JPS6317929B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved method for producing carbon fibers (including graphite fibers, hereinafter the same),
More specifically, an acrylic fiber that has been subjected to a specific split drawing process, has a predetermined single fiber denier, and has a specific residual capacity is used as a carbon fiber precursor, and is fired. In particular, the present invention relates to an industrially advantageous method for producing carbon fibers having excellent physical properties. It is already known to produce carbon fibers from acrylic fibers. Among the processes for manufacturing carbon fibers from acrylic fibers, the so-called flame-retardant process, in which heat treatment is performed in an oxidizing atmosphere to form a cyclized structure of naphthyridine rings in the fiber structure, is an extremely important process. This inevitably required a long heat treatment operation, which was the cause of low productivity. It is true that in order to avoid such low productivity, attempts have been made to achieve flame resistance by increasing the temperature reached or by selecting rapid temperature raising operations, but in either case, the heating transition point of the fiber Rapid reactions such as intermolecular cross-linking and intramolecular cyclization occur in the nearby temperature range, leading to local heat accumulation, generating pitch-tar-like substances, and eventually The reality is that carbon fibers with high physical properties have not been obtained due to problems such as fibers fusing together and a decrease in mechanical strength. For the purpose of reducing such heat accumulation, for example, an attempt was made to reduce the single yarn denier of the precursor (Special Publication No. 1973-
40574, etc.), but it is difficult to manufacture precursors by simply making the denier finer.
This impairs the processability and causes morphological instability such as fuzziness in the obtained precursor, which makes firing more technically difficult and also reduces the performance of the carbon fiber. In order to solve this problem, attempts have been made to specify the intrinsic viscosity of the starting polymer in addition to making the denier finer, as proposed in, for example, Japanese Patent Publication No. 50-29530, but this has not yet been a satisfactory technique. do not have. In addition, an attempt was made to reduce the amount of residual solvent in order to suppress abnormal heat generation and the generation of pitch and tar-like substances (Special Public Interest Publication in 1973).
29531, etc.), but in order to reduce the amount of residual solvent to an appropriate level, a special water washing device is required, and the use of this device causes the yarn to become disordered, so it is not recommended from an industrial perspective. It was difficult to say that it was advantageous. As a result of intensive studies to eliminate the drawbacks associated with conventional techniques, the inventors of the present invention have discovered that by using a predetermined acrylic fiber produced by adopting a specific manufacturing method as a precursor and firing it, It has been found that the firing time can be significantly shortened and carbon fibers with extremely high physical properties and high quality can be manufactured with industrial advantage. An object of the present invention is to propose an industrially advantageous method for producing carbon fibers having excellent physical properties and quality. Another object of the present invention is to propose technical knowledge for obtaining carbon fibers with high physical properties and high quality by short firing time. Other objects of the present invention will become clear from the detailed description below. Therefore, the above purpose is to produce carbon fibers from acrylic fibers made of an acrylic polymer containing 90% by weight or more of acrylonitrile bonded and produced by wet spinning or dry/wet spinning the polymer. , made by dividing the stretching into two or more stages before exiting the coagulation bath after spinning, and five or more stages in the entire fiber manufacturing process, and the single fiber denier is 1.5 denier or less, and the amount of residual solvent is 300 p.pm
This is achieved by firing the following acrylic fibers. As described above, by carrying out the specific division and distribution drawing according to the present invention, the force acting on the single fiber is efficiently dispersed, and the cross-sectional area of the single fiber minute portion is reduced.
The orientation becomes uniform, and an abnormal morphology develops on the fiber surface (two or several single fibers are pressed together with strong force and coalesce into one or a similar state,
In the subsequent process, the fiber is pulled off by a certain force, forming concave or convex portions on the fiber surface, or the surface layer is pulled to a width of about a fraction of the fiber diameter), and the final result is In addition to achieving uniform cyclization or crosslinking reactions and significantly improving firing operability, high-quality carbon fibers can be produced. In addition, because the single fiber denier is small in connection with the above-mentioned specific split drawing, heat accumulation during the flame resistance stage is small.
This makes it possible to bake for a short time. Furthermore, in addition to the specific division and fine denier form, there is almost no residual solvent, so that abnormal heat generation does not occur during the firing process, and firing operability can be improved. The desired purpose and effect are achieved only when these technical components of the present invention, which can be adopted independently (split stretching, fine denier, and residual solvent), are integrated, and even if none of them are absent, a satisfactory result can be achieved. You can't get it. Further, although each of the above configurations can be made independently, another feature of the present invention is that other fine denier and reduction of the amount of residual solvent can be achieved more effectively by employing division and distributed stretching. It can be said. In other words, it is not that fine deniering and solvent removal can be achieved as a result of adopting split stretching, but that the processability and effectiveness of the fine deniering process and solvent removal process, which are performed in separate steps or by other means, are increased to a certain level. He will play a role. As described above, what is important in carrying out the present invention is that the stretching is carried out in multiple stages, including two or more stages before exiting the coagulation bath after spinning, and five or more stages in the fiber manufacturing process as a whole. In other words, if multi-stage divisional stretching is performed after spinning and before exiting the coagulation bath, it is possible to easily perform high-magnification stretching in a liquid yarn or extremely high solvent concentration state similar to that of a liquid yarn. The burden of stretching (so-called cold water stretching, hot water stretching, steam stretching, dry heat stretching, etc.) can be reduced.
Moreover, since the orientation does not become very high during stretching in the coagulation bath, it is easy to draw in the steps after the coagulation bath, which has the advantage of not causing non-uniform stretching, and has excellent quality as a fired yarn ( A fine denier precursor (with no irregularities in cross-sectional area or orientation, and without the above-mentioned abnormal morphology) is used.
You can get good processability (no thread breakage etc.). Furthermore, in the coagulation bath, the flow of the coagulation bath liquid is maintained in parallel with the flow of the spun yarn, or in a nearly stationary state, so the phenomenon of bunching the single fibers together does not occur, and a high degree of stretching action is also added. At the same time as the denier becomes uniform and fine, the specific surface area increases, and as the yarn becomes thinner as it is drawn, water with a high solvent concentration contained in the swollen gel yarn is extruded from the yarn. Another characteristic is that the solvent speed is also faster. In addition, by performing divided stretching in five or more stages in the entire fiber manufacturing process, the load on the stretching points at each process stage can be divided and reduced, and a uniform stretching effect can be efficiently achieved, while at the same time, the strain on the stretching points can be reduced. Fibrillation (abnormal shape) accompanying this process is not caused, and it is also possible to increase the total stretching ratio through the fiber manufacturing process, producing highly oriented yarn (in other words, carbon fiber with high physical properties). It became possible to do so. Unless the number of multi-stage divisions according to the present invention is satisfied, the various advantages described above cannot be achieved. Further, as a preferred embodiment of the present invention,
The following points can be mentioned. That is, the total stretching ratio (hereinafter referred to as TD) in the entire fiber manufacturing process is defined as [nozzle hole area] ÷ [precursor cross-sectional area],
If the stretching ratio from after spinning to leaving the coagulation bath is FD, and the stretching ratio after leaving the coagulation bath until it is made into a precursor is SD, then TD = FD.
×SD (logTD=logFD+logSD) holds, but
In the present invention, TD is set to 12 or more, preferably 15 or more, and logFD is allocated so that it is 15% or more of logTD. For example, if a 1.5 denier precursor is manufactured using a nozzle with a nozzle hole diameter of 0.055 mm, the TD is 16.7.
FD to 1.53 (=10 ^0.15logTD ) or more, and SD to 10.9
(=16.7/1.53) The following applies. Of course, as long as FD and SD are maintained within the specified range, the number of stretching stages can be selected as appropriate (of course, the number of stretching stages should be 2 or more before exiting the coagulation bath, and 5 or more stages as a whole). (Although it is mandatory). For example, if you set FD to 8, 2 or more stages,
For example, the stretching ratio in each stage may be determined so that the FD is 8 in 4 stages. The stretching step from after spinning until exiting the coagulation bath involves using two or more coagulation baths or providing appropriate stretching points (non-rotating guides for direction change, drive rollers, etc.) in the coagulation bath. It includes not only the stretching performed, but also the so-called jet stretching in wet spinning and the stretching applied to the liquid yarn between the nozzle surface and the coagulation bath surface in dry/wet spinning. The stretching steps up to
As mentioned above, cold water stretching, hot water stretching, steam stretching,
Examples include dry heat stretching. Furthermore, in the present invention, it is necessary to be able to make the single fibers finer in denier and to remove the solvent remaining in the single fibers in a completely separate process in addition to carrying out the split stretching described above. In other words, no matter how much the above-mentioned splitting and distributive drawing are achieved, a precursor that does not satisfy the single fiber denier of 1.5 denier or less and the residual solvent amount of 300 p.pm or less will not be able to achieve the objectives and effects of the present invention. Become. For example, a precursor with a single fiber denier of 1.8 denier is produced by performing predetermined divisional multistage stretching in the precursor manufacturing process.
Although it is true that homogenization of each precursor is achieved, the firing processability is poor and the firing takes a long time, which is not industrially advantageous. For example, if the amount of residual solvent is as high as 500 p.pm despite the fine denier and split-stretched precursor, abnormal heat generation will occur during the firing process, causing mutual fusion of the fired yarns, which will reduce the firing processability. In addition to this, it becomes difficult to obtain carbon fibers of high quality and high physical properties due to the occurrence of abnormal morphology (a type of fibrillation) as described above. In addition, as for the above-mentioned fine denier and removal of residual solvent, the former is achieved by selecting the nozzle hole diameter, controlling the discharge amount by a gear pump, setting the total stretching ratio, etc., and the latter is by controlling the washing conditions such as the amount of washing water, washing temperature, water flow, etc. This can be done by optimizing the system, etc., and there are no particular limitations. Of course, it goes without saying that the divided multi-stage stretching operation as described above greatly contributes to achieving these goals. As described above, in the present invention, carbon fibers of high quality and high physical properties can only be produced by adopting the split drawing operation, reducing the denier, and removing the residual solvent in an integrated manner. The acrylic polymer used in the present invention contains at least 90% by weight of acrylonitrile and is prepared by copolymerizing other unsaturated monomers. Other unsaturated monomers include well-known ethylenically unsaturated compounds such as acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, vinyl acetate, sodium methalylsulfonate, and sodium p-styrenesulfonate. can. Acrylic polymers are produced by general polymerization methods, and when producing acrylic fibers from such polymers, organic solvents such as dimethylformamide, dimethylacetamide, and dimethyl sulfoxide are used as solvents;
An inorganic solvent such as nitric acid, an aqueous solution of zinc chloride, an aqueous solution of Rodan soda, etc. is used, and a spinning dope is prepared according to a conventional method, which is then spun and made into fibers. Such spinning means can be selected from known wet spinning methods and dry/wet spinning methods. In the practice of the present invention, it is preferable to adopt a dry/wet spinning method (because the stretching in this spinning means involves stretching a liquid yarn made of a spinning dope, so the viscoelastic properties of the spinning dope are suitable for spinning. (This is because it is done at high magnification and in a state that is close to completely non-oriented). The spun fiber bundle that has been spun and solidified (it is essential to undergo two or more stages of divided stretching during this process) is then subjected to cold water stretching, water washing, gel treatment, hot water stretching, and steam stretching. , dry heat stretching and drying (although it is essential that divisional stretching is performed in five or more stages during the period from spinning to drying). When producing carbon fibers from the acrylic fibers obtained in this way, any conventionally known firing method can be employed, but generally a flame-retardant process of heating to 150 to 400°C in an oxidizing atmosphere to cyclize is used. A firing method comprising a carbonization step of carbonizing or graphitizing the material by performing high-temperature firing in a non-oxidizing atmosphere or under reduced pressure is preferably employed. Note that air is suitable as an atmosphere for flameproofing, and nitrogen, helium, argon, etc. are suitable as an atmosphere for carbonization or graphitization. In order to produce carbon fibers with even better strength and modulus of elasticity, heating under tension is one of the preferred methods. Thus, by employing the method of the present invention as described above, it becomes possible to produce carbon fibers with high quality uniformity, high strength, and high modulus in a short time with good productivity. Carbon fiber, which has excellent performance, is also suitable for use as a material for forming composites to provide high quality performance.
It can now be used in a wide range of fields such as reinforcing materials, heating elements, and heat-resistant materials. In order to provide a better understanding of the invention, the following representative examples are presented. In the examples, percentages and parts are expressed on a weight basis unless otherwise specified. Example 1 15.5 parts _of an acrylic polymer consisting of 98% acrylonitrile and 2% methacrylic acid obtained by an aqueous suspension polymerization method using a ( _NH4 ) _2S2O8 / _{Na2SO3 -} based redox _catalyst , Spinning stock solution dissolved in 84.5 parts of 51.36% Rodan soda aqueous solution (held at 73℃)
was once discharged into the air through a spinneret (pore diameter: 0.15 mm, number of holes: 50), and then introduced into a coagulation bath consisting of a 14% rhodan soda aqueous solution at 3° C. for coagulation. At this time, the distance between the spinneret surface and the coagulation bath liquid level is
It was 0.3cm warm. After discharging, the stretching operation as shown in Table 1 was used to solidify the material, followed by 2.0 times cold stretching.
After washing with water (30℃), gel treatment is performed (PH2.2).
A precursor was produced by further stretching 2.4 times in hot water and stretching 2.08 times in steam, followed by drying. Table 1 also shows the total number of divided stretching steps employed in each stretching step (Process A). On the other hand, a spinning stock solution (50°C) obtained by dissolving 9.0 parts of the above acrylic polymer in 91.0 times the 47.2% Rodan Soda aqueous solution was passed through a spinneret (pore diameter 0.055 mm, number of holes 50) at -3°C. It was coagulated by extrusion into a coagulation bath consisting of a 12% Rodan soda aqueous solution. In addition, the steps from coagulation to drying follow the order of process A (however, No. 6 uses only 8.3 times hot water stretching, No. 7 uses steam stretching 1.73 times, and No. 8 uses hot water stretching 1.2 times and 2.0 times. 2
Divided into stages (No. 9 is 5.0 times hot water stretching and 2.0 times steam stretching), the number of stretching stages before exiting the coagulation bath after spinning and the total number of stretching stages were varied as shown in Table 1 to produce precursors. Process B). In both Process A and Process B, fine deniering and solvent removal behavior were adjusted by controlling the discharge amount and appropriately selecting an increase in the amount of washing water. The precursor thus obtained was first stretched 1.2 times at 180°C in an air atmosphere using an electric furnace.
Further, a flame-resistant yarn was obtained by continuously treating at 240℃ for 30 minutes and at 260℃ for 30 minutes, and then the flame-resistant yarn was continuously heated from 300℃ to 1300℃ for 2 minutes under a nitrogen atmosphere. Carbon fibers were obtained by increasing the temperature. The physical properties of the obtained carbon fibers are also listed in Table 1.

[Table] Example 2 Example 1 When preparing sample No. 8, the total draw ratio TD adopted in the process from spinning to drying was kept constant, and the precursor was prepared by changing the allocation of FD and SD as shown in Table 2. (Sample 10) was prepared and its spinning status was observed. As a result, single yarn breakage occasionally occurred and operability decreased.

【table】

Claims (1)

[Claims] 1. When producing carbon fibers from acrylic fibers made of an acrylic polymer containing 90% by weight or more of acrylonitrile bound and produced by wet spinning or dry/wet spinning of the polymer, a coagulation bath after spinning is required. The acrylic fiber is produced by dividing the drawing process into two or more stages and five or more stages in the entire fiber manufacturing process, and has a single fiber denier of 1.5 denier or less and a residual solvent amount of 300 p.pm or less. An improved method for producing carbon fiber, characterized in that: