JP5504678B2 - Polyacrylonitrile polymer solution, carbon fiber precursor fiber, and method for producing carbon fiber - Google Patents

Description

  The present invention relates to a method for producing a polyacrylonitrile-based polymer solution which gives excellent spinnability by a dry and wet spinning method in the production process of carbon fiber precursor fibers, and the production of carbon fiber precursor fibers and carbon fibers using the same. It is about the method.

  Carbon fibers are used in various applications because of their excellent mechanical and electrical properties. In recent years, in addition to conventional golf clubs, fishing rods and other sports and aircraft applications, the development of so-called general industrial applications such as automobile members, compressed natural gas (CNG) tanks, building seismic reinforcement members and ship members has progressed. It's getting on. Accordingly, there are strong demands for cost reduction and mass supply.

  Among the carbon fibers, the most widely used polyacrylonitrile (hereinafter abbreviated as PAN) carbon fiber is a spinning solution composed of a PAN polymer that is a precursor thereof. After spinning to obtain a carbon fiber precursor fiber, it is heated in an oxidizing atmosphere at a temperature of 200 to 400 ° C. to convert it into a flame resistant fiber, which is at least in an inert atmosphere at a temperature of 1000 ° C. It is manufactured industrially by heating and carbonizing at

  The improvement in the productivity of PAN-based carbon fibers is performed from the viewpoints of yarn production, flame resistance or carbonization of carbon fiber precursor fibers. Above all, with respect to the improvement of the productivity of the carbon fiber precursor fiber, the prior art has the following problems. That is, in spinning to obtain a carbon fiber precursor fiber, the number of spinneret holes and the critical speed (hereinafter also referred to as “spinnability”) for pulling the coagulated yarn associated with the characteristics of the PAN-based polymer solution. The productivity is determined by the limit draw ratio associated with the solidified structure. That is, in obtaining a multifilament carbon fiber precursor fiber, the productivity is limited by how much the final yarn forming speed determined by the product of the take-up speed and the draw ratio is increased. If the spinning speed is increased to improve productivity, the stretchability is reduced, and the production process tends to become unstable.On the other hand, decreasing the spinning speed stabilizes the production process, but the productivity decreases. There is a problem that it is difficult to achieve both improvement and stabilization of the production process.

  On the other hand, the present inventors have already proposed a technique for producing a carbon fiber precursor fiber that gives excellent spinnability by a dry-wet spinning method by using a PAN-based polymer having a specific molecular weight distribution. (See Patent Document 1). As a method for polymerizing a PAN polymer having such a specific molecular weight distribution, a polymerization initiator is introduced into a liquid containing a monomer mainly composed of acrylonitrile (hereinafter sometimes abbreviated as AN). And a polymerization method including a step of polymerizing the remaining unreacted monomer by additionally introducing a polymerization initiator separately between the step of polymerization and the completion of the polymerization (hereinafter sometimes abbreviated as multistage polymerization method). is suggesting. However, when trying to continuously produce the PAN-based polymer by batch polymerization using such a polymerization method, the quality and cost are in a trade-off relationship. That is, when polymerization is performed by the multistage polymerization method using the same polymerization tank without washing, an unreacted polymerization initiator remaining in the polymerization tank after the polymer solution is extracted (hereinafter abbreviated as residual polymerization initiator). ) And unreacted chain transfer agent (hereinafter sometimes abbreviated as “remaining chain transfer agent”), the molecular weight of the polymer obtained by the first introduction of the polymerization initiator is reduced. Quality fluctuations such as end. On the other hand, in order to eliminate the influence of such residual polymerization initiator and residual chain transfer agent, if the polymerization tank is washed at the end of each polymerization, the time from the preparation of the batch to the preparation of the next batch (hereinafter referred to as the batch cycle). The cost may increase due to a prolonged period of time and the use of a cleaning solution.

  Moreover, although the manufacturing method of the PAN-type polymer solution which has the specific molecular weight distribution similar to patent document 1 is also known (refer patent document 2), the method of obtaining a polymer with high quality and low cost similarly. Is not described.

  For polymers other than PAN, a technique for changing the polymerization temperature and polymerization initiator or obtaining a polymer having a specific molecular weight distribution by a multistage polymerization method is known (see Patent Documents 3 and 4). However, these documents do not describe a technique for obtaining a PAN-based polymer solution having a specific molecular weight distribution at a high quality and at a low cost.

  As described above, in the prior art, it is possible to obtain a PAN polymer having a specific molecular weight distribution that can increase the productivity in the yarn production process with high quality and low cost without reducing the productivity of the polymerization process. I couldn't.

JP 2008-248219 A JP 2008-214816 A Sho 49-20627 JP-T-2001-514111

  Therefore, an object of the present invention is to produce a high-quality, low-quality PAN-based polymer having a specific molecular weight distribution necessary for producing a carbon fiber precursor fiber that gives excellent spinnability by a dry-wet spinning method by a multistage polymerization method. An object of the present invention is to provide a method for reducing the amount of residual initiator and residual chain transfer agent in the polymerization tank after the polymer solution is extracted.

  In order to achieve the above object, the method for producing a precursor fiber for carbon fiber of the present invention has the following configuration.

That is, in the method for producing a polyacrylonitrile-based polymer solution of the present invention, a solution containing acrylonitrile and a polymerization initiator of 0.01 to 0.8 mmol / L is heated and polymerized to obtain a weight average molecular weight Mw of 80. A process for obtaining a polymer solution containing polyacrylonitrile and unreacted acrylonitrile in the range of 8 to 8 million, and a weight containing unreacted acrylonitrile and polyacrylonitrile obtained in the process A in the same polymerization tank as process A Add the polymerization initiator in such an amount that the ratio (A / B) of the polymerization initiator used in step A and the polymerization initiator in step B (A / B) is 0.001 to 0.2 and the chain transfer agent and heat the combined solution. By doing so, polyacrylonitrile-based polymerization is carried out in two steps of the B step in which the weight average molecular weight Mw of the polyacrylonitrile in the polymer solution is 100,000 to 700,000. A method for producing a body solution, wherein the heating temperature and / or heating in step B is such that the amount of residual polymerization initiator in the polymerization tank at the end of step B is 0 to 50% of the amount of polymerization initiator added in step A The time is adjusted.

Furthermore, in order to achieve said objective, the manufacturing method of the carbon fiber precursor fiber of this invention spin-drys the polyacrylonitrile-type polymer solution obtained by the said manufacturing method.
Furthermore, in order to achieve said objective, the manufacturing method of the carbon fiber of this invention has the following structure. That is, the carbon fiber manufacturing method of the present invention is obtained by a flameproofing step in which the carbon fiber precursor fiber obtained by the above manufacturing method is flameproofed in air at a temperature of 200 to 300 ° C., and a flameproofing step. A pre-carbonization step of pre-carbonizing the obtained fiber in an inert atmosphere at a temperature of 300 to 800 ° C., and carbonizing the fiber obtained in the pre-carbonization step in an inert atmosphere at a temperature of 1,000 to 3,000 ° C. It is a manufacturing method of carbon fiber which obtains carbon fiber sequentially through the carbonization process.

  According to the present invention, when a PAN-based polymer having a specific molecular weight distribution is produced by a multistage polymerization method, when batch polymerization is continuously performed, a specific polymerization condition is adopted, whereby a molecular weight for each batch. It becomes possible to obtain a high-quality PAN-based polymer with very little distribution fluctuation at low cost, and to obtain a carbon fiber with stable quality with high productivity.

  The present inventors batch-polymerize a PAN-based polymer having a specific molecular weight distribution that enables high-speed spinning by a dry-wet spinning method by a multistage polymerization method, and the amount of remaining initiator in the polymerization tank at the end of the polymerization The weight of the PAN-based polymer obtained by the first introduction of the polymerization initiator by adjusting the heating temperature and / or the heating time in the polymerization step so that the amount of the polymerization initiator is 0 to 50% of the first introduction amount of the polymerization initiator. It has been found that the average molecular weight (hereinafter abbreviated as Mw) is precisely controlled, and the PAN-based polymer can be obtained with high quality and low cost.

  In the present invention, the Mw of the PAN polymer to be polymerized is obtained by polymerization with the polymerization initiator for the second and subsequent times, with the PAN polymer having a small amount of Mw obtained by the polymerization with the first polymerization initiator as the A component. A PAN-based polymer having a small Mw is used as the B component. In addition, B component points out all the polymer components containing A component. Mw of A component is 800,000-8 million, Preferably it is 1,000,000-5 million. When the Mw of the A component is larger than 8 million, the productivity of the A component is lowered, and when the Mw is smaller than 800,000, the spinnability at the time of spinning using the obtained polyacrylonitrile polymer solution is not improved. On the other hand, the Mw of the B component is 100,000 to 700,000, preferably 200,000 to 500,000. Further, when the Mw of the B component is less than 100,000, the strength of the precursor fiber produced by spinning using the obtained polyacrylonitrile-based polymer solution is insufficient, and when it is greater than 700,000, spinning is performed to reduce the viscosity. Since it is necessary to reduce the polymer concentration in the solution, the amount of solvent used increases, which is disadvantageous in terms of cost.

  In the present invention, the various average molecular weights are measured by a gel permeation chromatograph (hereinafter abbreviated as GPC) method, and are obtained as polystyrene converted values.

  Moreover, when the component which remove | excluded A component from B component is called C component, it is preferable that the ratio of Mw of A component and Mw of C component is 2-45, and it is more preferable that it is 4-45. More preferably, it is -30. Mw can be controlled mainly by adjusting the concentrations of the polymerization initiator and the chain transfer agent in the reaction solution, and the smaller Mw is, the larger Mw tends to be. In each of the polymerization of the A component in the A step and the polymerization of the C component in the B step, the Mw is adjusted by adjusting the Mw by setting the concentration of the polymerization initiator (and the chain transfer agent) in the reaction solution as described below. The Mw of the component and the Mw of the C component can be controlled. The weight ratio of the A component and the C component is preferably 0.001 to 0.3, more preferably 0.005 to 0.2, and further preferably 0.01 to 0.1. preferable. By making the Mw ratio and the weight ratio within the above ranges, the spinnability is more effectively improved. The weight ratio of the A component and the C component can be controlled by adjusting the polymerization rate in each of the polymerization of the A component and the polymerization of the C component.

The method for producing a PAN-based polymer of the present invention is a PAN having an Mw of 800,000 to 8 million by heating and polymerizing a solution containing AN and 0.01 to 0.8 mmol / L of a polymerization initiator. And a step A for obtaining a polymer solution containing unreacted AN, a polymerization initiator and a chain in the polymer solution containing the unreacted AN and PAN obtained in step A in the same polymerization vessel as the step A. By adding a transfer agent and heating, polymerization is carried out in two steps, Step B, in which the Mw of PAN in the polymer solution is 100,000 to 700,000. By setting the polymerization initiator used in Step A to 0.01 to 0.8 mmol / L with respect to the polymerization reaction solution, Mw obtained in Step A can be controlled to 800,000 to 8 million.

  Further, the amount of the residual polymerization initiator in the polymerization tank at the end of the step B is 0 to 50%, preferably 0 to 40%, more preferably 0 to 20% of the amount of the polymerization initiator added in the step A. It is important to adjust the heating temperature and / or heating time of the process. In addition, the time of completion | finish of B process points out the time just before extracting a polymer solution from a polymerization tank. When the amount of residual polymerization initiator in the polymerization tank at the end of step B exceeds 50% of the amount of polymerization initiator added in step A, a decrease in Mw of component A due to an increase in the amount of radicals generated and an increase in polymerization rate occur. Since the variation between batches of the component A increases, it becomes difficult to precisely control the molecular weight in the step A. By controlling the amount of the remaining polymerization initiator in the polymerization tank at the end of the B process within the above range, the influence on the A process is reduced, and the molecular weight control in the A process can be precisely performed.

  Here, the polymerization initiator added in the B step is an amount such that the ratio (A / B) of the used amount of the polymerization initiator in the A step to the used amount of the polymerization initiator in the B step is 0.001 to 0.2. The polymerization initiator is used. When the A / B is less than 0.001, it is difficult to control the Mw obtained in the A process because the remaining initiator after the completion of the B process has a strong influence on the A process to be performed next. On the other hand, if A / B exceeds 0.2, unreacted AN remains in the B step, and the yield decreases, resulting in an increase in cost.

  Furthermore, if A / B is increased, the relative influence of radical generation by the residual polymerization initiator can be reduced, so the amount of residual polymerization initiator is 50% or less of the amount of polymerization initiator added in step A. It becomes easy. Therefore, A / B is preferably 0.03 to 0.1, and more preferably 0.04 to 0.08. When A / B is smaller than 0.03, the effect of lowering the relative influence of radical generation by the residual polymerization initiator is relatively small. When A / B is larger than 0.1, the amount of radical generation is reduced. In order to control, it is necessary to increase the difference between the polymerization temperature in the step A and the polymerization temperature in the step B, which may make it difficult to control the temperature.

  The polymerization initiator is preferably an oil-soluble or water-soluble azo compound, a peroxide, etc., and the polymerization initiator is halved in 10 hours from the viewpoint of easy handling from the safety aspect and industrially efficient polymerization. The temperature (hereinafter sometimes abbreviated as the radical generation temperature) is preferably 30 to 150 ° C., more preferably 40 to 100 ° C. Among them, an azo compound that does not cause the generation of oxygen that inhibits polymerization at the time of decomposition is preferably used, and in the case of polymerization by solution polymerization, an oil-soluble azo compound is preferably used from the viewpoint of solubility. Specific examples thereof include 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile) (radical generation temperature 30 ° C.), 2,2′-azobis (2,4-dimethylvaleronitrile) (radical). Generation temperature 51 ° C.) and 2,2′-azobisisobutyronitrile (radical generation temperature 65 ° C.). Moreover, when using a peroxide, you may coexist a reducing agent and promote radical generation.

  As for the amount of the remaining initiator during the polymerization, the experimental value and the calculated value obtained using the following formula show a good agreement. Use the calculated value obtained by examination.

C _{n + 0.1} = C _n × exp (−K _d × 0.1)
(C _n : initiator amount after n hours, C _n : initiator amount after n + 0.1 hours, K _d : initiator decomposition rate coefficient)
K _d = A × exp (−Ea / (8.31447 × T))
(A: constant, Ea: activation energy (J / mol), 8.31447: gas constant (J / K · mol), T: temperature (K))
For A and Ea, literature values such as catalogs are used. As a representative example, the values of the initiator used this time are shown below.

2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile)
[A = 4.527 × 10 ¹⁸ , Ea = 1.15 × 10 ⁵ ]
2,2'-azobis (2,4-dimethylvaleronitrile)
[A = 2.217 × 10 ¹⁸ , Ea = 1.21 × 10 ⁵ ]
2,2'-Azobisisobutyronitrile [A = 1.212 × 10 ¹⁹ , Ea = 1.31 × 10 ⁵ ]
The heating temperature and / or heating time in the B step is adjusted so that the amount of the remaining polymerization initiator in the polymerization tank at the end of the B step is 0 to 50% of the amount of polymerization initiator added in the A step. The amount of the residual polymerization initiator after completion of the B step is preferably 0 to 5% of the total amount of the polymerization initiator added in the A step and the B step. If the amount of residual polymerization initiator after the end of step B exceeds 5% of the amount of polymerization initiator added in step A and step B, A / B may be controlled in the range of 0.001 to 0.2. In some cases, the amount of the remaining polymerization agent after completion of the step B exceeds 50% of the amount of the polymerization initiator added in the step A.

As a means for adjusting the heating temperature in the B step to increase the consumption rate of the polymerization initiator, a temperature ΔT [ΔT = T _P −T _R ] obtained by subtracting the radical generation temperature T _R of the polymerization initiator from the polymerization tank temperature T _P. Is set to be 15 ° C. or higher. In addition, as a method of making ΔT 15 ° C. or higher, there are a method of increasing the polymerization tank temperature and a method of using a polymerization initiator having a low radical generation temperature, either of which may be used.

  Further, as a means for adjusting the heating time, there is a means for reducing the amount of the residual polymerization initiator by setting the polymerization time to be twice or more. The means for adjusting the heating time in the B process has a problem that the batch cycle becomes longer, and therefore, it is preferable to use it as an auxiliary means for adjusting the heating temperature in the B process.

  Usually, the radical generation of the polymerization initiator proceeds, and when the amount of the remaining polymerization initiator is reduced, the polymerization rate is greatly reduced, and the polymerization efficiency is deteriorated. Therefore, a polymerization method in which the polymerization initiator is completely used is adopted. In the present invention, however, it is important to reduce the amount of residual polymerization initiator by using up the polymerization initiator.

Moreover, in order to make it easy to adjust Mw obtained in A process, it is preferable that the solution containing the acrylonitrile of A process and 0.01-0.8 mmol / L polymerization initiator contains a chain transfer agent. When applying a chain transfer agent in such A process, it is preferable that the sum total of the chain transfer agent used at A process and B process is 0.1-5 mmol / L with respect to the reaction solution. By controlling to the said range, it becomes easier to control Mw of B component to 100,000-700,000. Moreover, it is preferable that ratio (A / B) of the usage-amount of the chain transfer agent in A process and the usage-amount of the chain transfer agent in B process is 0.04-0.8, More preferably, it is 0.1-0. .6. When the A / B is less than 0.04, the influence of the residual chain transfer agent after completion of the B step is strongly exerted on the A step in the polymerization of the next batch, and the Mw obtained in the A step is controlled in the polymerization of the next batch. May be difficult. On the other hand, when A / B exceeds 0.8, Mw tends to decrease in the B process of the same batch.

Further, the amount of chain transfer agent remaining in the polymerization tank at the end of the step B is preferably 0 to 25% of the amount of chain transfer agent used in the step A. As used herein, it refers to all chain transfer agents added in step A. When the amount of the chain transfer agent remaining in the polymerization tank at the end of the process B exceeds 25%, the Mw of the A component is reduced in the polymerization of the next batch even if the amount of the remaining polymerization initiator is 50% or less. For this reason, variation among batches of the component A often increases, and it is often difficult to precisely control the molecular weight in the step A. As a method for controlling the amount of residual chain transfer agent at the end of step B to 0 to 25% of the amount of chain transfer agent used in step A, (1) increase the consumption rate of the chain transfer agent, (2) increase the polymerization time. A method such as extension is conceivable. As a specific means of (1), the temperature ΔT [ΔT = T _P −T _R ] obtained by subtracting the radical generation temperature T _R of the polymerization initiator from the polymerization tank temperature T _P should be set to 15 ° C. or higher. There is a means to increase the amount of radical generation and thereby increase the consumption rate of the chain transfer agent. In addition, as a method of making ΔT 15 ° C. or higher, there are a method of increasing the polymerization tank temperature and a method of using a polymerization initiator having a low radical generation temperature, either of which may be used. As a specific means of (2), there is a means for reducing the amount of residual chain transfer agent by setting the polymerization time to twice or more. However, since there is a problem that the batch cycle becomes longer, it is preferable to use the method (1).

  As a composition of the PAN polymer suitably used in the present invention, acrylonitrile (AN) is preferably 93 to 100 mol%, and a monomer copolymerizable with AN is copolymerized if it is 7 mol% or less. Also good.

  As the monomer copolymerizable with AN, it is preferable that a component that promotes flame resistance is copolymerized. As a component that promotes flame resistance, for example, a compound having at least one carboxyl group or amide group is preferably used. As the amount of copolymerization of this component increases, the flameproofing reaction is promoted, the flameproofing treatment can be performed in a short time, and the productivity can be increased.

  Specific examples of components that promote flame resistance include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid, mesaconic acid, acrylamide and methacrylamide. The number of amide groups and carboxyl groups contained is more preferably two or more than one. From that viewpoint, the copolymerizable components for promoting flame resistance include acrylic acid and methacrylic acid. Acid, itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid and mesaconic acid are preferred, and itaconic acid and methacrylic acid are more preferred.

  The ratio of the above-mentioned flame resistance promoting component is preferably in the range of 0.2 to 2 mol%, more preferably 0.3 to 1 mol%. When the proportion of the flame retardant promoting component is less than 0.2 mol%, the flame resistance is insufficient, and the carbonization yield and tensile strength of the carbon fiber obtained in the carbonization step tend to be reduced. On the other hand, when the proportion of the flame resistance promoting component exceeds 2%, molecular fracture due to thermal decomposition in the flame resistance process becomes remarkable, and the tensile strength of the obtained carbon fiber may be lowered.

  As a solvent for polymerizing the above PAN-based polymer, an aqueous solution of zinc chloride, an aqueous solution of sodium thiosulfate, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, etc. can be used, but a PAN-based polymer having a desired molecular weight distribution. In order to obtain dimethylformamide or dimethyl sulfoxide, dimethyl sulfoxide is particularly preferred.

  Next, the manufacturing method of the carbon fiber precursor fiber of this invention is demonstrated. First, the above-mentioned 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 the polymerization and the spinning solvent are the same, a step of separating the obtained polyacrylonitrile and re-dissolving in the spinning solvent becomes unnecessary. Further, the PAN polymer solution may contain a solvent (so-called coagulant) that solidifies the PAN polymer such as water, methanol, ethanol, etc. as long as the PAN polymer does not coagulate. Components such as inhibitors may be included up to 5% by weight based on the PAN polymer.

  The polymer concentration of the PAN-based polymer solution is preferably in the range of 15 to 30% by weight, more preferably 17 to 25% by weight, and most preferably 19 to 23% by weight. If the polymer concentration is less than 15% by weight, the amount of solvent used is increased, which is not economical, and the coagulation rate in the coagulation bath is lowered, 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 may 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 copolymer solution. Specifically, after the PAN copolymer solution is weighed, the weighed PAN copolymer in a solvent that does not dissolve the PAN copolymer and is compatible with the solvent used for the PAN copolymer solution. After the polymer solution is mixed and the PAN copolymer solution is desolvated, the PAN copolymer is weighed. The polymer concentration is calculated by dividing the weight of the PAN copolymer after desolvation by the weight of the solution of the PAN copolymer before desolvation.

  The viscosity of the PAN polymer solution at a temperature of 45 ° C. is preferably in the range of 150 to 2,000 poise, more preferably 200 to 1,500 poise, and still more preferably 300 to 1,000 poise. It is a poise. When the solution viscosity is less than 150 poise, the formability of the spun yarn is lowered, and therefore the speed at which the yarn taken out from the die is taken, that is, the spinnability tends to be lowered. Further, when the solution viscosity exceeds 2,000 poise, gelation tends to occur and stable spinning tends to be difficult. The viscosity of the spinning solution can be controlled by the amount of polymerization initiator or chain transfer agent.

  In the present invention, the viscosity of the PAN-based 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-based polymer solution is in the range of 0 to 1,000 poises when the rotor rotational speed is 6 r. p. m. The viscosity of the spinning solution is in the range of 1,000 to 10,000 poise. p. m. Measure with

  Before spinning the PAN-based polymer solution, from the viewpoint of obtaining high-strength carbon fibers, the solution is passed, for example, through a filter having an opening of 1 μm or less to remove the polymer raw material and impurities mixed in each step. Is preferred.

  In the present invention, the above-mentioned PAN-based polymer solution can suppress the generation of fluff by any spinning method of wet spinning, dry spinning or dry wet spinning, and it is preferable. It is preferable to produce a fiber precursor fiber in order to increase the spinning speed and increase the spinning draft rate. The dry-wet spinning method is a spinning method in which a spinning solution is once discharged into the air from a die and then introduced into a coagulation bath to coagulate.

The spinning draft rate of the PAN-based polymer solution is preferably in the range of 12 to 100 times, the spinning draft rate is more preferably in the range of 13 to 50 times, and further preferably in the range of 13 to 35 times. It is. Here, the spinning draft rate refers to the surface speed of the roller (first roller) with the drive source that the spinning yarn (filament) first contacts after leaving the die (winding speed of the coagulated yarn), in the die hole. The value divided by the linear velocity (discharge linear velocity) of the PAN-based polymer solution. The discharge linear velocity is a value obtained by dividing the volume of the polymer solution discharged per unit time by the die hole area. Therefore, the discharge linear velocity is determined by the relationship between the solution discharge amount and the nozzle hole diameter. The PAN-based polymer solution exits from the die hole and comes into contact with the coagulation solution and gradually solidifies into a filament. At this time, although the filament is pulled by the first roller, the uncoagulated spinning solution is more easily stretched than the filament, and therefore the spinning draft rate indicates the magnification at which the spinning solution is stretched until it is solidified. That is, the spinning draft rate is expressed by the following formula.
・ Spinning draft rate = (coagulated yarn take-up speed) / (discharge line speed)
Increasing the spinning draft rate also greatly contributes to fiber diameter reduction. When the polyacrylonitrile-based polymer solution of the present invention is used as a spinning solution and the spinning draft rate does not exceed 12 times, it is difficult to reduce the single fiber fineness of the PAN-based fiber to 0.2 dtex or less. When decreasing, it is preferable to increase the spinning draft rate. Further, from the viewpoint of improving productivity, the higher the spinning draft rate, the better. However, since yarn breakage often occurs on the die surface, it is practically 100 or less. The discharge linear velocity is preferably 0.1 to 30 m / min. When the discharge linear velocity is less than 0.1 m / min, productivity decreases. On the other hand, when the discharge linear velocity exceeds 30 m / min, the liquid level fluctuation of the coagulation bath becomes remarkable, and the obtained fineness may be uneven.

  The take-up speed of the coagulated yarn determined by the discharge linear speed and the spinning draft rate is preferably 50 to 500 m / min. 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.

  The spinneret hole diameter is preferably 0.05 mm to 0.3 mm, more preferably 0.2 to 0.3 mm. When the diameter of the nozzle hole is smaller than 0.05 mm, it is necessary to discharge the spinning solution from the nozzle at a high pressure, the durability of the spinning device is lowered, and spinning from the nozzle becomes difficult. On the other hand, if 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 PAN polymer solution and a so-called coagulation promoting component. As the coagulation accelerating component, a component that does not dissolve the PAN-based polymer and is compatible with the solvent used in the PAN-based polymer solution is preferable. Specifically, it is preferable to use water. The conditions for the coagulation bath are preferably controlled so that the cross section of the coagulated yarn (single fiber) becomes a perfect circle, and the concentration of the organic solvent is preferably 70% or less of the concentration called the critical bath concentration. If the concentration of the organic solvent is high, the subsequent solvent cleaning step becomes long and the productivity is lowered. For example, when dimethyl sulfoxide is used as the solvent, the concentration of the aqueous dimethyl sulfoxide solution is preferably 5 to 85% by weight, more preferably 65 to 80% by weight. The temperature of the coagulation bath is preferably controlled so that the fiber side surface becomes smooth, and is preferably −10 to 30 ° C., more preferably 5 to 15 ° C.

  A PAN-based polymer solution is introduced into a coagulation bath and solidified to form a yarn, and then a carbon fiber precursor fiber is obtained through a water washing step, an in-bath drawing step, an oil agent application step, and a drying step. 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, 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.

  A known method can be used for the drying step. For example, a drying condition in which the drying temperature is 70 to 200 ° C. and the drying time is 10 seconds to 200 seconds gives preferable results. As an improvement in productivity and an improvement in 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 preferably used in terms of operational stability and cost, and the draw ratio is preferably 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, still more preferably 0.1. ~ 0.8 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 single fiber fineness (dtex) in the present invention is a weight (g) per 10,000 m of single fibers.

  The degree of crystal orientation of the carbon fiber precursor fiber of the present invention is preferably 85% or more, more preferably 90% or more. When the degree of crystal orientation is less than 85%, the strength of the obtained precursor fiber may be lowered.

  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, and the single fiber fineness is small, the number of filaments per yarn is preferably larger for the purpose of improving productivity, but too much In some cases, the flameproofing treatment cannot be uniformly applied to the inside of the bundle.

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

  The carbon fiber precursor fiber produced by the above-described method is subjected to a flame resistance treatment in air at a temperature of 200 to 300 ° C., preferably with a draw ratio of 0.8 to 2.5, and then 300 to 800. In an inert atmosphere at a temperature of ° C., preferably pre-carbonized while stretching at a stretch ratio of 0.9 to 1.5, preferably in an inert atmosphere at a maximum temperature of 1,000 to 3,000 ° C. Carbon fiber is produced by carbonizing while drawing at a draw ratio of 0.9 to 1.1.

  Here, the tension in the carbonization step is a value obtained by converting the tension (mN) measured before the roll on the exit side of the carbonization furnace into a single fiber and dividing by the fineness (dTex) of the carbon fiber precursor fiber at the time of absolute drying. Shall be shown.

  In the present invention, preliminary carbonization treatment and carbonization treatment are performed in an inert atmosphere. Examples of gases used in the inert atmosphere include nitrogen, argon, and xenon. Is preferably used. In the preliminary carbonization treatment, it is preferable to set the rate of temperature rise in the temperature range to 500 ° C./min or less. The maximum temperature in the carbonization treatment can be set to 1,200 to 3,000 ° C. according to the desired mechanical properties of the carbon fiber. Generally, the higher the maximum temperature in the carbonization treatment, the higher the tensile strength of the carbon fiber obtained. Although the modulus of elasticity increases, the tensile strength reaches a maximum in the vicinity of 1,500 ° C. Therefore, for the purpose of increasing both the tensile strength and the tensile modulus of elasticity, the maximum carbonization temperature is 1,200-1,700 ° C. It is preferable that it is 1,300-1,600 degreeC.

  The average single fiber diameter of the carbon fiber of the present invention is preferably 1.5 to 7.5 μm, more preferably 1.5 to 3.9 μm. When the average single fiber diameter is smaller than 1.5 μm, there may be a problem that productivity is deteriorated. On the other hand, if the average single fiber diameter is larger than 7.5 μm, the flameproofing treatment inside the single fiber becomes insufficient, which may cause a problem that the strand tensile elastic modulus is not improved.

  The obtained carbon fiber can be subjected to electrolytic treatment for its surface modification. The electrolytic solution used for the electrolytic treatment includes an acidic solution such as sulfuric acid, nitric acid and hydrochloric acid, an alkali solution such as sodium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, ammonium carbonate and ammonium bicarbonate, or a salt thereof as an aqueous solution. Can be used as Here, the amount of electricity required for the electrolytic treatment can be appropriately selected according to the carbonization degree of the carbon fiber to be applied.

  Electrolytic treatment can optimize the adhesion to the carbon fiber matrix in the resulting fiber reinforced composite material, causing brittle fracture of the composite material due to too strong adhesion and lowering the tensile strength in the fiber direction In addition, although the tensile strength in the fiber direction is high, the adhesive property with the resin is poor, and the problem that the strength characteristics in the non-fiber direction are not expressed is solved, and in the obtained fiber reinforced composite material, in both the fiber direction and the non-fiber direction A balanced strength characteristic is developed.

  After the electrolytic treatment, a sizing treatment can also be applied to give the carbon fiber a bundling property. As the sizing agent, a sizing agent having good compatibility with the matrix resin or the like can be appropriately selected according to the type of resin used.

  The carbon fibers produced by spinning the PAN-based polymer obtained in the present invention after spinning are formed by various molding methods such as autoclave molding as a prepreg, molding by resin transfer molding as a preform of a woven fabric, and molding by filament winding. Therefore, it can be suitably used as sports members such as aircraft members, pressure vessel members, automobile members, fishing rods, and golf shafts.

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

<Weight average molecular weight (Mw)>
A sample solution is prepared in which the polymer to be measured is dissolved in dimethylformamide (with 0.01 N lithium bromide) at a concentration of 0.1% by weight. For the prepared sample solution, a molecular weight distribution curve is obtained from a GPC curve measured under the following conditions using a GPC apparatus, and a weight average molecular weight Mw is calculated.
-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 For the molecular weight of the polymer, use at least six types of monodispersed polystyrenes with different molecular weights and known molecular weights to prepare an elution time-molecular weight calibration curve. It is determined by reading the molecular weight in terms of polystyrene corresponding to time.

  In Examples, CLASS-LC2010 manufactured by Shimadzu Corporation as a GPC apparatus, TSK-GEL-α-M (× 2) manufactured by Tosoh Corporation as a column, and TSK-guard Column α manufactured by Tosoh Corporation as dimethyl A calibration curve was prepared using Wako Pure Chemical Industries, Ltd. as formamide 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, those having molecular weights of 184000, 427000, 791000, 1300000, 1810000, and 4210000 were used, respectively.

<Polymer concentration in polymer solution>
The polymer solution used for spinning is weighed, and about 10 g is put into stirred water. When charging, the height of the charging is adjusted so that the thickness of the polymer solution is about 2 mm in diameter. The polymer produced by putting the polymer solution into water is put into a net, desolvated with hot water at 80 to 90 ° C. for 4 hours, dried at 120 ° C. for 4 hours, and cooled with a desiccator for 30 minutes or more. . The polymer concentration was determined by using the weight of the cooled polymer and the weight of the charged polymer solution.
Polymer concentration (%) = 100 × (weight of dry polymer) / (weight of charged polymer solution)
<Residual chain transfer agent concentration>
The polymer solution is placed in a 1 g sample bottle, 4 g of methanol is added thereto, and extraction is performed at room temperature for 3 hours. Thereafter, the extracted methanol was filtered through a membrane filter, and the amount of residual chain transfer agent was measured under the following conditions using gas chromatography.
Column: Capillary column Carrier gas flow rate: 30 mL / min
・ Temperature: 150 ℃
・ Sample filtration: Membrane filter (0.45μm cut)
・ Injection volume: 1μl
・ Detector: FID detector To determine the residual chain transfer agent concentration, create a calibration curve of peak area-concentration using a standard sample of chain transfer agent with a known concentration, and set the corresponding peak area on the calibration curve. It is determined by reading the concentration of the corresponding chain transfer agent.

  In Examples, GC-2014 manufactured by Shimadzu Corporation as a gas chromatography device, J & W Scientific DB-1 manufactured by Agilent Technologies as a capillary column, and Syringe Filter 13 mm Disposable Filter Device 0.45 μm Pore Size manufactured by Whatman as a membrane filter are used. , Respectively.

<Standard of grade grade of carbon fiber precursor fiber>
Inspection items were evaluated in three stages by counting the number of fluff and fluff while running a fiber bundle of 6000 filaments for 1 line at a speed of 1 m / min. The evaluation criteria are as follows.
-Grade 1: Less than 0.1 in 300 m of fiber bundle-Grade 2: 0.1 to 1 in 300 m of fiber bundle-Grade 3: One or more in 300 m of fiber bundle

<Standards for carbon fiber grades>
The inspection items were evaluated in three stages by counting the number of fluff and fluff while running a fiber bundle of 24000 filaments at a speed of 1 m / min after firing and before surface treatment / sizing treatment. The evaluation criteria are as follows.
Grade 1: Less than 0.1 in 30 m of fiber bundle Grade 2: 0.1 to 1 in 30 m of fiber bundle Grade 3: One or more in 30 m of fiber bundle

<Tensile strength and elastic modulus of carbon fiber bundle>
It was determined according to JIS R7601 (1986) “Resin-impregnated strand test method”. The resin impregnated strand of carbon fiber to be measured was 3,4-epoxycyclohexylmethyl-3,4-epoxy-cyclohexyl-carboxylate (100 parts by weight) / 3 boron trifluoride monoethylamine (3 parts by weight) / acetone (4 weights). Part) was impregnated with carbon fiber or graphitized fiber and cured at a temperature of 130 ° C. for 30 minutes. The number of carbon fiber strands measured was 6, and the average value of each measurement result was taken as the tensile strength. In this example, “Bakelite” (registered trademark) ERL4221 manufactured by Union Carbide Co., Ltd. was used as 3,4-epoxycyclohexylmethyl-3,4-epoxy-cyclohexyl-carboxylate.
[Comparative Example 1]
In a reaction vessel equipped with a stirring blade, 100 parts by weight of acrylonitrile and 200 parts by weight of dimethyl sulfoxide were placed. After substituting the space in the reaction vessel with nitrogen, the chemical addition and heat treatment were performed in accordance with the following conditions (condition 1) while stirring, and a polyacrylonitrile-based polymer solution was obtained by a solution polymerization method.
-As a radical initiator, add 2,10'-azobisisobutyronitrile (hereinafter sometimes abbreviated as AIBN) 0.010 parts by weight (0.2 mmol / L) to the reaction vessel.
(2) Temperature increase from 30 ° C to 70 ° C (temperature increase rate 120 ° C / hour)
(3) Hold for 40 minutes at a temperature of 70 ° C. (4) Decrease in temperature from 70 ° C. to 30 ° C. (Cooling rate 120 ° C./hour)
Mw of the obtained PAN polymer was 340.0 million. In order to polymerize the unreacted acrylonitrile remaining in the obtained polyacrylonitrile-based polymer solution, 170 parts by weight of dimethyl sulfoxide and 1 part by weight of itaconic acid were added to the reaction vessel, and then the drug was added according to the following conditions (condition 2). Addition and heat treatment were performed, and a PAN polymer solution was obtained by a solution polymerization method.
(1) 0.4 part by weight of AIBN and 0.1 part by weight (1.5 mmol / L) of octyl mercaptan (hereinafter sometimes abbreviated as OM) as a chain transfer agent are added to the polymer solution.
・ Temperature rise from 30 ° C to 60 ° C (Temperature increase rate 10 ° C / hour)
-Hold for 4 hours at a temperature of 60 ° C-Increase the temperature from 60 ° C to 80 ° C (temperature increase rate 10 ° C / hour)
-Hold | maintained at the temperature of 80 degreeC for 6 hours Mw of the obtained PAN-type polymer was 380,000, and the polymer concentration was 20.1%. The residual polymerization initiator concentration was 0.2 mmol / L (0.015 parts by weight, corresponding to 150% of the polymerization initiator added in Step A), and the residual chain transfer agent concentration was 0.04 mmol / L (0.042). Equivalent to parts by weight). After completion of the reaction, the obtained PAN-based polymer solution was withdrawn over one hour, and 98% of the whole could be withdrawn.

  Thereafter, the main polymerization was continuously repeated without washing the reaction vessel. As a result, the Mw after the polymerization under the condition 1 was 330.10,000 for the second time and 329.8 million for the third time.

Table 1 summarizes the results of Comparative Example 1 and the following Examples and Comparative Examples.

[Comparative Example 2]
A mixed solution prepared by mixing 110 parts by weight of an acrylonitrile / itaconic acid mixture (acrylonitrile: itaconic acid = 99.7 mol: 0.3 mol) and 390 parts by weight of dimethyl sulfoxide is placed in a reaction vessel equipped with a stirring blade. The inside space was replaced with nitrogen, and the reaction vessel temperature was set to 60 ° C. Then, the chemical addition and heat treatment in the following Step A and Step B were performed with stirring, and a PAN polymer was obtained by a solution polymerization method.

[Step A]
(1) Add AIBN as a radical initiator 0.008 part by weight (0.1 mmol / L) and OM as a chain transfer agent 0.013 part by weight (0.18 mmol / L), respectively, into the reaction vessel (2) Hold at 60 ° C. for 2 hours [Step B]
(1) After completion of step A, 0.43 parts by weight of AIBN (5.2 mmol / L) and 0.12 parts by weight (1.67 mmol / L) of OM were added to the reaction vessel, respectively (2) from 60 ° C. Temperature rise to 75 ° C (temperature rise rate 5 ° C / hour)
(3) Hold at 75 ° C. for 8 hours
The Mw of the PAN polymer obtained in Step B was 380,000 and the polymer concentration was 19.9%. Further, the concentration of the residual polymerization initiator at the end of Step B was 0.5 mmol / L (0.04 parts by weight, corresponding to 500% of the amount of the polymerization initiator added in Step A), and the residual chain transfer agent concentration was 0.13 mmol. / L (0.009 parts by weight, corresponding to 69% of the amount of chain transfer agent added in step A). After completion of the reaction, the obtained PAN-based polymer solution was withdrawn over one hour, and 98% of the whole could be withdrawn. Thereafter, when the main polymerization was repeated continuously without washing the reaction vessel, the Mw after the polymerization in the step A was 300,000 for the second time, 2905,000 for the second time, and 291 for the third time. It was 20,000.

[Example 1]
Polymerization was carried out in the same manner as in Comparative Example 2 except that the reaction time at 75 ° C. in Step B was changed from 8 hours to 18 hours. The amount of residual polymerization initiator at the end of Step B was 45% of the polymerization initiator added in Step A, and the amount of residual chain transfer agent was 6% of the chain transfer agent added in Step A. After the completion of the extraction of the PAN-based polymer solution, the main polymerization was repeated continuously without washing the reaction vessel. As a result, the Mw after the completion of the polymerization in the step A was 300,000 for the first time and 299 for the second time. It was 50,000 and the third was 299.4 million.

[Comparative Example 3]
Polymerization was carried out in the same manner as in Comparative Example 2 except that the polymerization temperature in Step B was changed from 75 ° C to 80 ° C. The amount of residual polymerization initiator at the end of Step B was 68% of the polymerization initiator added in Step A, and the amount of residual chain transfer agent was 8% of the chain transfer agent added in Step A. Thereafter, the main polymerization was continuously repeated without washing the reaction vessel. As a result, the Mw after completion of the polymerization in Step A was 300,000 for the first time, 298.6 million for the second time, and 298 for the third time. It was 40,000.

[Example 2]
Polymerization was performed in the same manner as in Comparative Example 2 except that the polymerization temperature in Step B was changed from 75 ° C to 85 ° C. The amount of residual polymerization initiator at the end of Step B was 2% of the polymerization initiator added in Step A, and the amount of residual chain transfer agent was 1% of the chain transfer agent added in Step A. Thereafter, when the main polymerization was repeated continuously without washing the reaction vessel, the Mw after the polymerization in the step A was 300,000 for the first time, 299.9 million for the second time, and 300 for the third time. It was 0.0 million.

[Example 3]
The AIBN added in the step A is 0.008 part by weight (0.1 mmol / L) to 0.016 part by weight (0.2 mmol / L), and OM is 0.013 part by weight (0.18 mmol / L) to 0. 008 parts by weight (0.11 mmol / L), AIBN added in Step B was changed from 0.43 parts by weight to 0.42 parts by weight, and OM was changed from 0.12 parts by weight to 0.13 parts by weight. The polymerization was carried out in the same manner as in Comparative Example 3 except that the reaction time at 60 ° C. was changed from 2 hours to 1.4 hours. The amount of residual polymerization initiator at the end of Step B was 34% of the polymerization initiator added in Step A, and the amount of residual chain transfer agent was 15% of the chain transfer agent added in Step A. Thereafter, when the main polymerization was repeated continuously without washing the reaction vessel, the Mw after the completion of the polymerization in the step A was 300,000 for the first time, 299.5 million for the second time, and 299 for the third time. It was 60,000.

[Example 4]
The AIBN added in step A is 0.008 parts by weight (0.1 mmol / L) to 0.032 parts by weight (0.4 mmol / L), and OM is 0.013 parts by weight (0.18 mmol / L) to 0. 004 parts by weight (0.06 mmol / L), AIBN added in Step B is changed from 0.43 parts by weight to 0.40 parts by weight, and OM is changed from 0.12 parts by weight to 0.13 parts by weight. The polymerization was carried out in the same manner as in Comparative Example 3 except that the reaction time at 60 ° C. was changed from 2 hours to 1 hour. The amount of residual polymerization initiator at the end of Step B was 17% of the polymerization initiator added in Step A, and the amount of residual chain transfer agent was 31% of the chain transfer agent added in Step A. Thereafter, when the main polymerization was repeated continuously without washing the reaction vessel, the Mw after the completion of the polymerization in the step A was 300,000 for the first time, 299.3 million for the second time, and 299 for the third time. It was 50,000.

[Example 5]
The AIBN added in step A is 0.008 parts by weight (0.1 mmol / L) to 0.065 parts by weight (0.8 mmol / L), and OM is 0.013 parts by weight (0.18 mmol / L) to 0. 001 parts by weight (0.01 mmol / L), AIBN added in Step B is changed from 0.43 parts by weight to 0.37 parts by weight, and OM is changed from 0.12 parts by weight to 0.13 parts by weight. The polymerization was carried out in the same manner as in Comparative Example 3 except that the reaction time at 60 ° C. was changed from 2 hours to 0.7 hours. The amount of residual polymerization initiator at the end of Step B was 8% of the polymerization initiator added in Step A, and the amount of residual chain transfer agent was 123% of the chain transfer agent added in Step A. Thereafter, the main polymerization was repeated continuously without washing the reaction vessel. As a result, the Mw after completion of the polymerization in the step A was 300,000 for the first time, 299,000 for the second time, and 299 for the third time. It was 10,000.

[Comparative Example 4]
The AIBN added in step A is 0.008 parts by weight (0.1 mmol / L) to 0.004 parts by weight (0.05 mmol / L), and OM is 0.013 parts by weight (0.18 mmol / L) to 0. 019 parts by weight (0.26 mmol / L), OM added in Step B was changed from 0.12 parts by weight to 0.11 parts by weight, and in Step A, the reaction time at 60 ° C. was changed from 2 hours to 2.9. Polymerization was carried out in the same manner as in Comparative Example 3 except that the time was changed. The amount of residual polymerization initiator at the end of Step B was 135% of the polymerization initiator added in Step A, and the amount of residual chain transfer agent was 5% of the chain transfer agent added in Step A. Thereafter, when the main polymerization was repeated continuously without washing the reaction vessel, the Mw after completion of the polymerization in the step A was 300,000 for the first time, 297.3 million for the second time, and 297 for the third time. It was 10,000.

[Example 6]
The polymerization initiator added in step A is 0.008 part by weight of AIBN (0.1 mmol / L) to 2,2′-azobis-2,4-dimethylvaleronitrile (hereinafter sometimes abbreviated as ADVN). 012 parts by weight (0.1 mmol / L), 0.013 parts by weight (0.18 mmol / L) to 0.012 parts by weight (0.16 mmol / L) of OM, and AIBN 0. Other than changing 43 parts by weight to ADVN 0.97 parts by weight, OM from 0.12 parts by weight to 0.11 parts by weight, and changing the reaction time at 60 ° C. from 2 hours to 0.8 hours in Step A Was polymerized in the same manner as in Comparative Example 2. The amount of residual polymerization initiator at the end of Step B was 0% of the polymerization initiator added in Step A, and the amount of residual chain transfer agent was 71% of the chain transfer agent added in Step A. Thereafter, the main polymerization was continuously repeated without washing the reaction vessel. As a result, the Mw after completion of the polymerization in the step A was 300,000 for the first time, 299.2 million for the second time, and 299 for the third time. It was 10,000.

[Example 7]
The ADVN added in step A is 0.012 parts by weight (0.1 mmol / L) to 0.002 parts by weight (0.02 mmol / L), and OM is 0.012 parts by weight (0.16 mmol / L) to 0. 030 parts by weight (0.42 mmol / L), ADVN added in Step B is changed from 0.97 parts by weight to 0.98 parts by weight, and OM is changed from 0.11 parts by weight to 0.09 parts by weight. The polymerization was carried out in the same manner as in Example 6 except that the reaction time at 60 ° C. was changed from 0.8 hours to 2 hours.
The amount of residual polymerization initiator at the end of Step B was 0% of the polymerization initiator added in Step A, and the amount of residual chain transfer agent was 23% of the chain transfer agent added in Step A. Thereafter, the main polymerization was continuously repeated without washing the reaction vessel. As a result, the Mw after completion of the polymerization in the step A was 300,000 for the first time, 297,000 for the second time, and 299 for the third time. It was 80,000.

[Example 8]
The polymerization initiator added in step A is abbreviated as AIBN 0.008 part by weight (0.1 mmol / L) to 2,2′-azobis-4-methoxy-2,4-dimethylvaleronitrile (hereinafter referred to as V-70). There are also 0.002 parts by weight (0.01 mmol / L) and 0.013 parts by weight (0.18 mmol / L) to 0.003 parts by weight (0.04 mmol / L) of OM. Polymerization was carried out in the same manner as in Comparative Example 2 except that the polymerization initiator was changed from 0.43 parts by weight of AIBN to 0.61 part by weight of V-70, and OM was changed from 0.12 parts by weight to 0.03 parts by weight. . The amount of residual polymerization initiator at the end of Step B was 0% of the polymerization initiator added in Step A, and the amount of residual chain transfer agent was 78% of the chain transfer agent added in Step A. Thereafter, when the main polymerization was repeated continuously without washing the reaction vessel, the Mw after the completion of the polymerization in the step A was 300,000 for the first time, 291,000 for the second time, and 299 for the third time. It was 20,000.

[Example 9]
In the same manner as in Comparative Example 2, except that the polymerization initiator added in Step B was changed from 0.43 parts by weight of AIBN to 0.59 parts by weight of V-70 and OM was changed from 0.12 parts by weight to 0.02 parts by weight. Polymerization was performed. The amount of residual polymerization initiator at the end of Step B was 1% of the polymerization initiator added in Step A, and the amount of residual chain transfer agent was 12% of the chain transfer agent added in Step A. Thereafter, the main polymerization was continuously repeated without washing the reaction vessel. As a result, the Mw after the polymerization in the step A was 300,000 for the first time, 299.9 million for the second time, and 299 for the third time. It was 90,000.

[Example 10]
The itaconic acid contained in the PAN polymer was neutralized by blowing ammonia gas into the PAN polymer solution obtained in the third polymerization in Example 3 until the pH was 8.5, and the spinning solution was Produced. The obtained PAN-based polymer solution was passed through a filter having a mesh opening of 0.5 μm, and then discharged into the air at a temperature of 40 ° C. at a temperature of 40 ° C. using a spinneret having a number of holes of 6,000 and a diameter of the nozzle hole of 0.15 mm. After passing through a space of about 2 mm, spinning was performed by a dry-wet spinning method introduced into a coagulation bath composed of an aqueous solution of 20% by weight dimethyl sulfoxide controlled at a temperature of 3 ° C. to obtain a coagulated yarn. The solidified yarn was obtained under the conditions of a discharge linear velocity of 7 m / min and a spinning draft rate of 24. The coagulated yarn thus obtained is washed with water and then stretched at 90 ° C. in warm water at a stretch ratio of 3 times in a bath, and further an amino-modified silicone-based silicone oil agent is added to obtain a stretch yarn in the bath. It was. The thus obtained stretched yarn in the bath was dried for 30 seconds using a roller heated to a temperature of 165 ° C., and 7 yarns were combined to give a total filament number of 42,000. Under the conditions, pressurized steam drawing was performed to obtain a carbon fiber precursor fiber having a single fiber fineness of 0.1 dtex and a filament number of 42,000. The quality of the obtained carbon fiber precursor fiber was excellent, the grade was 1, and the yarn passing through process was stable.

  The obtained carbon fiber precursor fiber was flameproofed for 90 minutes while being stretched at a stretch ratio of 1.0 in air having a temperature distribution of 240 to 260 ° C. to obtain flameproofed fibers. 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 firing process was all good and the grade was 1.

  When the strand physical property of the obtained carbon fiber bundle was measured, the strength was 8.0 GPa and the elastic modulus was 325 GPa.

  The physical properties of the carbon fiber precursor fiber and the carbon fiber in Example 10 and Comparative Example 5 are shown in Table 2.

[Comparative Example 5]
Carbon fiber precursor fibers and carbon fibers were obtained in the same manner as in Example 10 using the PAN-based polymer solution obtained by the third polymerization in Comparative Example 2. The grade of the obtained carbon fiber precursor fiber was 2, and the yarn passing through the spinning process was slightly unstable as compared with Example 10.

The strand properties of the obtained carbon fiber bundle were almost the same as those of Example 10 in both strength and elastic modulus, but the grade of carbon fiber was 2, and the firing process passability was slightly poor.

Claims (7)

A solution containing acrylonitrile and 0.01 to 0.8 mmol / L polymerization initiator is heated and polymerized to polymerize polyacrylonitrile having a weight average molecular weight Mw of 800,000 to 8 million and unreacted acrylonitrile. A step for obtaining a coalescence solution, and in the same polymerization vessel as in step A, in the polymer solution containing unreacted acrylonitrile and polyacrylonitrile obtained in step A, the amount of polymerization initiator used in step A and in step B By adding and heating the polymerization initiator in an amount such that the ratio (A / B) of the amount of polymerization initiator used is 0.001 to 0.2, the polyacrylonitrile in the polymer solution is heated. A method for producing a polyacrylonitrile-based polymer solution that is polymerized in two steps of the B step with a weight average molecular weight Mw of 100,000 to 700,000, and in the polymerization tank at the end of the B step A method for producing a polyacrylonitrile-based polymer solution, wherein the heating temperature and / or the heating time in step B are adjusted so that the amount of residual polymerization initiator is 0 to 50% of the amount of polymerization initiator added in step A. The method for producing a polyacrylonitrile-based polymer solution according to claim 1, wherein in step A, the solution containing acrylonitrile and 0.01 to 0.8 mmol / L polymerization initiator contains a chain transfer agent. The total of the chain transfer agents used in the A step and the B step is 0.1 to 5 mmol / L, and the ratio of the amount of chain transfer agent used in the A step to the amount of chain transfer agent used in the B step (A / B) is 0.04 to 0.8, and the amount of residual chain transfer agent in the polymerization tank at the end of step B is 0 to 25% of the amount of chain transfer agent used in step A. A method for producing a polyacrylonitrile-based polymer solution. The value (A / B) which divided the usage-amount of the polymerization initiator in A process by the usage-amount of the polymerization initiator in B process is 0.03-0.1, The poly in any one of Claims 1-3 A method for producing an acrylonitrile-based polymer solution. The polyacrylonitrile system according to any one of claims 1 to 4, wherein the amount of residual polymer initiator at the end of step B is 0 to 5% of the total amount of polymer initiator added in step A and step B. A method for producing a polymer solution. The manufacturing method of the carbon fiber precursor fiber which carries out dry-wet spinning of the polyacrylonitrile-type polymer solution obtained by the method in any one of Claims 1-5. The carbon fiber precursor fiber obtained by the method according to claim 6 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, a carbon fiber production method in which carbonization is performed in an inert atmosphere at a temperature of 1,000 to 3,000 ° C.