JP2009235662A - Method for producing carbon fiber precursor fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing carbon fiber precursor fiber improving spinning rate, directing reduction of carbon fiber cost and providing a high strength carbon fiber by accurately filtering foreign matters without causing filter blocked out, before discharging PAN-based polymer for producing carbon fiber precursor fiber from a spinneret. <P>SOLUTION: The method for producing carbon fiber precursor fiber includes filtration of a spinning solution obtained by solving a polyacrylonitrile based polymer with 1.5 or more of Mz/Mw which is a ratio of z average molecular weight Mz and a weight average molecular weight Mw, in a solvent, before spinning, wherein the filtration is performed by using a filtering device using a filtering member composed of a certified filtering layer (with smallest opening diameter) in which the basis weight of the certified filtering layer A (g/m<SP>2</SP>) and the density of material B (g/m<SP>3</SP>) satisfy formula: 0.01≤A/B×1000≤0.06, and having a filtration resistance coefficient of 5×10<SP>5</SP>to 30×10<SP>5</SP>cm<SP>-1</SP>. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  Since carbon fiber has higher specific strength and specific modulus than other fibers, it can be used as a reinforcing fiber for composite materials in addition to conventional sports applications, aerospace applications, automobiles, civil engineering / architecture, pressure vessels and Widely used in general industrial applications such as windmill blades, there is a strong demand for both higher performance and lower costs.

  Among the carbon fibers, the most widely used polyacrylonitrile (hereinafter sometimes referred to as PAN) carbon fiber is a spinning solution composed of a PAN polymer as a precursor, and wet spinning or dry spinning. Alternatively, after carbon fiber precursor fiber is obtained by dry and wet spinning, it is heated in an oxidizing atmosphere at a temperature of 200 to 400 ° C. to convert to a flame-resistant fiber, and in an inert atmosphere at a temperature of at least 1000 ° C. It is manufactured industrially by heating and carbonizing at Since carbon fiber is a brittle material and causes a decrease in strength due to slight surface defects and intrinsic defects, delicate attention has been paid to the generation of defects. It is natural to remove foreign matters such as dust in the raw material, but it is not only the strength reduction that removes the gel-like material formed by the spinning stock solution partly staying and thermally degrading from the die before discharging. It has also been carried out to reduce yarn breakage during the yarn making and firing process during discharge. For example, a method of filtering using a filter having an opening diameter of 5 μm or less (see Patent Document 1), a method of filtering using a sintered metal filter having a filtration accuracy of 5 μm or less (see Patent Document 2), and a step of opening diameter A method of performing multistage filtration by reducing the size (see Patent Document 3) has been proposed.

  On the other hand, in order to reduce the production cost of carbon fiber, the present inventors have developed a technique that can increase the spinning speed and increase the spinning draft rate by using a PAN-based polymer having a specific molecular weight distribution. Proposed (Japanese Patent Application No. 2007-269822). In general, in order to remove foreign matters such as gel-like substances before discharging from the die, it has been considered that a method of filtering with a filter medium having a large thickness and fineness is effective, but a PAN system having a specific molecular weight distribution Filtering to obtain carbon fiber precursor fibers with low foreign matter content to increase spinning speed and obtain high-strength carbon fibers by filtering foreign matters such as gels from spinning solutions containing polymers When a thick nonwoven fabric filter is used, the filtration pressure loss increases, and in particular, when the spinning speed is increased, the gel-like substance often flows into the spinning solution after filtration. In general, the polymer accumulates in the deep part of the filter medium, and after the deposition proceeds, the polymer flows out as a gel by pressure. As a result, the foreign matter is mixed again in the filtered and cleaned spinning solution. It is known to reduce the quality of the spinning solution prepared and must be avoided (see Patent Document 4). In addition, even if a finely crushed gel is slightly mixed in the spinning solution, it is often possible to produce precursor fibers without affecting the spinning process, but using such precursor fibers, Carbon fibers to be produced must be avoided because their physical properties are reduced. Therefore, in order to produce a precursor fiber for obtaining high-strength carbon fiber at an increased spinning speed, foreign matters such as gels are accurately filtered from the spinning solution before filtration, and after filtration, It is necessary to avoid mixing with the spinning solution.

Japanese Patent Laid-Open No. 58-220821 JP 59-88924 JP 2004-27396 A Japanese Patent Laying-Open No. 2003-24727 (paragraph 0008)

  The present invention solves the problems of the prior art described above, that is, not only can a foreign matter such as a gel-like material be accurately filtered from the spinning solution before filtration, but also prevents clogging of the filter medium, and after filtration. An object of the present invention is to propose a method capable of stably producing a carbon fiber precursor fiber by minimizing the amount of being mixed into the spinning solution.

In order to achieve the above object, the method for producing a carbon fiber precursor fiber of the present invention has the following configuration. That is, a carbon fiber precursor fiber is obtained by spinning a spinning solution in which a polyacrylonitrile-based polymer having a ratio of Z average molecular weight Mz to weight average molecular weight Mw of Mz / Mw of 1.5 or more is dissolved in a solvent. Prior to spinning, the filtration assurance layer basis weight A (g / m ² ) and material density B (g / m ³ ) have a filtration assurance layer satisfying the following formula, and the filtration resistance coefficient C is 5 to 30 ×. It is a manufacturing method of the carbon fiber precursor fiber which filters a spinning solution with the filter apparatus using the filter medium which is 10 < ⁵ > cm ^<-1 >.
0.01 ≦ A / B × 1000 ≦ 0.06

  According to the present invention, carbon fiber precursor fibers with little foreign matters such as gels can be produced at an increased spinning speed, so that the cost of carbon fibers can be reduced. In addition, by using carbon fiber precursor fibers with a small amount of foreign matter, high-strength carbon fibers with less yarn breakage and less fluff can be stably produced even in the firing step.

FIG. 1 is a schematic cross-sectional view showing a filter device that can be used in the present invention. FIG. 2 is a schematic cross-sectional view showing a leaf disk type filter that can be used in the present invention. FIG. 3 is a schematic cross-sectional view showing a filter device using a leaf disk type filter.

  In the present invention, spinning is performed using a spinning solution in which a PAN-based polymer having Mz / Mw, which is a ratio of Z average molecular weight Mz and weight average molecular weight Mw, of 1.5 or more is dissolved in a solvent. Since such a PAN-based polymer contains a polymer component having a large molecular weight, the effects of the present invention are remarkably exhibited.

  First, the PAN polymer that can be suitably used in the present invention will be described. In the present invention, a PAN-based 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 low molecular weight PAN-based polymer having an Mw of less than 300,000, since the connection between molecules in the fiber axis direction is reduced, it cannot withstand high stretching in the spinning and firing processes, and the strength as a carbon fiber is reduced. There are many cases. A larger Mw is preferable, but a high molecular weight PAN polymer with Mw exceeding 500,000 is too entangled, and the polymer concentration is lowered when such a high molecular weight PAN polymer is used. Inevitably, productivity may decrease. The Mw of the PAN-based polymer can be controlled by changing the amounts of monomers, radical initiators, chain transfer agents and the like during polymerization. The PAN-based polymer has a polydispersity Mz / Mw represented by a ratio of Z average molecular weight (hereinafter abbreviated as Mz) to Mw of 1.5 to 6.0, preferably 2.7 to 6. .0 is good.

  In the present invention, 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 (hereinafter abbreviated as Mn) is sensitively influenced by the low molecular weight substance contained in the polymer compound. On the other hand, Mw is sensitively influenced by the high molecular weight substance, and Mz is more sensitively influenced by the high molecular weight substance. Therefore, the spread of the molecular weight distribution can be evaluated by using Mw / Mn or Mz / Mw which are polydispersities. It is monodisperse when Mw / Mn is 1, and shows that the molecular weight distribution becomes broader around the low molecular weight side as it becomes larger, whereas the molecular weight distribution becomes higher as Mz / Mw becomes larger. It shows that it becomes broad around.

  As described above, since Mw / Mn and Mz / Mw are different, even if Mw / Mn is large, Mz / Mw does not necessarily increase.

  By using the PAN-based polymer as described above, a mechanism capable of producing a high-quality carbon fiber precursor fiber with less fuzz while achieving both improvement in productivity and stabilization is not necessarily clear. It is not a translation, but it is thought as follows. When the PAN-based polymer is stretched and deformed immediately after the mouthpiece hole, the ultrahigh molecular weight substance and the high molecular weight substance are entangled, and the molecular chain between the entanglement is tensioned around the ultrahigh molecular weight substance, resulting in a rapid increase in elongational viscosity. That is, strain hardening occurs. As the PAN polymer solution is thinned, the elongational viscosity of the thinned portion is increased and the flow is stabilized, so that the spinning speed can be increased, the spinning draft rate can be increased, and the spinning speed can be increased. By using a solution in which a PAN-based polymer as described above is dissolved in a solvent, the yarn will not break even if the yarn is wound at a high speed of 20000 mm / min, and the length of the yarn cannot be measured. Can do.

  When Mz / Mw is 1.5 or more, the stretchability is high, and an orientation state satisfactory as a carbon fiber precursor fiber can be obtained. On the other hand, when Mz / Mw is 2.7 or more, strain hardening is strongly developed, the spinning stability of the spinning solution is improved, and the productivity is greatly improved. In addition, when Mz / Mw is 2.7 or higher, high molecular weight components that should not be filtered when passing through the filter medium are often filtered. Therefore, in combination with the present invention, only foreign matters such as gel-like substances are efficiently obtained. The effect of filtering well is greatly increased. On the other hand, a PAN-based polymer having Mz / Mw of more than 6.0 may become too entangled, making it difficult to discharge the spinning solution from the die.

  In addition, Mw / Mn is preferably as small as possible because the smaller the content of low molecular components that are likely to be structural defects of the carbon fiber, and Mw / Mn is preferably smaller than Mz / Mw. That is, even if it is broad on both the high molecular weight side and the low molecular weight side, there is little decrease in ejection stability, but the low molecular weight side is preferably as sharp as possible, and Mz / Mw is higher than Mw / Mn. It is preferably 1.5 times or more, and more preferably 1.8 times or more. According to the study by the present inventors, in the radical polymerization such as aqueous suspension or solution method, which is usually performed in the polymerization of acrylonitrile (hereinafter abbreviated as AN), the molecular weight distribution is on the lower molecular weight side. Therefore, Mw / Mn becomes larger than Mz / Mw. Therefore, when performing polymerization under special conditions such as the type and ratio of the polymerization initiator and sequential addition, or when using general radical polymerization, there is a method of mixing two or more PAN-based polymers. The method of mixing is simple. The smaller the number of types to be mixed, the easier and the two types are often sufficient from the viewpoint of ejection stability.

  The Mw of the polymer to be mixed is a PAN-based polymer having a large Mw as the A component, and a PAN-based polymer having a small Mw is the B component. Is 1 million to 5 million, and Mw of the B component is preferably 50,000 to 900,000. The larger the difference between the Mw of the A component and the B component, the greater the Mz / Mw of the mixed polymer tends to increase. This is a preferred embodiment, but when the Mw of the A component is greater than 15 million, production of the A component When the Mw of the B component is less than 150,000, the strength of the precursor fiber may be insufficient, and it is realistic that Mz / Mw is 10 or less.

  Specifically, the ratio of the weight average molecular weight of the A component and the B component is preferably 4 to 45, and more preferably 20 to 45.

  The weight ratio of the A component and the B component is preferably 0.003 to 0.3, more preferably 0.005 to 0.2, and 0.01 to 0.1. Further preferred. When the weight ratio of the A component to the B component is less than 0.003, strain hardening may be insufficient, and when it is greater than 0.3, the discharge viscosity of the polymer solution may increase so that the discharge may become difficult.

  When mixing the polymer of component A and component B, a method of mixing both polymers and then diluting with a solvent, a method of mixing each of the polymers diluted in a solvent, and a high molecular weight material that is difficult to dissolve A method in which the B component is mixed and dissolved after diluting the A component in the solvent, and a solution in which the monomer constituting the B component is mixed with a solution obtained by diluting the high molecular weight A component in the solvent. It is possible to employ a mixing method. For mixing, a method of stirring in a mixing tank, a method of quantifying with a gear pump or the like and mixing with a static mixer, a method of using a twin screw extruder, or the like can be preferably employed. From the viewpoint of uniformly dissolving the high molecular weight product, a method of first dissolving the component A which is a high molecular weight product is preferable. In particular, in the case of producing a carbon fiber precursor, the dissolved state of the high molecular weight component A is extremely important, and even if a slight amount of undissolved material exists, it is recognized as a foreign substance. When it is filtered by the filter medium or small enough not to be filtered, a void may be formed inside the carbon fiber.

  Specifically, the polymer concentration of the component A with respect to the solvent, that is, when assuming a solution consisting only of the component A and the solvent, the polymer concentration of the component A in the solution is preferably 0.1 to 5% by weight. Then, the B component is mixed, or the monomers constituting the B component are mixed and polymerized. The polymer concentration of the component A is more preferably 0.3 to 3% by weight, and further preferably 0.5 to 2% by weight. More specifically, the polymer concentration of the component A is preferably a quasi-dilute solution in which the polymers are slightly overlapped as an aggregate state of the polymer, and the component B is mixed or the component B is mixed. When the constituent monomers are mixed and polymerized, the mixed state is likely to be uniform, so that a dilute solution that is in an isolated chain state is a more preferable embodiment. The concentration of the dilute solution is considered to be determined by the intramolecular exclusion volume determined by the polymer molecular weight and the solubility of the polymer in the solvent. It is less likely to aggregate and deposit in the filter media. When the polymer concentration exceeds 5% by weight, an undissolved product of component A may be present. When the polymer concentration is less than 0.1% by weight, it is effective because it is a dilute solution depending on the molecular weight. Is often saturated.

  As described above, the polymer concentration with respect to the solvent of the component A is preferably 0.1 to 5% by weight, and then the method of mixing and dissolving the component B may be used. It is preferable to employ a method of mixing a product obtained by diluting a product with a solvent and a monomer constituting the component B and mixing the monomers by solution polymerization.

  The method for adjusting the polymer concentration of the component A to the solvent to 0.1 to 5% by weight may be a method using dilution or a method using polymerization. When diluting, it is important to stir until it can be diluted uniformly, and the dilution temperature is preferably 50 to 120 ° C. The dilution time varies depending on the dilution temperature and the concentration before dilution, and may be appropriately set. When the dilution temperature is less than 50 ° C, it may take time to dilute, and when it exceeds 120 ° C, the component A may be altered. In addition, from the viewpoint of reducing the process of diluting the overlapping of the polymers and mixing them uniformly, from the production of the A component to the start of mixing of the B component, or the polymerization of the monomer constituting the B component. Meanwhile, the polymer concentration with respect to the solvent of the component A is preferably controlled in the range of 0.1 to 5% by weight. Specifically, when the component A is produced by solution polymerization, the polymerization is stopped when the polymer concentration is 5% by weight or less, and the component B is mixed therewith, or the monomer constituting the component B is mixed. This is a method of polymerizing the monomer. Usually, when the ratio of the charged monomer to the solvent is small, it is often difficult to produce a high molecular weight product by solution polymerization, so the ratio of the charged monomer is increased. However, when the amount is 5% by weight or less, the polymerization rate is low and a large amount of unreacted monomer remains. The B component may be mixed after removing the unreacted monomer by volatilization, but from the viewpoint of omitting the process, it is preferable to solution polymerize the B component using the unreacted monomer.

  The component A preferably used in the present invention desirably has compatibility with PAN, and is preferably a PAN-based polymer from the viewpoint of compatibility. As the composition, AN is preferably 93 to 100 mol%, and copolymerization may be carried out if the monomer copolymerizable with AN is 7 mol% or less, but the chain transfer constant of the copolymerization component is smaller than AN. When it is difficult to obtain the required Mw, it is preferable to reduce the amount of the copolymer component as much as possible.

  Examples of monomers copolymerizable with AN include acrylic acid, methacrylic acid, itaconic acid and alkali metal salts thereof, ammonium salts and lower alkyl esters, acrylamide and derivatives thereof, allyl sulfonic acid, methallyl sulfonic acid and Those salts or alkyl esters can be used.

  The polymerization method for producing the PAN-based polymer as component A can be selected from a solution polymerization method, a suspension polymerization method, an emulsion polymerization method, etc., and the purpose of uniformly polymerizing AN and copolymer components It is preferable to use a solution polymerization method. In the case of polymerizing using the solution polymerization method, as the solvent, for example, a solvent in which PAN is soluble, such as an aqueous zinc chloride solution, dimethyl sulfoxide, dimethylformamide, and dimethylacetamide, is preferably used. If it is difficult to obtain the required Mw, a solvent having a large chain transfer constant, that is, a solution polymerization method using a zinc chloride aqueous solution or a suspension polymerization method using water is also preferably used.

  As the composition of the PAN-based polymer, which is the B component suitably used in the present invention, AN is preferably 93 to 100 mol%, and a monomer copolymerizable with AN is copolymerized if it is 7 mol% or less. However, as the amount of the copolymerization component increases, molecular breakage due to thermal decomposition at the copolymerization portion becomes more prominent in the flameproofing step, and the tensile strength of the resulting carbon fiber decreases.

  Examples of the monomer copolymerizable with AN include, for example, acrylic acid, methacrylic acid, itaconic acid and alkali metal salts thereof, ammonium salts and lower alkyl esters, acrylamide and derivatives thereof, allyl, from the viewpoint of promoting flame resistance. Sulfonic acid, methallylsulfonic acid and their salts or alkyl esters can be used.

  The polymerization method for producing the B component PAN-based polymer can be selected from a solution polymerization method, a suspension polymerization method, an emulsion polymerization method, and the like. It is preferable to use a solution polymerization method. In the case of polymerizing using the solution polymerization method, as the solvent, for example, a solvent in which PAN is soluble, such as an aqueous zinc chloride solution, dimethyl sulfoxide, dimethylformamide, and dimethylacetamide, is preferably used. Among these, dimethyl sulfoxide is preferably used from the viewpoint of PAN solubility. The raw materials used for these polymerizations are preferably used after passing through a filter medium having a filtration accuracy of 1 μm or less.

  The aforementioned PAN-based polymer is dissolved in a solvent in which the PAN-based polymer is soluble, such as dimethyl sulfoxide, dimethylformamide, and dimethylacetamide, to obtain a spinning solution. In the case of using solution polymerization, if the solvent used for polymerization and the spinning solvent are the same, a step of separating the obtained PAN-based polymer and re-dissolving in the spinning solvent becomes unnecessary.

  The polymer concentration in the spinning solution is preferably in the range of 5 to 30% by weight, more preferably 14 to 25% by weight, and most preferably 18 to 23% by weight. If the polymer concentration is less than 5% by weight, the amount of solvent used increases, which is not economical, and the coagulation rate in the coagulation bath is reduced, and voids are generated inside, and a dense structure may not be obtained. On the other hand, when the polymer concentration exceeds 30% by weight, the viscosity increases and spinning tends to be difficult. The polymer concentration of the spinning solution can be adjusted according to the amount of solvent used.

  In the present invention, the polymer concentration is the weight percent of the PAN polymer contained in the PAN polymer solution. Specifically, after weighing the PAN-based polymer solution, the measured PAN-based polymer solution is removed to a solvent that does not dissolve the PAN-based polymer and is compatible with the solvent used for the PAN-based polymer solution. After solvent, the PAN polymer is weighed. The polymer concentration is calculated by dividing the weight of the PAN polymer after desolvation by the weight of the PAN polymer solution before desolvation.

  Further, the viscosity of the spinning solution at a temperature of 45 ° C. is preferably in the range of 15 to 200 Pa · s, more preferably in the range of 20 to 150 Pa · s, and more preferably in the range of 30 to 100 Pa · s. Most preferably. When the solution viscosity is less than 15 Pa · s, since the formability of the spun yarn is lowered, the speed at which the yarn taken out from the die is taken, that is, the spinnability tends to be lowered. Moreover, when solution viscosity exceeds 200 Pa * s, it will become easy to gelatinize and the tendency for a filter medium to become obstruct | occluded easily will be shown. The viscosity of the spinning solution can be controlled by the amount of polymerization initiator or chain transfer agent.

  The viscosity of the PAN polymer solution at a temperature of 45 ° C. can be measured with a B-type viscometer. Specifically, the PAN-based polymer solution placed in a beaker is immersed in a hot water bath adjusted to a temperature of 45 ° C. to adjust the temperature, and as a B-type viscometer, for example, B8L manufactured by Tokyo Keiki Co., Ltd. Using a viscometer, rotor No. 4 is used, and the viscosity of the PAN polymer solution is in the range of 0 to 100 Pa · s. p. m. The viscosity of the PAN-based polymer solution is in the range of 100 to 1000 Pa · s. p. m. Measure with

  In the present invention, prior to spinning the spinning solution as described above, the polymer raw material and impurities mixed in each step are removed through a filter device. The filter device in the present invention means a facility for filtering and removing foreign matters present in the spinning solution, an inflow path for guiding the spinning solution to be filtered into the filter device, and for filtering the spinning solution. Filter medium, an outflow path for guiding the filtered spinning solution to the outside of the filter device, and a container for storing these. Here, the filter medium is a means for filtering the spinning solution stored in the filter device.

  A filter device that can be used in the present invention will be described with reference to FIGS. However, FIGS. 1-3 are illustrations and this invention is not restrict | limited by these figures and description using these figures.

  FIG. 1 is a cross-sectional view of a filter device, in which a filter medium 2 and a support 3 having liquid permeability that suppresses deformation of the filter medium are fixed in a space formed in the filtration container 1. The spinning solution passes through the spinning solution inflow path 4, is filtered by the filter medium 2, and passes through the spinning solution outflow path 5 and exits from the filter device. In addition to this basic configuration, for example, as shown in FIG. 2, a leaf disk type filter having a filter medium 2 supported by a support 3 made of a porous plate or the like along its outer periphery and having an opening 6 to the spinning solution outflow passage As shown in FIG. 3, a filter device in which a plurality of sheets 7 are stacked and fixed between a core body 8 also serving as a spinning solution outflow path and a filter press 9 in a space formed in the filtration container 1 is also preferable. It is. That is, the core body 8 has an opening 10 on the side surface, and the spinning solution is filtered by the filter medium 2 in each leaf disk type filter 7 through the spinning solution inflow path 4, and the support body 3 and the leaf disk. It is filtered by flowing out through the opening 6 to the spinning solution outflow passage on the inner diameter side, the opening 10 of the core body, and the core body 8 in this order. The outer diameter of the leaf disk type filter is represented by a distance D, and the inner diameter of the leaf disk type filter is represented by a distance d. In a leaf disk type filter, the inner periphery of the donut is exposed on the support or is covered with a plate having an opening, and the spinning solution flowing in from the upper and lower surfaces of the leaf disk filter is discharged from the inner periphery. It has come to be.

  In addition to the leaf disc type filter, candle type and pleated candle type can also be selected, but the candle type and pleated candle type have a certain curvature compared to the leaf disc type filter that can use the filter medium almost on a flat surface. The leaf disk type filter is most preferred because it may cause the distribution of the aperture diameter to be widened and the cleaning performance to deteriorate.

  The filter medium 2 used in the present invention is a part that plays a direct role for removing foreign substances present in the spinning solution, and is required to have a predetermined aperture diameter with a narrow variation. Therefore, chemical stability, heat resistance, and a certain level of pressure resistance to the material to be treated are required. Examples of such filter media include a metal mesh made by weaving metal fibers, a glass nonwoven fabric, and a metal fiber nonwoven fabric that is made into a web by opening a fiber short fiber with a card machine or air raid method. A filter medium made of a sintered metal fiber structure in which the structure is fixed by sintering is preferably used. The material of the filter medium is not particularly limited as long as it is inactive to the spinning solution and has no elution component into the solvent. Specific examples of 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 metal fiber manufacturing method is a so-called focused fiber manufacturing method, a coil cutting method, a chatter vibration cutting method, in which a large number of wires are bundled into a bundle to reduce the diameter of the wire, and then each wire is separated to reduce the diameter of the wire. Etc. In the case of a wire mesh, since it is necessary to be a single fiber, not a fiber bundle, it can be obtained by a method of repeating wire drawing and heat treatment.

The spinning solution used for the carbon fiber precursor fiber causes a process abnormality and a decrease in strength even if a slight amount of foreign matter is present, so it is necessary to remove the foreign matter by filtration before reaching the die. As such, foreign substances such as gels are easily deformed by filtration pressure and easily pass through the filter medium. In order to increase the spinning speed in order to reduce the cost of carbon fibers, it is necessary to increase the amount of filtration per unit area of the filter medium. Easier to pass through. In order to achieve both a reduction in cost and a further increase in strength of the carbon fiber, a method for accurately filtering the gel-like material with a low filtration pressure is required. Conventionally, a method of filtering with a filter medium having a large thickness and a fine size has been the mainstream, and a method of collecting and preventing deformation of a gel-like material with a low filtration pressure has not been discussed. Therefore, as a result of repeated studies by the present inventors, a filter medium having a filtration guarantee layer having a basis weight A (g / m ² ) and material density B (g / m ³ ) satisfying the following formula, and It has been found that by using a filter medium having a filtration resistance coefficient C of 5 to 30 × 10 ⁵ cm ⁻¹ , a gel-like material can be accurately filtered with a low filtration pressure.
0.01 ≦ A / B × 1000 ≦ 0.06
Some filter media have a uniform wire diameter and filling rate along an axis perpendicular to the filter surface, but many are obtained by laminating a plurality of layers having different wire diameters and filling rates. The filtration guarantee layer refers to a layer having the finest pore diameter among layers constituting the filter medium, that is, a layer having the highest filtration accuracy. Of the layers constituting the filter medium, the portion excluding the filtration guarantee layer is referred to as a reinforcing layer, and details will be described later. In the case where there are intermittently a plurality of filtration guarantee layers having the same filtration accuracy, the integrated value is used. The basis weight of the filtration guarantee layer is shown as a mass (g) per 1 m ^{2 of the} filtration guarantee layer, that is, g / m ² . The filtration guarantee layer generally has a mechanical strength by fixing the structure through a process of sintering that promotes crystallization at the contact portion of the metal fiber. Even when the filtration guarantee layer is produced by sintering, the change in weight and area before and after sintering is negligible. Use. Although the value obtained by taking out only the filtration assurance layer portion after sintering may be used, when the basis weight of the filtration assurance layer before and after sintering is different, the value before sintering is preferentially used. The filtration resistance coefficient C is a value indicating the difficulty of passing the fluid through the filter medium, which can be calculated from the air flow per unit time.

  In order to reduce the outflow due to deformation or pulverization of the gel-like material existing in the spinning solution on the filter medium, it is necessary to reduce the shear stress applied to the gel-like material. Since the shear stress has a positive correlation with the pressure loss, it is effective to reduce the pressure loss in order to avoid the outflow of the gel. For that purpose, it is necessary to reduce the filtration resistance coefficient C which is proportional to the pressure loss. The filtration resistance coefficient C depends on the aperture diameter, filling rate, thickness, etc. of the filter medium.

  In particular, the filtration resistance coefficient C can be effectively reduced by adjusting the filling rate of the filter medium as described later. The filling rate of the filter medium is an average obtained by microscopically photographing the vertical cross sections of the filtration guarantee layer and the reinforcing layer constituting the filter medium, and measuring the area ratio of materials such as fibers in the visual field area at three locations by the image analysis method. The value is shown as a weighted average further weighted by the thickness of each layer. There is a positive correlation between the filling rate of the filter medium and the filtration resistance coefficient C. The higher the filling rate, the larger the filtration resistance coefficient C. To reduce the filtration resistance coefficient C, simply lowering the filling rate has the problem of reducing the filtration accuracy. Therefore, the wire diameter of the metal fibers constituting the filter medium should be reduced to 0.5 to 2.5 μm. Therefore, the filtration resistance coefficient C may be reduced.

  On the other hand, a PAN-based polymer having Mz / Mw of 1.5 or more and having a wide distribution on the high molecular weight side exhibits pressure loss behavior that cannot be explained only by the filtration resistance coefficient C, and does not have a long distribution on the high molecular weight side. Sudden filter media clogging may occur, which is not seen when filtering ordinary PAN-based polymers. When such clogging occurred, the molecular weight distribution after passing through the filter medium was changed from that before passing through, so it is presumed that high molecular weight components were deposited on the filter medium. It is known that when shear stress is applied to a polymer solution in which different components are compatible, a phenomenon called shear-induced phase separation occurs in which different components separate and form domains, respectively. Presumed to be. When shear-induced phase separation occurs in the flow field in the pipe, the degree of phase separation increases as the flow proceeds in the length direction of the flow path. Therefore, in order to avoid the filter medium clogging due to shear-induced phase separation, it is considered that the thickness of the filter medium should be controlled. However, in reality, the filter medium has the highest filtration accuracy and therefore the most shear stress is applied. As a result of examination, it became clear that it was effective to control the thickness of the filtration guarantee layer. A / B corresponds to the thickness (unit: m) when it is assumed that the filtration guarantee layer is compressed so that the aperture is zero, and hereinafter referred to as filtration guarantee layer compression thickness. A / B × 1000 is obtained by converting the filtration guarantee layer compression thickness into mm units. The compression guaranteed layer compression thickness can be used as a constant standard for the thickness regardless of the aperture diameter of the filtration guaranteed layer.

The filtration guarantee layer compression thickness A / B × 1000 is preferably 0.01 to 0.06 mm. If it is less than 0.01 mm, the filter medium cannot be secured with respect to the pressure loss that acts during filtration, and the filter medium breaks, causing a gelled material to flow out. If it exceeds 0.06 mm The filter medium is blocked by shear-induced phase separation. When the filtration guarantee layer is made of stainless steel, B is about 8 × 10 ⁶ g / m ^3, so the compression guarantee layer compression thickness is adjusted within the above range by controlling A to be 80 to 500 g / m ^2. Good.

The filtration resistance coefficient C is preferably ^{5 to} 30 × 10 ⁵ cm ⁻¹ , more preferably ^{5 to} 20 × 10 ⁵ cm ⁻¹ , and 5 to 10 × 10 ⁵ cm ^−1. Is most preferred. When the diameter is less than 5 × 10 ⁵ cm ⁻¹ , the pore diameter is large, the gel-like material passes through the eye, and when it exceeds 30 × 10 ⁵ cm ⁻¹ , the pressure loss is high and the gel-like material flows out. Will occur.

  Specifically, as a filter medium that satisfies the above-mentioned conditions, a wire having a wire diameter of 10 to 25 μm is used in a twill woven, warp yarn is 500 to 800 mesh, preferably 635 to 800 mesh, and weft yarn is 3500 to 6000 mesh, preferably 4300. Examples thereof include a wire mesh that is woven as ˜6000 mesh, and a single layer or a plurality of layers are laminated and sintered. Conventionally, filtration using a wire mesh is said to be unsuitable for filtration of a gel-like material because it is thin and coarse, but it contains a gel-like material using a fine wire mesh with a thin wire diameter and a high mesh. As a result of filtering the polymer solution, the inventors have obtained an unprecedented new finding that the gel-like material is less discharged. Moreover, it is also possible to use a sintered metal nonwoven fabric as a filter medium that satisfies the above conditions. Since a nonwoven fabric with a small wire diameter can be used, there is an advantage that the aperture diameter can be easily reduced, which is preferable. On the other hand, in order to compensate for the wide distribution of pore diameters that are common in non-woven fabrics, the thickness may be increased, but the number of filtration stages can be increased by reducing the wire diameter to 0.5 to 2.5 μm without increasing the thickness. Therefore, it is often solved. For non-woven fabrics, metal fibers and powders with an aspect ratio of 1 to 1000 can be used according to the purpose, and the pore diameter can be controlled. Mixing metal fibers and powders with different aspect ratios is also an effective means. It is.

  A conventional method may be used for the sintering, but it is preferable to control the pore diameters of the woven fabric and the nonwoven fabric by adjusting the sintering time, the sintering temperature, or the number of times of sintering.

  In the present invention, the filtration accuracy of the filter medium, which is closely related to the aperture diameter, is preferably 1 to 10 μm, more preferably 1 to 5 μm, and further preferably 1 to 3 μm. If the filtration accuracy is too high, foreign matter in the spinning solution after passing through the filter medium increases, which is not preferable. Therefore, the smaller the better, the smaller is 1 μm. The filtration accuracy of the filter medium in the present invention is defined by the particle diameter (diameter) of spherical particles capable of collecting 95% while passing through the filter medium. The measurement method conforms to JIS B8356, and a standard material is used for the particles.

In the present invention, the value of the residence time V / W in the filter medium indicated by the ratio between the effective volume V (L) of the filter medium and the polymer solution filtration flow rate W (L / min) is set to 0.01 to 10 minutes. It is also preferable to prevent the high molecular weight component from being filtered. Here, the effective volume V of the filter medium represents the spatial volume of the filter medium. Such a volume is calculated from the filter filtration area and the thickness of the filter medium. Although the filter medium may have a layer structure, it refers to the thickness of the narrowest part of the filter medium with the pore diameter. This thickness can be specified by cutting out a cross section of the filter medium and observing it with a microscope or the like. The polymer solution filtration flow rate W represents the volume flow rate of the spinning solution passing through the filter medium per minute, and the residence time V / W in the filter medium represents the average residence time of the spinning solution passing through the filter medium. When the molecular weight distribution is wide on the high molecular weight side, components having a high molecular weight are often filtered in a deep layer in the filter medium, and the filter medium is preferably thin. Therefore, when V / W exceeds 10 minutes, a component having a high molecular weight is often not filtered. On the other hand, when V / W is less than 0.01 minutes, the operation pressure of filtration increases, which is not preferable. A more preferable range of V / W is 0.1 to 5 minutes, and a more preferable range is 0.1 to 0.5 minutes. The compression guaranteed layer compression thickness of such filter media is controlled within the above range. Then, compared with the conventional product, the strength may decrease, and the filter medium may be broken even with a low pressure loss. Therefore, in such a case, as described above, by laminating a reinforcing layer having a filtration accuracy lower than that of the filtration guarantee layer on both the upper and lower sides or one side of the filtration guarantee layer, sintering is performed to obtain a filter medium. , Can give strength. The reinforcing layer may differ from the filtration guarantee layer in terms of basis weight, filling rate, material, and the like, and the number and order of lamination of both can be arbitrarily selected. The kind of the reinforcing layer is the same as that used for the filtration guarantee layer, such as a metal nonwoven fabric, a metal particle sintered body, and a metal mesh woven with metal fibers, and may be appropriately combined. In the case where the reinforcing layer is also arranged on the upstream side of the filtration guarantee layer, it is also preferable from the viewpoint of increasing the pressure resistance by pressure dispersion and multistage filtration of foreign matters by changing the aperture diameter stepwise. From this viewpoint, the number of layers constituting the filter medium is preferably 2 to 7 layers.

  In order to provide further pressure resistance, aside from the filter media, as a support on the upper and lower sides or downstream side, retainer mesh, punching metal, 0.1 to 0.5 mm metal wire is woven to about 10 to 100 # A sheet-like woven material, a flat screen obtained by rolling the sheet-like woven material, and the like can be used in combination. When these supports are stacked on the upstream side of the filter medium, there is an effect of preventing the filter medium from being damaged by foreign substances and improving the handling property during cleaning and reuse.

Filter medium, it is preferable that the 300~2500g / ^{m 2} a total basis weight which is the sum of the basis weight of the filter guarantees layer and reinforcing layer, and more preferably to 1000~2500g / ^{m 2.} From the viewpoint of reducing the pressure loss, the total basis weight is preferably small. However, if the total basis weight is less than 300 g / m ² , the filter medium may not withstand the pressure loss and may break. On the other hand, if the total basis weight is larger than 2500 g / m ² , the pressure loss of the filter medium increases, and the gel-like material may be deformed or crushed and flow out. In addition, when the total basis weight is in the range of 300 g / m ² or more and less than 1000 g / m ² , there is no problem at the beginning of filtration when the pressure loss is small, but when the filtration guarantee layer is a metal nonwoven fabric, the pressure loss increases when the pressure loss increases with time. The filter medium may not be able to withstand and may break. When the total basis weight of the filter medium is in the above range, it is particularly effective as a filter medium used for a leaf disk type filter that is flat and does not require bending, and easily increases the filtration area. On the other hand, when the filter media in the range where the total basis weight is applied is applied to a pleated filter or a candle filter that needs to be bent, the pore diameter distribution is widened by bending, and the filtration performance of the gel-like material may be lowered. .

  In the present invention, the filtration operation is such that the viscosity of the spinning solution decreases as the temperature of the spinning solution decreases, and the pressure loss can be reduced. Specifically, 20-80 degreeC is preferable and 20-40 degreeC is more preferable. By using the above-described filter medium, pressure loss can be greatly reduced as compared with the conventional method even when filtration is performed at a low temperature, and the outflow of gel-like material can be reduced. Equivalent to the discharge temperature at the base is also a preferable means for reducing the heating and cooling devices after the filter medium.

  In the present invention, it is important that the filter device using the filter medium having the highest filtration accuracy (small pore diameter) is as described above, but the pre-filter device is used before filtering with the filter device. May be filtered. In some cases, the spinning solution may contain large aggregates or gels. In this case, it is also preferable to filter the filter medium with reduced filtration accuracy in stages as a prefilter. Moreover, it is sometimes effective to use a sand or a toughmic filter that is generally known for reducing aggregates, and can be used as a prefilter as appropriate.

  In the present invention, the carbon fiber precursor fiber is produced by spinning the spinning solution filtered as described above by a dry, wet, or dry-wet spinning method. In particular, the dry and wet spinning method is preferably used because it exhibits the characteristics of the PAN-based polymer having the specific molecular weight distribution described above.

  The diameter of the die hole used for spinning is preferably 0.05 mm to 0.3 mm, and more preferably 0.1 to 0.15 mm. When the diameter of the nozzle hole is smaller than 0.05 mm, shearing stress is applied to the spinning solution, which may block the nozzle. On the other hand, when the diameter of the die hole exceeds 0.3 mm, it may be difficult to obtain a fiber having a single fiber fineness of 1.5 dtex or less.

  In the present invention, the coagulation bath preferably contains a solvent such as dimethyl sulfoxide, dimethylformamide and dimethylacetamide used as a solvent for the spinning solution and a so-called coagulation promoting component. As the coagulation accelerating component, a component that does not dissolve the PAN polymer and is compatible with the solvent used in the spinning solution is preferable, and specifically, water is preferably used. The conditions as the coagulation bath are preferably controlled so that the cross section of the single fiber in the coagulated yarn is as close to a perfect circle as possible, and the concentration of the solvent is preferably not more than a concentration called a critical bath concentration. If the concentration of the solvent is high, the subsequent solvent washing step becomes long and the productivity is lowered. For example, when dimethyl sulfoxide is used as the solvent, the concentration of the dimethyl sulfoxide aqueous solution is preferably 5 to 55% by weight, and more preferably 5 to 30% by weight. The temperature of the coagulation bath is preferably controlled so that the fiber side surface is as smooth as possible. Specifically, the temperature is preferably −10 to 30 ° C., more preferably −5 to 5 ° C.

  The spinning solution is introduced into a coagulation bath and coagulated to form a yarn to obtain a coagulated yarn, which is then taken up by a roller having a drive source, and the take-up speed of the coagulated yarn is 50 to 500 m / min. Is preferable from the viewpoint of exhibiting the characteristics of the PAN-based polymer solution having the specific molecular weight distribution described above. When the take-up speed is less than 50 m / min, the productivity is lowered, and when the take-up speed exceeds 500 m / min, the liquid level fluctuation of the coagulation bath becomes remarkable and the resulting fineness tends to be uneven.

  Thereafter, the taken-up coagulated yarn is usually subjected to a water washing step, an in-bath drawing step, an oil agent application step, and a drying step to obtain a carbon fiber precursor fiber. Moreover, you may add a dry heat extending process and a steam extending process to said process. The solidified yarn may be directly stretched in the bath without the water washing step, or may be stretched in the bath after removing the solvent by the water washing step. Usually, the stretching in the bath is preferably performed in a single or a plurality of stretching baths adjusted to a temperature of 30 to 98 ° C. The draw ratio at that time is preferably 1 to 5 times, and more preferably 1 to 3 times.

  After the stretching step in the bath, it is preferable to apply an oil agent made of silicone or the like to the stretched fiber yarn for the purpose of preventing adhesion between single fibers. As the silicone oil, it is preferable to use a silicone oil containing a modified silicone such as amino-modified silicone having high heat resistance.

  As the drying step, for example, a drying condition in which a drying temperature is 70 to 200 ° C. and a drying time is 10 seconds to 200 seconds gives preferable results. In order to improve the productivity and the degree of crystal orientation, it is preferable to stretch in a heating heat medium after the drying step. As the heating heat medium, for example, pressurized steam or superheated steam is suitably used in terms of operational stability and cost, and the draw ratio is usually 1.5 to 10 times.

  The single fiber fineness of the carbon fiber precursor fiber thus obtained is preferably 0.01 to 1.5 dtex, more preferably 0.05 to 1.0 dtex, 0.1 to 0 More preferably, it is .8 dtex. If the single fiber fineness is too small, the process stability of the yarn making process and the carbon fiber firing process may decrease due to the occurrence of yarn breakage due to contact with a roller or a guide. On the other hand, if the single fiber fineness is too large, the difference between the inner and outer structures of each single fiber after flame resistance will increase, and the processability in the subsequent carbonization process and the tensile strength and tensile modulus of the resulting carbon fiber will decrease. There is.

  The obtained carbon fiber precursor fiber is usually in the form of a continuous fiber (filament). The number of filaments per one yarn (multifilament) is preferably 1,000 to 3,000,000, more preferably 12,000 to 3,000,000, and still more preferably. The number is 24,000 to 2,500,000, and most preferably 24,000 to 2,000,000. Since the obtained carbon fiber precursor fiber has high drawability, the single fiber fineness can be made smaller than before, while the number of filaments per yarn is larger for the purpose of improving productivity. Although it is preferable, if it is too much, it may not be possible to uniformly treat the inside of the bundle.

  The carbon fiber precursor fiber obtained as described above can be made into carbon fiber according to a conventional method. That is, the carbon fiber precursor fiber obtained as described above is subjected to flame resistance treatment in air at a temperature of 200 to 300 ° C., and then pre-carbonized in an inert atmosphere at a temperature of 300 to 800 ° C. Then, carbonization is performed in an inert atmosphere at a temperature of 1,000 to 3,000 ° C. In particular, from the viewpoint of increasing the tensile elastic modulus of the carbon fiber, it is preferable that the tension in the carbonization treatment is 5.9 to 13 mN per unit fineness (dtex) of the precursor. Since the fiber precursor fiber is obtained, problems such as fluffing are unlikely to occur in the firing process.

Hereinafter, the present invention will be described more specifically with reference to examples. The measurement method used in this example will be described next.

<Carbon removal rate>
First, the carbon fine powder is mixed with the spinning solution to be measured by a mechanical stirrer so as to be 100 ppm to prepare a carbon fine powder mixed solution. As the carbon fine powder, activated carbon is crushed and sieved with a plain weave mesh having an opening diameter of 63 μm. Next, this carbon fine powder mixed solution is allowed to flow into the filter device shown in FIG. 1 in which the filter medium to be measured is arranged, and is filtered at a filtration rate of 127 L / m ³ / hour. The absorbance at a wavelength of 650 nm of the solution before and after filtration is measured, and the removal rate is calculated by substituting it into the following equation.

Removal rate (%) = (Absorbance before filtration−Absorbance after filtration) / Absorbance before filtration × 100 (%)
<Gel removal rate>
First, the gel-like product is mixed with the spinning solution to be measured by a mechanical stirrer so as to be 100 ppm to prepare a gel-like product mixed solution. After diluting 300 g of the gel-like mixture solution 20 times with dimethyl sulfoxide, it was passed through a glass filter GA-100 that had been measured for its dry weight in advance, and then the dry weight of the glass filter was measured and filtered. From the absolute dry weight difference between the front and rear glass filters, the weight (M ₁ ) of the gel-like material is determined. The gel-like product is prepared by heating the spinning solution obtained by the method described in Example 1 at 120 ° C. for 24 hours, and further lining the gel-like product with a plain weave mesh having an opening diameter of 1 mm. Next, this gel mixture solution is allowed to flow into the filter device shown in FIG. 1 in which the filter medium to be measured is arranged, and is filtered at a rate of 12.7 L / m ³ / hour. After diluting 300 g of the filtrate 20 times with dimethyl sulfoxide, the filtrate was passed through a glass filter GA-100 that had been measured for its dry weight in advance, and then the dry weight of the glass filter was measured. From the absolute dry weight difference, the weight (M ₂ ) of the gel-like material contained in 300 g of the filtrate after filtering the filter medium is determined. The removal rate is calculated by substituting the weights M ₁ and M ₂ obtained in this way into the formula of 100 × (1-M ₂ / M ₁ ).
<Number of microgels>
The spinning dope is allowed to flow into the filter apparatus shown in FIG. 1 in which the filter medium to be measured is arranged, and is filtered at a rate of 12.7 L / m ³ / hour. After diluting 50 g of the filtrate 20 times with dimethyl sulfoxide and passing through a PTFE membrane filter JHWP (0.45 μm), the surface of the membrane filter was observed with a fluorescence microscope, and the number of yellow bright spots per field of view was measured with a microgel. Number.
<Filter blockage limit speed>
The spinning solution to be measured is allowed to flow into the filter device shown in FIG. 1 in which the filter medium to be measured is arranged, and the relationship between the pressure loss and the flow rate is recorded while the flow rate is intermittently changed. Normally, when the flow rate is changed and waits for 5 minutes, the pressure loss shows a constant value, so that value is recorded as the pressure loss at the corresponding flow rate. As the flow rate is increased, the pressure loss increases with time at a certain flow rate, and the pressure loss exceeds 7 MPa within a few minutes. The observation point just before the flow rate is called the filter clogging limit speed. Strictly speaking, the filter clogging limit speed exists at one point between the flow rate of the pressure drop sudden rise and the observation point just before it, but is defined in this way for convenience of measurement.
<Various molecular weights: Mz, Mw, Mn>
A sample solution is prepared by dissolving 0.1% by weight of the polymer to be measured in dimethylformamide (0.01N-lithium bromide added). For the prepared specimen solution, a molecular weight distribution curve is obtained from a GPC curve measured under the following conditions using a GPC apparatus, and Mz, Mw, and Mn are calculated. The measurement was performed three times, and the values of Mz, Mw, and Mn were averaged and used.
-Column: Column for polar organic solvent GPC-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 Mw uses at least six types of monodispersed polystyrenes with different molecular weights and known molecular weights to create an elution time-molecular weight calibration curve, and corresponds to the corresponding elution time on the calibration curve. It is obtained by reading the molecular weight in terms of polystyrene.

In this example, CLASS-LC2010 manufactured by Shimadzu Corporation as a GPC device, and TSK-GEL-α-M (× 2) manufactured by Tosoh Corporation as a column and TSK-guard Column α manufactured by Tosoh Corporation, Calibration curves were manufactured by Wako Pure Chemical Industries, Ltd. as dimethylformamide and lithium bromide, 0.45 μm-FHLP FILTER manufactured by Millipore Corporation as a membrane filter, and RID-10AV manufactured by Shimadzu Corporation as a differential refractive index detector. As the monodisperse polystyrene for production, those having molecular weights of 184000, 427000, 791000, 1300000, 1810000 and 4240000 were used, respectively.
<Tensile strength and elastic modulus of carbon fiber bundle>
Determined according to JIS R7601 (1986) “Resin-impregnated strand test method”. The carbon fiber resin-impregnated strand to be measured is 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexyl-carboxylate (100 parts by weight) / 3 boron trifluoride monoethylamine (3 parts by weight) / acetone (4 parts by weight). ) Is impregnated into carbon fiber or graphitized fiber and cured at a temperature of 130 ° C. for 30 minutes. The number of carbon fiber strands to be measured is 6, and the average value of each measurement result is the tensile strength. In this example, “Bakelite” (registered trademark) ERL4221 manufactured by Union Carbide Co., Ltd. was used as 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexyl-carboxylate.
[Example 1]
100 parts by weight of AN, 1 part by weight of itaconic acid, 0.4 parts by weight of 2,2′-azobis (2-methylpropionitrile) (hereinafter abbreviated as AIBN) as a radical initiator, and octyl mercaptan as a chain transfer agent 1 part by weight was uniformly dissolved in 370 parts by weight of dimethyl sulfoxide, and it was put into a reaction vessel equipped with a reflux tube and a stirring blade. After the space in the reaction vessel was purged with nitrogen until the oxygen concentration reached 1000 ppm, the following heat treatments (1) to (4) were performed with stirring, and polymerized by a solution polymerization method to obtain a PAN polymer solution. Obtained.
(1) Temperature increase from 30 ° C to 60 ° C (temperature increase rate 10 ° C / hour)
(2) Hold for 4 hours at a temperature of 60 ° C. (3) Increase the temperature from 60 ° C. to 80 ° C. (temperature increase rate 10 ° C./hour)
(4) Hold for 6 hours at a temperature of 80 ° C. The polymer concentration of the obtained PAN-based polymer solution with respect to the solvent was slightly less than 20% by weight.

  The obtained PAN-based polymer solution was prepared so that the polymer concentration was 20% by weight, and then ammonia gas was blown until the pH reached 8.5 to neutralize itaconic acid, while the ammonium group was neutralized. Was introduced into the polymer to obtain a spinning solution.

The obtained spinning solution was evaluated for filter closing limit speed, carbon removal rate, gel removal rate, and number of microgels. The filter medium used at this time was made into a twilled woven mesh using SUS316 metal fibers with an average wire diameter of 20 μm as warp and SUS316 metal fibers with an average wire diameter of 13 μm as wefts, and then sintered. 220 g / m ^2, is obtained by a 85% filling factor, filtered guaranteed layer basis weight a, the material density B of the filtration warranty layer, the thickness of the filtration resistance coefficient C, and filtered guaranteed layer were as shown in Table 1.

  Next, the obtained spinning solution was filtered with the filter device shown in FIG. 3 in which the same filter medium as described above was placed, and then at a temperature of 40 ° C., a spinneret having a number of holes of 1,500 and a nozzle diameter of 0.15 mm. , Once discharged into the air, passed through a space of about 2 mm, and then spun by a dry-wet spinning method introduced into a coagulation bath consisting of an aqueous solution of 20% by weight dimethyl sulfoxide controlled at a temperature of 3 ° C. It was. The limit spinning draft rate at which yarn breakage occurred was measured by adjusting the amount of liquid fed to the die so that the discharge linear velocity was 2 m / min and changing the winding speed of the coagulated yarn. Moreover, after obtaining a coagulated yarn under the condition of a spinning draft ratio of 4, and washing with water, it was stretched at a stretching ratio of 3 times in a bath at 90 ° C. in warm water, and further provided with an amino-modified silicone-based silicone oil, at 165 ° C. Drying was performed for 30 seconds using a roller heated to a temperature, and pressure steam stretching was performed under a steam stretching ratio condition of 5 times to obtain a carbon fiber precursor fiber having a single fiber fineness of 0.8 dtex. The quality of the obtained carbon fiber precursor fiber was excellent, and the yarn passing through the spinning process was stable. The obtained carbon fiber precursor fiber is combined so that the number of filaments becomes 12,000, and flameproofing is performed for 90 minutes while stretching at a draw ratio of 1.0 in air having a temperature distribution of 240 to 260 ° C. As a result, flameproofed fibers were obtained. Subsequently, in the nitrogen atmosphere having a temperature distribution of 300 to 700 ° C., the obtained flame-resistant fiber is subjected to preliminary carbonization while being drawn at a draw ratio of 1.2, and further in a nitrogen atmosphere having a maximum temperature of 1500 ° C. , Carbonization was performed with the draw ratio set to 0.97 to obtain continuous carbon fibers. In this case, the baking process passability was good.

When the strand physical property of the obtained carbon fiber bundle was measured, the strength was 6.7 GPa and the elastic modulus was 320 GPa.
[Example 2]
100 parts by weight of AN, 1 part by weight of itaconic acid, and 130 parts by weight of dimethyl sulfoxide were mixed and placed in a reaction vessel equipped with a reflux tube and a stirring blade. The space in the reaction vessel was purged with nitrogen until the oxygen concentration reached 1000 ppm, and then, as a radical initiator, 0.002 part by weight of 2,2′-azobisisobutyronitrile (AIBN) was added and stirred as follows. (Hereinafter referred to as polymerization condition A) was subjected to heat treatment and polymerized by a solution polymerization method to obtain a primary solution of a PAN-based polymer.
Polymerization condition A
-Hold for 2 hours at a temperature of 70 ° C-Temperature drop from 70 ° C to 30 ° C
The primary solution of the obtained PAN-based polymer was poured into water to precipitate the polymer, which was washed with warm water at 80 ° C. for 2 hours and then dried at 70 ° C. for 4 hours to obtain a dried polymer. . Mz, Mw and Mn of the obtained dry polymer were 5.8 million, 3.4 million and 1.4 million, respectively. Moreover, the polymer concentration with respect to the solvent of the primary solution of the obtained PAN polymer was 1.5% by weight.

Next, in order to polymerize the unreacted AN remaining in the obtained primary solution, 240 parts by weight of dimethyl sulfoxide, 0.4 part by weight of AIBN as a radical initiator, and octyl mercaptan as a chain transfer agent are contained in the primary solution. After 0.1 part by weight was metered in and the space in the reaction vessel was purged with nitrogen until the oxygen concentration reached 1000 ppm, heat treatment was performed under the following conditions (referred to as polymerization conditions B) with further stirring. Polymerization Condition B for Obtaining Secondary Solution of PAN Polymer by Polymerizing Unreacted Monomer to be Prepared by Solution Polymerization Method
(1) Temperature increase from 30 ° C to 60 ° C (temperature increase rate 10 ° C / hour)
(2) Hold for 4 hours at a temperature of 60 ° C. (3) Increase the temperature from 60 ° C. to 80 ° C. (temperature increase rate 10 ° C./hour)
(4) Holding at 80 ° C. for 6 hours The polymer concentration of the obtained secondary solution with respect to the solvent was a little less than 20% by weight.

  Using the obtained secondary solution, various molecular weights of the PAN-based polymer contained therein were measured. Next, after preparing the polymer concentration to be 20% by weight using the obtained secondary solution, ammonia gas was blown until the pH became 8.5, thereby neutralizing itaconic acid and adding ammonium. Groups were introduced into the polymer to obtain a spinning solution. The obtained spinning solution was evaluated in the same manner as in Example 1 for the filter closing limit speed, the carbon removal rate, the gel removal rate, and the number of microgels.

Next, a carbon fiber bundle was obtained in the same manner as in Example 1 except that the spinning solution used was changed to the spinning solution obtained as described above. When the strand physical property of the obtained carbon fiber bundle was measured, the strength was 6.7 GPa and the elastic modulus was 330 GPa.
[Example 3]
A carbon fiber bundle was obtained in the same manner as in Example 2 except that the holding time in (1) of the polymerization condition A was changed to 1.5 hours. When the strand physical property of the obtained carbon fiber bundle was measured, the strength was 6.7 GPa and the elastic modulus was 330 GPa. The dry polymer obtained from the primary solution in the same procedure as in Example 1 had Mz, Mw and Mn of 5.8 million, 3.4 million and 1.4 million, respectively, and the polymer concentration with respect to the solvent of the primary solution was 0 The polymer concentration with respect to the solvent of the secondary solution was less than 20% by weight [Example 4].
The carbon fiber bundle was changed in the same manner as in Example 2 except that the oxygen concentration when the space in the reaction vessel was replaced with nitrogen was changed to 100 ppm and the holding temperature in (1) of the polymerization condition A was changed to 65 ° C. Obtained. When the strand physical property of the obtained carbon fiber bundle was measured, the strength was 6.7 GPa and the elastic modulus was 316 GPa. The dried polymer obtained from the primary solution in the same procedure as in Example 1 had Mz, Mw and Mn of 68,000, 5 million and 3.3 million, respectively, and the polymer concentration with respect to the solvent of the primary solution was 2 The polymer concentration with respect to the solvent of the secondary solution was less than 20% by weight.
[Example 5]
100 parts by weight of AN, 0.3 part by weight of itaconic acid, 0.003 part by weight of octyl mercaptan as a chain transfer agent, and 360 parts by weight of dimethyl sulfoxide were mixed and placed in a reaction vessel equipped with a reflux tube and a stirring blade. After replacing the space in the reaction vessel with nitrogen until the oxygen concentration reached 100 ppm, 0.003 part by weight of AIBN was added as a polymerization initiator, and heat treatment was performed under the following conditions while stirring, and polymerization was performed by a solution polymerization method. A primary solution of the PAN polymer was obtained.
-Hold at a temperature of 60 ° C for 3.5 hours The primary solution of the obtained PAN-based polymer is poured into water to precipitate the polymer, washed with warm water of 80 ° C for 2 hours, and then heated at a temperature of 70 ° C for 4 hours. Drying for a time gave a dry polymer. Mz, Mw and Mn of the obtained dry polymer were 4.8 million, 2.8 million and 1.2 million, respectively. The polymer concentration with respect to the solvent of the primary solution of the obtained PAN-based polymer was 0.5% by weight.

Next, 0.7 parts by weight of itaconic acid, 10 parts by weight of dimethyl sulfoxide, 0.4 parts by weight of AIBN as a polymerization initiator, and 0.01 part by weight of octyl mercaptan as a chain transfer agent were metered into the primary solution. Further, heat treatment was performed under the following conditions while stirring, and the remaining unreacted monomer was polymerized by a solution polymerization method to obtain a secondary solution of a PAN-based polymer.
(2) Hold for 2 hours at a temperature of 60 ° C. (3) Increase the temperature from 60 ° C. to 80 ° C. (temperature increase rate: 10 ° C./hour)
(4) Hold for 6 hours at a temperature of 80 ° C. The polymer concentration in the solvent of the obtained PAN-based polymer solution was less than 20% by weight. Next, the polymer concentration was 20 using the obtained secondary solution. After preparing so that it might become weight%, the ammonia group was introduce | transduced into the polymer, neutralizing itaconic acid by blowing in ammonia gas until pH became 8.5, and the spinning solution was obtained.

  The obtained spinning solution was evaluated in the same manner as in Example 1 for the filter closing limit speed, the carbon removal rate, the gel removal rate, and the number of microgels.

Next, a carbon fiber bundle was obtained in the same manner as in Example 1 except that the spinning solution used was changed to the spinning solution obtained as described above. When the strand physical property of the obtained carbon fiber bundle was measured, the strength was 6.7 GPa and the elastic modulus was 320 GPa.
[Example 6]
The spinning solution obtained in the same manner as in Example 1 was evaluated for the filter closing limit speed, the carbon removal rate, and the gel removal rate. The filter media used were SUS316 metal fibers with an average wire diameter of 20 μm as warp yarns, SUS316 metal fibers with an average wire diameter of 13 μm as weft yarns, sintered, and then filtered to guarantee filtration. A non-woven fabric formed using SUS316L metal fibers with an average wire diameter of 20 μm is laminated on a filtration guarantee layer having a layer basis weight of 220 g / m ² and a filling rate of 85%. Table 1 shows the material density B, the filtration resistance coefficient C, and the thickness of the filtration guarantee layer.

A carbon fiber bundle was obtained in the same manner as in Example 1 except that the filter medium used was changed to the one described above. When the strand physical property of the obtained carbon fiber bundle was measured, the strength was 6.7 GPa and the elastic modulus was 320 GPa.
[Comparative Example 1]
The filter medium to be used was formed by forming a nonwoven fabric using metal fibers made of SUS316L having an average wire diameter of 5 μm and then sintering to give a total basis weight of 1700 g / m ² and a filling rate of 50%. Except for changing to a filter medium having a basis weight A, a material density B of the filtration guarantee layer, a filtration resistance coefficient C and a thickness of the filtration guarantee layer as shown in Table 1, the filter clogging limit speed, carbon After evaluating the removal rate, the gel removal rate, and the number of microgels, an attempt was made to obtain a carbon fiber precursor fiber. However, a high-quality precursor fiber with high pressure loss during filtration and withstanding firing could not be obtained.
[Example 7]
The filter medium used is a SUS316L metal having an average wire diameter of 8 μm formed on a non-woven fabric using a SUS316L metal fiber having an average wire diameter of 2 μm and a filtration guarantee layer having a basis weight of 400 g / m ² and a filling rate of 20%. The nonwoven fabric formed using the fibers is stacked and then sintered, and the nonwoven fabric formed using the SUS316L metal fibers having an average wire diameter of 20 μm is laminated. Except for changing to a filter medium having the material density B, the filtration resistance coefficient C, and the thickness of the filtration guarantee layer as shown in Table 1, the filter clogging speed limit, the carbon removal rate, the gel removal rate, and While evaluating the number of microgels, a carbon fiber bundle was obtained. When the strand physical property of the obtained carbon fiber bundle was measured, the strength was 6.3 GPa and the elastic modulus was 320 GPa.
[Example 8]
The filter medium used is a SUS316L metal fiber having an average wire diameter of 6 μm and a filtration guarantee layer having a basis weight of 400 g / m ² and a filling rate of 20% formed on a nonwoven fabric using SUS316L metal fibers having an average wire diameter of 2 μm. The nonwoven fabric formed by using the SUS316L metal fiber having an average wire diameter of 20 μm is laminated and laminated, and the filtration assurance layer basis weight A, the material of the filtration assurance layer Except for the change to a filter medium whose density B, filtration resistance coefficient C, and filtration guarantee layer thickness are as shown in Table 1, filter clogging limit speed, carbon removal rate, gel removal rate and microgel were the same as in Example 1. While evaluating the number, a carbon fiber bundle was obtained. When the strand physical property of the obtained carbon fiber bundle was measured, the strength was 6.5 GPa and the elastic modulus was 320 GPa.
[Example 9]
The filter device used was changed to the one shown in FIG. 1, and the filter clogging limit speed, carbon removal rate, gel removal rate, and microgel were the same as in Example 8 except that the thickness of the filtration guarantee layer was changed to 0.2 mm. While evaluating the number, a carbon fiber bundle was obtained. When the strand physical property of the obtained carbon fiber bundle was measured, the strength was 6.5 GPa and the elastic modulus was 320 GPa.
[Example 10]
The filter medium used is a SUS316L metal fiber having an average wire diameter of 5 μm and a filtration guarantee layer having a basis weight of 400 g / m ² and a filling rate of 20% formed on a non-woven fabric using SUS316L metal fibers having an average wire diameter of 2 μm. The nonwoven fabric formed by using the SUS316L metal fiber having an average wire diameter of 20 μm is laminated and laminated, and the filtration assurance layer basis weight A, the material of the filtration assurance layer Except for changing to a filter medium whose density B, filtration resistance coefficient C, and thickness of the filtration guarantee layer are those shown in Table 1, filter clogging limit speed, carbon removal rate, gel removal rate and microgel were the same as in Example 9. While evaluating the number, a carbon fiber bundle was obtained. However, the pressure resistance of the filter medium was low, and the filter performance and the yarn production were good at the beginning. However, the filter medium broke when the increase in pressure loss with time reached 2.5 MPa. When the strand physical property of the obtained carbon fiber bundle was measured, the strength was 6.5 GPa and the elastic modulus was 320 GPa.
[Comparative Example 2]
The filter medium to be used was formed by forming a nonwoven fabric using metal fibers made of SUS316L having an average wire diameter of 5 μm and then sintering to give a total basis weight of 1700 g / m ² and a filling rate of 50%. Except for changing to a filter medium having a basis weight A, a material density B of the filtration guarantee layer, a filtration resistance coefficient C, and a thickness of the filtration guarantee layer as shown in Table 1, the filter clogging limit speed, carbon The removal rate, gel removal rate, and number of microgels were evaluated, and a carbon fiber bundle was obtained. When the strand physical property of the obtained carbon fiber bundle was measured, the strength was 6.0 GPa and the elastic modulus was 320 GPa. Compared with Example 1, the strength reduction considered to be due to the outflow of the gel-like material was observed.
[Example 11]
Except that the spinning solution used was changed to the spinning solution obtained in Example 2, the filter closing limit speed, the carbon removal rate, the gel removal rate and the number of microgels were evaluated and the carbon fiber bundle was obtained in the same manner as in Example 6. It was. When the strand physical property of the obtained carbon fiber bundle was measured, the strength was 6.7 GPa and the elastic modulus was 320 GPa.
[Example 12]
Except that the spinning solution used was changed to the spinning solution obtained in Example 2, the filter clogging limit speed, the carbon removal rate, the gel removal rate, and the number of microgels were evaluated and a carbon fiber bundle was obtained in the same manner as in Example 7. It was. When the strand physical property of the obtained carbon fiber bundle was measured, the strength was 6.3 GPa and the elastic modulus was 320 GPa.
[Example 13]
Except that the spinning solution used was changed to the spinning solution obtained in Example 2, the filter clogging limit speed, the carbon removal rate, the gel removal rate, and the number of microgels were evaluated and a carbon fiber bundle was obtained in the same manner as in Example 8. It was. When the strand physical property of the obtained carbon fiber bundle was measured, the strength was 6.5 GPa and the elastic modulus was 320 GPa.
[Example 14]
Except that the spinning solution used was changed to the spinning solution obtained in Example 2, the filter clogging limit speed, the carbon removal rate, the gel removal rate, and the number of microgels were evaluated and a carbon fiber bundle was obtained in the same manner as in Example 9. It was. When the strand physical property of the obtained carbon fiber bundle was measured, the strength was 6.5 GPa and the elastic modulus was 320 GPa.
[Example 15]
Except for changing the spinning solution used to the spinning solution obtained in Example 2, the filter clogging limit speed, the carbon removal rate, the gel removal rate, and the number of microgels were evaluated and a carbon fiber bundle was obtained in the same manner as in Example 10. It was. However, the pressure resistance of the filter medium was low, and the filter performance and the yarn production were good at the beginning. However, the filter medium broke when the increase in pressure loss with time reached 2.5 MPa. When the strand physical property of the obtained carbon fiber bundle was measured, the strength was 6.5 GPa and the elastic modulus was 320 GPa.
[Example 16]
The spinning solution used was changed to the spinning solution obtained in Example 2, and the filter media used were SUS316 metal fibers with an average wire diameter of 25 μm as warp yarns, and SUS316 metal fibers with an average wire diameter of 15 μm were used as weft yarns. A nonwoven fabric formed by using SUS316L metal fibers with an average wire diameter of 20 μm is laminated on a filter-guaranteed layer that is sintered after being formed into a twilled-weave mesh and has a filter-guaranteed layer weight of 290 g / m ² and a filling rate of 85%. Example 11 with the exception that the filtration guarantee layer basis weight A, the filtration guarantee layer material density B, the filtration resistance coefficient C, and the filtration guarantee layer thickness were changed to the filter media shown in Table 1. Similarly, the filter clogging limit speed, the carbon removal rate, the gel removal rate, and the number of microgels were evaluated, and a carbon fiber bundle was obtained.

When the strand physical property of the obtained carbon fiber bundle was measured, the strength was 6.7 GPa and the elastic modulus was 320 GPa.
[Example 17]
The spinning solution to be used was changed to the spinning solution obtained in Example 2, and the filter medium to be used was sintered after forming a non-woven fabric using SUS316L metal fibers having an average wire diameter of 2 μm to obtain a total basis weight of 1800 g / m ² , with a filling rate of 50%, changed to a filter medium with a filtration guarantee layer basis weight A, a material density B of the filtration guarantee layer, a filtration resistance coefficient C and a thickness of the filtration guarantee layer as shown in Table 1. In the same manner as in Example 11, the filter closing limit speed, the carbon removal rate, the gel removal rate, and the number of microgels were evaluated, and a carbon fiber bundle was obtained.

When the strand physical property of the obtained carbon fiber bundle was measured, the strength was 6.6 GPa and the elastic modulus was 320 GPa.
[Example 18]
The spinning solution to be used was changed to the spinning solution obtained in Example 2, and the filter medium to be used was sintered after forming a non-woven fabric using SUS316L metal fibers having an average wire diameter of 2 μm to obtain a total basis weight of 1800 g / m ² , with a filling rate of 50%, changed to a filter medium with a filtration guarantee layer basis weight A, a material density B of the filtration guarantee layer, a filtration resistance coefficient C and a thickness of the filtration guarantee layer as shown in Table 1. In the same manner as in Example 11, the filter closing limit speed, the carbon removal rate, the gel removal rate, and the number of microgels were evaluated, and a carbon fiber bundle was obtained.

  When the strand physical property of the obtained carbon fiber bundle was measured, the strength was 6.6 GPa and the elastic modulus was 320 GPa.

Table 1 summarizes the results of the filter media, the various molecular weights of the PAN-based polymer, the limit draft magnification during yarn production, the tensile strength of the obtained carbon fiber bundle, and the like in the examples and comparative examples described above.

  In the present invention, it is possible to produce a high-quality precursor fiber without impairing productivity by using a PAN-based polymer capable of performing high-speed spinning without causing a problem and filtering. In addition, by using the obtained precursor fiber, it is possible to produce a high-quality and high-strength carbon fiber stably even in the firing step, which is useful.

D: outer diameter of the leaf disk type filter d: inner diameter of the leaf disk type filter 1: filtration container 2: filter medium 3: support 4: spinning solution inflow path 5: spinning solution outflow path 6: opening to the outflow path 7: Leaf disk type filter 8: core body 9: filter holder 10: opening of the core body

Claims (5)

When a carbon fiber precursor fiber is obtained by spinning a spinning solution in which a polyacrylonitrile-based polymer having a ratio of Z average molecular weight Mz to weight average molecular weight Mw of Mz / Mw of 1.5 or more is dissolved in a solvent. Prior to spinning, the filtration assurance layer basis weight A (g / m ² ) and the material density B (g / m ³ ) have a filtration assurance layer satisfying the following formula, and the filtration resistance coefficient C is 5 × 10 ⁵ to 30 The manufacturing method of the carbon fiber precursor fiber which filters a spinning solution with the filter apparatus using the filter medium which is * 10 < ⁵ > cm < ^-1 >.
0.01 ≦ A / B × 1000 ≦ 0.06   The method for producing a carbon fiber precursor fiber according to claim 1, wherein the filter medium has a filtration guarantee layer with a thickness of 0.033 to 0.25 mm. Filter apparatus, the total basis weight is stacked plurality of leaf disc-type filter using the filter medium is 300~2500g / m ^2, the production method of precursor fiber of carbon fiber according to claim 1 or 2.   Production of the carbon fiber precursor fiber according to any one of claims 1 to 3, wherein the polyacrylonitrile-based polymer has an Mw of 300,000 to 500,000 and an Mz / Mw of 1.5 to 6.0. Method.   Mz / Mw is 2.7-6.0, The manufacturing method of the carbon fiber precursor fiber of Claim 4.

Images