JPS6113004B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for rapidly and efficiently producing carbon fibers of excellent quality using acrylonitrile fiber bundles as raw materials. More specifically, the present invention relates to a method for producing a high-strength carbon fiber bundle in which fibers do not coalesce or fuse together during high-temperature firing treatment. Since it was discovered that acrylonitrile fibers are useful as a raw material for high-strength, high-elastic carbon fibers, many proposals have been made regarding industrial-scale production methods and the like. In particular, when carbon fiber is used as a reinforcing material for a composite material, a high tensile strength is required, and it is desired that its performance can be stably obtained not only as a single fiber but also as a fiber bundle. In order to satisfy these demands, in the firing process for converting raw material acrylonitrile fiber bundles into target carbon fiber bundles, in other words, raw fibers are heated to
A preliminary oxidation step in a temperature range of 300℃, followed by a pre-carbonization step in an inert gas flow of nitrogen gas, etc. at a temperature of up to 700℃, and then a 2000°C treatment in an inert gas flow of nitrogen gas, argon gas, etc. It is essential to operate the carbonization process, which is processed at temperatures up to be. However, since the firing process that converts acrylonitrile fiber bundles into carbon fiber bundles involves extensive physical and chemical changes, the causal relationship between the two is still unclear, and there are many unresolved issues. There is. Therefore, it is necessary to examine the conditions that should be provided for the acrylonitrile fiber bundle for carbon fibers or the optimum firing method, especially from an industrial standpoint. The inventors of the present invention have conducted intensive studies on a method for quickly and efficiently manufacturing carbon fiber bundles using acrylonitrile fiber bundles as raw materials, and have confirmed that the first stage of the pre-oxidation process is extremely important in the above-mentioned firing process. did. That is, this step has the role of advancing the cyclization reaction and crosslinking reaction of the molecules constituting the acrylonitrile fiber, strengthening the intermolecular bonds, and modifying the molecular structure to be easily transferred to the carbonization reaction. Traditionally, the preliminary oxidation process is to process the fibrils in air at 200-300%
This is carried out by heat treatment at a temperature of °C, but in order for the above reaction to proceed sufficiently, a considerably long treatment time is required, and this is a major reason for the high price of carbon fiber. . The reactions in the preliminary oxidation step, mainly the cyclization reaction of the nitrile group and the oxidative crosslinking reaction accompanying oxygen absorption, are strongly influenced by the treatment temperature, and the higher the temperature, the faster the progress. Therefore, if the aim is to shorten the preliminary oxidation time as much as possible and perform rapid firing, an important research topic is the establishment of firing technology at higher temperatures. For example, the present inventors have found that when preliminary oxidation is carried out in an air stream at 240°C, a firing time of 1 to 3 hours is required, but this can be shortened to 20 to 40 minutes at 270°C. Preoxidation gradually increases the density of the fibers, reaching a preferred point of about 1.35-1.40 g/cm ³ . On the other hand, one of the biggest drawbacks of this method of shortening time by increasing temperature is that it significantly induces coalescence or fusing of filaments of the fibrils during the firing operation. Although the degree of this phenomenon varies depending on the composition of the fibrils, the surface structure of the fibers, the size of the number of fibers, etc., it has been confirmed that this phenomenon occurs in most cases with ordinary acrylonitrile fiber bundles. Furthermore, the carbon fiber bundles obtained by subsequent carbonization of oxidized fiber bundles in which coalescence or fusion phenomena have occurred have extremely large decreases in mechanical properties, especially tensile strength, and sometimes suffers from problems such as breakage during the carbonization process. It was clearly recognized that the coalescence or fusion phenomenon had a serious adverse effect on the performance of carbon fibers. From this point of view, the present inventors have conducted intensive studies on a method that shortens the processing time of the preliminary oxidation step and does not cause coalescence or fusion during firing, and as a result, they have arrived at the present invention. That is, the present invention relates to a method for producing acrylic carbon fiber, which is characterized by firing acrylic fiber containing a special silicon compound as a raw material fiber, and according to this method, short-time firing is possible. Furthermore, coalescence or fusion during preliminary oxidation treatment can be prevented, and carbon fibers with excellent mechanical performance can be obtained as single fibers or fiber bundles. As the silicon-based compound applicable to the present invention, a compound represented by general formula (1) or (2) is preferable. (However, R ₄ in the formula is

[Formula], and R′ is −(CH ₂ ) − _o . Also, X is a value that is 7000 stokes or less, Y is an integer from 1 to 15, and n is from 1 to
It is an integer of 3. ) (However, in the formula, R ₅ is hydrogen or an alkyl group having 6 or less carbon atoms, and a and b are integers of 1 to 10. X and Y are the same as in formula (1).) According to the present invention Silicon-based compounds are characterized by the introduction of oxygen-containing side chains, and when such specific silicon-based compounds are made into a hydrogen emulsion, they form a stable and uniform dispersion, improving uniform adhesion to acrylic fibers. It is inferred that coalescence during firing is further avoided. The silicone compounds represented by the above general formulas (1) and (2) are generally attached to acrylic fibers in an amount of 0.01 to 5.0% by weight based on the weight of the fibers. silicon compound
If it is less than 0.01% by weight, the object of the present invention will not be achieved, and if it is more than 5.0% by weight, the operability of the fibril manufacturing process will become unstable, which is not preferable. In the present invention, a polymer comprising at least 90 mol% or more of acrylonitrile is used. When the content of components other than acrylonitrile reaches 10 mol % or more, it is generally difficult to prevent the coalescence phenomenon, worsening firing operability, and sharply decreasing the physical properties of the target carbon fiber. Examples of copolymerization components other than acrylonitrile include acrylic acid, methacrylic acid, itaconic acid, acrylic acid derivatives such as methyl acrylate and methyl methacrylate, acrylamide such as acrylamide, methacrylamide, N-methylolacrylamide, and N,N-dimethylacrylamide. Derivatives, alkyl vinyl ketones such as methyl vinyl ketone and ethyl vinyl ketone, acrolein derivatives such as acrolein and methacrolein, vinyl pyridine derivatives such as 2-vinylpyridine and 2-methyl-5-vinylpyridine, sodium methacrylsulfonate, and styrene sulfone. Examples include sulfonic acid derivatives such as acid soda, vinyl acetate, methacrylonitrile, and the like. These may be used alone or in combination. The acrylonitrile copolymer can be prepared using conventional radical polymerization catalysts, such as azo compounds such as azobisisobutyronitrile, peroxides such as benzoyl peroxide and lauroyl peroxide, potassium persulfate/sodium hydrogen sulfite, and ammonium persulfate/hydrogen sulfite. It can be produced by conventionally known polymerization methods using a redox catalyst such as sodium, such as solution polymerization in dimethylformamide, aqueous suspension polymerization, and emulsion polymerization. The method for producing the fibrils of the present invention involves emulsifying a silicon-based compound into fibers that have been spun, washed, and in a water-swollen state (that is, before being dried and densified).
A method of adhesion treatment is used in which a treatment oil agent such as a dispersant or an antistatic agent is used. The raw material fiber thus obtained is then transferred to a normal firing process. First, while applying a certain tension,
Pre-oxidation treatment is carried out at temperatures between 230 and 330 °C in an oxygen-containing air stream, followed by pre-carbonization at temperatures up to 700 °C in an inert stream, followed continuously in a high purity inert air stream up to approximately 1500 °C. Carbonization treatment is carried out at a temperature of . Furthermore, if necessary, graphitization treatment is performed at a temperature within 3000℃. In sintering carbonization using the modified acrylic fiber of the present invention, preliminary oxidation treatment is performed at 270°C for example.
Even under extremely harsh short-time processing conditions, such as 30 minutes or approximately 10 minutes at 300°C, compared to when using normal raw material fibers, there is almost no coalescence or fusion between single fibers. , a flexible flame-resistant fiber is obtained, and the carbon fiber obtained by firing this fiber has excellent mechanical performance. As described above, the present invention uses the fibers to which the silicon compounds represented by the general formulas (1) and (2) are attached to the fibers as a precursor during the manufacturing process of acrylonitrile fibers for carbon fibers at relatively high temperatures. Because it has made it possible to quickly fire carbon fibers and produce high-performance carbon fibers, its industrial value is truly great. The present invention will be explained in more detail with reference to Examples. In the Examples, percentages other than tensile elongation of fiber properties are percentages by weight unless otherwise specified. Example 1 Acrylonitrile (hereinafter referred to as AN
) 97.0 mol%, methyl acrylate (hereinafter referred to as
(hereinafter referred to as MA) 1.0 mol%, methacrylic acid (hereinafter referred to as
MAA) has a composition of 2.0 mol%, and has a specific viscosity of
A copolymer of 0.190 (measured at 25°C by dissolving 0.10 g of the copolymer in 100 ml of a dimethylformamide solution containing 0.1N rhodan soda, the same applies hereinafter) was prepared. This copolymer was uniformly dissolved in DMAC to obtain a spinning stock solution with a copolymer concentration of 21.0%. The viscosity of the spinning dope was 510 poise at 50°C. This spinning dope was wet-spun through a spinneret with 10,000 holes and a hole diameter of 0.065 mm into a coagulation bath at 35° C. containing 68% DMAC and 32% water. The coagulated filament in a swollen state containing a large amount of solvent and water was stretched 7.5 times in warm water at 98°C, and at the same time, the solvent was removed. Further, the water-swollen stretched bundle was subjected to post-stretching by a factor of 2.0 in pressurized saturated steam at 2.5 kg/cm ² gauge pressure. Next, silicone compounds represented by the following general formulas (1)′, (2)′, and (3)′ are emulsified and dispersed in a spinning oil,
The silicone adhesion treatment was carried out by changing the concentration of the oil bath so that each had a predetermined amount. (However, R ₄ is

[Formula] and contains about 1% by weight of the epoxy group in the formula; viscosity at 25°C
5000-7000 centistokes) (However, R is a methyl group, the viscosity is 200 centistokes at 25°C, and X and Y cannot be expressed exactly, so they are shown as the viscosity above.) Next, the fiber bundle was dried on a roll with a surface temperature of 130°C and the internal structure of the fiber was densified to produce the raw material fibers shown in Table 1.

[Table] Fiber performance was measured using a Tensilon type tensile tester.
This was done in accordance with JIS L1074. The measurement atmosphere is 20
℃, 65%RH (the same applies below). The comparative sample (e) is a silicon compound emulsified in an oil bath.
They were manufactured through the same spinning process as Samples 1 to 9 except that they were not dispersed. In comparative samples (a) to (d), the amount of silicon-based compounds attached exceeds the claimed range of the present invention (0.01 to 5.0%), and in all samples, the thread was wound around the heated roll, making stable sampling impossible. It was impossible. These raw fibers were placed in a heated air oxidation furnace with a temperature gradient of 180 to 245°C under a tension of 140 mg/d.
The oxidation treatment was performed for 40 minutes.The oxidation treatment allowed the raw fiber to shrink in the range of 2.0 to 2.5%. The densities of the oxidized fibers (values measured at 30°C by toluene-carbon tetrachloride density gradient tube method, hereinafter the same) were all in the range of 1.37 to 1.39 g/cm ³ . These oxidized fibers were then passed through a pre-carbonization furnace in a nitrogen gas heating atmosphere with a temperature gradient of 320 to 700°C for a residence time of 7 minutes. then 700
The carbonization process was carried out in a nitrogen gas heating atmosphere with a temperature gradient of ~1100°C for a residence time of 4 minutes, and then
Carbon fibers were produced by heat treatment for 30 seconds in a nitrogen gas atmosphere at a temperature of 1350°C. The fusion properties of the oxidized fibers obtained by the above method and the performance of carbon fibers were evaluated in a second manner.
Shown in the table.

【table】

[Table] The carbon fiber tensile test values in the table are Tensilon
Using VTM-3 type, test length 25mm, tensile speed 2%/
It is shown as the average value obtained from 25 measurements in a measurement atmosphere of 20°C and 65% RH. From the results in Table 2, compared to the comparative sample (e) which was not treated with the compound of the present invention, sample 1 of the present invention
It can be seen that in samples 9 to 9, no coalescence occurred during the oxidation treatment, and the carbon fiber performance was also of high quality.

Claims (1)

[Claims] 1. Acrylic carbon characterized by firing acrylic fibers to which a silicon compound represented by the following general formula (1) or (2) is adhered in an amount of 0.01 to 5.0% by weight based on the weight of the fibers. Fiber manufacturing method. (However, in the formula, R ₄ is [Formula], R' is -(CH ₂ ) - _o , X is a value of 7000 centistokes or less, Y is an integer from 1 to 15, and n
is an integer from 1 to 3. ) (However, in the formula, R ₅ is hydrogen or an alkyl group having 6 or less carbon atoms, and a and b are integers of 1 to 10. X and Y are the same as in formula (1).)