JP4620394B2 - Method for producing stereoregular carbon fiber precursor copolymer - Google Patents

Description

  The present invention relates to a copolymer for a carbon fiber precursor capable of producing high-quality and high-performance carbon fibers. More specifically, solid-phase polymerization of adducts obtained by absorbing an unsaturated copolymer component containing acrylonitrile, an acrylic acid compound, and an acrylate ester compound as a main component in a crystalline metal halide compound as a template compound. In addition, when producing a copolymer for a carbon fiber precursor having an isotactic triad (hereinafter referred to as mm%) of 35% or more, the used template compound is recovered and activated and repeatedly used. The present invention relates to a method for producing a copolymer for use.

  In general, carbon fibers are widely used as reinforcing materials for various reinforcing materials such as aerospace, leisure goods and industrial materials because they have excellent mechanical properties, particularly high specific strength and specific elastic modulus. In addition, it is expected to be used for reducing the weight of automobiles due to its excellent mechanical properties, and is attracting attention as part of the growing problem of carbon dioxide reduction.

  The carbon fiber is produced by subjecting a fiber prepared from an organic polymer as a precursor to a flame resistance treatment in the presence of oxygen, and firing and carbonizing the fiber.

  Examples of the precursor include cellulose, phenolic resin, polyvinyl alcohol, vinylidene chloride, pitch, polyacrylonitrile (hereinafter sometimes simply referred to as PAN), and carbon fibers obtained from PAN fibers are It is excellent in mechanical properties such as strength and specific elastic modulus, and can be produced stably and uniformly in quality and performance.

  When making a PAN-based fiber flame resistant and producing carbon fiber through carbonization, it was usual to require heat treatment for a long time in a high-temperature oxidizing atmosphere of 200 to 400 ° C. as a flameproofing treatment condition. . This is because when the precursor PAN fiber is made flame resistant at a temperature of 500 ° C. or higher in a short period of time, a rapid exothermic decomposition reaction causes the self-combustion and decomposition of the polymer, thereby forming the desired carbon skeleton. Because you can't. Moreover, in such a high-temperature long-time heat treatment, not only economic problems such as high energy consumption or poor productivity, but also quality problems such as strength reduction due to fusion between single fibers, Furthermore, there are problems in the process such as yarn breakage due to high temperature, and there has been a demand for improvement industrially.

  Many proposals have been made so far to avoid these problems. For example, using a PAN precursor copolymerized with a specific amount of a polymerizable unsaturated carboxylic acid ammonium salt (for example, see Patent Document 1 and Patent Document 2), or copolymerizing a long-chain alkyl ester of a polymerizable unsaturated carboxylic acid The use of the prepared PAN as a precursor is disclosed (for example, see Patent Document 3).

  These have a certain effect on the promotion of the flameproofing reaction, but the copolymer may be blocked due to the low copolymerizability of the unsaturated carboxylic acid. Further, when the content of the carboxylic acid component having poor heat resistance is increased, there is a drawback in that the yield accompanying thermal decomposition is reduced in the flameproofing step following the polymerization step.

  On the other hand, it has been shown that by copolymerizing α-chloroacrylonitrile with acrylonitrile, the flame resistance time can be greatly shortened, and the problem of low productivity can be solved (see, for example, Patent Document 4 and Patent Document 5). However, in order to sufficiently shorten the flameproofing time, it is necessary to copolymerize a large amount of expensive α-chloroacrylonitrile component, which is economically disadvantageous as opposed to improvement in productivity.

  Further, it is disclosed that flame resistance is improved by using a terpolymer in which itaconic acid and an acrylamide monomer are incorporated in acrylonitrile (see, for example, Patent Document 6). In addition to the difficulty in obtaining a copolymer, excessive itaconic acid can cause exothermic reactions that can damage the fiber structure, and excessive acrylamide monomer can cause fiber fusion. Control is complicated and productivity is a problem.

  In addition, a hydroxymethylene group (for example, see Patent Document 7), a halogenated alkyl ester of an unsaturated carboxylic acid (for example, see Patent Document 8), or a silicon or fluorine-containing unsaturated monomer (for example, see Patent Document 9) is used as a copolymerization component. Although used, none of them showed satisfactory effects in terms of both price and performance.

  Conventionally, as a copolymer for carbon fiber precursors and a carbon fiber precursor, a copolymer containing atactic polyacrylonitrile which is not regulated in three-dimensional structure obtained by ordinary radical copolymerization or the like has been used.

  On the other hand, research focusing on the stereoregularity and flameproofing reaction of polyacrylonitrile fiber is also underway. For example, in the flameproofing reaction of PAN fibers, it is known that oxidation and cyclization of adjacent nitrile skeletons initiate the reaction (see, for example, Non-Patent Document 1).

  Furthermore, past studies have reported that in these thermally induced reactions, the microstructure of the polymer, that is, the stereoregularity of the polymer backbone represented by tacticity, can affect the reaction temperature and reaction rate. It was. For example, it has been shown that the formation of an imine skeleton from a cyano group by heat proceeds preferentially at a lower temperature in an isotactic linkage than in an atactic or syndiotactic linkage (for example, Non-Patent Document 2 and Non-Patent Document 2). Reference 3).

As a method for producing these polymers, D.C. M.M. Solid state photopolymerization at low temperature (−78 ° C.) using urea / monomer adducts reported by WHITE et al. (For example, see Non-Patent Document 4), anionic polymerization using organomagnesium or the like as an initiator (for example, non- For example, see Patent Document 5). The composition of the obtained polymer, and tacticity of the polyacrylonitrile main chain may be quantified identified by ¹ H-NMR and ¹³ C-NMR. However, although the polyacrylonitrile homopolymer having isotacticity obtained by the above method, that is, iso-PAN can surely reduce the flameproofing temperature, the exothermic peak width accompanying the flameproofing observed in DSC measurement is It will be very narrow.

  This fact means that iso-PAN is forced to have rapid flame resistance, and the quality of the carbon fiber obtained due to the thermal damage is lowered. Further H. According to the method reported by KUWAHARA et al., Acrylonitrile, methyl methacrylate, vinyl acetate, and 4-vinylpyridine were added to a slurry obtained by dispersing crystalline anhydrous magnesium chloride in a hydrocarbon solvent typified by toluene or heptane. It is taught that a polymer having isotacticity can be obtained when a polar vinyl monomer such as the above is brought into contact to form an adduct, and a radical polymerization initiator is added thereto for polymerization (Non-patent Document 6).

  However, this method has problems that the radical initiator and the monomer are heterogeneous, the initiator efficiency is lowered, and the growth end radical is chain-transferred to the solvent, making it difficult to obtain a high molecular weight product.

  Thus, the literature, reports, etc. which examined using the copolymer containing polyacrylonitrile in which the three-dimensional structure was regulated as a copolymer for carbon fiber precursors and carbon fiber precursors having excellent flame resistance reactivity have been reported so far. It was not known.

JP-A-48-63029 Japanese Examined Patent Publication No. 58-48643 Japanese Patent Laid-Open No. 61-152812 Japanese Patent Publication No.49-14404 Japanese Patent Publication No. 6-27368 Japanese Patent Laid-Open No. 11-117123 JP-A-52-53995 JP-A-52-55725 JP-A-2-14013 W. Watt, “Proceeding of the International Carbon Fiber Conference London,” Paper No., “Proceeding of the International Carbon Fiber Conference London”. 4,1971 N. A. Kobasova et al., “VYSOKOMOLEKURYARNYE SOEDINNIYA SERIYA A”, Russia, 13 (1), 1971, P.A. 162-167 M. A. Geiderikh et al., “VYSOKOMOLEKURYARNYE SOEDINNIYA SERIYA A”, Russia, 15 (6), 1973, P.M. 1239-1247 D. M. A. WHITE, “JOURNAL OF THE AMERICA CHEMICAL SOCIETY”, 1960, 82, 5671. Nakano et al. (Y NAKANO), “Polymer PREPRINTS”, 1994, 35 (3). 249-55 Kuwahara et al. (H. KUWAHARA), "Polymer PREPRINTS", 2002, 43 (2), 978-9.

  The object of the present invention is to reduce the flame-proofing process and lower the temperature essentially without using a large amount of a particularly expensive and special copolymerization monomer or a template compound as a catalyst, thereby suppressing fusion and thermal decomposition between fibers. It is to provide a method for producing a copolymer for a carbon fiber precursor.

In order to solve the above-mentioned problems, the present inventors diligently studied on a method for controlling the three-dimensional structure of a copolymer for a carbon fiber precursor containing polyacrylonitrile as a main component.
As a result, when an adduct obtained by absorbing acrylonitrile and an unsaturated copolymerization component into a specific metal halide is solid-phase polymerized, it is surprising that the isotactic triad (mm%) is 35% or more based on isotactic triad (mm%). A copolymer for carbon fiber precursors having a techity is obtained, and the metal halide can be separated from the polymer as a solution after solid-phase polymerization, and is easily solidified and activated when subjected to heat treatment. The inventors have found that it can be used repeatedly as a template compound, and have completed the present invention.

That is, the object of the present invention is to
The unsaturated copolymerization component mainly composed of acrylonitrile, an acrylic acid compound, and an acrylic ester compound is at least one selected from the group consisting of anhydrous metal halides in the crystalline state belonging to groups IIA to IIB of the periodic table The adduct is brought into contact with the template compound of the above to form an adduct, and this is solid-phase polymerized so that the isotactic triad (mm%) of the acrylonitrile constituent chain is 35% based on the total triad of the chain (mm% + mr% + rr%). A method for producing a copolymer for a carbon fiber precursor having the above isotacticity,
After completion of the solid phase polymerization, the template compound is recovered, activated by heat treatment at 100 ° C. or higher, and then reused as a solid phase polymerization catalyst. By the method for producing a copolymer for a carbon fiber precursor, Achieved.

  The present invention is a method for producing a copolymer for a carbon fiber precursor that enables rapid flameproofing treatment under mild conditions in the production of carbon fiber, and does not require cryogenic temperatures as in the conventional method, It is possible to obtain a copolymer for a carbon fiber precursor having a high molecular weight and high isotacticity. According to the method of the present invention, in order to control the steric structure of PAN, the template compound is separated and recovered from the polymer as a solution after washing with a solvent and then activated by heat dehydration, thereby avoiding the generation of enormous industrial waste. It is possible.

  Further, since the energy generated during the flameproofing treatment is reduced, fusion between the carbon fibers can be prevented, and thermal degradation and the accompanying performance degradation can be suppressed. In particular, when the fineness of the carbon fiber is large, the surface area is small with respect to the generated energy, so that the effect seems to be remarkable. In addition, the half-value width of the exothermic peak accompanying the generated energy is widened, so that the energy generated during the flameproofing treatment is not generated at a stretch, but it is gradually generated to suppress heat fusion and thermal decomposition between fibers. Can do. In addition, the sterically controlled copolymer for carbon fiber precursors has cyano groups close to each other compared to the conventional atactic one, and can easily form a huge hexagonal network layer. It is possible to obtain a high elastic modulus carbon fiber that could not be realized.

  Thus, the carbon fiber precursor copolymer and carbon fiber precursor produced by the method of the present invention are preferably used as a precursor for economically producing high-quality, high-performance carbon fibers with high productivity. Can do.

Hereinafter, the present invention will be described in detail.
In the production method of the present invention, a periodic table using polyacrylonitrile, an acrylic acid compound, an acrylic ester compound and an unsaturated copolymerization component (hereinafter sometimes referred to as a monomer for simplicity) as a template compound. Obtained as a result of heat-treating at least one kind selected from the group consisting of fluoride, chloride, bromide and iodide, or a solvate thereof, in the crystalline state belonging to group IIA to group IIB When an adduct obtained by absorption in at least one template compound selected from an anhydride is solid-phase polymerized, a carbon fiber precursor having an isotacticity of 35% or more based on an isotactic triad (mm%) is used. A polymer can be produced.

  Anhydrous metal halides in the crystalline state have a structure in which a metal cation and a pair of halogen ions are arranged in an orderly manner, and the monomer is a metal cation via an unpaired electron on its oxygen atom or nitrogen atom. Can be coordinated to.

  In this case, the arrangement of the monomer is regulated according to the order of the metal cation and the counter anion, the size, or the distance between the ions. The arrangement varies depending on the type of template compound to be selected. Crystalline anhydrous metal halides belonging to groups IIA to IIB of the periodic table are preferably used as isotactic stereocontrolled template compounds.

  Examples include anhydrous iron chloride (II), anhydrous iron chloride (III), anhydrous cobalt chloride (II), anhydrous nickel chloride (II), anhydrous manganese chloride (II), anhydrous manganese chloride (III), anhydrous chloride Chromium (III), anhydrous magnesium chloride, anhydrous calcium chloride, anhydrous lanthanum chloride (III), anhydrous yttrium chloride (III), anhydrous iron (II) bromide, anhydrous iron (III) bromide, anhydrous cobalt (II) bromide , Anhydrous nickel bromide (II), anhydrous manganese bromide (II), anhydrous manganese bromide (III), anhydrous chromium bromide (III), anhydrous magnesium bromide, anhydrous calcium bromide, anhydrous lanthanum bromide (III) , Anhydrous yttrium bromide (III), anhydrous iron (II) iodide, anhydrous iron (III) iodide, anhydrous cobalt (II) iodide, anhydrous nickel iodide ( I), anhydrous manganese iodide (II), anhydrous manganese iodide (III), anhydrous magnesium iodide, anhydrous calcium iodide, anhydrous lanthanum iodide (III), and anhydrous yttrium iodide (III), Is anhydrous iron chloride (II), anhydrous cobalt chloride (II), anhydrous magnesium chloride, anhydrous magnesium bromide, particularly preferably anhydrous magnesium chloride and anhydrous cobalt chloride (II).

  These may be used as a mixture of two or more, and may be a so-called double salt such as alum or hydrotalcite in which two or more metal cations are present in a single crystal system. In addition, as a result of removing water contained in the crystals by heat treatment, the above-mentioned compounds giving anhydrous metal halides, that is, iron (II) chloride tetrahydrate, iron chloride (III) hexahydrate, cobalt chloride ( II) monohydrate, cobalt chloride (II) hexahydrate, nickel chloride (II) monohydrate, nickel chloride (II) hexahydrate, manganese chloride (II) tetrahydrate , Chromium (III) chloride hexahydrate, magnesium chloride hexahydrate, calcium chloride dihydrate, calcium chloride hexahydrate, lanthanum chloride (III) heptahydrate, yttrium chloride (III) hexahydrate, iron bromide (II) n hydrate, iron bromide (III) n hydrate, cobalt bromide (II) monohydrate, nickel bromide 1 Hydrate, Manganese bromide (II) tetrahydrate, Chromium bromide (III) n hydrate , Magnesium bromide hexahydrate, calcium bromide monohydrate, lanthanum bromide (III) n hydrate, yttrium bromide III n hydrate, iron iodide (II) Tetrahydrate, iron (III) iodide, 9 hydrate, cobalt (II) iodide, n hydrate, nickel iodide, n hydrate, manganese iodide (II), n hydrate, Magnesium iodide, n hydrate, calcium iodide, monohydrate, lanthanum iodide (III), n hydrate, yttrium iodide (III), n hydrate (where n is the number of hydrates specified) The system which is not done is shown.).

  The monomer is brought into an adduct when brought into contact with a metal halide in a crystalline state in an inert gas atmosphere. This step is preferably performed in an atmosphere of inert gas such as nitrogen or argon. When a gas containing oxygen such as air is used, the polymerization initiator or carbon fiber having a sufficient degree of polymerization will cause deactivation of the radical growth terminal. A precursor copolymer cannot be obtained. The molar ratio (A / M) between the monomer and the metal halide in the crystalline state may be within a range in which the adduct can maintain a solid state, and is preferably 0.1 or more and less than 5.0.

  When A / M is less than 0.1, the monomer coordinated to the metal compound in the crystalline state is not sufficient to give a high molecular weight, and a substantial polymer cannot be obtained. When A / M is 5.0 or more, the upper limit of the monomer that can be absorbed and coordinated by the metal halide compound in the crystalline state is already exceeded, and the surplus monomer causes normal radical polymerization, so that the obtained carbon fiber precursor is obtained. The stereoregularity of the copolymer for use decreases. The adduct thus prepared can be transferred to a suitable container under an inert gas atmosphere and then subjected to solid phase polymerization.

  There are roughly two types of solid-phase polymerization methods, one is thermal solid-phase polymerization in which an initiator capable of generating radical species by thermal decomposition coexists, and the other is electromagnetic wave solidification that irradiates radical-generating electromagnetic waves. Phase polymerization. Thermal solid-phase polymerization includes a method in which an adduct between a monomer and a template compound is adjusted, and then an initiator is dissolved in a small amount of an organic solvent, and a method in which a solution in which an initiator is dissolved in a monomer is added to the template compound in advance. However, considering the uniform distribution of the initiator, the latter is a preferred embodiment.

  At the time of addition, both a method of allowing the metal halide to stand and absorbing spontaneously and a method of giving an appropriate stirring to the adduct are possible. In addition, the polymerization initiator in the present invention may be any one that is generally used in radical polymerization, such as azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2 ′. -Azobis (4-methoxy-2,4-dimethylvaleronitrile), dimethyl-2,2-azobis (2-methylpropionate), 1,1- (cyclohexane-1-carbonitrile), 2,2-azobis (2-methylbutyronitrile), azo compounds typified by 2,2-azobis [N- (2-propenyl) -2-methylpropionamide], organic peroxides typified by benzoyl peroxide, peroxysulfuric acid Manganese acetylacetate, a redox initiator represented by a combination of potassium / sodium sulfite and N, N-dimethylaniline / benzoyl peroxide One electron release, like radical (III), cobalt acetylacetonate (II), and pentacyanobenzylcobaltate, iron (II) sulfate / hydrogen peroxide (Fenton reagent), resulting in the progress of radical polymerization A transition metal compound that can be used is preferably used.

  On the other hand, electromagnetic solid phase polymerization is advantageous in that it is not particularly necessary to add a polymerization initiator in order to generate radicals by irradiation with electromagnetic waves. The electromagnetic wave used here is not particularly limited as long as it has sufficient energy to generate radicals on the monomer molecule, such as ultraviolet rays, X-rays, γ rays, monochromatic visible rays, natural light, electron beams, etc. Is mentioned. In this case, a method of adding a photosensitizer to enhance the effect of electromagnetic wave irradiation is also preferable.

  The temperature conditions suitable for solid phase polymerization are -80 ° C or higher and lower than 150 ° C. Below -80 ° C, not only the polymerization reaction rate is extremely reduced, but also the energy consumption for cooling is remarkable. On the other hand, at 150 ° C. or higher, the monomer dissociates as a gas from the metal halide, and a sufficient Mv copolymer for carbon fiber precursor cannot be obtained.

  The adduct that has completed the solid-phase polymerization is composed of a metal halide and a copolymer for a carbon fiber precursor. Accordingly, the metal halide can be removed from the carbon fiber precursor copolymer by elution with water, methanol, ethanol, acetone, dilute hydrochloric acid, dilute nitric acid or the like that can dissolve the metal halide. Recovery of the metal halide can be achieved by evaporating and drying the solvent used for the elution. However, the solvate of the metal halide compound thus obtained cannot be reused as it is because it contains the solvent used at the time of elution in the crystal.

  Therefore, the recovered material is activated before being reused for polymerization. Activation can be achieved by heating, but it is necessary to carry out at 100 ° C. or higher, and more preferably heat treatment at 130 ° C. or higher. Further, even when the recovered product is a solvent having a boiling point of 100 ° C. or less, such as methanol or acetone, these may interact strongly with the metal halide. It is necessary to carry out at 100 ° C. or higher.

  When the activation temperature is less than 100 ° C., the solvent in the template compound cannot be completely removed, and the remaining solvent causes crystal defects in the hexagonal system or the trigonal system. Needless to say, when a template compound having crystal defects is used for polymerization, the isotacticity of the obtained copolymer for a carbon fiber precursor is lowered. The activation may be performed by heating with reduced pressure, or heating in which a compound having a dehydrating ability coexists as a dehydrating aid. In order to facilitate the activation process, it is preferable to use a solvent having a relatively low boiling point such as water, acetone or methanol for the recovery of the template compound.

  The method of using the template compound recovered and activated in this way is the same as the template compound used for the first polymerization.

  The isotactic triad (mm%) of the polyacrylonitrile component in the copolymer for carbon fiber precursor obtained by such a method satisfies at least 35 mol%, usually 60 mol% or more. Here, the isotactic triad (mm%) is an addition polymerization type polymer in which three consecutive repeating units in a polymer are considered, and the side chains of adjacent monomer units are all meso (m and (Abbreviated) refers to the relationship of arrangement.

  That is, the isotactic triad is a ratio of mm chain. When the mm% is less than 35 mol%, a sufficient effect is not exerted on the flame resistance properties based on the three-dimensional structure of polyacrylonitrile, and it is not different from a carbon fiber precursor copolymer which is substantially atactic.

  By using the carbon fiber precursor copolymer and carbon fiber precursor obtained by the method of the present invention, the flameproofing treatment can be carried out at a lower temperature and in a shorter time than when a conventional atactic carbon fiber precursor copolymer is used. Can be done. As a result, not only can energy be saved significantly, but quality problems such as strength reduction due to fusion between single fibers and process problems such as yarn breakage can be solved.

  Furthermore, the carbon fiber precursor of the present invention has a distance between adjacent cyano groups and a main chain having a 3/1 helical structure. Therefore, in the flameproofing process, the flameproofing proceeds quickly, and the pyridine condensed ring structure to be formed is linear, that is, a polynaphthyridine skeleton, so that the hexagonal network formed in the subsequent carbonization process or graphitization process. Sufficient growth of the face layer can be expected, and carbon fibers having a high elastic modulus can be produced.

  The carbon fiber precursor copolymer in the present invention refers to an amorphous polymer mainly composed of an acrylonitrile component, and the carbon fiber precursor in the present invention refers to a carbon fiber precursor copolymer wet-spun, dry-wet spinning, Or it refers to the state of being formed into a fiber through a spinning process such as dry spinning. That is, it refers to the state before performing the flameproofing treatment and the heating carbonization treatment.

  Conventionally known compounds can be used as the acrylic acid-based compound that serves as a copolymerization partner for acrylonitrile, but acrylic acid, methacrylic acid, and itaconic acid are preferably used. As the acrylic ester compound, the alkyl group at the ester site has 1 to 20 carbon atoms, such as methyl acrylate, ethyl acrylate, isopropyl acrylate, cyclohexyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, methacrylic acid. Acid cyclohexyl and the like can be particularly preferably used. Furthermore, polar vinyl monomers such as methacrylonitrile, vinyl acetate, acrylamide, maleic anhydride, and N-vinylpyrrolidone, and aromatic vinyl compounds such as styrene, vinylpyridine, and vinylimidazole are preferably used as the unsaturated copolymerization component. it can. These unsaturated copolymerization components may be used alone or in combination.

  As a result of the copolymerization, a random copolymer in which acrylonitrile and an acrylic acid compound, an acrylate ester compound, and an unsaturated copolymer component are randomly arranged, or a chain of an acrylonitrile chain and an unsaturated copolymer component is formed. A block copolymer is obtained. The role of copolymer components other than acrylonitrile is to suppress the self-heating caused by the intramolecular cyclization reaction in flame resistance, reduce the thermal damage given to the carbon fiber precursor, and the pyridone ring and cyclic imide formation reaction in the early stage of flame resistance Although it is responsible for triggering intramolecular and intermolecular cyclization reactions, excessive copolymerization of unsaturated copolymerization components for that purpose leads to a decrease in carbon fiber performance and a decrease in carbon yield. Accordingly, the mol% of the copolymer component other than acrylonitrile is not particularly limited, but is preferably less than 20 mol% in the copolymer for carbon fiber precursor.

  The copolymer for a carbon fiber precursor of the present invention can be produced by a conventionally known technique. Although there is no restriction | limiting in particular as a specific spinning method, A normal wet spinning method, a dry-type spinning method, or a dry-wet spinning method etc. are used. In the present invention, the carbon fiber precursor copolymer yarn obtained at this point is referred to as a carbon fiber precursor. In addition, isotactic-rich polyacrylonitrile components may be partially made flame resistant by heat treatment such as drawing in the yarn making process, but those containing these modified structures are also included in the scope of the carbon fiber precursor of the present invention. It is.

  The carbon fiber precursor of the present invention is subjected to a flameproofing treatment at a temperature of 150 to 300 ° C., a heat carbonization treatment of 300 to 2000 ° C. in an inert gas atmosphere, and a graphite growth process of 2000 to 2500 ° C. After that, it is converted to carbon fiber. As the atmosphere for the flameproofing treatment, an inert gas atmosphere such as nitrogen can be adopted, but it is more preferable to adopt an active gas atmosphere such as air from the viewpoint of shortening the flameproofing treatment time. Moreover, there exists a problem in which the elasticity modulus of the carbon fiber obtained will fall at the low temperature like carbonization temperature is less than 300 degreeC. In addition, said carbon fiber can further surface-treat, oil agent application | coating, and a sizing process as needed.

  The reason why the flameproofing treatment can be promptly performed at a low temperature in the carbon fiber precursor copolymer and the carbon fiber precursor having a high mm% can be estimated as follows. That is, as described above, the flameproofing reaction involves an intramolecular cyclization reaction between adjacent cyano groups. Therefore, an isotactic structure in which cyano groups are meso-positioned is advantageous for cyclization of adjacent cyano groups in a positional manner. It is thought that the reaction proceeds with a smaller activation energy. Therefore, it is considered that the flameproofing treatment can be performed at a low temperature in the isotactic structure. In addition, since the carbon fiber precursor has an isotacticity-induced 3/1 helical structure, a linear condensed pyridine ring, that is, a polynaphthyridine skeleton is formed when flame resistance is achieved. For this reason, the size of the hexagonal mesh layer that grows at the stage of carbonization and graphitization becomes larger than when a conventional atactic carbon fiber precursor is used, and the strength of the obtained carbon fiber increases.

  Hereinafter, the present invention will be described more specifically with reference examples and examples. However, the present invention is not limited to the following reference examples and examples.

For electromagnetic solid phase polymerization using γ-rays in the examples, an adduct was sent to the Japan Isotope Association to request irradiation. Monomer conversion in polymerization and the composition of the obtained copolymer for carbon fiber precursor are from 1H-NMR, and stereoregularity (tacticity) is 13C-NMR measurement (270 MHz JNR-EX-270 JEOL Datum Co., Ltd.) Manufactured, solvent: dimethyl sulfoxide-d6), and isotactic triad (mm), syndiotactic triad (rr), and heterotactic triad (mr) were determined. The intrinsic viscosity of the copolymer for carbon fiber precursor was measured in N, N′-dimethylformamide at 35 ° C. or in dimethyl sulfoxide at 50 ° C. using an S-40 standard Ubbelohde viscometer. Further, the intrinsic viscosity [η] was calculated using the reduced viscosity ηsp / C obtained in each solvent and the following empirical formulas 1 and 2.
[Equation 1]
[Η] = 0.6712 × ηsp / C + 0.063
(In N, N′-dimethylformamide at 35 ° C.)
[Equation 2]
[Η] = − 0.1578 × [ηsp / C] 2 + 0.9524 × ηsp / C−0.002
(In dimethyl sulfoxide at 50 ° C)

[Reference Example 1]
Under a dry nitrogen stream, 50 g of anhydrous cobalt (II) chloride was placed in a three-necked flask and kept at 10 ° C. or lower with an ice bath. A separately prepared three-necked flask was purged with nitrogen, and 25.4 ml of acrylonitrile, 1.5 ml of methyl acrylate, 0.9 ml of dibutyl itaconate, and 188 mg of azobisisobutyronitrile were mixed to obtain a monomer solution. This was added to anhydrous cobalt (II) chloride and completely absorbed to form an adduct. Subsequently, the three-necked flask containing the adduct was placed in a hot-air circulating dryer, and thermal solid-state polymerization was performed at 70 ° C. for 12 hours. After solid phase polymerization, the adduct was poured into water, and anhydrous cobalt chloride was dissolved and extracted and removed to obtain a copolymer for a carbon fiber precursor. The copolymer was washed with acetone and then dried at 40 ° C. for a whole day and night. The obtained copolymer for carbon fiber precursor was 9.6 g (yield 47.1%).

^When the composition of the copolymer was estimated by ¹ H-NMR measurement, the acrylonitrile component, methyl acrylate component, and dibutyl itaconate component were 96.6%, 0.9%, and 2.5%, respectively. Moreover, when ¹³ C-NMR measurement was performed and tacticity was quantified, it was mm / mr / rr = 88.5 / 7.2 / 4.3, and it was confirmed to have high isotacticity. The intrinsic viscosity [η] calculated based on ηsp / C measured in dimethyl sulfoxide at 50 ° C. was 1.01.

[Reference Example 2]
92.0 g of cobalt chloride hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) was placed in a three-neck flask and heated to 150 ° C. while reducing the pressure to 10 Torr. After about 10 minutes from the start of heating, cobalt chloride hexahydrate turned blue-purple, and further turned pale blue after 1 hour.

  At this point, activation was terminated and the three-necked flask was brought to a nitrogen atmosphere. A separately prepared three-necked flask was purged with nitrogen, and 25.4 ml of acrylonitrile, 1.5 ml of methyl acrylate, 0.9 ml of dibutyl itaconate, and 188 mg of azobisisobutyronitrile were mixed to prepare a monomer solution. In addition to the activated cobalt chloride, this was again used as an adduct.

Thereafter, thermal solid state polymerization was carried out in the same procedure as in Reference Example 1. The obtained copolymer for carbon fiber precursor was 14.1 g (yield 61.8%). ^When the composition of the copolymer was estimated by ¹ H-NMR measurement, the acrylonitrile component, methyl acrylate component, and dibutyl itaconate component were 95.4%, 2.1%, and 2.5%, respectively.

Moreover, when ¹³ C-NMR measurement was performed and tacticity was quantified, it was mm / mr / rr = 88.3 / 7.8 / 3.9, and it was confirmed to have high isotacticity. The intrinsic viscosity [η] calculated based on ηsp / C measured in dimethylsulfoxide at 50 ° C. was 1.14.

[Example 1]
Water was removed from the cobalt chloride aqueous solution dissolved and extracted in Reference Example 1 using an evaporator. 45.6 g of the obtained red solid cobalt chloride hexahydrate was obtained. This was activated in the same manner as in Reference Example 2 and used for thermal solid phase polymerization in the same manner as in Reference Example 1. The obtained copolymer for carbon fiber precursor was 9.2 g (yield 40.4%). ^When the composition of the copolymer was estimated by ¹ H-NMR measurement, the acrylonitrile component, methyl acrylate component, and dibutyl itaconate component were 95.1%, 1.7%, and 3.2%, respectively. Moreover, when 13C-NMR measurement was performed and tacticity was quantified, it was mm / mr / rr = 88.1 / 8.0 / 3.9, and it was confirmed to have high isotacticity. The intrinsic viscosity [η] calculated based on ηsp / C measured in dimethyl sulfoxide at 50 ° C. was 1.84.

[Comparative Example 1]
Cobalt chloride was activated in the same manner as in Example 6 except that 90 ° C. was adopted as the heating temperature. Unlike the anhydrous cobalt chloride, the obtained cobalt chloride had a bluish purple color, and this was used for the same thermal solid-state polymerization as in Example 3. When the composition of the obtained copolymer for carbon fiber precursor was estimated, the acrylonitrile component, methyl acrylate component, and dibutyl itaconate component were 94.8%, 2.0%, and 3.2%, respectively. ^The triad tacticity was quantified by performing ¹³ C-NMR measurement. As a result, mm / mr / rr = 28.9 / 49.3 / 21.8, which was 17.9 g of a substantially atactic copolymer for carbon fiber precursor. It was confirmed that (yield 78.5%) was obtained. The intrinsic viscosity [η] obtained using an Ubbelohde viscometer in N, N′-dimethylformamide at 35 ° C. was 1.51.

  According to the production method of the present invention, a copolymer for carbon fiber precursor having isotacticity can be produced while recovering and activating the template compound and repeatedly using it to reduce industrial waste as much as possible. In addition, the use of the copolymer makes it possible to construct a low-temperature and gentle carbon fiber production process, which is expected to reduce the environmental load including energy saving and improve the performance of the carbon fiber.

Claims (3)

The unsaturated copolymerization component mainly composed of acrylonitrile, an acrylic acid compound, and an acrylic ester compound is at least one selected from the group consisting of anhydrous metal halides in the crystalline state belonging to groups IIA to IIB of the periodic table The adduct is brought into contact with the template compound of the above to form an adduct, and this is solid-phase polymerized so that the isotactic triad (mm%) of the acrylonitrile constituent chain is 35% based on the total triad of the chain (mm% + mr% + rr%). A method for producing a copolymer for a carbon fiber precursor having the above isotacticity,
A method for producing a copolymer for a carbon fiber precursor, comprising recovering the template compound after completion of the solid-phase polymerization, activating it by heat treatment at 100 ° C. or higher, and then reusing it as a solid-phase polymerization catalyst.   The anhydrous metal halide is an anhydrous metal halide obtained by heat-treating at least one selected from the group consisting of solvates of metal halides in the crystalline state belonging to groups IIA to IIB of the periodic table. Item 2. The production method according to Item 1.   The production method according to claim 1, wherein the crystal system of the anhydrous metal halide belongs to a hexagonal system or a trigonal system.