JPH07133318A - Acrylonitrile polymer solution and production thereof - Google Patents

Abstract

PURPOSE:To obtain a solution of an acrylonitrile polymer in an organic solvent which has good thermal stability and is less apt to gel by regulating the conductance of the solution to a specific value. CONSTITUTION:The solution comprises an acrylonitrile polymer (a) obtained by aqueous suspension polymerization using an inorganic redox polymerization initiator and an organic solvent (b) in which the polymer (a) is soluble. It has a conductance of 75S/cm or lower. This solution is obtained by purifying a solution (c) of the polymer (a) in the solvent (b) by contacting the solution (c) with an ion exchanger insoluble in the solvent (b) to remove ionic impurities consisting mainly of cations and anions from the solution (c).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an acrylonitrile-based fiber, and an acrylonitrile-based polymer solution capable of producing an acrylonitrile-based polymer fiber having excellent thermal stability, which is a raw material for producing carbon fiber obtained by firing the acrylonitrile-based fiber, And a method for manufacturing the same.

[0002]

2. Description of the Related Art Acrylic fibers have excellent bulkiness, texture, and dyeing clarity similar to wool, and are used in a wide range of applications. This acrylic fiber is prepared by dissolving an acrylonitrile-based polymer as a raw material in an organic solvent or an inorganic solvent, and spinning it into a spinning solution such as a wet spinning method, a dry spinning method, or a dry-wet spinning method to form a staple or a filament. It has been commercialized. The acrylonitrile-based polymer as a raw material is generally produced by polymerizing an acrylonitrile monomer and a monomer copolymerizable therewith by a radical polymerization reaction. In addition, the acrylonitrile fiber obtained by the above method is carbonized through a firing process, and the carbon fiber has high performance in terms of strength, elastic modulus, heat resistance, etc. It is used for various purposes.

The suspension polymerization method, which is an aqueous heterogeneous polymerization of acrylonitrile-based monomers, has a long history and is a widely adopted method for producing acrylonitrile-based polymers.
It has advantages such as easy control of the quality of the obtained polymer, easy recovery of unreacted monomer from the manufacturing process, and easy management of the entire manufacturing process (Maruzen Co., Ltd. Published by the company, edited by the Textile Society, "Textile Handbook, Raw Material Edition").
For the production of this acrylonitrile-based polymer, a continuous suspension polymerization method using water as a reaction medium is adopted, and an inorganic initiator is generally used as a polymerization initiator. A monomer containing an acrylonitrile monomer as a main component is treated with an inorganic initiator (for example, ammonium persulfate-ammonium hydrogen sulfite-
(Ferrous sulfate oxidation-reduction system combination) and polymerized with sulfuric acid water as a reaction medium, the polymerized acrylonitrile-based polymer forms particles, and an aqueous dispersion of the polymer particles is formed. Obtained in the state. After completion of the polymerization, the aqueous dispersion of the polymer was filtered off, and the obtained polymer particles were washed,
By drying, an acrylonitrile-based polymer that is a raw material for acrylic fibers is obtained.

In order to obtain an acrylonitrile polymer by the continuous aqueous suspension polymerization method, it is preferable to use an aluminum reaction vessel as the reaction vessel. When an acrylonitrile-based polymer is produced by the water-based continuous suspension polymerization method, when a stainless steel reaction vessel or a glass-lined reaction vessel is used as the reaction vessel, the generated acrylonitrile-based polymer adheres to the vessel wall of the reaction vessel. This is because it is substantially impossible to continuously polymerize the acrylonitrile-based monomer by suspension polymerization due to the generation of the scale. When an acrylonitrile-based monomer is subjected to aqueous suspension polymerization using an aluminum reaction vessel as a reaction vessel, the reaction system is an acidic aqueous solution, so that the aluminum surface is corroded and dissolved to prevent scale formation. ing.

To terminate the aqueous suspension polymerization, a polymerization terminator is added to the polymerization system. The polymerization terminator used when the acrylonitrile-based polymer is produced by the aqueous suspension polymerization method is required to have a function of neutralizing the acidic aqueous solution of the reaction system, for example, sodium oxalate and ethylenediamine. An electrolyte such as sodium tetraacetate salt or sodium bicarbonate is used.

As described above, in the method for producing an acrylonitrile polymer by the aqueous suspension polymerization method, at least the electrolyte caused by the polymerization initiator, the electrolyte generated by the corrosion dissolution of the surface of the polymerization kettle, and the electrolyte caused by the polymerization terminator are used. It is being done in the presence. Moreover, since the acrylonitrile-based polymer dispersed in the aqueous phase during the aqueous suspension polymerization grows into polymer particles having a diameter of several tens of microns as the polymerization reaction proceeds, the above-mentioned various electrolytes are contained in the polymer particles. Mixing is inevitable.

By the way, in order to produce an acrylonitrile-based precursor fiber for carbon fiber using an acrylonitrile-based polymer produced by the conventional aqueous suspension polymerization,
The acrylonitrile-based polymer after polymerization is washed, dried, and dissolved in a solvent to prepare an acrylonitrile-based polymer dope solution, and the dope solution is spun by a wet spinning method, a dry-wet spinning method or a dry spinning method to prepare a carbon fiber precursor. Manufactures body fibers. However, when the acrylonitrile polymer dope solution obtained as described above is used as a dope solution for producing a high quality acrylic fiber, various problems are caused. For example, the dope solution used for producing the precursor fiber for carbon fiber needs to be kept at a high temperature (100 ° C) for a relatively long time in order to perform good spinning, but the dope solution kept at this high temperature is Yellow coloring becomes noticeable, and the dope solution itself gels, resulting in a decrease in solution fluidity. Due to this, stable spinning cannot be secured using this dope solution, and as a result, a yarn breakage phenomenon occurs,
It becomes difficult to produce a carbon fiber precursor fiber of sufficient quality. Further, the various electrolytes contained in the acrylonitrile fiber obtained as described above are deposited as an inorganic electrolyte in the firing step of the precursor fiber, and the stability of the firing step is reduced. In addition, the carbon fiber obtained by using the precursor fiber obtained as described above also causes a decrease in strength and a decrease in quality.

[0008]

[Problems to be Solved by the Invention] When an acrylic fiber or an acrylic fiber which is a precursor for carbon fiber production is produced from an acrylonitrile polymer obtained by an aqueous suspension polymerization method as a raw material, the acrylonitrile polymer particles are The electrolyte, which is an ionic impurity taken in, has a drawback that the spinnability is deteriorated and the quality of the obtained acrylic fiber is deteriorated.

The inventors of the present invention have found that the solvent solution of the acrylonitrile polymer obtained by the aqueous continuous suspension polymerization method is colored yellow or gels by heating for a long time, and its fluidity decreases. It was confirmed that the above-mentioned various electrolytes, which are impurities remaining in the acrylonitrile-based polymer particles obtained by the aqueous suspension polymerization method, are responsible. As described above, in continuous aqueous suspension polymerization of an acrylonitrile-based polymer, the polymer is handled by an electrolyte by a polymerization initiator, an electrolyte by corrosion dissolution of the surface of an aluminum-made polymerization kettle, and an electrolyte by a polymerization terminator added to a recovered polymerization system. Since it is carried out in the presence of, etc., in the acrylonitrile-based polymer polymer particles dispersed as particles in the aqueous phase, various electrolytes are mixed up to the inside, and it is sufficient to wash the polymer particles with water only after the polymerization. , Even if it is possible to remove the electrolyte on the surface of the polymer particles,
It is difficult to remove the electrolyte trapped inside the polymer particles by washing with water. In particular, the acrylonitrile-based polymer polymerized using the aqueous suspension polymerization method using an inorganic polymerization initiator, the terminal retains the ionized form,
Since various electrolytes, which are impurities, form counterions with this and are bound in the polymer, it is extremely difficult to remove the acrylonitrile polymer particles by washing with water.

[0010]

Therefore, the present inventors have
As a result of studying to obtain an organic solvent solution of an acrylonitrile-based polymer without the above-mentioned problems, the electrolyte as an impurity is an acrylonitrile-based polymer in an organic solvent solution, and the solution is purified by an ion exchange resin to give a solution in the solution. The present invention has been completed, knowing that the inorganic electrolyte present in the can be completely eliminated or can be made extremely small. That is, the gist of the present invention is a solution comprising an acrylonitrile polymer produced by an aqueous suspension polymerization method using an inorganic redox polymerization initiator, and an organic solvent capable of dissolving the polymer, Conductivity is 75 μS / cm
An acrylonitrile-based polymer solution having excellent thermal stability, and an acrylonitrile-based polymer obtained by an aqueous suspension polymerization method using an inorganic redox polymerization initiator, and an organic solvent capable of dissolving the polymer Impurity which is an iron compound or its ion, an aluminum compound or its ion, or a sulfate ion contained in the polymer solution by bringing a solution containing a solvent into contact with a substance having an ion-exchange ability that is insoluble in the organic solvent. The method for producing an acrylonitrile-based polymer solution is characterized in that the above is purified and removed.

Thus, the iron compound or its ion,
Aluminum compound or its ion, an acrylonitrile-based polymer solution having an extremely low content of impurities such as sulfate ion can remarkably improve its gelation property, and thus this solution is also used as a dope solution used for producing carbon fiber precursor fibers. , Shows very good suitability. Further, even when the precursor fiber is produced by a semi-dry wet spinning method using this dope solution, abnormal flow due to gelation of the dope solution can be prevented, so that the spinnability thereof is improved. Further, in the firing step of the precursor fiber obtained by the above method, precipitation of an inorganic substance can be eliminated, the stability of the firing step can be improved, and the strength and quality of the obtained carbon fiber can be improved.

The acrylonitrile-based polymer obtained by the aqueous suspension polymerization using an inorganic redox polymerization initiator is converted into an acrylonitrile-based polymer containing no or only a very small amount of an electrolyte by polymerizing the acrylonitrile-based polymer. Is dissolved in an organic solvent capable of dissolving the polymer to obtain a dope solution, and the dope solution is brought into contact with a substance having an ion exchange performance which is not dissolved in the organic solvent, for example, an ion exchange resin or an ion exchange fiber. It was possible to obtain it by carrying out a high-level purification of removing impurities such as an iron compound or its ion, an aluminum compound or its ion contained in the acrylonitrile polymer.

The present invention will be described in detail below. The present invention is directed to an acrylonitrile polymer obtained by an aqueous suspension polymerization method using an inorganic redox polymerization initiator. The inorganic redox polymerization initiator that can be used can be selected from ordinary oxidizing agents and reducing agents.
In the case of a redox polymerization initiator composed of a combination of an oxidizing agent and a reducing agent, typical ones are ammonium persulfate, potassium persulfate, sodium persulfate, etc. as the oxidizing agent,
As the reducing agent, sodium sulfite, ammonium sulfite, sodium hydrogen sulfite, ammonium hydrogen sulfite,
Examples thereof include sodium thiosulfate, ammonium thiosulfate, sodium dithionite, sodium formaldehyde sulfoxylate, L-alcorbic acid and dextrose. In these redox-based polymerization initiators, compounds such as ferrous sulfate or copper sulfate can also be used in combination. Among them, a combination of ammonium persulfate-sodium bisulfite (or ammonium) -ferrous sulfate is preferable. Although any ratio of reducing agent / oxidizing agent can be used, it is preferable to set the equivalent ratio of reducing agent / oxidizing agent in the range of 1 to 4 in order to promote the polymerization of acrylonitrile more efficiently.

The acrylonitrile polymer used in carrying out the present invention may be a homopolymer of an acrylonitrile monomer or a copolymer of a monoolefinic monomer copolymerizable with acrylonitrile. At least 60% by weight in these acrylonitrile polymers
It is necessary to include the acrylonitrile monomer unit of This is because an acrylonitrile-based synthetic fiber made of an acrylonitrile-based polymer having an acrylonitrile monomer unit content of less than 60% by weight tends to be unable to retain its original fiber function. Examples of the monoolefinic monomer copolymerizable with acrylonitrile include acrylic acid, methacrylic acid and their esters, acrylamide, vinyl acetate, styrene, vinyl chloride, vinylidene chloride, maleic anhydride, N-substituted maleimide. , Butadiene, isoprene, p-sulfonylmethallyl ether, methallylsulfonic acid, allylsulfonic acid, styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-sulfoethylmethacrylate and salts thereof. .

Polymerization of the acrylonitrile monomer is carried out as follows. That is, the polymerization reaction temperature is preferably 30 to 80 ° C. When the polymerization temperature exceeds 80 ° C., acrylonitrile evaporates from the polymerization reaction system and is dispersed outside the reaction system, and the polymerization conversion rate of acrylonitrile decreases. On the other hand, if the polymerization temperature is lower than 30 ° C., the polymerization rate of acrylonitrile decreases, which not only lowers the productivity of the acrylonitrile-based polymer but also impairs the polymerization stability. It is preferable to use ion-exchanged water as the polymerization medium. Further, the ratio of water to the monomers present in the polymerization system (hereinafter, water /
The ratio (referred to as the monomer ratio) may be any ratio, but the water / monomer ratio is preferably in the range of 1.0 to 5.0. The average residence time of the monomers in the polymerization reaction kettle may be in the range of the usual polymerization time adopted when the acrylonitrile polymer is produced by the aqueous suspension polymerization method. The hydrogen ion concentration in the polymerization reaction vessel may be in the range where the catalyst used causes a rapid oxidation / reduction reaction, and is preferably in the acidic range of pH 2.0 to 4. As the reaction kettle, it is preferable to use an aluminum reaction kettle. When an aqueous suspension polymerization of acrylonitrile is carried out using an aluminum reaction kettle, the reaction system is kept acidic with sulfuric acid at a pH of 2 to 4, so that the polymer produced by the progress of the polymerization is the reactor wall. Even if it adheres to, there is an advantage that it is easily peeled off due to dissolution due to corrosion of the surface of aluminum and does not adhere as scale.

A polymerization terminator is added to the aqueous dispersion of the polymer taken out of the reaction system from the polymerization kettle to terminate the polymerization reaction. As the terminator for the polymerization reaction, any of the above-mentioned ones which are usually used when an acrylonitrile polymer is produced by aqueous suspension polymerization can be used without any problem. The aqueous dispersion of the acrylonitrile polymer to which the polymerization terminator has been added then recovers the unreacted monomers. As a method of recovering the unreacted monomer, a method of directly distilling an aqueous dispersion of the polymer, or once dehydrated and separated into an aqueous phase containing the unreacted monomer and the polymer, the aqueous phase is separated. There are methods such as distillation. As a dehydrating and washing machine used for carrying out the latter method, a rotary vacuum filter, a centrifugal dehydrator, or the like, which is a commonly known filter dehydrator, can be used. When separating the acrylonitrile-based polymer from the aqueous dispersion phase of the polymer using these devices, in order to carry out the separation more efficiently, a coagulant such as ammonium sulfate, aluminum sulfate or sodium sulfate is added to the aqueous phase. Alternatively, in order to promote aggregation of the polymer in the aqueous phase, it is preferable to add an operation such as heating the polymer-containing solution. Water remaining in the separated polymer is removed by applying a normal drying method to the polymer.

Next, the acrylonitrile polymer obtained as described above is dissolved in an organic solvent. The organic solvent used for carrying out the present invention is required to be a solvent in which the acrylonitrile polymer is dissolved, and it is particularly preferable to use dimethylformamide, dimethylacetamide, dimethylsulfoxide and the like. The acrylonitrile-based polymer solution of the present invention comprises 5 to 35% by weight of an acrylonitrile-based polymer and 95 to 65% of an organic solvent.
It is preferable that the solution is composed of 10% by weight. The reason why the polymer content in the acrylonitrile-based polymer solution is 5 to 35% by weight is that it is considered that the spinnability of the solution is kept good, and the polymer content is less than 5% by weight. In the solution, a sufficient spinnability cannot be ensured because the concentration of the polymer is too low.On the other hand, an acrylonitrile polymer solution having a polymer content of more than 35% by weight has a high viscosity of the polymer solution. This is because too good spinnability cannot be ensured.

In the present invention, the acrylonitrile polymer solution as described above is brought into contact with a substance having an ion exchange ability which is insoluble in an organic solvent to remove the ionic impurities present in the solution. Examples of the substance having an ion exchange ability that can be used include crosslinked ion exchange resins and crosslinked ion exchange fibers.
It is more preferable to use a crosslinked ion exchange resin composed of a divinylbenzene-styrene copolymer. It is necessary that the substance having an ion-exchange ability used in carrying out the present invention has an affinity with a dope solution in which an acrylonitrile polymer is dissolved in an organic solvent.

Examples of the substance having an ion exchange capacity include strong cation exchange resins having a sulfonic acid group as a functional group. The ionic species contained in the dope solution to be ion-exchanged are cation species and anion species. In the case of both ionic species, both a strong acid type cation exchange resin having a sulfonic acid group and a strong base type anion exchange resin having a quaternary amino group are used. In order to capture the heavy metal contained in the dope solution, it is preferable to use a chelate ion exchange resin having a functional group such as iminodiacetic acid type and polyamine type.
Further, a weak acid type cation exchange resin having a carboxylic acid group such as methacrylic acid or acrylic acid as a functional group, or a weak base type anion exchange resin having a primary, secondary or tertiary amine type functional group as a functional group is doped. It is preferable to use them together depending on the properties of the solution. As the ion exchange resin used for carrying out the present invention, a strong acid type cation exchange resin having a sulfonic acid group is used alone, or a strong acid type cation exchange resin having a sulfonic acid group and a quaternary amino group are held. It is particularly preferable to use both the strong base type anion exchange resin and the strong base type anion exchange resin.

The ion exchange resin is preferably used in an amount of 0.01 to 100 parts by weight based on 100 parts by weight of the acrylonitrile polymer solution. If the amount used is less than 0.01 parts by weight, the ion exchange capacity is insufficient and it becomes impractical. On the other hand, if the amount used exceeds 100 parts by weight, handling of the dope solution for ion exchange becomes complicated,
It is not practical because it is economically disadvantageous and the recovery of the ion exchange resin from the dope solution requires more time than necessary.

In carrying out the present invention, it is preferable to carry out the acrylonitrile polymer solution and the ion exchange resin in either a tubular reactor or a tank reactor. The reality is that the tubular reactor is filled with the ion-exchange resin, the acrylonitrile-based polymer dope solution is continuously fed into the tubular reactor, and the solution is allowed to flow while passing through the reactor. Target. Purification of the acrylonitrile polymer solution with an ion exchange resin is carried out at a reaction temperature of 15 to 150 ° C. When the ion exchange reaction temperature is less than 15 ° C, the viscosity of the acrylonitrile polymer solution increases,
The fluidity is poor and the ion exchange reaction hardly progresses substantially. Also, when the ion exchange reaction temperature exceeds 150 ° C, the thermal stability of the ion exchange resin itself used is insufficient,
In fact, it cannot be used for a long time.

When the acrylonitrile polymer solution is purified by the ion exchange resin according to the method of the present invention, the amount of impurities mainly composed of iron compound or its ion, aluminum compound or its ion, and sulfate ion is contained in the solution. Decrease. The conductivity of the solution thus obtained is 75 μS / cm
Below, the thermal stability is good and the dope solution is resistant to gelation. The thermal stability of the acrylonitrile polymer dope solution in which the conductivity of the solution exceeds 75 μS / cm due to the presence of the iron compound or its ion, the aluminum compound or its ion, and the sulfate ion, etc. is reduced.
The decrease in thermal stability of the acrylonitrile polymer dope solution causes various troubles in the acrylic fiber manufacturing process as described above, and has a great adverse effect on the quality of the acrylic fiber obtained.

Hereinafter, the present invention will be described in more detail with reference to Examples.

[0024]

Example 1 A polymerization reaction vessel with a stirring blade having a capacity of 80 liters (a reaction vessel is an aluminum vessel and an agitating blade is an aluminum-coated turbine type) is used.
Charge 35 liters of water adjusted to 3 and add acrylonitrile.
98.5% by weight, methacrylic acid 1.5% by weight, ammonium persulfate 1.5% by weight, ammonium hydrogen sulfite 4.5% by weight,
Ferrous sulfate _{(FeSO 4 · 7H 2 O)} 0.00005 wt%, sulfuric acid 0.085
What was each melt | dissolved in ion-exchange water so that it might be set to weight% was continuously supplied to the reaction container.

Further, ion-exchanged water was separately supplied so that the total amount of ion-exchanged water would be 400% by weight. The temperature of the reaction system was raised to 55 ° C., sufficient stirring was carried out, and the average staying time of the reaction mixture in the reaction vessel was set to 80 minutes, and the raw materials adjusted as described above were continuously supplied to carry out the weight reaction. .

The polymer aqueous dispersion was continuously taken out from the overflow port of the reaction vessel, and an aqueous solution of the polymerization terminator in which 0.5% by weight of ammonium oxalate and 1.5% by weight of ammonium bicarbonate were dissolved in ion-exchanged water was taken out. The polymer aqueous dispersion was continuously added at a rate of 0.2%, ion-exchanged water was further added, the polymer was separated from the reaction system by a rotary vacuum filter, and washed with ion-exchanged water. did. The obtained wet polymer was molded into pellets by a screw type extruder and then dried by an air dryer to obtain an acrylonitrile polymer having the composition shown in Table 1.

The polymer dried as described above is dissolved in dimethylformamide at a solid concentration of 23% by weight to obtain a polymer solution, which is a strong acid type cation exchange resin having a sulfonic acid group (Mitsubishi Chemical Corporation. Manufactured by PK-228LH) (10 mm in diameter, 300 mm in length, 15 tubes, total amount of ion-exchange resin: 200 g) and a tube filled with an anion-exchange resin having a quaternary amino group (10 mm in diameter, Length 300
mm, 15 pieces, total amount of ion exchange resin 200 g) was fed to the pipe containing the acrylonitrile polymer solution at a flow rate of 0.5 cm / sec in the resin-filled pipe to give the acrylonitrile polymer shown in Table 1. A solution was obtained. The results of measuring the electric conductivity and thermal stability are also shown in Table 1. This acrylonitrile polymer solution was used as a spinning stock solution,
After passing through a hole and a spinneret with a diameter of 0.15 mm, a 78% dimethylformamide aqueous solution (15 ° C.) was used as a coagulation bath and was spun by a semi-dry wet spinning method, and the obtained yarn was continuously washed and stretched, An aminosiloxane-based oil agent was attached so as to be 1.0% by weight based on the weight of the fiber, and further subjected to dry densification treatment to obtain a precursor fiber having a single fiber fineness of 1.0 denier. This precursor fiber was continuously fed by a roll drive to a flameproofing furnace in a hot air atmosphere having a temperature gradient in the range of 225 to 260 ° C. by a conventional method, and a flameproofing treatment was carried out for a residence time of 34 minutes. The flame-resistant yarn thus obtained was subjected to carbonization in a nitrogen gas atmosphere with a temperature gradient in the range of 320 to 700 ° C. and a heat treatment furnace at 1,350 ° C. at a residence time of 7 minutes and 45 minutes, respectively. Chemical firing was performed to obtain carbon fibers. The performance of the obtained carbon fiber is shown in Table 1.

[0028]

Example 2 An acrylonitrile polymer was obtained in the same manner as in Example 1, and this polymer was dissolved in dimethylformamide to a solid concentration of 23% by weight to prepare a polymer solution having a sulfonic acid group. A tube filled with strong acid type cation exchange resin (PK-228LH manufactured by Mitsubishi Kasei) (diameter 10 mm, length 300 mm, 15 tubes, total ion exchange resin amount)
200 g) and a tube filled with an anion exchange resin having a quaternary amino group (diameter 10 mm, length 300 mm, number 15)
Pipe, the total amount of ion exchange resin 200g)
Flow rate of the acrylonitrile-based polymer solution in a resin-filled pipe
The solution was fed at a rate of 0.25 cm / sec to obtain an acrylonitrile polymer solution shown in Table 1. The results of measuring the electric conductivity and the thermal stability are shown in Table 1. Using this acrylonitrile polymer solution as a spinning dope, spinning was carried out by the same semi-dry wet spinning method as in Example 1 to produce a precursor fiber, and this precursor fiber was made flame resistant in the same manner as in Example 1, Carbonization was performed to obtain carbon fibers. The performance of the obtained carbon fiber is shown in Table 1.

[0029]

Comparative Example 1 An acrylonitrile polymer was obtained in the same manner as in Example 1, and this polymer was dissolved in dimethylformamide to a solid concentration of 23% by weight to obtain a polymer solution having sulfonic acid groups. Tube filled with strong acid type cation exchange resin (Mitsubishi Chemical Co., PK-228LH)
10mm, length 300mm, 15 pieces, total amount of ion exchange resin 2
The acrylonitrile-based polymer solution shown in Table 1 was obtained by feeding the acrylonitrile-based polymer solution into a pipe containing 00 g) at a flow rate of 0.5 cm / sec in the resin-filled pipe.
The results of measuring the electric conductivity and thermal stability are also shown in Table 1. Using this acrylonitrile polymer solution as a spinning dope, spinning was carried out by a semi-dry wet spinning method in the same manner as in Example 1 to obtain an acrylonitrile precursor fiber, and this precursor fiber was fired in the same manner as in Example 1. Treatment was performed to obtain carbon fibers. The performance of the obtained carbon fiber is shown in Table 1.

[0030]

Comparative Example 2 An acrylonitrile polymer was obtained in the same manner as in Example 1, and this polymer was dissolved in dimethylformamide to a solid content concentration of 23% by weight to obtain an acrylonitrile polymer solution. The results of measuring the electrical conductivity and thermal stability of this solution are shown in Table 1. Using this polymer solution as a spinning dope, spinning was performed in the same manner as in Example 1 to obtain a precursor fiber. The precursor fiber was subjected to the same firing treatment as in Example 1 to obtain a carbon fiber. The thermal stability of the dope is inferior to that of the present invention, and there is much precipitation of inorganic substances in the firing step of the obtained precursor fiber, and the performance of the carbon fiber obtained from this precursor fiber is also low. , There was uneven performance.

[0031]

[Table 1] The measurement of the evaluation items in Table 1 is as follows. (1) Conductivity A spinning solution containing 23% polymer / 77% solvent (dimethylformamide) was kept warm at 60 ° C. for measurement. (2) Thermal stability of spinning stock solution A spinning stock solution of 23% polymer / 77% solvent (dimethylformamide) was placed in a viscosity tube, immersed in a thermostat and kept at 85 ° C, and the change in viscosity was measured by a ball drop value. ○ No increase in viscosity (gelation) was observed for up to 20 days. △ No increase in viscosity (gelation) was observed for up to 15 days. × No increase in viscosity (gelation) was observed for up to 5 days. (3) Strand strength Measured according to the resin-impregnated strand strength test method specified in JIS R 7601. The number of measurements was 10, and the value in Table 1 shows the average value. The variation coefficients of the strand strength and the strand elastic modulus were obtained according to the equations 1, 2 and 3.

[Equation 1]

[Equation 2]

[Equation 3]

Claims (2)

[Claims] 1. An inorganic redox polymerization initiator is used,
An acrylonitrile polymer solution comprising an acrylonitrile polymer obtained by an aqueous suspension polymerization method and an organic solvent capable of dissolving the polymer, and the conductivity of the solution is 75 μm.
Acrylonitrile polymer solution with S / cm or less. 2. An inorganic redox polymerization initiator is used,
A solution of an acrylonitrile polymer obtained by an aqueous suspension polymerization method and an organic solvent capable of dissolving the polymer,
By contacting with an ion exchange material that is not soluble in the organic solvent, the ionic impurities mainly containing cations and anions contained in the polymer solution are removed and purified, and the conductivity of the solution is 75 μm.
A method for producing an acrylonitrile-based polymer solution, which is S / cm or less.