JP5424824B2 - Carbon fiber precursor acrylic fiber and method for producing the same - Google Patents

Description

  The present invention relates to a carbon fiber, a carbon fiber precursor acrylic fiber, and a method for producing the same.

  It is known that carbon fibers have a high specific strength and specific elastic modulus compared to other fibers. For this reason, in addition to conventional sports and aerospace applications, composite fibers are being widely deployed in general industrial applications such as automobiles, civil engineering, architecture, pressure vessels, and windmill blades. Furthermore, there is a high demand for higher strength and higher elastic modulus in sports and aerospace applications that have been used in the past.

  Among the carbon fibers, polyacrylonitrile-based carbon fibers are the most widely used. Polyacrylonitrile-based carbon fiber is, for example, an acrylic fiber to which an oil agent composition is attached as a carbon fiber precursor, and the carbon fiber precursor is heated to 200 to 400 ° C. in an oxygen-existing atmosphere to form a flame-resistant fiber. It is obtained by conversion and subsequent carbonization in an inert atmosphere at 1000 ° C. or higher. The carbon fiber obtained by this method is widely used industrially as a reinforcing fiber for composite materials because of its excellent mechanical properties.

As a promising method for increasing the strength and elastic modulus of carbon fibers, there is a method for reducing foreign substances contained in and adhered to the carbon fiber precursor acrylic fibers. According to this method, the generation of scratches and voids on the surface can be reduced in the firing process, and the strength reduction of the carbon fiber can be suppressed.
For example, a method for reducing the amount of foreign matter in an acrylic polymer by multi-stage filtration of a polymerization raw material has been proposed (for example, Patent Document 1). In Patent Document 1, a polymerization raw material is subjected to multistage filtration with a filter having a minimum pore size of 0.6 μm to 0.2 μm to obtain an acrylonitrile polymer, and this acrylonitrile polymer is subjected to multistage filtration with a filter of 1.5 μm to 0.5 μm. The amount of foreign matter is reduced by treating with a bath, stretching bath, and washing water.
In addition, for example, a method for producing a precursor for carbon fiber production in which a dope solution composed of an acrylonitrile-based polymer and an organic solvent is treated with an ion exchanger and the treated dope solution is spun has been proposed (for example, Patent Documents). 2). In Patent Document 2, the content of metal ions is reduced by treating the dope solution with an ion exchanger.

JP-A-1-271401 JP-A-5-156523

However, in patent document 1, although the raw material from superposition | polymerization to extending | stretching, coagulating solution, and washing water are microfiltered, the cleaning of the oil agent composition to adhere is not considered. In addition, in Patent Document 1, since many filtration filter facilities are required, an installation space is required around the polymerization line, the spinning device, and the like, and the facility cost increases. In patent document 2, cleaning of the oil agent composition to which it adheres is not considered. Further, the carbon fiber is required to be further improved in strength and elastic modulus.
Then, this invention aims at the carbon fiber and carbon fiber precursor acrylic fiber which are high intensity | strength and high elasticity modulus, and its manufacturing method.

  Here, in Patent Document 2, the strength and elastic modulus of the carbon fiber are influenced by the aluminum content regardless of the iron element content, and the carbon fiber iron element content and the carbon fiber There is no correlation between the strength and the elastic modulus. However, as a result of diligent study focusing on the content of iron element contained in the carbon fiber precursor acrylic fiber, the present inventors have obtained the following knowledge. The strength and elastic modulus of the carbon fiber were influenced not only by the amount of iron element contained in the entire carbon fiber precursor acrylic fiber but also by the amount of iron adhered on the surface. For this reason, by reducing the amount of iron element (iron content) in the carbon fiber precursor acrylic fiber and the amount of iron element adhering to the surface (iron adhesion amount), the carbon fiber is further strengthened and increased in strength. It has been found that the elastic modulus can be increased, and has led to the following inventions.

That is, the carbon fiber precursor acrylic fiber of the present invention is characterized in that the iron abundance is 0.3 × 10 ⁻⁶ g / g or less and the iron adhesion amount is 0.1 × 10 ⁻⁶ g / g or less. And

The method for producing a carbon fiber precursor acrylic fiber of the present invention spins a raw material purification step in which an acrylonitrile polymer solution is brought into contact with a substance having ion exchange ability with iron ions, and an acrylonitrile polymer solution treated in the raw material purification step. Spinning step, oil agent raw material purification step for bringing oil agent composition and / or water into contact with substance having ion exchange ability with iron ion, and dispersion preparation step for preparing oil agent dispersion by mixing oil agent composition and water And a step of impregnating the fiber obtained in the spinning step with the oil dispersion and adhering the oil composition. The amount of iron element in the oil dispersion is preferably 0.5 × 10 ⁻⁶ g / g or less, and in the dispersion preparation step, the oil dispersion is prepared by emulsifying by a phase inversion temperature method. preferable.

  The carbon fiber of the present invention is obtained by firing the carbon fiber precursor acrylic fiber of the present invention.

  According to the present invention, it is possible to increase the strength and elastic modulus of carbon fibers.

(Carbon fiber precursor acrylic fiber)
The carbon fiber precursor acrylic fiber (hereinafter referred to as precursor fiber) of the present invention has an iron abundance of 2.0 × 10 ⁻⁶ g / g or less and an iron adhesion amount of 1.0 × 10 ⁻⁶ g / g. It is as follows.

The iron element that is inherent to or adheres to the precursor fiber is an iron element that is contained or adhered in any form such as iron ions and iron compounds.
The iron abundance of the precursor fiber is 2.0 × 10 ⁻⁶ g / g or less, and more preferably 0.5 × 10 ⁻⁶ g / g or less. By making the iron abundance of the precursor fiber within the above range, it is possible to increase the strength and elasticity of the obtained carbon fiber. In addition, the iron abundance of the precursor fiber is an amount obtained by removing the amount of iron attached to the surface of the precursor fiber from the total amount of iron contained in the precursor fiber.

The iron adhesion amount of the precursor fiber is 1.0 × 10 ⁻⁶ g / g or less, and more preferably 0.1 × 10 ⁻⁶ g / g or less. By making the iron adhesion amount of the precursor fiber within the above range, the obtained carbon fiber can be increased in strength and elastic modulus. In addition, when the precursor fiber is a single fiber, the iron adhesion amount of the precursor fiber is the adhesion amount on the surface of the single fiber. When the precursor fiber is a bundle of two or more single fibers (hereinafter referred to as fiber bundle), it refers to the amount of adhesion of the surface of each single fiber constituting the fiber bundle.

The precursor fiber is a fiber obtained by spinning an acrylonitrile polymer.
The acrylonitrile polymer used in the present invention is a polymer obtained by polymerizing acrylonitrile as a main monomer. The acrylonitrile polymer is not limited to a homopolymer obtained only from acrylonitrile, but may be an acrylonitrile polymer using other monomers in addition to the main component acrylonitrile.

  The blending amount of acrylonitrile in the acrylonitrile polymer can be determined in consideration of the quality required for the obtained carbon fiber, and is preferably 96 to 98.8% by mass, for example. If the blending amount of acrylonitrile is 96% by mass or more, the excellent quality and performance of the carbon fiber can be maintained without causing the fusion of the fibers in the firing step for converting the precursor fiber into the carbon fiber. In addition, the heat resistance of the acrylonitrile polymer is not lowered, and drying can be suppressed when the precursor fiber is spun. Furthermore, adhesion between single fibers can be avoided in processing such as stretching with a heating roller or pressurized steam. If the amount of acrylonitrile is 98.5% by mass or less, the solubility in the solvent does not decrease, the precipitation / coagulation of the acrylonitrile polymer can be prevented, and the stability of the spinning dope can be maintained. Can be manufactured.

  Monomers other than acrylonitrile can be blended in the acrylonitrile polymer. As a monomer other than acrylonitrile, a vinyl monomer that can be copolymerized with acrylonitrile can be appropriately selected, and a vinyl monomer that improves the hydrophilicity of the acrylonitrile polymer, has a flame resistance promoting effect. Vinyl monomers are preferred.

Examples of the monomer that improves the hydrophilicity of the acrylonitrile polymer include vinyl compounds having a hydrophilic functional group such as a carboxyl group, a sulfo group, an amino group, and an amide group. Examples of the monomer having a carboxyl group include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid, mesaconic acid and the like, among which acrylic acid, methacrylic acid, and itaconic acid are preferable. Examples of the monomer having a sulfo group include allyl sulfonic acid, methallyl sulfonic acid, styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, vinyl sulfonic acid, and sulfopropyl methacrylate. Acid, methallylsulfonic acid, styrenesulfonic acid, and 2-acrylamido-2-methylpropanesulfonic acid are preferred. Examples of the monomer having an amino group include dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, tertiary butylaminoethyl methacrylate, allylamine, o-aminostyrene, and p-aminostyrene. Of these, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminoethyl acrylate, and diethylaminoethyl acrylate are preferable. As the monomer having an amide group, acrylamide, methacrylamide, dimethylacrylamide, and crotonamide are preferable. By blending such a monomer, the hydrophilicity of the acrylonitrile polymer is improved. When the hydrophilicity is improved, the density of the obtained precursor fiber is improved, and generation of microvoids in the surface layer portion can be suppressed. The above-mentioned monomers can be used alone or in combination of two or more.
As for the compounding quantity of the monomer which improves the hydrophilicity of such an acrylonitrile polymer, 0.5-2 mass% is preferable in an acrylonitrile polymer.

Examples of the monomer having an effect of promoting flame resistance include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid, mesaconic acid, or alkali metal salts or ammonium salts thereof, acrylamide, methacrylamide, etc. Is mentioned. Among them, a monomer having a carboxyl group is preferable from the viewpoint of obtaining a higher flame resistance-promoting effect with a small amount of blending, and a carboxyl group-containing vinyl monomer such as acrylic acid, methacrylic acid, and itaconic acid is more preferable. . By mix | blending such a monomer, the time of the flame-proofing process mentioned later can be shortened, and manufacturing cost can be reduced. The above-mentioned monomers can be used alone or in combination of two or more.
As for the compounding quantity of the monomer which has such a flame-resistant acceleration | stimulation effect, 0.5-2 mass% is preferable in an acrylonitrile polymer.

Precursor fibers are those to which an oil composition is attached.
The oil agent composition can be determined in consideration of the function required for the precursor fiber, and for example, a silicone oil agent composition is preferable. Examples of the silicone-based oil composition include silicone oils such as amino-modified silicone and epoxy-modified silicone. Of these, amino-modified silicone is preferable. Examples of the amino-modified silicone include side-chain primary amino-modified silicone, side-chain primary and secondary amino-modified silicone, and both-end amino-modified silicone. By using such a silicone-based oil composition, it is possible to obtain carbon fibers that can be produced with high production efficiency and have excellent mechanical properties by increasing the fiber converging property in the spinning process.

  The adhesion amount of the oil agent composition on the precursor fiber is preferably 0.1 to 2% by mass, and more preferably 0.5 to 1.5% by mass with respect to the dry mass of the precursor fiber. When the adhesion amount of the oil composition is less than 0.1% by mass, it may be difficult to sufficiently develop the function of the oil composition. When the adhesion amount of the oil agent composition exceeds 2% by mass, the excessively adhered oil agent composition may be polymerized in the firing step to cause adhesion between single fibers.

(Production method)
The precursor fiber manufacturing method of the present invention includes a raw material purification step in which an acrylonitrile polymer solution is brought into contact with a substance having an ion exchange ability with iron ions (hereinafter referred to as an iron ion exchanger), and an acrylonitrile weight treated in the raw material purification step. A spinning process for spinning a coalesced solution, an oil agent raw material purification process in which an oil agent composition and / or water is brought into contact with a substance having an ion exchange ability with iron ions, and the oil agent composition and the water are mixed to prepare an oil agent dispersion. And a step of impregnating the fiber obtained in the spinning step with the oil dispersion (oil agent composition attaching step).

[Raw material purification process]
The raw material purification step is a step of bringing the acrylonitrile polymer solution into contact with the iron ion exchanger to remove iron ions in the acrylonitrile polymer solution and reducing the content of iron element.

The acrylonitrile polymer solution is a spinning dope obtained by dissolving an acrylonitrile polymer in a solvent.
The solvent can be determined in consideration of the type of acrylonitrile polymer, and examples thereof include organic solvents such as dimethylacetamide, dimethylsulfoxide, and dimethylformamide, and aqueous solutions of inorganic compounds such as zinc chloride and sodium thiocyanate. , Dimethyl sulfoxide, and dimethylformamide are preferable in that a dense precursor fiber is obtained.

  Although the density | concentration of the acrylonitrile polymer of an acrylonitrile polymer solution is not specifically limited, For example, 17-25 mass% is preferable and 19-25 mass% is more preferable. If the content is 17% by mass or more, a dense coagulated yarn can be obtained, and if it is 25% by mass or less, an appropriate viscosity and fluidity can be obtained as a spinning dope.

  The iron ion exchanger is not dissolved in the solvent of the acrylonitrile polymer solution, and examples thereof include a crosslinked ion exchange resin and a crosslinked ion exchange fiber. Of these, a cross-linked ion exchange resin made of vinylbenzene-styrene is preferred because of its versatility. This is because the iron ion exchanger needs to have an affinity with a solvent in order to remove iron ions in the acrylonitrile polymer solution and must not be dissolved by the solvent.

  Examples of the iron ion exchanger include strong acid cation exchange resins having sulfonic acid groups as functional groups, weak acid cation exchange resins having carboxylic acid groups such as methacrylic acid and acrylic acid, iminodiacetic acid type, Examples include polyamine type chelating resins. Among these, strong acid cation exchange resins are preferred from the viewpoint of improving the iron ion removal system. As an iron ion exchanger, it can use individually by 1 type or in combination of 2 or more types as appropriate.

  In the raw material purification process, together with an iron ion exchanger, a strongly basic anion exchanger having a quaternary amino group as a functional group, and a weakly basic anion exchange having a primary, secondary or tertiary amine as a functional group The body can be used together. By using these anion exchangers together, anions such as chlorine ions and silica can be removed, the impurity concentration in the acrylonitrile polymer solution can be reduced, and the strength and elastic modulus of the carbon fiber can be improved. For the reasons described above, in the raw material purification step, it is preferable to use a strong acid cation exchange resin alone or a combination of a strong acid cation exchange resin and a strongly basic anion exchange resin.

  The raw material purification step only needs to be able to contact the acrylonitrile polymer solution with the iron ion exchanger. For example, after adding the iron ion exchanger to the acrylonitrile polymer solution using a tank reactor and stirring for an arbitrary time, the iron ion exchanger A method for removing the exchanger (batch method) can be mentioned. Further, for example, there is a method (continuous method) in which a tubular reactor is used, an iron ion exchanger is filled in the tubular reactor to form an ion exchange layer, and the acrylonitrile polymer solution is circulated through the ion exchange layer. Can be mentioned. Among these, from the viewpoint of production efficiency and the like, a continuous method using a tubular reactor is preferable.

The addition amount of the iron ion exchanger to the acrylonitrile polymer solution in the batch method is preferably 0.01 to 100% by mass with respect to the acrylonitrile polymer solution, for example. If the amount is less than 0.01% by mass, the removal of iron ions may be insufficient. If the amount exceeds 100% by mass, the recovery of the iron ion exchanger becomes complicated and the running cost tends to increase.
The amount of iron ion exchanger charged in the tubular reactor in the continuous process can be determined in consideration of the amount of acrylonitrile polymer solution treated.

  In the raw material purification step, for example, it is preferable to contact the acrylonitrile polymer solution and the iron ion exchanger in a temperature range of 15 to 135 ° C. If it is less than 15 degreeC, the viscosity of an acrylonitrile polymer solution will become high, fluidity | liquidity will fall, it will become difficult to contact with an iron ion exchanger, and an ion exchange reaction will not advance easily. If it exceeds 135 ° C., the iron ion exchanger has insufficient thermal stability and cannot be used for a long period of time.

  The contact time (treatment time) between the acrylonitrile polymer solution and the iron ion exchanger in the raw material purification step may be determined according to the amount of iron ions contained in the acrylonitrile polymer solution and the type and amount of the iron ion exchanger. it can.

In the raw material purification step, it is preferable to reduce the amount of iron element in the acrylonitrile polymer solution as much as possible, for example, 2.0 × 10 ⁻⁶ g / g or less in terms of acrylonitrile polymer (hereinafter referred to as polymer). It is preferable to be 0.5 × 10 ⁻⁶ g / g or less. By setting it within the above range, the iron content of the obtained precursor fiber is set to 2.0 × 10 ⁻⁶ g / g or less, and the strength and elasticity of the carbon fiber can be increased.

[Spinning process]
The spinning step is a step of spinning the acrylonitrile polymer solution treated in the raw material purification step to obtain fibers (coagulated yarn). As the spinning method, for example, a wet spinning method in which spinning is directly performed in a coagulation bath, a dry spinning method in which coagulation is performed in air, and a dry wet spinning method in which spinning is performed once in air and then coagulated in a coagulation bath. For example, a known spinning method can be used. Among these, from the viewpoint of further improving the strength and elastic modulus of the carbon fiber, the wet spinning method or the dry wet spinning method is preferable.

  Examples of the spinning shaping by the wet spinning method or the dry-wet spinning method include a method in which the acrylonitrile polymer solution is spun into a coagulation bath from a nozzle having a hole having a substantially circular cross section.

As the coagulation bath, it is preferable to use an aqueous solution containing a solvent used for the acrylonitrile polymer solution. Such a coagulation bath is preferred from the viewpoint of easy solvent recovery.
In addition, the coagulation bath is preferably one in which iron ions are removed by contact with an iron ion exchanger. By using such a coagulation bath, the iron adhesion amount of the precursor fiber can be reduced.

  When using the aqueous solution containing a solvent as a coagulation bath, the solvent concentration in the aqueous solution is preferably 50 to 85% by mass. If it is in the said range, a precursor fiber will be made into the precise | minute structure without a void generation | occurrence | production, and a carbon fiber with high strength and a high elastic modulus can be obtained. In addition, stretchability can be secured and productivity is excellent.

  Although the temperature of a coagulation bath is not specifically limited, 10-60 degreeC is preferable. If it is in the said range, a precursor fiber will be made into the precise | minute structure without a void generation | occurrence | production, and a carbon fiber with high strength and a high elastic modulus can be obtained. In addition, stretchability can be secured and productivity is excellent.

  In the spinning process, the coagulated yarn can be drawn in a coagulation bath or a drawing bath. Alternatively, the coagulated yarn can be drawn in the air and then drawn again in the bath. Alternatively, the coagulated yarn can be made into a water-swollen state by washing with water before or after stretching or during stretching.

Examples of the stretching bath include water and an aqueous solution containing a solvent used for the acrylonitrile polymer solution.
The stretching bath is preferably one in which the iron ions are removed by contacting with the iron ion exchanger. By using such a drawing bath, the iron adhesion amount of the precursor fiber can be reduced.

  Drawing is performed by putting the coagulated yarn in a coagulation bath of 50 to 98 ° C. or a drawing bath and applying tension to the coagulated yarn. For example, the stretching may be performed at a desired ratio once, or may be performed at a desired ratio by stretching in two or more stages. For example, it is preferable that stretching in the air and stretching in the stretching bath are combined and stretched 5 to 15 times in total. By stretching in this way, the carbon fiber can be increased in strength and elastic modulus.

[Oil agent raw material purification process]
In the oil agent raw material purification step, the oil agent composition and / or water, which is the raw material of the oil agent dispersion prepared in the dispersion preparation step described later, is brought into contact with the iron ion exchanger to remove iron ions. In this step, in addition to the oil composition and water, additives such as an emulsifier blended in the oil dispersion may be brought into contact with the iron ion exchanger.
In the oil agent raw material purification step, the constituent materials such as the oil agent composition, water, and additives may be brought into contact with the iron ion exchanger, respectively, or the mixed liquid in which the constituent materials are mixed may be brought into contact with the iron ion exchanger. .

  In the oil agent raw material purification step, either a batch method or a continuous method may be used as in the raw material purification step.

The iron ion exchanger used in the oil material purification process is the same as the iron ion exchanger used in the raw material purification process. Moreover, you may use together an iron ion exchanger and an anion exchanger.
In the oil agent raw material purification step, it is preferable to reduce as much as possible the content of iron element in the raw material of the oil agent dispersion.

[Dispersion preparation process]
The dispersion liquid preparation step is a step of preparing an oil agent dispersion using the raw material of the oil agent dispersion obtained in the oil agent raw material purification step. The oil agent dispersion is obtained by dispersing an oil agent composition in water, and examples thereof include an oil agent composition dispersed in water using an emulsifier.
The blending amounts of the oil composition, water, and emulsifier in the oil dispersion can be determined in consideration of the function required for the precursor fiber.

  If necessary, additives such as an antioxidant, an antistatic agent, an antifoaming agent, an antiseptic, an antibacterial agent, and a penetrating agent can be added to the oil dispersion. Such additives can be used singly or in appropriate combination in order to improve the stability and adhesion characteristics of the oil dispersion in consideration of the production equipment and use environment of the precursor fiber.

As the antioxidant, a known substance can be used, and preferably a phenol-based or sulfur-based antioxidant. Examples of phenolic antioxidants include 2,6-di-t-butyl-p-cresol, 4,4′-butylidenebis- (6-t-butyl-3-methylphenol), 2,2′-methylenebis- ( 4-methyl-6-tert-butylphenol), 2,2′-methylenebis- (4-ethyl-6-tert-butylphenol), 2,6-di-tert-butyl-4-ethylphenol, 1,1,3 -Tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, n-octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, tetrakis [methylene-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] methane, triethylene glycol bis [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) Propionate], tris (3,5-di -t- butyl-4-hydroxybenzyl) isocyanurate. Examples of sulfur-based antioxidants include dilauryl thiodipropionate, distearyl thiodipropionate, dimyristyl thiodipropionate, and ditridecyl thiodipropionate. Such antioxidant can be used individually by 1 type or in combination of 2 or more types.
Although the compounding quantity of the antioxidant in an oil agent composition is not specifically limited, 1-5 mass% is preferable.

  A known substance can be used as the antistatic agent. Antistatic agents are roughly classified into ionic types and nonionic types, and ionic types include anionic, cationic and amphoteric, and nonionic types include polyethylene glycol type and polyhydric alcohol type. From the viewpoint of antistatic, ionic type is preferable, among them aliphatic sulfonate, higher alcohol sulfate ester salt, higher alcohol ethylene oxide adduct sulfate ester, higher alcohol phosphate ester salt, higher alcohol ethylene oxide adduct sulfate phosphate ester salt, More preferred are quaternary ammonium salt type cationic surfactants, betaine type amphoteric surfactants, higher alcohol ethylene oxide adducts polyethylene glycol fatty acid esters, polyhydric alcohol fatty acid esters and the like. Such antistatic agents can be used singly or in appropriate combination of two or more.

  In the dispersion preparation process, once a water-in-oil emulsion is formed with a homomixer while warming, the oil is dispersed by the phase inversion temperature method to lower the temperature and invert the phase to make an oil-in-water emulsion. It is preferable to prepare a liquid. Since the phase inversion temperature method can perform phase inversion using a polytetrafluoroethylene (PTFE) container or the like, it is possible to reduce the mixing of iron into the oil dispersion. In addition, the oil composition is dispersed in water with a small droplet size, and a stable emulsion is obtained. For example, in the forced emulsification method in which an oil agent composition, water, an emulsifier, etc. are charged into a gorin type homogenizer (gorin mixer) and emulsified, the raw material of the oil agent dispersion is emulsified directly in contact with the metal member, so the homogenizer Therefore, there is a possibility that iron is mixed into the oil dispersion.

The amount of iron element in the oil dispersion thus obtained is preferably 0.5 × 10 ⁻⁶ g / g or less, and more preferably 0.1 × 10 ⁻⁶ g / g or less. By setting it within the above range, the strength of the carbon fiber can be increased and the elastic modulus can be increased by setting the iron adhesion amount of the precursor fiber to 1.0 × 10 ⁻⁶ g / g or less.

[Oil agent composition adhesion process]
The oil agent composition attaching step is a step in which the fiber obtained in the spinning step is impregnated with the oil agent dispersion obtained in the dispersion preparing step, and the oil agent composition is attached.
The fiber to which the oil composition is adhered is a coagulated yarn, and is preferably a coagulated yarn in a water-swelled state obtained after, for example, stretching in the bath and then stretching or washing in the bath.

As a method for impregnating the coagulated yarn with the oil dispersion, known methods such as a roller method, a guide method, a spray method, a dip method, and the like can be used. The roller method is a method in which a roller is placed so that its axial direction is horizontal, the lower part of the roller is immersed in an oil dispersion, and the coagulated yarn is brought into contact with the upper part of the roller. In the guide method, a fixed amount of oil dispersion is discharged from a guide by a pump, and the coagulated yarn is brought into contact with the surface of the guide. In the spray method, a certain amount of oil dispersion is sprayed from a nozzle onto a coagulated yarn. In the dip method, the coagulated yarn is immersed in the oil dispersion and then squeezed with a roller or the like to remove excess oil dispersion.
From the viewpoint of uniform adhesion, a dip method is preferred in which the coagulated yarn is sufficiently impregnated with the oil dispersion and the excess oil dispersion is removed.

The oil composition adhering step may be impregnated once with the oil dispersion by the above-described method, or may be a multi-stage treatment in which the above-described method is repeated twice or more. From the viewpoint of more uniformly attaching the oil agent composition to the coagulated yarn, it is preferable to use a multistage treatment.
Thus, a precursor fiber in which the oil agent composition is attached to the coagulated yarn can be produced.

[Drying process]
The precursor fiber of the present invention may be subjected to the production of carbon fiber as it is obtained in the oil agent composition attaching step, or a drying step is provided after the oil agent attaching step to dry and dense the precursor fiber. May be used.
A drying process can dry precursor fiber by a conventionally well-known method, for example, drying with a heating roller is mentioned as a preferable drying method. Note that the number of heating rollers may be one or two or more.
The drying temperature in the drying step is preferably a temperature exceeding the glass transition temperature of the precursor fiber. By treating at such a drying temperature, drying and densification of the precursor fiber can be achieved. Although drying temperature changes with fluctuation | variation of the moisture content of a precursor fiber, it is preferable to determine in the range of 100-200 degreeC, for example.

  In the drying step, the precursor fiber can be dried and then subjected to pressurized steam stretching. By performing the steam stretching under pressure, the denseness and orientation degree of the precursor fiber can be further increased, and the carbon fiber can be further increased in strength and elastic modulus. Pressurized steam stretching is a method of stretching in a pressurized steam atmosphere. According to pressurized steam drawing, drawing at a high magnification is possible, stable spinning can be performed at a higher speed, and at the same time, it contributes to improving the denseness and orientation degree of the obtained fiber.

The pressurized steam stretching includes, for example, a method in which the precursor fiber is preheated with a heating roller and then tension is applied to the precursor fiber in the presence of pressurized steam. In such pressurized steam stretching, it is preferable to preheat the precursor fiber by setting the temperature of the heating roller immediately before the pressurized steam stretching apparatus to 120 to 190 ° C. When the temperature of the heating roller is less than 120 ° C., the temperature of the precursor fiber does not rise sufficiently and the drawability is lowered.
Moreover, it is preferable to control the fluctuation rate of the water vapor pressure in the pressurized water vapor stretching to 0.5% or less.
Thus, by controlling the fluctuation rate of the temperature of the heating roller and the water vapor pressure, it is possible to suppress the fluctuation of the draw ratio made to the precursor fiber and the fluctuation of the tow fineness caused by the fluctuation.

  The pressure of water vapor in the pressurized water vapor stretching is preferably 200 kPa / g or more so that the stretching of the heated roller and the characteristics of the pressurized water vapor stretching method appear clearly. The water vapor pressure is preferably adjusted as appropriate in consideration of the treatment time. If the pressure is high, leakage of water vapor may increase. Therefore, it is preferably about 600 kPa / g or less industrially.

  After the drying step, the precursor fiber is cooled to a normal temperature state by passing it through a room temperature roll or the like. The cooled precursor fiber is wound around a bobbin by a winder, or transferred into a can and stored, and used for the production of carbon fiber.

[Baking process]
In the firing step, the precursor fibers are fired to obtain carbon fibers. A baking process consists of a flame-proofing process and a carbonization process, and a graphitization process is provided as needed. The conditions for each treatment in the firing step are not particularly limited, but it is preferable to set conditions under which structural defects such as voids are unlikely to occur inside the fiber.

<Flame resistance treatment>
In the flameproofing treatment, the precursor fiber is heated for an arbitrary time under tension or stretching conditions in an oxidizing atmosphere to form a flameproof fiber. Examples of the flameproofing method include a hot air circulation method and a fixed hot plate method having a porous plate surface.
The heating temperature of the flameproofing treatment is, for example, 200 to 300 ° C.
In flame-resistant treatment is preferably the density of the oxidized fiber is processed until the ^{1.30g / cm 3 ~1.50g / cm 3} .

<Carbonization treatment>
In the carbonization treatment, the carbon fiber is obtained by heating the flame resistant fiber obtained by the flame resistance treatment in an inert gas atmosphere. Carbonization treatment consists of a pre-carbonization operation and a carbonization operation.
The pre-carbonization operation is performed under a tension in an inert gas atmosphere having a maximum temperature of 550 to 800 ° C., and in a temperature range of 300 to 500 ° C., the heating rate is 500 ° C./min or less, preferably 300 ° C./min or less. Then, the flame-resistant fiber is heated to form a pre-carbonized fiber. This pre-carbonization operation can improve the mechanical properties of the carbon fiber.
As the inert gas, a known inert gas such as nitrogen, argon, helium or the like can be adopted, but nitrogen is desirable in terms of economy.
The carbonization operation is performed by heating the pre-carbonized fiber at a temperature increase rate of 500 ° C./min or less, preferably 300 ° C./min or less in a temperature range of 1000 to 1200 ° C. in an inert atmosphere of 1200 to 3000 ° C. Carbon fiber. This carbonization operation can improve the mechanical properties of the carbon fiber.
The atmospheric gas is the same as that of the pre-carbonization operation.

<Surface treatment>
The obtained carbon fiber is further subjected to a surface treatment to improve the adhesion to the matrix of the composite material. As the surface treatment method, vapor phase or liquid phase treatment can be used, and electrolytic treatment is preferable from the viewpoints of productivity and prevention of variation. Examples of the electrolytic solution used for the electrolytic treatment include an aqueous acid solution such as sulfuric acid, nitric acid, and hydrochloric acid, an alkaline aqueous solution such as sodium hydroxide, potassium hydroxide, and tetraethylammonium hydroxide, or an aqueous solution of these salts. Among them, an aqueous solution containing ammonium ions is preferable, and examples thereof include an aqueous solution of ammonium nitrate, ammonium sulfate, ammonium persulfate, ammonium chloride, ammonium bromide, or a mixture thereof.
The amount of electricity in the electrolytic treatment can be determined according to the carbon fiber. For example, the higher the degree of carbonization, the higher the amount of electricity supplied.

The obtained carbon fiber is further subjected to sizing treatment as necessary. The sizing agent used for the sizing treatment can be determined according to the type of the matrix, and those having good compatibility with the matrix are preferable.
By applying these surface treatments to the carbon fiber, the adhesion between the carbon fiber and the matrix becomes an appropriate level, and mechanical properties balanced in the vertical and horizontal directions are exhibited.

As described above, the precursor fiber of the present invention can reduce the iron content of the precursor fiber to 2.0 × 10 ⁻⁶ g / g or less by treating the acrylonitrile polymer solution with an iron ion exchanger. In addition, by treating the raw material of the oil dispersion with an iron ion exchanger, the iron adhesion amount of the precursor fiber can be reduced to 1.0 × 10 ⁻⁶ g / g or less. By preparing the oil dispersion by the phase inversion temperature method, the iron adhesion amount of the precursor fiber can be reduced with higher accuracy. Thus, as for the precursor fiber of this invention, the iron abundance and the iron adhesion amount are controlled below a fixed numerical value. For this reason, the carbon fiber obtained by carbonizing the precursor fiber of the present invention can exhibit high strength and high elastic modulus.

  The reason why the strength and elastic modulus of the carbon fiber are improved by reducing the iron adhesion amount of the precursor fiber is not clear, but can be estimated as follows. In the flameproofing treatment, the precursor fiber is heated at 200 to 300 ° C. At this time, the iron element is considered to inhibit the flameproofing reaction by being heated to 200 to 300 ° C. in an oxygen-existing atmosphere. . And as a result of inhibiting flameproofing reaction, the intensity | strength and elastic modulus of carbon fiber will be reduced. From this, it is estimated that the strength and elastic modulus of the carbon fiber can be improved by reducing the iron adhesion amount of the precursor fiber.

  In the above-described embodiment, the oil agent dispersion is prepared using the oil agent dispersion raw material obtained in the oil agent raw material purification step. For example, after preparing the oil agent dispersion, the oil agent dispersion is converted into an iron ion exchanger. May be processed.

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto.
(Measuring method)
Total amount of iron in precursor fiber, amount of iron adhering to precursor fiber, amount of iron in precursor fiber, amount of iron element in acrylonitrile polymer solution (spinning stock solution), amount of iron element contained in oil dispersion and its raw material The strand strength and elastic modulus of the carbon fiber were evaluated by the following methods.

[Total amount of iron]
100 g of the precursor fiber was weighed in a platinum crucible, and the platinum crucible was placed on a hot plate and heated. Heating was performed until no smoke was generated (preliminary heat treatment). Subsequently, the platinum crucible was put into a muffle furnace, and the precursor fiber was incinerated at 600 ° C. (incineration treatment). After ashing, a platinum crucible was placed on a hot plate and heated. While heating, 2 mL of a hydrochloric acid aqueous solution of concentrated hydrochloric acid: pure water (mass ratio) = 1: 1 was added to the platinum crucible to dissolve the ash, and further heated to concentrate the solution of the ash to a dry solid size. (Dissolution / concentration treatment). This concentrate was dissolved in a 0.1 mol / L hydrochloric acid aqueous solution and made up to 10 mL, and used as a measurement sample (sample treatment). Using this measurement sample, the total amount of iron was measured by ICP emission spectrometry. The ICP emission analysis was measured using an ICP emission analyzer (manufactured by Thermo Electron, IRIS-AP advantage).

[Iron adhesion amount]
After drying 100 g of the precursor fiber at 105 ° C. for 1 hour, it was immersed in methyl ethyl ketone (MEK) at 90 ° C. for 8 hours, and the attached oil agent composition was extracted into the MEK solvent. The MEK extract was concentrated with an evaporator. After the concentrate was transferred to a platinum crucible, a preheating treatment, an ashing treatment, a dissolution / concentration treatment, and a sample treatment were performed in the same manner as the total amount of iron to obtain a measurement sample. The amount of iron element of the obtained measurement sample was measured by ICP emission spectrometry in the same manner as the total amount of iron.
Subsequently, the precursor fiber after extraction of the oil agent composition was placed in a hydrochloric acid aqueous solution of concentrated hydrochloric acid: pure water (mass ratio) = 1: 1, heated and stirred overnight at 80 ° C., and then the sample was filtered to obtain a filtrate. It was. After the filtrate was put in a platinum crucible, a preheating treatment, an ashing treatment, a dissolution / concentration treatment, and a sample treatment were performed in the same manner as the total amount of iron to obtain a measurement sample. The amount of iron element of the obtained measurement sample was measured by ICP emission analysis in the same manner as the total amount of iron.
The sum of the measured values of each iron element amount was defined as the iron adhesion amount.

[Abundance in iron]
The value obtained by subtracting the iron adhesion amount from the total iron amount was defined as the iron abundance.

[Amount of iron element in spinning dope]
After putting 100 g of the spinning dope into a platinum crucible, a preheating treatment, an ashing treatment, a dissolution / concentration treatment, and a sample treatment were performed in the same manner as the total amount of iron to obtain a measurement sample. The amount of iron element of the obtained sample for measurement was measured by ICP emission spectrometry in the same manner as the total amount of iron. In the table, the amount of iron element in the spinning dope is described as a polymer conversion (per gram of acrylonitrile polymer).

[Amount of iron element contained in oil dispersion and its raw materials]
After putting 100 g of a sample into a platinum crucible, a preheating treatment, an ashing treatment, a dissolution / concentration treatment, and a sampling treatment were performed in the same manner as the total amount of iron to obtain a measurement sample. The amount of iron element of the obtained sample for measurement was measured by ICP emission spectrometry in the same manner as the total amount of iron.

[Carbon fiber strand strength, elastic modulus]
The carbon fiber strand strength and elastic modulus were measured according to an epoxy resin-impregnated carbon fiber strand method according to JIS-R-7601. The number of measurements was 10 times, and the average value was used as an evaluation target.

Example 1
[Production of acrylonitrile polymer]
The acrylonitrile polymer was produced by supplying each raw material to an overflow type polymerization vessel as follows and stirring while maintaining the temperature in the polymerization vessel at 50 ° C., washing and drying the overflowed polymerization slurry. In the polymerization vessel, 74.75% by mass of deionized water and 25% by mass of monomer (composition ratio: acrylonitrile (AN): acrylamide (AAm): methacrylic acid (MAA) (mass ratio)) = 96: 3: 1) Each raw material is continuously supplied so as to be 0.1 mass% ammonium persulfate, 0.15 mass% ammonium bisulfite, and 2 mass ppm ferrous sulfate heptahydrate, and the pH is 3.0. Thus, an appropriate amount of sulfuric acid was added. The composition of the obtained acrylonitrile polymer was AN: AAm: MAA (mass ratio) = 96.5: 2.7: 0.8.

[Production of acrylonitrile polymer solution (spinning solution)]
21.2% by mass of the acrylonitrile polymer obtained above and 78.8% by mass of dimethylformamide were mixed and dissolved by heating to obtain a solution. 10 parts by mass of strongly acidic cation exchange resin (product name: PK218H type, functional group: sulfonic acid group, manufactured by Mitsubishi Chemical Corporation) is added to 100 parts by mass of the acrylonitrile polymer to the obtained solution. The mixture was stirred in a PTFE-coated container at 30 ° C. for 30 minutes. After stirring, the mixture was filtered through a PTFE filter having an opening of 5 μm to remove the ion exchange resin, and a spinning dope was obtained. Table 1 shows the amount of iron element contained in the spinning dope.

[Production of oil dispersion]
After mixing 40 parts by mass of an emulsifier (manufactured by Kao Corporation, product name: Emulgen 108) with 100 parts by mass of amino-modified silicone (manufactured by Shin-Etsu Chemical Co., Ltd., product name: KF-8002) in a PTFE container, The mixture was stirred with a PTFE-coated homomixer while adding 25 parts by mass of water to obtain a gel. While stirring this gel with a homomixer, amino-modified silicone was added so as to be 9 equivalents to the emulsifier. Subsequently, water was added while stirring with a homomixer so that water: amino-modified silicone: emulsifier (mass ratio) = 98.65: 1.2: 0.15 to obtain an oil dispersion. Amino-modified silicone, emulsifier, and water are 10 parts by mass of strongly acidic cation exchange resin (manufactured by Mitsubishi Chemical Corporation, product name: PK218H type, functional group: sulfonic acid group) with respect to 100 parts by mass of each raw material before use. The mixture was added and stirred in a PTFE-coated container at 60 ° C. for 30 minutes. After stirring, the product was filtered through a PTFE filter having an opening of 5 μm to remove the ion exchange resin. Table 1 shows the amount of iron element in the oil dispersion and its raw material.

[Precursor fiber production]
The spinning solution was discharged into a coagulation bath composed of an aqueous dimethylacetamide solution having a concentration of 67% by mass and a temperature of 38 ° C. from a spinning nozzle having a pore diameter of 75 μm and a hole number of 6000 to obtain a coagulated yarn. The obtained coagulated yarn was stretched 1.1 times in air, then washed and desolvated while being stretched 3.0 times in hot water. The solvent-removed coagulated yarn was immersed in the oil dispersion and densely dried with a 140 ° C. heating roller. Next, a precursor fiber having a circular cross section with a single fineness of 1.2 dtex was produced at a drawing speed of 100 m / min by stretching 3.0 times in steam at a pressure of 0.22 MPa. Table 1 shows the total amount of iron, the amount of iron present, and the amount of iron adhesion of the produced precursor fiber.

[Manufacture of carbon fiber]
The precursor fiber was passed through a flameproofing furnace having a temperature gradient of 220 to 260 ° C. (flameproofing treatment) and fired in a carbonization furnace having a temperature gradient of 400 to 1300 ° C. in a nitrogen atmosphere (carbonization treatment). Thereafter, electrolytic oxidation treatment and sizing treatment were performed to obtain carbon fibers. Table 1 shows the evaluation results of carbon fiber strand strength and elastic modulus of the obtained carbon fiber.
The obtained carbon fiber had a strand strength of 5.9 GPa and an elastic modulus of 290 GPa.

(Example 2)
Carbon fibers were obtained in the same manner as in Example 1 except that no treatment was performed with an ion exchange resin during the production of the spinning dope. Table 1 shows the measurement results.
The obtained carbon fiber had a strand strength of 5.8 GPa and an elastic modulus of 270 GPa.

(Example 3)
Except for adding a dimethylacetamide solution of 5.0% by mass of iron (III) nitrate so that the amount of iron element in the spinning dope immediately before spinning is 0.35 × 10 ⁻⁶ g / g (vs. polymer). In the same manner as in Example 1, carbon fibers were obtained. Table 1 shows the measurement results.
The obtained carbon fiber had a strand strength of 5.8 GPa and an elastic modulus of 280 GPa.

Example 4
Except for adding a dimethylacetamide solution containing 5.0% by mass of iron (III) nitrate so that the amount of iron element in the spinning dope immediately before spinning is 2.0 × 10 ⁻⁶ g / g (in terms of polymer). In the same manner as in Example 1, carbon fibers were obtained. Table 1 shows the measurement results.
The obtained carbon fiber had a strand strength of 5.7 MPa and an elastic modulus of 280 GPa.

(Example 5)
Carbon fibers were obtained in the same manner as in Example 1 except that iron (III) nitrate was added to the oil dispersion so that the amount of iron element in the oil dispersion was 0.5 × 10 ⁻⁶ g / g. . Table 1 shows the measurement results.
The carbon fiber obtained had a strand strength of 5.7 GPa and an elastic modulus of 270 GPa.

(Comparative Example 1)
Carbon fibers were obtained in the same manner as in Example 1 except that the spinning dope and the oil dispersion were produced under the following conditions. The spinning dope was prepared without treatment with an ion exchange resin. The oil dispersion is obtained by mixing 10 parts by mass of an emulsifier (manufactured by Kao Corporation, product name: Emulgen 108) with 90 parts by mass of amino-modified silicone (manufactured by Shin-Etsu Chemical Co., Ltd., product name: KF-8002). After emulsification with a gorin mixer (product name: pressure homogenizer gorin type, manufactured by SMT Co., Ltd.), water was added to produce. The composition of the obtained oil dispersion was water: amino-modified silicone: emulsifier (mass ratio) = 98.65: 1.2: 0.15. In producing the oil dispersion, none of the amino-modified silicone, the emulsifier, and water was treated with the ion exchange resin. Table 1 shows the measurement results.
The obtained carbon fiber had a strand strength of 5.3 MPa and an elastic modulus of 250 GPa.
Compared with Example 1, since the amount of iron adhering to the precursor fiber was larger, the strand strength of the carbon fiber was reduced by 0.6 GPa and the elastic modulus was lowered by 40 GPa.

(Comparative Example 2)
Except that it was not treated with an ion exchange resin during the production of the spinning dope and iron (III) nitrate was added to the oil dispersion so that the amount of iron element in the oil dispersion was 2.0 × 10 ⁻⁶ g / g. Carbon fibers were obtained in the same manner as in Example 1. Table 1 shows the measurement results.
The obtained carbon fiber had a strand strength of 4.9 GPa and an elastic modulus of 230 GPa.
Compared with Example 1, since the amount of iron adhering to the precursor fiber was large, the strand strength of the carbon fiber was reduced by 1.0 GPa and the elastic modulus was reduced by 60 GPa.

(Comparative Example 3)
Carbon fibers were obtained in the same manner as in Example 1 except that the oil dispersion was produced in the same manner as in Comparative Example 1. Table 1 shows the measurement results.
The obtained carbon fiber had a strand strength of 4.8 GPa and an elastic modulus of 230 GPa.
Compared to Example 1, the amount of iron adhering to the precursor fiber was large, so the strand strength of the carbon fiber was reduced by 1.1 GPa and the elastic modulus was reduced by 60 GPa.

(Comparative Example 4)
Carbon fibers were obtained in the same manner as in Example 1, except that iron nitrate (III) was added to the oil dispersion so that the amount of iron element in the oil dispersion was 2.0 × 10 ⁻⁶ g / g. . Table 1 shows the measurement results.
The obtained carbon fiber had a strand strength of 5.0 GPa and an elastic modulus of 240 GPa.
Compared with Example 1, since the amount of iron adhering to the precursor fiber was large, the strand strength of the carbon fiber was reduced by 0.9 GPa and the elastic modulus was reduced by 50 GPa.

(Comparative Example 5)
A dimethylacetamide solution containing 5.0% by mass of iron (III) nitrate was added to the spinning dope so that the amount of iron element in the spinning dope immediately before spinning was 0.35 × 10 ⁻⁶ g / g (vs. polymer). In the same manner as in Example 1, except that iron (III) nitrate was added to the oil dispersion so that the amount of iron element in the oil dispersion was 2.0 × 10 ⁻⁶ g / g. Obtained. Table 1 shows the measurement results.
The obtained carbon fiber had a strand strength of 5.0 GPa and an elastic modulus of 240 GPa.
Compared with Example 1, since the amount of iron adhering to the precursor fiber was large, the strand strength of the carbon fiber was reduced by 0.9 GPa and the elastic modulus was reduced by 50 GPa.

(Comparative Example 6)
A dimethylacetamide solution of 5.0% by mass of iron (III) nitrate was added so that the amount of iron element in the spinning dope immediately before spinning was 0.35 × 10 ⁻⁶ g / g (vs. polymer), Carbon fibers were obtained in the same manner as in Example 1 except that the dispersion was produced in the same manner as in Comparative Example 1. Table 1 shows the measurement results.
The obtained carbon fiber had a strand strength of 4.9 GPa and an elastic modulus of 250 GPa.
Compared to Example 1, the amount of iron adhering to the precursor fiber was large, so the strand strength of the carbon fiber was reduced by 1.0 GPa and the elastic modulus was reduced by 40 GPa.

(Comparative Example 7)
Except for adding a dimethylacetamide solution of 5.0% by mass of iron (III) nitrate so that the amount of iron element in the spinning dope immediately before spinning is 5.0 × 10 ⁻⁶ g / g (vs. polymer conversion). In the same manner as in Example 1, carbon fibers were obtained. Table 1 shows the measurement results.
The obtained carbon fiber had a strand strength of 5.2 GPa and an elastic modulus of 240 GPa.
Compared to Example 1, the amount of precursor fibers contained in iron was large, so that the strand strength of the carbon fibers was reduced by 0.7 GPa and the elastic modulus was reduced by 50 GPa.

(Comparative Example 8)
Carbon fibers were obtained in the same manner as in Example 1 except that iron (III) nitrate was added to the oil dispersion so that the amount of iron element in the oil dispersion was 1.0 × 10 ⁻⁶ g / g. . Table 1 shows the measurement results.
The obtained carbon fiber had a strand strength of 5.1 GPa and an elastic modulus of 230 GPa.
Compared with Example 1, since the amount of iron adhering to the precursor fiber was large, the strand strength of the carbon fiber was reduced by 0.8 GPa and the elastic modulus was reduced by 60 GPa.

(Comparative Example 9)
A carbon fiber was obtained in the same manner as in Comparative Example 1 except that the spinning stock solution, amino-modified silicone, emulsifier, and water were treated with an ion exchange resin in the same manner as in Example 1 in the production of the spinning stock solution and the oil dispersion. . Table 1 shows the measurement results.
The obtained carbon fiber had a strand strength of 5.0 GPa and an elastic modulus of 250 GPa.
Compared with Example 1, since the amount of iron adhering to the precursor fiber was large, the strand strength of the carbon fiber was reduced by 0.9 GPa and the elastic modulus was lowered by 40 GPa.

As is clear from Table 1, Examples 1 to 5 in which the iron internal amount of the precursor fiber was 2.0 × 10 ⁻⁶ g / g or less and the iron adhesion amount was 1.0 × 10 ⁻⁶ g / g or less. Both strand strength and elastic modulus were improved as compared with Comparative Examples 1-9. In particular, it has been found that the strand strength and the elastic modulus can be improved by reducing the iron adhesion amount of the precursor fiber. This means that the precursor fiber of Example 4 (total iron amount 2.1 × 10 ⁻⁶ g / g, iron adhesion amount 0.2 × 10 ⁻⁶ g / g) and the precursor fiber of Comparative Example 8 (total iron amount) 2.6 × 10 ⁻⁶ g / g, iron adhesion amount 2.5 × 10 ⁻⁶ g / g), although the total iron amount is approximate, Example 4 with less iron adhesion amount is carbon. It is clear from the fact that the strand strength and elastic modulus of the fiber are high.

Claims (4)

Carbon fiber precursor acrylic fibers having an iron abundance of 0.3 × 10 ⁻⁶ g / g or less and an iron adhesion amount of 0.1 × 10 ⁻⁶ g / g or less. A raw material purification step in which an acrylonitrile polymer solution is brought into contact with a substance having an ion exchange capacity with iron ions;
A spinning step of spinning the acrylonitrile polymer solution treated in the raw material purification step;
An oil agent raw material purification step in which an oil agent composition and water are brought into contact with a substance having ion exchange ability with iron ions;
A dispersion preparation step of mixing the oil composition and the water to prepare an oil dispersion having an iron element amount of 0.5 × 10 ⁻⁶ g / g or less ;
A carbon fiber precursor having a step of impregnating the fiber obtained in the spinning step with an oil dispersion having an iron element amount of 0.5 × 10 ⁻⁶ g / g or less and adhering the oil composition. Method for producing body acrylic fiber. A raw material purification step in which an acrylonitrile polymer solution is brought into contact with a substance having an ion exchange capacity with iron ions;
A spinning step of spinning the acrylonitrile polymer solution treated in the raw material purification step;
A dispersion preparation step of mixing an oil composition and water to prepare an oil dispersion;
The oil dispersion is brought into contact with a substance having an ion exchange capacity with iron ions, and the amount of iron element in the oil dispersion is 0.5 × 10 5. ^-6 an oil raw material purification step of g / g or less;
The fiber obtained in the spinning process has an iron element amount of 0.5 × 10 ^-6 a method for producing a carbon fiber precursor acrylic fiber, the method comprising impregnating an oil agent dispersion liquid of g / g or less and adhering the oil agent composition.   The said dispersion liquid preparation process is a manufacturing method of the carbon fiber precursor acrylic fiber of Claim 2 or 3 which emulsifies with a phase inversion temperature method and prepares an oil agent dispersion liquid.