JP2012193465A - Acrylic precursor fiber for carbon fiber, method for producing the same, and carbon fiber obtained from the precursor fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an acrylic precursor fiber for a carbon fiber that is good in spinnability and excellent in carbonization yield after calcination process, and a carbon fiber obtained from the precursor fiber at low cost.SOLUTION: The acrylic precursor fiber for a carbon fiber comprises a mixture that contains 1 to 100 pts.mass of carbon black with respect to 100 pts.mass of a polyacrylonitrile-based polymer, in which the carbon black has a dibutyl phthalate absorption amount of 100 (cm/100 g) or less, and pH of an aqueous dispersion comprising 90 pts.mass of water and 10 pts.mass of the carbon black is to be 7.0 or more and 8.0 or less.

Description

  The present invention relates to an acrylic precursor fiber for carbon fiber having good spinnability and excellent carbonization yield after the firing step, and a method for producing carbon fiber obtained from the precursor fiber.

  Carbon fiber is widely used in aircraft parts, railway vehicle parts, ship parts and sporting goods because of its mechanical and chemical properties and light weight, and more recently in general industries such as automobiles. I am trying to do. The level of required mechanical properties is increasing, and there is a strong demand for enhanced production capacity.

  Conventionally, a polyacrylonitrile-based precursor fiber bundle (hereinafter referred to as a PAN-based precursor fiber bundle) is subjected to carbon fiber treatment through the following steps. First, several tens to several hundreds of PAN-based precursor fiber bundles are subjected to flame-resistant heat treatment in an oxidizing atmosphere at 200 to 300 ° C. by the flame-resistant treatment process, and the obtained flame-resistant fiber bundles are subjected to the carbonization treatment process. Firing in an inert atmosphere at 300 ° C. or higher to obtain carbon fibers.

  The flameproofing process and the carbonization process are important processes that affect the physical properties and productivity of carbon fibers. In the flameproofing process, the polymer chain constituting the acrylic fiber is oxidized and the nitrile group bonded to the polymer chain is cyclized to have a thermally stable structure that can pass through the subsequent carbonization process. Carbon fiber having high strength and elastic modulus can be obtained by converting to fiber, promoting oxidation in a high temperature inert atmosphere in the carbonization step, and densifying the structure.

  However, there is a problem that a decomposition reaction containing carbon atoms is released as a waste gas due to a chemical reaction that occurs in the process of firing the carbon fiber, resulting in a low carbonization yield and poor productivity. The carbonization yield here is the ratio (%) of the mass of carbon fiber after weight loss and the mass of acrylic fiber before passing through the firing process, due to the heat energy applied in the firing process. It is used as an index of carbon fiber productivity. From the viewpoint of reducing the production cost of carbon fiber, establishment of a technique for improving the carbonization yield and improving the productivity of carbon fiber in the firing process is desired.

  In order to improve carbonization yield of carbon fiber, there is a method of previously containing carbon black in a polyacrylonitrile-based polymer for carbon fiber precursor fiber.

  For example, Patent Document 1 discloses a technique in which carbon black is contained in a polyacrylonitrile-based polymer for carbon fiber precursor fibers. Patent Document 2 describes a technique for efficiently dispersing carbon black to be contained using a basic compound as a dispersant. When an additional test was conducted using these techniques, the carbon fiber precursor composition was spinnable, and the carbonization yield of the baked carbon fiber showed a relatively high value.

JP 2007-182657 A JP 2008-169535 A

  However, in the methods described in Patent Documents 1 and 2, carbon black becomes agglomerated in the spinning stock solution due to secondary agglomeration when the spinning stock solution is prepared, and the fluidity tends to deteriorate. Furthermore, due to the interaction between the surface-treated carbon black and the dispersing agent of the basic compound, the viscosity of the spinning dope increases at the time of dispersion and fluidity tends to deteriorate, and the spinning productivity tends to decrease. It was seen.

In order to solve this problem, the acrylic precursor fiber for carbon fiber of the present invention has the following configuration. Dibutyl phthalate absorption of ¹⁰⁰ (cm 3 / 100g) or less, the carbon black pH of the aqueous dispersion is 7.0 to 8.0 when dispersed so as to be 10 mass% of water, polyacrylonitrile It is a manufacturing method of the acrylic precursor fiber for carbon fibers comprised with the mixture containing 1-100 mass parts with respect to 100 mass parts of polymers.

  Moreover, in order to solve the said subject, the manufacturing method of the carbon fiber of this invention has the following structure. That is, this is a method for producing carbon fibers obtained by flame-proofing and carbonizing acrylic precursor fibers for carbon fibers produced by the above-described method.

  ADVANTAGE OF THE INVENTION According to this invention, it has favorable spinnability and can manufacture the carbon fiber acrylic precursor fiber for carbon fibers excellent in the carbonization yield after a baking process, and the carbon fiber obtained from the precursor fiber at low cost.

The acrylic precursor fiber for carbon fiber in the present invention has the following configuration. That respect polyacrylonitrile-based polymer to 100 parts by mass, and a dibutyl phthalate absorption of ¹⁰⁰ (cm 3 / 100g) or less and pH of the aqueous dispersion when the dispersion so as to be 10 mass% water 7. It is an acrylic precursor fiber for carbon fiber composed of a mixture containing 1 to 100 parts by mass of carbon black of 0 or more and 8.0 or less.

(Dibutyl phthalate (DBP) absorption)
The dibutyl phthalate (DBP) absorption amount is ¹⁰⁰ (cm 3 / 100g) or less carbon black, according to the "DBP absorption of Determination" of JIS K6217-4 (2001), measured using the Abu soap door meter DBP absorption, as refers to those made to ¹⁰⁰ (cm 3 / 100g) or less. This DBP absorption amount is an index of the size of the structure which is a secondary aggregate of carbon black. If the structure is too large, the dispersibility in the spinning dope deteriorates, and the acrylic precursor fiber for carbon fiber is deteriorated. Not only is the spinnability at the time of production impaired, but also causes poor stretchability at the time of producing carbon fibers, the elastic modulus of the resulting carbon fibers, and the strength decreases. Further, according DBP absorption 1~100 ^(cm 3 / 100g), preferably should be in 10~80 ^(cm 3 / 100g), more preferably 30~70 ^(cm 3 / 100g). When the DBP absorption amount is large, carbon black tends to form secondary aggregates, which may impair the fluidity of the spinning dope.

  The carbon black in the present invention is preferably carbon black whose surface is not particularly surface-treated, or carbon black whose surface is slightly basic-treated. The degree of the surface oxidation treatment is such that the pH of the aqueous dispersion when carbon black is dispersed in water to a concentration of 10% by mass is 7.0 or more and 8.0 or less, more preferably 7.5 or more and 8.0 or less. What is good. If the pH is less than 7, the carbon black in the spinning dope is difficult to disperse uniformly, and the dispersibility in the spinning dope may be insufficient.

  The degree of the surface oxidation treatment can be determined by measuring the pH of the aqueous dispersion when carbon black is dispersed in water at 10% by mass using a pH tester.

The carbon black in the present invention is preferably a carbon black having a nitrogen adsorption specific surface area of 40 m ² / g or less. Carbon black having a nitrogen adsorption specific surface area of 40 m ² / g or less uses an automatic specific surface area measuring device in accordance with “Method of obtaining specific surface area—nitrogen adsorption method—single point method” of JIS K6217-2 (2001). nitrogen adsorption specific surface area measured Te refers to those made below 40 m 2 / ^g. This nitrogen adsorption specific surface area is an index of the primary particle size of carbon black, and if the specific surface area is too large, it indicates that many fine particles are present in the spinning dope. When the amount present is small, it is easy to disperse uniformly, but when the mass part of the carbon black is increased, it becomes easy to form a structure that is a carbon black secondary aggregate described later. If the structure is too large, the dispersibility in the spinning dope deteriorates, and not only the spinnability when producing the acrylic precursor fiber for carbon fibers is impaired, but also poor stretchability when producing carbon fibers, This causes a decrease in the elastic modulus and strength of the obtained carbon fiber. Also, such nitrogen adsorption specific surface area 1~40m ² / g, it is better preferably 5~35m ² / g, more preferably 10 to 30 m ² / g.

  In the present invention, the blending amount of carbon black contained in the spinning solution of acrylic precursor fiber for carbon fiber is 100 mass of polyacrylonitrile polymer from the viewpoint of carbonization yield of carbon fiber and handling property when spinning. It is good to set it as 1-100 mass parts with respect to a part, Preferably it is 50-100 mass parts, More preferably, it is 80-100 mass parts. If the amount of carbon black is too large, the fluidity of the spinning dope will decrease, and clogging and thread breakage of the die filter will easily occur.

  The carbon black contained in the spinning solution of the acrylic precursor fiber for carbon fiber in the present invention is preferably a dispersion in which carbon black is sufficiently dispersed in a solvent. As a solvent for dispersing carbon black, a solvent in which a polyacrylonitrile-based polymer such as DMSO, DMF, or DMAc is soluble can be used.

  Such a dispersion can be prepared by any of common solid-liquid mixing methods such as ultrasonic, self-revolving mixer, planetary mixer, homomixer, homogenizer, ball mill and bead mill. You may adjust by combining.

  Furthermore, it is preferable that the dispersion further contains a basic compound from the viewpoint of enabling the carbon black to be more uniformly dispersed. The basic compound may be a basic surface-treated carbon black. Specifically, the basic compound here is preferably a compound having an amino group or ammonia. As the amino group contained in the molecule, any of a primary amino group, a secondary amino group and a tertiary amino group can be used. The compound having an amino group includes an aliphatic amine attached to an aliphatic chain and an aromatic amine attached directly to an aromatic ring. In the present invention, either an aliphatic amine or an aromatic amine may be used.

  Examples of compounds having such amino groups include methylamine, trimethylamine, triethylamine, ethylenediamine, diethylenetriamine, triethylenetetramine, monoethanolamine, diethanolamine, methyldiethanolamine, triethanolamine, benzylamine, phenylethylamine, aniline, dimethylaniline, etc. Is preferably used.

  Among these basic compounds, methylamine, diethanolamine, and methyldiethanolamine are more preferably used from the viewpoint that carbon black can be uniformly dispersed in a smaller amount.

  In the present invention, when a basic compound is contained, its content is based on 100 mass parts of carbon black from the viewpoint of the interaction with carbon black and the heat resistance and denseness of the acrylic precursor fiber for carbon fiber. And preferably 5 parts by mass or less. When the content is higher than 5 parts by mass, the content of the basic compound to be added is increased, the solubility of the polyacrylonitrile-based polymer to be added later is reduced in the organic solvent, the density of the original yarn after spinning is reduced, and the carbon after firing is reduced. This may lead to a decrease in fiber strength and elastic modulus.

  The polyacrylonitrile polymer used for the spinning solution of acrylic precursor fiber for carbon fiber of the present invention has fewer defects due to copolymer components when it is made into carbon fiber, and improves the quality and performance of carbon fiber. For the purpose, it is preferable to polymerize 90% by mass or more, preferably 96% by mass or more of acrylonitrile.

  The polyacrylonitrile-based polymer used in the present invention has no restrictions on the copolymer component, molecular weight distribution, stereoregularity, etc., and promotes flame resistance as a copolymer component in order to promote flame resistance treatment for carbon fiber. It is good to copolymerize the monomer which has an effect | action 0.1 to 5 mol%. As the flame resistance promoting component, those having at least one carboxyl group or amide group are preferably used. Further, as the flame resistance reaction becomes higher, the flame resistance treatment can be performed in a shorter time, and the productivity can be increased. Therefore, it is desirable to increase the copolymerization amount of the flame resistance promoting component. However, on the other hand, as the amount of copolymerization increases, the exothermic rate increases and the risk of runaway reaction may occur. Therefore, the range is preferably not more than 5 mol%, more preferably 0.5 to 3 mol%. Preferably, it is more preferable to set it as 1-3 mol%.

  As specific examples of the monomer having a flame resistance promoting action, acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid, mesaconic acid, acrylamide, methacrylamide and the like are preferably used. Acrylamide and methacrylamide are more preferably used from the viewpoint of promoting flame resistance in the firing step and improving solubility in solvents.

  In order to produce the polyacrylonitrile-based polymer used in the present invention, any of known polymerization methods such as solution polymerization and suspension polymerization can be used. When employing solution polymerization, a solvent in which a polyacrylonitrile-based polymer such as DMSO, DMF, or DMAc is soluble is used. Among these, DMAc is more preferably used from the viewpoint of solubility of the polyacrylonitrile-based polymer.

  In order to produce a spinning stock solution of acrylic precursor fiber for carbon fiber used in the present invention, it is prepared by sufficiently dissolving the polyacrylonitrile polymer in the carbon black dispersion. The solvent of the carbon black dispersion must be a solvent in which the polyacrylonitrile polymer is soluble, and is preferably the same as the solvent used in the production of the polyacrylonitrile polymer from the viewpoint of simplifying the process. If a polyacrylonitrile-based polymer is dissolved in a solvent and carbon black is added and dispersed, the viscosity of the spinning dope increases, the fluidity may be deteriorated, and there is a possibility that it is not uniformly dispersed.

  In the present invention, the acrylic precursor fiber for carbon fiber can be produced by the following steps. In the method of the present invention, the above-described spinning solution is spun from a die by a wet spinning method or a dry-wet spinning method and introduced into a coagulation bath to coagulate the fibers. From an industrial viewpoint, a wet spinning method excellent in productivity is preferable.

  In the present invention, the coagulation bath is preferably an aqueous solution containing materials used for the spinning dope, and is set so as to reduce the porosity of the coagulated yarn by adjusting the concentration of the contained solvent. Generally, depending on the solvent used, for example, when DMAc is used, the concentration of DMAc is 50 to 80% by mass, preferably 60 to 75% by mass. The temperature of the coagulation bath is preferably low, and is usually 50 ° C. or lower, more preferably 40 ° C. or lower. If the temperature of the coagulation bath is lowered, a denser yarn can be obtained. However, if the temperature is lowered too much, the take-up speed of the coagulated yarn is lowered and the productivity is lowered.

  In the method of the present invention, the swollen yarn obtained above is washed and drawn in the washing and drawing steps. In addition, about the order of washing | cleaning and extending | stretching, you may perform washing | cleaning first and may carry out simultaneously. Although there is no restriction | limiting in particular as a washing | cleaning method, The method of immersing in the water generally used, especially warm water is good.

  The stretching method may be a method of stretching while being immersed in water or warm water, a dry heat stretching method in the air using a hot plate or a roller, or stretching in a box furnace where hot air is circulated. However, it is not limited to these. From an economical viewpoint, it is preferable to carry out in warm water. The draw ratio is preferably 1 to 8 times. However, when performing secondary stretching later, it is preferable to set in consideration of the stretching ratio.

  In the method of the present invention, the washed and stretched yarn obtained above in the oil agent application step is guided to an oil bath containing a silicone oil agent, and the silicone oil agent is applied to the yarn. As the oil agent, a silicone-based oil agent containing a silicone compound is used. As the silicone oil, dimethyl silicone oil or organically modified silicone oil is preferably used, and amino-modified silicone oil having high heat resistance is more preferable. Usually, a silicone compound and a nonionic emulsifier are mixed and emulsified. In some cases, an antioxidant, various additives, and an organic substance not containing a silicone atom can be mixed.

  In the method of the present invention, the yarn provided with the silicone-based oil obtained above in dry densification is dry densified. As a method for drying and densifying, it is generally performed by contacting with a hot plate or a heating roller, and drying with a heating roller is preferably used. The higher the drying temperature, the more the crosslinking reaction of the silicone oil agent is promoted, and it is also preferable from the viewpoint of productivity. Therefore, it can be set as high as possible without causing fusion between single fibers. Specifically, 150 ° C. or higher is preferable, and 180 ° C. or higher is more preferable. Moreover, it is preferable that the drying time is a time for the yarn to dry sufficiently.

  In the method of the present invention, if necessary, the dried and densified yarn obtained above can be secondarily stretched. Examples of the secondary stretching method include dry heat stretching and steam stretching.

  In the present invention, the single fiber fineness of the carbon fiber acrylic precursor fiber to be obtained is preferably 0.5 to 2.0 dtex, more preferably 0.6 to 1.5 dtex. If the single fiber fineness is too small, the processability of the yarn-making process and the firing process may decrease due to a decrease in spinnability and the occurrence of yarn breakage due to contact between rollers and guides. In addition, if the single fiber fineness is too large, the difference between the inner and outer structures of each single fiber after flame resistance increases, and the process passability in the subsequent carbonization process, the tensile strength of the resulting carbon fiber, and the tensile elastic modulus may decrease. is there.

  Moreover, the carbon fiber of this invention can be manufactured in the following processes.

  In the method of the present invention, in the flameproofing step, the above-mentioned acrylic precursor fiber for carbon fiber is heated in an oxidizing atmosphere at 200 to 300 ° C. to obtain a flameproofed fiber bundle. As the oxidizing atmosphere, known oxidizing atmospheres such as air, oxygen and nitrogen dioxide can be adopted, but air is preferable from the viewpoint of economy. The flameproofing treatment time is preferably 30 to 120 minutes from the viewpoint of enhancing the productivity and performance of the carbon fiber. By making the time required for the flameproofing treatment to be 30 minutes or more, the flameproofing reaction becomes sufficient, and it becomes difficult to produce uneven spots, and it becomes difficult to cause fluff and bundle breakage in the subsequent carbonization process. Productivity is improved. On the other hand, by setting the time required for the flameproofing treatment to 120 minutes or less, it is not necessary to enlarge the flameproofing device or reduce the flameproofing treatment speed, thereby improving productivity.

  In the method of the present invention, in the pre-carbonization step, the flame-resistant fiber bundle is put into a first carbonization furnace and pre-carbonized to obtain a pre-carbonized fiber bundle. The inside of the first carbonization furnace is an inert atmosphere having a temperature of 300 ° C. or more and less than 1,000 ° C., and the acrylic precursor fiber bundle that has been subjected to flame resistance treatment is moved forward while traveling in the inert atmosphere. Carbonized. In addition, the flow of the inert atmosphere which circulates in the 1st carbonization furnace may be a parallel direction with respect to the to-be-processed fiber, or a perpendicular direction, and is not specifically limited. As the inert atmosphere, a known inert atmosphere such as nitrogen, argon, or helium can be adopted, but nitrogen is desirable from the viewpoint of economy.

  In the present invention, in the carbonization step, the pre-carbonized fiber bundle is put into a second carbonization furnace and carbonized to obtain a carbonized fiber bundle. The inside of the second carbonization furnace is an inert atmosphere having a maximum temperature of 1,000 ° C. or more and 3,000 ° C. or less, and the pre-carbonized fiber bundle is carbonized while traveling in the inert atmosphere. The In addition, the flow of the inert atmosphere in a 2nd carbonization furnace may be a parallel direction with respect to the to-be-processed fiber to travel, or a perpendicular direction, and is not specifically limited. The inert atmosphere can be selected from the known inert atmospheres exemplified above, but nitrogen is desirable from the viewpoint of economy.

  By performing the firing process stepwise as described above, the carbonization yield of the obtained carbon fiber is 55% or more by suppressing the mass that the fiber is decomposed and burned off by thermal energy as much as possible.

  Further, the obtained carbonized fiber bundle may be subjected to a surface treatment before the sizing treatment step. For example, it is preferable to improve the affinity and adhesiveness between the carbon fiber and the matrix resin in the composite material by performing an electrolytic oxidation treatment in an electrolytic solution or an oxidation treatment in a gas phase or a liquid phase.

  In the sizing process, a sizing process and a drying process are performed. The method of sizing treatment is not particularly limited as long as a desired sizing agent can be applied to the carbonized fiber bundle. Examples thereof include a roller sizing method, a roller dipping method, and a spray method.

  The sizing treatment liquid used for the sizing treatment is not particularly limited, and a sizing treatment solution having characteristics suitable for various high-order processing can be selected. For example, in order to uniformly impregnate the yarn, it can be a solution containing a sizing agent, an emulsion, or a sizing treatment liquid in a suspended state, which is attached to a carbonized fiber bundle, and the solvent or What is necessary is just to be able to dry and remove the dispersion medium.

  The main components of the sizing agent in the sizing treatment liquid are epoxy resin, epoxy-modified polyurethane resin, polyester resin, phenol resin, polyamide resin, polyurethane resin, polycarbonate resin, polyetherimide resin, polyamideimide resin, polyimide resin, bismaleimide Resins, urethane-modified epoxy resins, polyvinyl alcohol resins, polyvinyl pyrrolidone resins, polyether sulfone resins and the like can be mentioned, and are not particularly limited.

  The ratio of the sizing agent in the sizing treatment liquid is not particularly limited, and is preferably 0.2 to 20% by mass, more preferably 3 to 10% by mass. By setting the ratio of the sizing agent in the sizing treatment liquid to 0.2% by mass or more, a desired function can be sufficiently imparted to the carbon fiber. In addition, by setting the ratio of the sizing agent in the sizing treatment liquid to 20% by mass or less, the adhesion amount of the sizing agent becomes appropriate, and the impregnation property of the matrix resin when used as a composite material in a subsequent process is good. Become.

  Although the solvent or dispersion medium used for the sizing treatment liquid is not particularly limited, it is preferable to use water from the viewpoints of handleability and safety.

  The adhesion amount of the sizing agent in the carbon fiber bundle is preferably 0.3 to 5.0% by mass, and more preferably 0.4 to 3.0% by mass. By setting the adhesion amount of the sizing agent to 0.3% by mass or more, a desired function can be sufficiently imparted to the carbon fiber. Moreover, the impregnation property of the matrix resin at the time of utilizing as a composite material by a post process becomes favorable because the adhesion amount of a sizing agent shall be 3.0 mass% or less.

  In the drying process after the sizing process, the solvent or dispersion medium of the sizing process liquid is removed by drying. The conditions in this case are preferably a temperature of 120 to 300 ° C. and a range of 10 seconds to 10 minutes, and more preferably a temperature of 150 to 250 ° C. and a range of 30 seconds to 4 minutes. By setting the drying temperature to 120 ° C. or higher, the solvent can be sufficiently removed. Moreover, the quality of the carbon fiber bundle by which the sizing process was carried out can be maintained by making drying temperature into 300 degrees C or less.

  The method for the drying treatment is not particularly limited, and examples thereof include a method of drying by contacting with a hot roll using steam as a heat source, and a method of drying in an apparatus in which hot air is circulated.

Hereinafter, the present invention will be described more specifically with reference to examples. In this example, various characteristics were measured as follows.
<Nitrogen adsorption specific surface area of carbon-based fine particles>
According to JIS K6217-2 (2001) “Method for obtaining specific surface area—nitrogen adsorption method—single point method”, measurement was performed using an automatic specific surface area measuring apparatus.
<DBP absorption of carbon black>
It was measured using an abstract meter according to “How to determine DBP absorption” in JIS K6217-4 (2001).
<PH measurement of carbon black>
10 g of carbon black was added to 100 ml of water, heated with stirring, cooled after boiling, and the pH of the supernatant was measured.
<Carbonization yield>
Water is added to the spinning solution in which the polyacrylonitrile-based polymer is sufficiently dissolved in the carbon black dispersion to remove the solvent, and then the polymer composition is isolated. The polymer composition is subjected to a flameproofing treatment in a vertical flow batch flameproofing furnace at 230 ° C. for 40 minutes, further at 260 ° C. for 40 minutes, a total temperature rising time of 10 minutes, and a total of 90 minutes. Thereafter, the sample was freeze-dried and pulverized, and then heated to 1100 ° C. at a temperature increase rate of 50 ° C./min using a differential thermal thermal mass (TG / DTA: TA Instruments DTA Q-500) measuring device. At this time, the mass of the test specimen after heating was a, the specimen mass before measurement was b, and the mass ratio a / b × 100 (%) was the carbonization yield of the specimen.
<Spinnability evaluation>
A spinning stock solution prepared by dissolving in DMAc so that the solid content concentration of carbon black and polyacrylonitrile-based polymer was 21.2% by mass was prepared. The spinning stock solution had a number of die holes of 2000 and a die hole diameter of 0.075 mm. From the die, the amount of discharge is adjusted to 2 L / hr, and wet spinning is performed to discharge into a coagulation bath of DMAc 67 mass% and water 33 mass%. At that time, the take-up speed is gradually increased, and the speed when the broken yarn is observed in the coagulation bath (the limit coagulation bath speed) is used as an index of spinnability.

Example 1
Acrylonitrile polymer comprising 96% acrylonitrile units, 3% acrylamide units, and 1% methacrylic acid units (the amount of carboxylic acid groups is 7.0 × 10 ⁻⁵ equivalents, the intrinsic viscosity (η) is 1.7), DMAc To obtain a polyacrylonitrile polymer. In addition, 100 parts by mass of carbon black (manufactured by Tokai Carbon Co., Ltd., product name: Seast S) was weighed with respect to 100 parts by mass of the solid content of the polymer, dispersed in DMAc, and further added with 1 part by mass of methylamine. The mixture was stirred at 100 rpm for 30 minutes with an Oak mixer (dynamic mixer), and then 20 minutes at 20 rpm with a bead mill (manufactured by Ashizawa, product name: TYPE STITS) to obtain a carbon black dispersion. In the carbon black dispersion, the polyacrylonitrile polymer is dissolved so that the total solid concentration of the carbon black and the polyacrylonitrile polymer is 21.2% by mass, and 100 rpm is obtained with an Oaks mixer (dynamic mixer). Was stirred for 30 minutes to obtain a spinning solution of the target acrylic precursor fiber for carbon fiber. Table 1 shows the DBP absorption amount and pH of the carbon black used and the measurement results of the spinnability of the obtained spinning dope. When the carbonization yield and spinnability of this spinning dope were measured, the carbonization yield was as high as 74.2%, and the critical coagulation bath speed was 18 m / min.

  A spinneret having a hole diameter of 0.075 mm and a hole number of 2000 was used to obtain a coagulated yarn by a discharge wet spinning method in a DMAc aqueous solution (coagulation bath) having a temperature of 38 ° C. and a concentration of 68%. Next, the coagulated yarn was stretched 6 times while removing the solvent in warm water at 60 ° C to 98 ° C. The drawn yarn was immersed in a 1% aqueous solution of an aminosilicon-based oil and then dried and densified with a heating roller at 180 ° C. to obtain a carbon fiber precursor fiber having a single yarn fineness of 1.2 dtex and a filament count of 2000.

  Six obtained carbon fiber precursor fibers were combined to give a total filament number of 12,000, and subjected to a flame resistance treatment while being drawn at a draw ratio of 0.94 in air at 230 to 260 ° C. A modified fiber was obtained.

  Subsequently, preliminary carbonization is performed while stretching at a stretch ratio of 1.0 in a nitrogen atmosphere at 400 ° C. to 700 ° C., and further, carbonization is performed by setting the stretch ratio to 0.95 in a nitrogen atmosphere at a maximum temperature of 1350 ° C. The carbon fiber was obtained by processing.

(Example 2)
A spinning dope and carbon fiber were obtained in the same manner as in Example 1 except that the carbon black to be dispersed was changed from Seast S to Mitsubishi Chemical, product name: # 5. Table 1 shows the DBP absorption amount and pH of the carbon black used and the measurement results of the spinnability of the obtained spinning dope. When the carbonization yield and spinnability of this spinning dope were measured, the carbonization yield was as high as 72.2%, the limiting coagulation bath speed was 14 m / min, which was sufficient to obtain an acrylic precursor fiber for carbon fiber. The value is shown.

(Comparative Example 1)
A spinning dope was obtained in the same manner as in Example 1 except that the carbon black to be dispersed was changed from Seast S to Asahi Carbon Co., Ltd., product name: SUN BLACK X605. Table 1 shows the DBP absorption amount and pH of the carbon black used and the measurement results of the spinnability of the obtained spinning dope. When the carbonization yield and spinnability of this spinning dope were measured, the carbonization yield was 68.4%, but massive carbon black was observed in the spinning dope, causing clogging immediately in the filter and solidifying. Since thread breakage occurred frequently in the bath, the critical coagulation bath speed could not be measured, and the spinnability was not sufficient.

(Comparative Example 2)
A spinning dope was obtained in the same manner as in Example 1 except that the carbon black to be dispersed was changed from Seast S to Asahi Carbon Co., Ltd., product name: SUN BLACK X45. Table 1 shows the DBP absorption amount and pH of the carbon black used and the measurement results of the spinnability of the obtained spinning dope. When the carbonization yield and spinnability of this spinning dope were measured, the carbonization yield was 74.1%, but the spinning dope was poor in fluidity and was agglomerated due to the aggregation of carbon black that could not be dispersed in the die filter. Since clogging occurred and discharge was poor, the critical coagulation bath speed could not be measured, and the spinnability was not sufficient.

(Comparative Example 3)
A spinning dope was obtained in the same manner as in Example 1 except that the carbon black to be dispersed was changed from Seast S to Mitsubishi Chemical, product name: MA-100. Table 1 shows the DBP absorption amount and pH of the carbon black used and the measurement results of the spinnability of the obtained spinning dope. The carbonization yield and spinnability of this spinning stock solution were measured. The carbonization yield was 75.6%, but the fluidity of the spinning stock solution was poor and clogging was caused by the aggregation of carbon black developed in the die filter. Since the yarn breakage occurred frequently in the raising coagulation bath, the spinning property was not sufficient.

Claims (4)

Dibutyl phthalate absorption ¹⁰⁰ (cm 3 / 100g) or less, pH of aqueous dispersion consisting of water 90 parts by weight of carbon black 10 parts by weight of carbon black is 7.0 to 8.0, polyacrylonitrile heavy Acrylic precursor fibers for carbon fibers composed of a mixture containing 1 to 100 parts by mass with respect to 100 parts by mass of the coalescence. The acrylic precursor fiber for carbon fiber according to claim 1, wherein the carbon black has a nitrogen adsorption specific surface area of 40 m ² / g or less.   Carbon which manufactures precursor fiber by wet or dry wet spinning method by mixing a dispersion liquid in which carbon black is dispersed in a solvent and a polymer solution in which a polyacrylonitrile polymer is dispersed in a solvent to prepare a spinning stock solution. A method for producing an acrylic precursor fiber for fiber.   A carbon fiber obtained by flameproofing and carbonizing the acrylic precursor fiber for carbon fiber according to any one of claims 1 to 3.