JP2010174422A - Precursor for producing carbon fiber and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a precursor for producing carbon fibers which produces high strength carbon fibers, has high product yield with little yarn breakages (number of yarns broken in a process) in steps for producing the carbon fibers. <P>SOLUTION: The precursor for producing carbon fibers is an acrylonitrile-based precursor having a weight average molecular weight of 100,000-1,000,000, and has an average pore diameter of 35 nm or less, which is calculated from a half pressure value of the total amount of mercury obtained from a mercury invasion curve when mercury is pressed into the precursor in measuring pore distribution by a mercury pressure step of the precursor. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a precursor obtained by spinning a spinning stock solution composed of a high molecular weight polymer solution for producing high-strength carbon fiber, wherein the precursor has high yarn yield and low product breakage in the carbon fiber production process. And a manufacturing method thereof.

  Conventionally, it is widely known that a precursor for producing carbon fibers is used as a raw material, and flame-resistant treatment is performed on the precursor to obtain flame-resistant fibers, and further, the flame-resistant fiber is carbonized to obtain high-performance carbon fibers. It has been. This method is also practiced industrially.

  Generally, a precursor for carbon fiber production is obtained by spinning a spinning stock solution consisting of an aqueous solution of an acrylonitrile-based polymer zinc chloride or an organic solvent solution to obtain a polyacrylonitrile-based (PAN-based) raw fiber, and washing the PAN-based raw fiber with water. It is manufactured by applying oil, drying, steam stretching, and if necessary, heat setting or secondary oil application. This precursor is subjected to a flameproofing treatment in which partial oxidation is performed while stretching or shrinking in an oxidizing atmosphere of 200 to 300 ° C., and then carbonized in an inert gas atmosphere of 300 ° C. or higher, usually 1000 ° C. or higher. Fiber is produced.

  Various processes have been proposed for improving the strength of carbon fibers and stabilizing the carbon fiber production process. Among various processes, for example, Patent Documents 1 and 2 propose a spinning process.

  In Patent Document 1, the spinning stock solution (PAN polymer solution) at 45 ° C. is specified to have a viscosity of 300 to 1000 poise, thereby extending the breaking time when the spinning stock solution is stretched. It has been proposed to stabilize the carbon fiber manufacturing process.

  However, the production method of Patent Document 1 does not mention defoaming of the spinning dope.

  In Patent Document 2, it is proposed to manufacture a carbon fiber having high strength and high elastic modulus by defining the pore radius measured by mercury porosimetry as 14 nm or less and 11 nm or less for the denseness of the precursor. .

  However, the carbon fiber obtained by the production method of Patent Document 2 has no description regarding the importance of defoaming the spinning stock solution, and the strength of the obtained carbon fiber is as low as 4400 MPa or less, and it is not satisfactory to improve the strength of the carbon fiber. It is enough.

JP 2008-38327 A (Claims) JP-A-4-257313 (Claims)

  While the present inventor has repeatedly studied to solve the above problems, not only the viscosity of the spinning stock solution but also the acrylonitrile polymer contained in the spinning stock solution is used for improving the stability of the carbon fiber production process. It was considered important that the polymer had a weight average molecular weight of 100,000 or more as measured by transmission chromatography (GPC). The weight average molecular weight of the acrylonitrile polymer used in Patent Document 1 is about 20,000, and an acrylonitrile polymer having such a molecular weight is usually used for the production of a precursor.

  In addition, it was considered important for improving the strength of the carbon fiber that the precursor is dense, that is, the void contained in the precursor is small or the void size is small. For this purpose, it is necessary to sufficiently defoam the spinning solution.

  However, a spinning dope containing a high molecular weight acrylonitrile-based polymer has a high viscosity. This high-viscosity spinning stock solution is not easily defoamed. As a result, the precursor obtained contains a large amount of voids, and there is a problem that high-strength carbon fibers cannot be obtained.

  While further studying this problem, when the spinning stock solution for dissolving the high molecular weight acrylonitrile-based polymer is defoamed using a self-revolving stirring and defoaming device, the resulting precursor is unique. The present inventors have found that the void size is small and the number of voids is reduced.

  The carbon fiber obtained by making the precursor flame resistant and carbonized has high strength, and its production process is stabilized. The present invention has been completed based on the above findings.

  Therefore, an object of the present invention is to provide a precursor for producing carbon fiber and a method for producing the same, which solve the above-mentioned problems.

  The present invention for achieving the above object is described below.

  [1] An acrylonitrile-based precursor having a weight average molecular weight of 100,000 to 1,000,000, and the total amount of mercury obtained from a mercury intrusion curve when the precursor is injected into the precursor in the measurement of pore distribution by mercury intrusion method The precursor for carbon fiber manufacture whose average pore diameter calculated from the pressure value of the half of this is 35 nm or less.

  [2] An acrylonitrile-based precursor having a weight average molecular weight of 100,000 to 1,000,000, which is obtained from a nitrogen gas adsorption curve when adsorbed on the precursor in the pore distribution measurement by the nitrogen gas adsorption method of the precursor. A precursor for producing carbon fibers having an average pore diameter of 30 nm or less calculated from an adsorption amount that is half the amount of nitrogen gas.

  [3] By defoaming a spinning dope consisting of an acrylonitrile-based polymer solution having a weight average molecular weight of 100,000 to 1,000,000 using an axially inclined rotation type agitation deaerator or a revolutionary agitation deaerator For producing a carbon fiber, characterized by obtaining a spinning stock solution that does not foam when left standing at 25 ° C. under a reduced pressure of 13 hPa for 10 minutes and that does not contain bubbles in the polymer solution, and then spinning the spinning stock solution Precursor manufacturing method.

  [4] The method for producing a precursor for carbon fiber production according to [3], wherein the spinning dope has a viscosity at 45 ° C. of 2000 to 4000 poise.

  [5] The method for producing a precursor for carbon fiber production according to [3], wherein the polymer concentration of the spinning dope is 7 to 25% by mass.

  Since the precursor for carbon fiber production of the present invention has a small average pore diameter determined from the measurement of pore distribution by the mercury intrusion method or the nitrogen gas adsorption method, there are few defect portions that greatly affect the strength of the fiber. The carbon fiber obtained by making the precursor flame resistant and carbonized has high strength, and its production process is stabilized.

  According to the method for producing a precursor for producing carbon fiber of the present invention, a spinning stock solution comprising a high molecular weight acrylonitrile-based polymer solution is defoamed using a self-revolving stirring and defoaming device, so that defoaming can be efficiently performed. As a result, a precursor having a small void size and few voids can be obtained.

It is a schematic explanatory drawing which shows an example of the axially inclined autorotation type stirring deaerator used when manufacturing the precursor of this invention. It is a schematic explanatory drawing which shows an example of the self-revolving type stirring deaerator used when manufacturing the precursor of this invention.

  Hereinafter, the present invention will be described in detail.

  The precursor for producing carbon fiber of the present invention is prepared by spinning a spinning stock solution comprising a solvent solution such as an aqueous solution of zinc chloride of acrylonitrile polymer having a weight average molecular weight of 100,000 to 1,000,000, preferably 150,000 to 800,000 or dimethylformamide. Obtained. When the weight average molecular weight of the acrylonitrile-based polymer is less than 100,000, the strength of the obtained carbon fiber is lowered. Further, yarn breakage (number of process breakage) in the carbon fiber production process increases. If the weight average molecular weight of the acrylonitrile-based polymer exceeds 1,000,000, it is difficult to spin the stock solution.

  The average pore diameter (mercury) calculated from the pressure value of half of the total mercury amount, which is obtained from the mercury intrusion curve at the time of intrusion into the precursor in the measurement of pore distribution by the mercury intrusion method of the precursor for carbon fiber production of the present invention. The pore diameter is 35 nm or less, preferably 11 to 33 nm. In the measurement of pore distribution by the nitrogen gas adsorption method, the average pore diameter (nitrogen pore diameter) calculated from the adsorption amount half of the total nitrogen gas amount obtained from the nitrogen gas adsorption curve when adsorbed on the precursor is 30 nm. Hereinafter, it is preferably 7 to 27 nm.

  When the mercury pore diameter exceeds 35 nm or the nitrogen pore diameter exceeds 30 nm, the strength of the carbon fiber obtained by making the spun precursor flame resistant and carbonized decreases, and the number of process yarn breaks increases. Therefore, it is not preferable. When the mercury pore diameter is less than 11 nm or when the nitrogen pore diameter is less than 7 nm, the strength of the carbon fiber is not improved so much, and there is no point in further reducing the pore diameter. In addition, if the pore diameter is too small, the oxygen permeability becomes low in the flameproofing step, and the flameproofing speed decreases. In addition, the flameproof state differs greatly between the fiber core and the fiber surface, leading to a decrease in fiber strength.

  The precursor for carbon fiber production of the present invention, and the flameproof fiber and carbon fiber obtained using this precursor can be produced, for example, by the following method.

<Spinning stock solution>
The spinning dope used for production of the precursor for producing carbon fiber of the present invention is an aqueous solution of an acrylonitrile-based polymer in zinc chloride or an aprotic solvent solution such as dimethylformamide or dimethyl sulfoxide. The acrylonitrile-based polymer has a weight average molecular weight of 100,000 to 1,000,000, preferably 150,000 to 800,000.

  The acrylonitrile-based polymer may be obtained by polymerizing a monomer containing acrylonitrile at 90% by mass or more, preferably 95% by mass or more. Examples of the monomer to be copolymerized include methyl acrylate, itaconic acid, methacrylic acid and the like.

  As described above, the molecular weight of the acrylonitrile-based polymer for producing carbon fibers of the present invention is higher than the molecular weight of the conventionally used acrylonitrile-based polymer. Therefore, the spinning dope containing this polymer has a high viscosity of 2000 to 4000 poise.

  In order to more reliably control the viscosity of the spinning dope, the concentration of the acrylonitrile polymer in the spinning dope is preferably 7 to 25% by mass.

  The spinning dope is defoamed using an axially inclined automatic stirring and defoaming device, preferably using an automatic revolution and stirring and defoaming device.

As shown in FIG. 1, the axially inclined autorotation type stirring and defoaming device rotates the container 2 in the X direction, and the inclination angle θ ₁ of the autorotation shaft 4 with respect to the gravity direction 6 is 40 to 50 degrees, preferably 45 degrees. The device 8 that simultaneously performs stirring and defoaming in a short time under reduced pressure. By using this apparatus 8, the high-viscosity spinning dope can be sufficiently defoamed while being sufficiently stirred without entraining bubbles.

As shown in FIG. 2, the revolution-revolution type agitation / deaeration apparatus has a revolution axis 10 in which the container 2 rotates in the X direction and the inclination angle θ ₂ with respect to the rotation axis 4 is 40 to 50 degrees, preferably 45 degrees. An apparatus 12 having a mechanism that revolves in the Y direction and that simultaneously performs stirring and defoaming in a short time under reduced pressure. By using this apparatus 12, the high-viscosity spinning dope can be sufficiently agitated without entraining bubbles and can be degassed more efficiently than the axially inclined rotation type agitation and deaeration apparatus. The direction of the revolution shaft 10 is preferably the direction of gravity in order to reduce the load applied to the device.

  In the case of a stirring and defoaming apparatus having such a mechanism, conditions such as the number of rotations and revolutions may be appropriately adjusted depending on properties such as the viscosity of the spinning dope and the size of the container, and are not particularly limited. However, the following conditions are preferable.

  In the case of using the axially inclined rotation type stirring and deaerator shown in FIG. 1, the rotation speed is preferably 300 to 1000 rpm, more preferably 400 to 800 rpm. The diameter of the container is preferably 100 to 800 mm, more preferably 200 to 600 mm. The pressure in the decompressed container is preferably 4 to 20 kPa, and more preferably 8 to 16 kPa.

  When defoaming with this axially inclined rotation type stirring and defoaming apparatus, the defoaming time is usually within 30 minutes, preferably 5 to 20 minutes, more preferably 8 to 15 minutes. By this defoaming operation, when the spinning stock solution is allowed to stand at room temperature (25 ° C.) under a reduced pressure of 13 hPa (10 Torr) for 10 minutes, the phenomenon that bubbles are generated on the liquid surface and the bubbles are generated in the stock solution is visually observed. It will not be observed in

  Further, as described above, in the defoaming of the spinning stock solution using the above-mentioned axially inclined rotation type stirring and defoaming apparatus, unreacted monomers contained in the spinning stock solution are also removed (demonomer).

  In the case of using the rotation and revolution type stirring and defoaming device shown in FIG. 2, the rotation speed is preferably 300 to 1000 rpm, more preferably 400 to 800 rpm. The diameter of the container is preferably 100 to 800 mm, more preferably 200 to 600 mm. The revolution speed is preferably 500 to 3000 rpm, more preferably 1000 to 2000 rpm. The revolution diameter is preferably 500 to 1500 mm, and more preferably 700 to 1300 mm. The pressure in the decompressed container is preferably 4 to 20 kPa, and more preferably 8 to 16 kPa.

  When defoaming with this self-revolving type stirring and defoaming apparatus, the defoaming time is usually within 30 minutes, preferably 5 to 20 minutes, more preferably 8 to 15 minutes. By this defoaming operation, when the spinning stock solution is allowed to stand at room temperature (25 ° C.) under a reduced pressure of 13 hPa (10 Torr) for 10 minutes, the phenomenon that bubbles are generated on the liquid surface and the bubbles are generated in the stock solution is visually observed. It will not be observed in

  In addition, as described above, even in the defoaming of the spinning dope using the self-revolving stirring deaerator, the unreacted monomer contained in the spinning dope is also removed (demonomer) as in the case of the axially tilting stirring defoaming device. )

<Spinning>
This spinning dope is spun from a spinneret having 100 to 48000, preferably 3000 to 24000 holes in one spinneret. In this spinning, wet spinning, in which spinning is performed directly in a coagulation bath containing a coagulating liquid cooled to a low temperature (solvent-water mixed solution at the time of spinning), or first discharged into air, then 0.5. A dry-wet spinning method is used in which a space of about 5 mm is introduced into a coagulation bath and coagulated. Furthermore, a dry spinning method can also be used. Of these, the wet spinning method is more preferable because it is not affected by the depth of wrinkles formed on the surface of the carbon fiber with respect to the undulation of the water surface of the coagulation bath. Furthermore, a wet spinning method using an aqueous zinc chloride solution is particularly preferable.

  The coagulated raw fiber is preferably washed and dried. During the water washing, during drying, and / or after drying, the acrylonitrile-based crude precursor is obtained by steam stretching 2 to 5 times, preferably 2.5 to 4.5 times.

  For the raw fiber, after washing with water and / or drying, for the purpose of improving heat resistance and spinning stability, a silicone-based oil, for example, a combination of a permeable oil having a hydrophilic group and an amino-modified silicone-based oil May be given.

<Precursor>
The raw fiber after spinning, drying, steam drawing, oil application, etc., as described above, is used for producing carbon fibers in which the acrylonitrile-based polymer has the aforementioned weight average molecular weight and the aforementioned average pore diameter. Become a precursor. Moreover, this precursor has few voids. The diameter of the precursor is preferably 10 to 30 μm.

<Flame resistance treatment>
The precursor is subsequently subjected to a flameproofing treatment in which it is partially oxidized by heating in heated air at 200 to 280 ° C. for 10 to 30 minutes. By this flameproofing treatment, in the case of acrylonitrile fiber, the precursor causes cyclization reaction of acrylonitrile fiber and increases the amount of oxygen bond to make it infusible and flame retardant to obtain acrylonitrile flameproof fiber (OPF). .

This flameproofing treatment is generally drawn in a draw ratio range of 0.85 to 1.30, but 0.95 or more is more preferable in order to obtain a carbon fiber with high strength and high elastic modulus. By this flameproofing treatment, a flameproof fiber having a fiber density of 1.3 to 1.5 g / cm ³ is obtained. The tension at the time of flame resistance is not particularly limited as long as it does not exceed the range of the draw ratio.

  In order to stabilize the flameproofing process, it is also effective to apply a known process oil to the precursor for carbon fiber production prior to the flameproofing process.

<First carbonization treatment>
The flame-resistant fiber can be carbonized by employing a conventionally known method. For example, a temperature gradient is gradually applied in a firing furnace (first carbonization furnace) at 300 to 800 ° C. in a nitrogen atmosphere, and the tension of the flame-resistant fiber is controlled so that the first carbonization (first carbonization) is performed under tension. )do.

<Second carbonization treatment>
To further promote carbonization and graphitization (high crystallization of carbon), raise the temperature in an inert gas atmosphere such as nitrogen, gradually apply a temperature gradient in the firing furnace (second carbonization furnace), The first carbonized fiber is fired under relaxed conditions by controlling the tension.

  About a calcination temperature, a temperature gradient is applied in a 2nd carbonization furnace, Preferably it is 800 to 2500 degreeC in a maximum temperature range, More preferably, 1200 to 2100 degreeC is good.

  If the residence time in the high-temperature part in the furnace becomes long, graphitization proceeds too much, and brittle carbon fibers are obtained, which is not preferable.

<Surface oxidation treatment>
The second carbonized fiber is subsequently subjected to surface oxidation treatment. A gas phase or liquid phase treatment can also be used for the surface oxidation treatment, but the liquid phase treatment is preferable from the viewpoint of easy process control and productivity. Among the liquid phase treatments, electrolytic treatment using an electrolytic solution is preferable from the viewpoint of liquid safety and stability. Examples of the electrolytic solution used for the electrolytic oxidation treatment include inorganic acids such as sulfuric acid, nitric acid, and hydrochloric acid, inorganic hydroxides such as sodium hydroxide and potassium hydroxide, and inorganic salts such as ammonium sulfate, sodium carbonate, and sodium bicarbonate. Can be mentioned.

<Sizing process>
The fiber after the surface oxidation treatment is subsequently subjected to sizing treatment as necessary. The sizing method can be carried out by a conventionally known method, and the sizing agent is preferably used after changing its composition as appropriate according to the application, and after uniformly adhering.

  The carbon fiber obtained by the above manufacturing method has a high strength of 6200 MPa or more.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. Moreover, the evaluation method about the various physical properties of the coagulated yarn in each Example and a comparative example, a precursor, a flame-proof fiber, and carbon fiber was implemented by the above-mentioned method or the following methods.

<Density>
Measured by Archimedes method. The sample fiber was degassed in acetone and measured.

<Molecular weight>
The sample solution was obtained by dissolving in dimethylformamide (0.01N-lithium chloride added) so that the concentration of the acrylonitrile polymer was 0.1% by mass. The obtained sample solution was measured for molecular weight using a gel permeation chromatography (hereinafter simply referred to as GPC) apparatus. The measurement conditions are the following GPC apparatus: CLASS-LC10 manufactured by Shimadzu Corporation
Column: Column for polar organic solvent GPC [TSK-GEL-α-M (× 2) manufactured by Tosoh Corporation]
Dimethylformamide and lithium chloride: Wako Pure Chemical Industries, Ltd. Flow rate: 1 ml / min Temperature: 40 ° C
Sample filtration: Membrane filter (0.5μ-FHLP FILTER manufactured by Millipore Corporation)
Injection volume: 0.1ml
Detector: differential refractive index detector [RID-10AV manufactured by Shimadzu Corporation]
Monodispersed polystyrene for preparing a calibration curve: as shown in molecular weights 184000, 427000, 791000, and 1300000. A molecular weight distribution curve was determined from the measured GPC curve, and Mw was calculated.

  An elution time-molecular weight calibration curve was prepared in advance using at least three types of monodispersed polystyrenes having different molecular weights and known molecular weights. Using the calibration curve, the molecular weight corresponding to the elution time of the corresponding sample was read. As the copolymerization amount, the amount used was used regardless of whether or not the copolymerization was carried out.

<Average pore diameter by mercury porosimetry (mercury pore diameter)>
It was immersed in a solution in which the ethanol concentration was concentrated in three steps with a mixed solution of ethanol and pure water, and all the solution in the yarn was replaced with ethanol so that the fiber structure did not change. This was immersed in liquid nitrogen and completely condensed, and then dried under vacuum (3 Pa or less) for 24 hours while cooling the surroundings.

About 0.2 g of this dried sample was precisely weighed and placed in a mercury intruder, the inside of the container was evacuated (20 Pa or less), and then filled with mercury. Then, the pore distribution was measured. The pressure was up to 420 MPa. The pore diameter is the following formula pore diameter d = −4σcos θ / p
σ: Surface tension of mercury θ: Contact angle (140 °)
p: Calculated by pressure. The average pore diameter was a pore diameter calculated from a pressure value that was half of the total mercury amount, which was obtained from a mercury intrusion curve at the time of press-fitting.

<Average pore diameter by nitrogen gas adsorption method (nitrogen pore diameter)>
The pore diameter by gas adsorption is basically the same as the mercury pore diameter in the pretreatment. However, in the case of gas adsorption, the obtained partial pressure was converted into a pore diameter by the BJH method (a known conversion method).

<Strength of carbon fiber (CF strength)>
The tensile strength (CF strength) of the carbon fiber was measured by the method specified in JIS R 7608.

<Thread breakage in the carbon fiber manufacturing process>
Thread breakage status in the carbon fiber manufacturing process is as follows: ○ The number of process breaks per day is less than 2 / day △… The number of process breaks per day is 2 / day or more and less than 6 / day ×… Process breaks per day The number of yarns was evaluated in three stages of 6 yarns / day or more.

Example 1
Acrylonitrile (95% by mass), methyl acrylate (4% by mass), and itaconic acid (1% by mass) were precisely weighed as monomers, charged into the polymerization vessel together with a zinc chloride aqueous solution, and stirred while warming to 53 ° C. The monomer concentration at this time was 8.5% by mass. A polymerization agent was charged with a reducing agent (sodium hydrogen sulfite) and an oxidizing agent (sodium persulfate) and polymerized to obtain a precursor spinning dope.

  This spinning dope is vacuum-revolved and stirred and degassed (ARV-5000 manufactured by Sinky Corporation: rotation speed 500 rpm, container diameter 200 mm, rotation speed 1000 rpm, rotation diameter 700 mm, rotation axis relative to rotation axis Degradation and defoaming were carried out simultaneously for 10 minutes at an inclination angle of 45 degrees. The defoamed spinning solution was left in a vacuum of 13 hPa (10 Torr) for 10 minutes. There was no appearance of bubbles emerging from the surface of the spinning dope. There were no bubbles in the spinning dope. The polymer concentration of the spinning dope and the viscosity of the spinning dope were measured and found to be 7.5% by mass and 2200 poise. As shown in Table 1, the molecular weight of the polymer in the spinning dope was approximately 200,000.

  This spinning stock solution is discharged through a spinneret having 3000 holes in one spinneret into a coagulation bath made of a 25% by mass zinc chloride aqueous solution at 2 ° C., coagulated and washed with water, and then a silicon-based oil is used. After applying 0.06 mass% with respect to the mass of the raw material fiber, the raw material fiber after washing with water was obtained.

  The washed raw fiber was brought into contact with a heat roller and dried to obtain a PAN-based rough precursor having a diameter of 20.5 μm. This crude precursor was sent to a steam drawing machine and drawn at a draw ratio of 3.2 to obtain a precursor. The fineness of the obtained precursor was 1.27 dtex. Table 1 shows the mercury pore diameter and nitrogen pore diameter of the obtained precursor.

To this precursor, 0.03% by mass of process oil was applied and subjected to a flameproofing treatment for 20 minutes using a hot air circulation type flameproofing furnace set at a temperature of 250 ° C. to obtain a flameproofing fiber having a density of 1.35 g / cm ^3. Obtained.

  The flameproofed fiber was passed through a temperature range of 300 to 600 ° C. in a nitrogen atmosphere to perform a first carbonization treatment.

  The first carbonized fiber was subjected to a second carbonization treatment by passing through a temperature range of 600 to 1500 ° C. in a nitrogen atmosphere.

  Next, this second carbonized fiber was subjected to a surface treatment using an aqueous ammonium sulfate solution as an electrolytic solution at an electric quantity of 30 coulomb per 1 g of carbon fiber.

  Subsequently, a sizing agent was applied by a known method and dried to obtain carbon fibers having CF strength shown in Table 1. In addition, the yarn breakage in the carbon fiber production process was small, and the process stability was good.

Example 2
In Example 1, after introducing a reducing agent and an oxidizing agent and polymerizing, the same procedure as in Example 1 was conducted except that a precursor spinning stock solution was obtained by leaving it under the same conditions for 12 hours in order to increase the degree of polymerization. A spinning dope was obtained. The polymer concentration of the spinning dope and the viscosity of the spinning dope were measured and found to be 12% by mass and 3500 poise. As shown in Table 1, the molecular weight of the polymer in this spinning dope was approximately 500,000.

  This spinning dope was subjected to dry and wet spinning through a space of 2 mm using a coagulation bath made of a 25% by mass zinc chloride aqueous solution at 2 ° C. Subsequently, after washing with water in the same manner as in Example 1, it was treated with a silicone-based oil agent, dried, densified, and stretched to obtain a precursor of this example. The fineness of the obtained precursor was 1.16 dtex. Table 1 shows the mercury pore diameter and nitrogen pore diameter of the obtained precursor.

  The precursor was subjected to flameproofing treatment, first carbonization treatment, second carbonization treatment, surface treatment, sizing agent treatment, and drying treatment in the same manner as in Example 1 to obtain CF fibers having CF strength shown in Table 1. It was. In addition, the yarn breakage in the carbon fiber production process was small, and the process stability was good.

Comparative Example 1
Using the raw material of Example 1, instead of using the ARV-5000 manufactured by Sinky in the defoaming step, the spinning dope was put into a pool tank with jacket warm water, and heated at 37 ° C. with a vacuum pump for 6 hours. Defoaming was performed while standing in a vacuum (standing + vacuum defoaming). When this defoamed spinning solution was left in a vacuum of 13 hPa (10 Torr) for 10 minutes, air bubbles emerged from the surface of the solution, and bubbles were present in the spinning solution. As shown in Table 1, the molecular weight of the polymer in the spinning dope was approximately 200,000.

  This spinning dope was subjected to wet spinning as in Example 1. Subsequently, after washing with water in the same manner as in Example 1, it was treated with a silicone-based oil agent, dried, densified, and stretched to obtain a precursor of this example. The fineness of the obtained precursor was 1.22 dtex. Table 1 shows the mercury pore diameter and nitrogen pore diameter of the obtained precursor.

  As in Example 1, this precursor was subjected to flameproofing treatment, first carbonization treatment, second carbonization treatment, surface treatment, sizing agent treatment, and drying treatment. Similarly, carbon fiber was obtained.

  Since the foam was not sufficiently defoamed in the defoaming operation, the obtained precursor had a large mercury pore diameter and a nitrogen pore diameter. Carbon fibers were produced using this precursor, but high-strength carbon fibers could not be obtained. In addition, the yarn breakage in the carbon fiber production process was large, and the process stability was not good.

Comparative Example 2
In the defoaming step, the spinning solution is put into a pool tank with jacket warm water, stirred at 30 rpm using a stirring blade while being heated to 37 ° C., and kept at a vacuum of 13 hPa (10 Torr) for 6 hours with a vacuum pump. The same operation as in Example 1 was performed except that defoaming (stirring + vacuum defoaming) was performed. As in Comparative Example 1, bubbles were entrained in the spinning dope, and a good precursor could not be obtained. The carbon fiber produced using this precursor had low strength. In addition, the yarn breakage in the carbon fiber production process was large, and the process stability was not good.

Comparative Example 3
Acrylonitrile (95% by mass), methyl acrylate (4% by mass), and itaconic acid (1% by mass) were precisely weighed as monomers, put into a polymerization can together with a zinc chloride aqueous solution, and stirred while heating to 60 ° C. The monomer concentration at this time was 10 mass%. A polymerization agent was charged with a reducing agent (sodium hydrogen sulfite) and an oxidizing agent (sodium persulfate) to polymerize the polymer. The polymer was filtered off with a filter paper to obtain a high molecular weight polymer.

  A spinning dope was obtained in the same manner as in Example 1 except that this was dissolved in an aqueous zinc chloride solution to obtain a precursor spinning dope. The polymer concentration of the spinning dope and the viscosity of the spinning dope were measured and found to be 15% by mass and 4300 poise. As shown in Table 1, the molecular weight of the polymer in the spinning dope was approximately 1,200,000.

  In the same manner as in Example 1, this stock solution for spinning was discharged through a spinneret having 3000 holes in one spinneret and into a coagulation bath composed of an aqueous zinc chloride solution at 2 ° C. and 25% by mass. However, the viscosity was so high that spinning was impossible, and even a precursor could not be obtained as well as carbon fiber.

Comparative Example 4
A spinning dope was obtained in the same manner as in Example 1, except that the raw materials (monomer, zinc chloride aqueous solution, reducing agent, oxidizing agent) used in Example 1 were stirred while being heated to 40 ° C. under normal pressure. . The polymer concentration of the spinning dope and the viscosity of the spinning dope were measured and found to be 9% by mass and 1800 poise. As shown in Table 1, the molecular weight of the polymer in this spinning dope was as low as about 80,000.

  Carbon fibers were obtained in the same manner as in Example 1 except that this spinning dope was used. However, due to the low molecular weight of the polymer in the spinning dope, high strength carbon fibers could not be obtained. In addition, the number of yarn breaks in the carbon fiber manufacturing process was rather large.

2 container 4 inclination angle X rotation relative to rotation axis 6 gravity direction 8 axis tilt rotation type stirrer degassing apparatus 10 revolution shaft 12 revolving stirrer deaerator theta ₁ revolution axis of the tilt angle theta ₂ rotation axis relative to the gravity direction of the rotation axis Direction Y Revolution direction

Claims (5)

An acrylonitrile-based precursor having a weight average molecular weight of 100,000 to 1,000,000, which is half of the total mercury amount obtained from a mercury intrusion curve when the precursor is pressed into the precursor in the measurement of pore distribution by mercury intrusion method. A precursor for producing carbon fibers having an average pore diameter calculated from a pressure value of 35 nm or less. Total amount of nitrogen gas, which is an acrylonitrile-based precursor having a weight average molecular weight of 100,000 to 1,000,000, obtained from a nitrogen gas adsorption curve when adsorbed on the precursor in the measurement of pore distribution by the nitrogen gas adsorption method of the precursor The precursor for carbon fiber manufacture whose average pore diameter calculated from the adsorption amount of the half is 30 nm or less. A spinning dope consisting of an acrylonitrile-based polymer solution having a weight average molecular weight of 100,000 to 1,000,000 is defoamed by using an axially inclined rotation type stirring and defoaming device or a self-revolving type stirring and defoaming device, and 25 ° C. A precursor for spinning a carbon fiber, which is not foamed when left standing for 10 minutes under a reduced pressure of 13 hPa and contains no bubbles in the polymer solution, and then spinning the spinning solution. Method. The method for producing a precursor for carbon fiber production according to claim 3, wherein the spinning solution has a viscosity at 45 ° C of 2000 to 4000 poise. The method for producing a precursor for producing carbon fibers according to claim 3, wherein the polymer concentration of the spinning dope is 7 to 25% by mass.

Images