JPH0424446B2 - - Google Patents

Description

Detailed Description of the Invention "Field of Industrial Application" The present invention is a carbon fiber having the characteristics of high strength and high elasticity, and has excellent homogeneity between each single fiber, and is free from yarn defects such as fuzz. The present invention relates to a multi-stage flame-retardant treatment method for acrylonitrile-based polymer fiber bundles that can produce carbon fiber bundles with reduced flame resistance.

"Prior Art" As is well known, the production of carbon fibers usually involves a flame-retardant process in which acrylonitrile polymer fibers are heat-treated in an oxidizing atmosphere, and a carbon fiber process in which the resulting flame-retardant fibers are heat-treated in an inert atmosphere. It is broadly divided into two stages: The flame-retardant process for acrylonitrile polymer fibers is usually carried out at 200-300°C in an oxidizing atmosphere for 2-4 hours, and this flame-retardant process accounts for more than 90% of the total time required for the carbon fiber manufacturing process. occupies . Therefore, it is said that the reduction in carbon fiber production costs lies in the reduction of the time required for this flame-retardant reaction.

One method for shortening this flame-retardant process is to increase the flame-retardant temperature, as shown in Japanese Patent Publication No. 47-35938. (As shown in Textile Res. J. 30 882-896 (1960), the flame-retardant reaction is an exothermic reaction, which causes a runaway reaction and induces ignition in the acrylonitrile polymer fiber. Even when such ignition is not induced, when treated with this method, the treated acrylonitrile polymer fibers have a flame-resistant structure on the outer periphery of the fiber, but a structure that is insufficiently flame-resistant on the inside. This results in a flame-retardant yarn with a non-uniform flame-retardant structure.Such flame-retardant yarns cause undesirable phenomena such as fluffing and yarn breakage during the carbonization process that is carried out later, making it difficult to carry out an efficient carbonization reaction. It is difficult to carry out this process, making it impossible to obtain high-performance carbon fibers.However, there is a special method that does not have these difficulties and shortens the flame-retardant treatment time for acrylonitrile polymer fibers to 5 to 30 minutes. This method is disclosed in Publication No. 51-25487.This method heat-treats acrylonitrile polymer fibers for 5 to 20 hours until the equilibrium moisture content reaches 4%.
After being treated under flame-retardant treatment conditions such as
This is a method of carbonizing at a temperature of 1000°C or higher. However, as seen in many known documents, the flame-retardant treated yarn with an equilibrium moisture content of 4% does not have a sufficient flame-retardant structure, and its cross section has a remarkable double structure. Flame-resistant fibers such as these are thermally decomposed in the subsequent carbonization process, and microvoids are formed in the resulting fibers, resulting in a tensile strength of 400 kg/kg.
It is difficult to make high-strength carbon fiber of mm ² or more.

In this way, the runaway reaction in the flame-retardant process and the heterogeneous flame-retardant reaction of acrylonitrile polymer fibers increase as the number of acrylonitrile polymer fibers constituting the acrylonitrile polymer fiber bundle increases. I end up. A method for efficiently making such acrylonitrile polymer fiber bundles with a large number of single fibers flame resistant was disclosed in Japanese Patent Application Laid-Open No. 58-163729.
It is shown in the publication No. This method uses single fiber fineness
0.5~1.5 denier, number of filaments 1000~30000
200 to 260 acrylonitrile polymer fiber bundles
The oxygen content of this fiber bundle in a flameproofing furnace at ℃
7% incompletely flame resistant yarn (this prevents inter-fiber fusion during subsequent higher flame resistant treatment), and then further treated under high temperature flame resistant conditions. This method involves carbonizing the yarn after making it into a completely flame-resistant yarn with an oxygen content of 9.5% or more. but,
Although this method does not cause yarn fuzz or yarn breakage, the processing conditions for changing incompletely flame-resistant yarn to fully flame-resistant yarn are harsh, so microvoids are likely to occur within the yarn, and furthermore, microvoids are likely to occur in the yarn. The oxygen content of
Because the cross-linked structure caused by oxygen is highly developed, it is not possible to perform elongation treatment that is effective in improving the performance of carbon fibers obtained in the carbonization process, and the resulting carbon fibers have a high The tensile strength is
350Kg/ ^mm2 or less.

"Problems to be Solved by the Invention" As mentioned above, acrylonitrile polymer fiber bundles with a large number of single fibers, such as 1,000 to 15,000 acrylonitrile polymer fibers, are particularly difficult to form into sheets. It is a flame-resistant material that can perform high-speed flame-retardant treatment on precursors arranged in parallel within 60 minutes, and can also be subjected to elongation treatment to improve the performance of carbon fibers in the subsequent carbonization process. At present, the technology for obtaining synthetic fibers has not yet been perfected.

"Means for Solving the Problems" In response, the present inventors have conducted extensive research to solve the above problems, and have come to the following findings. That is, (a) in the prior art, the oxygen diffusion rate between the acrylonitrile fiber bundles was insufficient, so that the permeation of oxygen into the cross section of the acrylonitrile single fibers tended to be slow.

(b) Therefore, it has become necessary to increase the flame-resistant density of the flame-resistant fibers to be subjected to the carbonization process to 1.40 g/cc or more, resulting in the above-mentioned disadvantages.

(c) Based on this, by selecting flame-resistant conditions that increase the oxygen diffusion rate into the acrylonitrile-based polymer fiber bundle, the above-mentioned disadvantages can be significantly improved, and the flame-resistant yarn obtained thereby Carbon fibers made from these materials can have extremely high performance.

The present invention has been made based on the above findings. That is, the gist of the present invention is to
When flame-proofing an acrylonitrile polymer fiber bundle containing at least 90% by weight of acrylonitrile in an oxidizing atmosphere using three or more furnaces with different treatment temperatures, the total treatment time for each stage is 20 minutes. When flame-retardant treatment is performed for at least 60 minutes and at a fiber density ρk of 1.34 to 1.40 g/cc after flame-retardation, the range of fiber density ρn after each step of treatment is calculated using the following formula (). The fiber density was obtained from a graph of the density change with respect to the flame-retardant treatment time under a constant temperature condition at various temperatures of the fiber bundle prepared in advance from the same fiber bundle as the acrylonitrile polymer fiber bundle to be flame-retardant treated. The present invention provides a multi-stage flame-retardant treatment method for an acrylonitrile polymer fiber bundle, characterized in that the multi-stage flame-retardant treatment is carried out by setting a treatment temperature to obtain a ρn range.

(ρk-ρo)×{ _o 〓 ⁿ⁼¹ tn／ _k 〓 ⁿ⁼¹ tn}＋ρo−0.01≦ρn≦(ρk-ρo)×{ _o 〓 ⁿ⁼¹ tn／ _k 〓 ⁿ⁼¹ tn}＋ρo＋0. 01...() However, ρn is the density of the fiber after the n-th stage treatment (g/cc), ρo is the raw material acrylonitrile polymer fiber density (g/cc), and ρk is the fiber density after the flame-retardant treatment, from 1.34 to Value in the range of 1.40 g/cc tn is the n-th flame-retardant treatment time k is the number of flame-retardant treatment stages "effect" 10% or more and other copolymerizable
It consists of a copolymer with a vinyl monomer of less than % by weight. This polymer can be produced by various methods such as solution polymerization, suspension polymerization, and emulsion polymerization, and preferably has a reduced viscosity of 1.0 to 10.0.

Fibers made from polymers containing less than 90% by weight of acrylonitrile units have low flame retardant reactivity, so it is necessary to increase the flame retardant initiation temperature.
Once the flame resistance reaction is started, there is a tendency for a runaway reaction to occur, so it is preferable that the acrylonitrile polymerization unit is 95% by weight or more.

Other copolymerizable vinyl monomers to be copolymerized with acrylonitrile are components that promote the flame resistance reaction of acrylonitrile polymer fibers and contribute to shortening the flame resistance time, such as hydroxyethyl acrylonitrile, methyl vinyl ketone, etc. ,
Methyl acrylate, acrylic acid, methacrylic acid, itaconic acid, t-butyl methacrylate, etc. can be used, but the amount of copolymerization of these components is limited to the total amount.
The content is preferably 10% by weight or less, preferably 5% by weight or less.

The above acrylonitrile polymer is usually spun using a wet spinning method or a dry-wet spinning method, and has a single fiber fineness of 0.3 to 1.5 deniers and a filament count of 1000.
~15,000 acrylonitrile polymer fiber bundles are preferred. Fibers with a single fiber fineness of less than 0.3 denier are not preferred because they tend to lack strength when used as raw material fibers for producing carbon fibers. On the other hand, if the denier exceeds 1.5 denier, the rate of oxygen diffusion into the cross section of the fiber during the flame resistant process decreases, and there is a tendency that it becomes difficult to form a uniform flame resistant yarn.

On the other hand, when the number of filaments is less than 1000, the processability in the flame-resistant process is good, but the productivity of the flame-resistant yarn decreases rapidly. On the other hand, for large filaments with a total number of more than 15,000, oxygen diffusion into the acrylonitrile polymer fiber bundle is hindered during the flame-retardant process, and the fibers on the outer surface of the fiber bundle and the fibers on the inner surface of the fiber bundle are Differences in flame resistance performance tend to appear between the two.

The characteristics that must be possessed by a flame-resistant fiber bundle that can produce high-performance carbon fibers are the absence of fluff, and 2.
% or more, preferably 5% or more, and generates less tar.
A flame-resistant fiber bundle with such performance is 1000
There is no significant difference in flame-resistant fiber density between the fibers located on the outside of the fiber bundle composed of ~15,000 filaments and the fibers located in the center;
It is necessary that the flame resistance within the cross section of a single flame resistant fiber be as uniform as possible.

In order to oxidize an acrylonitrile polymer fiber bundle consisting of 1,000 to 15,000 filaments and make it into a flame-retardant fiber bundle with the above-mentioned properties, it must pass through the n-th stage of a plurality of flame-retardant furnaces. This is possible if the fiber density, which indicates the degree of improvement in flame resistance of the flame-resistant treated yarn, satisfies the conditions defined by the above formula ().

In the first half of the flameproofing process, if ρn is larger than the value on the right side of equation (), high-temperature treatment is required to initially increase the fiber density, as shown by line A in FIG. Therefore, ignition due to reaction runaway and fiber fusion are likely to occur, making it difficult to shorten the flame resistance process. In addition, in conventional technology, in order to avoid runaway reactions associated with high-temperature treatment, the first half of the flameproofing process is performed at a relatively low temperature, as shown by line B in Figure 1, and the second half, where runaway reactions are less likely to occur, is rapidly accelerated. It is necessary to increase the density of the flame-resistant fibers, which results in the formation of microvoids in the cross-section of the resulting flame-resistant fibers, and a large difference in the degree of flame resistance between the inner and outer surfaces of the fibers. It can be seen that such short-time flame resistant fibers show no stretchability at all in the subsequent carbonization treatment step and tend to generate fuzz.

On the other hand, in the present invention, ρn is expressed as
When flame ^- retardant conditions are adopted that _fall within the range specified by
The relationship is almost linear, and the total flame resistance treatment time
_k 〓 Even when ⁿ⁼¹ tn is set within 60 minutes, the difference between the ρox of the outer fibers and the ρox of the inner fibers of the flame-resistant fiber bundle obtained is extremely small. It can be seen that uniform flame resistance within the cross section can be efficiently achieved, and a flame resistant fiber bundle with very little inter-fiber fusion and adhesion is produced. ρo is usually about 1.18, and ρk is 1.34 to 1.34 in the present invention.
1.40, especially in the range of 1.35 to 1.38. Flame-resistant yarns with a ρk value of less than 1.34 undergo rapid thermal decomposition during the carbonization process, and tend to generate fluff.
Therefore, carbon fibers with good performance cannot be obtained. Conversely, if the ρk value exceeds 1.40, it is difficult to obtain high-performance carbon fibers with a tensile strength of 400 Kg/mm ² or more.

On the other hand, the flame-resistant fiber of the present invention has a ρk of 1.35~
Since it has a value in the range of 1.40, even if the flame-proofing process is shortened, it can be stretched by 3 to 25% without causing an abnormal thermal decomposition reaction in the carbonization process, and has excellent performance. It can be made of carbon fiber. In the present invention, the flameproofing treatment time _k 〓 ⁿ⁼¹ tn is 20 to 60
There is a noticeable effect in the range of minutes.

The number of stages of the multistage flameproofing furnace used in the present invention is
The number of stages may be at least 3, preferably 3 to 6, and if the number of stages is too large, it is not economical, increases equipment restrictions, and is undesirable in terms of workability.

The multi-stage flameproofing of the present invention is an effective method when firing a single or a plurality of acrylonitrile polymer fiber bundles having a single fiber fineness of 0.3 to 1.5 deniers and a filament number of 1000 to 15000. This method is particularly effective when arranging tens to hundreds of acrylonitrile polymer fiber bundles in parallel in a sheet shape and firing them. When arranging them in a sheet form and firing them, the pitch width between each fiber bundle is set so that the rate of oxygen diffusion into the acrylonitrile polymer fiber bundles is not inhibited, and the rate of flame resistance satisfies the formula (). Furthermore, the object of the present invention can be fully achieved by controlling the temperature increase rate. The flame-resistant yarn obtained by this method can be fired while being sufficiently elongated in the carbonization process, and is a flame-resistant yarn that can produce carbon fibers with excellent performance. The processing time is also significantly reduced compared to the conventional method.

Example 1 An acrylonitrile polymer fiber bundle consisting of a density of 1.18 g/cc, a single fiber denier of 1.3 d, and 12,000 filaments was prepared in 5 temperature zones and the processing length of each stage was 8 m from the 1st stage to the 4th stage. , the fifth row is 5.3
Each stage of flame retardant treatment is completed in a total of 30 minutes using a hot air circulation multi-stage flame retardant furnace (total treatment length of 37.3 m) consisting of a The subsequent density range was determined using equation (). The processing time for each stage was as follows.

1st stage processing time…6.43 minutes 2nd stage processing time…6.43 minutes 3rd stage processing time…6.43 minutes 4th stage processing time…6.43 minutes 5th stage processing time…4.26 minutes Total processing time…30 minutes And density (ρo ) is 1.18 g/cc, and the density (ρk) is 1.36 g/cc.
When flame-retardant treatment is applied to up to
₁
≦(1.18+0.01)+(1.36−1.18)×(6.43/30) 1.2086≦ρ ₁ ≦1.2286.

Furthermore, the density range after the second and subsequent stages of processing was similarly calculated. Table 1 shows the density ranges (calculated density ranges) after each step of processing determined in this way.

Next, from the graph shown in FIG. 2, the processing temperature for achieving the above calculated density range was read. FIG. 2 is a graph showing the density change of the acrylonitrile polymer fiber bundle determined in advance at various temperatures and with respect to the flame resistance treatment time under constant temperature conditions.

First, regarding the first stage treatment temperature, the temperature at which the density falls within the range of 1.2086 to 1.2286 g/cc after about 6.4 minutes was read from FIG. 2, and that temperature was defined as the first stage treatment temperature. The temperature of this first stage treatment was 241°C.

Next, regarding the second stage treatment temperature, take the density after the first stage treatment as the initial (starting) density, read the temperature at which the density reaches 1.2472 to 1.2672 g/cc after about 6.4 minutes, and set that temperature to the second stage. The temperature was set as the eye treatment temperature. The temperature of this second stage treatment was 245°C.

Further, the processing temperatures for the third and subsequent stages were similarly read from FIG. 2, and the above operations were repeated to set the processing temperatures for each stage. Table 1 shows the processing temperatures of each stage determined in this manner. Under this temperature condition, 50 acrylonitrile polymer fiber bundles were arranged so that the pitch between the fiber bundles was approximately 4 mm, and the feeding speed was 67.8 m/hr and the take-up speed was 74.6 m/hr.
A flame-retardant treatment was performed which gave a substantial 10% elongation at hr and took 30 minutes. The fiber bundle being conveyed through the flameproofing furnace had substantially no gaps and was in the form of a sheet. This flame-retardant treatment was carried out continuously for 24 hours, but there was no ignition due to reaction runaway, and the flame-retardant fiber bundle obtained was satisfactory, with no fusion or fuzz. After 24 hours of operation, the fibers after each stage treatment were sampled and their densities were measured using a density gradient tube. As shown in Table 1, the densities at all stages were within the calculated density range.

The obtained flame-resistant fiber bundle was then continuously passed through a pre-carbonization furnace at 600°C and a carbonization furnace at 1400°C under a nitrogen atmosphere for carbonization treatment. At this time, when the elongation rate in the pre-carbonization furnace was varied until fluff was generated, there was no fluff at all up to 12%, and slight fluff was observed at 14%. Next, carbonization treatment was carried out by setting the elongation rate of the pre-carbonization furnace to 8%, but the obtained carbon fibers had very little fluff, and had a tensile strength of 480Kg/mm ² and an elastic modulus of 24Ton. / ^mm2 , it was a high performance product.

Comparative Example 1 In Example 1, the temperature conditions were changed to those shown in Table 2, and flameproofing treatment was performed. The flame-retardant treatment was stable with no fluff or fusion. Next, carbonization treatment was carried out in the same manner as in Example 1, but a lot of fuzz occurred in the pre-carbonization furnace, and no elongation could be imparted. Therefore, carbonization treatment was carried out with the elongation rate in the pre-carbonization furnace set to zero, but a lot of fuzz was generated in the carbonization furnace, and the obtained carbon fibers were not worthy of evaluation.

In addition, the fiber density after each stage of flame resistance treatment was determined in Example 1.
As a result of measurement using the same method as shown in Table 2, the fiber densities of the first to third stages were values that deviated from the calculated density range shown in Table 1.

Comparative Example 2 In Example 1, only the first stage and second stage were used, and the flame resistance finished density was 1.36 after 30 minutes of treatment.
When the processing temperature that satisfies the formula () in the case of g/cc was determined in the same manner as in Example 1, the first
The temperature in the first stage was 245°C, and the temperature in the second stage was 265°C. Flameproofing treatment was carried out at this temperature for 30 minutes at a take-up speed of 74.6 m/hr, but due to runaway reaction, the fiber bundle was cut in the second stage, making treatment impossible.

"Effects of the Invention" As explained above, according to the multi-stage flame-retardant treatment method for acrylonitrile-based polymer fiber bundles according to the present invention, it has the characteristics of high strength and high elasticity, and the homogeneity between each single fiber is improved. Acrylonitrile-based polymer fiber bundles can be efficiently flame-resistant treated so that carbon fiber bundles with excellent properties and fewer yarn defects such as fuzz can be easily produced.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the treatment time and the flame-resistant fiber density in the present invention and the conventional flame-retardant treatment method for acrylonitrile-based polymer fiber bundles, and FIG. It is a graph showing the density change with respect to the flame resistance treatment time under constant temperature conditions.

【table】

【table】

Claims (1)

[Scope of Claims] 1. When flame-proofing an acrylonitrile polymer fiber bundle containing at least 90% by weight of acrylonitrile in an oxidizing atmosphere using three or more furnaces with different treatment temperatures, each The range of fiber density ρn after each stage treatment when the total stage treatment time is 20 minutes or more and 60 minutes or less, and flame-retardant treatment is performed so that the fiber density ρk after flame-retardation is 1.34 to 1.40 g/cc is calculated using the following formula (), and the density of the fiber bundle prepared in advance from the same fiber bundle as the acrylonitrile polymer fiber bundle to be flame-retardant treated is determined by the flame-retardant treatment time at various temperatures and at a constant temperature condition. 1. A multi-stage flame-retardant treatment method for an acrylonitrile-based polymer fiber bundle, characterized in that the flame-retardant treatment is performed by setting a treatment temperature to bring the fiber density ρn within the range described above based on a graph of changes. (ρk-ρo)×{ _o 〓 ⁿ⁼¹ tn／ _k 〓 ⁿ⁼¹ tn}＋ρo−0.01≦ρn≦(ρk-ρo)×{ _o 〓 ⁿ⁼¹ tn／ _k 〓 ⁿ⁼¹ tn}＋ρo＋0. 01...() However, ρn is the density of the fiber after the n-th stage treatment (g/cc), ρo is the raw material acrylonitrile polymer fiber density (g/cc), and ρk is the fiber density after the flame-retardant treatment, from 1.34 to Value in the range of 1.40 g/cc tn is the n-th flame-retardant treatment time k is the number of flame-retardant treatment stages 2 A state in which a large number of acrylonitrile polymer fiber bundles are aligned and the fiber bundles are substantially shaped into a sheet. 2. A multi-stage flame-retardant treatment method for an acrylonitrile polymer fiber bundle according to claim 1, wherein