JP4228009B2 - Method for producing acrylonitrile-based precursor fiber for carbon fiber - Google Patents

Description

  The present invention relates to a polyacrylonitrile-based precursor fiber for producing carbon fibers and a method for producing the same.

  Carbon fiber and graphite fiber (collectively referred to as “carbon fiber” in the present application) having polyacrylonitrile fiber as a precursor are used for aerospace applications, sports / leisure applications, etc. due to their excellent mechanical properties. Commercially produced and sold as a high-performance composite reinforcing fiber material. In recent years, demands for applications in general industrial fields such as automobile / ship use and building material use are increasing. In the market, high-quality and inexpensive carbon fibers are required to improve the performance of these composite materials.

  Unlike the acrylic fiber for clothing, the acrylonitrile-based fiber as a precursor of the carbon fiber is an intermediate product for producing the final carbon fiber. Therefore, it is required to provide carbon fibers with excellent quality and performance. At the same time, it is excellent in stability during spinning of the precursor fiber, and has high productivity in the firing process of carbon fibers, and is provided at low cost. It is extremely important to be able to obtain.

  From such a viewpoint, many proposals have been made on acrylic fibers for the purpose of increasing the strength and elasticity of carbon fibers. Among them, there are proposals such as increasing the degree of polymerization of the raw material polymer and reducing the content of copolymerization components other than acrylonitrile. As for the spinning method, a dry-wet spinning method is generally employed.

  However, when the content of copolymer components other than acrylonitrile is reduced, the solubility of the raw material copolymer in the solvent is generally lowered, the stability of the spinning stock solution is impaired, and the viscosity of the stock solution increases rapidly. Correspondingly, it is necessary to decrease the copolymer concentration of the spinning dope. As a result, the precipitation and solidification properties of the copolymer are remarkably increased, and the resulting fiber is easily devitrified and a large number of voids are easily generated therein. Therefore, this is not a stable production method.

  In the dry-wet spinning method, the polymer solution extruded from the nozzle is once discharged into the air, and then continuously led to a coagulation bath to form fibers. If this is made smaller, there will be a problem of adhering adjacent fibers, and there is a limit to increasing the number of holes.

  In general, low-cost production of acrylonitrile-based precursor fibers is advantageous in increasing the density of nozzle holes and requires relatively little investment in production equipment. Yes. However, the obtained fiber tow generally has many single fiber cuts and fluffs, the resulting precursor fiber has low tensile strength and elastic modulus, and the precursor fiber structure has low density and orientation. Therefore, the mechanical performance of the carbon fiber obtained by firing this is generally insufficient.

  As a condition of the precursor fiber to obtain high-quality carbon fiber, it is very important that there is no minute defect that causes breakage after being converted to carbon fiber, reducing such defects For this purpose, the tensile strength and elastic modulus of the precursor fiber are high, the denseness of the fiber structure is high, the copolymer is highly oriented in the direction of the fiber axis, and the fluctuation rate of tow fineness is high. Smallness is required.

  For example, Patent Document 1 reports that the denseness of the fiber structure is referred to while using a wet spinning method. As a measure representing the denseness, the amount of iodine adsorbed and the thickness of the skin layer to which iodine is adsorbed are defined. ing. However, the precursor fiber obtained here has a low density of about 1 to 3% by weight of iodine, and the obtained precursor fiber has a low tensile strength and elastic modulus. It was very difficult to get.

  On the other hand, Patent Document 2 discloses a precursor fiber whose surface structure is highly densified by a dry-wet spinning method. Further, Patent Document 3 and Patent Document 4 disclose precursor fibers having high tensile strength and elastic modulus and highly oriented copolymer in the fiber axis direction by dry-wet spinning method. Although the quality of the obtained carbon fiber is improved by using these precursor fibers, the productivity is low because the dry-wet spinning method is used. Compared with fibers obtained by wet spinning, fibers obtained by dry-wet spinning have a smooth surface, so that the convergence is good. On the other hand, fusion between fibers in the firing process, and opening during sheet prepreg molding are possible. It has drawbacks such as being susceptible to poor fineness. Furthermore, the acrylonitrile content of the polymer in these inventions is substantially 99.0% by weight or more, and from the viewpoint of the stability of the spinning dope and the precipitation solidification of the copolymer, It was insufficient.

  In order to obtain a precursor fiber having a densified surface structure while using a wet spinning method, studies using pressurized steam drawing have been made as a drawing method that can obtain a higher draw ratio.

  For example, Patent Document 5 discloses a precursor fiber having a densified surface structure using a wet spinning method. Precursor fibers are densified by using coagulated fibers having a specific copolymer composition and specific physical properties and simultaneously using pressurized steam drawing. However, since an appropriate range of drawing conditions after coagulation is not considered at all, it is insufficient to obtain a precursor fiber having high density and high congruency. Moreover, there is no description about the fluctuation rate of the strength / elastic modulus, crystal orientation degree, and tow fineness of the obtained precursor fiber, and the physical properties and properties of the precursor fiber necessary for obtaining a high-quality carbon fiber are still available. It was not known. Furthermore, when spinning at a high speed such as a spinning speed of 100 m / min or more, stable spinning is difficult.

As described above, any of the conventional techniques is insufficient as a precursor fiber for obtaining a high-quality and inexpensive carbon fiber and a method for producing the precursor fiber.
JP 58-214518 A JP-A-63-35821 JP 60-21905 A Japanese Patent Laid-Open No. 62-117814 JP-A-7-70812

  The present invention has been made in view of such conventional problems, and can produce high-quality carbon fiber at a low cost by firing in a shorter time, and has high strength, high elastic modulus and denseness. And a high-speed and stable production method of acrylonitrile-based precursor fibers for carbon fibers with a high degree of orientation and a small tow fineness variation rate, with no yarn breakage for a long time by a wet spinning method and less generation of fuzz. For the purpose.

The present invention relates to an acrylonitrile copolymer comprising 96.0 to 98.5% by weight of acrylonitrile units, 1.0 to 3.5% by weight of acrylamide units and 0.5 to 1.0% by weight of carboxyl group-containing vinyl monomer units. The polymer is wet-spun to obtain a coagulated fiber having a tensile modulus of 1.1 to 1.59 cN / dtex, and then stretched in the bath, or primary stretched in the air and stretched in the bath, and the oil agent is applied and heated. A method for producing an acrylonitrile-based precursor fiber for carbon fiber that continuously performs secondary stretching accompanied by pressurized steam stretching after drying and densification by a roller, wherein the heating roller just before introducing the yarn into the pressurized steam stretching apparatus The temperature is set to 120 to 190 ° C., the fluctuation rate of the water vapor pressure in the pressurized water vapor drawing is controlled to 0.5% or less, and the secondary draw ratio relative to the total draw ratio Ratio relates to a method for producing a carbon fiber for acrylonitrile based precursor fiber characterized by stretching to greater than 0.2.

  At this time, in one aspect of the present invention, the total draw ratio is preferably 13 or more.

  According to the present invention, carbon capable of producing high-quality carbon fiber at a low cost by firing in a shorter time, high strength, high elastic modulus, high density and high degree of orientation, and low tow fineness variation rate An acrylonitrile-based precursor fiber for fibers can be provided.

  In addition, the acrylonitrile-based precursor fiber for carbon fiber having such properties can be stably produced at high speed with no generation of fuzz by a wet spinning method without causing yarn breakage for a long time.

  The acrylonitrile-based precursor fiber for carbon fiber of the present invention has little longitudinal fineness unevenness, and the carbon fiber obtained by firing the same has little longitudinal fineness unevenness. As a result, the unevenness of the spreadability in the longitudinal direction is reduced, so that the prepreg can be formed with a productivity about 30% higher than that of the conventional carbon fiber.

  Hereinafter, the present invention will be described in detail.

The present specification also discloses the invention of the following acrylonitrile-based precursor fiber for carbon fiber.
(1) An acrylonitrile-based precursor fiber for carbon fibers produced from an acrylonitrile-based copolymer containing 96.0 to 98.5% by weight of acrylonitrile units, having a tensile strength of 7.0 cN / dtex or more and a tensile modulus of 130 cN Carbon having an iodine adsorption amount of 0.5% by weight or less per fiber weight, a crystal orientation degree π by wide-angle X-ray diffraction of 90% or more, and a variation rate of tow fineness of 1.0% or less. Acrylonitrile precursor fiber for fiber.
(2) The acrylonitrile copolymer is 96.0 to 98.5 wt% of acrylonitrile units, 1.0 to 3.5 wt% of acrylamide units, and 0.5 to 1.0 wt% of carboxyl group-containing vinyl monomer units. The acrylonitrile-based precursor fiber for carbon fiber according to (1), comprising:
(3) The acrylonitrile-based precursor fiber for carbon fiber according to (1) or (2), which is produced by a wet spinning method.

  Further, the present specification also discloses an invention of a carbon fiber obtained by making the acrylonitrile-based precursor fiber for carbon fiber according to any one of (1) to (3) flameproofed and carbonized.

  The acrylonitrile-based copolymer (hereinafter also simply referred to as copolymer) used for the production of the acrylonitrile-based precursor fiber for carbon fiber (hereinafter referred to as precursor fiber) of the present invention has 96.0 acrylonitrile as a monomer unit. Contains ˜98.5% by weight. If the acrylonitrile unit in the copolymer is less than 96% by weight, the fiber is heat-sealed in the firing process (flame-proofing process and carbonization process) when converted to carbon fiber, and the quality and performance of the carbon fiber are reduced. Easy to lose. Further, the heat resistance of the copolymer itself is lowered, and when spinning the precursor fiber, adhesion between single fibers is likely to occur in a process such as fiber drying or stretching with a heating roller or pressurized steam. On the other hand, when the content of the acrylonitrile unit in the copolymer exceeds 98.5% by weight, the solubility in the solvent is lowered, the stability of the spinning dope is impaired, and the precipitation and solidification properties of the copolymer are reduced. It becomes remarkably high and stable production of precursor fibers tends to be difficult.

  In the present invention, the copolymer preferably contains 1.0 to 3.5% by weight of acrylamide units as monomer units. By setting the content of acrylamide units in the copolymer to 1.0% by weight or more, the structure of the precursor fiber becomes sufficiently dense, and carbon fibers having excellent performance can be obtained. In addition, the flame resistance in the flame resistance process is greatly affected by subtle fluctuations in the copolymer composition. If the acrylamide unit content is 1.0% by weight or more, stable carbon fiber production is possible. Can do. Acrylamide is highly random copolymerizable with acrylonitrile, and it is thought that a ring structure is formed in a form very similar to acrylonitrile by heat treatment, and thermal decomposition in an oxidizing atmosphere is very small. Compared with a carboxyl group-containing vinyl monomer, it can be contained in a large amount. However, if the content of acrylamide units in the copolymer is increased, the content of acrylonitrile units in the copolymer is decreased, and the heat resistance of the copolymer is lowered as described above. The following are appropriate.

  Furthermore, in this invention, it is preferable to contain 0.5 to 1.0 weight% of carboxyl group containing vinylic monomer units as a monomer unit in a copolymer. Examples of the carboxyl group-containing vinyl monomer include acrylic acid, methacrylic acid, itaconic acid and the like. When the content of the carboxyl group-containing vinyl monomer unit is too small, the flameproofing reaction is slow, so that it is difficult to obtain high-performance carbon fibers by short-time firing. In the case where the flameproofing treatment is performed in a short time, the flameproofing temperature must be increased, so that a runaway reaction is likely to occur, which may cause problems in terms of process passability and safety. In addition, when the content of the carboxyl group-containing vinyl monomer unit in the copolymer increases, the flame resistance reactivity increases, so that the vicinity of the fiber surface layer reacts rapidly during the flame resistance treatment, while the reaction at the center portion Due to the delay, the flame-resistant fiber forms a double-section structure. However, in such a structure, in the next higher temperature carbonization step, the decomposition of the portion where the flameproof structure in the fiber center portion is not developed cannot be suppressed, so that the performance of the carbon fiber, particularly the tensile elastic modulus, is significantly lowered. This tendency becomes conspicuous as the flameproofing time is shortened.

  From the viewpoints of stretchability in precursor fiber spinning and carbon fiber performance, etc., the degree of polymerization of the copolymer is preferably such that the intrinsic viscosity [η] is 0.8 or more. If the degree of polymerization is too high, the solubility in a solvent will decrease, and voids due to lowering the copolymer concentration, reduction in stretchability and spinning stability, etc. can be seen, so usually the intrinsic viscosity [η] is 3.5 or less is preferable.

  The precursor fiber of the present invention is manufactured by a wet spinning method using such a copolymer, and has a tensile strength of 7.0 cN / dtex or more, a tensile modulus of 130 cN / dtex or more, and an iodine adsorption. The amount is 0.5% by weight or less per fiber weight, the degree of crystal orientation π by wide-angle X-ray diffraction is 90% or more, and the variation rate of tow fineness is 1.0% or less.

  When the tensile strength of the precursor fiber is less than 7.0 cN / dtex, or the tensile elastic modulus is less than 130 cN / dtex, the mechanical performance of the carbon fiber obtained by firing the precursor fiber becomes insufficient.

  If the amount of iodine adsorbed by the precursor fiber exceeds 0.5% by weight, the denseness or congruency of the fiber structure is impaired and becomes inhomogeneous, which becomes a defect point when firing into carbon fiber. The performance of is reduced. Here, the iodine adsorption amount is the amount of iodine adsorbed by the fiber, and is a scale indicating the degree of denseness of the fiber structure. The smaller the value, the denser the fiber.

  When the crystal orientation degree π of the precursor fiber is less than 90%, the tensile strength / elastic modulus of the precursor fiber is lowered, and the mechanical performance of the carbon fiber obtained by firing the precursor fiber becomes insufficient. Further, if an attempt is made to obtain a crystal with a very high degree of crystal orientation π, a higher draw ratio is required, and stable spinning becomes difficult, so the industrially easy range is usually 95% or less. .

  Here, the degree of crystal orientation by wide-angle X-ray analysis is a scale indicating the degree of orientation of the copolymer molecular chains constituting the fiber in the fiber axis direction, and the diffraction point on the equator line of the fiber by wide-angle X-ray analysis. It is a value calculated from the half width H of the circumferential intensity distribution by the degree of orientation π (%) = ((180−H) / 180) × 100.

  Further, when the variation rate of the toe fineness of the precursor fiber is larger than 1.0%, not only the variation in the tow weight per unit length after being converted into the carbon fiber increases, but also a defect that causes breakage. May cause problems such as an increase in tensile strength and a gap between the tows during molding of the sheet-like prepreg. Here, the fluctuation rate of the toe fineness is a fluctuation rate when the tow fineness is continuously measured in the longitudinal direction of the tow.

  Further, the precursor fiber of the present invention preferably has a surface roughness coefficient in the range of 2.0 to 4.0. When the degree of unevenness on the surface is this level, fusion between fibers at the time of flameproofing treatment is suppressed, so that the process passability at the time of flameproofing treatment becomes good. Further, when the obtained carbon fiber is formed into a composite such as a prepreg, the impregnation property between the carbon fibers of the matrix resin is improved. Those having a surface roughness coefficient in this range can be obtained by a wet spinning method. Here, the surface roughness coefficient is a secondary (reflected) electron curve reflected from the fiber surface by scanning primary electrons in a direction perpendicular to the fiber axis (fiber diameter direction) using a scanning electron microscope. When observed, it is a value obtained by l / d ′ from the diameter direction length d ′ of the central part 60% of the fiber diameter and the total length (linear conversion length) l of the secondary electron curve in the range of d ′. is there.

  Next, the manufacturing method of the precursor fiber of this invention is demonstrated.

  The polymerization method of the acrylonitrile copolymer used in the present invention can be any of known polymerization methods such as solution polymerization and slurry polymerization, but removes unreacted monomer, polymerization catalyst residue, and other impurities as much as possible. Is preferred.

  In the present invention, the copolymer is wet-spun into a coagulated fiber, and then stretched in a bath, or primary stretched by air stretch and stretch in a bath, and secondary stretched by pressurized steam stretch.

  First, in the case of wet spinning, the aforementioned acrylonitrile copolymer is dissolved in a solvent to obtain a spinning dope. The solvent at this time can be appropriately selected from known solvents such as organic solvents such as dimethylacetamide, dimethylsulfoxide and dimethylformamide, and aqueous solutions of inorganic compounds such as zinc chloride and sodium thiocyanate.

  The spinning shaping is performed by spinning the spinning solution into a coagulation bath through a nozzle hole having a circular cross section. As the coagulation bath, an aqueous solution containing a solvent used for the spinning dope is usually used.

  The solidified fiber before stretching obtained at this time has a tensile modulus of 1.1 to 2.2 cN / dtex (dtex = decitex is based on the weight of the copolymer in the solidified fiber). preferable. When the tensile elastic modulus of the coagulated fiber is less than about 1.1 cN / dtex, it tends to cause non-uniform stretching in the initial stage of the spinning process such as in a coagulation bath, and may cause variations in tow fineness and single fiber fineness inside the tow. is there. Furthermore, since the increase in the drawing load and the change in drawability become remarkable in each spinning step, stable continuous spinning may be difficult.

  On the other hand, if the tensile modulus exceeds about 2.2 cN / dtex, single fiber breakage in the coagulation bath is likely to occur, leading to a decrease in stretchability and stability in the subsequent process, and a high degree of orientation in the fibers. It becomes difficult to have.

  Such coagulated fibers are controlled by adjusting the copolymer composition, solvent, spinning nozzle, discharge rate from the nozzle, and controlling the stock solution concentration, coagulating bath concentration, coagulating bath temperature, spinning draft, etc. to an appropriate range. can get.

  Next, the coagulated fiber is primarily stretched. In the drawing in the bath, the coagulated yarn is drawn in a coagulation bath or a drawing bath. Or you may extend | stretch in a bath, after partially extending | stretching in the air. Stretching in the bath is usually carried out in a stretching bath at 50 to 98 ° C. by dividing it into multiple stages of once or twice, and washing may be performed before or after or simultaneously.

  The fiber after drawing and washing in the bath is subjected to oil agent treatment by a known method and then dried and densified. The temperature for drying and densification needs to be performed at a temperature exceeding the glass transition temperature of the fiber, but the temperature may vary depending on the drying state from the water-containing state, and the temperature is a method using a heating roller of about 100 to 200 ° C. Is preferred. At this time, the number of heating rollers may be one or more.

  In this way, after the primary stretching, after applying the oil agent and drying the moisture content of the fiber to 2% by weight or less, particularly 1% by weight or less by a heating roller, the secondary stretching with continuous pressurized steam stretching is performed. Is preferred. The heating efficiency of the yarn in pressurized steam is improved, drawing can be done with a more compact device, and at the same time, the occurrence of phenomena such as adhesion between single fibers can be greatly reduced, and the resulting fibers can be dense. This is because the properties and the degree of orientation can be further increased.

  Next, secondary stretching accompanied by pressurized steam stretching will be described. The pressurized steam stretching method is a method of stretching in a pressurized steam atmosphere, and since it can be stretched at a high magnification, it can perform stable spinning at a higher speed, and at the same time, the denseness and orientation degree of the resulting fiber. Contributes to improvement.

  In the present invention, in the secondary stretching accompanying this pressurized steam stretching, the temperature of the heating roller immediately before the pressurized steam stretching apparatus is controlled to 120 to 190 ° C., and the variation rate of the steam pressure in the pressurized steam stretching is controlled to 0.5% or less. is important. By doing in this way, the fluctuation | variation of the draw ratio made to a thread | yarn and the fluctuation | variation of the tow | fineness degree generated by it can be suppressed. If it is less than 120 degreeC, the temperature of the acrylonitrile type | system | group precursor fiber for carbon fibers will not fully rise, but a drawability will fall.

  The secondary stretching ratio is determined by the speed difference between both rollers on the inlet side and the outlet side of the pressurized steam stretching apparatus. In the present invention, the roller immediately before the vapor stretching apparatus is usually a heating roller, which can also serve as the final heating roller for drying and densification. In the present invention, the secondary stretching is a two-stage stretching of stretching by a heating roller and stretching by pressurized steam performed by the difference in speed between the rollers on the inlet side and the outlet side of the pressurized steam stretching apparatus.

  Since the magnification stretched by this heating roller is determined by the temperature of the heating roller and the stretching tension of the yarn in the secondary stretching, if the stretching tension of the secondary stretching varies, the magnification stretched by the heating roller is fluctuate. The secondary stretch ratio at the same time is always kept constant due to the difference in speed between the rollers on the inlet side and the outlet side of the pressurized steam stretcher, so the stretch ratio with the pressurized steam is the stretch ratio of the heated roller. It fluctuates with fluctuation. That is, the distribution of stretching by a heating roller and stretching by pressurized steam varies.

  In pressurized steam drawing, the appropriate processing time for exhibiting excellent drawing performance varies depending on the yarn running speed, water vapor pressure, etc., the faster the yarn running speed and the lower the water vapor pressure. Long processing time is required. In the production of industrial precursor fibers, a treatment length of several tens of centimeters to several meters is usually required, and a part that suppresses steam leakage is also required. A time difference occurs. In the same time, the synergy between the draw ratio by the heating roller and the draw ratio by the pressurized steam is constant, but the draw ratio applied to the yarn is not heated at the same time on the device. It fluctuates due to fluctuations in the distribution of the stretching by the roller and the stretching by the pressurized steam, resulting in a variation in the tow fineness.

  For this reason, reducing the delay time between drawing with a heated roller and drawing with pressurized steam as much as possible is effective in suppressing fluctuations in the draw ratio applied to the yarn, and reducing the length of the pressurized steam drawing device as much as possible. Is effective. However, in order to sufficiently heat the yarn and to ensure industrially stable stretchability, a pressurized steam stretcher of a certain length is required. The fluctuation of was inevitable. The present inventors have studied to solve this problem, and in order to suppress fluctuations in the draw ratio applied to the yarn, that is, to suppress fluctuations in the distribution between the drawing by the heating roller and the drawing by the pressurized steam, the heating roller is used. It was clarified that it is important to suppress the draw ratio and to reduce the fluctuation of the drawing tension of the yarn in the secondary drawing.

  As described above, since the stretching by the heating roller is determined by the temperature of the heating roller and the generated tension of the yarn in the secondary stretching, the temperature of the heating roller is decreased and the water vapor pressure in the pressurized steam stretching is increased. Can be suppressed. If the heating roll temperature is lowered too much, the heating efficiency of the yarn in the pressurized steam is lowered, so the temperature is controlled within the range of 130 to 190 ° C. Further, the pressure of the water vapor in the pressurized steam stretching is preferably 200 kPa · g (gauge pressure, the same applies hereinafter) or more so that the stretching of the heated roller and the characteristics of the pressurized steam stretching method appear clearly. The water vapor pressure is preferably adjusted as appropriate in consideration of the processing time, but if the pressure is increased, the leakage of water vapor may increase. Therefore, about 600 kPa · g or less is sufficient industrially.

  On the other hand, fluctuations in the stretching tension of the yarn in the secondary stretching can be suppressed by keeping the water vapor pressure constant in the pressurized steam stretching. It is preferable to control the fluctuation of the pressure of the pressurized steam to 0.5% or less. The property of the pressurized steam is preferably controlled so as not to exceed about 3 ° C. higher than the saturated steam temperature of the pressure and not include liquid-suitable water.

  By setting the conditions for secondary stretching in this way, it is possible to suppress the fluctuation of the draw ratio made to the yarn for the first time, and to stably stretch at a high ratio, and the secondary stretch for all the draw ratios. The ratio can be increased. Even in a high-speed spinning where a high draw ratio is required, for example, a winding speed of 100 m / min or more, high-quality precursor fibers can be produced stably.

  Furthermore, in the present invention, the ratio of the secondary draw ratio to the total draw ratio (secondary draw ratio / total draw ratio) is set to be larger than 0.2, and in a more preferred embodiment, the total draw ratio is further set to 13 or more. As a result, a precursor fiber having excellent spinning stability and extremely excellent tensile properties, denseness, and orientation can be obtained even if a wet spinning method is used.

  When the total draw ratio is less than 13, sufficient orientation cannot be given to the fiber, so that the denseness and the degree of orientation are not sufficient. Also, if the draft in the coagulation bath is increased by reducing the draw ratio in order to increase the productivity, the single fiber breakage tends to occur due to the high draft in the coagulation bath, and the stretchability is reduced and stabilized in the subsequent process. It is easy to cause deterioration. In addition, if the total draw ratio is too large, it is difficult to perform stable continuous spinning due to an increase in the draw load in primary stretching or secondary stretching. Therefore, the total draw ratio is preferably 25 or less under normal conditions.

  In addition, in order to fully exhibit the high stretchability of the pressurized steam stretching method and the properties that improve the denseness and degree of orientation of the fibers, the ratio of the secondary stretching ratio to the total stretching ratio should be larger than 0.2. is required. By doing so, the drawing load in the primary drawing can be reduced, so there is no occurrence of single fiber breakage, and there is no reduction in drawability or stability in pressurized steam drawing. Therefore, it is possible to obtain a precursor fiber that is satisfactory in all of denseness, congruency, mechanical properties, quality, and production stability. These phenomena become more prominent when the spinning speed is high. In addition, since the ratio of the secondary draw ratio to the total draw ratio is too large, the stability of continuous spinning tends to decrease due to an increase in the load of the secondary draw even if it is too large. It is preferable to make it 0.35 or less.

  When the carbon fiber obtained by firing the acrylonitrile-based precursor fiber for carbon fiber of the present invention is aligned in one direction to be a prepreg, it can be prepreg with a productivity about 30% higher than that of the conventional carbon fiber. This is because the carbon fiber acrylonitrile-based precursor fiber, and hence the carbon fiber, has less unevenness in the longitudinal direction, and thus the unevenness in the longitudinal direction of the fiber decreases.

Hereinafter, the present invention will be described more specifically with reference to examples. Of the following examples, Examples 1 and 3 to 6 are examples included in the scope of the present invention, and Example 2 is a reference example related to the present invention. Copolymer composition, intrinsic viscosity [η] of copolymer, tensile elastic modulus of coagulated fiber, tensile strength / elastic modulus of precursor fiber, and carbon fiber (abbreviated as CF in the table) in Examples and Comparative Examples Strand strength / elastic modulus, iodine adsorption amount, crystal orientation degree by wide-angle X-ray analysis, tow fineness fluctuation rate, surface roughness coefficient, fiber moisture content, and water vapor pressure fluctuation rate in pressurized steam drawing are as follows. It was measured.

(B) “Copolymer composition”
^It was measured by ¹ H-NMR method (JEOL GSX-400 type superconducting FT-NMR).

(B) “Intrinsic viscosity of copolymer [η]”
Measured with a dimethylformamide solution at 25 ° C.

(C) “Tensile modulus of coagulated fiber”
After collecting the coagulated fiber bundle, a tensile test with Tensilon was quickly conducted in an atmosphere at a temperature of 23 ° C. and a humidity of 50% at a sample length (grip interval) of 10 cm and a pulling speed of 100 m / min.

The elastic modulus was expressed by cN / dtex by obtaining the fineness of the coagulated fiber bundle (dtex: the weight of the copolymer per 10,000 m of coagulated fiber bundle) by the following formula.
dtex = 10000 × f × Qp / V
f: number of filaments, Qp: copolymer discharge amount per nozzle hole (g / min), V: solidified fiber take-up speed (m / min)
(D) "Tensile strength / elastic modulus of precursor fiber"
Single fibers were collected and subjected to a tensile test with Tensilon in an atmosphere of a temperature of 23 ° C. and a humidity of 50% at a sample length (grip interval) of 2 cm and a pulling speed of 2 cm / min.

  For the strength / elastic modulus display, the fineness (dtex; weight per 10000 m of single fiber) of the single fiber was obtained and indicated by cN / dtex.

(E) “Strand strength and elastic modulus of carbon fiber”
It measured according to JIS-7601.

(F) "Method for measuring iodine adsorption"
Precisely weigh 2 g of precursor fiber and place it in a 100 ml Erlenmeyer flask. 100 ml of an iodine solution (100 g of potassium iodide, 90 g of acetic acid, 10 g of 2,4-dichlorophenol, and 50 g of iodine dissolved in distilled water) was added to 100 ml, and the mixture was shaken at 60 ° C. for 50 minutes for iodine adsorption treatment. went. Thereafter, the adsorbed yarn is washed with ion-exchanged water for 30 minutes, rinsed with distilled water, and then subjected to centrifugal dehydration. The dehydrated yarn was put in a 300 ml beaker, 200 ml of dimethyl sulfoxide was added and dissolved at 60 ° C. This solution was subjected to potentiometric titration with an aqueous 0.01 mol / l silver nitrate solution to determine the amount of iodine adsorbed.

(G) “Measurement of crystal orientation by wide-angle X-ray analysis”
This is a value calculated from the half-value width H of the circumferential intensity distribution at the analysis point on the equator line of the polyacrylonitrile fiber by the wide-angle X-ray analysis method.
Degree of orientation π (%) = ((180−H) / 180) × 100
Wide-angle X-ray analysis (counter method)
(1) X-ray generator RU-200 manufactured by Rigaku Denki Co., Ltd.
X-ray source: CuKα (using Ni filter)
Output: 40KV 190mA
(2) Goniometer Rigaku Denki Co., Ltd. 2155D1
Slit system: 2MM 0.5 ° × 1 °
Detector: Scintillation counter (H) “Change rate of toe fineness”
In the longitudinal direction of the precursor fiber tow, 1 m long tow was cut accurately 100 times continuously, dried for 12 hours with a dryer at 85 ° C., and the weight after drying was measured. The rate of change was determined by the formula.
Fluctuation rate (%) = (σ / E) × 100
σ: Standard deviation of measurement data, E: Average value of measurement data (I) “Measurement method of surface roughness coefficient”
First, contrast conditions of the scanning electron microscope apparatus were adjusted using a magnetic tape as a standard sample. That is, using a high-performance magnetic tape as a standard sample, a secondary electron curve was observed under the conditions of acceleration voltage: 13 kV, magnification: 1000 times, scanning speed: 3.60 m / sec, and the average amplitude was about 40 mm. The contrast condition was adjusted so that Then, after such adjustment, temporary electrons are scanned in the direction perpendicular to the precursor fiber axis of the sample (fiber diameter direction), and the secondary (reflected) electron curve reflected from the fiber surface is displayed on the cathode ray tube using a line profile device. This was photographed on a film at a photographing magnification of 10,000 times. In this case, the acceleration voltage is 13 kV and the scanning speed is 0.18 cm / second.

  The secondary electron curve photograph thus obtained is further doubled at the time of printing, that is, the total magnification is 20000 times to obtain a secondary electron curve diagram (photograph). A typical example is shown in FIG. In the figure, d is the fiber diameter, d 'is the area obtained by removing 20% of the left and right ends of the fiber diameter, that is, the length in the diameter direction of the central portion of the fiber diameter, and d' = 0.6d. Further, l is the total length (linear conversion length) of the secondary electron curve in the range of d ′.

  From l and d ', the surface roughness coefficient is obtained by l / d'.

(Nu) "Measurement of moisture content of fiber"
The fiber was dried with an oven at 85 ° C. for 12 hours, and the weights W1 and W2 before and after drying were measured and calculated by the following formula.
Moisture content (%) = ((W1-W2) / W2) × 100
(L) “Variation rate of water vapor pressure in pressurized water vapor drawing”
In pressurized steam stretching, the pressure inside the stretching apparatus was monitored for 40 seconds, pressure data was collected every 0.04 seconds, and the variation rate was determined by the following equation.
Fluctuation rate (%) = (σ / E) × 100
σ: standard deviation of measurement data, E: average value of measurement data [Example 1]
A copolymer consisting of 97.1% by weight of acrylonitrile, 2.0% by weight of acrylamide and 0.9% by weight of methacrylic acid and having an intrinsic viscosity [η] of 1.7 is converted to dimethyl so as to have a copolymer concentration of 23% by weight. Dissolved in formamide to obtain a spinning dope. This spinning dope was discharged into a dimethylformamide aqueous solution having a concentration of 70% by weight and a temperature of 35 ° C. using a 12000 hole nozzle, and was wet-spun. The tensile modulus of the obtained coagulated fiber was 1.59 cN / dtex.

  Next, the coagulated fiber was washed and desolvated while being stretched 4.75 times in boiling water, then immersed in a silicone-based oil bath solution, and dried and densified with a 140 ° C. heating roller. The water content at this time was 0.1% by weight or less. Subsequently, the film was stretched 2.8 times in pressurized steam of 294 kPa · g and then re-dried to obtain a precursor fiber. The winding speed at this time was 100 m / min. In addition, during the pressurized steam stretching, the temperature of the heating roller immediately before the pressurized steam stretching apparatus is controlled to 140 ° C., and the variation rate of the steam pressure in the pressurized steam stretching is controlled to 0.2% or less, and supplied to the pressurized steam stretching chamber. Water vapor was removed from the liquid by a drain trap, and the temperature of the pressurized steam drawing chamber was adjusted to 142 ° C.

  The total draw ratio was 13.3, and the ratio of the secondary draw ratio to the total draw ratio was 0.21.

  In addition, the adjustment of the water vapor pressure in the pressurized water vapor drawing is performed by sending the data obtained by the Yamatake Honeywell's JPG940A and BSTJ300 pressure transmitters installed in the drawing machine to the Yokogawa Electric PID digital indicating and adjusting machine. Was performed by changing the opening degree of the automatic pressure control valve.

  During the spinning process, almost no single fiber breakage or fluff was observed, and the spinning stability was good. This precursor fiber has a tensile strength of 7.5 cN / dtex, a tensile elastic modulus of 147 cN / dtex, an iodine adsorption amount of 0.2% by weight, a crystal orientation degree π of 93% by wide-angle X-ray analysis, and a variation rate of tow fineness. Was 0.6% and the surface slip coefficient was 3.0.

This fiber was heat-treated for 30 minutes in a hot-air circulating flame-proofing furnace at 230 to 260 ° C. in air while giving 5% elongation to obtain a flame-resistant fiber having a fiber density of 1.368 g / cm ^3. A low temperature heat treatment is performed for 1.5 minutes at a maximum temperature of 600 ° C. and an elongation rate of 5% in a nitrogen atmosphere, and further, about 1.5% under a high temperature heat treatment furnace having a maximum temperature of 1400 ° C. under a −4% elongation. Minute processed. The obtained carbon fiber had a strand strength of 4800 MPa and a strand elastic modulus of 284 GPa.

[Comparative Examples 1-3]
The coagulation bath conditions were 60% by weight of a dimethylformamide aqueous solution (Comparative Example 1) at a temperature of 35 ° C., 73% by weight of a dimethylformamide aqueous solution (Comparative Example 2) at a temperature of 35 ° C., a concentration of 70% by weight and a temperature of 50 ° C. Spinning was carried out in the same manner as in Example 1 except that the aqueous solution was dimethylformamide (Comparative Example 3).

  In Comparative Example 1, fluff was frequently generated, and it was difficult to obtain precursor fibers continuously. In Comparative Examples 2 and 3, after obtaining the precursor fiber, it was fired under the same conditions as in Example 1. Table 1 shows the tensile elastic modulus of the coagulated fiber, the fuzziness of the precursor fiber, the tensile strength and elastic modulus, the amount of iodine adsorbed, the wide-angle X-ray orientation, and the strand properties of the carbon fiber.

[Comparative Examples 4 and 5]
The conditions of the pressurized steam stretching are respectively the temperature of the heating roller immediately before the pressurized steam stretching apparatus is 195 ° C., the variation rate of the steam pressure in the pressurized steam stretching is about 0.7% (Comparative Example 4), the heating just before the pressurized steam stretching apparatus Spinning was carried out in the same manner as in Example 1 except that the temperature of the roller was 140 ° C., the fluctuation rate of the water vapor pressure in pressurized steam drawing was about 0.7% (Comparative Example 5).

  In Comparative Example 4, the variation rate of the toe fineness of the precursor fiber was 1.7%, and in Comparative Example 5, the variation rate of the toe fineness of the precursor fiber was 1.2%.

[Examples 2 to 4]
The same acrylonitrile copolymer as in Example 1 was used, and a dimethylacetamide solution having a copolymer concentration of 21% by weight was used as a spinning stock solution. In a dimethylacetamide aqueous solution having a concentration of 70% by weight and a temperature of 35 ° C. using a 12,000-hole nozzle. And wet spinning.

  Subsequently, the fiber was stretched 1.5 times in the air, washed and desolvated while being stretched in boiling water, then immersed in a silicon-based oil bath solution, and dried and densified with a 140 ° C. heating roller. . Subsequently, after stretching in pressurized steam of 294 kPa · g, re-drying was performed to obtain a precursor fiber. The winding speed at this time was 100 m / min. In addition, during the pressurized steam stretching, the temperature of the heating roller immediately before the pressurized steam stretching apparatus is controlled to 140 ° C., and the variation rate of the steam pressure in the pressurized steam stretching is controlled to 0.2% or less, and supplied to the pressurized steam stretching chamber. Water vapor was removed from the liquid by a drain trap, and the temperature of the pressurized steam drawing chamber was adjusted to 142 ° C.

  Furthermore, this fiber was baked on the same conditions as Example 1, and the carbon fiber was obtained. Ratio of secondary draw ratio to total draw ratio and total draw ratio, tensile modulus of coagulated fiber, fluff degree of precursor fiber, tensile strength and modulus, iodine adsorption, wide-angle X-ray orientation, tow fineness The variation rate and the strand characteristics of the carbon fiber are shown in Table 1.

[Comparative Example 6]
The ratio of the secondary draw ratio to the total draw ratio was the value shown in Table 1, and the other conditions were the same as in Example 2. Further, this fiber was fired under the same conditions as in Example 2 to obtain a carbon fiber. Table 1 shows the tensile elastic modulus of the coagulated fiber, the degree of fluff of the precursor fiber, the tensile strength and elastic modulus, the amount of iodine adsorbed, the wide-angle X-ray orientation degree, and the strand characteristics of the carbon fiber.

[Comparative Examples 7 to 11]
The composition of the acrylonitrile copolymer was set to the value shown in Table 2, and all other conditions were obtained in the same manner as in Example 2 to obtain a precursor fiber, followed by further firing. Table 2 shows the tensile elastic modulus of each coagulated fiber, the degree of fluff of the precursor fiber, the tensile strength and elastic modulus, the amount of iodine adsorbed, the wide-angle X-ray orientation, and the strand properties of the carbon fiber. In the case of Comparative Example 7, combustion and smoke generation occurred in the flameproofing process.

[Example 5]
The same acrylonitrile copolymer as in Example 1 was used, and a dimethylacetamide solution having a copolymer concentration of 21% by weight was used as a spinning stock solution. In a dimethylacetamide aqueous solution having a concentration of 70% by weight and a temperature of 35 ° C. using a 12,000-hole nozzle. Wet spinning.

  Subsequently, this fiber was stretched 1.5 times in the air, washed and desolvated while being stretched in boiling water, then immersed in a silicone-based oil bath solution, and dried and densified with a 160 ° C. heating roller. . Subsequently, after stretching in pressurized steam of 294 kPa · g, re-drying was performed to obtain a precursor fiber. The winding speed at this time was 140 m / min. In addition, during the pressurized steam stretching, the temperature of the heating roller immediately before the pressurized steam stretching apparatus is controlled to 140 ° C., and the variation rate of the steam pressure in the pressurized steam stretching is controlled to 0.2% or less, and supplied to the pressurized steam stretching chamber. Water vapor was removed from the liquid by a drain trap, and the temperature of the pressurized steam drawing chamber was adjusted to 142 ° C.

  Furthermore, this fiber was baked on the same conditions as Example 1, and the carbon fiber was obtained. Ratio of secondary draw ratio to total draw ratio and total draw ratio, tensile elastic modulus of coagulated fiber, degree of fluff of precursor fiber, tensile strength and elastic modulus, iodine adsorption amount, wide-angle X-ray orientation degree, tow fineness fluctuation rate Table 2 shows the strand characteristics of carbon fiber and carbon fiber.

[Example 6]
The obtained carbon fibers obtained in Comparative Example 4 were each formed into a sheet-like shape so that the carbon fiber basis weight was 125 g / m ² . A resin film (resin basis weight 27 g / m ² ) coated with Mitsubishi Rayon Co., Ltd. epoxy resin # 340 on the release paper is stacked on the upper and lower surfaces so that the epoxy resin is in contact with the carbon fiber, passed through a prepreg manufacturing machine, and 125 g / An m ² prepreg was produced. As the production rate was gradually increased, the spreadability of the carbon fibers was lowered, and about 1 mm wide splits without carbon fibers were generated at 2 to 3 locations every 4 to 5 m. The prepreg manufacturing machine used at this time was composed of 7 pairs of heated flat metal press rolls, 1 pair of cooling rolls, and 1 pair of rubber take-up rolls, and an epoxy resin was applied onto the release paper. The carbon fiber is supplied in a state of being sandwiched between the resin films, heated on the surface of the press roll to fluidize and press the resin, and the carbon fiber layer is impregnated with the resin. Then, after cooling, it is taken up by a pair of rubber rolls to obtain a prepreg.

  Next, when the carbon fiber was replaced with the carbon fiber obtained in Example 1, a prepreg without split was stably produced even at a production rate 30% higher than the production rate at which splitting occurred in the carbon fiber of Comparative Example 4. did it.

[Comparative Example 12]
Example 1 An acrylonitrile-based precursor fiber for carbon fiber was obtained in the same manner as in Example 1 except that the roller temperature before the heated steam stretching apparatus was 115 ° C. There was much fuzz and winding was difficult.

  According to the present invention, carbon capable of producing high-quality carbon fiber at a low cost by firing in a shorter time, high strength, high elastic modulus, high density and high degree of orientation, and low tow fineness variation rate An acrylonitrile-based precursor fiber for fibers can be provided.

  In addition, the acrylonitrile-based precursor fiber for carbon fiber having such properties can be stably produced at high speed with no generation of fuzz by a wet spinning method without causing yarn breakage for a long time.

  The acrylonitrile-based precursor fiber for carbon fiber of the present invention has little longitudinal fineness unevenness, and the carbon fiber obtained by firing the same has little longitudinal fineness unevenness. As a result, the unevenness of the spreadability in the longitudinal direction is reduced, so that the prepreg can be formed with a productivity about 30% higher than that of the conventional carbon fiber.

It is a secondary electron curve figure for measuring a surface roughness coefficient.

Explanation of symbols

d Fiber diameter d ′ The total length of the secondary electron curve in the range of the length l d ′ of the diameter direction of the central portion 60% of the fiber diameter (linear conversion length)

Claims (4)

An acrylonitrile copolymer comprising 96.0 to 98.5% by weight of acrylonitrile units, 1.0 to 3.5% by weight of acrylamide units, and 0.5 to 1.0% by weight of carboxyl group-containing vinyl monomer units is wet. spun involves pulling after the elastic modulus was coagulated fiber is 1.1~1.59cN / dtex, after primary drawing by Shin Nakanobu bath with the bath during stretching or air stretching, the pressurized steam drawing In the method for producing acrylonitrile-based precursor fiber for carbon fiber that performs secondary stretching, the temperature of the heating roller immediately before introducing the yarn into the pressurized steam stretching apparatus is set to 120 to 190 ° C. The water vapor pressure fluctuation rate is controlled to 0.5% or less, and stretching is performed such that the ratio of the secondary stretching ratio to the total stretching ratio is greater than 0.2. Method of producing a carbon fiber for acrylonitrile based precursor fiber.   The method for producing an acrylonitrile-based precursor fiber for carbon fiber according to claim 1, wherein the total draw ratio is 13 or more. The method for producing an acrylonitrile-based precursor fiber for carbon fiber according to claim 1 or 2 , wherein a water vapor pressure at the time of the pressurized water vapor stretching is 200 kPa (gauge pressure) or more. The method for producing an acrylonitrile-based precursor fiber for carbon fiber according to any one of claims 1 to 3 , wherein the moisture content of the fiber when performing the pressurized steam drawing is 2% by weight or less.

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