MXPA01000751A - Acrylonitril-based precursor fiber for carbon fiber and method for production thereof - Google Patents

Abstract

An acrylonitrile-based precursor fiber for carbon fiber which is produced from an acrylonitrile copolymer containing 96.0 to 98.5 wt.%of acrylonitrile units and has a tensile strength of 7.0 cN/dtex or more, a tensile modulus of 130 cN/dtex or more, an iodine adsorption number of 0.5 wt.%or more relative to the total weight of a fiber, a degree of crystal orientation&pgr;of 90%or more as measured by the wide angle X-ray diffraction method and a coefficient of variation for tow fineness of 1.0%or less. The precursor fiber can be used for producing a high quality carbon fiber with a calcination for a relatively short time at a low cost, since it has a high strength, a high modulus, a high compactness, a high degree of orientation, and a low coefficient of variation for tow fineness.

Description

PRECURSOR FIBER BASED ON ACRILONITRI OR FOR CARBON FIBER AND METHOD FOR ITS PRODUCTION Technical Field This invention relates to precursor fibers based on polyacrylonitrile for the formation of carbon fibers, and to a process for their preparation.

Background Art 10 Carbon fibers and graphite fibers (collectively referred to herein as "carbon fibers") formed by the use of polyacrylonitrile-based fibers as precursors, have excellent mechanical properties, and consequently, are commercially produced and sold as fibrous reinforcements of high performance composite materials for use in aerospace applications, in sports and recreation applications, and the like. Moreover, in recent years, the demand for carbon fibers is growing in the industrial applications in general, such as in automotive and marine applications, and in the applications? And materials for the construction. Therefore, in order to improve the performance of these composite materials, are desired in the market or wild beasts of coal ". econó ~: cas qae have ana high quality In contrast to acrylic fibers for use in clothing, acrylonitrile-based fibers to be used as precursors of carbon fibers are only intermediary products for the formation of carbon fibers as final products. Accordingly, it is not only desirable to provide acrylonitrile-based fibers capable of producing carbon fibers having excellent quality and performance, but it is also very important that the acrylonitrile-based fibers have good stability during spinning of the fibers. precursor fibers, which exhibit high productivity in the ignition step to form the carbon fibers, and which can be provided at a low cost. From this point of view, a large number of proposals have been made in order to provide acrylonitrile-based fibers capable of producing carbon fibers having high strength and high elasticity. These proposals include, for example, an increase in the degree of polymerization of the starting polymer, and a reduction in the content of the different co-polymerized components of the acrylonitrile. With regard to the method of spinning, dry-wet spinning is commonly employed. However, when the content of the copolymers other than acrylomethyl is reduced, the solubility of the resulting copolymer in the solvents is generally reduced. This not only reduces the stability of the spinning solution, but also causes an extreme increase in the viscosity of the spinning solution, making it necessary to reduce the concentration of the copolymer in the spinning solution in a corresponding manner. Consequently, the copolymer shows a marked tendency toward precipitation and coagulation, so that the resulting fibers with Often, they may suffer devitrification or develop a large number of voids in them. Therefore, this production method can not be considered as stable. Because the process of dry-wet spinning comprises extruding a polymer solution through a nozzle into the air, and then continuously passing it through a coagulating bath to form filaments, it is easy to obtain dense coagulated filaments. On the other hand, the reduction in the separation of the holes of the nozzle will cause a problem, in which the adjacent filaments can adhere to each other. Accordingly, there is a limit to the number of holes in the nozzle. In general, it is convenient - a higher density of nozzle orifices for the production of low cost. 2 ^ the first precursors based et acr? Lon_crilc Z * »* J Mfr». Wa & igfc * ». -. MSgiíitteA, - > : } * xz :. compliance with the above, the wet spinning process is being used, partly because it requires a relatively low cost of production equipment. However, the resulting filament tow generally includes many broken filaments and a lot of fluff. Accordingly, the resulting precursor fibers have a low tensile strength and a low elastic modulus, and the structure of the precursor fibers is less dense and has a low degree of orientation. Consequently, the mechanical properties of the carbon fibers obtained by igniting them are generally not satisfactory. In order for the precursor fibers used to form high quality carbon fibers, it is very important that they are free from minute defects that will be responsible for the breakage after they are converted to carbon fibers. In order to minimize these defects, it is necessary that the precursor fibers have a high tensile strength and a high elastic modulus, that their fiber structure is highly dense, that the copolymer is highly oriented in the direction of the fiber axis. , and that the graao of variation in the size of the tow is small. For example, Japanese Patent Laid-open Number 214513 / '83 mentions the density of the fiber structure, while the wet-spinning process is employed. As ~ ed? Das of the density we have the amount of yeto » .jaüajna &? iA * ¿j aai? ta i? adsorbed and the thickness of the skin layer in which the iodine is adsorbed, as defined herein. However, the precursor fiber thus obtained has a low density, as demonstrated by an iodine adsorption of about 1 to 3 weight percent, and also has a low tensile strength and a low elastic modulus. Consequently, it is very difficult to produce a carbon fiber that has a high quality. On the other hand, Japanese Patent Number Open 35821 / '88 discloses a precursor fiber which has been prepared by the dry-wet spinning process, and which has a high-densified surface structure. Furthermore, Japanese Patent Laid-Open Nos. 21905 / '85 and 117814 /' 87 disclose precursor fibers which are also have been prepared by the dry-wet spinning process, and have a high tensile strength and a high elastic modulus, and comprise a copolymer highly oriented in the direction of the fiber axis. Although an improvement in carbon fiber quality can be achieved As a result of the use of these precursor fibers, their productivity is ba; a deoido to the use of dry-wet spinning process. Moreover, the fibers prepared by dry-wet spinning have a smoother surface, comparing with the prepared fibers by means of the river bank. The trímeras beasts exhibit good beam forming properties, but also have several disadvantages, because they tend to merge with each other in the ignition step, and because they tend to show a poor possibility of opening in the formation of a sheet type preform. In addition, the polymers used in this invention have practically an acrylonitrile content of not less than 99.0 weight percent. In accordance with the above, from the standpoint of the stability of the spinning solution and the tendency of the copolymer towards precipitation and coagulation, these processes are unsatisfactory for the stable preparation of a precursor fiber. In order to obtain a precursor fiber having a densified surface structure while using the wet spinning process, stretching with pressurized steam as ur has been investigated. stretch method to achieve a higher stretch ratio. For example, Japanese Patent A-c. No. 70812 / '95 discloses a precursor fiber which is prepared by the wet spinning process, but has a densified surface structure. In this patent, densification of a precursor fiber has been achieved through the use of an copolymer having a specific composition, and coagulated fiber having specific properties, in combination with pressurized steam drawing. However, because no consideration is given to the appropriate range of stretching conditions after coagulation, this process is unsatisfactory for the purpose of preparing a precursor fiber that has a high degree of density and a high degree of orientation. Moreover, because no mention is made of the strength, of the elastic modulus, of the degree of orientation of the crystal, and of the degree of variation in the Because of the fineness of the tow of the resulting precursor fiber, the properties of a precursor fiber that are required for the formation of a carbon fiber having excellent quality are still unknown. In addition, it has been difficult to spin a precursor fiber stably at a high speed of spinning of not less than 100 meters per minute. Accordingly, all conventional techniques have failed to provide a satisfactory precursor fiber for the formation of a high-quality and inexpensive carbon fiber, and a satisfactory process for its production. preparation.

Disclosure of the Invention The present invention has been made in view of the above-described problems of the prior art, and r. objete of it is to provide a fierce precursor based on acrylonitrile for the formation of a carbon fiber that has a high strength, a high elastic modulus, a high degree of density, a high degree of orientation, and a low degree of variation in the fineness of the tow, and therefore it can be used to form a high-quality carbon fiber in an economical way, igniting for a shorter period of time, as well as a wet spinning process whereby this precursor fiber based on acrylonitrile for fiber formation carbon having such properties, can be prepared in a fast and stable manner without frequently breaking the fiber, and without producing any appreciable amount of fluff. The present invention relates to a fiber acrylonitrile-based precursor for the formation of a carbon fiber which is prepared from an acrylonitrile-based copolymer containing from 96.3 to 98.5 weight percent of acrylonitrile units, the acrylonitrile-based precursor fiber having a resistance to tensile not less than 7.0 cN / dtex, elastic modulus in tension of not less than 130 cN / dtex, an iodine adsorption not greater than 0.5 weight percent, based on the weight ie the fiber, a degree of orientation of the cr_stal (~ not of 90 percent, determined by an X-ray analysis of wide angle, and a degree of Yanacon in 1 = fineness you the '.' ^ - Sra-a ^ a-ji tow no greater than 1.0 percent. The above-mentioned acrylonitrile-based copolymer is preferably composed of 96.0 to 98.5 weight percent of acrylonitrile units, 1.0 to 3.5 weight percent of acrylamide units, and 0.5 to 1.0 weight percent of acrylonitrile units. vinyl monomer containing carboxyl. In one embodiment of the present invention, the wet spinning process is preferably used as the The method for spinning the precursor fiber based on acrylonitrile, for the formation of a carbon fiber. The present invention also relates to a process for the preparation of a precursor fiber based on acrylonitrile for the formation of a carbon fiber, which comprises The steps of wet spinning an acrylonitrile-based copolymer to form a coagulated fiber, subjecting the coagulated fiber to primary stretching, which comprises stretching in the bath, or a combination of stretching in the air and stretching in the bath, and subdue fiber is coagulated to a secondary stretch involving pressurized steam stretching, wherein the temperature of the heating roller located immediately before the introduction of the fiber in a pressurized steam drawing device is set at 120-190 ° C. controls the degree of variation in pressure? Steam used in the pressurized steam stretch to not be greater than 0.5 percent, and the coagulated fiber is stretched in such a way that the ratio of the secondary stretch to the proportion of the overall stretch is greater than 0.2. In one embodiment of the present invention, the overall stretch ratio is preferably not less than 13. The present invention is described more specifically hereinafter. The acrylonitrile-based copolymer (which can be referred to hereinafter simply as the copolymer), used for the preparation of the acrylonitrile-based precursor fiber for the formation of a carbon fiber (hereinafter referred to as the precursor fiber) , in accordance with the present invention, contains from 96.0 to 98.5 weight percent of acrylonitrile units as monomer units. If the content of acrylonitrile units in the copolymer is less than 96 weight percent, the fiber may undergo heat fusion in the ignition step (which comprises the flame test and carbonization substeps), to convert it into a carbon fiber, in such a way that the quality and performance of the carbon fiber tend to be reduced. Moreover, because the thermal resistance of the copolymer is reduced, the filaments tend to adhere to each other during the spinning of the precursor fiber, i.e., in the fiber drying step, or in the fiber drawing step. with a heating roller with pressurized steam. On the other hand, if the content of acrylonitrile units in the copolymer is greater than 98.5 weight percent, the solubility of the copolymer in the solvents is reduced, and consequently, the stability of the spinning solution is reduced. Moreover, the copolymer shows a marked tendency towards precipitation and coagulation, making it difficult prepare a precursor fiber stably. Moreover, the copolymer used in the present invention preferably contains 1.0 to 3.5 weight percent of acrylamide units as monomer units. When the content of acrylamide units in the The copolymer is 1.0 weight percent or more, the structure of the precursor fiber becomes sufficiently dense, and therefore, a carbon fiber having excellent performance is obtained. Moreover, the flame test reactivity in the flame test step is very affected due to slight changes in the composition of the copolymer. However, if the content of acrylamide units is 1.0 percent by weight or greater, a carbon fiber can be stably produced. In addition, it is believed that acrylamide has a high random copolyzability with acrylonitrile, and more, that a heat treatment makes the acrylamide forms a ring structure in a manner very similar to that of aclonitrile. In particular, acrylamide is very susceptible to thermal decomposition in an oxidizing atmosphere, so that it can be contained in greater amounts, compared to the carboxyl-containing vinyl monomers, which will be described later. However, as the content of acrylamide units in the copoiimer is increased, the content of acrylonitrile units in the copolymer is reduced, and the thermal resistance of the copolymer is reduced, as described above. In accordance with the foregoing, the content of acrylamide units is suitably not greater than 3.5 weight percent. In addition, the copolymer used in the present invention preferably contains 0.5 to 1.0 weight percent of carboxyl-containing vinyl monomer units as the monomer units. The usable carooxyl-containing vinyl monomers include, for example, acrylic acid, methacrylic acid, and itaconic acid. If the content of carboxyl-containing vimole units is unduly low, the flame test reaction is too slow, so that it becomes difficult to obtain a high-performance carbonaceous unit by means of a period of time. short period of time. With the object of real-zar _ flame test treatment in a short period of time, the flame test temperature must inevitably be raised. These high temperatures tend to induce uncontrolled reactions, and can cause problems from the point of view of the properties of process travel, and safety. On the other hand, if the content of carboxyl-containing vinyl monomer units is unduly high, the flame test reactivity becomes so high that the region adjacent to the surface of the fiber reacts rapidly during the flame test treatment, while the reaction of the central portion is delayed. Accordingly, the flameproof fiber exhibits a double structure in its cross section. However, with this structure, it can not be avoided that the central portion of the fiber, where no The flame-proof structure was developed, decomposed in the successive carbonization step at a higher temperature, resulting in a noticeable wording in the performance (in particular, the elastic modulus in tension) in the carbon fiber. This tendency becomes more pronounced as the flame test treatment time is reduced. In addition, from the point of view of the possibility of stretching in the spinning of the precursor fiber, / the manifestation of the performance of the carob fiber, the gra? O Polymerization of the copolymer preferably should be such that its limiting viscosity [?] is not less? e 0.8. If the degree of polymerization is unduly high, the solubility in solvents is reduced. A reduction in the concentration of the copolymer tends to produce voids and to cause a reduction in the possibility of stretching and spinning stability. For these reasons, it is usually preferable that its limiting viscosity [?] is not less than 3.5. The precursor fiber of the present invention is formed from this copolymer according to the wet spinning process *, and has a tensile strength of not less than 7.0 cN / dtex, an elastic modulus in tension not less than 130 cN / dtex, an iodine adsorption not greater than 0.5 percent by weight, based on the weight of the fiber, a degree of crystal orientation (71) not less than 9C percent, determined by an X-ray analysis of wide angle, and a degree of variation in the fineness of the tow not greater than 1.0 percent. If the tensile strength of the precursor fiber is less than 7.0 cN / dtex, or its elastic modulus in tension is less than 130 cN / dtex, the carbon fiber obtained by igniting this precursor fiber has insufficient mechanical properties. If the iodine adsorption of the precursor fiber is greater than 0.5 weight percent, the density or orientation of the fiber structure is reduced, and the fiber becomes heterogeneous. This creates effect sites in the ignition step to convert the precursor fiber into a carbon fiber, and consequently, results in a reduction in the performance of the resulting carbon fiber. As used herein, the term "iodine adsorption" refers to the amount of iodine adsorbed on the fiber, and serves as a measure of the density degree of the fiber structure. Small values indicate that the fiber is denser. 10 If the degree of orientation - the crystal (p) of the precursor fiber is less than 90 percent, the precursor fiber shows a reduction in the tensile strength and tensile elastic modulus, and the carbon fiber obtained by ignition of this precursor fiber - 5 has insufficient mechanical properties. On the other hand, with the object of achieving a very high degree of orientation of the crystal (Ti), a higher stretch ratio is required, and this makes stable spinning difficult. The range in which you can easily prepare the precursor fiber over an industrial base is usually not greater than 95 percent. As used herein, the term "degree of orientation of the crystal as determined by an x-ray analysis of an angle" is a measure of the degree of orientation of the "olecular = s chains of the dream co-polymer they constitute the fiber in the direction of the axis of the fiber. From the wide half (H) of the circumferential intensity distribution of the points? E diffraction on an equatorial line of the fiber, as recorded by a wide-angle X-ray analysis, the degree of orientation can be calculated (7t ) according to the following equation: Degree of orientation (p) = ((180-H = / (180) x 100 Furthermore, if the degree of variation in the fineness of the tow of the precursor fiber is greater than 1C by percent, the resulting carbon fiber shows a wide variation in the weight of the tow per unit length, but it is also possible that it causes problems, such as an increase in the defects responsible for the breakage, a reduction in the tensile strength, and the creation of gaps between the attached tows during the formation of a leaf-type preform As used herein, the term "degree of variation in the fineness of the tow" refers to the degree of variation determined on the basis of The fineness is a tow consecutively in the longitudinal direction of the tow. Furthermore, the precursor fiara of the present invention preferably has a roughness coefficient? shallow in the range? e C.2 to 4.0. When the precursor fibers have this degree of surface roughness, the melting of the fibers during the flame test is suppressed, so that they exhibit pro-processes processes during the treatment and flame test. Moreover, when the resulting carbon fibers are formed in a composite material, such as a preform, the penetrability of the matrix resin in the space between the carbon fibers is improved. The precursor fibers having a surface roughness coefficient within this range can be prepared by the wet spinning process. As used herein, the term "surface roughness coefficient" refers to a value obtained by using a scanning electron microscope to scan a fiber with primary electrons in a direction perpendicular to the axis of the fiber (i.e. , in the direction of the diameter of the fiber), observing a curve of secondary electrons (reflected?) that are reflected from the surface of the flora, and calculating 1 / d ', in? on? ed' is the diametral length of the central part of the fiber corresponding to 60 percent of the diameter of the fiber, and 1 is the total length? e the secondary electron curve in the range of d '(converted to the length? e a straight line). Now, will the process for the preparation of a conformal precursor fiber be discussed later in the present? with the present invention. In order to prepare the copolymer coat in aclonite-rile-use the present invention, it is possible to We will use any well-known polymerization techniques, such as solution polymerization and paste polymerization. It is preferable to remove unreacted monomers, polymerization catalyst residues, and other impurities from the resulting copolymer as much as possible. In the present invention, the above mentioned copolymer is spun wet to form a coagulated fiber. Subsequently, this coagulated fiber is undergoes a primary stretch comprising stretching in the bath, or a combination of stretching in the air and stretching in the bath, and then to a secondary stretch comprising pressurized steam drawing. In the step of wet spinning, the copolymer based on acrylonitrile previously dissolved is dissolved in a solvent to prepare a spinning solution. The solvent used for this purpose can be selected from among well-known solvents, including organic solvents, such as imethylacetamide, suífóxi? O? E? Imetiío, and dimetilfonamida; and aqueous solutions of inorganic compounds, such as chloroform, zinc and thiocyanate, and sodium. The spinning is done by extruding the solution and spinning previously mentioned through the holes. nozzle having a cross-section circlar, hac to_ »a coagulation bath. Normally an aqueous solution containing the solvent used for the spinning solution, such as the coagulation bath, is used. Prior to stretching, the thus coagulated fiber obtained preferably has an elastic modulus in tension of 1.1 to 2.2 cN / dtex [dtex (decitex) at a value based on the weight of the copolymer in the coagulated fiber]. If the elastic modulus in tension of the coagulated fiber is less than about 1.1 cN / dtex, the fiber tends to stretch from a non-uniform manner in the initial stages of the spinning process (for example, in the coagulation bath), resulting in a variation in the fineness of the tow and in the fineness of the filaments a? Intro the tow. Moreover, because the different steps of the spinning process suffer from a noticeable increase in the load of stretching, and a considerable variation in the possibility of stretching, it may become difficult to perform the continuous spinning in a stable manner. On the other hand, if the elastic modulus in tension is greater? Approximately 2.2 cN /? Tex, tends to present breakage? The filament in the bath? Coagulation, and the subsequent steps can suffer a reduction in the possibility of stretching and in the stabilized ?. As a consequence, it may become difficult to produce a highly oriented fiber. 25 This coagulated fiber can be obtained through the control of the copolymer composition, the solvent, the spinning nozzle, and the extrusion rate from the nozzle, and regulating the concentration of the solution and spinning, the concentration and temperature of the coagulation bath, the spinning extraction , and the like, to get to be within the appropriate ranges. Then, the coagulated fiber is subjected to a primary stretch. Stretching can be performed in the bath by stretching the coagulated fiber in the coagulation bath or in a stretch bath. Alternatively, the coagulated fiber can be stretched partially in air, and then stretched in a bath. Stretching in the bathroom is usually done in a bath and stretched at 50-98 ° C, either in a single stage, or in two or 15 more stages. The fiber can be washed before, after, or during the stretch. After the stretch in the bath and the lava? C, the fiber is treated with a lubricant in a well known way, and then it is densified by drying. Eeta 20? Dry? Ensification? Or need to be performed at a temperature higher than the temperature? E transition to fiber glass. In practice, without heat, this temperature may vary, because the refrigerator is in a wet state or in a dry state. Densification by drying is preferably carried out with r. roller ae j¿ * JM¿. «. ¿> j.- M * fe-ÜisB. > ? t < »J. - * A »^ 16aMftÉÍf8E« f¡ir? heating that has a temperature of approximately 100 ° C to 200 ° C. For this purpose, one or more heating rollers can be used. Therefore, it is preferable that, after the primary stretch, the fiber is treated with a lubricant, and dried to a moisture content of not more than 2 weight percent (in particular, not more than 1 weight percent) , by means of a heating roller, and continuously subjected to a secondary stretch involving pressurized steam stretching. The reason for this is that the heating efficiency of the fiber in the pressurized steam is improved to allow stretching in a more compact equipment, and that it is possible to minimize the development of phenomena that damage quality (for example, the adhesion of filaments), to cause an additional improvement in density? and in the graft? orientation of the resulting fiber. Next, the secondary stretch that involves stretching with pressurized steam is explained. Stretching with pressurized steam is a method that involves stretching a fiber in an atmosphere of pressurized steam. This method can not only achieve a high proportion of stretch, and therefore, allows stable spinning at a higher speed, but also contributes to an increase in density and in the degree of orientation of the resulting fiber. In the present invention, it is important that, in the secondary stretch involving pressurized steam stretching, the temperature? The heating roller located immediately before the pressurized steam drawing machine, is set at 120-190 °. C, and the variation of the pressure? E steam in the steam stretch pressurizes? Or is controlled to not be greater? 0.5 percent. This makes it possible to minimize the variations in the proportion of stretch applied to the fiber, and the following variants in the fineness of the tow. If the temperature of the heating roller is less than 120 ° C, the temperature of the acrylonitrile-based precursor fiber for the formation of a carbon fiber does not rise enough to cause a reduction in the possibility of stretching. The proportion of the stretch is determined by the difference between the speeds of the rollers located on the sides, and the entrance and exit of the machine, and the stretching with pressurized steam. In the present invention, the roller located immediately before the steam drawing machine pressurizes or is normally a heating roller, and can also serve as the roller for final heating for densification by drying. In the present invention, the secondary stretch is a two-stage stretching comprising stretching with the heating roller based on the difference between the speeds of the rollers located at the inlets and the entrance and exit of the rollers. the pressurized steam stretching machine, and stretch with pressurized steam. The stretch ratio imparted by the heating roller is determined by the temperature of the heating roller and the stretching tension of the fiber in the secondary stretch. Accordingly, the proportion of stretch imparted by the heating roller varies with the tension? E stretch in the secondary stretch. It must have been that the proportion of the secondary stretch in a fixed period of time is always kept constant by the difference between the velocities of the rollers located on the entrance and the extension sides of the stretch machine. Pressurized steam, the proportion of stretch imparted by the pressurized steam varies with the proportion of the stretch imparted by the heating roller. That is, the distribution between the proportion of the stretch imparted by the heating roller and the proportion of the stretch imparted by the pressurized steam varies. In pressurized steam stretching, the appropriate treatment time to achieve - excellent stretch performance varies according to fiber travel speed, vapor pressure, and the like. TO I measure that the speed of the fiber travel becomes higher, and as the vapor pressure becomes lower, a longer treatment time is required. In the industrial production of precursor fibers, a treatment section ranging from several tens of centimeters to several meters is normally required. Moreover, because a section is also required to prevent steam leakage, there is a delay between the stretching with the heating roller and the stretching with the pressurized steam. In a fixed period of time, the sum of the stretch ratio imparted by the heating roller and the stretch ratio imparted by the pressurized steam remains constant. However, in the actual equipment, both types of stretching are not performed in a concurrent manner. Consequently, the proportion of stretch imparted to the fiber varies with the? Distribution between the stretch with the roller? And heating, and the stretching with the steam pressurizes?, And eventually causes variations in the fineness of the tow. For this reason, in order to eliminate the variations in the proportion of the stretch imparted to the fiber, it is effective to minimize the delay between the stretch with the roller and the heating, and the stretch with the steam budget. ?or. In accordance with the above, it is effective to make the length of the machine Stretch with steam as small as possible. However, in order to heat the fiber sufficiently, and ensure the possibility of industrially stable stretching, the pressurized steam stretch machine needs to have a certain length. Therefore, the prior art has not been successful in avoiding variations in the proportion of stretch imparted to the fiber. The present inventors made an investigation with a view to solving this problem, and now they have revealed that, in order to suppress the variations in the proportion of stretch imparted to the fiber, and consequently, the variations in the distribution between the stretch with the heating roller and stretching with pressurized steam, it is important to suppress the proportion of stretch imparted by the heating rod, and to minimize the variations in the stretching tension of the fiber in the secondary stretch. As previously stated, the proportion of stretch imparted by the roller to the heating is determined by the temperature of the heating roller and the stress produced in the fiber by the secondary stretch. In accordance? With the above, this can be suppressed by the refraction of the temperature, the heating rod, and by raising the pressure of the steam used in the stretching with steam cresuriza? o. If the temperature of the heating roller is unduly low, the heating efficiency of the fiber in the pressurized steam is reduced. In accordance with the above, the heating roller is adjusted to a suitable temperature in the range of 130 ° C to 190 ° C. Moreover, in order to allow the suppression of stretching with the heating roller, and that the characteristics of the pressurized steam stretch are clearly displayed, the steam pressure used in the pressurized steam drawing is preferably not less than 200 KPa »G (meter pressure, later on in the same). Preferably, this vapor pressure is suitably regulated by considering the treatment time. However, unduly high pressures can increase the leakage of steam. From an inertial point of view, a vapor pressure no greater than that is approximately 600 KPa »g. On the other hand, the variations in tension and stretch of the fiber in the secondary stretch can suppress the pressure, the steam used in the pressurized steam stretch., constant. Variations in pressure - steam pressurizes or preference are controlled not to be greater - 0.5 percent. Moreover, it is also preferable to control the properties of the pressurized steam, ie such that the temperature is not higher than the saturated steam temperature at the pressure of interest by about 3 ° C, and there are no droplets. of water contained in it. By determining the conditions of the secondary stretch in the manner described above, it has first become possible to suppress the variations in the proportion of stretch imparted to the fiber, to make a stable yarn at a high stretch ratio, and to increase the proportion of the secondary stretch to the proportion of the overall stretch. Especially in the case of spinning? E high speed? which is performed, for example, at an extraction rate of 100 meters per minute, and therefore requires a high stretch ratio, a high quality precursor fiber can be stably prepared. More so, in a modali? A? Preferred of the present invention, the ratio of the ratio of the secondary stretch to the proportion of the overall stretch (proportion of the secondary stretch / proportion to the overall stretch) is greater than 0.2. As a most preferred entity, the proportion of the global stretch is not less than 13. Therefore, one is achieved. excellent stability? and spinning. As a result, even through the use of the process of spinning in the humid, it is possible to obtain a precursor fiber that has excellent tensile properties, a high degree of density, and a high degree of orientation. global is less than 13, the fiber can not be oriented enough, and therefore, the dense? and the degree of orientation of the resulting fiber are insufficient. Furthermore, if the extraction in the coagulation bath is increased in order to compensate for the reduction in the stretch ratio, and thus improve productivity, filament breaks tend to occur due to the high extraction in the bath. coagulation, and subsequent steps may suffer from a reduction in the possibility of stretching and in stability. If the overall stretch ratio is unduly high, a stable continuous spin is difficult, due to the higher stretch loads in the primary stretch and in the secondary stretch. Under ordinary conditions, the proportion of the overall stretch preferably is not greater than 25. Moreover, in order to have the pressurized steam stretch method fully exhibit its high capacity it is the stretch and its characteristics to improve the? ensi? a? and the degree of orientation of the fiber, the proportion? e the proportion? the stretch secondary to the proportion of the global stretch needs to be greater? e 0.2. This can reduce the loads in the primary stretch, so that no filament break is present, and even more, there is no reduction in the possibility of stretching or in the stability of the stretch. with pressurized steam. Accordingly, a precursor fiber can be obtained that is satisfactory with respect to all the properties of density, mechanical properties, quality, and production stability. These phenomena become more pronounced as the spinning speed increases. If the ratio of the secondary stretch ratio to the overall stretch ratio is unduly high, the The stability of the continuous yarn tends to be reduced due to a greater load in the secondary stretch. In accordance with the above, it is usually preferable that the ratio of the secondary stretch ratio to the overall stretch ratio is not greater than 0.35. 15 When the carbon fibers obtained light the precursor fibers based on acrylonitrile for the formation of carbon fibers of conformity? With the present invention, they are configured in one direction to form a preform, they can be made in a preform with a productivity approximately 30 percent higher, compared with conventional carbon fibers. The reason for this is that acrylonitrile-based precursor fibers for the formation of carbon fibers, and consequently, coal beasts, have varying variation. longitudinal in fineness, and therefore, the fibers? -h .. '.s &. and coal have little longitudinal variation in possibility of *. opening.

* «? Best Mode for Carrying Out the Procedure The present invention is described more specifically with reference to the following examples. In each of the examples and comparative examples, the copolymer composition, the limiting viscosity [?] Of the copolymer, the elastic modulus in tension of the coagulated fiber, the tensile strength, and the elastic modulus of the precursor fiber, the strength of the strand and the elastic modulus of the carbon fiber (abbreviated as CF in the tables), the adsorption of iodine, the degree of orientation of the crystal by means of analysis? X-rays? e wide angle, the gra Variation in the fineness of the tow, the surface roughness coefficient, the content of the fiber, and the degree of variation in the pressure of steam in the pressurized steam stretch. or, they were determined according to the following methods. (a) "Copolymer composition" This was determined by means of 1 H-NM spectroscopy (with Nihon Denshi Mo? elo GSZ-400 Supercon? uctmg FT-NMR). (b) "Viscoside? limiting [?]? the copolymer" This was observed with a solution of ethylformamide at 25 ° C. (c) "Stressed elastic modulus?" The fiber coagulates? a "A bundle of coagulated filaments was collected, and rapidly subjected to a tensile test with a Tensilon in an atmosphere having a temperature of 23 °. C, and a humidity of 50 percent. The test conditions included a sample section (clamping distance) of 10 centimeters, and a velocity? of extraction of 10 centimeters per minute. The fineness (dtex: the weight of the copolymer per 10,000 meters of the coagulated filament bundle) of the coagulated filament bundle was determined according to the following equation, and the elastic modulus was expressed in cN / dtex. '5 dtex = 10,000 x f x Qp / V in don? e f is the number? e filaments, Qp is the extrusion velocity (grams / minute) of the copoimer by hole in the nozzle, and V is the velocity? Extraction 2) (meters / minute)? The fiber coagulates? (?) "Resistance to traction and elastic modulus? The precursor fiber" A filament was cut out and subjected to a tensile test with a Tensilon in an atmosphere having a temperature of 23 ° C and a temperature of 23 ° C. 50 percent wetting test conditions included a 2-centimeter stretch of sample (clamping stability), and an extraction rate of 2 centimeters per minute.5 Fineness (dtex: weight per 10,000 meters of filament) ) of the filament was determined, and the resistance and the elastic modulus were expressed in cN / dtex. (e) "Resistance of the strand and elastic modulus of the fiber 10? e carbon" These were looked at according to the method? Escritc in JIS-7601. (f) "Method for determination of iodine adsorption" 15 Precisely fiber 2 grams were weighed, and placed in an Erlenmeyer flask and 102 milliliters. Then, 100 milliliters was added to a solution, and I prepared it by dissolving 100 grams of potassium iodide, 90 grams of acetic acid, 10 grams of 2,4-20-chlorophenol, and 50 grams of iodine. enough distilled water to make a total volume of 1,000 liter), the flask was stirred at 60 ° C for 50 minutes to perform an iodine adsorption treatment. Subsequently, the fibers that had undergone the aasorption treatment were washed ccn aqua ion exchanged for 30 minutes, it will be washed JJ additionally with destxWrda water, and then dehydrated by centrifugation. The dehydrated fibers were placed in a 300 milliliter beaker. After the addition of 200 milliliters of dimethyl sulfoxide, the fibers were dissolved therein at 60 ° C. The amount of iodine adsorbed was determined by subjecting this solution to a potentiometric titration, using an aqueous solution of 0.01 mol / liter of silver nitrate. (g) "Method for determining the degree of orientation of the crystal, mediated by wide-angle X-ray analysis" This is a value obtained by recording the diffraction points on an equatorial line of a fiber based in polyacrylonitrile by x-ray analysis, and wide angle, and calculate the gravity orientation (p) from the wide medium (H) of the? distribution? and intensi? a? circumferential? e points? e? IFracció according to the following equation.

Cradle? E orientation (p) (%) = ((180-H) / 180) x 100 X-ray analysis? Wide angle (counter method) 1) X-ray generator? J 2OC0, manufactured by Rigaku Corp ..

X-ray source: Cuka (with a Ni filter). Output: 40 kV, 190 mA. (2) Goniometer 2155D1, manufactured by Rigaku Corp .. 5 Division system: 2MM, 0.5 ° x Io Detector: scintillation counter (h) "Degree of variation in the fineness of the tow" In the longitudinal direction of a fiber tow the precursor, the tow was cut consecutively to obtain 100 segments that had a length of precisely 1 meter. After these segments were dried in a dry oven at 85 ° C for 12 hours, the dry weight of each segment was measured. The degree of variation was determined according to the following equation.

Graao of variation (%) = (s / E) x 130 in dor.?e s is the? deviation are? ar? e? atos') me? i? os, / E is the average value of median data. (i) "Measurement for the determination of a coefficient of roughness above the Prime", and that the conditions of "contrast of an electron microscope with exoloration, using a tape, were adjusted. As a standard sample, specifically, using a high-performance magnetic tape as a standard sample, a secondary electron curve was observed under conditions that included an acceleration voltage of 13 kV, an amplification of 1,000 diameters, and a velocity of 3.6 cm / second scan.Therefore, the contrast conditions were adjusted in such a way that the average amplitude would be equal to about 40 millimeters.After this adjustment, a sample of a precursor figure with primary electrons was scanned in a direction perpendicular to the axis of the fiber (ie, in the direction of a diameter of the fiber) Using a line profile apparatus, an e-curve was displayed Secondary lenses (reflected) reflected from the surface of the fiber on the screen of a Brown tube, and were photographed on a film at an amplification? e 10,000 diameters. In this step, the acceleration voltage was 13 kV, and the scanning speed was 0.18 centimeters / second. The photograph of secondary electrons thus obtained was printed a? Emás while it was being amplified twice (ie, in a global amplification? E 20, OCD? Ameters). Consequently, a? Iagram? E curve? E secondary electrons (photograph) was obtained. Figure 1 shows a typical example of it. In this figure, d is the - ^ aa diameter of the fiber, and d 'is the diametral length of the left region after an end part of 20 percent has been removed from each side of the diameter of the fiber (ie, the diametral length of the part central 5 corresponding to 60 percent of the diameter of the fiber), and therefore, d '= 0.6d. 1 is the total length of the secondary electron curve in the range of d '(converted to the length of a straight line). From the values of 1 and d ', the coefficient 10 of surface roughness can be determined by calculating 1 / d'. (j) "Determination of moisture content of fiber" A fiber was dried in a dryer at 85 ° C for 12 hours, and its weight Wl was measured before drying, and its weight 2 was measured after drying. Your content? Hume? was determined according to the following equation.

Humidity test (%) ((Wl-W2) / W2) x 100 (k) "Degree of variation? E the pressure? Steam in the pressurized steam stretch?" Or "During the steam stretch pressurized?, The pressure inside the stretch machine was monitored? For 40 seconds. Pressure data was collected at 2 ^ intervals of 3.04 seconds, and the degree of determined according to the following equation.

Degree of variaJJ ÉJp (%) (s / E) x 100 at don? E s is the standard deviation of the measured data, and E is the average value of the measured data.

[Example 1] A composite copolymer of 97.1 percent by weight of acrylonitrile, 2.0 percent acrylamide, and 0.9 percent by weight of methacrylic acid, and that it had a viscosity? limiting [?] of 1.7, was dissolved in dimethylformamide to prepare a spinning solution having a 23 percent copolymer concentration in weight. Using an eyelet having 12,000 holes, this spinning solution was spun into a wet extruded solution to a hamstring solution that had a concentration of 70 percent by weight, and a temperature? 35 ° C. the resulting coagulant fiber had an elastic modulus in tension? E 1.59 cN /? Tex. After the coagulated fiber was washed and desolvated in hot water while being stretched at a stretch ratio of 4.75, the fiber was immersed in a bath of a lubricating and silicicidal solution, and densified by drying on a hot cloth at 140 ° C.

The resulting fiber had a moisture content not greater than 0.1 percent. Subsequently, the fiber was stretched in pressurized steam having a 294 KPa «g portion, at a stretch ratio of 2.8, and then dried again to obtain a precursor fiber. This precursor fiber was wound at a speed of 100 meters per minute. During the stretch with pressurized steam, the temperature of the heating roller located immediately before the pressurized steam drawing machine was adjusted to 140 ° C, and the degree of variation of the steam pressure in the steam stretch pressurizes? It was controlled to not be higher - 0.2 percent. The steam supplied the chamber with pressurized steam or water droplets were released by means of a drain trap, and the temperature of the pressurized steam stretch chamber was adjusted to 142 ° C. The proportion of the overall stretch was 13.3, and the ratio of the proportion of secondary stretch to the proportion of the overall stretch was 0.21. The control of the pressure and the pressure on the steam stretch was carried out by the transmitters KPG940A and BSTJ300 (manufactured by Yamatake-Honeywell Corp. on the stretch machine, sending the data). resulting to a PID digital indication controller. manufactured by Yokogawa Electcc Ccrp.), and i - ^ y? 's changing the opening of an automatic pressure control valve according to the instructions, from the control indicated. In the shaping step, filament breakage and lint production was rarely observed, indicating good spinning stability. This precursor fiber had a tensile strength of 7.5 cN / dtex, a tensile elastic modulus of 147 cN / dtex, an iodine adsorption of 0.2 percent by weight, a degree of orientation : 0 (p) of 93 percent, determined by wide-angle X-ray analysis, a degree of variation in the fineness of the tow of 0.6 percent, and a surface roughness coefficient of 3.0. Using a 5-flame flame test furnace? Hot air, this fiber was heat treated in air at 230-260 ° C, under a stretch? 5 percent for 30 minutes, to form a flame-resistant fiber with a density of 1,368 grams / cubic centimeter. Subsequently, this fiber was subjected to a treatment by heat at low temperature in a nitrogen atmosphere, at a maximum temperature of 600 ° C, under a stretch of 5 per cent for 1.5 minutes. Then, using a heat treatment method at a high temperature, with a maximum temperature of 1,400 ° C, an additional stretch in the atmosphere was treated additionally in the center faith, faith »^ ..-". «e- ^» *, ^^ a ^ a «^ MgiWtffW ^^ a &faith ^ S ^^ fea- ^ ¿^ afe-Ji approximately 1.5 minutes. The resulting carbon fiber had a strand strength of 4,800 MPa, and an elastic modulus of the strand of 284 GPa.

[Comparative Examples 1-3] The spinning was performed in the same manner as in Example 1, except that the coagulation bath comprised an aqueous solution of dimethylformamide having a concentration of 60 weight percent, and a 35 ° C (Comparative Example 1), an aqueous solution of dimethylformamide having a concentration of 73 percent by weight and a temperature of 35 ° C (Comparative Example 2), or an aqueous solution of dimethylformamide that had a concentration of 70 percent by weight, and a temperature? 50 ° C (Comparative Example 3). In Comparative Example 1, a lot of fluff was produced, and it was easy to form a precursor fiber continuously. In Comparative Examples 2 and 3, the resulting precursor fiber was ignited under the same conditions. than in Example 1. The tension elastic modulus? The fiber coagulates? The amount? of lint, the tensile strength, the elastic modulus, the elasticity, and the grain, and the orientation of the wide-angle X-rays of the precursor fiber, and the characteristics of the strand of the fiber from coal, are shown in the Taela 1 '§ & « [Comparative Examples 4 and 5] The spinning was performed in the same manner as in Example 1, except that the stretching conditions were altered with pressurized steam. Specifically, the temperature of the heating roller located immediately before the pressurized steam drawing machine was 195 ° C, and the degree of variation of the steam pressure in the pressurized steam drawing was about 0.7 percent (Example Comparative 4), or the temperature of the heating roller located immediately before the pressurized steam drawing machine was 140 ° C, and the degree of variation of the vapor pressure in the stretch cor. Estimated steam was about 0.7 percent (Comparative Example 5). In Comparative Example 4, the fine variation in the fineness of the tow of the precursor fiber was 1.7 percent, while, in Comparative Example 5, the degree of variation in the fineness of the tow? the leading fiber was? 1.2 percent.

[Examples 2 to 4] The same olymerc based on acrylonitrile, which was used in the Example 1, was dissolved in dimethylacetamide to prepare a spinning solution having a concentration of the copolymer of 21 weight percent. Using a nozzle having 12,000 holes, this spinning solution was spun wet by extruding it into an aqueous solution of dimethylacetamide having a concentration of 70 weight percent, and a temperature of 35 ° C. Subsequently, the resulting fiber was stretched in air at a stretch ratio of 1.5, then washed and desolvated in hot water while being stretched. Subsequently, the fiber was immersed in a bath, a silicone lubricating solution, and dried by drying on a heating roller at 140 ° C. Subsequently, the fiber was stretched in pressurized steam having a pressure of 294 KPa »g, and then dried again to provide a precursor fiber. This precursor fiber was wound at a speed of 100 meters per minute. During the pressurized steam stretch, the temperature? The heating wire located immediately before the steam pressurizing machine was adjusted to 140 ° C, and the gravity was controlled? variation? e the pressure? steam in the stretch with steam pressurizes? or not to be greater than 0.2 per cientc. The steam supplied to the stretch chamber with pressurized steam released droplets of water from a drainage trap, and the ÍS = a £ SfcS_ ^ ¡^^^^ - s ^ s ^ £ a! & ^ É ^, »-;». M «fcA? N« a.4fe-the pressurized steam stretching chamber was set at 142 ° C. In addition, this fiber "'*" was ignited under the same conditions as in Example 1, to obtain a carbon fiber With respect to each example, the ratio of overall stretch and the ratio? E the proportion of secondary stretch to the overall stretch ratio, the elastic modulus in tension of the coagulated fiber, the amount of lint, the tensile strength, the elastic modulus, the adsorption of iodine, the degree of orientation in wide-angle x-rays, and the gravity The variation in the fineness of the tow of the precursor fiber, and the characteristics of the carbon fiber strand, are shown in Table 1.

[Comparative Example 6] A precursor fiber was prepared under the same conditions as in Example 2, except that the secondary stretch ratio to the overall stretch ratio was altered to the value shown in Table 1. A? Emás, this fiber was ignited under the same conditions as in Example 2, to obtain a carbon fiber. The elastic modulus in tension of the coagulated fiber, the amount of fluff, the tensile strength, the elastic modulus, the adsorption of iodine, and the degree of orientation in X-rays of xs aflited &i ^ i3MfejSft «? i ^^« ait ««? w * 3ej ^ 'and wide angle of the precursor fiber, and the characteristics of the carbon fiber strand, are shown in Table 1.

[Comparative Examples 7 to 11] Precursor fibers were prepared, and ignited under the same conditions as in Example 2, except that the composition of the acrylonitrile-based copolymer was altered as shown in Table 2. With respect to each example, the elastic modulus in tension of the coagulated fiber, the amount? The fluff, the tensile strength, the elastic modulus, the iodine adsorption, and the degree of orientation in wide-angle X-rays of the precursor fiber, and the characteristics of the carbon fiber strand, are shown in Table 2. In the case of Comparative Example 7, the precursor fiber was burned and vaporized in the flame test step.

[Example 5] The same acrylonitrile-based copolymer that was used in Example 1 was solved in? Ethylacetamide to prepare a solution and spinning which had a concentration? E copolymer? 21 percent by weight . Using a nozzle having 12,000 holes, this spinning solution was spun into wet extrudate to an aqueous solution, lacerated, had a concentration of 70 percent by weight, and a temperature of 35 ° C. . Subsequently, the resulting fiber was stretched in air at a stretch ratio of 1.5, and then washed and desolvated in hot water while being stretched. Subsequently, the fiber was immersed in a bath of a silicone lubricant solution, and densified by drying on a heating roller at 160 ° C. Subsequently, the fiber was stretched in pressurized steam with a pressure of 294 KPa »g, and then dried again to obtain a precursor fiber. This precursor fiber was wound at a speed? ? e 140 meters per minute. During the pressurized steam stretch, the temperature of the heating roller located immediately before the presumed steam drawing machine was adjusted to 140CC, and the degree of variation of the vapor pressure in the steam stretch was controlled. Or not to be greater? 0.2 percent. Steam supplied to the chamber? Stretching with presumptive steam was released from droplets? E water by me? A trap? And drainage, and chamber temperature? Steam stretch budget was adjusted to 142 : C. In addition, this fiber was ignited under the same conditions as in Example 1, to obtain a carbon fiber. The overall stretch ratio, and the ratio of the secondary stretch ratio to the proportion S- '. -afc-S of global stretch, the elastic modulus in tension of the coagulated fiber, the amount of fluff, the tensile strength, the elastic modulus, the iodine adsorption, the degree of orientation in wide-angle X-rays, and the degree of variation in the fineness of the tow of the precursor fiber, and the characteristics of the carbon fiber strand, are shown in Table 2.

[Example 6] The carbon fibers obtained in Comparative Example 4 were arranged in parallel to form a sheet having a basis weight of carbon fiber of 125 grams / square meter. Two resin films (with a resin basis weight of 27 grams / square meter) were prepared by the Application of Epoxy Resin = 340 (manufactured by Mitsubishi Rayon Co., Ltd., to the mold release paper, and the previous sheet was sandwiched between them, so that the epoxy resin would come into contact with the fibers? In coal was passed through a production machine? preforms to produce a preform with a base weight of 125 grams / square meter. A edi? A that increases the speed grae? The projection was reduced, the possibility of carbon fiber opening was reduced, and grooves appeared, approximately 1 millimeter anche, that r-e included cane fiber, at a frequency of 2 to 3 ~ -ia £ »« fcfc. mtaiBiSfc ?. ' -jMÍfc *? ls¿ «- * _ ~. »« «« ™ = ».. ^ * .. x»., ..,. . ^^^. ,,, .r,. ,, u- ^ ~ 8m ^ ", r. ..r, ...... _ ^ T _ "& jfaj. jB _s »r rM, slots by 4 to 5 meters. The production machine and preforms used in this example consisted of 7 pairs of heated flat metallic press rolls, a pair of cooling rollers, and a pair of rubber extraction rollers. When the carbon fibers sandwiched between the resin films prepared by applying an epoxy resin to the mold release paper were fed thereto, the resin was fluidized by heating on the surfaces of the press rolls, and compressed to make the resin penetrate the carbon fiber layer. Subsequently, the resulting preform was cooled and extracted by means of a pair of rubber rods. Then, the carbon fibers were replaced by carbon fibers obtained in Example 1. Was it possible to stably produce a preform without grooves, even at a speed? Production 30 percent higher than the production rate at which the grooves with the carbon fibers appeared Comparative Example 4. [Comparative Example 12] A precursor base fiber was prepared. in acrylonitrile for the formation of a carbon fiber in the same manner as in Example 1, except that the temperature of the roller located before the machine and the steam stretch was set to 115 . This fiber produced muena fluff, could not be rolled facimenté. ! ** s? * otes) AN: acrylonitrile; AAM: acrylamide; MAA: methacrylic acid. 49 TABLE 2 otas) 1 *) AN / AA / MAA is the composition of the case where no monomeric units are indicated. aci L lome, i l ?; ?? M: acrilam da; MAA: methacrylic acid; 2-HEMA: 2-hydroxyethyl acrylate; AM- I gave acetone-acr the going.

Operability in the Industry In accordance with the present invention, a precursor fiber based on acrylonitrile is provided for the formation of a carbon fiber having a high strength, a high elastic modulus, a high degree of density, a high degree of orientation, and a low degree of variation in the fineness of the tow, and therefore, can be used to form a high quality carbon fiber in an economical manner, igniting for a shorter period of time. Moreover, according to the wet spinning process, a precursor fiber based on acrylonitrile can be prepared quickly and stably for the formation of a fiber which has these properties without breaking. e the fiber frequently, and without producing any amount? appreciable lint. The precursor fiber based on acrylonitrile for the formation of a carbon fiber in compliance? with the present invention, it has a substantial uniformity of fineness in the longitudinal direction, and the carbon fiber obtained by its ignition also fulfills an umformi? a? substantial? fineness in the? longitudinal direction. Esco causes less variation of possibility? It is opened in the longitudinal direction, in such a way that carbon fiber can be formed in preforms with a high yield. approximately 30 percent higher, compared to conventional carbon fibers.

Brief Description of Drawing 5 Figure 1 is a secondary electron curve diagram for the determination of a roughness coefficient? superficial.

Definition of Characteristics d is the diameter of the fiber. d 'is the diametral length of a central part of the fiber that corresponds to 60 percent of the diameter of the fiber. 1 is the length? total? e the curve of secondary electrons in the range of d '(converted to the length of a straight line). "-g- yy ^ £ & *

Claims (10)

1. A precursor fiber based on acrylonitrile for the formation of a carbon fiber, which is prepared from an acrylonitrile-based copolymer containing from 96.0 to 98.5 weight percent of acrylonitrile units, having this precursor fiber based on acrylonitrile a tensile strength not less than 7.0 cN / dtex, an elastic modulus in tension not less than 130 cN /? tex, an absorption of 10 iodine not greater than 0.5 percent by weight based on fiber weight, a grain, or orientation, glass (p) not less than 90 percent, determined by the analysis? X-rays wide angle, and a gradation of variation in the fineness of the tow not greater than 1.0 percent.

2. A precursor fiber based on acrylonitrile for the formation of a fiber of price as claimed in claim 1, wherein the copolymer based on acrylonitrile is made up of 96.0 to 93.5 weight percent of bound? Acrylonitrile, the 1.0 to 3.5 percent in 20 weight? E acrylate units, and 0.5 to 1.0 weight percent of carboxyl-containing "vinyl lonomer" units

3. A precursor fiber is based on acrylating polymer for the formation of a fiber? carcón as claimed in 25 claim 1 or 2, which is formed by the wet spinning process.

4. A process for the preparation of a precursor fiber based on acrylonitrile for the formation of a carbon fiber, which comprises the steps of wet spinning an acrylonitrile-based copolymer to form a coagulated fiber, subjecting the coagulated fiber to stretching primary which comprises stretching in the bath, or a combination of stretching in air and stretching in the bath, and subjecting the coagulated fiber to a secondary stretch that involves stretching with pressurized steam, or at the temperature of the rust? The localized heating immediately prior to the introduction of the fiber in the pressurized steam stretch machine is adjusted to 120-190 ° C, the degree of variation of steam pressure in the pressurized steam stretch is controlled not to be greater than 0.5 percent, and the cgula fiber is stretched in such a way that the proportion ratio of the secondary stretch to the overall stretch ratio is greater than 0.2.

5. A process for the preparation of a precursor fiber based on acrylonitrile for the formation of a carbon fiber as claimed in claim 4, where the proportion of the overall stretch is not lower. 13. A process for the preparation of a precursor flora based on acrylonitrile for the formation of a carbon fiber as claimed in claim 4 or 5, wherein the acrylonitrile-based copolymer is composed of 96.0 to 98.5 weight percent of acrylonitrile units, 1.0 to 3.5 weight percent of acrylamide units, 5 and 0.5 to 1.0 weight percent of vinyl monomer units containing carboxyl. 7. A process for the preparation of a precursor fiber based on acrylonitrile for the formation of a carbon fiber as claimed in any of the 10 claims 4 to 6, in which, before stretching, the coagulated fiber has a tension elastic modulus of 1.2 to 2.2 cN / dtex. 8. A process for the preparation of a precursor fiber based on acrylonitrile for the formation of a 15 carbon fiber as claimed in any one of claims 4 to 7, where the steam-pressurized stretch is performed at a vapor pressure not less than 200 KPa (pressure? Ei me? I? Or) . 9. A process for the preparation of a fiber > ) precursor based on acrylonitrile for the formation of a carbon fiber as claimed in any of claims 4 to 8, on which the fiber subjected to the stretch with steam preeurizes? A content? Hume? no more? 2 percent by weight. 25 10. A carbon fiber covered by test flame and carbonization of a precursor fiber based on acrylonitrile for the formation of a carbon fiber as claimed in any of claims 1 to 3.