JPH02191723A - Production of fire-resistant yarn - Google Patents

Abstract

PURPOSE:To obtain the title yarn at high speed, stably and efficiently by making acrylonitrile-based yarn fire-resistant in an oxidizing atmosphere at a specific temperature while repeatedly bringing the yarn into contact with a roller type treating device under a specific condition. CONSTITUTION:Acrylonitrile-based yarn (preferably one having 0.7-1.25 denier of single yarn) is made fire-resistant while repeatedly being brought into contact with a roller type treating device in an oxidizing atmosphere at 200-300 deg.C under a condition wherein passing time of the yarn of non-contact part between the rollers in one time is <=20 seconds in the case of <1.28-1.30g/cm<3> density of fire-resistant yarn and <=1 minute in the case of >=1.28-1.30 density of fire- resistant yarn to give the aimed yarn. The temperature in the surroundings of the rollers wherein the yarn is brought into contact with the rollers is preferably 20-50 deg.C lower than the temperature of the non-contact part between the rollers. The rollers are equipped with several slits in the length direction, from which hot air 20-50 deg.C lower than the temperature of the non-contact part is preferably sprayed at <=5m/second speed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a novel method for producing flame-resistant fibers.

[Conventional technology]

The flame-retardant treatment process in the conventional carbon fiber manufacturing method is 2.
A large number of rollers were installed in a flameproofing furnace in which an oxidizing gas heated to 00 to 300° C. was circulated, and the precursor fiber bundle was processed while being reciprocated many times. In this method, in order to increase productivity, if the amount of fiber bundles introduced into the flameproofing furnace is increased or the atmospheric temperature in the flameproofing furnace is raised, the heat generated by the oxidation reaction tends to accumulate in the fibers. However, there was a problem in that the temperature of the fibers increased rapidly, causing a runaway reaction in which the fibers were burned and cut. Therefore, in order to solve this problem, in the conventional flame-retardant treatment process, it was necessary to manufacture at extremely low productivity by treating at a relatively low temperature of around 200 to 250 degrees Celsius for a long time of 60 to 200 minutes. Ta. As a result, the productivity of the carbon fiber manufacturing process is low (9), and the carbon fibers that are finally obtained are quite expensive.

Therefore, in order to overcome this drawback, for example,
Publication No. 21596 describes that flame-retardant treatment is performed by intermittently bringing precursor fibers into contact with a roller heated to 200 to 400°C, and that the flame-retardant treatment time is shortened to 20 to 30 minutes. . This method differs from conventional flame-retardant treatment methods because it uses a conduction heating method, which prevents reaction heat from accumulating within the fibers and prevents runaway reactions from occurring even at extremely high temperatures, reducing the flame-retardant treatment time. KFi is valid. However, since the soybean material is brought into direct contact with a heated roller, fibers tend to fuse together during the flame-retardant treatment, and since the treated surface is only on one side, treatment unevenness tends to occur in the thickness direction. Therefore, carbon fibers obtained from such flame-resistant fibers cannot have sufficient performance.

In addition, in order to overcome the above-mentioned drawbacks, for example,
No. 1-167025 discloses that the fibers are pre-oxidized in an oxidizing atmosphere and then treated in a high temperature treatment zone I of 25
A five-step treatment method in which the heating element heated to 0 to 550°C is brought into repeated and intermittent contact, and finally the high temperature treatment zone (2) is treated at 250 to 350°C in an oxidizing atmosphere.
It has been proposed that flame resistance be achieved in a short period of 30 minutes. This three-stage treatment method is advantageous in that it shortens the flame-retardant time compared to the conventional atmosphere heating method, and in that it prevents fusion and eliminates processing unevenness compared to the single-heat roller method.

However, the table shows that even though the fibers treated in this way can be used as flame-resistant fibers, if they are carbonized as flame-resistant fibers used in the production of carbon fibers, they will not break. It occurs frequently and tends to cause problems in the process.

This becomes more noticeable as the flameproofing treatment time becomes shorter, and is particularly noticeable when the flameproofing treatment time is from about ten minutes to less than that. According to studies conducted by the present inventors, it has been found that this is caused by structural unevenness occurring in the cross-sectional direction of the fibers. Oxygen, which plays a very important role in forming a thermally stable flame-resistant yarn structure that can withstand the carbonization process that follows flame-proofing, diffuses over time in the cross-sectional direction of the fiber, If the treatment is carried out for a short time, the diffusion of oxygen into the fibers will not be able to catch up, and the fibers will take on a double structure with only the surface layer made flame resistant. When flame-resistant fibers with such a structure are treated under the temperature conditions used in the carbonization process, they tend to cause doubling, which causes the fibers to break due to the difference in reactivity K caused by the structural unevenness, resulting in unstable stability. It is difficult to produce carbon fibers with sufficient performance.

[Problem to be solved by the invention]

The object of the present invention is to provide a method for producing flame-resistant fibers that overcomes the above-mentioned drawbacks, and specifically, to provide a highly efficient and safe flame-resistant method for producing carbon fibers, and from the flame-resistant fibers obtained thereby. The object of the present invention is to provide a flame-retardant treatment method that can produce carbon fibers with sufficient performance.

[Means to solve the problem]

The gist of the present invention is that the single yarn denier α7-1.
When making the acrylonitrile fiber bundles of No. 25 flame resistant by repeatedly contacting them with a loaf-type processing device in an oxidizing atmosphere at 200 to 300°C, the time it takes to pass through the non-contact area between the lobes is 1.28 to 1. Fi is less than 20 seconds when the fiber is less than .3017 cm", Fi is less than 1 minute when it is 1.28 to 15 Gr/cm' or more, and the temperature near where the fiber contacts the roller is 20 to 50 times lower than the temperature of the non-contact area. The objective is to produce flame-resistant fibers using a mathematical device that lowers the temperature by 0.degree. C. and at the same time blows heated air at that temperature through slits provided in a roller at a speed of 5 m/sec or less.

According to the studies conducted by the present inventors, the flame-retardant reaction is mainly controlled by (i) the limitation of the treatment temperature due to runaway reaction, and (li) the diffusion rate of oxidizing gas between and within the fibers. It was found that these two factors needed to be well controlled in order to complete the process in a short time. To explain this more specifically, in order to shorten the flameproofing treatment time, it is first necessary to raise the treatment temperature to increase the speed of the cyclization and oxidation reactions. When such a treatment method is used in a flameproofing furnace, the temperature within the fibers rises rapidly due to the rapid heat generation accompanying the oxidation reaction, which tends to cause a runaway reaction that causes burning and cutting of the fiber bundles. In addition, by reducing the number of components in the fiber bundle or widening the voids between the fibers, it is possible to prevent such runaway reactions to a large extent, and in this case, the density of the fibers can be reduced within a fairly short period of time to become a flame-resistant yarn. It is possible to increase the density to the required level, but because the fiber consumes oxygen at a high rate and the diffusion rate of oxidizing gas into the fiber is low, the oxidation reaction occurs only in the surface layer, resulting in very large density unevenness in the cross-sectional direction. This results in a flame-resistant fiber with Such flame-resistant fibers are easy to cut during the carbonization process due to their double structure.
It is difficult to consistently produce high quality carbon fiber.

The inventors of the present invention have conducted repeated studies to overcome the two problems of the runaway reaction and the diffusion of oxidizing gas, and as a result, they have arrived at the method of the present invention. The temperature at which the runaway reaction occurs shifts to a higher temperature side as the degree of treatment increases because the calorific value decreases as the oxidation of the fiber progresses, but this upward trend is not a monotonous increase, and the fiber density is 1.28 to 5.
0? /cs", it tends to increase rapidly.

In a fiber density range higher than this, a runaway reaction will not occur unless the processing temperature is raised to about the decomposition temperature of polyacrylonitrile. Also, even in areas below this (1,28~
1.3017 cm" or less), it takes some time for heat to accumulate in the fibers, so if heat is removed before the temperature rises to the decomposition temperature of the fibers, runaway reactions can be suppressed quite effectively. According to studies by the present inventors, the time required is approximately 10 minutes for a sheet containing 12,000 single Denny A/1.25 dpf filaments per width.
~20 seconds. If neutering is performed before this time Km, a runaway reaction will not occur. however,
The amount of heat generated by the oxidation reaction at this time is quite enormous, and it is impossible to remove this amount of heat by contact with rollers (about 30 cm) used in ordinary flameproofing furnaces. If some kind of cooling means is not taken, the roller surface temperature will rise, causing fiber fusion, making it impossible to obtain a flame-resistant yarn suitable for producing carbon fibers. According to the studies of the present inventors regarding this, in a roller contact type heat removal means, if the roller contact time is about 3 to 5 seconds, polyacrylonitrile fibers
A fusion phenomenon occurs at about 40°C. Like the runaway temperature, the fusion temperature of the fibers also increases as the flame-retardant treatment progresses, and when the fiber density exceeds 1.28 to t s o t/, -, the fusion phenomenon no longer occurs. Therefore, at least in the first stage of processing, the temperature around the roller needs to be 240° C. or lower. As a method for cooling the roller and its surrounding area, it is effective to separate the roller chamber and blow out air from a slit-type roller. If this method is adopted, the amount of heat generated by the fibers can be sufficiently removed even with a roller of a normal diameter.

Furthermore, the slit type roller has the advantage that it can effectively prevent fibers from being wrapped around the roller during flameproofing treatment.

This eliminates the work of removing the fibers from wrapping around the rollers, making it possible to place the rollers in a closed system, making it possible to create a furnace for high-temperature, short-time processing. FIG. 1 specifically shows a flameproofing furnace according to the method of the present invention derived from the above study results.

This furnace effectively combines the removal of reaction heat by conduction and the heat treatment by convection, and with this, it is possible to perform flameproofing treatment at high temperatures and in a short time while effectively preventing runaway reactions.

Next, the diffusion rates between and within fibers will be described. la
The diffusion rate between m becomes a problem as the flame retardant treatment becomes more dense, but this can be considerably accelerated by the wind speed during the convection heat treatment. It has been found that applying hot air perpendicularly to the yarn at a speed of 2 to 5 m/sec is sufficient to achieve high density. However, no matter how much the wind speed was increased, no promoting effect was observed for diffusion within the fibers at normal oxygen concentrations in the air, and it was found that the speed was dependent only on time. This speed is quite slow in high-temperature treatment above 260°C, and single yarn DennyA
/1.25d fiber is treated at 260-290°C for 10-20 minutes, the ratio of the oxidized layer area to the cross-sectional area is approximately 6
It was only 0-704. This ratio is close to the limit for a flame-resistant yarn structure, and if the ratio decreases below this, no matter how high the overall density is, fluff and yarn breakage are likely to occur in the next carbonization process, and the resulting The performance of carbon fiber is also considerably lower. Therefore, the diameter of the acrylonitrile 17~ type fibers to be treated cannot be made larger than this. Furthermore, when the fiber diameter is made thinner than 1.25 d, the proportion of oxidized layer increases due to the increase in surface area, and K becomes a preferable flame-resistant fiber to produce carbon fiber with less structural unevenness, but α
Fibers with a diameter smaller than 7d have a poor spinning yield, resulting in high costs and, as a result, are not cheap flame-resistant fibers.Acrylonitrile fibers used for this purpose have a diameter of 07~ 1.25 (l is preferred.

According to the method of the present invention, a sheet material containing 12,000 acrylonitrile fibers per 1.25 (l)
By carrying out the flame-retardant treatment for 0 to 20 minutes, it is possible to obtain a flame-retardant yarn bundle in which 60 mm or more of the cross-sectional area of the fibers is oxidized. Since it is impossible to reduce the processing time to less than 40 to 60 minutes in a normal flameproofing furnace due to the occurrence of runaway reactions, the method of the present invention can increase the processing speed by about 2 to 6 times and is inexpensive. This makes it possible to produce a large amount of flame-resistant yarn and, by extension, a large amount of cheap, high-performance recombinant fiber.

〔Example〕

The present invention will be specifically explained below using Examples.

Example 1 Single yarn Denny/L' 1.25 cl, 20 acrylonitrile fiber bundles with 12,000 filaments, 5
The sheet-like materials arranged at 1II1K intervals were subjected to flame-retardant treatment using a treatment apparatus as shown in FIG. In addition, in the convection heating zone, hot air of 260 to 270°C is applied perpendicularly to the fiber bundle at a speed of 3 m/sec, and the temperature of the hot air blown from the roll chamber and rollers is 220 to 230°C in the first stage. In this case, the temperature was set at 240 to 250°C. Processing time for the first stage is 10 minutes (
1 pass processing time flfi f 5 seconds), 2nd F9 processing time 5 minutes (1 bus processing time 30 seconds) daughter/I/1
After 5 minutes of treatment, the flame-retardant density reached 1.58 f/crs. When the cross-section of this flame-retardant fiber was observed under a microscope, the proportion of the oxidized layer was 80 to 85 tatami of the total cross-sectional area. The same fiber was pre-carbonized in a furnace with a gradient of 300 to 600°C in a nitrogen atmosphere, and then heated at 1400°C in a nitrogen atmosphere.
The carbonized area passed through the process stably without thread breakage, fluff, etc., and the tensile strength was 570, 97W'', and the elastic modulus was 2.
5 ton/m" of carbon fiber was obtained.

Comparative Example 1 The processing apparatus shown in Fig. 1 was used, and the temperature of the hot air blown from the roller chamber and rollers was set to 260 to 270°C, the same as that of the convection heating zone in both the first and second stages. Treatment was performed under similar conditions. The obtained flame-resistant yarn was severely fused and was quite brittle. When the same fiber was carbonized under the same conditions as in Example 1, fuzzing at nine places and edge breakage occurred frequently, and the performance of the obtained carbon fiber was low, with a tensile strength of 270 kp/- snow and an elastic modulus of 18 totx/+w. .

Comparative Example 2 The treatment was carried out under the same conditions as in Example 1, except that the diameter of the acrylonitrile fiber used was 1.32 d. The obtained flame-resistant yarn did not fuse and was very flexible, but even with a fiber density of 1.37 f 7 cm, the proportion of oxidized layer was 40 to 50. The same fiber was used in Example 1. When carbonized under the same conditions as above, the fibers were cut in the furnace and could not be made into carbon fibers.

Example 2 The treatment was carried out under the same conditions as in Example 1, except that the diameter of the acrylonitrile fiber used was CL9d. The ratio of the oxidized layer in the cross section of the obtained flame-resistant yarn was 954, and the density was 1.5.
7 f/am''. When the same was carbonized under the same conditions as in Example 1, carbon fibers with a tensile strength of 580, 97 wx'' and an elastic modulus of 26 ton/m'' were obtained.

[Brief explanation of the drawing]

FIG. 1 shows a conceptual diagram of a flameproofing furnace suitable for carrying out the method of the present invention.

Claims (1)

[Claims] 1. When making acrylonitrile fibers flame resistant by repeatedly contacting them with a roller treatment device in an oxidizing atmosphere at 200°C to 300°C, the time it takes to pass through the non-contact area between the rollers once is Thread density 1.28-1.30g/cm
Less than ^3: 20 seconds or less, 1.28 to 1.30 g/cm
A method for producing a flame-resistant fiber, characterized in that the manufacturing time is 1 minute or less at ^3 or more. 2 The temperature around the roller where the fibers come into contact with the roller is
2. The method according to claim 1, wherein the temperature is 20 to 50[deg.] C. lower than the temperature of the non-contact area between the rollers. 3. The method according to claim 1, wherein the roller is provided with several slits in the length direction, and heated air which is 20 to 50 degrees Celsius lower than the temperature of the non-contact portion is blown out from the roller at a speed of 5 m/sec or less. 4 Acrylonitrile fiber has a single yarn denier of 0.7~
1.25.