JP2005113305A - Flameproof fiber, carbon fiber and method for producing them - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a carbon fiber having excellent cost performance and a flameproof fiber suitable for obtaining the same and to provide methods for producing the flameproof fiber and the carbon fiber, which are suitable for producing them and have high productivity. <P>SOLUTION: The method for producing the flameproof fiber comprises heat-treating a precursor fiber in the presence of at least one kind of an organic compound at 50-400°C so that a weighting percentage represented by formula: weighting percentage=äWo×DR-Wp}/Wp×100 (Wo: flameproof fiber weight (g/m); Wp: precursor fiber weight (g/m); DR: total draw ratio in flameproof treatment) reaches 10-1,000%. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to flame-resistant fibers, carbon fibers, and methods for producing them. More specifically, the present invention relates to a carbon fiber excellent in cost performance, a flame-resistant fiber suitable for obtaining the carbon fiber, and a method for producing them at a low cost.

  Carbon fibers are used in various applications because of their excellent mechanical and electrical properties. In recent years, in addition to conventional golf clubs, fishing rods and other sports and aircraft applications, development of so-called general industrial applications such as automobile members, CNG tanks, seismic reinforcement of buildings, ship members, etc. has progressed. Performance is required.

  Industrially, carbon fibers are manufactured through flameproofing of precursor fibers such as polyacrylonitrile by heat treatment in air at 200 to 300 ° C. and carbonization by heat treatment in an inert atmosphere at 300 to 3000 ° C. At this time, nitrogen atoms, hydrogen atoms, and oxygen atoms contained in the precursor fiber are desorbed by thermal decomposition, and finally the carbon fiber has a carbon content of 95% or more. The carbon content of polyacrylonitrile most frequently used as a precursor fiber is around 68%, and the yield of carbon fiber based on the precursor fiber (hereinafter referred to as carbonization yield) is ideal in the case of Although it is around 70%, in the above-described industrial production method, elimination of carbon atoms also occurs, so that the actual situation is around 50%. Including the low carbonization yield, the raw material cost occupies a large proportion of the carbon fiber manufacturing cost, and how to reduce the raw material cost is important to reduce the carbon fiber manufacturing cost.

  On the other hand, several techniques have been proposed in order to improve the carbonization yield.

  For example, a technique is disclosed in which flame-resistant fibers are heat-treated in a non-oxidizing or oxidizing atmosphere prior to carbonization, and then carbonized for a short time (for example, Patent Document 1). Although the yield is certainly improved by such a technique, the value is below 60%, which is not a high level. In addition, according to the study by the present inventors, the present technology merely suppresses the weight loss by skipping the heat treatment at around 500 ° C. where the decomposition is most remarkable and then rapidly carbonizing. There is a problem that the structure of the obtained carbon fiber becomes insufficient and a decrease in elastic modulus is unavoidable.

Furthermore, a technique is disclosed in which sulfur is mixed with an acrylonitrile polymer, which is a raw material of polyacrylonitrile precursor fiber, and then spun and fired (for example, Patent Document 2). Although this technology suppresses oxidative degradation in flame resistance and can achieve a carbonization yield of over 60%, it deteriorates the stability of the spinning dope due to sulfur addition, and harmful such as H ₂ S and SO ₂ in the flame resistance process. There are problems such as the generation of reactive sulfur compounds, and it is difficult to apply as an industrial technique.

  In addition, a technique for making flame resistance in the presence of iodine gas is disclosed (for example, Patent Document 3). According to the present technology, an ideal carbonization yield of polyacrylonitrile precursor fiber of 70% can be obtained, but iodine gas is harmful, and this is a laboratory level technology as disclosed in the examples. I do not get.

A technique for flameproofing an organic compound or fluorine compound using an inorganic compound as described above is also disclosed (for example, Patent Document 4). According to the present technology, although a yield exceeding 50% is obtained, it is not a level exceeding 60%, and the yield improvement effect is not sufficient.
JP 51-75124 A JP 58-109625 A JP 2002-160912 A International Publication No. 02/095100 Pamphlet

  An object of the present invention is to provide a carbon fiber excellent in cost performance and a flame-resistant fiber suitable for obtaining the carbon fiber. Furthermore, it is providing the flame-resistant fiber and the manufacturing method of carbon fiber with high productivity suitable for manufacturing these.

  In order to solve the above problems, the present invention employs the following means. That is, in the presence of at least one kind of organic compound, the precursor fiber is heat-treated at 50 to 400 ° C. so that the weight increase rate represented by the following formula 1 is 10 to 1000%.

Increase rate = {Wo · DR−Wp} / Wp × 100 (1 formula)
Wo: Flame resistant fiber weight (g / m)
Wp: Precursor fiber weight (g / m)
DR: Total stretch ratio during flameproofing treatment Further, the method is a carbon fiber manufacturing method in which the flameproofed fiber obtained by the above method is heat-treated at 300 to 3000 ° C. in an inert atmosphere.

The surface spacing d ₀₀₂ corresponding to the 002 plane measured by X-ray diffraction is oxidized fiber is at least 0.351Nm.

  Furthermore, it is a polyacrylonitrile-based carbon fiber having a nitrogen content NC (% by weight) and a crystal size Lc (angstrom) satisfying the following formula.

0 <NC <−5.5 × Lc + 13.3 (2 formulas)
1.75 <Lc <2.40 (3 formulas)

  According to the flameproof fiber and carbon fiber production method of the present invention, the carbonization yield can be improved. Furthermore, the carbon fiber of the present invention is excellent not only in mechanical properties but also in electrical conductivity, and is suitable as a reinforcing fiber for a fiber-reinforced composite material.

  The present inventors have found that the carbonization yield can be significantly improved in the production of carbon fiber by using the flame-resistant fiber of the present invention obtained by heat treatment in the presence of an organic compound, and the present invention has been achieved. . Although the mechanism by which the carbonization yield is greatly improved by such a method is not necessarily clear, the carbon derived from the organic compound is incorporated into the precursor fiber in some form and is carbonized together with the precursor fiber in the carbonization step. Seems to be.

  In the prior art, since the precursor fiber is made into carbon fiber while being reduced in weight by making it flame resistant and carbonized, it is impossible to obtain a carbonization yield exceeding the carbon content of the precursor fiber. On the other hand, in the present invention, the carbon source is introduced from the outside of the fiber in the form of an organic compound in the flameproofing process and carbonized together with the fiber substrate, so that the carbonization yield can be greatly improved, and the organic material is cheaper than the precursor fiber. By applying the compound, the production cost of the carbon fiber can be reduced.

Oxidized fiber of the present invention, the surface spacing d ₀₀₂ corresponding to the 002 plane measured by X-ray diffraction is not less than 0.351Nm.

The interplanar spacing d ₀₀₂ corresponding to the 002 plane measured by X-ray diffraction corresponds to the average distance of the cyclized structure, and the wider d ₀₀₂ is, the more advantageous and more preferable the improvement of the carbonization yield. Is 0.353 nm or more, more preferably 0.355 nm or more. The upper limit is about 0.370 nm. If it is less than 0.351 nm, the effect of improving the yield becomes insufficient. The interplanar spacing is the diffraction angle corresponding to the peak of the 002 plane appearing in the vicinity of 2θ = 24 to 26 ° in the spectrum obtained by X-ray diffracting the flame resistant fiber using CuKα ray as an X-ray source and scanning in the equator direction. It can be obtained from the following four formulas from 2θ.

Interplanar spacing d ₀₀₂ (nm) = λ / {2 × sin θ} (Expression 4)
λ: wavelength of CuKα ray = 0.15418 nm
θ: Bragg angle Further, when polyacrylonitrile fiber is used as the precursor fiber, the degree of cyclization of the flame-resistant fiber of the present invention measured by an infrared spectrophotometer is preferably 10 to 100. The degree of cyclization is more preferably 12 to 98, and still more preferably 15 to 95. The degree of cyclization is the ratio of the absorption peak value corresponding to the nitrile group and the naphthyridine ring as defined by the following formula 5, and the larger the value, the less the nitrile group and the more the cyclization proceeds. If the degree of cyclization is less than 10, cyclization is insufficient and the carbonization yield may be reduced. Moreover, when it exceeds 100, cyclization will advance too much and the strand strength of the carbon fiber obtained may fall.

Degree of cyclization = I ₁₆₀₀ / I ₂₂₄₀ (5 formulas)
I ₁₆₀₀ : Absorption peak value corresponding to a naphthyridine ring of ₁₆₀₀ cm ^-1 I ₂₂₄₀ : Absorption peak value corresponding to a nitrile group of ₂₂₄₀ cm ^-1 The degree of cyclization is obtained by freeze-pulverizing flame-resistant fibers and diluting with KBr. It can be determined by measuring with an infrared spectrophotometer.

  The specific gravity of the flameproof fiber of the present invention is preferably 1.3 to 1.5, more preferably 1.32 to 1.45, and still more preferably 1.34 to 1.4. If it is less than 1.3, not only the heat resistance is insufficient and yarn breakage occurs in the continuous carbonization process, the operability is deteriorated, but the quality and quality of the obtained carbon fiber are deteriorated. If it exceeds 1.5, densification in the subsequent pre-carbonization step will be hindered, and the quality and quality of the resulting carbon fiber will deteriorate. Such specific gravity can be measured according to the method of JIS R7601.

  The flameproof fiber of the present invention is preferably derived from polyacrylonitrile fiber. This is because a flame-resistant fiber derived from polyacrylonitrile fiber using polyacrylonitrile as a precursor fiber has high strength and elongation and is suitable for obtaining a high-strength carbon fiber.

The polyacrylonitrile-based carbon fiber of the present invention preferably has a nitrogen content NC (% by weight) and a crystal size Lc (angstrom) satisfying the following formulas (2) and (3).
0 <NC <−5.5 × Lc + 13.3 (2 formulas)
1.75 <Lc <2.40 (3 formulas)
Here, the nitrogen content can be measured with a so-called CHN analyzer. The crystal size Lc corresponds to the peak of the 002 plane appearing in the vicinity of 2θ = 25 to 26 ° in the spectrum obtained by X-ray diffraction of the flame-resistant fiber using CuKα ray as an X-ray source and scanning in the equator direction. It can be obtained from the half width B _e (°) by the following six equations.

Crystal size Lc (nm) = λ / (B ₀ × COSθ) (6)
λ: X-ray wavelength = 0.15148 nm
B ₀ = (B _e ² −B ₁ ² ) ^1/2
(B ₁ is a device constant. Here, 1.046 × 10 ⁻² rad)
θ = Bragg angle The above formulas 2 and 3 are: 0 <NC <−5.5 × Lc + 12.9
1.75 <Lc <2.35
Is more preferable. 0 <NC <−5.5 × Lc + 12.6
1.75 <Lc <2.30
Is more preferable.

In the prior art, the nitrogen content and crystal size of the polyacrylonitrile-based carbon fiber can be controlled by the carbonization temperature and the carbonization time, but it is difficult to control independently, and the relationship between the two depends on the carbonization temperature and the carbonization time. It is decided almost unambiguously. In the present invention, a polyacrylonitrile fiber is used as a precursor fiber, and a carbon source can be introduced from the outside of the precursor fiber by adopting a production method as described later, so that it is the same as that of a conventional polyacrylonitrile-based carbon fiber. The nitrogen content under carbonization conditions can be greatly reduced. Thereby, while maintaining the strand strength and the elastic modulus, the resistivity can be reduced and the conductivity can be increased, which is suitable for an electronic device casing or the like that requires electromagnetic shielding characteristics. In this case, the resistivity is preferably 0.8 × 10 ^{−3 to} 1.6 × 10 ⁻³ (Ω · cm). From the viewpoint of conductivity, the lower the resistivity, the better. However, it can be appropriately controlled in view of cost.

Here, the resistivity is obtained by the following eight formulas by taking one single fiber from a carbon fiber bundle and measuring the electrical resistance value by a four-terminal method with a test length of 10 cm.
Resistivity (Ω · cm) = R × S / 50 (8 formulas)
Here, for R, different electrical fibers in the carbon fiber bundle are measured for electrical resistance values at n = 10, and the average value is defined as R (Ω). Moreover, the weight per 1 m and specific gravity of a carbon fiber bundle are measured, and the cross-sectional area S per single fiber is calculated from the following nine formulas.

Cross-sectional area S (cm ² ) = (A / 100) / B / C (9 formulas)
A: Weight of carbon fiber bundle per meter (g / m)
B: Specific gravity of carbon fiber bundle (g / cm ³ )
C: Number of single fibers of carbon fiber bundle (number)
Here, the specific gravity B can be measured according to the method described in JIS R7601. For example, ethanol is used as the reagent. Specifically, 1.0 to 1.5 g of carbon fiber bundles are collected and the weight D is measured, and then impregnated in ethanol with a known specific gravity (specific gravity ρ), and the carbon fiber bundle weight (E) in ethanol is calculated. Measure and calculate the specific gravity according to the following 10 equations.

Specific gravity B of carbon fiber bundle B = (D × ρ) / (DE) (10)
Further, the carbon fiber of the present invention may be a bundle-like carbon fiber in which the carbon fibers are bundled, preferably 1000 to 300000, more preferably 3000 to 100000, still more preferably 6000 to 50000, particularly A bundle-like carbon fiber in which 12000 to 24000 single fibers are bundled is preferable from the viewpoint of handleability. Such bundle-like carbon fibers preferably have a strand tensile strength of 3 GPa or more. More preferably, the strand tensile strength is 4 GPa or more, and further preferably the strand tensile strength is 5 GPa or more. If the strand tensile strength is less than 3 GPa, there may be a case where sufficient tensile strength is not obtained when a fiber-reinforced composite material is obtained. Such strand tensile strength is preferably as high as possible, but about 10 GPa is sufficient for the purpose of the present invention.

  Further, the bundle-like carbon fiber preferably has a strand tensile elastic modulus of 200 GPa or more. More preferably, the elastic modulus is 230 GPa or more, and still more preferably the elastic modulus is 270 GPa or more. If the strand elastic modulus is less than 200 GPa, the elastic modulus when the fiber-reinforced composite material is obtained may not be sufficient. The higher the tensile tensile modulus of the strand, the better. However, about 500 GPa is sufficient for the purpose of the present invention.

  Such strand tensile strength and tensile modulus can be determined by a tensile test conducted in accordance with JIS R7601 after impregnating a resin having the following composition into a carbon fiber bundle and curing at 130 ° C. for 35 minutes. The tensile modulus can be determined from the slope of the load-elongation curve obtained by the test.

(Resin composition)
• 3,4-epoxycyclohexylmethyl-3,4-epoxy-cyclohexane-carboxylate 100 parts by weight • Boron trifluoride monoethylamine 3 parts by weight • Acetone 4 parts by weight Next, production of flame-resistant fiber and carbon fiber of the present invention A method will be described.

  The method for producing flame-resistant fibers according to the present invention is such that the precursor fiber is heat-treated at 50 to 400 ° C. in the presence of at least one organic compound so that the weight increase rate represented by the following formula 1 is 10 to 1000%. Is introduced into the inside of the fiber to produce a flame-resistant fiber.

  The weight increase rate is defined as follows. Here, the flame resistant fiber weight Wo is measured as follows. First, about 1 g of flameproof fiber is sampled, the flameproof fiber is immersed in 10 g of water, and washed for 3 minutes while applying ultrasonic waves. Replace the water and repeat the same operation 3 times. Furthermore, the cleaning liquid is changed in the order of benzene, acetone, and ethanol, and the same operation is repeated three times each. The fire-resistant fiber after washing is air-dried at 20 ° C. for 12 hours and then weighed to make its weight Wo. By this method, the weight increase due to the organic compound supported inside the fiber can be measured.

Increase rate = {Wo · DR−Wp} / Wp × 100 (1 formula)
Wo: Flame resistant fiber weight (g / m)
Wp: Precursor fiber weight (g / m)
DR: Total stretch ratio during flameproofing treatment The higher the rate of weight increase, the higher the carbonization yield, preferably 20 to 500%, more preferably 30 to 200%. If it is less than 10%, the surface spacing of the flame-resistant fibers obtained is less than 0.351 nm, a sufficient carbonization yield improvement effect is not obtained, and even if the obtained flame-resistant fibers are carbonized, nitrogen content as described above The carbon fiber of the present invention having a low amount cannot be obtained. If it exceeds 1000%, it will be difficult to maintain the fiber form, and the strand strength and elastic modulus of the resulting carbon fiber will decrease.

  In the method for producing flame-resistant fibers of the present invention, the organic compound that coexists with the precursor fiber during the heat treatment may be any of gas, liquid, and solid, as long as the above-described weight increase rate can be achieved. It is not limited. From the viewpoint of easy contact with the fibers uniformly, it is preferably a gas or a liquid, and more preferably a liquid from the viewpoint of handling.

  Further, the higher the carbon content of the organic compound, the more preferable from the viewpoint of increasing the carbonization yield. Specifically, it is preferably 20% by weight or more, more preferably 40% by weight or more, and 60% by weight. More preferably, it is the above. Carbon content here means the weight ratio of the carbon atom which occupies in a compound, for example, in the case of methanol, it will be 38 weight%.

  As the organic compound, it is preferable to appropriately select a compound having a functional group having an affinity for the precursor fiber according to the kind of the precursor fiber. Among these, it is preferable that the organic compound contains at least one functional group selected from an amino group, an imino group, a nitrilo group, and a hydroxyl group in terms of introducing the organic compound into the inside of the fiber. More preferably, it is more preferably 3 or more.

  Specific examples of the organic compound include amines, alcohols, phenols, amino alcohols, and the like. More specifically, octylamine, dioctylamine, trioctylamine, ethanediamine, propanediamine, butanediamine, diethylenetriamine, triethylenetetramine, aminoethylpiperazine, 1,8-diazabicycloundecene (5,4,0 ) -7 and other aliphatic amines, aromatic amines such as aniline and toluidine, glycols such as ethylene glycol, diethylene glycol, triethylene glycol and glycerin, phenols such as phenol, cresol and aminophenol, monoethanolamine, diethanolamine and triethanol More preferred are amino alcohols such as amine and 2- (2-aminoethylamino) ethanol.

  The boiling point of the organic compound is preferably higher than the heat treatment temperature because it can be processed at normal pressure. Specifically, the boiling point is preferably 100 ° C. or higher, more preferably 150 ° C. or higher, and further preferably 200 ° C. or higher.

  Moreover, it is preferable from an economical viewpoint that this organic compound is water-soluble from the viewpoint of washing and removing the extra portion adhering to the outside of the fiber.

Further, the organic compound is preferably a compound having a solubility parameter δ of 5 to 20. Here, the solubility parameter δ is the solubility parameter δ = c ^ 1/2 where c is the cohesive energy density of the solvent.
The cohesive energy density c is defined by the following equation where ΔHv is the heat of evaporation per unit volume of the solvent, Vm is the molar volume, T is the temperature, and R is the gas constant.

c = (ΔHv−RT) / Vm
The solubility parameter δ of polyacrylonitrile suitable as a precursor fiber is about 15. The solubility parameter δ of the organic compound is in the specific range described above, and by making it a specific affinity, the carbon source can reach the inside of the single fiber of the polyacrylonitrile fiber. This is suitable for uniformly and rapidly supplying the organic compound to obtain the above-mentioned increase rate. The solubility parameter δ is more preferably 8-18, and even more preferably 10-16.

  When performing heat treatment in the presence of an organic compound, it is preferable that at least one oxidizing agent is present in addition to the organic compound. The presence of the oxidizing agent is preferable because it can promote introduction of the organic compound into the fiber. The oxidizing agent may be an inorganic or organic oxidizing agent. Examples of the inorganic oxidizing agent include inorganic acids such as nitric acid, hydrochloric acid, phosphoric acid and sulfuric acid, potassium permanganate, potassium dichromate and hydrogen peroxide. These oxidizing agents have a high oxidizing power and may induce degradation of the fibers themselves, and organic oxidizing agents are more preferable. The organic oxidant preferably has at least one structure selected from a nitro group, an N-oxyl structure, an N-oxide structure, and an N-hydroxy structure.

  Specific examples of those having a nitro group include nitrobenzene, nitrotoluene, nitroxylene, nitronaphthalene and the like. Specific examples of those having an N-oxyl structure include phthalimido-N-oxyl, 2,2,6,6-tetramethylpiperidine-1-oxyl, bis (2,2,6,6-tetramethylpiperidine-1- Preferred examples include oxyl) sebacate. Specific examples of those having an N-oxide structure include 4-picoline-N-oxide, isoquinoline-N-oxide, dipyridyl-N, N′-dioxide and the like. Specific examples of those having an N-hydroxy structure preferably include N-hydroxyphthalimide, N-hydroxysuccinimide, N-hydroxymaleimide and the like.

  In the present invention, heat treatment is performed in the coexistence with the above-described organic compound, and the organic compound is supported inside the fiber. In order to achieve the above increase rate, it is necessary to appropriately adjust the temperature and time of the heat treatment. Basically, the higher the temperature and the longer the time, the higher the weight increase rate. However, depending on the compound used, if the temperature is raised too much or if the time is too long, the fiber will decompose, and the weight gain rate may decrease.Considering the reactivity and affinity between the compound and the fiber The temperature and time for heat treatment should be set. The optimum values of the temperature and time during the heat treatment vary depending on the compound, and thus cannot be limited to one, but the heat treatment temperature needs to be set to 50 to 400 ° C. If the temperature is below 50 ° C., it is impossible to achieve the above-mentioned increase rate in a practical time. If the temperature is above 400 ° C., the fiber weight loss is remarkable, and the high carbonization yield intended by the present invention is obtained. Absent. The heat treatment temperature is more preferably 70 to 300 ° C, further preferably 90 to 200 ° C. The heat treatment time may be set to a time required to achieve the above-described increase / decrease rate, but is preferably a short time economically, more preferably 1 second to 300 minutes, and more preferably 5 seconds. More preferably, it is -120 minutes.

  In the present invention, the heat treatment in the coexistence with the organic compound may be performed separately from the step of making the precursor fiber flame resistant or may be performed simultaneously. For example, heat treatment in the presence of an organic compound may be performed, and then heat treatment may be performed in the air and flame resistance may be performed in the same manner as in the past, and heat treatment and flame resistance in the presence of the organic compound may be performed simultaneously. After heat-treating with flame resistance, heat treatment in the presence of the organic compound may be performed. In short, heat treatment in the presence of an organic compound may be performed before the carbonization step.

  From the viewpoint of simplifying the process, it is preferable to carry out the supporting heat treatment and flame resistance simultaneously. In order to achieve flame resistance, some kind of oxidant is necessary, and it is preferable to coexist the oxidant as described above.

  In the present invention, as the precursor fiber, polyacrylonitrile fiber, pitch fiber, phenol fiber, rayon fiber, cellulose fiber, and other fibers derived from natural lignin can be used. It is preferable to use polyacrylonitrile as a precursor fiber in that it has high strength and elongation and is suitable for obtaining a high-strength carbon fiber.

  Here, the polyacrylonitrile fiber may be 100% acrylonitrile, but is preferably a copolymer from the viewpoint of improving the flame resistance efficiency and from the standpoint of yarn production. As the copolymerization component, acrylic acid, methacrylic acid, itaconic acid and the like are preferably mentioned as so-called flame resistance promoting components, and more preferably, a part or all of these are neutralized with ammonia, acrylic acid, methacrylic acid, Or the copolymer which consists of an ammonium salt of itaconic acid is mentioned. From the viewpoint of improving the yarn production, methacrylic acid esters, acrylic acid esters, allyl sulfonic acid metal salts, methallyl sulfonic acid metal salts, and the like are preferably copolymerizable.

  The total amount of the above-mentioned copolymer is preferably 0 to 10 mol%, more preferably 0.1 to 6 mol%, and further preferably 0.2 to 2 mol%. If the amount of the copolymer is small, the yarn-forming property is lowered, and if the amount of the copolymer is large, the heat resistance is lowered and the fusion process is likely to occur in the subsequent flameproofing process. It is good to do.

  A method for polymerizing such a copolymer is not particularly limited, and a solution polymerization method, a suspension polymerization method, an emulsion polymerization method and the like can be applied.

  When spinning the acrylic copolymer, an organic or inorganic solvent can be used, but it is preferable to use an organic solvent, and specific examples include dimethyl sulfoxide, dimethylformamide, dimethylacetamide and the like.

  As described above, a spinning dope comprising an acrylic copolymer and a solvent is spun from a die by a wet spinning method, a dry wet spinning method, a dry spinning method, or a melt spinning method, preferably a wet spinning method or a dry wet spinning method. And introduced into a coagulation bath to coagulate the fiber.

  In the wet spinning method and the dry and wet spinning method, the surface roughness of the precursor fiber surface can be controlled by appropriately controlling the coagulation rate, the stretching method, and the like. For example, when the coagulation speed is increased, a coagulated fiber having a thick skin layer formed on the fiber surface and a small fibril unit constituting the fiber can be obtained, and the coagulated fiber is drawn by a method described later. A precursor fiber suitable for obtaining carbon fibers having a smooth surface and a surface area ratio of 1.0 to 1.2 is preferable. However, if the coagulation rate is too high, the internal structure of the coagulated yarn becomes coarse, and carbon fibers having high strand strength may not be obtained. Therefore, it is preferable to set the coagulation rate in consideration of both.

  In the present invention, the coagulation bath can contain a so-called coagulation promoting component, and the coagulation rate can be controlled by the temperature of the coagulation bath and the concentration of the coagulation promoting component. Specifically, the higher the coagulation bath temperature and the greater the amount of the coagulation promoting component, the faster the coagulation rate. As the coagulation accelerating component, a component that does not dissolve the acrylic copolymer and is compatible with the solvent used in the spinning dope can be used. Specifically, it is preferable to use water.

  After being introduced into a coagulation bath and coagulating the yarn, acrylic fibers are obtained through washing with water, stretching, application of oil, drying and the like. Moreover, it can also extend | stretch with steam after oil agent provision. Here, the solidified yarn may be stretched directly in a stretching bath without being washed with water, or may be stretched in a bath after removing the solvent by washing. Such stretching in a bath is usually performed in a single or a plurality of stretching baths whose temperature is adjusted to 30 to 98 ° C., and in these washing baths and stretching baths, inclusion of the solvent used in the spinning dope described above in an aqueous solution. The rate should be the upper limit of the content of the solvent in the coagulation bath.

  After the bath stretching, it is preferable to apply an oil agent made of silicone or the like to the yarn. Such a silicone oil agent is preferably a modified silicone and an amino-modified silicone having high heat resistance.

  The yarn stretched in the bath and provided with the oil agent is preferably dried by heating. It is efficient to carry out the drying treatment by bringing it into contact with a roll heated to 50 to 200 ° C. It is preferable to dry the yarn until the moisture content of the yarn is 1% by weight or less, thereby densifying the fiber structure.

  The precursor fiber used in the present invention is preferably a bundle-like precursor fiber, and the number of filaments per yarn is preferably 1,000 to 300,000, more preferably 3,000 to 100,000. More preferably, it is 6,000-50,000, Most preferably, it is 12000-24000.

  The single fiber fineness of the precursor fiber used in the present invention is preferably 0.6 to 30 dtex, more preferably 1 to 25 dtex, and further preferably 2 to 20 dtex. The larger the single fiber fineness, the larger the fiber diameter of the obtained carbon fiber, which can suppress buckling deformation under a compressive stress when used as a reinforcing fiber of a composite material, which is preferable from the viewpoint of improving the compressive strength.

  In the flameproof fiber manufacturing method of the present invention, in the flameproofing treatment step, the specific gravity of the flameproof fiber obtained is preferably 1.3 to 1.5, more preferably 1.32 to 1.45, still more preferably. It is preferable to heat-process until it becomes 1.34-1.4. If the specific gravity of the flameproof fiber is less than 1.3, thread breakage may occur in the subsequent carbonization step, and the process may not be possible. If it exceeds 1.5, the strand strength of the carbon fiber obtained may be reduced.

  When performing the heat treatment and flameproofing treatment under the organic compound described above while continuously supplying polyacrylonitrile fiber, the flameproofing treatment can be performed while stretching. In that case, the total stretching ratio is preferably 0.9 to 1.7, more preferably 1.0 to 1.6, and still more preferably 1.1 to 1.5. When the draw ratio is less than 0.9 or exceeds 1.7, the tensile strength and tensile elongation of the resulting flameproof fiber may be lowered.

  After the heat treatment in the presence of the organic compound, the extra organic compound adhering thereto can be removed. As a removal method, heating, drying treatment under reduced pressure, washing with a low boiling point solvent, or the like can be used. It is preferable from an economical point of view to remove excess organic compounds and further recover and reuse them.

  Carbon fiber can be produced by heat-treating and carbonizing the flame-resistant fiber obtained by the above-described method in an inert atmosphere at 300 to 3000 ° C. From the viewpoint of equipment, the carbonization treatment is performed by dividing it into a preliminary carbonization step of 300 ° C or higher and lower than 1000 ° C, a carbonization step of 1000 ° C or higher and lower than 2000 ° C, and a graphitization step of 2000 ° C or higher and 3000 ° C or lower. preferable. The maximum treatment temperature of the carbonization treatment can be selected according to the desired physical properties of the carbon fiber, and the graphitization step can be omitted.

  The carbonization treatment is preferably performed on a flameproof fiber under tension or stretching conditions. More preferably, the draw ratio is 0.8 to 1.3, and more preferably 0.9 to 1.2. If the draw ratio is less than 0.8, the resulting carbon fiber strand strength may be insufficient, and if it exceeds 1.3, fluff and yarn breakage increase, and the quality of the obtained carbon fiber is low. May be lower.

  The carbon fiber obtained by the above-described method can be subjected to electrolytic treatment for surface modification. As an electrolytic solution used for the electrolytic treatment, an acidic solution such as sulfuric acid, nitric acid, and hydrochloric acid, an alkali such as sodium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, or a salt thereof can be used as an aqueous solution. Here, the amount of electricity required for the electrolytic treatment can be appropriately selected depending on the carbon fiber to be applied.

  By such electrolytic treatment, the adhesion between the carbon fiber and the matrix resin can be optimized in the obtained composite material, and balanced strength characteristics can be expressed in the obtained composite material.

  Thereafter, a sizing treatment can be performed to impart convergence to the obtained carbon fiber. As the sizing agent, a sizing agent having good compatibility with the resin can be appropriately selected according to the type of resin used.

  The carbon fiber obtained in this way can be prepreg and then molded into a composite material. After forming a preform such as a woven fabric, it is combined by a hand lay-up method, a pultrusion method, a resin transfer molding method, etc. It can also be formed into a material. Further, it can be formed into a composite material by a filament winding method or by injection molding after chopped fiber or milled fiber.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely using an Example, this invention is not limited at all by these Examples. The production conditions of each example are summarized in Table 1, and the characteristics of the obtained flame-resistant fibers and carbon fibers are summarized in Tables 2 and 3.

Each measured value in this example was measured by the following method.
<Surface spacing d ₀₀₂ of flame resistant fiber>
20 mg of a fiber bundle cut to a length of 40 mm was precisely weighed and aligned so that the sample fiber axes were exactly parallel, and then impregnated with a thin collodion solution to prepare a prism sample having a uniform thickness of 1 mm. The obtained sample was measured using an X-ray diffractometer manufactured by Rigaku Corporation. The measurement was carried out using CuKα rays monochromated with a Ni filter as an X-ray source, an output of 40 KV-20 mA, and a scintillation counter as a counter. From the Bragg angle θ of the diffraction peak corresponding to the surface index (002) in the vicinity of 2θ = 24 to 26 °, the surface interval d ₀₀₂ was determined by the following four equations.

Interplanar distance d ₀₀₂ (nm) = λ / {2 × sin θ} (Expression 4)
λ: X-ray wavelength = 0.15418 nm
θ: Bragg angle <degree of cyclization of flame resistant fiber>
The flame-resistant fiber was freeze-pulverized to obtain a powder sample, and 2 mg was accurately weighed and thoroughly mixed with 300 mg potassium bromide powder (made by Merck, for FT-IR), and then pressure-molded to obtain a diameter of about 13 mm. Tablet samples were made. The obtained sample was measured using a Paragon 1000 infrared spectrophotometer manufactured by Perkin Elmer, Inc., and an absorption spectrum of 1000 cm ⁻¹ to 3000 cm ⁻¹ was obtained. From the obtained spectrum, an absorption peak value corresponding to 1600 cm ⁻¹ naphthyridine ring and an absorption peak value corresponding to 2240 cm ⁻¹ nitrile group were read and calculated according to the following formula (5).

Degree of cyclization = I ₁₆₀₀ / I ₂₂₄₀ (5 formulas)
I ₁₆₀₀ : Absorption peak value corresponding to a naphthyridine ring of ₁₆₀₀ cm ^-1 I ₂₂₄₀ : Absorption peak value corresponding to a nitrile group of ₂₂₄₀ cm ^-1 <specific gravity of flameproof fiber>
The specific gravity of the flameproof fiber was measured according to the method described in JIS R7601. As a reagent, ethanol (special grade manufactured by Wako Pure Chemical Industries, Ltd.) was used without purification. 1.0 to 1.5 g of flameproof fiber bundle was collected and dried at 120 ° C. for 2 hours. After the absolute dry weight (A) was measured, it was impregnated with ethanol having a known specific gravity (specific gravity ρ), and the flame-resistant fiber bundle weight (B) in ethanol was measured. The specific gravity was calculated according to the following formula (7).

Flameproof yarn specific gravity = (A × ρ) / (A−B) (Expression 7)
<Nitrogen content of carbon fiber>
It measured using Yanagimoto Seisakusho CHNCorder ModelMT-3. The sample weighed about 1-2 mg and used it. The combustion conditions were a sample decomposition furnace temperature of 930 ° C., an oxidation furnace temperature of 850 ° C., a reduction furnace temperature of 550 ° C., a helium flow rate of 180 ml / min, and an oxygen flow rate of 20 ml / min.
<Crystal size of carbon fiber>
20 mg of a fiber bundle cut to a length of 40 mm was precisely weighed and aligned so that the sample fiber axes were exactly parallel, and then impregnated with a thin collodion solution to prepare a prism sample having a uniform thickness of 1 mm. The obtained sample was measured using an X-ray diffractometer manufactured by Rigaku Corporation. The measurement was carried out using CuKα rays monochromated by a Ni filter as an X-ray source, an output of 40 KV-20 mA, and a scintillation counter as a counter. From the half-value width Be of the diffraction peak corresponding to the plane index (002) in the vicinity of 2θ = 25 to 26 °, the crystal size Lc was obtained by the following six equations.

Crystal size Lc (nm) = λ / (B0 × COSθ) (6)
λ: X-ray wavelength = 0.15148 nm
B0 = (Be ² −B1 ² ) ^1/2
(B1 is a device constant. Here, 1.046 × 10 ⁻² rad)
θ = Bragg angle <Resistivity measurement of carbon fiber>
The resistivity of the carbon fiber was determined by the following eight formulas.
Resistivity (Ω · cm) = R × S / 50 (8 formulas)
Here, R and S were determined by measurement as follows. First, one single fiber was taken out from the carbon fiber bundle, and the electrical resistance value was measured by a 4-terminal method with a test length of 10 cm. Similarly, for different single fibers, the electrical resistance value was measured at n = 10, and the average value was defined as R (Ω). Next, the weight and specific gravity per meter of the carbon fiber bundle were measured, and the cross-sectional area S per single yarn was calculated from the following nine formulas.

Cross-sectional area S (cm ² ) = (A / 100) / B / C (9 formulas)
A: Weight of carbon fiber bundle per meter (g / m)
B: Specific gravity of carbon fiber bundle (g / cm ³ )
C: Number of single fibers of carbon fiber bundle (number)
In addition, specific gravity followed the method of JISR7601. As a reagent, ethanol (special grade manufactured by Wako Pure Chemical Industries, Ltd.) was used without purification. After collecting 1.0 to 1.5 g of carbon fiber bundles and measuring the weight (D), the carbon fiber bundles were impregnated with ethanol having a known specific gravity (specific gravity ρ), and the flame-resistant fiber bundle weight (E) in ethanol was measured. . Specific gravity was calculated according to the following 10 formulas.

Flameproof fiber bundle specific gravity = (D × ρ) / (DE) (10)
<Measurement of carbon fiber strength and elastic modulus>
It measured according to JIS R7601. The test piece was prepared by impregnating carbon fiber with the following resin composition and curing conditions of heat treatment at 130 ° C. for 35 minutes.

Resin composition: 3,4-epoxycyclohexylmethyl-3,4-epoxy-cyclohexane-carboxylate (100 parts by weight) / 3 boron fluoride monoethylamine (3 parts by weight) / acetone (4 parts by weight)
As 3,4-epoxycyclohexylmethyl-3,4-epoxy-cyclohexane-carboxylate, ERL-4221 manufactured by Union Carbide Corporation was used.
[Example 1]
A copolymer consisting of 99.5 mol% of acrylonitrile and 0.5 mol% of itaconic acid was polymerized by a solution polymerization method using dimethyl sulfoxide as a solvent, and ammonia gas was blown until the pH reached 8.5, and itaconic acid was added. While neutralizing, an ammonium group was introduced into the acrylic copolymer to obtain a spinning dope having a copolymer component content of 22% by weight.

  This spinning dope was discharged into air at 40 ° C. using a spinneret having a diameter of 0.15 mm and a hole number of 3,000, passed through a space of about 4 mm, and then 35% dimethyl controlled at 3 ° C. A coagulated yarn was obtained by a dry and wet spinning method introduced into a coagulation bath made of an aqueous solution of sulfoxide.

  The coagulated yarn was washed with water, then stretched 3.5 times in warm water, and further an amino-modified silicone-based silicone oil was applied to obtain a stretched yarn.

  The drawn yarn is dried and densified using a 160 ° C. heating roller, and drawn in 0.3 MPa-G pressurized steam, so that the total draw ratio of yarn production is 13 times, and the single fiber fineness is 1 .1 dtex, 3000 polyacrylonitrile fibers were obtained.

  The obtained polyacrylonitrile fiber was combined into 12,000 single fibers, and heat-treated at 200 ° C. for 2 hours in a liquid phase composed of the following organic compound and oxidizing agent to obtain flame-resistant fibers. Polyacrylonitrile fiber was continuously supplied, and the total draw ratio during the flameproofing treatment was 1.2.

Organic compound: 50 parts by weight of o-toluidine Oxidizing agent: 50 parts by weight of o-nitrotoluene The flameproofed fiber was washed with water and dried at 280 ° C. for 5 minutes, and then heated in an inert atmosphere at a heating rate of 500 ° C./min. The temperature was raised from 300 ° C. to 1000 ° C., pre-carbonized, and then carbonized at a maximum temperature of 1400 ° C. in an inert atmosphere to obtain carbon fibers.

The physical properties of the obtained flame-resistant fiber and carbon fiber were measured by the method described above. The measurement results are summarized in Tables 2 and 3.
[Example 2]
Except for setting the heat treatment time in the liquid phase to 4 hours, flame-resistant fibers and carbon fibers were obtained in the same manner as in Example 1, and each physical property was evaluated. The measurement results are summarized in Table 2.
[Example 3]
Flame retardant fibers and carbon fibers were obtained in the same manner as in Example 1 except that the organic compound in the liquid phase used was changed to diethylene glycol and the heat treatment time in the liquid phase was changed to 1 hour, and each physical property was evaluated. The measurement results are summarized in Table 2.
[Example 4]
Flame retardant fibers and carbon fibers were obtained in the same manner as in Example 1 except that the organic compound in the liquid phase to be used was changed to diethanolamine and the heat treatment time in the liquid phase was changed to 1 hour, and each physical property was evaluated. The measurement results are summarized in Table 2.
[Example 5]
The organic compound in the liquid phase to be used was changed to 1,8-diazabicycloundecene (5,4,0) -7, and the heat treatment time in the liquid phase was changed to 1 hour. Then, flame-resistant fibers and carbon fibers were obtained, and each physical property was evaluated. The measurement results are summarized in Table 2.
[Comparative Example 1]
Polyacrylonitrile fibers obtained by the method described in Example 1 were combined to obtain 12,000 single fibers, and subjected to flame resistance treatment at 240 ° C. for 2 hours in air to obtain flame resistant fibers. Polyacrylonitrile fiber was continuously supplied, and the total draw ratio during the flameproofing treatment was 1.0.

This flame resistant fiber was carbonized by the method described in Example 1 to obtain carbon fiber.
The physical properties of the obtained flame-resistant fiber and carbon fiber were measured by the method described above. The measurement results are summarized in Tables 2 and 3.
[Comparative Example 2]
Flame retardant fibers and carbon fibers were obtained in the same manner as in Example 1 except that the organic compound in the liquid phase used was changed to only diethylene glycol and the heat treatment time in the liquid phase was changed to 1 hour, and each physical property was evaluated. . The measurement results are summarized in Table 2.
[Comparative Example 3]
In the same manner as in Example 1 except that the organic compound in the liquid phase used was changed to only diethylene glycol, the heat treatment temperature in the liquid phase was 240 ° C., and the heat treatment time was 0.5 hours, Each physical property was evaluated. The measurement results are summarized in Table 2.
[Comparative Example 4]
Flame-resistant fibers and carbon fibers were obtained in the same manner as in Example 3 except that the heat treatment temperature in the liquid phase was 240 ° C. and the heat treatment time was 0.5 hours, and each physical property was evaluated. The measurement results are summarized in Table 2.
[Example 6] Polyacrylonitrile fibers obtained by the method described in Example 1 were combined to make 12,000 single fibers, subjected to flame resistance treatment in air at 240 ° C for 2 hours, and then diethanolamine as an organic compound. Heat-treated at 210 ° C. for 0.5 hour in a liquid phase consisting of only flame-resistant fibers was obtained. Polyacrylonitrile fiber was continuously supplied, and the total draw ratio during the flameproofing treatment was 1.2.

This flame resistant fiber was carbonized by the method described in Example 1 to obtain carbon fiber.
The physical properties of the obtained flame-resistant fiber and carbon fiber were measured by the method described above. The measurement results are summarized in Table 2.
[Example 7]
Flame-resistant fiber was obtained in the same manner as in Example 6 except that the organic compound used was changed to a liquid phase containing only N-aminoethylethanolamine, the heat treatment temperature in the liquid phase was 140 ° C., and the heat treatment time was 0.5 hours. And carbon fiber was obtained and each physical property was evaluated. The measurement results are summarized in Table 2.
[Example 8]
The flameproof fiber and carbon fiber were changed in the same manner as in Example 6 except that the organic compound used was changed to a liquid phase containing only diethanoltriamine, the heat treatment temperature in the liquid phase was 140 ° C., and the heat treatment time was 0.5 hour. Each physical property was evaluated. The measurement results are summarized in Table 2.
[Example 9]
Flame-resistant fibers and carbon fibers were obtained in the same manner as in Example 6 except that the organic compound used was changed to a liquid phase containing only triethanoltetramine, the heat treatment temperature in the liquid phase was 140 ° C., and the heat treatment time was 0.5 hours. Each physical property was evaluated. The measurement results are summarized in Table 2.
[Example 10]
In the same manner as in Example 6, except that the organic compound used was changed to a liquid phase containing only N-aminoethyltetramine, the heat treatment temperature in the liquid phase was 140 ° C., and the heat treatment time was 0.5 hours, Carbon fiber was obtained and each physical property was evaluated. The measurement results are summarized in Table 2.
[Example 11] Carbon fibers were obtained in the same manner as in Example 1 except that the maximum carbonization temperature was changed to 1700 ° C. Table 3 summarizes the measurement results of each physical property.
[Comparative Example 5] Carbon fibers were obtained in the same manner as in Comparative Example 1 except that the maximum temperature of the carbonization treatment was changed to 1700 ° C. Table 3 summarizes the measurement results of each physical property.

  As shown in Tables 2 and 3, according to the flame-resistant fiber and carbon fiber production method of the present invention, it is possible to improve the carbonization yield, and the carbon fiber of the present invention has a conventional elasticity having the same degree of elasticity. It can be seen that the nitrogen content is low and the electrical conductivity is excellent compared to carbon fiber.

Claims (8)

A method for producing flame-resistant fibers, wherein the precursor fibers are heat-treated at 50 to 400 ° C. in the presence of at least one organic compound so that the weight increase rate represented by the following formula 1 is 10 to 1000%.
Increase rate = {Wo · DR−Wp} / Wp × 100 (1 formula)
Wo: Flame resistant fiber weight (g / m)
Wp: Precursor fiber weight (g / m)
DR: Total stretch ratio during flameproofing treatment The method for producing flame resistant fibers according to claim 1, wherein the organic compound has a carbon content of 20% or more. The method for producing a flame resistant fiber according to claim 1 or 2, wherein the organic compound contains at least one functional group selected from an amino group, an imino group, a nitrilo group, and a hydroxyl group. The method for producing flame-resistant fibers according to claim 1, wherein the heat treatment is performed in the presence of at least one oxidizing agent. The method for producing flame-resistant fibers according to claim 4, wherein the oxidizing agent is a compound having at least one of a nitro group, an N-hydroxy structure, an N-oxide structure, and an N-oxyl structure. The manufacturing method of the carbon fiber which heat-processes the flame resistant fiber obtained by the manufacturing method in any one of Claims 1-5 at 300-3000 degreeC by inert atmosphere. Oxidized fiber surface spacing d ₀₀₂ corresponding to the 002 plane measured by X-ray diffraction is not less than 0.351Nm. A polyacrylonitrile-based carbon fiber having a nitrogen content NC (% by weight) and a crystal size Lc (nm) satisfying the following formulas 2 and 3.
0 <NC <−5.5 × Lc + 13.3 (2 formulas)
1.75 <Lc <2.40 (3 formulas)