JP7166233B2 - Flame-resistant fiber, method for producing same, and method for producing carbon fiber - Google Patents

Description

TECHNICAL FIELD The present invention relates to a flameproof fiber, a method for producing the same, and a method for producing carbon fiber.

As a method for producing carbon fibers, conventionally, a method of subjecting a carbon fiber precursor obtained by spinning polyacrylonitrile to a flameproofing treatment and then a carbonizing treatment has been mainly adopted (for example, JP-B-37- 4405 (Patent Document 1), JP-A-2015-74844 (Patent Document 2), JP-A-2016-40419 (Patent Document 3), JP-A-2016-113726 (Patent Document 4)). Since the polyacrylonitrile used in this method is difficult to dissolve in inexpensive general-purpose solvents, it is necessary to use expensive solvents such as dimethylsulfoxide and N,N-dimethylacetamide during polymerization and spinning. There was a problem of high cost.

Further, Japanese Patent Application Laid-Open No. 2013-103992 (Patent Document 5) describes 96 to 97.5 parts by mass of acrylonitrile units, 2.5 to 4 parts by mass of acrylamide units, and 0.01 to 0.01 parts by mass of a carboxylic acid-containing vinyl monomer. A carbon fiber precursor fiber made of a polyacrylonitrile-based copolymer of 5 parts by mass is described. Although this polyacrylonitrile-based copolymer contains acrylamide units and carboxylic acid-containing vinyl monomer units that contribute to the water solubility of the polymer, since these contents are small, it is insoluble in water. Spinning) requires the use of an expensive solvent such as N,N-dimethylacetamide, which raises the problem of high carbon fiber production costs.

Furthermore, when polyacrylonitrile and its copolymer are subjected to heat treatment, rapid heat generation occurs, accelerating the thermal decomposition of polyacrylonitrile and its copolymer, which reduces the yield of carbon materials (carbon fibers). There was a problem. For this reason, when producing a carbon material (carbon fiber) using polyacrylonitrile or a copolymer thereof, it is necessary to gradually increase the temperature over a long period of time so as not to generate abrupt heat generation during the temperature rising process of the flameproofing treatment. It was necessary to raise the temperature to

On the other hand, acrylamide-based polymers containing a large amount of acrylamide units are water-soluble polymers, and water, which is inexpensive and has a low environmental impact, can be used as a solvent during polymerization and molding processes (filming, sheeting, spinning, etc.). Therefore, it is expected that the manufacturing cost of carbon materials will be reduced. For example, Japanese Patent Application Laid-Open No. 2018-90791 (Patent Document 6) describes a carbon material precursor composition containing an acrylamide-based polymer and at least one additive component selected from the group consisting of acids and salts thereof, and a method for producing a carbon material using the same. In addition, Japanese Patent Application Laid-Open No. 2019-26827 (Patent Document 7) describes an acrylamide/cyanide containing 50 to 99.9 mol% of acrylamide-based monomer units and 0.1 to 50 mol% of vinyl cyanide-based monomer units. A carbon material precursor comprising a vinyl copolymer, a carbon material precursor composition containing the carbon material precursor and at least one additional component selected from the group consisting of acids and salts thereof, and A method for producing a carbon material using these is described. However, the carbonization yield in these methods for producing carbon materials is not always sufficient, and there is still room for improvement.

Japanese Patent Publication No. 37-4405 JP 2015-74844 A JP 2016-40419 A JP 2016-113726 A JP 2013-103992 A JP 2018-90791 A JP 2019-26827 A

The inventors of the present invention have found that carbonization of flame-resistant fibers obtained by subjecting acrylamide-based polymer fibers to flame-resistant treatment may reduce the productivity and strength of carbon fibers. It was found that one of the reasons for this is yarn breakage during fiber transportation and carbonization.

The present invention has been made in view of the above-mentioned problems of the prior art, and is derived from an acrylamide-based polymer, and has excellent load resistance at high temperatures, high strength, high elastic modulus, and high carbonization yield. An object of the present invention is to provide a fiber, a method for producing the same, and a method for producing a carbon fiber capable of producing the carbon fiber at a high yield.

As a result of intensive research to achieve the above object, the present inventors found that the infrared absorption spectrum of the obtained flame-resistant fiber under an oxidizing atmosphere while applying a predetermined tension to the acrylamide-based polymer fiber. Heat treatment until the ratio (I _A /I _B ) of the intensity (I _A ) of the absorption peak A existing in the range of 1595 cm ⁻¹ and the intensity (I _B ) of the absorption peak B at 1648 cm ⁻¹ reaches a predetermined value. By applying (flameproofing treatment), a flameproofed fiber having excellent load resistance at high temperatures, high strength, high elastic modulus and high carbonization yield can be obtained. By applying, it was found that carbon fibers can be obtained at a high yield, and the present invention was completed.

That is, the flame-resistant fiber of the present invention is derived from an acrylamide polymer, has an absorption peak A in the range of 1560 to 1595 cm ⁻¹ in the infrared absorption spectrum, and the intensity (I _A ) of the absorption peak A and The ratio (I _A /I _B ) to the intensity (I _B ) of the absorption peak B at 1648 cm ⁻¹ is 0.5 to 10 (preferably 0.7 to 10).

In addition, in the method for producing a flame-resistant fiber of the present invention, while applying a tension of 0.07 to 200 mN/tex to the acrylamide polymer fiber, under an oxidizing atmosphere, 1560 in the infrared absorption spectrum of the obtained flame-resistant fiber The ratio (I _A /I _B ) of the intensity (I _A ) of the absorption peak A existing in the range of 1595 cm ⁻¹ and the intensity (I _B ) of the absorption peak B at 1648 cm ⁻¹ is 0.5 to 10. It is a method characterized by applying heat treatment to.

In the method for producing a flame-resistant fiber of the present invention, when the acrylamide-based polymer fiber further contains at least one additive component selected from the group consisting of acids and salts thereof, the heat treatment is at least It is preferably applied at a temperature in the range of 260 to 450° C., and if the acrylamide-based polymer fiber does not contain an additive component consisting of an acid, a salt thereof, or a mixture thereof , the heat treatment is at least 310° C. It is preferably applied at a temperature in the range of -500°C.

Further, the method for producing a carbon fiber of the present invention is a method characterized by subjecting the flame-resistant fiber of the present invention to a carbonization treatment. and carbonizing the flame-resistant fiber.

The reason why the method for producing a flame-resistant fiber of the present invention can obtain a flame-resistant fiber having excellent load resistance at high temperatures, high strength, a high elastic modulus, and a high carbonization yield is not necessarily clear, but the present invention The inventors conjecture as follows. That is, the intensity (I _A ) of the absorption peak A existing in the range of 1560 to 1595 cm ⁻¹ in the infrared absorption spectrum of the obtained flame-resistant fiber under an oxidizing atmosphere while applying a predetermined tension to the acrylamide-based polymer fiber. and the intensity (I _B ) of the absorption peak B at 1648 cm ⁻¹ , the acrylamide-based polymer is subjected to heat treatment (flame resistance treatment) until the ratio (I _A /I _B ) reaches a predetermined value. Not only the imide ring structure generated by be done. In addition, the structure in which two or more polycyclic rings are continuous is not limited to the structure in which two or three rings shown in the following formula are continuous, and may be a structure in which four or more polycyclic rings are continuous. .

Such a structure in which two or more rings are continuous has excellent heat resistance, and since it has both high strength and high elastic modulus, the flameproof fiber of the present invention has high heat resistance, It is presumed to have excellent load resistance at high temperatures, and to exhibit high strength and high elastic modulus. Furthermore, it is presumed that such a flame-resistant fiber with excellent heat resistance suppresses thermal decomposition during carbonization, so that the carbonization reaction proceeds efficiently and exhibits a high carbonization yield.

According to the present invention, it is possible to obtain a flame-resistant fiber derived from an acrylamide-based polymer, having excellent load resistance at high temperatures, high strength, high elastic modulus and high carbonization yield. In addition, carbon fibers can be produced at a high yield by subjecting such flame-resistant fibers to a carbonization treatment.

4 is a graph showing infrared absorption spectra of flame-resistant fibers obtained in Example 3 and Comparative Example 1. FIG.

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will now be described in detail with reference to its preferred embodiments.

[Method for producing flame-resistant fiber]
First, the method for producing the flame-resistant fiber of the present invention will be described. In the method for producing a flame-resistant fiber of the present invention, while applying a tension of 0.07 to 200 mN/tex to an acrylamide-based polymer fiber, the obtained flame-resistant fiber has an infrared absorption spectrum of 1560 to 1595 cm in an oxidizing atmosphere. Heat until the ratio (I _A /I _B ) of the intensity (I _A ) of the absorption peak A existing in the range of ⁻¹ and the intensity (I _B ) of the absorption peak B at 1648 cm ⁻¹ is 0.5 to 10. This is a method of applying a treatment (flameproof treatment).

(acrylamide polymer)
The acrylamide-based polymer used in the present invention may be a homopolymer of an acrylamide-based monomer or a copolymer of an acrylamide-based monomer and another polymerizable monomer. A copolymer of an acrylamide-based monomer and another polymerizable monomer is preferable from the viewpoint of improving the rate.

The acrylamide-based polymer used in the present invention contains at least an aqueous solvent (water, alcohol, etc., and a mixed solvent thereof) and an aqueous mixed solvent (a mixed solvent of the aqueous solvent and an organic solvent (tetrahydrofuran, etc.)). It is preferably soluble in one. As a result, when spinning an acrylamide-based polymer, dry spinning, dry-wet spinning, wet spinning, or electrospinning using the aqueous solvent or the aqueous mixed solvent is possible, and the flame-resistant fiber and the It becomes possible to manufacture carbon fibers. In addition, when the additive component described later is blended with the acrylamide polymer, wet mixing using the aqueous solvent or the aqueous mixed solvent is possible, and the acrylamide polymer and the additive component described later can be uniformly and safely at low cost. Mixing becomes possible. The content of the organic solvent in the aqueous mixed solvent is not particularly limited as long as the acrylamide polymer, which is insoluble or sparingly soluble in the aqueous solvent, dissolves when mixed with the organic solvent. In addition, among such acrylamide-based polymers, acrylamide-based polymers that are soluble in the aqueous solvent are preferable from the viewpoint that flame-resistant fibers and carbon fibers can be produced safely at a lower cost. A soluble (water-soluble) acrylamide-based polymer is more preferred.

Furthermore, the upper limit of the weight average molecular weight of the acrylamide polymer used in the present invention is not particularly limited, but is usually 5 million or less, preferably 2 million or less, and 1 million, from the viewpoint of the spinnability of the acrylamide polymer. The following is more preferable, 400,000 or less is still more preferable, and 300,000 or less is particularly preferable. The lower limit of the weight-average molecular weight of the acrylamide-based polymer is not particularly limited, but is usually 10,000 or more, preferably 20,000 or more, more preferably 30,000 or more, from the viewpoint of the strength of the acrylamide-based polymer fiber. 40,000 or more is particularly preferable. The weight average molecular weight of the acrylamide polymer is measured using gel permeation chromatography.

The lower limit of the content of the acrylamide-based monomer unit in the copolymer of the acrylamide-based monomer and other polymerizable monomer is 50 mol% or more from the viewpoint of the solubility of the copolymer in an aqueous solvent or an aqueous mixed solvent. Preferably, 60 mol % or more is more preferable, and 70 mol % or more is particularly preferable. The upper limit of the acrylamide monomer unit content is preferably 99.9 mol% or less, more preferably 99 mol% or less, and more preferably 95 mol% or less, from the viewpoint of improving the carbonization yield of the flame-resistant fiber. More preferably, 90 mol % or less is particularly preferable, and 85 mol % or less is most preferable.

The lower limit of the content of the other polymerizable monomer unit in the copolymer of the acrylamide-based monomer and the other polymerizable monomer is 0.1 mol% or more from the viewpoint of improving the carbonization yield of the flame-resistant fiber. is preferred, 1 mol % or more is more preferred, 5 mol % or more is even more preferred, 10 mol % or more is particularly preferred, and 15 mol % or more is most preferred. Further, the upper limit of the content of the other polymerizable monomer unit is preferably 50 mol% or less, more preferably 40 mol% or less, more preferably 30 mol, from the viewpoint of solubility of the copolymer in an aqueous solvent or an aqueous mixed solvent. % or less is particularly preferred.

Examples of the acrylamide-based monomers include acrylamide; N- alkylacrylamide; N-cycloalkylacrylamide such as N-cyclohexylacrylamide; dialkylacrylamide such as N,N-dimethylacrylamide; dialkylaminoalkylacrylamide such as dimethylaminoethylacrylamide and dimethylaminopropylacrylamide; N-(hydroxymethyl)acrylamide, Hydroxyalkylacrylamides such as N-(hydroxyethyl)acrylamide; N-arylacrylamides such as N-phenylacrylamide; diacetone acrylamide; N,N'-alkylenebisacrylamides such as N,N'-methylenebisacrylamide; methacrylamide; N-alkylmethacrylamides such as N-methylmethacrylamide, N-ethylmethacrylamide, Nn-propylmethacrylamide, N-isopropylmethacrylamide, Nn-butylmethacrylamide, N-tert-butylmethacrylamide; N - N-cycloalkyl methacrylamides such as cyclohexyl methacrylamide; dialkyl methacrylamides such as N,N-dimethyl methacrylamide; dialkylaminoalkyl methacrylamides such as dimethylaminoethyl methacrylamide and dimethylaminopropyl methacrylamide; N-(hydroxymethyl ) hydroxyalkyl methacrylamides such as methacrylamide and N-(hydroxyethyl) methacrylamide; N-aryl methacrylamides such as N-phenylmethacrylamide; diacetone methacrylamide; N, such as N,N'-methylenebismethacrylamide; N'-alkylene bis methacrylamides can be mentioned. These acrylamide-based monomers may be used alone or in combination of two or more. Among these acrylamide-based monomers, acrylamide, N-alkylacrylamide, dialkylacrylamide, methacrylamide, N-alkylmethacrylamide, and dialkylmethacrylamide are preferable from the viewpoint of high solubility in aqueous solvents or aqueous mixed solvents. , acrylamide is particularly preferred.

Examples of other polymerizable monomers include vinyl cyanide-based monomers, unsaturated carboxylic acids and salts thereof, unsaturated carboxylic anhydrides, unsaturated carboxylic acid esters, vinyl-based monomers, and olefin-based monomers. Examples of the vinyl cyanide monomer include acrylonitrile, methacrylonitrile, 2-hydroxyethyl acrylonitrile, chloroacrylonitrile, chloromethacrylonitrile, methoxyacrylonitrile, methoxymethacrylonitrile and the like. Examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, itaconic acid, and the like. Examples of the salt of the unsaturated carboxylic acid include metal salts of the unsaturated carboxylic acid (e.g., sodium salt, potassium salt, etc.), ammonium salts, amine salts and the like; examples of the unsaturated carboxylic anhydride include maleic anhydride and itaconic anhydride; examples of the unsaturated carboxylic acid ester include methyl acrylate, methyl methacrylate, Examples include 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate. Examples of the vinyl-based monomer include aromatic vinyl-based monomers such as styrene and α-methylstyrene, vinyl chloride, and vinyl alcohol. Examples of olefinic monomers include ethylene and propylene. These other polymerizable monomers may be used alone or in combination of two or more. Among these other polymerizable monomers, from the viewpoint of improving the spinnability of the acrylamide polymer and the carbonization yield of the flame-resistant fiber, vinyl cyanide monomers are preferred, and acrylonitrile is particularly preferred. From the viewpoint of solubility in aqueous solvents or aqueous mixed solvents, unsaturated carboxylic acids and salts thereof are preferred.

Methods for synthesizing such acrylamide polymers include known polymerization reactions such as radical polymerization, cationic polymerization, anionic polymerization, living radical polymerization, solution polymerization, suspension polymerization, precipitation polymerization, dispersion polymerization, emulsion polymerization (e.g. , reversed-phase emulsion polymerization) can be employed. Among the above polymerization reactions, radical polymerization is preferred from the viewpoint that an acrylamide-based polymer can be synthesized at low cost. When solution polymerization is employed, it is preferable to use a solvent in which the raw material monomer and the obtained acrylamide polymer are dissolved. It is more preferable to use an alcohol, etc., and a mixed solvent thereof, etc.) or the aqueous mixed solvent (a mixed solvent of the aqueous solvent and an organic solvent (tetrahydrofuran, etc.)), It is particularly preferable to use the aqueous solvent, Most preferably, water is used.

In the radical polymerization, conventionally known radical polymerization initiators such as azobisisobutyronitrile, benzoyl peroxide, 4,4'-azobis(4-cyanovaleric acid), ammonium persulfate, and potassium persulfate are used as polymerization initiators. agent can be used, and when the aqueous solvent or the aqueous mixed solvent is used as the solvent, 4,4′-azobis(4-cyanovaleric acid), ammonium persulfate, potassium persulfate A radical polymerization initiator soluble in a solvent or the aqueous mixed solvent (preferably the aqueous solvent, more preferably water) is preferred. Further, from the viewpoint of reducing the molecular weight of the acrylamide-based polymer and improving the spinnability of the acrylamide-based polymer, instead of or in addition to the polymerization initiator, a conventionally known polymerization accelerator such as tetramethylethylenediamine or n-dodecylmercaptan It is preferable to use a molecular weight modifier such as alkyl mercaptan, etc., it is preferable to use the polymerization initiator and the polymerization accelerator in combination, and it is particularly preferable to use ammonium persulfate and tetramethylethylenediamine in combination.

Although the temperature of the polymerization reaction is not particularly limited, it is preferably 35° C. or higher, and 40° C. or higher from the viewpoint of reducing the weight average molecular weight Mw of the obtained acrylamide polymer and improving the spinnability of the acrylamide polymer. It is more preferably 50° C. or higher, particularly preferably 70° C. or higher, and most preferably 75° C. or higher.

(acrylamide polymer fiber)
The acrylamide-based polymer fiber used in the present invention is made of the acrylamide-based polymer described above, and its fineness is not particularly limited, but is preferably 1×10 ⁻⁸ to 100 tex/fiber, and 1×10 ⁻⁶ to 60 tex/fiber. / book is more preferred, 0.001 to 40 tex / book is more preferred, 0.01 to 10 tex / book is even more preferred, 0.02 to 2 tex / book is particularly preferred, 0.03 to 0.4 tex / book is Most preferred. If the fineness of the acrylamide-based polymer fiber is less than the above lower limit, yarn breakage tends to occur, and stable winding and flameproofing treatment tend to be difficult. and the structural difference near the center becomes large, and the tensile strength and tensile elastic modulus of the obtained carbon fiber tend to decrease.

The average fiber diameter of the acrylamide polymer fibers is not particularly limited, but is preferably 3 nm to 300 μm, more preferably 30 nm to 250 μm, still more preferably 1 to 200 μm, even more preferably 3 to 100 μm, and even more preferably 4 to 40 μm. is particularly preferred, and 5 to 20 μm is most preferred. If the average fiber diameter of the acrylamide-based polymer fiber is less than the above lower limit, fiber breakage tends to occur, and stable winding and flameproofing treatment tend to be difficult. The difference in structure between the surface layer and the center tends to increase, and the tensile strength and tensile modulus of the resulting carbon fiber tend to decrease.

Further, the acrylamide-based polymer fiber is not particularly limited, but preferably has a density of 1.20 g/cm ³ or more, more preferably 1.21 g/cm ³ or more, in an absolute dry state. It is more preferably 1.22 g/cm ³ or more, particularly preferably 1.23 g/cm ³ or more, most preferably 1.24 g/cm ³ or more. By using acrylamide-based polymer fibers having such a density, the cyclization reaction due to the flameproofing treatment tends to be accelerated, and the carbonization yield of the flameproofed fibers after the flameproofing treatment tends to be improved.

In addition, the acrylamide-based polymer fiber can be used as it is for producing flame-resistant fibers and carbon fibers without adding additives such as acids. is accelerated, and further, the formation of a structure in which two or more polycyclic rings are continuous is accelerated, so that the intensity ratio (I From the viewpoint that _A /I _B ) tends to be a predetermined value, the acrylamide polymer fiber contains at least one additive component selected from the group consisting of acids and salts thereof in addition to the acrylamide polymer. may be included. By subjecting the acrylamide-based polymer fiber containing the additive component to flame-resistant treatment while applying tension, the formation of a cyclic structure due to dehydration reaction and deammonification reaction is accelerated, and further, a structure in which two or more rings are continuous. is accelerated, and the intensity ratio ( _IA /IB) between the absorption peak A and the absorption peak _B in the infrared absorption spectrum tends to become a predetermined value, so that the load resistance at high temperatures is excellent, Flameproofed fibers with high strength, high modulus and high char yield are obtained. Moreover, in the flame-resistant fiber of the present invention, at least part of the additive component and its residue may remain. Further, the carbonization treatment may be performed by adding the additive component to the flameproof fiber.

From the viewpoint of further improving the load resistance, strength, elastic modulus, and carbonization yield of the flame-resistant fiber made from the acrylamide-based polymer fiber at high temperatures, the content of such an additive component is the acrylamide-based polymer 100. It is preferably 0.1 to 100 parts by mass, more preferably 0.2 to 50 parts by mass, still more preferably 0.5 to 30 parts by mass, particularly preferably 1 to 20 parts by mass, and 1 to 10 parts by mass. part is most preferred.

Examples of the acid include inorganic acids such as phosphoric acid, polyphosphoric acid, boric acid, polyboric acid, sulfuric acid, nitric acid, carbonic acid and hydrochloric acid, and organic acids such as oxalic acid, citric acid, sulfonic acid and acetic acid. Examples of such acid salts include metal salts (eg, sodium salts, potassium salts, etc.), ammonium salts, amine salts and the like, with ammonium salts and amine salts being preferred, and ammonium salts being more preferred. In particular, among these additive components, the load resistance, strength, elastic modulus, and carbonization yield of flame-resistant fibers made from acrylamide-based polymer fibers at high temperatures are further improved, but phosphoric acid, Polyphosphoric acid, boric acid, polyboric acid, sulfuric acid, and ammonium salts thereof are preferred, and phosphoric acid, polyphosphoric acid, and ammonium salts thereof are particularly preferred.

The additive component is preferably soluble in at least one of the aqueous solvent and the aqueous mixed solvent (more preferably the aqueous solvent, particularly preferably water). As a result, when producing an acrylamide-based polymer fiber containing an additive component, wet mixing using the aqueous solvent or the aqueous mixed solvent is possible, and the acrylamide-based polymer and the additive component are uniformly mixed at low cost. Safe mixing becomes possible. In addition, dry spinning, dry-wet spinning, wet spinning, or electrospinning using the aqueous solvent or the aqueous mixed solvent becomes possible, and flameproof fibers and carbon fibers can be produced safely at low cost.

Such an acrylamide-based polymer fiber can be produced (manufactured) as follows. First, the acrylamide-based polymer or an acrylamide-based polymer composition containing the acrylamide-based polymer and the additive component is spun. At this time, the acrylamide-based polymer or the acrylamide-based polymer composition in a molten state may be melt-spun, spunbonded, meltblown, or centrifugally spun, but the acrylamide-based polymer or the acrylamide-based polymer composition may In the case of being soluble in the solvent or the aqueous mixed solvent, from the viewpoint of enhancing the spinnability, the acrylamide polymer or the acrylamide polymer composition is dissolved in the aqueous solvent or the aqueous mixed solvent, and the resulting aqueous Spinning using a solution or an aqueous mixed solution, or the solution of the acrylamide-based polymer after polymerization described above or the solution of the acrylamide-based polymer composition obtained by wet mixing described later, as it is or after adjusting it to a desired concentration, Spinning is preferred. As such a spinning method, dry spinning, wet spinning, dry-wet spinning, gel spinning, flash spinning, or electrospinning is preferred. As a result, acrylamide-based polymer fibers having a desired fineness and average fiber diameter can be produced (manufactured) safely at low cost. Moreover, from the viewpoint that acrylamide-based polymer fibers can be produced safely at a lower cost, it is more preferable to use the aqueous solvent as the solvent, and it is particularly preferable to use water.

The concentration of the acrylamide-based polymer in the aqueous solution or the aqueous mixed solution is not particularly limited, but from the viewpoint of productivity improvement and cost reduction, a high concentration of 20% by mass or more is preferable. If the concentration of the acrylamide polymer becomes too high, the viscosity of the aqueous solution or the aqueous mixed solution increases and the spinnability decreases. As such, it is preferable to adjust the concentration to allow spinning.

Methods for producing the acrylamide-based polymer composition include a method of directly mixing the additive component with the acrylamide-based polymer in a molten state (melt mixing), and a method of dry-blending the acrylamide-based polymer and the additive component (dry method). mixing), the fibrous acrylamide-based polymer is immersed in an aqueous solution or aqueous mixed solution containing the additive component, or in a solution in which the acrylamide-based polymer is not completely dissolved but the additive component is dissolved. However, when the acrylamide-based polymer and the additive component to be used are soluble in the aqueous solvent or the aqueous mixed solvent, the acrylamide-based polymer and A method of mixing the acrylamide-based polymer and the additive component in the aqueous solvent or the aqueous mixed solvent (wet mixing) is preferable from the viewpoint that the additive component can be uniformly mixed. As wet mixing, when the above-mentioned polymerization is carried out in the above-mentioned aqueous solvent or the above-mentioned aqueous mixed solvent in synthesizing the acrylamide-based polymer, a method of mixing the above-mentioned additive components after the polymerization may also be adopted. can be done. Furthermore, by removing the solvent from the resulting solution, the acrylamide polymer composition can be recovered and used for the production of carbon fibers described later. It can also be used as it is for the production of carbon fibers, which will be described later. In the wet mixing, the aqueous solvent is preferably used as the solvent, and water is more preferably used, from the viewpoint that the acrylamide-based polymer composition can be produced safely at a lower cost. Furthermore, the method for removing the solvent is not particularly limited, and at least one of known methods such as distillation under reduced pressure, reprecipitation, hot air drying, vacuum drying, and freeze drying can be employed.

Such acrylamide-based polymer fibers may be used as single fibers or as fiber bundles. When the acrylamide-based polymer fiber is used as a fiber bundle, the number of filaments per yarn is not particularly limited, but from the viewpoint of improving the high productivity and mechanical properties of the flame-resistant fiber and carbon fiber, the number of filaments is from 50 to 50. 96,000 is preferred, 100 to 48,000 is more preferred, 500 to 36,000 is even more preferred, and 1,000 to 24,000 is particularly preferred. If the number of filaments per yarn exceeds the above upper limit, uneven firing may occur during the flameproofing treatment.

Further, such acrylamide-based polymer fibers may be coated with a conventionally known oil agent such as a silicone-based oil agent from the viewpoint of bundling property of fibers, improvement of handling property, and prevention of adhesion between fibers.

(Method for producing flame-resistant fiber)
In the method for producing a flame-resistant fiber of the present invention, while applying a tension of 0.07 to 200 mN/tex to the acrylamide polymer fiber, the resulting flame-resistant fiber has an infrared absorption spectrum of 1560 to 1560 in an oxidizing atmosphere. Until the ratio (I _A /I _B ) of the intensity (I _A ) of the absorption peak A existing in the range of 1595 cm ⁻¹ and the intensity (I _B ) of the absorption peak B at 1648 cm ⁻¹ reaches 0.5 to 10. This is a method of applying heat treatment (flameproof treatment). The acrylamide-based polymer fiber used in the present invention is resistant to thermal decomposition by the flame-resistant treatment, and the structure of the acrylamide-based polymer is converted to a highly heat-resistant structure by the flame-resistant treatment. , which exhibits excellent load bearing capacity at high temperatures, high strength, high elastic modulus and high carbonization yield. In particular, in the acrylamide-based polymer fiber containing the additive component, the deammonification reaction and dehydration reaction of the acrylamide-based polymer are promoted by the catalytic action of the acid or its salt, which is the additive component. (imide ring structure) and polycyclic structures with two or more rings are easily formed, and the structure of the acrylamide polymer is easily converted into a structure with high heat resistance. , the modulus and carbonization yield are higher.

The absorption peak B at 1648 cm ⁻¹ in the infrared absorption spectrum of the flame-resistant fiber is an absorption peak derived from the carbonyl group of the acrylamide polymer. On the other hand, the absorption peak A existing in the range of 1560 to 1595 cm ⁻¹ in the infrared absorption spectrum of the flame-resistant fiber is, for example, a ladder structure in which two or more six-membered rings represented by the following formula are condensed, R- Absorption peaks derived from NH bonds, CN bonds, C=N bonds, and C=O bonds in the N=C-NH-C(=O)-structure (the structure enclosed by the dashed line) . In the present invention, the structure formed by the flameproofing treatment is not limited to the structure represented by the following formula. For example, a ladder structure consisting of four or more six-membered rings may be formed. .

When the acrylamide-based polymer fiber is subjected to a flame-resistant treatment, the adjacent acrylamide groups are usually bonded to each other to form one imide ring. As shown, by performing flameproofing treatment at a specific temperature, a ladder structure is formed in which two or more six-membered rings are condensed and have an absorption peak A in the range of 1560 to 1595 cm ⁻¹ in the infrared absorption spectrum. . This ladder structure in which two or more six-membered rings are condensed has excellent heat resistance, excellent load resistance at high temperatures, and exhibits high strength and high elastic modulus. Therefore, the flame-resistant fiber containing many ladder structures in which two or more six-membered rings are condensed, that is, the flame _- resistant fiber in which the intensity ratio ( _IA /IB) of the absorption peaks in the infrared absorption spectrum is within a predetermined range The modified fiber has excellent heat resistance, excellent load bearing capacity at high temperatures, and exhibits high strength, high elastic modulus and high carbonization yield.

In the method for producing the flame-resistant fiber of the present invention, until the intensity ratio (I _A /I _B ) of such absorption peaks is 0.5 to 10, preferably 0.7 to 10, more preferably is 1.0 to 9, more preferably 1.2 to 8, particularly preferably 1.4 to 7, most preferably 1.8 to 6, heat treatment (flame resistant chemical treatment). When the absorption peak strength ratio ( _IA /IB) of the flame _- resistant fiber is less than the lower limit, the load-bearing property, strength, elastic modulus and carbonization yield of the flame-resistant fiber at high temperatures tend to decrease, On the other hand, in order to obtain a flameproof fiber in which the absorption peak intensity ratio ( _IA / _IB ) exceeds the upper limit, it is necessary to increase the amount of energy by lengthening the flameproofing treatment time. Decomposition tends to increase, and the effect of increasing the carbonization yield tends to saturate even if the flameproofing treatment time is lengthened.

Further, in the method for producing a flame-resistant fiber of the present invention, the tension applied to the acrylamide-based polymer fiber is 0.07 to 200 mN/tex, and the intensity ratio (I _A /I _B ) of the absorption peak is a predetermined Although there is no particular limitation as long as it is within the range of It is more preferably 0.30 to 10 mN/tex, most preferably 0.35 to 5 mN/tex. If the tension applied to the acrylamide-based polymer fiber is less than the lower limit, the strength ratio ( _IA /IB) of the absorption peak does not reach a predetermined value, and the high _- temperature load bearing capacity, strength, and Elastic modulus and carbonization yield tend to decrease. On the other hand, if the upper limit is exceeded, the acrylamide-based polymer fiber may be cut during the flameproofing treatment. In the present invention, the tension (unit: mN/tex) applied to the acrylamide-based polymer fiber is the tension (unit: mN) applied to the acrylamide-based polymer fiber during the flameproofing treatment. It is a value divided by the fineness (unit: tex) in the absolute dry state, that is, the tension per unit fineness of the acrylamide-based polymer fiber. Moreover, the tension applied to the acrylamide polymer fibers can be adjusted by a load cell, a spring, a weight, or the like on the exit side of a heating device such as a flameproofing furnace.

Furthermore, in the method for producing a flame-resistant fiber of the present invention, the flame-resistant treatment is performed under conditions (temperature, time, etc.) in which the absorption peak intensity ratio ( _IA / _IB ) becomes a predetermined value. Although there is no particular limitation, it is preferably applied at a temperature within the range of 150 to 500 ° C., more preferably at a temperature within the range of 200 to 500 ° C., and within the range of 250 to 450 ° C. is more preferably applied at a temperature of The flameproofing treatment applied at such a temperature includes not only the flameproofing treatment at the temperature within the above range, but also the flameproofing treatment in the process of raising the temperature up to the temperature within the above range. good too.

In particular, when the acrylamide-based polymer fiber contains the additive component, the flameproofing treatment is preferably performed at a temperature in the range of 260 to 450°C, more preferably in the range of 270 to 450°C. is more preferably applied at a temperature in the range of 290-440°C, even more preferably in the range of 310-430°C, and even more preferably in the range of 330-440°C. It is particularly preferred to apply at a temperature in the range of 420°C, most preferably in the range of 380-410°C. The flameproofing treatment in this case may include not only the flameproofing treatment at the temperature within the above range, but also the flameproofing treatment in the process of raising the temperature up to the temperature within the above range.

Further, when the acrylamide-based polymer fiber does not contain the additive component, the flameproofing treatment is preferably performed at a temperature within the range of 310 to 500°C, more preferably within the range of 320 to 450°C. is more preferably applied at a temperature in the range of 340-440°C, even more preferably in the range of 350-430°C, and even more preferably in the range of 360-440°C. It is particularly preferred to be applied at a temperature within the range of 420°C, most preferably within the range of 370-410°C. In addition, the flameproofing treatment in this case may include not only the flameproofing treatment at the temperature within the above range, but also the flameproofing treatment in the process of raising the temperature up to the temperature within the above range.

If the flameproofing treatment is performed at a temperature lower than the lower limit of the temperature range, the strength ratio (I _A / _IB ) of the absorption peak of the flameproof fiber does not become a predetermined value, and the load capacity of the flameproof fiber at high temperature is increased. The properties, strength, elastic modulus and carbonization yield tend to decrease. On the other hand, if the flameproof treatment is performed at a temperature exceeding the upper limit of the above temperature range, the energy cost during production tends to increase.

The flameproofing treatment time (heating time at the maximum temperature during the flameproofing treatment) is not particularly limited, and long-term heating (for example, more than 2 hours) is possible, but 1 to 120 minutes is preferable, and 2 to 60 minutes is more preferred, 3 to 50 minutes is even more preferred, and 4 to 40 minutes is particularly preferred. By setting the heating time in the flameproofing treatment to the lower limit or more, the carbonization yield can be improved.

[Flame-resistant fiber]
The flame-resistant fiber of the present invention is derived from an acrylamide polymer, has an absorption peak A in the range of 1560 to 1595 cm ⁻¹ in the infrared absorption spectrum, and the intensity (I _A ) of the absorption peak A and 1648 cm ⁻¹ The fiber has a ratio (I _A /I _B ) of 0.5 to 10 to the intensity (I _B ) of the absorption peak B of ¹ . Such a flame-resistant fiber has excellent heat resistance and excellent load resistance at high temperatures, and exhibits high strength, high elastic modulus, and high carbonization yield. Due to the fact that cuts are less likely to occur, the use of the flameproof fiber of the present invention makes it possible to produce carbon products with a high yield.

On the other hand, a flame-resistant fiber that does not have an absorption peak in the range of 1560 to 1595 cm ⁻¹ or a flame-resistant fiber that has an absorption peak intensity ratio (I _A /I _B ) that is less than the lower limit has high load resistance at high temperatures, The strength, elastic modulus, and carbonization yield tend to decrease, and on the other hand, in order to obtain a flameproof fiber in which the intensity ratio ( _IA / _IB ) of the absorption peak exceeds the upper limit, the flameproofing treatment time is prolonged. The decomposition of the flameproof fibers tends to increase, and even if the flameproof treatment time is lengthened, the effect of increasing the carbonization yield tends to be saturated. In addition, from the viewpoint of improving the load resistance, strength, elastic modulus and carbonization yield at high temperatures, the absorption peak intensity ratio (I _A /I _B ) is preferably 0.7 to 10. 0 to 9 are more preferred, 1.2 to 8 are even more preferred, 1.4 to 7 are particularly preferred, and 1.8 to 6 are most preferred.

The average fiber diameter of the flame-resistant fiber of the present invention is not particularly limited, but is preferably 3 nm to 300 μm, more preferably 30 nm to 150 μm, still more preferably 1 to 60 μm, even more preferably 3 to 20 μm, and 4 to 20 μm. 15 μm is particularly preferred and 5-10 μm is most preferred. If the average fiber diameter of the flame-resistant fibers is less than the above lower limit, the conveyability of the flame-resistant fiber bundle before or during the carbonization treatment may decrease, and some fibers may be cut. If it exceeds, the difference in structure between the surface layer and the center of the fiber increases during carbonization, and the tensile strength and tensile modulus of the resulting carbon fiber tend to decrease.

In addition, from the viewpoint of improving the carbonization yield of the flame-resistant fiber, the average fiber diameter of the flame-resistant fiber of the present invention is 5 times greater than the average fiber diameter of the acrylamide-based polymer fiber before the flame-resistant treatment. % or more is preferable, 10% or more is more preferable, 15% or more is more preferable, 20% or more is particularly preferable, 25% or more is particularly preferable, and 30% or more is most preferable. preferable.

[Method for producing carbon fiber]
The method for producing the carbon fiber of the present invention is a method of subjecting the flame-resistant fiber of the present invention to a carbonization treatment. and a step of subjecting the carbonized fiber to a carbonization treatment.

As a method for performing the flameproofing fiber carbonization treatment, the flameproofing fiber is subjected to a heat treatment in an inert atmosphere (in an inert gas such as nitrogen, argon, or helium) at a temperature higher than the temperature in the flameproofing treatment. (carbonization). As a result, the flameproof fibers are carbonized to obtain the desired carbon fibers. The heating temperature in such carbonization treatment is preferably 500° C. or higher, more preferably 1000° C. or higher. Incidentally, the "carbonization treatment" according to the present invention may generally include "graphitization" performed by heating at 2000 to 3000° C. in an inert gas atmosphere. Moreover, the upper limit of the heating temperature is preferably 3000° C. or less, more preferably 2500° C. or less. Furthermore, the heating time in the carbonization treatment is not particularly limited, but is preferably 30 seconds to 60 minutes, more preferably 1 to 30 minutes. In the carbonization treatment, for example, heat treatment (preliminary carbonization treatment) is first performed at a temperature of less than 1000° C., followed by heat treatment (carbonization treatment) at a temperature of 1000° C. or higher, and then 2000° C. or higher. Heat treatment (graphitization treatment) can be performed a plurality of times, such as performing heat treatment (graphitization treatment) at a temperature of .

The average fiber diameter of the carbon fibers thus obtained is not particularly limited, but is preferably 3 nm to 300 μm, more preferably 30 nm to 150 μm, still more preferably 1 to 60 μm, still more preferably 3 to 20 μm, and 4 to 20 μm. 15 μm is particularly preferred and 5-10 μm is most preferred. If the average fiber diameter of the carbon fibers is less than the above lower limit, in the case of producing a composite material using a resin or the like as a matrix, if the viscosity of the matrix is high, impregnation of the resin or the like into the carbon fiber bundles will be insufficient, and the tensile strength of the composite material will be reduced. On the other hand, exceeding the above upper limit tends to reduce the tensile strength of the carbon fiber.

EXAMPLES The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples. Each acrylamide-based polymer and each acrylamide-based polymer fiber used in Examples and Comparative Examples were prepared by the following method.

(Preparation Example 1)
100 parts by mass of a monomer consisting of 75 mol% acrylamide (AM) and 25 mol% acrylonitrile (AN) and 4.36 parts by mass of tetramethylethylenediamine were dissolved in 566.7 parts by mass of ion-exchanged water, and the resulting aqueous solution was treated with a nitrogen atmosphere. After adding 3.43 parts by mass of ammonium persulfate while stirring at the bottom, the mixture was heated at 70°C for 150 minutes, then heated to 90°C over 30 minutes, and then heated at 90°C for 1 hour for polymerization reaction. was performed (polymerization rate: 87%). The resulting aqueous solution was dropped into methanol to precipitate a copolymer, which was recovered and vacuum-dried at 80° C. for 12 hours to form a water-soluble acrylamide/acrylonitrile copolymer (AM/AN copolymer, AM /AN = 80 mol%/20 mol%) powder (p-1) was obtained.

(Preparation Example 2)
100 parts by mass of acrylamide (AM) and 8.78 parts by mass of tetramethylethylenediamine are dissolved in 2912 parts by mass of ion-exchanged water, and 1.95 parts by mass of ammonium persulfate is added to the resulting aqueous solution while stirring under a nitrogen atmosphere. After the addition, a polymerization reaction was carried out at 60° C. for 3 hours. The resulting aqueous solution was dropped into methanol to precipitate a homopolymer, which was collected and vacuum-dried at 80° C. for 12 hours to obtain a water-soluble polyacrylamide (PAM, AM=100 mol %) powder (p-2). ).

(Production example 1)
The AM/AN copolymer (AM/AN=80 mol%/20 mol%) powder (p-1) obtained in Preparation Example 1 was dissolved in ion-exchanged water, and dry spinning was performed using the resulting aqueous solution. An acrylamide polymer fiber (f-1) was produced. 600 acrylamide polymer fibers (f-1) were bundled to prepare an acrylamide polymer fiber bundle, and the fineness of the acrylamide polymer fiber bundle, the fineness of the single fiber and the average fiber diameter (acrylamide When the average fiber diameter of the polymer fiber (f-1) was determined, the fineness of the fiber bundle was 198 tex, the fineness of the single fiber was 0.33 tex/fiber, and the average fiber diameter of the single fiber was 18 μm. .

<Fineness of acrylamide-based polymer fiber bundle and its single fiber>
The mass of the acrylamide-based polymer fiber bundle is measured and calculated by the following formula:
Fiber bundle fineness [tex] = fiber bundle mass [g] / fiber length [m] × 1000 [m]
By calculating the fineness of the fiber bundle, the fineness of the single fibers constituting the fiber bundle (the fineness of the acrylamide-based polymer fiber) was obtained.

<Average fiber diameter of acrylamide-based polymer fiber>
The density of the acrylamide-based polymer fiber bundle was measured using a dry automatic densitometer (“Accupic II 1340” manufactured by Micromeritics), and the following formula:
D={(Dt×4×1000)/(ρ×π×n)} ^1/2
[In the above formula, D represents the average fiber diameter [μm] of the single fibers constituting the fiber bundle, Dt represents the fineness [tex] of the fiber bundle, and ρ represents the density [g/cm ³ ] of the fiber bundle. , n represent the number of single fibers constituting the fiber bundle. ]
The average fiber diameter of the single fibers constituting the fiber bundle (average fiber diameter of the acrylamide-based polymer fibers) was calculated.

(Production example 2)
The AM/AN copolymer (AM/AN=80 mol%/20 mol%) powder (p-1) obtained in Preparation Example 1 was dissolved in deionized water, and 100% of the AM/AN copolymer was added to the resulting aqueous solution. Phosphoric acid was added in an amount of 3 parts by mass and completely dissolved. Dry spinning was performed using the obtained aqueous solution to produce an acrylamide polymer fiber (f-2). 350 acrylamide polymer fibers (f-2) were bundled to prepare an acrylamide polymer fiber bundle, and in the same manner as in Production Example 1, the fineness of the acrylamide polymer fiber bundle, the fineness of the single fiber, and the average fiber diameter ( When the average fiber diameter of the acrylamide polymer fiber (f-2) was determined, the fineness of the fiber bundle was 133 tex, the fineness of the single fiber was 0.38 tex/fiber, and the average fiber diameter of the single fiber was 19 μm. Met.

(Production example 3)
An acrylamide polymer fiber (f-3) was produced in the same manner as in Production Example 2, except that 3 parts by mass of diammonium hydrogen phosphate was added to 100 parts by mass of the AM/AN copolymer instead of phosphoric acid. did. 600 acrylamide polymer fibers (f-3) were bundled to prepare an acrylamide polymer fiber bundle, and in the same manner as in Production Example 1, the fineness of the acrylamide polymer fiber bundle, the fineness of the single fiber, and the average fiber diameter ( When the average fiber diameter of the acrylamide polymer fiber (f-3) was determined, the fineness of the fiber bundle was 276 tex, the fineness of the single fiber was 0.46 tex/fiber, and the average fiber diameter of the single fiber was 21 μm. Met.

(Production example 4)
Production Example 1 except that the PAM (AM = 100 mol%) powder (p-2) obtained in Preparation Example 2 was used instead of the AM/AN copolymer powder (p-1) obtained in Preparation Example 1. Acrylamide-based polymer fiber (f-4) was produced in the same manner. An acrylamide polymer fiber bundle was produced by bundling 600 acrylamide polymer fibers (f-4), and in the same manner as in Production Example 1, the fineness of the acrylamide polymer fiber bundle, the fineness of the single fiber, and the average fiber diameter ( When the average fiber diameter of the acrylamide polymer fiber (f-4) was determined, the fineness of the fiber bundle was 240 tex, the fineness of the single fiber was 0.40 tex/fiber, and the average fiber diameter of the single fiber was 20 μm. Met.

(Example 1)
A precursor fiber bundle was prepared by bundling 600 acrylamide polymer fibers (f-1) obtained in Production Example 1, and this precursor fiber bundle was placed in a heating furnace and heated from 50° C. under an air atmosphere. After raising the temperature to 150°C at 10°C/min, while applying a tension of 0.4 mN/tex to the precursor fiber bundle, the temperature was increased from 150°C to 360°C (flameproofing treatment temperature (maximum temperature during flameproofing treatment). ) at a rate of 10° C./min, and subsequently, while applying a tension of 0.4 mN/tex to the precursor fiber bundle, 360° C. (flameproofing treatment temperature (maximum temperature during flameproofing treatment)) to obtain a flameproof fiber bundle.

Four bundles of the obtained flameproof fiber bundles were bundled to prepare a flameproof fiber bundle composed of 2400 flameproof fibers, and the flameproof fiber bundle was conveyed into a heating furnace and heated at 1000°C for 3 minutes in a nitrogen atmosphere. was subjected to heat treatment (carbonization treatment) to obtain a carbon fiber bundle.

(Example 2)
A flameproof fiber bundle and a carbon fiber bundle were produced in the same manner as in Example 1, except that the flameproofing treatment temperature (maximum temperature during flameproofing treatment) was changed to 400°C.

(Example 3)
Instead of the acrylamide polymer fiber (f-1), 350 acrylamide polymer fibers (f-2) obtained in Production Example 2 were bundled to prepare a precursor fiber bundle. A flameproof fiber bundle was produced in the same manner as in Example 1, except that the maximum temperature at the time) was changed to 350°C. Further, a carbon fiber bundle was produced in the same manner as in Example 1, except that 8 bundles of the flameproof fiber bundles were bundled to produce a flameproof fiber bundle composed of 2800 flameproof fibers.

(Example 4)
A flameproof fiber bundle and a carbon fiber bundle were produced in the same manner as in Example 3, except that the flameproofing treatment temperature (maximum temperature during flameproofing treatment) was changed to 400°C.

(Example 5)
Instead of the acrylamide polymer fiber (f-1), 600 acrylamide polymer fibers (f-3) obtained in Production Example 3 were bundled to prepare a precursor fiber bundle, and the flameproofing treatment temperature (flameproofing treatment Example 1 except that the maximum temperature at 300 ° C., the flameproofing treatment time (heating time at the maximum temperature) was changed to 30 minutes, and the tension applied to the precursor fiber bundle was changed to 0.2 mN / tex. A flameproof fiber bundle and a carbon fiber bundle were produced in the same manner.

(Example 6)
A flameproof fiber bundle and a carbon fiber bundle were produced in the same manner as in Example 5, except that the flameproofing treatment temperature (maximum temperature during flameproofing treatment) was changed to 320°C.

(Example 7)
Instead of the acrylamide polymer fiber (f-1), 600 acrylamide polymer fibers (f-4) obtained in Production Example 4 were bundled to prepare a precursor fiber bundle, and the flameproofing treatment temperature (flameproofing treatment A flameproof fiber bundle and a carbon fiber bundle were produced in the same manner as in Example 1, except that the maximum temperature at 350° C. and the tension applied to the precursor fiber bundle were changed to 0.2 mN/tex.

(Example 8)
A flameproof fiber bundle and a carbon fiber bundle were produced in the same manner as in Example 7, except that the flameproofing treatment temperature (maximum temperature during flameproofing treatment) was changed to 400°C.

(Comparative example 1)
The flameproofing treatment temperature (maximum temperature during flameproofing treatment) was 300°C, the flameproofing treatment time (heating time at the maximum temperature) was 30 minutes, and the tension applied to the precursor fiber bundle was 0.2 mN/tex. A flameproof fiber bundle and a carbon fiber bundle were produced in the same manner as in Example 1, except that the

(Comparative example 2)
Except that the flameproofing treatment temperature (maximum temperature during flameproofing treatment) was changed to 320°C, the flameproofing treatment time (heating time at the maximum temperature) was changed to 30 minutes, and no tension was applied to the precursor fiber bundle. prepared a flameproof fiber bundle and a carbon fiber bundle in the same manner as in Example 1.

(Comparative Example 3)
The AM/AN copolymer (AM/AN=80 mol%/20 mol%) powder (p-1) obtained in Preparation Example 1 was placed in a heating furnace and heated in an air atmosphere from room temperature to 350° C. (flameproofing). After raising the temperature to the treatment temperature (maximum temperature during flameproofing treatment) at 10°C/min, heat treatment (flameproofing treatment) at 350°C (flameproofing treatment temperature (maximum temperature during flameproofing treatment)) for 30 minutes. to obtain a flameproof powder.

The obtained flameproof powder was placed in a heating furnace, heated from room temperature to 1000° C. at a rate of 20° C./min in a nitrogen atmosphere, and then heat-treated (carbonized) at 1000° C. for 3 minutes. A powder was obtained.

(Comparative Example 4)
A flameproof powder and a carbon powder were produced in the same manner as in Comparative Example 3, except that the flameproofing treatment temperature (maximum temperature during the flameproofing treatment) was changed to 400°C.

(Comparative Example 5)
The AM/AN copolymer (AM/AN=80 mol%/20 mol%) powder (p-1) obtained in Preparation Example 1 was added to deionized water so that the AM/AN copolymer concentration was 20% by mass. 3 parts by mass of diammonium hydrogen phosphate was added to 100 parts by mass of the AM/AN copolymer to the resulting aqueous solution and completely dissolved. Water was distilled off from the obtained aqueous solution under reduced pressure, and the precipitated solid component was vacuum-dried and then pulverized to obtain a precursor mixed powder containing the AM/AN copolymer and diammonium hydrogen phosphate. Obtained.

Same as Comparative Example 3, except that the precursor mixed powder was used instead of the AM/AN copolymer powder (p-1), and the flameproofing treatment time (maximum temperature during flameproofing treatment) was changed to 10 minutes. Then, a flameproof powder and a carbon powder were produced.

(Comparative Example 6)
Flame-resistant powder was prepared in the same manner as in Comparative Example 3, except that the flame-resistant treatment temperature (maximum temperature during flame-resistant treatment) was changed to 300°C and the flame-resistant treatment time (heating time at the maximum temperature) was changed to 10 minutes. and carbon powder were produced.

(Comparative Example 7)
A flameproof powder and a carbon powder were prepared in the same manner as in Comparative Example 3, except that the flameproofing treatment temperature (maximum temperature during the flameproofing treatment) was changed to 300°C.

(Comparative Example 8)
Instead of the acrylamide polymer fiber (f-1), 600 acrylamide polymer fibers (f-4) obtained in Production Example 4 were bundled to prepare a precursor fiber bundle, and the flameproofing treatment temperature (flameproofing treatment A flameproof fiber bundle and a carbon fiber bundle were produced in the same manner as in Example 1, except that the maximum temperature at 300° C. was changed to 300° C. and no tension was applied to the precursor fiber bundle.

<Average fiber diameter of flame resistant fiber>
The obtained flame-resistant fiber bundle was observed using a microscope (“Digital Microscope VHX-1000” manufactured by Keyence Corporation), and 10 measurement points of the fiber diameter of the single fiber were randomly extracted and the flame-resistant fiber bundle was obtained. The fiber diameters of the flame-resistant single fibers constituting the fiber bundle were measured, and the average value (average fiber diameter of the flame-resistant fibers) was obtained. Table 1 shows the results.

<Infrared spectroscopic analysis of flame-resistant fiber (or flame-resistant powder)>
ATR method (ATR crystal: Zn—Se, measurement wavenumber range: 650 to 4000 cm ⁻¹ , resolution: 4 cm ⁻¹ ). FIG. 1 shows infrared absorption spectra of the flameproof fiber bundles obtained in Example 3 and Comparative Example 1 as an example.

The presence or absence of absorption peak A (1560 to 1595 cm ⁻¹ ) was confirmed in the obtained infrared absorption spectrum. Table 1 shows the results. For example, as is clear from the results shown in FIG. 1, the presence of an absorption peak A within the range of 1560 to 1595 cm ⁻¹ was confirmed in the infrared absorption spectrum of the flameproof fiber bundle obtained in Example 3. was not confirmed in the infrared absorption spectrum of the flameproof fiber bundle obtained in Comparative Example 1.

Further, based on the obtained infrared absorption spectrum, the ratio (I _A /I _B ) of the intensity (I _A ) of the absorption peak A and the intensity (I _B ) of the absorption peak B (1648 cm ⁻¹ ) was calculated. asked. Table 1 shows the results. Incidentally, the intensity ratio of the absorption peak, the baseline (dotted line in FIG. 1) is a straight line connecting the absorbance of 650 cm ^-1 and the end point of the absorption peak near 1850 cm ^-1 , the baseline at the position of each absorption peak to the peak top (broken line in FIG. 1) was measured, and the ratio of these heights was obtained.

<High-temperature load resistance of flame-resistant fibers>
The obtained flameproof fiber bundle was placed in a heating furnace, a weight of a predetermined mass was attached, and the temperature was raised from room temperature to 350°C at a rate of 10°C/min in a nitrogen atmosphere, followed by heat treatment at 350°C for 10 minutes. The presence or absence of fiber breakage was observed. This measurement is performed using weights of various masses, and the mass per 1000 fibers is calculated from the mass of the weight when the cut of the fiber is confirmed. Loadability was evaluated. Table 1 shows the results.
A: The withstand load at high temperature is 15 g or more per 1000 fibers.
B: The withstand load at high temperature is 8 g or more and less than 15 g per 1000 fibers.
C: The load capacity at high temperature is less than 8 g per 1000 fibers.

<Tensile strength and tensile modulus of flame-resistant fiber>
A single fiber was taken out from the obtained flame-resistant fiber bundle, and a tensile test (marked line distance: 25 mm, tensile speed: 1 mm/min), the tensile strength and tensile modulus were measured, and the average value of five measurements was obtained.

<Average fiber diameter of carbon fiber>
The obtained carbon fiber bundle was observed using a microscope (“Digital Microscope VHX-1000” manufactured by Keyence Corporation), and 10 measurement points of the fiber diameter of the single fiber were randomly extracted and the carbon fiber bundle was measured. The fiber diameters of the carbon fibers constituting the were measured, and the average value (average fiber diameter of the carbon fibers) was obtained. Table 1 shows the results.

<Carbonization yield>
The carbonization yield is calculated by the following formula:
Carbonization yield [%]=mass of carbon fiber bundle [mg]/mass of flameproof fiber bundle before carbonization [mg]×100
obtained by Table 1 shows the results. As for the mass of the flameproof fiber bundle before carbonization, the amount of water adsorbed to the flameproof fiber bundle was calculated by vacuum-drying the flameproof fiber bundle at 120°C for 2 hours, and a value was obtained in consideration of this water content. used.

As shown in Table 1, the absorption peak A (1560 to 1595 cm ^-1 ) and the absorption peak B (1648 cm ^-1 ) in the infrared absorption spectrum of the flame-resistant fiber obtained while applying a predetermined tension to the acrylamide polymer fiber. ¹ ) and the strength ratio (I _A /I _B ) to a predetermined value, when heat treatment is performed in an oxidizing atmosphere (Examples 1 to 8), the load resistance at high temperatures is excellent. , resulting in flameproofed fibers with high strength, high modulus and high char yield.

On the other hand, when heat treatment was performed without applying a predetermined tension (Comparative Examples 2 and 8), no absorption peak A was observed in the infrared absorption spectrum of the obtained flame-resistant fibers, and no absorption peak A was observed at high temperatures. The load resistance, strength and elastic modulus of the fiber were poor, and the carbonization yield was also low. Further, even when the heat treatment was performed while applying a predetermined tension, when the absorption peak A was not observed in the infrared absorption spectrum of the obtained flame-resistant fiber (Comparative Example 1), the obtained flame-resistant fiber The treated fiber was inferior in load bearing property at high temperature, fiber strength and elastic modulus, and the carbonization yield was also low.

Further, when the acrylamide-based polymer powder was heat-treated (Comparative Examples 3 to 7), no absorption peak A was observed in the infrared absorption spectrum of the obtained flame-resistant powder. This is probably because tension could not be applied to the acrylamide polymer powder.

Specifically, as is clear from the results shown in Examples 1 to 2 and 7 to 8, by performing heat treatment (flameproofing treatment) at a temperature of 350° C. or higher while applying a predetermined tension, In the infrared absorption spectrum of the flame-resistant fiber, the intensity ratio (I _A /I _B ) between the absorption peak A (1560 to 1595 cm ^-1 ) and the absorption peak B (1648 cm ^-1 ) has a predetermined value, and can be used at high temperatures. It has been found to have excellent load bearing properties, high strength, high modulus and high carbonization yield.

On the other hand, as is clear from the results shown in Comparative Examples 1 to 2 and 8, even when no tension was applied (Comparative Examples 2 and 8) or when a predetermined tension was applied, heat treatment at 300 ° C. treatment) (Comparative Example 1), the resulting flame-resistant fiber has no absorption peak A in the infrared absorption spectrum, and is inferior in high-temperature load resistance, fiber strength, and elastic modulus. It was found that the carbonization yield was also low.

However, as is clear from the comparison between Example 5 and Comparative Example 1, even when a predetermined tension is applied and heat treatment (flameproof treatment) is performed at 300° C., phosphate is added to the acrylamide polymer fiber. ^With _the ^addition _of It has been found to have a high strength, a high elastic modulus and a high carbonization yield, and to have excellent load bearing properties at high temperatures.

Moreover, as is clear from the results shown in Examples 1, 3 to 5, and 7 and Comparative Example 1, the obtained flame-resistant fiber has an absorption peak intensity ratio (I _A /I _B ) in the infrared absorption spectrum. It was found that the higher the , the higher the load bearing capacity, tensile strength, tensile modulus and carbonization yield at high temperatures tended to improve.

As described above, according to the present invention, it is possible to obtain a flame-resistant fiber derived from an acrylamide-based polymer and having excellent load resistance at high temperatures, high strength, high elastic modulus, and high carbonization yield. In addition, carbon fibers can be produced at a high yield by subjecting such flame-resistant fibers to a carbonization treatment.

Furthermore, since such carbon fibers are excellent in various properties such as lightness, strength, modulus of elasticity, and corrosion resistance, they are It can be widely used as a material for various applications such as materials for industrial applications, materials for robots, materials for communication equipment, medical materials, electronic materials, wearable materials, windmills, golf shafts, and sporting goods such as fishing rods. In addition, since the flameproof fiber obtained by the present invention is excellent in heat resistance and flame retardancy, it can be used not only as an intermediate raw material for carbon fiber, but also as a flameproof and heat insulating material, a spatter sheet, various filters, and the like. .

Claims (7)

Derived from an acrylamide polymer, an absorption peak A exists in the range of 1560 to 1595 cm ⁻¹ in the infrared absorption spectrum, and the intensity of the absorption peak A (I _A ) and the intensity of the absorption peak B at 1648 cm ⁻¹ ( I _B ), the flame-resistant fiber having a ratio (I _A /I _B ) of 0.5-10. 2. The flame-resistant fiber according to claim 1, wherein the absorption peak intensity ratio (I _A /I _B ) is 0.7-10. 3. A method for producing a carbon fiber, wherein the flame resistant fiber according to claim 1 or 2 is carbonized. While applying a tension of 0.07 to 200 mN/tex to the acrylamide polymer fiber, the absorption peak A existing in the range of 1560 to 1595 cm ^-1 in the infrared absorption spectrum of the resulting flame-resistant fiber under an oxidizing atmosphere. A flame-resistant fiber characterized by being subjected to heat treatment until the ratio (I _A /I _B ) of the intensity (I _A ) to the intensity (I _B ) of the absorption peak B at 1648 cm ⁻¹ reaches 0.5 to 10. manufacturing method. The acrylamide-based polymer fiber further contains at least one additive component selected from the group consisting of acids and salts thereof, and the heat treatment is performed at a temperature in the range of at least 260 to 450°C. The method for producing a flame-resistant fiber according to claim 4, characterized in that The acrylamide-based polymer fiber does not contain an additive component consisting of an acid, a salt thereof, or a mixture thereof , and the heat treatment is performed at a temperature in the range of at least 310 to 500°C. 5. The method for producing a flame-resistant fiber according to 4. a step of producing a flame-resistant fiber by the method according to any one of claims 4 to 6; and a step of carbonizing the flame-resistant fiber;
A method for producing carbon fiber, comprising:

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