JP6728938B2 - Carbon fiber precursor fiber bundle and method for producing carbon fiber bundle - Google Patents

Description

The present invention relates to a method for producing a carbon fiber precursor fiber bundle for obtaining a high-performance and high-quality carbon fiber bundle, and a method for producing a carbon fiber bundle.

Since carbon fiber has higher specific strength and specific elastic modulus than other fibers, it is used as a reinforcing fiber for composite materials in addition to conventional sports and aviation/space applications, as well as automobiles, civil engineering/construction, pressure vessels and It is widely used for general industrial applications such as wind turbine blades, and there is a strong demand for both higher performance and lower cost.

Among the carbon fibers, the most widely used polyacrylonitrile-based carbon fiber is a carbon fiber precursor fiber obtained by wet spinning, dry spinning or dry-wet spinning a spinning solution composed of a polyacrylonitrile polymer as a precursor. After obtaining the bundle, by heating it in an oxidizing atmosphere at a temperature of 180 to 400° C. to convert it into a flameproof fiber bundle, and heating it in an inert atmosphere at a temperature of at least 1000° C. to carbonize it. Manufactured industrially.

Since carbon fiber is a brittle material and causes strength reduction due to slight surface defects and internal defects, delicate attention has been paid to the generation of defects. It is natural to remove foreign substances such as dust in the raw material, but it is not only the strength decrease that the gel-like substance formed by the spinning solution partially staying and thermally degrading is removed from the spinneret before it is discharged. It has also been performed in order to reduce yarn breakage in the yarn making/firing process during discharging. For example, a method of filtering using a filter having an opening diameter of 5 μm or less (see Patent Document 1) or a method of using a sintered metal filter having a filtration accuracy of 5 μm or less (see Patent Document 2), and the opening diameter in stages A method (see Patent Document 3) has been proposed in which the size is made smaller to perform multistage filtration.

Further, since carbon fiber has a high manufacturing cost, various methods for reducing the manufacturing cost have been studied. In order to reduce the production cost of carbon fibers, the inventors of the present invention propose a technique capable of increasing the spinning speed and the spinning draft rate by using a polyacrylonitrile-based polymer having a specific molecular weight distribution. (See Patent Document 4).

JP-A-58-220821 JP-A-59-88924 JP 2004-27396 A JP, 2008-248219, A

However, with the method of simply reducing the aperture diameter of the filter and the filtration accuracy as in Patent Documents 1 and 2, clogging of the filter is accelerated and the filtering pressure increase rate of the filter is significantly increased. In other words, there is a problem that the filter life is short and it is necessary to stop the spinning process every time the filter is replaced. Further, in the method of Patent Document 3, since filtration is performed in multiple stages, an extra space for installing the filter device is required, which makes mass production difficult in a limited space.

Further, when the polyacrylonitrile-based polymer of Patent Document 4 is filtered with a filter, there is a problem that a pressure rise during filter filtration is likely to occur and the filter life is likely to be shortened.

The present invention solves the above-mentioned problems with the prior art, that is, not only can foreign matters such as gels be filtered accurately from the spinning solution before filtration, but also clogging of the filter medium can be suppressed. It is an object of the present invention to propose a method capable of stably producing a high quality carbon fiber precursor fiber bundle and a carbon fiber bundle.

In order to achieve the above object, a method for producing a carbon fiber precursor fiber bundle according to an embodiment of the present invention has the following configuration. That is, in the method for producing a carbon fiber precursor fiber bundle of the present invention, when obtaining a carbon fiber precursor fiber bundle by spinning a spinning solution in which a polyacrylonitrile-based polymer is dissolved in a solvent, prior to spinning, filtration accuracy Filtering the spinning solution using a filter medium having B (μm) and a filter medium thickness C (μm) and a condition that the filtration rate A (cm/hour) satisfies the following formulas (1) and (2). And a method for producing a carbon fiber precursor fiber bundle.

A ³ ≦−100×B+0.3×C+150 (1)
0.1≦A≦15 (2).

In order to achieve the above object, a method for producing a carbon fiber precursor fiber bundle according to another embodiment of the present invention has the following configuration. That is, in the method for producing a carbon fiber precursor fiber bundle of the present invention, when obtaining a carbon fiber precursor fiber bundle by spinning a spinning solution in which a polyacrylonitrile-based polymer is dissolved in a solvent, prior to spinning, filtration accuracy Using a filter medium having B (μm) and a basis weight D (g/m ² ) of the filter medium, the spinning solution is filtered under the condition that the filtration rate A (cm/hour) satisfies the following formulas (3) to (5). A method for producing a carbon fiber precursor fiber bundle, comprising:

D−600/(α×β)≧0 (3)
α=1-1(1+exp(7-A)) (4)
β=1-1(1+exp(−0.23×B)) (5).

In addition, in the method for producing a carbon fiber precursor fiber bundle of the present invention, it is also preferable to filter the spinning solution under conditions satisfying all the expressions (1) to (5).

According to the present invention, regardless of the molecular weight distribution of the polyacrylonitrile-based polymer used, not only can foreign matter in the spinning solution be efficiently removed, but high performance and high-quality stability can be achieved by suppressing clogging of the filter. As a result, a carbon fiber precursor fiber bundle that can obtain a high quality carbon fiber bundle can be manufactured. Furthermore, a high-strength carbon fiber bundle can be manufactured.

The present inventors have arrived at the present invention as a result of extensive studies on a method for producing a carbon fiber precursor fiber bundle capable of suppressing clogging of a filter while maintaining high quality.

The carbon fiber precursor fiber bundle of the present invention is obtained by spinning a spinning solution in which a polyacrylonitrile-based polymer is dissolved in a solvent. The polyacrylonitrile-based polymer used in the present invention is not only a homopolymer obtained only from acrylonitrile, but also a polyacrylonitrile-based copolymer using another monomer in addition to acrylonitrile as the main component. good.

The monomer used to obtain the polyacrylonitrile polymer is preferably 90 to 100% by mass of acrylonitrile, and the copolymerizable monomer is preferably less than 10% by mass. The flameproofing reaction is promoted by adding a copolymerizable monomer, but the smaller the amount, the more the fusion of fibers in the firing process for converting the carbon fiber precursor fiber bundle into the carbon fiber bundle. Therefore, the amount of the copolymerizable monomer is more preferably 0.1 to 2% by mass, since the excellent quality and performance of the obtained carbon fiber bundle can be maintained. When the amount of the copolymerizable monomer is 0.1% by mass or more, the flameproofing reaction accelerating effect is often sufficient, and when the amount of the copolymerization is 2% by mass or less, the flameproofing is sufficiently performed inside the flameproof yarn. The reaction is likely to proceed and often satisfies the range of the peak intensity ratio of the infrared spectrum described later.

Examples of the monomer copolymerizable with acrylonitrile include acrylic acid, methacrylic acid, itaconic acid and their alkali metal salts, ammonium salts and lower alkyl esters, acrylamide and its derivatives, allylsulfonic acid, methallylsulfonic acid and Those salts or alkyl esters can be used.

In the present invention, a polyacrylonitrile polymer having a weight average molecular weight (hereinafter abbreviated as Mw) of 300,000 to 500,000 is preferably used. In the case of a polyacrylonitrile polymer having a Mw of 300,000 or more, the connection between the molecular chains in the fiber axis direction is improved, so that it can withstand high drawing in the spinning and firing steps, and the strength as carbon fiber is increased. You can Further, when a polyacrylonitrile-based polymer having a Mw of 500,000 or less is used, the entanglement of molecular chains can be set within an appropriate range. Therefore, even when such a high-molecular-weight polyacrylonitrile-based polymer is used, the weight in the spinning solution is increased. It is not necessary to lower the coalescence concentration, and high productivity can be maintained. The polyacrylonitrile-based polymer preferably has a polydispersity Mz/Mw represented by the ratio of the Z average molecular weight (hereinafter, abbreviated as Mz) and Mw of 1.5 to 6.0, More preferably, it is 2.7 to 6.0.

In the present invention, the above-mentioned various average molecular weights are measured by a gel permeation chromatograph (hereinafter abbreviated as GPC) method and are obtained as polystyrene equivalent values. The polydispersity Mz/Mw has the following meaning. That is, the number average molecular weight Mn (hereinafter abbreviated as Mn) sensitively receives the contribution of the low molecular weight substances contained in the polymer compound. On the other hand, Mw is sensitively influenced by the high molecular weight substance contained in the high molecular weight compound, and Mz is more sensitively influenced by the high molecular weight substance. Therefore, by using the polydispersity Mw/Mn or Mz/Mw, the spread of the molecular weight distribution can be evaluated. When Mw/Mn is 1, it is monodisperse, and as this value increases, the molecular weight distribution becomes broad around the low molecular weight side, whereas as Mz/Mw increases, the molecular weight distribution increases. It shows that the high molecular weight is the center. As described above, since Mw/Mn and Mz/Mw show different points, a large Mw/Mn does not necessarily mean a large Mz/Mw.

When Mz/Mw is 1.5 or more, the drawability is high, and the carbon fiber precursor fiber bundle can be in a satisfactory orientation state. Further, when Mz/Mw is 6.0 or less, the entanglement of the polyacrylonitrile-based polymer can be suppressed within an appropriate range, and troubles such as difficulty in discharging the spinning solution from the spinneret can be suppressed. You can When Mz/Mw is in the range of 2.7 to 6.0, strain hardening is strongly expressed, the stability of the spinning solution is improved, and the productivity can be greatly improved, which is preferable.

By using a polyacrylonitrile polymer having a polydispersity Mz/Mw of 2.7 to 6.0, the spinning draft can be increased and the spinning speed can be increased. The spinning draft is defined as the surface speed of a roller having a driving source with which the spinning solution leaves the spinneret and comes into contact with the spinning solution for the first time (hereinafter, abbreviated as the take-up speed of the coagulated yarn). Value divided by the linear velocity (hereinafter, may be abbreviated as ejection linear velocity). The discharge linear velocity is a value obtained by dividing the volume of the spinning solution discharged per unit time (hereinafter, may be abbreviated as discharge amount) by the total area of the spinneret holes. Therefore, the discharge linear velocity is determined by the relationship between the discharge amount of the spinning solution, the number of holes in the spinneret, and the hole diameter. The spinning solution exits the spinneret, contacts the coagulation bath, and gradually solidifies to become a coagulated yarn. At this time, the spun yarn passing through the coagulation bath is pulled by the first roller, but the uncoagulated spinning solution is more easily stretched than the spun yarn, so the spinning draft almost solidifies the spinning solution. It is synonymous with the magnification that is stretched by. That is, the spinning draft is represented by the following formula.
-Spun draft = (take-off speed of coagulated yarn) / (discharge linear velocity).

If the spinning draft can be increased, the take-up speed of the coagulated yarn can be increased without increasing the discharge linear velocity, so that the spinning speed can be increased. Further, the critical spinning draft is a critical speed at which the coagulated yarn can be wound up without causing yarn breakage, and the higher the critical spinning draft is, the higher the spinning speed becomes, which is preferable. ..

The mechanism by which the spinning draft can be increased by setting the polydispersity Mz/Mw to 2.7 to 6.0 has not been clarified, but is considered as follows. When the polyacrylonitrile-based polymer solution is stretched and deformed immediately after the spinneret hole, the ultrahigh molecular weight substance and the high molecular weight substance are entangled, and the molecular chain between the entanglement points around the ultrahigh molecular weight substance becomes tense to increase the extensional viscosity. A sharp increase, that is, strain hardening occurs. As the polyacrylonitrile-based polymer solution is thinned, the extensional viscosity of the thinned portion is increased and the flow is stabilized, so that the spinning draft can be increased and the spinning speed can be increased.

The above-mentioned polyacrylonitrile-based polymer is dissolved in a solvent in which the polyacrylonitrile-based polymer is soluble, such as dimethyl sulfoxide, dimethylformamide, dimethylacetamide, nitric acid, an aqueous solution of zinc chloride, an aqueous solution of rhodanese, to prepare a spinning solution. When using solution polymerization for the production of polyacrylonitrile-based polymer, if the solvent used for the polymerization and the spinning solvent are the same, the resulting polyacrylonitrile-based polymer is separated, the step of redissolving in the spinning solvent is It is unnecessary and preferable.

In the present invention, prior to spinning the spinning solution as described above, it is passed through a filter device to remove polymer raw materials and impurities mixed in each step. The filter device in the present invention means a facility for filtering and removing foreign substances existing in the spinning solution, and an inflow path for guiding the spinning solution to be filtered into the filter device and for filtering the spinning solution. The filter medium, the outflow passage for guiding the filtered spinning solution to the outside of the filter device, and the container for accommodating them. Here, the filter medium is a means for filtering the spinning solution contained in the filter device.

As the form of the filter medium, leaf disk type, candle type, pleated candle type and the like are used. In contrast to the candle type and pleated candle type in which the filter medium has a certain curvature, the leaf disk type filter has the advantage that the aperture size distribution is difficult to spread and the cleaning property is easy to maintain because the filter medium can be used in a nearly flat shape. ,preferable.

The filter medium used in the present invention is a part that plays a direct role in removing foreign substances existing in the spinning solution, and it is required to hold the defined opening diameter with a narrow variation. Chemical stability, heat resistance and pressure resistance to some extent with respect to the substance to be treated are required. As such a filter medium, a wire mesh produced by weaving metal fibers, a glass nonwoven fabric, a filter medium made of a sintered metal fiber structure, or the like is preferably used. The material of the filter medium is not particularly limited as long as it is inert to the spinning solution and has no component eluted in the solvent, but metal is preferable from the viewpoint of strength and cost. Specific metals include stainless steel (SUS304, SUS304L, SUS316, SUS316L, etc.), Inconel (registered trademark), Hastelloy (registered trademark), and various alloys based on nickel, titanium, and cobalt. The manufacturing method of the metal fiber is a so-called converging fiber manufacturing method in which a large number of wire rods are bundled into a bundle and the wire diameter is reduced and then each wire is separated to reduce the wire diameter, a coil cutting method, and a chatter vibration cutting method. And so on. In the case of a wire net, it is necessary to use single fibers instead of fiber bundles, and thus it can be obtained by a method of repeating wire drawing and heat treatment.

In filtration of the spinning solution, the smaller the filtration accuracy is, the easier it is to remove foreign matter in the spinning solution, but the clogging of the filter medium is likely to occur. Further, the thicker the filter, the easier it is to remove the foreign matter in the spinning solution, but the pressure loss in the filter medium increases and the stability of the manufacturing process decreases. Up to now, the above-mentioned tendency has been known, but the optimum filtration conditions differ for each filter medium, and no finding has been obtained that can be generalized to filtration of the spinning solution. Therefore, when changing the filter medium, it takes a huge amount of time and cost to optimize the filtration conditions.

Therefore, as a result of intensive studies conducted by the present inventors, as one embodiment, a filter medium having a filtration accuracy B (μm) and a filter medium thickness C (μm) is used, and a filtration rate A (cm/hour) By filtering the spinning solution under conditions satisfying (1) and the following formula (2), both efficient removal of foreign matter in the spinning solution and suppression of filter clogging are achieved, and stable and high-quality carbon is obtained. It has been found that a fiber precursor fiber bundle can be produced.

A ³ ≦−100×B+0.3×C+150 (1)
0.1≦A≦15 (2).

Here, the filtration rate A (cm/hour) is the filtration amount (cm ³ /hour) of the spinning solution per unit time that passes through the unit area (cm ² ) of the filter medium, and per unit time It can be calculated by dividing the filtration rate (cm ³ /hour) of the spinning solution by the total area (cm ² ) of the filter medium. The filtration accuracy B (μm) is the particle size (diameter) of spherical particles that can collect 95% while passing through the filter medium, and is measured according to the JIS standard method (JIS-B8356-8). I can. Further, if the relationship between the bubble point and the filtration accuracy obtained by the JIS standard method (JIS-K3832) is investigated in advance, the filtration accuracy can be estimated from the value of the bubble point. The filter medium thickness C (μm) is calculated by cutting out a vertical cross section of the filter medium and using the average value of arbitrary 5 points observed with a microscope or the like. When the filter medium is laminated instead of a single layer, the value obtained by adding the average values of the thicknesses of the layers is defined as the filter medium thickness C. In addition, when the protective layer which does not participate in the removal of foreign matters and is only intended to improve the strength of the filter medium is included, the thickness excluding the protective layer is defined as the filter medium thickness C.

When the filtration rate A is within the range defined by the formulas (1) and (2), it is possible to improve the quality of the carbon fiber precursor fiber bundle and suppress the clogging of the filter.

When the filter material thickness C is a constant value, the upper limit of the filtration speed A at which both the improvement of the quality of the carbon fiber precursor fiber bundle and the suppression of the filter clogging can be measured. , And the coefficient is 100. When Formula (1) is satisfied by reducing the value of the filtration accuracy B, it is possible to suppress deterioration of the quality of the carbon fiber precursor fiber bundle. Further, if Expression (1) is satisfied by reducing the value of the filtration rate A, the clogging of the filter can be suppressed.

When the filtration accuracy B is a constant value, the upper limit of the filtration speed A at which both the improvement of the quality of the carbon fiber precursor fiber bundle and the suppression of the filter clogging can be measured. , And the coefficient is 0.3. When the formula (1) is satisfied by increasing the value of the filter medium thickness C, it is possible to suppress the deterioration of the quality of the carbon fiber precursor fiber bundle. Further, if Expression (1) is satisfied by reducing the value of the filtration rate A, the clogging of the filter can be suppressed.

When the filtration rate A is larger than 0.1, the total area of the filter medium is not significantly increased and the spinning speed is not extremely lowered, and therefore the production can be performed with economical equipment. When the filtration rate A is less than 15, the pressure loss when passing through the filter medium can be kept within a certain range, so that the stability of the manufacturing process can be maintained. The filtration rate A is preferably less than 8 and more preferably less than 3.

When the filtration rate A is included in the range defined by the formula (1) and the formula (2), the mechanism that can improve the quality of the carbon fiber precursor fiber bundle and suppress the clogging of the filter is described below. Can be thought of as.

That is, the larger the value of the filtration accuracy B is, the harder it is to capture foreign matter. However, by reducing the filtration rate A, it is possible to prevent the foreign matter from slipping through the filter medium, and thus the equations (1) and (2) are changed. It is considered that the fall rate of foreign matter can be suppressed in the range satisfying the condition. Further, as the value of the filtration accuracy B is smaller, the foreign matter is caught in the flow passage in the filter medium, so that the capturing rate of the foreign matter is increased. However, the deformation of the foreign substance completely blocks the flow passage, so that the filter medium is easily clogged. .. However, by reducing the filtration rate A, it is possible to suppress the deformation of the foreign matter, and therefore it is possible to prevent the flow path in the filter medium from being completely blocked by the deformation of the foreign matter and to prevent clogging of the filter medium. To be

For the above reasons, it is possible to achieve both improvement of the quality of the carbon fiber precursor fiber bundle and suppression of filter clogging within the range where the expressions (1) and (2) are satisfied. Regarding the filter medium thickness C, the larger the filter medium thickness C, the easier it is to capture the foreign matter. Therefore, if the filtration rate A is increased, the foreign matter capture rate decreases as long as the equation (1) and the equation (2) are satisfied. do not do.

Further, as a result of intensive studies by the present inventors, as another embodiment of the present invention, the filtration rate A (cm/hour), the filtration accuracy B (μm) of the filter medium, and the basis weight D (g/m ² ) of the filter medium. ) Satisfies the following formulas (3) to (5), the spinning solution is filtered, thereby efficiently removing foreign matters in the spinning solution and suppressing clogging of the filter. It has been found that the carbon fiber precursor fiber bundle of can be manufactured.

D−600/(α×β)≧0 (3)
α = 1-1/(1+exp(7-A)) (4)
β = 1-1/(1+exp(−0.23×B)) (5).

In the present invention, the filter material basis weight D (g/m ² ) is the total basis weight of the filter medium body, excluding the mesh layers that may be laminated for the purpose of protecting the filter medium body, and has an arbitrary area. It can be calculated by measuring the mass of the cut filter media and dividing this mass by the area.

The larger the basis weight D of the filter medium is, the higher the capturing rate of the foreign matter is. Then, the effect of the filter material areal weight D on the improvement of the quality of the carbon fiber precursor fiber bundle and the suppression of the clogging of the filter was measured while changing the filtration speed A and the filtration accuracy B, and at any filtration speed and filtration accuracy. It was confirmed that there exists the lowest filter material areal weight (hereinafter, referred to as the minimum filter material areal weight) capable of both improving the quality of the carbon fiber precursor fiber bundle and suppressing the clogging of the filter. According to the results of this experiment, the minimum filter material areal weight can be expressed by using the mutually independent parameters α and β as shown in the second term on the left side of the equation (3), and α is the filtration represented by the equation (4). As a function of velocity A, β is defined as a function of filtration accuracy B shown in equation (5). The larger the α×β, the smaller the minimum filter material areal weight, and the smaller α×β, the larger the minimum filter material areal weight. As for the movements of individual variables, the larger the filtration rate A is, the smaller α is and the larger the minimum filter material areal weight is. The smaller the filtration rate A is, the larger α is and the smaller the minimum filter material areal weight is. Similarly, the larger the filtration accuracy B is, the smaller β is and the larger the minimum filter material weight is, and the smaller the filtration accuracy B is, the larger β is and the smaller the minimum filter material weight is. Although the mechanism by which the improvement of the quality of the carbon fiber precursor fiber bundle and the suppression of the clogging of the filter can be achieved at the same time by performing the filtration under the conditions satisfying the expressions (3) to (5) is not always clear, Can be thought of as. That is, the smaller the filtration accuracy is, the more easily foreign matter is caught in the flow path in the filter medium, and the foreign matter can be effectively trapped. On the other hand, the filter is easily clogged. It is considered that the flow path in the filter medium is unlikely to be clogged because the deformation and spread of the foreign matter in the filter medium are suppressed.

When a polyacrylonitrile-based polymer having a polydispersity Mz/Mw of 2.7 to 6.0 is used as the polyacrylonitrile-based polymer in the spinning solution, the formula (1) and the formula (2), or the formula Under the conditions satisfying (3) to (5), it is possible to improve the quality of the carbon fiber precursor fiber bundle and suppress the clogging of the filter at the same time, and further improve the productivity by improving the spinning speed. It is possible.

A mechanism capable of achieving both improvement in quality of carbon fiber precursor fiber bundles and suppression of filter clogging even when a polyacrylonitrile-based polymer having a polydispersity Mz/Mw of 2.7 to 6.0 is used. Although it has not been clarified yet, it can be considered as follows.

In the polyacrylonitrile-based polymer having the above-mentioned specific molecular weight distribution, the smaller the filtration accuracy B is, the higher the shear rate is, and the clogging due to the deposition of the high molecular weight component in the filter medium is likely to occur. ) And equation (2) or equations (3) to (5) are satisfied, the shear rate can be kept below a certain level, and the deposition of components having a high molecular weight can be suppressed. Further, the larger the filter medium thickness C or the filter medium basis weight D, the more easily components with a high molecular weight are deposited in the filter medium, but in the range that satisfies the formulas (1) and (2), or the formulas (3) to (5). The shear rate can be kept below a certain level, and the deposition of high molecular weight components can be suppressed.

Further, in the present invention, it is preferable that the filtration accuracy B (μm) satisfies the following formula (6).
B≧3 (6).

When the filtration accuracy B is 3 or more, the clogging of the filter can be suppressed more effectively. The reason for this phenomenon is not clear, but it is considered as follows. By reducing the filtration rate A, the deformation of the foreign matter can be suppressed, and it is possible to prevent the flow path in the filter medium from being completely blocked by the deformation of the foreign matter, but as the value of the filtration accuracy B increases, the filtration pressure tends to decrease, Since the degree of deformation of foreign matter is reduced, the effect of suppressing filter clogging is likely to appear.

When a polyacrylonitrile-based polymer having a polydispersity Mz/Mw of 2.7 to 6.0 is used as the polyacrylonitrile-based polymer in the spinning solution, [Formula (1) and Formula (2)] and Alternatively, under the condition that the formula (6) is satisfied in addition to the [formulas (3) to (5)], the effect of suppressing the clogging of the filter can be made more effective. The mechanism is considered as follows.

That is, when the filtration accuracy B is 3 or more, the shear rate received when passing through the filter medium can be suppressed to a lower range, and the deposition of components having a high molecular weight can be suppressed more effectively. It is considered that the effect of suppressing filter clogging seen in (1) and formula (2)] and/or [formulas (3) to (5)] becomes more prominent.

In the present invention, the spinning solution filtered as described above is spun by a wet or dry-wet spinning method to produce a carbon fiber precursor fiber bundle. Among them, the dry-wet spinning method is particularly preferably used because it exhibits the characteristics of the polyacrylonitrile-based polymer having the above-mentioned specific molecular weight distribution.

The spinning solution is introduced into a coagulation bath to be coagulated, and the coagulated fiber obtained is passed through a washing process, a drawing process in a bath, an oil agent applying process and a drying process to obtain a carbon fiber precursor fiber bundle. Further, a dry heat drawing step or a steam drawing step may be added to the above steps. The coagulated yarn may be drawn directly in the bath by omitting the water washing step, or may be drawn in the bath after removing the solvent by the water washing step. In-bath stretching is usually preferably carried out in a single or a plurality of stretching baths whose temperature is controlled at 30 to 98°C.

The average fineness of the single fibers contained in the carbon fiber precursor fiber bundle thus obtained is preferably 0.5 to 1.5 dtex, more preferably 0.5 to 1.1 dtex, and 0 More preferably, it is 0.5 to 0.8 dtex. By setting the single fiber fineness to 0.5 dtex or more, the occurrence of yarn breakage due to contact with a roller or a guide can be suppressed, and the process stability in the yarn making process and the firing process of the carbon fiber bundle can be maintained. In addition, by setting the single fiber fineness to 1.5 dtex or less, the difference in the internal and external structures of each single fiber after flame resistance is reduced, and the processability in the subsequent carbonization step, the tensile strength and the tensile elasticity of the obtained carbon fiber bundle are increased. The rate can be improved. If the single fiber fineness is 1.1 dtex or less, it is easy to suppress the difference between the inner and outer structures without significantly reducing the flameproofing treatment rate, and it is sufficient to set it to 0.8 dtex or less.

The resulting carbon fiber precursor fiber bundles are usually in the form of continuous fibers. The number of filaments per yarn is preferably 1,000 to 36,000.

Since the carbon fiber precursor fiber bundle of the present invention is a high-quality carbon fiber precursor fiber bundle in which foreign substances are reduced, a firing step (specifically, flameproofing treatment, preliminary carbonization treatment, and carbonization treatment) It is possible to maintain high process stability in the treatment step) and obtain a high-quality carbon fiber bundle. Further, by passing through the firing process described below, the effect of increasing the strength by reducing foreign matter can be maximized. More specifically, when subjecting the carbon fiber precursor fiber bundle oxidation step, resulting oxidized fiber is the ratio of the peak intensity of 1453cm ^-1 to the peak intensity of 1370 cm ^-1 in the infrared spectra 0. range of from 70 to 0.75, and the ratio of the peak intensity of 1254cm ^-1 to the peak intensity of 1370 cm ^-1 in the infrared spectra is preferably controlled to be in the range of 0.50 to 0.65. The peak at 1453 cm ^{−1 in} the infrared spectrum is derived from an alkene and decreases with the progress of flame resistance. Peak Peak and 1254cm ^-1 of 1370 cm ^-1 is a peak derived from the flame-resistant structure (are respectively considered naphthyridine ring and hydrogenated naphthyridine ring structures.), Increases with the progress of oxidization. If the specific gravity of the obtained oxidized fiber is 1.35, the ratio of the peak intensity of 1453cm ^-1 to the peak intensity of 1370 cm ^-1 is about 0.63 to 0.69. In the flameproofing step, it is general to reduce the peak derived from polyacrylonitrile as much as possible to increase the carbonization yield, but in a preferred embodiment of the present invention, the flameproofing is performed so as to leave a large amount of alkene. Set process conditions. By subjecting the flameproof fiber having such a structure to the preliminary carbonization step, the tensile strength of the obtained carbon fiber bundle can be effectively increased. Furthermore, it is also preferable that the ratio of the peak intensity of 1254cm ^-1 to the peak intensity of 1370 cm ^-1 is set flame conditions such that 0.50 to 0.65. The peak at 1254 cm ⁻¹ is often found in a portion where flame resistance is insufficient, and the clear reason is not clear, but if this structure is large, the tensile strength of the obtained carbon fiber tends to decrease. Such a peak intensity ratio decreases with progress of flame resistance, and the initial decrease is particularly large. However, depending on the flame resistance condition, the peak intensity ratio may not be 0.65 or less even if the time is increased.

In order to make these two peak intensity ratios compatible within the intended range, basically, the amount of the copolymerization component contained in the polyacrylonitrile-based polymer constituting the carbon fiber precursor fiber bundle is small, and The conditions may be set mainly by reducing the fineness of the fiber precursor fiber bundle and increasing the flameproofing temperature in the latter half. The ratio of the peak intensity of 1453cm ^-1 to the peak intensity of 1370 cm ^-1 in the infrared spectra were heat treated to a range of from 0.98 to 1.10 (the first oxidation step), followed by the first oxidation step at a temperature higher than the ratio range of 0.70 to 0.75 of the peak intensity of 1453cm ^-1 to the peak intensity of 1370 cm ^-1 in the infrared spectrum and,, 1254Cm to the peak intensity of 1370 cm ^-1 in the infrared spectrum It is preferable to perform the heat treatment (second flameproofing step) by setting the flameproofing time to 5 to 14 minutes, preferably 5 to 10 minutes until the ^-1 peak intensity ratio falls within the range of 0.50 to 0.65. In order to shorten the flameproofing time of the second flameproofing step, the flameproofing temperature may be adjusted to a high level, but an appropriate flameproofing temperature depends on the characteristics of the polyacrylonitrile precursor fiber bundle. The carbon fiber bundle center temperature is preferably 280 to 310° C., more preferably 280 to 300° C., and further preferably 285 to 295° C. in order to control in the above infrared spectrum range. The flameproofing temperature does not have to be constant and may be set in multiple stages. In order to increase the tensile strength of the obtained carbon fiber, it is preferable that the flameproofing temperature is high and the flameproofing time is short. In the first flameproofing step, it is preferable that the flameproofing time is preferably 8 to 25 minutes, more preferably 8 to 15 minutes, and the flameproofing temperature is within the above range.

The flameproofing time described here means the time during which the fiber bundle stays in the flameproofing furnace, and the flameproofing fiber bundle means the fiber bundle before pre-carbonization. Further, the peak intensity described here is the absorbance of each wavelength after baseline correction of the spectrum obtained by measuring the infrared spectrum by sampling a small amount of flameproofed fiber, and especially the peak division etc. Not performed. In addition, the sample is diluted with KBr so that the concentration of the sample is 0.67% by mass and measured. In this way, the infrared spectrum may be measured every time the flameproofing condition setting is changed, and the conditions may be examined by trial and error according to a preferable manufacturing method described later. The tensile strength of the carbon fiber can be controlled by appropriately controlling the infrared spectrum peak strength ratio of the flame-resistant fiber.

In the present invention, flame resistance means heat treatment at 200 to 400° C. in an oxygen atmosphere concentration of ±5 mass% in the air.

In the present invention, the total flame-proof treatment time can be appropriately selected, preferably in the range of 13 to 20 minutes. Further, for the purpose of improving the tensile strength of the obtained carbon fiber bundle, the specific gravity of the obtained flameproof fiber bundle is preferably in the range of 1.28 to 1.32, more preferably 1.30 to 1.32. Set the flameproofing treatment time to. The more preferable flameproofing treatment time depends on the flameproofing temperature. If the specific gravity of the flameproof fiber bundle is 1.28 or more, the tensile strength of the carbon fiber bundle may decrease, and if the specific gravity of the flameproof fiber bundle is 1.32 or less, the tensile strength can be increased. The specific gravity of the flameproof fiber bundle is controlled by the flameproofing treatment time and the flameproofing temperature. Further, the timing of switching from the first flameproofing process to the second flameproofing process is preferably within the range of 1.21 to 1.23 in specific gravity. Also in this case, the specified range in the infrared spectrum is preferentially controlled. The preferable range of the flameproofing treatment time and flameproofing temperature varies depending on the characteristics of the carbon fiber precursor fiber bundle and the copolymer composition of the polyacrylonitrile-based polymer.

In the flameproofing step, the specific gravity of the carbon fiber precursor fiber bundle is 1.22 or more, and the integrated value of the amount of heat given to the fiber during the heat treatment at 220° C. or more is preferably 50 to 150 J·h. /G, and more preferably 70 to 100 J·h/g. It is easy to increase the tensile strength of the obtained carbon fiber by adjusting the integrated value of the amount of heat given in the latter half of the flameproofing process within such a range. The integrated value of the amount of heat is calculated by the following formula using the flameproofing temperature T(K), the residence time t(h) of the flameproofing furnace, and the heat capacity of the polyacrylonitrile-based precursor fiber bundle of 1.507 J/g·°C. It is the calculated value.
Integrated value of heat quantity (J·h/g)=T×t×1.507
When there are a plurality of temperature conditions in the flameproofing step, the amount of heat may be calculated from the residence time at each temperature and integrated.

After the flame-proofing step, it is preferable to perform a preliminary carbonization step, and then carbonize at a maximum temperature of 1000 to 3000° C. in an inert atmosphere. The temperature of the carbonization step is preferably higher from the viewpoint of increasing the strand elastic modulus of the obtained carbon fiber, but if it is too high, the strength in the high strength region may decrease, and it is set in consideration of both. Is good. A more preferable temperature range is 1200 to 2000°C, and a still more preferable temperature range is 1200 to 1600°C.

The carbon fiber bundle obtained as described above is subjected to an oxidation treatment to introduce an oxygen-containing functional group in order to improve the adhesiveness with the matrix resin. As the oxidation treatment method, vapor phase oxidation, liquid phase oxidation and liquid phase electrolytic oxidation are used, but liquid phase electrolytic oxidation is preferably used from the viewpoint of high productivity and uniform processing. The liquid-phase electrolytic oxidation method is not particularly specified, and a known method may be used.

After such an electrolytic treatment, a sizing treatment can be performed in order to impart a sizing property to the obtained carbon fiber bundle. As the sizing agent, a sizing agent having good compatibility with the matrix resin can be appropriately selected according to the type of matrix resin used in the composite material.

The tensile strength of the carbon fiber bundle of the present invention is preferably 7.5 GPa or more, more preferably 7.7 GPa, further preferably 7.9 GPa. Here, the tensile strength is a value evaluated by a resin-impregnated strand tensile test of a carbon fiber bundle. Since the carbon fiber precursor fiber produced by the method for producing a carbon fiber precursor fiber bundle of the present invention has a reduced amount of foreign matter, it is possible to obtain a carbon fiber containing few defects that cause destruction, and the specific The effect of increasing the strength by passing through the firing step is easily exhibited, and a carbon fiber bundle having a tensile strength of 7.5 GPa or more can be obtained.

In a preferred embodiment of the carbon fiber bundle of the present invention, the tensile elastic modulus in the resin-impregnated strand tensile test (simply referred to as the strand elastic modulus) is 240 to 440 GPa, preferably 280 to 400 GPa, and more preferably 310. ~400 GPa. A tensile elastic modulus of 240 to 440 GPa is preferable because it has an excellent balance between tensile elastic modulus and tensile strength. The tensile modulus can be obtained by the method described in <Strand tensile test of carbon fiber> described later. At this time, the strain range is 0.1 to 0.6%. The tensile elastic modulus of the carbon fiber bundle can be controlled mainly by applying tension to the fiber bundle or changing the carbonization temperature in any heat treatment process in the manufacturing process of the carbon fiber bundle.

Hereinafter, the present invention will be described in more detail with reference to Examples. Here, Examples 2, 4, 7, 9 to 24, 26 are examples of the present invention, and Examples 1, 3, 5, 6, 8, 25, 27 are reference examples. The measuring method used in this example will be described below.

<Various molecular weights: Mz, Mw, Mz/Mw>
A polymer solution to be measured was dissolved in dimethylformamide (0.01N-lithium bromide added) at a concentration of 0.1% by mass to prepare a sample solution. With respect to the prepared sample solution, a GPC device was used to obtain a molecular weight distribution curve from a GPC curve measured under the following conditions, and a Z-average molecular weight Mz and a weight-average molecular weight Mw were calculated. Furthermore, Mz/Mw was calculated from the values of Mz and Mw.
・Column: Polar organic solvent system GPC column ・Flow rate: 0.5 ml/min ・Temperature: 75°C
・Sample filtration: Membrane filter (0.45μm cut)
・Injection volume: 200 μl
-Detector: Differential refractive index detector.

For the molecular weight distribution curve, a calibration curve of elution time-molecular weight is created by using at least six types of monodisperse polystyrene with known molecular weights having different molecular weights, and the polystyrene-equivalent molecular weight corresponding to the corresponding elution time is read on the calibration curve. I asked for it.

In the examples, Shimadzu Corporation CLASS-LC2010 is used as a GPC device, and Tosoh Corporation TSK-GEL-α-M (×2)+Tosoh Corporation TSK-guard Column α is used as a column and dimethyl is used as dimethyl. Formamide and lithium bromide manufactured by Wako Pure Chemical Industries, Ltd., Millipore Corporation's 0.45 μm-FHLP FILTER as a membrane filter, and Shimadzu's RID-10AV as a differential refractive index detector were used to create a calibration curve. As the monodisperse polystyrene for use, those having a molecular weight of 184000, 427,000, 791000, 1300000, 1810000, and 4210,000 were used, respectively.

<Determination of quality of carbon fiber precursor fiber bundle>
While running a carbon fiber precursor fiber bundle of 6000 filaments at a speed of 1 m/min, a single fiber break (hereinafter referred to as fluff) and an aggregate of single fiber breaks (hereinafter referred to as a pill) in the fiber bundle are formed. The total number was counted and evaluated in three levels. The evaluation criteria are as follows. When the carbon fiber precursor fiber bundle is 3000 filaments, the number of fluffs and pills is 1.4 times, and when the carbon fiber precursor fiber bundle is 12000 filaments, the number of fluffs and pills is 0.7 times. By doing so, the evaluation criteria can be matched. The figures are rounded to the nearest whole number.
⊚: 1 or less per 600 m of fiber. ◯: 2 to 4 per 600 m of fiber. Δ: 5 to 30 per 600 m of fiber.

<Judgment of filter life>
The amount of filtrate passing per unit filtration area from the start of filtration until the pressure loss of the filter medium during spinning increased by 1 MPa was measured and evaluated in three levels. The evaluation criteria are as follows.
· ◎: 50L / cm ² or more · ○: less than 25L / cm ² more than ^{50L / cm 2 · △: 25L} / cm less than ^2.

<Evaluation of spinning limit draft>
The filtered spinning solution was once discharged into the air from the spinneret at a temperature of 40° C., passed through a space of 2 mm, and then introduced into a coagulation bath consisting of an aqueous solution of 20 mass% dimethyl sulfoxide controlled at a temperature of 3° C. When spinning by the dry-wet spinning method, the speed at which yarn breakage occurs is measured by adjusting the liquid delivery rate to the spinneret so that the discharge linear velocity is 2 m/min and changing the winding speed of the coagulated yarn. .. The value obtained by dividing the winding speed at which yarn breakage occurred by the linear discharge speed was evaluated as the spinning limit draft.

<Carbon fiber strand tensile test>
The tensile modulus, tensile strength and stress-strain curve of the carbon fiber resin-impregnated strand were determined according to JIS R7608 (2008) "Resin-impregnated strand test method". The strand elastic modulus E was measured in the strain range of 0.1 to 0.6%, and the initial elastic modulus was obtained from the slope of the stress-strain curve at zero strain. The test piece was prepared by impregnating a carbon fiber bundle with the following resin composition and curing the material by heat treatment at a temperature of 130° C. for 35 minutes.

[Resin composition]
*3,4-epoxycyclohexylmethyl-3,4-epoxy-cyclohexane-carboxylate (100 parts by mass)
・Boron trifluoride monoethylamine (3 parts by mass)
-Acetone (4 parts by mass).

The number of strands measured was 6, and the arithmetic average value of each measurement result was used as the strand tensile elastic modulus and tensile strength of the carbon fiber. In Examples and Comparative Examples described later, as the above 3,4-epoxycyclohexylmethyl-3,4-epoxy-cyclohexane-carboxylate, Union Carbide Co., Ltd., "BAKELITE (registered trademark)" ERL-. 4221 was used. The strain was measured using an extensometer.

<Specific gravity measurement>
1.0 to 3.0 g of fiber was collected and absolutely dried at 120° C. for 2 hours. Next, after measuring the absolute dry mass A(g), the fiber mass B(g) in the solvent bath was measured after impregnating with ethanol and sufficiently defoaming, and the fiber specific gravity=(A×ρ)/(A The fiber specific gravity was determined according to -B).

<Infrared spectrum intensity ratio>
The flame-resistant fiber to be used for the measurement was measured by accurately weighing 2 mg after freeze-grinding, mixing it well with 300 mg of KBr, putting it in a molding jig, and applying a pressure of 40 MPa for 2 minutes using a pressing machine. Tablets were prepared. The tablet was set in a Fourier transform infrared spectrophotometer, and the spectrum was measured in the range of 1000 to 2000 cm ^-1 . The background correction was performed by subtracting the minimum value from each intensity so that the minimum value was 0 in the range of 1700 to 2000 cm ⁻¹ . As the Fourier transform infrared spectrophotometer, Paragon 1000 manufactured by Perkin Elmer was used.

<Determination of quality of carbon fiber bundle>
In the same manner as the carbon fiber precursor bundle, while running a carbon fiber bundle of 6000 filaments at a speed of 1 m/min, single fiber breaks (hereinafter referred to as fluff) and aggregates of single fiber breaks in the fiber bundle ( Hereinafter, the total number of hairballs) was counted and evaluated in three levels. The evaluation criteria are as follows. In addition, when the carbon fiber bundle is 3000 filaments, the number of fluffs and pills is 1.4 times, and when the carbon fiber bundle is 12000 filaments, the number of fluffs and pills is 0.7 times. You can match the standards. The figures are rounded to the nearest whole number.
⊚: 1 or less per 600 m of fiber. ◯: 2 to 4 per 600 m of fiber. Δ: 5 to 30 per 600 m of fiber.

[Example 1]
100 parts by mass of acrylonitrile, 1 part by mass of itaconic acid, 0.4 parts by mass of 2,2′-azobisisobutyronitrile as a radical initiator, and 0.1 part by mass of octyl mercaptan as a chain transfer agent, 370 parts by mass of dimethyl sulfoxide. Was uniformly dissolved in the reaction solution and placed in a reaction vessel equipped with a reflux tube and a stirring blade. After substituting the space in the reaction vessel with nitrogen, heat treatment was carried out under the following polymerization condition A while stirring, and polymerization was carried out by the solution polymerization method to obtain a polyacrylonitrile polymer solution.
(Polymerization condition A)
(1) Hold at 61°C for 4 hours (2) Raise temperature from 61°C to 80°C (heating rate 10°C/hour)
(3) Hold at a temperature of 80°C for 6 hours.

Using the obtained polyacrylonitrile-based polymer solution, various molecular weights of the polyacrylonitrile-based polymer contained therein were measured. Then, the obtained polyacrylonitrile-based polymer solution was used to adjust the polymer concentration to 20% by mass to prepare a spinning solution.

The obtained spinning solution was introduced into a filter device and filtered. The filter medium used was a sintered metal filter having a filtration accuracy B of 1 μm, a thickness C of the filter medium of 800 μm, and a basis weight of the filter medium D of 2500 g/m ² , and the filtration rate A was 3 cm/hour.

The filtered spinning solution was once discharged into the air from a spinneret having a hole number of 1500, passed through a space, and then spun by a dry-wet spinning method in which it was introduced into a coagulation bath made of an aqueous solution of dimethylsulfoxide to obtain a coagulated thread. .. In addition, after washing the coagulated yarn with water, it is drawn in warm water of 90° C. at a draw ratio of 3 times in a bath, and a silicone oil agent is further applied, followed by drying using a roller heated to a temperature of 160° C. Pressurized steam drawing was performed under double steam drawing ratio conditions to obtain a carbon fiber precursor fiber bundle having a single fiber fineness of 0.8 dtex.

[Example 2]
A carbon fiber precursor fiber bundle was obtained in the same manner as in Example 1 except that the filter medium was changed to a sintered metal filter having a filtration accuracy B of 9 μm, a filter medium thickness C of 3200 μm, and a filter medium weight D of 6400 g/m ^2. It was

[Comparative Example 1]
A carbon fiber precursor fiber bundle was obtained in the same manner as in Example 1, except that the filter medium was changed to a sintered metal filter having a filtration accuracy B of 10 μm, a filter medium thickness C of 1600 μm, and a filter medium weight D of 3200 g/m ^2. It was

[Example 3]
Under the filtration conditions, a carbon fiber precursor fiber bundle was obtained in the same manner as in Example 1 except that the filtration speed A was changed to 6 cm/hour and the number of holes in the spinneret was changed to 3000.

[Comparative example 2]
A carbon fiber precursor fiber bundle was obtained in the same manner as in Example 3, except that the filter medium was changed to a sintered metal filter having a filtration accuracy B of 9 μm, a filter medium thickness C of 3200 μm, and a filter medium weight D of 6400 g/m ^2. It was

[Example 4]
A carbon fiber precursor fiber bundle was obtained in the same manner as in Example 3 except that the filter medium was changed to a sintered metal filter having a filtration accuracy B of 9 μm, a filter medium thickness C of 6400 μm, and a filter medium weight D of 12800 g/m ^2. It was

[Comparative Example 3]
Under the filtration conditions, a carbon fiber precursor fiber bundle was obtained in the same manner as in Example 3 except that the filtration rate A was changed to 12 cm/hour.

[Comparative Example 4]
A carbon fiber precursor fiber bundle was obtained in the same manner as Comparative Example 3 except that the filter medium was changed to a sintered metal filter having a filtration accuracy B of 9 μm, a filter medium thickness C of 6400 μm, and a filter medium weight D of 12800 g/m ^2. It was

[Example 5]
100 parts by mass of acrylonitrile, 0.01 part by mass of 2,2′-azobisisobutyronitrile as a radical initiator, and 200 parts by mass of dimethyl sulfoxide were mixed and put in a reaction vessel equipped with a reflux tube and a stirring blade. It was After substituting the space in the reaction vessel with nitrogen, a heat treatment under the following polymerization condition B was performed with stirring, and the solution was polymerized to obtain a primary solution of a polyacrylonitrile-based polymer solution.

(Polymerization condition B)
(1) Temperature increase from 30°C to 61°C (temperature increase rate 120°C/hour)
(2) Hold at a temperature of 61° C. for 3 hours.

The obtained primary solution was poured into water to precipitate a polymer, which was washed with warm water at 80° C. for 2 hours and then dried at a temperature of 70° C. for 4 hours to obtain a dried polymer. The Mz and Mw of the obtained dry polymer were 5.8 million and 3.4 million, respectively.

The polymer concentration of the obtained primary solution was 1.5% by mass. Here, in order to polymerize the unreacted acrylonitrile remaining in the primary solution of the obtained polyacrylonitrile-based polymer, 170 parts by mass of dimethyl sulfoxide, 1 part by mass of itaconic acid, and as a radical initiator were added to the primary polymerization solution. 0.4 parts by mass of 2,2′-azobisisobutyronitrile and 0.1 parts by mass of octyl mercaptan as a chain transfer agent were uniformly dissolved and put into a reaction vessel equipped with a reflux tube and a stirring blade. After substituting the space in the reaction vessel with nitrogen, heat treatment was carried out under the following polymerization condition A while stirring, and polymerization was carried out by a solution polymerization method to obtain a secondary solution of a polyacrylonitrile polymer.

(Polymerization condition A)
(1) Hold at 61°C for 4 hours (2) Raise temperature from 61°C to 80°C (heating rate 10°C/hour)
(3) Hold at a temperature of 80°C for 6 hours.

Using the obtained secondary solution, various molecular weights of the polyacrylonitrile polymer contained therein were measured. Then, using the obtained secondary solution, the polymer concentration was adjusted to 20% by mass to prepare a spinning solution. A carbon fiber precursor fiber bundle was obtained in the same manner as in Example 1 except that the spinning solution was changed to the spinning solution obtained as described above.

[Example 6]
A carbon fiber precursor fiber bundle was obtained in the same manner as in Example 5, except that the filter medium was changed to a sintered metal filter having a filtration accuracy B of 2 μm, a filter medium thickness C of 400 μm and a filter medium weight D of 1700 g/m ^2. It was

[Example 7]
A carbon fiber precursor fiber bundle was obtained in the same manner as in Example 5 except that the filter medium was changed to a sintered metal filter having a filtration accuracy B of 9 μm, a filter medium thickness C of 3200 μm, and a filter medium weight D of 6400 g/m ^2. It was

[Example 8]
Under the filtration conditions, a carbon fiber precursor fiber bundle was obtained in the same manner as in Example 5 except that the filtration rate A was changed to 6 cm/hour and the number of holes in the spinneret was changed to 3000.

[Comparative Example 5]
A carbon fiber precursor fiber bundle was obtained in the same manner as in Example 8 except that the filter medium was changed to a sintered metal filter having a filtration accuracy B of 10 μm, a filter medium thickness C of 1600 μm and a filter medium weight D of 3200 g/m ^2. It was

[Example 9]
A carbon fiber precursor fiber bundle was obtained in the same manner as in Example 8 except that the filter medium was changed to a metal sintered filter having a filtration accuracy B of 9 μm, a filter medium thickness C of 6400 μm, and a filter medium weight D of 12800 g/m ^2. It was

[Example 10]
The filter medium was changed to a sintered metal filter having a filtration accuracy B of 6 μm, a thickness C of the filter medium of 1800 μm and a basis weight of the filter medium of 6400 g/m ² , and the filtration speed A was changed to 3 cm/hour under the filtration conditions. A carbon fiber precursor fiber bundle was obtained in the same manner as in Example 8 except that the number of holes in No. 1 was changed to 1500.

Tables 1-1 and 1-2 show Mw and Mz/Mw of the polyacrylonitrile-based polymers, spinning conditions, specifications of the filters used, and spinning results in the above Examples and Comparative Examples.

[Examples 11 to 27 and Comparative Examples 6 to 9]
Each of the carbon fiber precursor fiber bundles obtained in Examples 1 to 4 and Comparative Examples 1 to 4 was stretched in an oven in an air atmosphere using the conditions of flameproofing temperature and flameproofing time shown in Table 2, respectively. A flameproofing treatment was performed while stretching at a ratio of 1. The properties of the fiber bundle after the first furnace flame resistance and the flame resistant fiber bundle were as shown in Table 2. The obtained flame-resistant fiber bundle was subjected to a preliminary carbonization treatment while being drawn at a draw ratio of 1.15 in a nitrogen atmosphere at a temperature of 300 to 800° C. to obtain a preliminary carbonized fiber bundle. The obtained pre-carbonized fiber bundle was carbonized in a nitrogen atmosphere at a maximum temperature of 1500° C. and a tension of 14 mN/dTex. Table 3 shows the physical properties and grades of the final carbon fiber bundle obtained by subjecting the obtained carbon fiber bundle to surface treatment and sizing agent coating treatment. In Comparative Examples 6 to 9, the quality of the carbon fiber precursor fiber bundle was poor, and fluff was scattered in each of the steps of flame resistance, pre-carbonization, and carbonization, so that it was always necessary to monitor the step.

Claims (10)

When a spinning solution obtained by dissolving a polyacrylonitrile polymer in a solvent is spun to obtain a carbon fiber precursor fiber bundle, prior to spinning, a filter medium having a filtration accuracy B (μm) and a filter medium thickness C (μm) is used. The spinning solution is filtered under the conditions that the filtration accuracy B (μm) satisfies the following formula (6) and the filtration rate A (cm/hour) satisfies the following formulas (1) and (2). A method for producing a carbon fiber precursor fiber bundle, which is characterized.
A ³ ≦−100×B+0.3×C+150 (1)
0.1 ≤ A ≤ 15 (2)
B≧3 (6) Prior to spinning, when a spinning solution prepared by dissolving a polyacrylonitrile polymer in a solvent is spun to obtain a carbon fiber precursor fiber bundle, it has a filtration accuracy B (μm) and a filter material basis weight D (g/m ² ). Using a filter medium, filtering the spinning solution under the conditions that the filtration accuracy B (μm) satisfies the following formula (6) and the filtration rate A (cm/hour) satisfies the following formulas (3) to (5). A method for producing a carbon fiber precursor fiber bundle, comprising:
D−600/(α×β)≧0 (3)
α = 1-1/(1+exp(7-A)) (4)
β=1-1/(1+exp(−0.23×B)) (5)
B≧3 (6) The method for producing a carbon fiber precursor fiber bundle according to claim 1 or 2, wherein the spinning solution is filtered under the condition that all the expressions (1) to (5) are satisfied. The polyacrylonitrile-based polymer, Mw is from 300,000 to 500,000, Mz / Mw is 1.5 to 6.0, the carbon fiber precursor fiber bundle according to any one of claims 1 to 3 Production method. The polyacrylonitrile-based polymer, the copolymerization component to acrylonitrile polyacrylonitrile copolymer consisting by 0.1 to 2 wt% copolymer of the total monomers, according to any one of claims 1-4 Of the carbon fiber precursor fiber bundle of the above. After obtaining carbon fiber precursor fiber bundle by the method according to any one of claims 1 to 5 for processing oxidization treatment and carbonization of the carbon fiber precursor fiber bundle, method of producing a carbon fiber bundle. The carbon fiber precursor fiber bundle, the first oxidation step of oxidization 8-25 minutes until the ratio of 1453cm ^-1 peak intensity in the range of 0.98 to 1.10 for the 1370 cm ^-1 peak intensity of the infrared spectrum was carried out, further, the ratio range of 0.70 to 0.75 of 1453cm ^-1 peak intensity to 1370 cm ^-1 peak intensity of the infrared spectrum and,, 1254Cm ^-1 peak intensity to 1370 cm ^-1 peak intensity of the infrared spectrum The second flameproofing step of flameproofing for 5 to 14 minutes to obtain a flameproofed fiber bundle until the ratio becomes 0.50 to 0.65 is obtained, and then the flameproofed fiber bundle is heated to 1000 to 3000°C. The method for producing a carbon fiber bundle according to claim 6 , wherein a carbonization step of carbonizing in an inert atmosphere is performed. The method for producing a carbon fiber bundle according to claim 7 , wherein a total treatment time for flameproofing is set to a range of 13 to 20 minutes. Flame resistance so that the integrated value of the amount of heat given when heat treated in air at 220°C or higher is within the range of 50 to 150 J·h/g when the specific gravity of the fiber being flameproofed is 1.22 or higher. The method for producing a carbon fiber bundle according to claim 7 or 8 . The specific gravity of the flame resistant fiber bundle is oxidization to be in the range of 1.28 to 1.32 The method of producing a carbon fiber bundle according to any one of claims 7-9.