JPH05156523A - Acrylonitrile based carbon fiber and its production - Google Patents

Abstract

PURPOSE:To obtain the subject carbon fiber having high performance and high strength by solving the point at issue of acrylonitrile based polymer prepared by an aqueous suspension polymerization. CONSTITUTION:The objective carbon fiber is obtained by baking a precursor for an acrylonitrile based carbon fiber produced using, as a raw material, an acrylonitrile based polymer obtained by an aqueous suspension polymerization using an inorganic redox initiator. The carbon fiber contains 0-3ppm iron compound or its ion and 0-10ppm aluminum compound or its ion as impurities and has excellent mechanical strength stability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon fiber comprising an acrylonitrile polymer obtained by an aqueous suspension polymerization and having excellent mechanical performance expression, and a method for producing the same.

[0002]

BACKGROUND OF THE INVENTION Acrylic fibers are widely used in clothing materials because of their texture similar to wool, and recently, they have been widely used as precursor fibers (precursor) for carbon fiber production and carbon fibers obtained by firing them. It's being used. In the production of carbon fibers, generally, a precursor is converted into flame-resistant fibers by heat treatment in an oxidizing atmosphere at 200 to 400 ° C.,
Subsequent to this, a method of carbonizing in a non-oxidizing atmosphere of at least 1000 ° C. is industrially adopted as a method for producing an acrylic carbon fiber. The carbon fiber obtained in this manner has further improved performance as a composite material due to its excellent physical properties, and is used as a primary structural member of an aircraft, particularly in the aviation field. In the field of such composite materials, the demand for high mechanical strength of carbon fibers is increasing at present.

However, various techniques have been studied for increasing the strength of acrylic carbon fibers. However, precursors used as raw materials are used in the firing process when converting the precursor fibers for producing carbon fibers into carbon fibers. Since it undergoes a great deal of physical and chemical changes, the causal relationship between the firing conditions and the conditions that the raw material precursor should have has not been clarified yet, so many unsolved problems are involved.

The conventional techniques for improving precursors are: (1) Improvement in polymer composition such as copolymerization composition and degree of polymerization (2) Oil agent component for avoiding fusion of single fibers in precursor firing step Improvement (3) Improvements such as roughness of the fiber surface, cracks existing on the surface, or defects such as voids are minimized.

For example, regarding (1), Japanese Patent Publication No. 63-2
In Japanese Patent Publication No. 95713, the degree of polymerization of an acrylonitrile polymer is regulated, and Japanese Patent Publication No. 21401
In JP-A-3, a specific copolymer composition is used. Regarding (2), the silicone oil is regulated in JP-B-54-134123, and regarding (3), JP-B-63.
No. 29513 discloses an improvement that minimizes defects such as roughness of the fiber surface, cracks existing on the surface, and voids.

However, according to these methods, although the performances are improved in those technologies, it is hard to say that they are decisive methods for producing the desired high performance carbon fiber. The currently demanded high performance is, for example, carbon fiber having a strand strength of 500 kg / mm ² and that the performance is stably produced.

In order to stably produce carbon fibers having high mechanical strength, it is necessary that the precursor used as the raw material has stable spinning operability, and a flame-proofing step of converting the precursor into oxidized fibers, and further In the subsequent carbonization step, it is necessary that the single fibers are not fused to each other and that fluff, yarn breakage, etc. do not occur during the firing step.

The precursor for producing an acrylic carbon fiber is generally a raw material of an acrylonitrile polymer obtained by an aqueous suspension polymerization method, and a wet or semi-dry wet spinning method through a dissolving step in a solvent for dissolving the polymer. Manufactured by. The suspension polymerization method, which is a heterogeneous polymerization in water as a method for producing an acrylonitrile-based polymer, has a long history and is a widely adopted production method, and it is easy to control the quality of the polymer. Features include easy recovery of reaction monomers and easy control of the entire process.

Aqueous suspension polymerization as a method for producing an acrylonitrile polymer is a method in which water is used as a reaction medium in a continuous suspension polymerization system. At this time, a polymerization initiator such as ammonium persulfate is used. Inorganic initiators are used. The acrylonitrile polymer produced by continuous suspension polymerization is filtered, dried, dissolved in a solvent that dissolves the polymer, and then spun by various methods.

As described above, an inorganic initiator (for example, a combination of ammonium persulfate-ammonium bisulfite-ferrous sulfate oxidation-reduction system) is used as a main component of the acrylonitrile monomer as a reaction medium. When a polymerization reaction is carried out using sulfuric acid-acidified water, particles of the produced polymer are formed, and the acrylonitrile polymer can be obtained in the state of an aqueous dispersion. After completion of the polymerization, the aqueous dispersion of the polymer is filtered, washed and dried to obtain an acrylonitrile-based polymer which is a raw material for the acrylic precursor.

In order to obtain an acrylonitrile polymer by continuous aqueous suspension polymerization, an aluminum reaction vessel is essential as a reaction vessel. When an acrylonitrile-based polymer is produced by a water-based continuous suspension polymerization reaction, it is practically impossible to continuously use it in a reaction vessel made of stainless steel or glass lined due to scale formation due to adhesion of the acrylonitrile-based polymer. On the other hand, when aluminum is used as the reaction container, since the reaction system is an acidic aqueous solution, the aluminum surface is corroded and dissolved,
It is said to prevent scale generation.

To terminate the polymerization reaction, a polymerization terminator is added. As a polymerization terminator in the case of producing this polymer by aqueous suspension polymerization, it is necessary to retain the function of neutralizing the acidic aqueous solution of the reaction system, ammonium oxalate,
An aqueous solution of ammonium bicarbonate in electrolyte is used.

The acrylonitrile polymer produced by the above-mentioned aqueous suspension polymerization method is produced in the presence of an electrolyte by a polymerization initiator, an electrolyte by corrosion of a polymerization vessel, an electrolyte by addition of a polymerization terminator and the like. .. Moreover, the acrylonitrile-based polymer forms polymer particles of several tens of microns and becomes dispersed particles in the water system as the polymerization reaction proceeds, but the above-mentioned various electrolytes are mixed in the polymer particles. Therefore, in order to produce an acrylonitrile polymer by the aqueous continuous suspension polymerization, it is necessary to wash the produced polymer with a sufficient amount of water. However, even if the surface of the produced polymer can be washed, it is difficult to wash the electrolyte trapped inside the polymer with water.

At present, in the production of an acrylonitrile-based polymer by such an aqueous suspension polymerization, an acrylonitrile-based polymer is dissolved in a solvent that dissolves the acrylonitrile-based polymer by passing through an insufficient washing state to a drying step. An acrylic precursor is manufactured by using a polymer dope solution and spinning it in a wet or semi-dry wet method. The acrylonitrile-based polymer dope solution containing such impurities (the above-mentioned electrolyte) causes various problems when producing an acrylic precursor.

For example, when the dope solution used in the spinning process for producing an acrylic precursor is heated and held at about 100 ° C. for a long time, yellow coloring becomes noticeable, and the dope solution itself gels to lower the solution fluidity. It is considered that the main cause of this is the electrolyte as an impurity contained in the acrylonitrile polymer.

Further, it is considered that the yellow coloring phenomenon of the precursor itself occurs due to the impurities, and when producing a high quality precursor, it has a great influence on the quality of the resulting carbon fiber. Similarly, if the dope solution itself gels and causes a decrease in solution fluidity, stable spinnability cannot be ensured, resulting in a yarn breakage phenomenon.

Furthermore, in the production of an acrylic precursor by semi-dry wet spinning, impurities (the above-mentioned electrolyte) dissolved in the dope solution of the acrylonitrile polymer are condensed in the guide in the spinning bath, causing thread breakage, Not only will productivity be significantly reduced, but in carbon fiber production,
It is said that it causes fluffing and causes deterioration of strength performance.

[0018]

An acrylonitrile polymer obtained by an aqueous suspension polymerization method is dissolved in an organic solvent to prepare a dope solution, and a carbon fiber is produced from the dope solution through a precursor for a carbon fiber. The problem that the turbid polymerization method has is that impurities that cannot be mixed during the production of the polymer by the aqueous suspension polymerization method remain in the polymer. This causes a problem in the performance of the precursor and the carbon fiber obtained by firing the precursor.

Therefore, an object of the present invention is to solve the problems of such an aqueous suspension polymerization method, and to provide a precursor and an acrylonitrile polymer dope solution suitable for producing carbon fibers obtained by firing the precursor. Then, the present invention provides a carbon fiber using a precursor which is industrially advantageous as a raw material, and a method for producing the same by spinning by a wet or semi-dry wet method.

[0020]

Means for Solving the Problems The gist of the present invention is that for an acrylonitrile-based carbon fiber produced from an acrylonitrile-based polymer obtained by an aqueous suspension polymerization method using an inorganic redox initiator as a raw material. A carbon fiber which is obtained by firing a precursor (precursor) and has an iron compound or its ion as an impurity of 0 to 3 ppm and an aluminum compound or its ion of 0 to 10 ppm as an impurity, which is excellent in mechanical strength stability.

Furthermore, the present invention comprises a solution of an acrylonitrile polymer obtained by water-based suspension polymerization using an inorganic redox initiator and an organic solvent capable of dissolving the polymer, which is insoluble in the organic solvent. Dope of an acrylonitrile-based polymer having excellent thermal stability obtained by purifying and removing an iron compound or its ion, an aluminum compound or an impurity that is an ion contained in the polymer with a substance having an ion exchange ability. A method for producing carbon fiber having excellent mechanical strength stability, characterized by comprising firing a precursor for producing carbon fiber obtained by spinning the solution by a wet method or a semi-dry wet method.

The present invention will be described in detail below. The present invention is obtained by aqueous suspension polymerization using an inorganic redox initiator, and an iron compound or an ion thereof as an impurity,
An acrylonitrile-based polymer obtained by purifying and removing an aluminum compound or an impurity that is an ion thereof, is spun into an acrylonitrile-based precursor using this as a raw material, and carbon having excellent mechanical strength stability is obtained by firing the precursor. In fiber.

Examples of the inorganic redox initiator include commonly used inorganic peroxides such as ammonium persulfate and potassium persulfate. As a reducing agent used as a polymerization aid, sodium sulfite, ammonium sulfite,
Typical examples include sodium hydrogen sulfite, ammonium hydrogen sulfite, sodium thiosulfate, ammonium, sodium dithionite, sodium formaldehyde sulfoxylate, L-ascorbic acid and dextrose, and ferrous sulfate or sulfuric acid. Compounds such as copper can also be used in combination. Among them, the combination of ammonium persulfate-sodium hydrogen sulfite (ammonium) -ferrous sulfate is preferable.

The acrylonitrile polymer used in the present invention may be composed of a repeating unit composed of an acrylonitrile monomer and a monoolefinic monomer copolymerizable therewith. Here, the acrylonitrile-based polymer must be composed of at least 60% by weight of an acrylonitrile monomer. If the content of the acrylonitrile monomer is less than 60% by weight, the mechanical strength performance originally possessed by the acrylonitrile carbon fiber cannot be retained.

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,
Isobrene and the like can be mentioned.

When the acrylonitrile polymer according to the present invention is produced by an aqueous suspension polymerization method using an inorganic redox initiator, the polymerization initiator used is a usual oxidizing agent or reducing agent as described above. You can choose from. Commonly used oxidizing agents such as ammonium persulfate, potassium persulfate, sodium persulfate, ammonium hydrogen sulfite, sodium thiosulfate, ammonium bisulfite, sodium dithionite, sodium formaldehyde sulfoxylate, L-ascorbic acid, dext A reducing agent such as rose is typical.

Any ratio of reducing agent / oxidizing agent is possible, but it is preferable to set the equivalent ratio of oxidizing agent / reducing agent to 1 to 4 in order to promote the polymerization more efficiently.

The polymerization reaction temperature is preferably 30 to 80 ° C. The reason for this is that when the polymerization temperature exceeds 80 ° C., acrylonitrile evaporates and is dispersed outside the reaction system, thereby lowering the polymerization conversion rate of acrylonitrile. Further, if the temperature is lower than 30 ° C, the polymerization rate decreases, which not only lowers the productivity but also impairs the polymerization stability.

Ion-exchanged water is preferably used as the polymerization medium. Further, the ratio of ion-exchanged water to the monomer (hereinafter referred to as water / monomer ratio) can be any ratio, but preferably the water / monomer ratio is 1.0 to
It is in the range of 5.0.

The average residence time of the monomers in the polymerization reaction vessel is preferably the time defined when a usual acrylonitrile polymer is produced by the aqueous suspension polymerization method. The hydrogen ion concentration in the polymerization reaction vessel may be within a range in which the catalyst used causes a rapid oxidation / reduction reaction, and preferably in an acidic region of pH 2.0 to 3.5.

For the polymer taken out from the polymerization kettle, a polymerization terminator is added to stop the reaction. There is no problem as long as the polymerization reaction terminator is normally used when the acrylonitrile polymer is produced by aqueous suspension polymerization. After adding a polymerization terminator to the aqueous polymer solution, unreacted monomers are recovered. As a method of recovering the unreacted monomer, there is a method of directly distilling the polymer aqueous solution, or a method of dehydrating once and separating the unreacted monomer from the polymer and then distilling, but both methods can be adopted. ..

As the dehydration washing machine in the latter case, a rotary vacuum filtration machine, a centrifugal dehydration machine and the like which are generally known filtration dehydration machines are used. In separating the polymer from the aqueous polymer solution using these devices, a coagulant such as ammonium sulfate, aluminum sulfate, or sodium sulfate is added in order to perform it more efficiently, or the polymer is used in the sense of promoting the aggregation of the polymer. Operations such as raising the temperature of the aqueous solution can also be performed. The water remaining in the polymer is removed by the usual drying method.

The acrylonitrile-based polymer containing at least 60% acrylonitrile obtained by the aqueous suspension polymerization method is dissolved in an organic solvent. As an organic solvent,
It is necessary that the solvent dissolves the acrylonitrile polymer. Among them, dimethylformamide, dimethylacetamide and dimethylsulfoxide are preferably used.

The ratio of the polymer to the organic solvent is preferably a solution containing a concentration of the acrylonitrile polymer of 5 to 35% by weight and an organic solvent of 95 to 65% by weight capable of dissolving the acrylonitrile polymer. The reason why the content of the acrylonitrile polymer is 5 to 35% by weight is that if the content is less than 5% by weight, the polymer concentration is too low to ensure satisfactory spinnability of the precursor. On the other hand, when it exceeds 35% by weight, the viscosity of the polymer solution becomes too high and the spinnability cannot be secured.

The acrylonitrile polymer solution containing 5 to 35% by weight of acrylonitrile polymer and 95 to 65% by weight of organic solvent is purified by a substance having an ion exchange ability which is insoluble in the organic solvent. Examples of the substance having an ion exchange ability that does not dissolve in an organic solvent include a crosslinked ion exchange resin, a crosslinked ion exchange fiber, and the like. Among them, a divinylbenzene-styrene crosslinked ion exchange resin is generally used. And is preferable. In the dope state of the acrylonitrile polymer dissolved in an organic solvent, impurities in the polymer are purified and removed by a cross-linking ion exchange resin, an affinity with the organic solvent is required, and the organic solvent This is because it must be a crosslinked resin so as not to dissolve.

As the functional group having an ion exchange function,
A strong cation exchange resin having a sulfonic acid group may be mentioned. When the ion species purified by ion exchange are both cation and anion species, an ion composed of a strong cation exchange resin having a sulfonic acid group and a strong anion exchange resin having a quaternary amino group. Use both with exchange resins. To capture heavy metals, chelating resins of iminodiacetic acid type and polyamine type, weak cation exchange resins of methacrylic acid and acrylic acid, and weak anion exchange resins of primary, secondary, and tertiary amine types are used. Etc., and the use of both the weak cation exchange resin and the same weak anion exchange resin.

Among these, a strong cation exchange resin having a sulfonic acid group, or both a strong cation exchange resin having a sulfonic acid group and a strong anion exchange resin having a quaternary amino group. Use is particularly preferred.

The amount of ion exchange resin or ion exchange fiber used in the present invention is preferably 0.01 to 100% by weight based on 100% by weight of the acrylonitrile polymer solution. When the amount is less than 0.01% by weight, the ion exchange capacity is remarkably deteriorated, which is not practical. When it exceeds 100% by weight, it is not practical because it is economically disadvantageous and it takes more time and effort than necessary to recover the substance having ion-exchange ability.

Purification of the acrylonitrile polymer solution with a substance having an ion exchange capacity is carried out in the temperature range of 15 to 150 ° C. When the temperature is lower than 15 ° C, the viscosity of the acrylonitrile polymer solution is increased, the fluidity is deteriorated, and the ion exchange reaction hardly progresses substantially. On the other hand, if it exceeds 150 ° C., the heat stability of the ion-exchange substance itself is insufficient, and it cannot be used for a long period of time.

The apparatus used for purifying the acrylonitrile polymer solution with a substance having an ion exchange capacity may be either a tubular reactor or a tank reactor.
For example, a process in which a tubular reactor is filled with an ion exchange resin and an acrylonitrile-based polymer dope solution is continuously supplied and purified while flowing is more realistic.

According to the method of the present invention, impurities are purified and removed from a dope solution obtained by dissolving an acrylonitrile polymer obtained by using an inorganic redox initiator in an organic solvent by using a substance capable of ion exchange. In a carbon fiber obtained by firing a precursor produced by spinning by a wet method or a semi-dry wet method, an iron compound or its ion as an impurity is 0 to 3 ppm, preferably 0 to 1 ppm, and an aluminum compound or its ion is It is 0 to 10 ppm, preferably 0 to 5 ppm.

Here, the respective amounts of the iron compound or its ion and the aluminum compound or its ion are defined by the fact that ferrous sulfate is used as the polymerization initiator used in the aqueous suspension polymerization specified in the invention. Acrylonitrile-based polymer produced by using it as a polymerization aid, by using an aluminum kettle as a reaction kettle in an aqueous suspension continuous polymerization reaction, and corroding and dissolving the aluminum kettle because the reaction system is an acidic aqueous solution. This is because the above metals or their ions are always present as impurities in the coalescence.

When the iron compound or its ion as an impurity exceeds 3 ppm and the aluminum compound or its ion exceeds 10 ppm, it causes the thermal stability of the acrylonitrile polymer dope solution, and also the acrylonitrile polymer. When the thermal stability of the dope solution decreases, it becomes difficult to secure the mechanical strength stability of the carbon fiber obtained by firing the obtained precursor.

Further, when a glass container is used when an acrylonitrile polymer is obtained by aqueous suspension polymerization, and when a metal such as an iron compound is not used as a polymerization aid, an iron compound or the like as an impurity is substantially contained. Although the metal compound or its ion, the aluminum compound or its ion does not exist, the aqueous suspension continuous polymerization is practically impossible, and because of poor polymerization stability, etc. The heat stability of the acrylonitrile polymer dope solution gives good results.

5 to 35% by weight of a polymer purified with a substance having an ion exchange ability, 95 to 65% by weight of an organic solvent, iron or its ion as an impurity of 3 ppm or less as an impurity with respect to an acrylonitrile polymer, and aluminum or its ion. The acrylonitrile-based polymer solution whose content is 10 ppm or less is spun into a precursor by a wet or semi-dry wet method.

With respect to the spinning method, spinning is carried out by a wet or semi-dry wet method according to a conventional method to obtain a precursor. Specifically, the coagulated yarn discharged into the coagulation bath by a wet or semi-dry wet method is washed and drawn in a hot water bath by an ordinary method,
After applying the process oil, it is dried and densified. If necessary, stretching means such as dry heat stretching and steam stretching may be taken.

The firing step is not particularly limited, and the method usually employed can be employed as it is. That is, the precursor obtained by the above method is first pre-oxidized in an oxygen-containing gas at a temperature of 200 to 400 ° C., and then carbonized in an inert gas stream at a temperature of at least 1000 ° C. If necessary, graphitization is performed at a temperature within 3000 ° C.

[0048]

EXAMPLES The present invention will be specifically described below with reference to examples. In the text, “part” and “%” represent parts by weight and% by weight.

Example 1 A polymerization reaction kettle with a capacity of 801 (a reaction vessel made of aluminum and a stirring blade made of an aluminum coating turbine type) was charged with 351 ion-exchanged water (pH = 3), and acrylonitrile 98.5 was charged. Parts, methacrylic acid 1.5
Parts, 1.5 part of ammonium persulfate, 4.5 parts of ammonium bisulfite, ferrous sulfate (FeSO ₄ · 7H ₂ O)
Dissolved in ion-exchanged water so as to be 0.00005 parts and sulfuric acid 0.085 parts, respectively, and continuously supplied. Further, ion-exchanged water was separately supplied so that the total amount of ion-exchanged water would be 400 parts. The polymerization temperature was maintained at 60 ° C., sufficient stirring was performed, and the average residence time was 80 minutes, and the raw materials were continuously supplied to carry out the polymerization reaction.

The aqueous polymer dispersion was continuously taken out from the overflow port of the reactor, and 0.5 parts of ammonium oxalate and 1.5 parts of ammonium bicarbonate as a polymerization terminator were added thereto.
Part of ion-exchanged water was added with an aqueous solution at a rate of 0.2 part, and ion-exchanged water was further added, and then unreacted monomer and excess polymerization aid residue were removed by a rotary vacuum filter. Washed. 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 shown in Table 1.

22 parts of the dry polymer obtained above was dissolved in 78 parts of dimethylformamide to obtain a polymer solution, and a strong ion exchange resin having a sulfonic acid group (Diaion HPK55H manufactured by Mitsubishi Kasei Co., Ltd.) was added. ) Add 10 parts, and mix and stir in a kneader at 80 ° C. for 30 minutes,
The solution was filtered through a 100-mesh wire net to remove the ion exchange resin, and the acrylonitrile polymer solution shown in Table 1 was obtained.
Table 1 shows the results of thermal stability of the acrylonitrile polymer solution.

Using this acrylonitrile-based polymer solution, through a 1500-hole, 0.15 mmφ die,
Semi-dry wet spinning was performed on a 78% dimethylformamide aqueous solution (15 ° C), followed by washing and stretching, and then an aminosiloxane-based oil agent was added to the precursor fiber weight in an amount of 1.0%, followed by dry densification treatment. And a precursor of 1.0 denier was obtained.

This precursor was subjected to 225 according to a conventional method.
Continuously supplied by a roll drive to a flameproofing furnace in a hot air atmosphere having a temperature gradient in the range of up to 260 ° C. and a residence time of 3
The flameproofing treatment was performed in 4 minutes. The flame-resistant yarn thus obtained was subjected to carbonization in a nitrogen gas atmosphere in a carbonization furnace having a temperature gradient in the range of 320 to 700 ° C. and a heat treatment furnace at 1350 ° C. with a residence time of 7 minutes and 45 minutes, respectively. Chemical firing was performed to obtain carbon fibers. Table 1 shows the characteristics of the obtained carbon fibers.

Example 2 15 parts of the polymer obtained in Example 1 was dissolved in 85 parts of dimethylacetamide to give an acrylonitrile polymer solution,
Five discs (thickness 5 mm, diameter 50 mm, stainless steel disc, ion exchange resin amount 10 g) packed in a bed shape with a strong ion exchange resin having a sulfonic acid group (Diaion PK228 manufactured by Mitsubishi Kasei Co., Ltd.) were incorporated. Add 1 acrylonitrile polymer solution to the polymer dope pipe.
The solution was fed at a rate of 50 g / min to obtain an acrylonitrile polymer solution shown in Table 1.

Using this acrylonitrile polymer solution, wet spinning was carried out through a 12000 hole, 0.075 mmφ spinner into a 68% dimethylacetamide aqueous solution (35 ° C.), followed by washing, drawing, oiling, and dry densification. After the treatment, the same firing as in Example 1 was performed. Table 1 shows the characteristics of the obtained carbon fibers.

Example 3 22 parts of the polymer obtained in Example 1 was dissolved in 78 parts of dimethylformamide to obtain an acrylonitrile polymer solution, and a strong ion exchange resin having a sulfonic acid group (Amberlyst 15, Rohm & 80 g / min of the acrylonitrile-based polymer solution was placed in a polymer dope pipe in which 10 discs (thickness 5 mm, diameter 50 mm, stainless steel disc, ion exchange resin amount 10 g) packed in a bed shape were incorporated. The solution was fed at a speed to obtain an acrylonitrile polymer solution shown in Table 1.

Using this acrylonitrile-based polymer solution, through a 1500-hole, 0.15 mmφ die,
After semi-dry wet spinning in a 78% dimethylformamide aqueous solution (15 ° C.), followed by washing and stretching,
An aminosiloxane oil agent was applied in an amount of 1.0% based on the weight of the fiber, and further subjected to a dry densification treatment to obtain a 1.0 denier precursor. This was fired in the same manner as in Example 1. Table 1 shows the characteristics of the obtained carbon fibers.

Example 4 15 parts of the polymerized portion obtained in Example 1 was used as dimethylacetamide 8
Dissolved in 5 parts to give an acrylonitrile-based polymer solution, and a disk (thickness: 5) filled with a strong ion exchange resin having a sulfonic acid group (Diaion PK228) in a bed shape.
mm, 50 mm diameter stainless steel disk 5 pieces of ion exchange resin 10 g) and a disk filled with a strong anion exchange resin (Diaion PA312) having a quaternary amine in a bed shape (thickness 5 mm, diameter 50 mm stainless steel disk The acrylonitrile-based polymer solution was fed at a rate of 150 g / min to a polymer-doped pipe in which 5 sheets of an ion exchange resin (10 g) were alternately incorporated to obtain an acrylonitrile-based polymer solution shown in Table 1. ..

Using this acrylonitrile-based polymer solution, through a 1500-hole, 0.15 mmφ die,
Semi-dry wet spinning was performed on a 78% dimethylacetamide aqueous solution (15 ° C.), followed by washing and stretching, and then an aminosiloxane oil agent was added in an amount of 0.5 to 1.5 based on the weight of the fiber.
% And further subjected to a dry densification treatment to obtain a 1.0 denier precursor. This was fired in the same manner as in Example 1. Table 1 shows the characteristics of the obtained carbon fibers.

Comparative Example 1 The acrylonitrile polymer solution obtained in Example 1 was spun in the same manner as in Example 1 without carrying out ion exchange resin purification to obtain a precursor. The precursor thus obtained was subjected to the same firing treatment as in Example 1 to obtain carbon fibers. Collectively, the results are shown in Table 1. The thermal stability of the dope was inferior to that of Example 1, and the performance of the obtained carbon fiber was low,
There was uneven performance.

Comparative Example 2 The acrylonitrile polymer solution of Example 2 was spun in the same manner as in Example 2 without purifying the ion exchange resin. The precursor thus obtained was subjected to the same firing treatment as in Example 1 to obtain carbon fibers. Collectively, the results are shown in Table 1. The thermal stability of the dope was inferior to that of Example 1, the performance of the obtained carbon fiber was low, and the performance was uneven.

[0062]

[Table 1]

The evaluation items in Table 1 are measured as follows. Polymerization conversion rate The aqueous dispersion after the polymerization was collected, and the polymer content was collected by filtration to determine the polymer yield as the polymerization conversion rate. Specific viscosity A polymer having a concentration of 0.5 g was dissolved in 100 ml of dimethylformamide, and the solution viscosity (Ubbelohde viscometer) was measured at 25 ° C. Sodium ion content The polymer and fiber were burned and the ash content obtained was used to measure by flame color measurement.

Ammonium Ion Amount The polymer and fibers were heated with water to extract ammonium ions, which were measured by a colorimetric method. Iron and Aluminum Content Polymers and fibers were burned and the ash content obtained was used to measure by atomic absorption spectrometry. Polymer Solution Viscosity Using a dope having the indicated polymer concentration, the ball drop time was measured in an oil bath at 85 ° C. to measure the solution viscosity. The change with time was similarly performed.

Polymer solution color tone Using the dope having the indicated polymer concentration, the color condition was visually evaluated immediately after heating to 85 ° C. in an oil bath at 85 ° C. Polymer Composition Polymer composition was determined using a Proton NMR instrument. AN represents acrylonitrile.

Strand Strength Measured according to the resin-impregnated strand strength test method specified in JIS-R7601. The number of measurements is n = 10, and Table 1 shows the average value. Coefficients of variation in strand strength and strand modulus were calculated according to the following formulas.

[0067]

[Equation 1]

[0068]

[Equation 2]

S: Standard deviation CV: Coefficient of variation (%) χ ₁ : Individual measurement value n = Number of measurements

[0070]

The acrylonitrile polymer solution according to the present invention is excellent in thermal stability, is also excellent in removing impurities, and the obtained carbon fiber precursor (precursor) is obviously less colored. The carbon fiber of the present invention obtained from this has high quality and high performance and enables further expansion of applications in the field of composite materials, and its industrial significance is great.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Osamu Kato 20-1 Miyuki-cho, Otake-shi, Hiroshima Mitsubishi Rayon Co., Ltd. Otake Works (72) Inventor Yoshio Manabe 20-1 Miyuki-cho, Otake-shi, Hiroshima Mitsubishi Rayon Co., Ltd. Otake Office

Claims (2)

[Claims] 1. A precursor for an acrylonitrile-based carbon fiber, which is produced from an acrylonitrile-based polymer obtained by an aqueous suspension polymerization method using an inorganic redox initiator as a raw material, and is used as an impurity. Carbon fiber having an iron compound or its ion of 0 to 3 ppm and an aluminum compound or its ion of 0 to 10 ppm, which is excellent in mechanical strength stability. 2. An ion exchange ability which does not dissolve in an organic solvent from a solution comprising an acrylonitrile polymer obtained by an aqueous suspension polymerization method using an inorganic redox initiator and an organic solvent capable of dissolving the polymer. Carbon obtained by spinning a dope solution obtained by purifying and removing an iron compound contained in the polymer, or an ion thereof, an aluminum compound or an impurity that is an ion thereof, by a wet method or a semi-dry wet method. A method for producing a carbon fiber, which comprises firing a precursor for producing a fiber.