JPS623245B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing flame-resistant fibers and carbon fibers. Conventionally, a method is known in which acrylonitrile fibers are used as a precursor (raw material) and subjected to oxidation treatment (flame-resistant treatment) to obtain flame-resistant fibers, and then carbonized to obtain carbon fibers. The time required to produce such fibers is very long, and as a result, flame-resistant fibers and carbon fibers become expensive, and despite their excellent properties, demand for them has not increased. In addition, since flame-retardant treatment takes a long time to perform, a flame-retardant furnace with a multi-stage roller group is usually used as a device for this purpose, but at that time, the treated fibers often break into single fibers. This tends to cause the fibers to wrap around the lifting rollers, resulting in process troubles and fiber bundles with a lot of fuzz.
has been considered a problem. On the other hand, various proposals have been made to improve the strength of carbon fiber, and as a result of successively solving various problems, the strength, which was initially around 200 kg/mm ² , has improved dramatically, but even higher Strong carbon fiber is desired. In view of the above circumstances, the present inventors conducted research on a method for shortening the flame-retardant treatment time and producing fiber bundles with high strength and less fuzz, and as a result, the following became clear. (1) In order to speed up the flame resistance of acrylonitrile fibers, it is known to copolymerize vinyl monomers with acidic groups and to include zinc; The rate of flame resistance of fibers containing zinc in an acrylonitrile copolymer copolymerized with zinc is greatly increased compared to the case where each zinc is contained alone, and a so-called synergistic effect is observed. (2) It is known that the strength of carbon fibers is improved by including zinc in the fibers, but when the fibers contain acidic groups, the zinc content is greater than the equivalent amount of the acidic groups. The strength of the carbon fibers reduced. This is thought to be due to stress concentration occurring in the excess zinc when shearing force acts between molecules constituting the fibers. (3) Fibers shrink as a result of the oxidation reaction, and this shrinkage can be divided into contraction due to relaxation of molecular orientation in the early stage of the oxidation reaction and contraction associated with the cyclization reaction in the latter stage of the oxidation reaction. (3-4%)
The two can be distinguished based on. (4) The oxidation reaction rate of acrylonitrile fibers is accelerated by the introduction of acidic groups and zinc, and therefore the shrinkage at the initial stage of the reaction becomes larger and faster than when these are not included. This is thought to be due to the molecules being fixed by the introduced components. Therefore, in the early stage of the oxidation reaction, the tension must be adjusted in order to fix the molecules in a highly oriented manner. (5) Shrinkage due to the cyclization reaction is reduced compared to the case without acidic groups and zinc. This is thought to be due to the immobilization of molecules as described above. (6) Normally, flame resistance weakens the fibers, but it is nevertheless required to keep the fibers under tension and maintain a high molecular orientation. This resulted in fiber bundles with a lot of fuzz. However, if the molecular orientation is fixed at the initial stage of the flameproofing reaction, it is only necessary to apply tension at the initial stage, and there is no need to maintain tension throughout the entire stage. From this point of view, if tension is stopped at a later stage, the occurrence of fuzz due to single yarn breakage can be reduced. The present inventors conducted further research based on the above findings and arrived at the present invention. That is, the present invention is composed of a copolymer containing 5 x 10 ^-2 to 50 x 10 ^-2 mol% of a vinyl monomer having an acidic group and at least about 96 mol% of acrylonitrile; This is a method for producing flame-resistant fibers and carbon fibers, in which acrylonitrile fibers containing zinc in an amount such that 50 to 100 equivalent % of counterions are replaced with zinc are oxidized and, if desired, then carbonized. In a preferred embodiment of the present invention, the acrylonitrile fiber is passed through a multistage roller group to
Oxidation treatment is carried out at 300°C, and at this time, until the amount of oxygen bonded to the fiber is 3 to 4% (by weight), depending on the progress of the reaction, a shrinkage of 20 to 50% of the free shrinkage rate of the fiber is applied, In the subsequent oxidation treatment step,
The free shrinkage rate of the fiber during this period depends on the progress of the reaction.
This is a method for producing flame-resistant fibers that undergoes oxidation treatment while giving 50 to 70% shrinkage. Further, if desired, the flame-resistant fiber thus obtained is subjected to carbonization treatment in a non-oxidizing atmosphere at 500 to 2000° C. while giving shrinkage of 40 to 70% of the free shrinkage rate. Such acrylonitrile fibers are excellent as raw material fibers for the production of flame-resistant fibers, and by using them, flame-resistant fibers with less fluff due to single fiber breakage can be obtained, and high-strength carbon fibers can be obtained. can be obtained. Here, the vinyl monomer having an acidic group is a monomer copolymerizable with acrylonitrile, such as allylsulfonic acid, methallylsulfonic acid, acrylic acid, methacrylic acid, itaconic acid, or salts thereof. The amount of vinyl monomers having these acidic groups is
5 of the monomers constituting the acrylonitrile polymer
×10 ⁻² to 50×10 ⁻² mol%. 5×10 ^-2 mol%
If the amount is less than 50 x 10 ^-2 mol%, the rate of flame resistance will not be very fast, and if it exceeds 50 x 10 -2 mol%, the rate of flame resistance will progress excessively, resulting in a two-layered structure of the flame resistant fibers, and as a result, high strength carbon fibers. You won't be able to get it. Neutral vinyl monomers such as methyl acrylate, methyl methacrylate, and acrylamide may also be used as copolymerization components, but it is necessary that at least 95 mol% be acrylonitrile. If the acrylonitrile component is less than this, the quality of the obtained carbon fiber will deteriorate. To introduce zinc into the acidic groups of acrylonitrile polymer fibers, during water washing and desolvation after wet spinning,
or subsequently introducing the fiber into an aqueous solution containing a water-soluble zinc compound such as zinc chloride or zinc sulfate;
Alternatively, when a concentrated zinc chloride aqueous solution is used as the solvent, the degree of desolvation is adjusted during water washing to obtain a fiber containing 50 to 100 molar equivalents of zinc based on the equivalent of acidic groups in the polymer. For spinning acrylonitrile polymer, dimethylformamide, dimethyl sulfoxide, which is usually used for spinning acrylonitrile polymer fiber,
Organic solvents such as dimethylacetamide and ethylene carbonate, and inorganic solvents such as rhodan salt and nitric acid are used, but the use of zinc chloride-based aqueous solutions is particularly preferred from the viewpoint of the process. For example, a polymer consisting of 0.35 mol% of sodium methallylsulfonate, 1.27 mol% of acrylic acid, and 98.38 mol% of acrinitrile is dissolved in a 60% zinc chloride aqueous solution, and a polymer solution obtained is wet-spun through pores. During water washing and desolvation, 30, 60,
After adjusting water washing so that 90,120% equivalent of zinc remains in the fibers, drying and stretching in pressurized steam, acrylonitrile fibers with a single fiber of 1 denier and 3000 fibers are mixed with methane. Using methyl acrylate instead of 0.35 mol% of sodium lylsulfonate, a polymer made of 1.9 mol% of methyl acrylate and 98.1 mol% of acrylonitrile was obtained as described above, using an acrylonitrile-based fiber as a comparative example. These fibers were oxidized until the amount of oxygen bonded was 12%, and then carbonized to obtain carbon fibers.The relationship between the amount of oxygen bonded by the oxidation treatment and oxidation time, and the tensile strength of the obtained carbon fibers. The strength is shown in Table 1.

[Table] As is clear from Table 1, in the comparative examples of fibers that do not contain sulfonic acid, the rate of flame resistance increases slightly when zinc is added, but the rate of flame resistance becomes even faster when sulfonic acid is added. The rate of flame resistance increases, and when sulfonic acid and zinc are included, the rate of flame resistance becomes even faster. Contains sulfonic acid groups and zinc, and in terms of their equivalents, the strength of carbon fiber is not so high when it contains 30% (equivalent) of the equivalent of the sulfonic acid groups, whereas the strength of carbon fiber is not so high.
At ~90%, the strength of carbon fiber is even higher. On the other hand, in the case of 120%, the strength of the carbon fiber actually decreases. In this way, only fibers that contain acidic groups and contain 50 to 100% (equivalent) of zinc relative to the equivalent of the acidic groups can be made into carbon fibers that have a high flame resistance rate and high strength. If it is less than 50%,
It is clear that the effect on the flame resistance rate and the strength of carbon fibers is not remarkable, and if it exceeds 100%, the strength of carbon fibers actually decreases and becomes worse. When flame-retardantly treating acrylonitrile polymer fiber bundles containing acidic groups, they are treated in an oxidizing atmosphere such as oxygen or air through a group of multistage rollers.
Oxidation treatment at 200-300℃. At this time, depending on the progress of the reaction, when the amount of oxygen bonded to the fiber reaches 3 to 4%, the shrinkage of the fiber is 20 to 50% of the free shrinkage rate of the fiber. This is because when acidic groups and bonded zinc are included, the oxidation reaction proceeds quickly, the free shrinkage rate increases, and the molecules are fixed faster, so the shrinkage relative to the free shrinkage rate is smaller than when these components are not included. This is because the oxidation reaction is carried out in a relatively tensioned state to suppress relaxation of molecular orientation. 20% shrinkage
If the size is smaller, more single fibers will break at the initial stage of flame-retardant treatment. If the shrinkage is greater than 50%, it is difficult to obtain carbon fibers with high strength. In the latter stage of the flame-retardant reaction, which is a further advanced stage of the flame-retardant treatment under such conditions, the treatment is performed while giving a shrinkage of 50 to 70% of the free shrinkage rate. The contraction
If it is smaller than 50%, single fiber breakage is likely to occur, and 70
%, the strength will not increase. Here, the free shrinkage rate is the shrinkage (rate) measured at each stage according to the progress of the treatment under the conditions of flameproofing treatment or carbonization treatment of the fibers to be treated, applying a load to the extent that the fibers do not slacken. It is. The flame-resistant fiber obtained by the flame-retardant treatment as described above can be used as it is for heat-resistant and flame-retardant purposes.
Or it is then subjected to carbonization treatment. Carbonization is carried out in an inert atmosphere such as nitrogen, argon, helium, etc. at 500 to 2000° C. while giving a shrinkage of 40 to 70% of the free shrinkage rate of the fiber. If the shrinkage rate is less than 40%, fluff will occur frequently and the process will become unstable. On the other hand, if it exceeds 70%, the molecular orientation will be disordered and carbon fibers with sufficient strength will not be obtained. As is clear from the above, the present invention was first completed as a result of focusing on acrylonitrile fibers with a special composition and investigating changes in the structure and physical properties of the fibers during the flame-retardant process. According to the present invention, it is possible to obtain flame-resistant fibers with good quality and physical properties by increasing the flame-proofing speed and shortening the flame-proofing time, and furthermore, it is possible to obtain carbon fibers with high strength and less fuzz. A more detailed explanation will be given below with reference to Examples. Example 1 Sodium methallylsulfonate 7×10 ^-2 mol%, methyl acrylate 1.5 mol% and acrylonitrile
A solution with a polymer concentration of 9% by weight, in which a polymer consisting of 98.43 mol% is dissolved in a 59% by weight zinc chloride aqueous solution, is passed through a nozzle with a nozzle diameter of 0.06 mm and a number of holes of 6000 to form a 25% by weight zinc chloride aqueous solution. After extrusion, the mixture was washed with water and the solvent was removed. During the solvent removal process, hydrochloric acid was added to the washing water to adjust the pH to 4.3, and the amount of zinc in the fibers was determined by the equivalent amount of sulfonic acid contained.
1.28 meq/100g fiber equivalent to 55%
It contained 0.704 milliequivalents/100 grams of fiber. During solvent removal, it was stretched 4.2 times, dried, and then stretched 3.4 times in saturated steam at 120° C. to obtain an acrylonitrile fiber bundle with a single fiber fineness of 0.7 and 6000 filaments. The single fiber strength of this acrylonitrile fiber bundle is 6.8 g/d, elongation 8.5%, and Young's modulus 10.
It was g/d. The acrylonitrile fiber bundle thus obtained was
Using the flame-retardant equipment shown in the figure, the temperature in the air is 263℃35.
Processed for minutes. Under these oxidation conditions, the free shrinkage rate was 17% when the amount of oxygen bonds was 3.3%, so the shrinkage rate at this point was set to be 5.8%, and the free shrinkage rate was until the amount of oxygen bonds was 3.3%. 20～
50% range, and up to 3.3% oxygen bonding range is 20 to 50% of the free shrinkage rate.
The rate was 2.9% for up to roller number 1, 4.4% for up to roller number 2, and 5.8% for up to roller number 3. The free shrinkage rate was measured again for the treated fiber with an oxygen bond content of 3.3%, and roller numbers 4, 5, 6, and 7 were 9.5%, 11.5%, and 12.5%, respectively, so that the free shrinkage rate was 50 to 70%. , 13%. The flame-resistant fiber obtained in this way has a good quality without any trouble due to the generation of fuzz, and has a tensile strength of 3.5.
g/d, tensile elongation 11%, bound oxygen content 12.5%, 20℃
Moisture content 8.8% at relative humidity 80%, specific gravity 1.38
g/cm ³ (20℃) and did not burn with a pine flame. The flame-resistant fiber thus obtained was carbonized at 1400° C. in an N ₂ gas atmosphere, giving a shrinkage of 6.75%, which corresponds to 45% of the free shrinkage rate of 15% in carbonization. The equipment used for carbonization was a resistance heating tube furnace with an inner diameter of 15 mm.
It had a diameter of φmm and a length of 500mm. Atmosphere of this tube furnace
_N2 gas flow rate 1/min, processing time 1400℃
Processed the residence time of the zone to 30 seconds. The performance of the obtained carbon fiber is strand strength 390
Kg/mm ² , tensile modulus of elasticity 24.5 T/mm ² , and the number of fluff per 5 m of fiber bundle was 12, which was a fiber bundle with little fuzz.

[Brief explanation of the drawing]

FIG. 1 shows a schematic diagram of a flameproofing furnace with multistage rollers. FIG. 2 shows the relationship between the amount of oxygen bonds and the free shrinkage rate and the shrinkage conditions in Example 1.

Claims (1)

[Claims] 1 Vinyl monomer having acidic group 5×10 ^-2 to 50
x10 ^-2 mol % and at least about 96 mol % acrylonitrile, an acrylonitrile system containing zinc in an amount such that 50 to 100 equivalent % of the counter ion of the acidic group is replaced with zinc. A method for producing flame-resistant fibers and carbon fibers, which comprises subjecting fibers to oxidation treatment and, if desired, carbonization treatment. 2. The production method according to claim 1, wherein the vinyl monomer having an acidic group is a vinyl monomer having a sulfonic acid or a salt thereof. 3. Oxidation treatment is carried out for 200 to 300 times through a multi-stage roller group.
℃, and at this time, until the amount of oxygen bonded to the acrylonitrile fiber is 3 to 4%, depending on the progress of the reaction, shrinkage of 20 to 50% of the free shrinkage rate of the fiber is applied during the subsequent oxidation treatment step. The free shrinkage rate of the fiber during this period varies from 50 to 50 depending on the progress of the reaction.
Oxidation treatment is performed while giving a shrinkage of 70%, and then, if desired, carbonization treatment is performed in a non-oxidizing atmosphere at 500 to 2000°C while giving a shrinkage of 40 to 70% of the free shrinkage rate of the treated fiber. A manufacturing method according to claim 1, characterized in that: