JP2008127697A - Spinning dope for carbon fiber precursor fiber and method for producing carbon fiber precursor fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a spinning dope for an acrylic precursor, which has a small remaining acrylonitrile amount, suppressed gelation and an improved heat stability. <P>SOLUTION: The spinning dope for a carbon fiber precursor fiber is obtained by dissolving a polyacrylonitrile polymer prepared by copolymerizing at least one acid monomer selected from the group consisting of acrylic acid, methacrylic acid and itaconic acid and has a remaining ratio of an unreacted acrylonitrile of 0.001-1 wt.% and contains 0.01-3 wt.% of an alkylating agent. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an acrylic fiber stock solution having good stability over time.

  Polyacrylonitrile polymers are used as raw materials for acrylic fibers such as carbon fiber precursor fibers. Acrylic fiber generally used as a precursor fiber for carbon fiber is a spinning solution consisting of a polyacrylonitrile polymer and a solvent, which is wet-spun or dry-wet-spun and shaped into a fiber, and then stretched, washed, and dried and densified. It is obtained through The final product, carbon fiber, is obtained by high-temperature treatment of the precursor fiber in the firing process, and in order to obtain high-performance carbon fiber, it must be a high-quality precursor fiber that does not generate fuzz or break yarn. Is preferred. In general, a spinning stock solution for acrylic fibers has poor thermal stability, and a spinning stock solution having high thermal stability is required to obtain stable acrylic fibers. As a method for obtaining a stable spinning stock solution, Patent Document 1 discloses a technique of adding formic acid or nitric acid to a spinning stock solution. An acrylonitrile polymer containing formic acid or nitric acid recovers formic acid or nitric acid therefrom. Not only is difficult, but the ionization degree of the acid monomer to be copolymerized is low because the acrylonitrile polymer is acidic, the hydrophilicity of the acrylonitrile polymer is lowered, and voids are easily generated during solidification, and the carbon fiber to be produced There was a problem that the characteristics of the film deteriorated. Therefore, Patent Document 2 discloses a method in which ammonia, hydrazine, amine, or the like is mixed with an acrylonitrile polymer to replace the terminal hydrogen of the carboxyl group with ammonia, hydrazine, quaternary ammonium ions, or the like. Patent Document 3 discloses a method of adding water to an acrylic fiber spinning dope, but the spinning dope stability effect by water is low, and water is a strong coagulant of acrylonitrile polymer, and piping. There is a problem that the solidified acrylonitrile polymer adheres to the pipe and closes the pipe. Furthermore, Patent Document 4 discloses an acrylic fiber spinning stock solution containing 0.01 to 3% by weight of an ethylenic double bond compound. The acrylonitrile disclosed in the examples is considered to be a Class 1 designated substance in the Act on Promotion of Improvement in Management (PRTR Law) regarding the grasp of the amount of specified chemical substances released into the environment, and there are concerns about adverse effects on the human body Therefore, it is not preferable that the polymer stock solution contains a large amount.

Various methods for reducing the residual acrylonitrile in the acrylic fiber spinning dope have been studied. For example, Patent Document 5 shows a method of filling a filler and dispersing a polymer solution in a degassing tank that has been depressurized. However, the spinning stock solution in which the remaining acrylonitrile is only reduced decreases in thermal stability, and the spinning stock solution staying in the pipe for a long time gels and mixes with a part of the spinning stock solution that flows, leading to yarn breakage. There is a problem that there is a problem, and there is a demand for a fiber spinning dope with a small amount of residual acrylonitrile and high stability over time.
Japanese Patent Laid-Open No. 9-3722 JP-A-53-2126325 JP-A-8-246230 JP 2002-249924 A JP 2002-363214 A

  An object of the present invention is to provide an acrylic fiber stock solution with good thermal stability in which the amount of residual acrylonitrile is small, the thermal stability is improved, and gelation is suppressed, in view of the background of the prior art.

  In order to solve this problem, the present invention has the following configuration. That is, a spinning stock solution for carbon fiber precursor fibers in which an acrylonitrile polymer obtained by copolymerizing at least one acid monomer among acrylic acid, methacrylic acid, and itaconic acid is dissolved in a solvent, and is contained in the stock solution The unreacted acrylonitrile residual ratio is 0.001 to 1% by weight, and the alkylating agent is contained in an amount of 0.01 to 3% by weight, or a spinning solution for carbon fiber precursor fibers or acrylic acid Then, after obtaining a preliminary solution in which an acrylonitrile polymer obtained by copolymerizing at least one acid monomer selected from the group consisting of methacrylic acid and itaconic acid is dissolved in a solvent, unreacted monomers in the preliminary solution are removed. Thereafter, an alkylating agent is mixed, and this is a method for producing a spinning dope for carbon fiber precursor fibers.

  According to the present invention, an acrylic fiber stock solution with little unreacted acrylonitrile and good thermal stability can be obtained, and a precursor and carbon fiber with good quality and quality can be produced.

  Hereinafter, the present invention will be described in more detail.

  The spinning solution for carbon fiber precursor fiber of the present invention having good thermal stability is an acrylic fiber spinning solution comprising an acrylonitrile polymer, a solvent and an alkylating agent, and the residual ratio of unreacted acrylonitrile is 0.001-1. The alkylating agent is contained in an amount of 0.01 to 3% by weight based on the acrylic fiber stock solution.

  The acrylonitrile polymer preferably contains 90% by weight or more, more preferably 95% by weight or more, and still more preferably 98% by weight or more of acrylonitrile, and in addition to acrylonitrile, a monomer having an ethylenic double bond is preferably 0.8. A copolymer containing 1% by weight or more and 10% by weight or less. If the amount of acrylonitrile is less than 90% by weight, the quality of the carbon fiber may be deteriorated. Other monomers having an ethylenic double bond include, for example, vinyl esters such as vinyl acetate; acrylic acid, methacrylic acid, itaconic acid, and esters thereof such as methyl acrylate and methyl methacrylate, or salts thereof. Although certain sodium acrylate, sodium methacrylate, etc., or acrylamide can also be used, in the present invention, at least selected from the group consisting of acrylic acid, methacrylic acid, and itaconic acid in the sense of promoting flame resistance. A kind of acid monomer is used.

In the present invention, when the residual ratio of unreacted acrylonitrile exceeds 1% by weight, unreacted monomers are released out of the system during spinning, so that not only the working environment is deteriorated but also the influence on the environment is deteriorated. The amount of unreacted monomer is preferably small, but the minimum value is about 0.001% by weight. More preferably, it is 0.001 to 0.1% by weight. The solvent in the present invention is not particularly limited as long as it can uniformly dissolve the acrylonitrile polymer. N, N-dimethylformamide, dimethyl sulfoxide Dimethylacetamide, thiocyanate aqueous solution, zinc chloride aqueous solution and the like can be preferably used.

  The alkylating agent in the present invention is an organic compound in which an alkyl group and an electronegative atom or substituent are bonded, and when mixed with an amine compound, alcohol compound, or thiol compound, a hydrogen atom on the nitrogen atom of the amine compound, A compound in which a hydrogen atom on an oxygen atom of an alcohol compound and a hydrogen atom on a sulfur atom of a thiol compound are substituted with an alkyl group. Preferred examples of the alkylating agent include sulfuric acid ester, sulfonic acid ester, phosphoric acid triester, phosphoric acid diester, phosphoric acid monoester, phosphonic acid diester, phosphonic acid monoester, phosphinic acid ester, and carbonate ester. More preferably, the alkylating agent is dimethyl methylphosphonate, diethyl methylphosphonate, dimethyl ethylphosphonate, diethyl ethylphosphonate, dimethyl 2-oxopropylphosphonate, diethyl cyanophosphonate, dimethyl allylphosphonate, dimethyl hydroxyethylphosphonate, phosphoric acid. Examples include trimethyl, triethyl phosphate, trimethyl phosphonoacetate, triethyl phosphonoacetate, methyl methanesulfonate, methyl ethanesulfonate, ethyl methanesulfonate, methyl propanesulfonate, dimethyl sulfate, diethyl sulfate, dimethyl carbonate, diethyl carbonate, and ethylene carbonate. . In particular, as the alkylating agent, trimethyl phosphate, triethyl phosphate, dimethyl carbonate, diethyl carbonate, and ethylene carbonate are preferably used from the viewpoint of alkylation reaction activity and handling safety. Among them, trimethyl phosphate is preferable from the viewpoint of alkylation reaction activity. Is more preferable. The mechanism by which the gelation is suppressed by the alkylating agent is not necessarily clear, but the alkylating agent reacts with the amino group terminal generated by cyclization of the acrylonitrile polymer in the spinning dope to produce an alkylamine, and the adjacent molecule This is considered to suppress the crosslinking reaction with the nitrile group.

  The alkylating agent in the present invention is preferably soluble in a solvent in order to be uniformly mixed with the acrylonitrile polymer in the spinning dope. Moreover, it is preferable that it does not remain in the fiber after spinning, and it is preferable that it is soluble in a coagulant. Examples of the coagulant include water and ethanol, but water is preferable from the viewpoint of safety.

  In the present invention, the content of the alkylating agent needs to be 0.01 to 3% by weight, preferably 0.05 to 2% by weight, more preferably 0.1 to 2% by weight with respect to the spinning dope. %. If the content is less than 0.01% by weight, the effect of thermal stability is reduced. If the content exceeds 3% by weight, the physical properties of the precursor fiber are affected, and the quality of the precursor fiber is lowered.

  In the spinning dope of the present invention, in the acrylonitrile polymer, the hydrogen ion of the carboxylic acid group derived from the acid monomer is replaced with at least one ion selected from the group consisting of ammonium ion, sodium ion and quaternary ammonium ion. Thus, the pH is preferably 7-11. If the pH is lower than 7, the spinning dope becomes acidic, so the degree of ionization of the acid monomer to be copolymerized is low, the hydrophilicity of the acrylonitrile polymer is reduced, and voids are likely to occur during solidification, and the properties of the carbon fiber produced are reduced. There are things to do. On the other hand, if the pH is higher than 11, the basicity of the spinning dope becomes strong, which may promote cyclization of the acrylonitrile polymer and lower the physical properties of the carbon fiber. Preferably it is 8-10. The pH of the spinning dope can be measured by the following method. That is, 12 g of distilled water was added to 1.5 g of the spinning dope, the acrylonitrile polymer was coagulated to extract water-soluble components, and the obtained aqueous solution was measured using an electrode-type hydrogen ion concentration meter.

  In the present invention, the concentration of the acrylonitrile polymer in the spinning dope is preferably 10 to 30% by weight. When the concentration of the acrylonitrile polymer in the spinning dope is less than 10% by weight, the polymer is insufficiently aggregated in the coagulation step to form fibers with many voids, and the characteristics such as the tensile strength and compressive strength of the carbon fiber may be deteriorated. When the concentration is higher than 30% by weight, gelation of the spinning dope becomes remarkable, and stable fiberization may be difficult. More preferably, it is 14 to 22% by weight. The concentration of the acrylonitrile polymer in the spinning dope is measured as follows. That is, 10 g of a spinning stock solution in which a polyacrylonitrile polymer was dissolved was poured into 2000 l of water, solidified, and further treated with running water in 90 ° C. warm water for 2 hours to completely remove the solvent, and then dried at 120 ° C. for 2 hours. After weight is measured. The ratio obtained by dividing the weight of the polymer after the solvent removal by the weight of the spinning dope before the solvent removal is taken as the polymer concentration.

  In the present invention, the intrinsic viscosity of the acrylonitrile polymer is preferably in the range of 1 to 4 from the viewpoint of the stability of the spinning dope. When the molecular weight is lower than 1, the spinnability may be lowered. When the molecular weight exceeds 4, the gelation tends to occur and stable spinning may be difficult. The intrinsic viscosity is preferably 1.4 or more, more preferably 1.5 or more as a lower limit, and more preferably 3 or less, and even more preferably 2.8 or less as an upper limit. . The intrinsic viscosity can be controlled by the monomer concentration during polymerization, the amount of initiator and chain transfer agent, and the like.

  In the present invention, the intrinsic viscosity is an intrinsic viscosity calculated based on a specific viscosity measured using an Ostwald viscometer with N, N-dimethylformamide as a solvent and keeping the acrylonitrile polymer at 25 ° C. Say. Specifically, the measurement is performed according to the following procedure. 150 mg of the polymer for carbon fiber precursor fiber, which was previously heat-treated at 120 ° C. for 2 hours and completely dried, is maintained at 25 ° C. and dissolved in 50 ml of sodium N thiocyanate 0.1 mol / liter added N, N-dimethylformamide. The obtained solution was temperature-controlled in a hot water bath at 25 ° C., and the drop time between the marked lines was measured with an accuracy of 1/100 second using an Ostwald viscometer that was temperature-controlled at 25 ° C. in advance. Let time be t (seconds). Similarly, sodium thiocyanate 0.1 mol / liter added N, N-dimethylformamide in which the carbon fiber precursor fiber polymer is not dissolved is also measured, and the drop time is defined as t0 (seconds). The intrinsic viscosity [η] is calculated using the following formula.

[Η] = {(1 + 1.32 × ηsp) ^1/2 −1} /0.198
ηsp = (t / t0) −1
Such a spinning dope is prepared by obtaining a preliminary solution in which an acrylonitrile polymer copolymerized with the above acid monomer is dissolved in a solvent, and then removing unreacted monomers in the preliminary solution, and then an alkylating agent. Can be obtained by mixing. As the polymerization method of the acrylonitrile polymer, methods such as solution polymerization and aqueous suspension polymerization can be used.

  In the present invention, the unreacted monomer can be removed by a method such as Japanese Patent Publication No. 48-29797 and Japanese Patent Application Laid-Open No. 2002-363214.

  In the present invention, after removing unreacted acrylonitrile, the alkylating agent is added so as to be 0.01 to 3% by weight in the spinning dope. In order to mix the alkylating agent, only the alkylating agent may be mixed directly with the preliminary solution, or an acrylating agent solution once dissolved in the same solvent as that used for the preliminary solution may be mixed. However, when the alkylating agent is solid at room temperature, that is, powder, it is preferable from the viewpoint of uniformity to mix an acrylating agent solution dissolved in the same solvent as the solvent used for the preliminary solution in advance. When the alkylating agent is mixed with the preliminary solution, for example, a mixing device such as a static mixer, an extruder or a kneader is preferably used.

In the present invention, by adding any one of ammonia, hydrazine, and a quaternary amine compound to the solution from which the unreacted monomer in the preliminary solution has been removed, the acrylonitrile polymer is neutralized, whereby the carboxylic acid derived from the acid monomer is obtained. The hydrogen ion of the acid group is substituted with at least one ion selected from the group consisting of ammonium ion, sodium ion and quaternary ammonium ion, so that the pH value falls within the above range, and the hydrophilicity and denseness of the acrylonitrile polymer are Improves. The amount to be neutralized is preferably 0.6 to 1.2 equivalents of the acid monomer used in the acrylonitrile polymer. When the amount is less than 0.6 equivalent, the hydrophilicity of the acrylonitrile polymer is lowered, the voids of the precursor fiber are increased, and the properties such as the tensile strength of the carbon fiber are lowered. If it is higher than 1.2, the alkalinity of the acrylic precursor spinning dope becomes strong, which may promote cyclization of the acrylonitrile polymer and lower the quality of the carbon fiber. More preferably, it is 0.7-1.1. Such neutralization treatment may be before or after mixing the alkylating agent solution.
Next, the manufacturing method of the carbon fiber precursor fiber of this invention is demonstrated. In the present invention, the carbon fiber precursor fiber is produced by wet spinning or dry wet spinning of the above-described spinning solution.

  The above-described spinning solution is discharged from a spinneret by a wet spinning method or a dry-wet spinning method and introduced into a coagulation bath to coagulate the fibers. The coagulation bath preferably contains a solvent such as N, N-dimethylformamide, dimethyl sulfoxide, dimethylacetamide, thiocyanate aqueous solution or zinc chloride aqueous solution used as a solvent for the spinning dope and a so-called coagulation promoting component. As the coagulation accelerating component, a component that does not dissolve the polyacrylonitrile polymer and is compatible with the solvent used for the spinning dope can be used. Specifically, it is preferable to use water as a coagulation promoting component.

  After the fiber yarn spun into the coagulation bath is introduced and coagulated, the carbon fiber precursor fiber is usually obtained through a water washing step, a bath drawing step, an oil agent application step, a drying heat treatment step and a steam drawing step. .

  The yarn after the coagulation bath treatment may be directly stretched in the bath without the water washing step, or may be stretched in the bath after the solvent is removed by the water washing step. Such stretching in the bath is usually preferably performed in one or more stretching baths adjusted to a temperature of 30 to 98 ° C. The draw ratio is preferably 1 to 5 times, more preferably 2 to 4 times.

  In the oil agent application step, it is preferable to apply an oil agent made of silicone or the like to the yarn for the purpose of preventing adhesion between single fibers. As such a silicone oil agent, it is preferable to use a modified silicone, and one containing an amino-modified silicone having high heat resistance can be used.

  In the drying heat treatment step, it is preferable to contact a roller heated at a temperature of 160 to 200 ° C. Further, in the steam stretching step, it is preferably stretched 3 times or more, more preferably 4 times or more, and further preferably 5 times or more in the pressurized steam.

  The single fiber fineness of the carbon fiber precursor fiber obtained in the present invention is preferably 0.7 to 1.5 dtex. When the single fiber fineness is less than 0.7 dtex, the operability may be lowered due to a decrease in spinnability in the spinning process, or the productivity per number of nozzle holes may be lowered, resulting in a significant increase in cost. On the other hand, if the single fiber fineness exceeds 1.5 dtex, the difference between the internal and external structures of the flameproofed fiber obtained by flameproofing becomes remarkable, and the tensile strength and tensile elastic modulus of the finally obtained carbon fiber may decrease. is there.

  In the present invention, the number of filaments per yarn of the carbon fiber precursor fiber is preferably 1,000 to 300,000, more preferably 6,000 to 300,000, and still more preferably. Is 12,000-50,000. The number of filaments is preferably 1,000 or more for the purpose of improving productivity. However, when the number exceeds 300,000, the flame cannot be uniformly treated even inside the precursor fiber yarn, and the carbon fiber Characteristics such as tensile strength may be deteriorated.

  The carbon fiber precursor fiber thus obtained was subjected to flameproofing treatment in an oxidizing atmosphere such as air at a temperature of 200 to 300 ° C., preferably while stretching at a stretch ratio of 0.8 to 1.5. Thereafter, in an inert atmosphere such as nitrogen at a temperature of 300 to 800 ° C., precarbonization treatment is preferably performed while stretching at a stretch ratio of 0.9 to 1.5, and a maximum temperature of 1,000 to 2,000 ° C. is achieved. In an inert atmosphere such as nitrogen, the carbon fiber is carbonized by stretching while preferably stretching at a stretching ratio of 0.9 to 1.1.

Further, the obtained carbon fiber is subjected to surface modification for acidic modification such as sulfuric acid, nitric acid and hydrochloric acid, alkali such as sodium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, ammonium carbonate and ammonium bicarbonate or the like. In the fiber-reinforced composite material, the adhesiveness with the carbon fiber matrix can be optimized. In addition, after the electrolytic treatment, a sizing treatment can also be performed in order to give the carbon fiber convergence. 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.

Hereinafter, the present invention will be described more specifically with reference to examples. The evaluation method was as follows.
<Measurement of pH of precursor spinning stock solution>
12 g of distilled water was added to 1.5 g of the polyacrylonitrile solution to solidify the acrylonitrile polymer and extract water-soluble components. The obtained aqueous solution was measured using a glass electrode type hydrogen ion concentration meter manufactured by Toa Denpa Kogyo Co., Ltd.
<Remaining amount of acrylonitrile>
4.0 g of methanol was added to 1.0 g of the polyacrylonitrile solution, and the monomer component in the acrylonitrile polymer was extracted. Acrylonitrile concentration was measured by analyzing the obtained methanol solution by gas chromatography.
Gas chromatography condition apparatus: GC-2014 (manufactured by Shimadzu Corporation)
Column: Capillary column DB-1 (manufactured by Shimadzu GLC)
Sample injection volume: 0.4 μL
<Intrinsic viscosity>
150 mg of acrylonitrile polymer which had been heat-treated at 120 ° C. for 2 hours and completely dried was dissolved in 50 ml of sodium thiocyanate 0.1 mol / liter added N, N-dimethylformamide (both Wako Pure Chemicals special grade) at 25 ° C. . The temperature of the resulting solution was adjusted to 25 ° C., and the Ostwald viscometer previously adjusted to 25 ° C. was used to measure the drop time between the marked lines with an accuracy of 1/100 second. Seconds). Similarly, sodium thiocyanate 0.1 mol / liter added N, N-dimethylformamide in which the polyacrylonitrile polymer for carbon fiber precursor fiber was not dissolved was also measured, and the drop time was defined as t0 (seconds). The intrinsic viscosity [η] was calculated using the following formula.

[Η] = {(1 + 1.32 × ηsp) ^1/2 −1} /0.198
ηsp = (t / t0) −1
<Evaluation of gelation of stock solution>
After the spinning solution was transferred to a 100 cc heat-resistant bottle, the spinning solution was allowed to stand at 100 ° C. in an oven, and the viscosity of the acrylonitrile polymer solution was measured after a predetermined time. In this embodiment, an oven FS-32D manufactured by Advantech was used. The viscosity was evaluated by adjusting the temperature of the spinning dope to 45 ° C. ± 0.5 ° C. and measuring the viscosity using a B-type viscometer. Specifically, the acrylic precursor spinning stock solution placed in a beaker is immersed in a warm 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. Measured with
<Tensile strength and tensile modulus of carbon fiber>
Determined according to JIS R7601 (1986) “Resin-impregnated strand test method”. Here, the resin-impregnated strand of carbon fiber to be measured was “BAKELITE (registered trademark)” ERL 4221 (100 parts by weight) / 3 boron trifluoride monoethylamine (3 parts by weight) / acetone (4 weights) manufactured by Union Carbide Corporation. Part) was impregnated into carbon fiber and cured at 130 ° C. for 30 minutes. The number of strands measured was 6, and the average value of each measurement result was the tensile strength and tensile modulus of the carbon fiber.
<Standards for carbon fiber grades>
The inspection items were evaluated in three stages by counting the number of fluff and fluff while running the fiber bundle at a speed of 1 m / min after firing and before surface treatment / sizing treatment. The evaluation criteria are as follows.
-Grade 1: within 1 fiber 15m-Grade 2: 2-15 in fiber 15m-Grade 3: 16 or more in fiber 15m
Example 1
Acrylonitrile (99% by weight) and itaconic acid (1% by weight) were polymerized by adding azoisobutyroacrylonitrile as a polymerization initiator in dimethyl sulfoxide to obtain a preliminary solution having a polymer concentration of 20% by weight and an intrinsic viscosity of 2.0. This preliminary solution was heated to 75 ° C. with a heat exchanger, filled with a stainless steel filler, and supplied to a degassing tank whose pressure was reduced to 1500 Pa to obtain a polymer stock solution having an unreacted monomer amount of 0.01% by weight. After neutralizing the polymer stock solution by injecting ammonia gas so as to be 1.0 equivalent to the carboxyl group of itaconic acid in the polymer, trimethyl phosphate was further added in an amount of 1% by weight in the spinning stock solution. And mixed with a static mixer to obtain a spinning dope having a viscosity at 45 ° C. of 70 (Pa · S). The pH of this spinning dope was measured and found to be 9.0. The obtained spinning dope was allowed to stand at 50 ° C. for 1 month, passed through a filter with an opening of 0.5 μm, and then discharged into the air at a temperature of 40 ° C. using a spinneret with a pore number of 3,000. After passing through a space of about 3 mm, a coagulated yarn was obtained by a dry and 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. The coagulated yarn was washed with water by a conventional method, then stretched in warm water, and an amino-modified silicone silicone oil was further applied. The drawn yarn in the bath is subjected to a drying heat treatment using a roller heated to a temperature of 170 ° C., and then drawn in a pressurized steam at a temperature of 150 to 190 ° C. to obtain a single fiber fineness of 1.1 dtex and a filament number of 3 1,000 polyacrylonitrile-based precursor fibers were obtained. Next, four obtained precursor fibers are combined and the total number of filaments is set to 12,000, followed by flameproofing in air at a temperature of 240 to 260 ° C., followed by 300 to 700 ° C. A preliminary carbonization treatment was performed in a nitrogen atmosphere at a temperature, and the preliminary carbonized yarn was further carbonized in a nitrogen atmosphere at a maximum temperature of 1,500 ° C. to obtain carbon fibers. About the obtained carbon fiber, strand tensile strength was measured and the quality grade was determined. The obtained results are shown in Table 1. Further, the viscosity at 45 ° C. measured after the spinning solution was allowed to stand at 100 ° C. was unchanged at 70 (Pa · S) after 15 days, 30 days, and 45 days, and was not gelled.
Comparative Example 1
A spinning dope was obtained in the same manner as in Example 1 except that trimethyl phosphate was not added. The spinning stock solution had a viscosity of 70 (Pa · S) at 45 ° C., but the spinning stock solution measured after standing at 100 ° C. for 15 days had lost fluidity and became a gel. After the spinning solution was left at 50 ° C. for 1 month, precursor fibers were prepared in the same manner as in Example 1, and subsequently carbon fibers were prepared. The obtained strand tensile strength and quality grade results are shown in Table 1.
Comparative Example 2
A spinning dope was obtained in the same manner as in Example 1 except that the amount of trimethyl phosphate added was changed to 10% by weight. The viscosity of the spinning dope at 45 ° C. is 70 (Pa · S), and the viscosity at 45 ° C. of the spinning dope measured after standing at 100 ° C. is 70 (Pa · S) after 15, 30 and 45 days. ) And no gelation. The spinning solution was allowed to stand at 50 ° C. for 1 month, and then precursor fibers were prepared in the same manner as in Example 1. Subsequently, carbon fibers were prepared. The strand tensile strength and quality grade obtained were greatly reduced. The results are shown in Table 1.
Comparative Example 3
A spinning dope was obtained in the same manner as in Example 1 except that the amount of trimethyl phosphate added was changed to 0.001% by weight. The spinning stock solution had a viscosity of 70 (Pa · S) at 45 ° C., but the spinning stock solution measured after standing at 100 ° C. for 15 days had lost fluidity and became a gel. After the spinning solution was left at 50 ° C. for 1 month, precursor fibers were prepared in the same manner as in Example 1, and subsequently carbon fibers were prepared. The obtained strand tensile strength and quality grade results are shown in Table 1.
Comparative Example 4
A spinning dope having a viscosity at 45 ° C. of 70 (Pa · S) was obtained in the same manner as in Example 1 except that 0.2% by weight of formic acid was added in place of trimethyl phosphate. The pH of this stock solution was measured and found to be 4.0. The spinning stock solution had a viscosity of 70 (Pa · S) at 45 ° C., but the spinning stock solution measured after standing at 100 ° C. for 15 days had no change at 70 (Pa · S) and was gelled. However, after 30 days, it lost its fluidity and gelled. In addition, after leaving the spinning dope at 50 ° C. for 1 month, a precursor fiber was prepared in the same manner as in Example 1, and then a carbon fiber was prepared. Results of the obtained strand tensile strength and quality grade were shown. It is shown in 1.
Example 2
A spinning dope was obtained in the same manner as in Example 1 except that the amount of trimethyl phosphate added was changed to 0.5% by weight. The viscosity of the spinning dope at 45 ° C. is 70 (Pa · S), and the viscosity at 45 ° C. of the spinning dope measured after standing at 100 ° C. is 70 (Pa · S) after 15, 30 and 45 days. ) And no gelation. The spinning solution was allowed to stand at 50 ° C. for 1 month, and then precursor fibers were prepared in the same manner as in Example 1. Subsequently, carbon fibers were prepared. The obtained strand tensile strength and quality grade results are shown in Table 1.
Example 3
A spinning dope was obtained in the same manner as in Example 1 except that the amount of trimethyl phosphate added was changed to 2.0% by weight. The viscosity of the spinning dope at 45 ° C. is 70 (Pa · S), and the viscosity at 45 ° C. of the spinning dope measured after standing at 100 ° C. is 70 (Pa · S) after 15, 30 and 45 days. ) And no gelation. The spinning solution was allowed to stand at 50 ° C. for 1 month, and then precursor fibers were prepared in the same manner as in Example 1. Subsequently, carbon fibers were prepared. The obtained strand tensile strength and quality grade results are shown in Table 1.
Example 4
A spinning dope was obtained in the same manner as in Example 1 except that the amount of trimethyl phosphate added was changed to 0.05% by weight. The spinning stock solution has a viscosity at 45 ° C. of 70 (Pa · S), and the spinning stock solution measured after standing at 100 ° C. at 45 ° C. has a viscosity of 70 (Pa · S) after 15 and 30 days. There was no change and no gelation, but after 45 days it had gelled. Further, after this spinning stock solution was allowed to stand at 50 ° C. for 30 days, precursor fibers were prepared by the same method as in Example 1, and subsequently carbon fibers were prepared. The obtained strand tensile strength and quality grade results are shown in Table 1.
Example 5
A spinning dope was obtained in the same manner as in Example 1 except that neutralization with ammonia gas was not performed. The pH of this stock solution was measured and found to be 6.0. The spinning stock solution had a viscosity of 70 (Pa · S) at 45 ° C., and the spinning stock solution measured at 45 ° C. after standing at 100 ° C. had a viscosity of 70 (Pa · S) after 15, 30 and 45 days. However, the spinning solution was allowed to stand at 50 ° C. for 1 month, and the results of strand tensile strength and grade of carbon fiber prepared by the same method as in Example 1 are shown in Table 1. Shown in
Example 6
A spinning dope was obtained in the same manner as in Example 1 except that the amount of ammonia gas added was changed to 2.0 equivalents during neutralization. The pH of this stock solution was measured and found to be 11.5. The viscosity of the spinning dope at 45 ° C. is 70 (Pa · S), and the viscosity at 45 ° C. of the spinning dope measured after standing at 100 ° C. is 70 (Pa · S) after 15, 30 and 45 days. However, the quality of the carbon fiber prepared by the same method as in Example 1 deteriorated after the spinning solution was allowed to stand at 50 ° C. for 1 month. The results of the strand tensile strength are also shown in Table 1.
Example 7
A spinning dope was obtained in the same manner as in Example 1 except that 1.0% by weight of triethyl phosphate was added instead of trimethyl phosphate. The viscosity of this spinning dope at 45 ° C. is 70 (Pa · S), and the viscosity at 45 ° C. of the spinning dope measured after standing at 100 ° C. changes at 70 (Pa · S) after 15 and 30 days. There was no gelation, but it was gelled after 45 days. The spinning solution was allowed to stand at 50 ° C. for 1 month, and then precursor fibers were prepared in the same manner as in Example 1. Subsequently, carbon fibers were prepared. The obtained strand tensile strength and quality grade results are shown in Table 1.
Example 8
A spinning dope was obtained in the same manner as in Example 1 except that 1.8% by weight of ethylene carbonate was added instead of trimethyl phosphate. The spinning stock solution had a viscosity of 68 (Pa · S) at 45 ° C., and the spinning stock viscosity measured at 45 ° C. after standing at 100 ° C. did not change after 15 days, 30 days, and 45 days. It was not converted. The spinning solution was allowed to stand at 50 ° C. for 1 month, and then precursor fibers were prepared in the same manner as in Example 1. Subsequently, carbon fibers were prepared. The obtained strand tensile strength and quality grade results are shown in Table 1.
Example 9
A spinning dope was obtained in the same manner as in Example 1 except that 1.0% by weight of dimethyl carbonate was added instead of trimethyl phosphate. The viscosity of this spinning dope at 45 ° C. is 70 (Pa · S), and the viscosity at 45 ° C. of the spinning dope measured after standing at 100 ° C. changes at 70 (Pa · S) after 15 and 30 days. There was no gelation, but it was gelled after 45 days. The spinning solution was allowed to stand at 50 ° C. for 1 month, and then precursor fibers were prepared in the same manner as in Example 1. Subsequently, carbon fibers were prepared. The obtained strand tensile strength and quality grade results are shown in Table 1.
Example 10
A spinning dope was obtained in the same manner as in Example 1 except that 2.0% by weight of diethyl carbonate was added instead of trimethyl phosphate. The viscosity of the spinning dope at 45 ° C. is 71 (Pa · S), and the viscosity at 45 ° C. of the spinning dope measured after standing at 100 ° C. changes at 71 (Pa · S) after 15 and 30 days. There was no gelation, but it was gelled after 45 days. The spinning solution was allowed to stand at 50 ° C. for 1 month, and then precursor fibers were prepared in the same manner as in Example 1. Subsequently, carbon fibers were prepared. The obtained strand tensile strength and quality grade results are shown in Table 1.

Claims (7)

An acrylonitrile polymer obtained by copolymerizing at least one acid monomer selected from the group consisting of acrylic acid, methacrylic acid and itaconic acid is dissolved in a solvent, and the residual ratio of unreacted acrylonitrile is 0.001 to 1% by weight. A spinning dope for carbon fiber precursor fibers, wherein the alkylating agent is contained in an amount of 0.01 to 3% by weight. In the acrylonitrile polymer, the hydrogen ion of the carboxylic acid group derived from the acid monomer is substituted with at least one ion selected from the group consisting of ammonium ion, sodium ion and quaternary ammonium ion. The spinning dope for carbon fiber precursor fibers according to claim 1, wherein the pH value measured by the method described above is 7 to 11. The spinning solution for carbon fiber precursor fiber according to claim 1 or 2, wherein the alkylating agent is trimethyl phosphate. After obtaining a preliminary solution in which an acrylonitrile polymer obtained by copolymerization of at least one acid monomer selected from the group consisting of acrylic acid, methacrylic acid and itaconic acid is dissolved in a solvent, an unreacted monomer in the preliminary solution is obtained. A method for producing a spinning dope for carbon fiber precursor fiber, comprising removing and then mixing an alkylating agent in a proportion of 0.01 to 3% by weight in the spinning dope. The method for producing a spinning dope for carbon fiber precursor fiber according to claim 4, wherein mixing of the alkylating agent is mixing an alkylating agent solution dissolved in the same solvent as the solvent used for the preliminary solution. After removing unreacted monomers in the preliminary solution, at least one compound selected from the group consisting of ammonia, sodium hydroxide and quaternary amine compounds is added, and carboxylic acid groups derived from acid monomers in the polymer are added. The method for producing a spinning dope for carbon fiber precursor fiber according to claim 4 or 5, wherein neutralization is performed. A method for producing a carbon fiber precursor fiber, wherein the spinning solution according to any one of claims 1 to 3 is wet-spun or dry-wet-spun.