers, and single fibers of 0.5 to 15 deniers are used. Such oxidation treatment of acrylonitrile-based fiber bundles is carried out in an oxidizing atmosphere, for example, in air at a temperature of 200 to 400
It is carried out at ℃. The tension during processing is 40 to 60% of the free shrinkage rate of the fiber at the processing temperature when producing flame-resistant fiber bundles for carbon fiber production.
In the case of activated carbon, it is performed in a 50 to 90% contracted state. The density of the fiber bundle also varies depending on the processing temperature, but is less than 600 g/ ^m2 , preferably 200 to 400 g/ ^m2.
is within the range of The oxidation treatment is carried out until the amount of oxygen binding reaches 15% by weight or more, and the fiber bundle in which the amount of oxygen binding has reached 4.5 to 8% by weight is subjected to the opening treatment. The opening treatment here means opening the fiber bundle to separate the fibers from sticking together, separating the stuck fibers, and making them into single fibers, and various methods can be considered as means for this purpose. For example, methods include applying high vibrations to fiber bundles in air or water, folding them, and ``squeezing'' them with rollers, fixing pins, bars, etc. A particularly preferred method is a method in which the fiber bundle is bent and rubbed. In FIG. 2, 1 indicates a stator and 2 indicates a fiber bundle. The bending angle α of the fiber bundle is preferably 25 to 60 degrees, particularly preferably 35 to 45 degrees. If the angle is smaller than 25 degrees, the fiber bundle will have low elongation, leading to fiber deterioration or breakage.
Furthermore, if the temperature is 60 degrees or higher, the opening effect will be low. A specific method is as shown in FIG. When performing fiber opening treatment, the amount of oxygen binding is 4.5 to 8% by weight.
It is best to do it when If opening treatment is performed before the amount of oxygen binding is 4.5% by weight, re-agglutination will occur in the subsequent oxidation process.
While the effect of the opening process disappears, if the process is performed when oxidation has progressed to 8% by weight or more, the strength and elongation of the fibers has decreased, resulting in folding or cutting of the fibers. It is also difficult to separate the stalemates. Most preferably, the opening treatment is performed when the amount of oxygen bonding is 5 to 7% by weight. The temperature of the opening process is 80°C or more than the temperature before the opening process.
It is best to do this at a temperature as low as 200℃. If the process is carried out at a low temperature below 80°C, the fibers will be compressed, resulting in increased adhesion, and if the process is carried out at a low temperature above 200°C, the adhesion will be difficult to remove. Furthermore, if an iron compound, a titanium compound, an aluminum compound, a silicon compound, a carbon powder, etc. are attached to or contained in the fibers before the opening treatment, and then the opening treatment is performed, the effect is further doubled. When the fiber opening treatment is performed in the middle of the oxidation process as described above, the incidence of sticking occurs is significantly reduced. For example, acrylonitrile 90%, acrylamide
A 1.5 million denier (single fiber fineness 2 denier) made of 10% acrylonitrile fiber is oxidized in air at 260°C, and the amount of oxygen bonded in the fiber is determined by the bending angle using the apparatus shown in Figure 3 A at the following stages. 50 degrees, and the temperature is 80 degrees Celsius, which is 180 degrees lower than the oxidation temperature.
After bending twice and then oxidizing at 270℃,
Table 1 summarizes the sticking occurrence rate, fiber strength, and spinnability (reactor test) of flame-resistant fibers with an oxygen binding content of 20%.

[Table] In order to investigate the effect of bending angle, 90,000 denier (single fiber fineness 3 denier) made of acrylonitrile fiber with a composition of 90% acrylonitrile and 10% vinylidene chloride was oxidized in air at 250°C. When the amount of oxygen binding in the fiber was 6%, the fiber was continuously bent seven times at various bending angles at a temperature of 60°C, which is 190°C lower than the oxidation temperature, using the apparatus shown in Figure 3A. , and further oxidized at 270℃ to create a flame-resistant fiber with an oxygen bonding amount of 19.5%.The stability of this flame-resistant fiber in the latter half of the oxidation process, the occurrence rate of adhesion, and the fiber strength of the flame-resistant fiber were investigated. It is summarized in Table 2.

【table】

[Table] Next, the No. 1 and No. 5 flame-resistant fibers obtained in Table 2 are
Activated in steam at 1000℃, specific surface area 1000
Fibrous activated carbon of m ² /g was obtained. The activation yield and fiber strength of these activated carbons are as follows.

[Table] As described above, according to the present invention, the sticking of fibers was reduced, the heat generated from the fibers during the flameproofing process was diffused to the surroundings without being stored, and production efficiency was also improved. On the other hand, the flame-retardant fibers produced also have excellent spinnability due to their low adhesion, and can be used as raw materials for fibrous activated carbon with excellent activation yields and high fiber strength.They can also be used as raw materials for carbon fibers with high strength. Things can be manufactured. Examples of the present invention will be described below. Example 1 Acrylonitrile 94%, methyl acrylate 6%
450,000 denier acrylonitrile fiber bundle (single fiber fineness 3 denier) consisting of fibers with a copolymer composition of
was oxidized in air at 250℃ until the amount of oxygen bonded was 6.5%, opened at 85℃ using the equipment shown in Figure 3A, and further
It was treated at 270°C, and the amount of oxygen bonded was oxidized to 19.5%. The fiber strength of this flame-resistant fiber bundle is 26.5Kg/mm ²
The incidence of sticking of this fiber was 2.4%. This fiber bundle was activated at 900° C. in steam to produce fibrous activated carbon with a specific surface area of 1050 m ² /g. The activated carbon obtained had an activation yield of 25% and a fiber strength of 40 kg/mm ² . Comparative Example When the fibers of Example 1 were subjected to oxidation treatment under the same treatment conditions without being subjected to the opening treatment, the fibers frequently stuck together, the stuck portions were cut, and a satisfactory flame-resistant fiber could not be obtained. Therefore, the oxidation temperature is relaxed,
It was oxidized at 260°C to an oxygen bond amount of 19.5%. The obtained flame-resistant fiber had a fiber strength of 21 Kg/mm ² and a sticking occurrence rate of 17.5%. The obtained fibers were activated at 900℃ in steam, and the specific surface area
1000 m ² /g of fibrous activated carbon was obtained. The activation yield at this time was 20% and the strength of the fibrous activated carbon was 20 kg/mm ² .

[Brief explanation of the drawing]

FIG. 1 shows the occurrence of sticking as the oxidation treatment progresses when tow is oxidized. FIG. 2 is an explanatory diagram showing the angle of the bending process of the present invention. FIG. 3 is a schematic view showing an embodiment of the bending process of the present invention, in which A shows the bending and scratching process using a fixed bar, B shows the process using the combined gears, and C shows the bending process using the crimper.

Claims (1)

[Claims] 1. When an acrylonitrile fiber bundle (tow) is oxidized in an oxidizing atmosphere to produce a flame-resistant fiber bundle, when the oxidation treatment is performed to an oxygen bond content of 4.5 to 8% by weight, A method for producing a flame-resistant fiber bundle, which comprises opening the treated fiber bundle and continuing the oxidation treatment until the amount of oxygen binding reaches 15% by weight or more. 2. The method according to claim 1, wherein the opening treatment includes bending and rubbing the fiber bundle to be treated at an angle of 25 to 60 degrees. 3. The method according to claim 1, wherein the temperature during the opening treatment is about 80 to 200°C lower than the temperature of the fiber bundle before the treatment.