JP2004183194A - Carbon fiber bundle, acrylonitrile-based precursor fiber to the carbon fiber and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carbon fiber capable of realizing excellent characteristics in various composite materials corresponding to their applications, to provide a precursor fiber to the carbon fiber, and to provide a method for producing the precursor fiber. <P>SOLUTION: A bundle of the carbon fiber contains 70 wt% or more of single fibers of which the each consists of the carbon fiber and has a ratio of a single fiber torsional strength to a single fiber torsional modulus of elasticity of ≥0.1. The acrylonitrile-based precursor fiber to the carbon fiber has such a total draw ratio and a size of crystalline region as to satisfy the inequalities: (size of crystalline region, in nm)≥0.92×(total draw ratio)+6; and (total draw ratio)≥6, wherein the size of crystalline region is obtained from reflection of (100)-surfaces of polyacrylonitrile. The method for producing the acrylonitrile-based precursor fiber to the carbon fiber comprises drawing the fiber in a wet-heat state at a draw ratio in a specified range, before densifying the fiber in a dry state. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a carbon fiber bundle used as a reinforcing fiber material in various composite materials, particularly a carbon fiber bundle excellent in strength development, an acrylonitrile precursor fiber for the carbon fiber, and a method for producing the same.

  BACKGROUND ART Conventionally, carbon fibers using acrylic fibers as precursors have been widely used as reinforcing fiber materials for high-performance composite materials for aerospace applications, sports and leisure applications due to their excellent mechanical properties. Further, as the use of carbon fiber has spread to industrial applications, further improvement in the performance of carbon fiber is required.

  In response to such demands, Patent Literature 1, Patent Literature 2, and Patent Literature 3 propose a method for improving the performance of a carbon fiber composite material by controlling the surface smoothness of carbon fibers.

  However, since carbon fibers are very thin with a diameter of less than 10 μm, the surface irregularities are very fine in spite of the extremely large curvature of the fiber surface.If the fiber cross section is not circular, the fiber surface has multiple curvatures. There is, and because the smoothness measured in the fine section is not necessarily uniform throughout the fiber, the surface smoothness represented by the average of the measured values may not be sufficiently reliable, In some cases, the relationship between the measured surface smoothness and the performance of the carbon fiber and the composite material did not always match.

  Further, Patent Document 3 proposes, as a method for obtaining high-strength carbon fibers, a technique in which a wet heat drawing ratio of precursor fibers obtained by a wet spinning method is the most preferable range of 2 times or less.

  However, when the conditions such as the polymer composition, the spinning solution solvent, and the spin bath conditions are different, it may not be possible to adapt to the various varieties being produced. Further, in this method, since the draw ratio before dry densification is low, if the productivity is not changed, the draw ratio after dry densification needs to be much larger than usual. In such a case, cutting of the entire yarn or cutting of the whole yarn may not be performed, but partial cutting of the yarn may occur, resulting in fluff and deterioration of quality, and deterioration in processability in the spinning and firing processes. Yes, it is not an excellent method for actual production.

  Patent Literature 4 proposes a technique for improving the torsional elasticity by adding a different element to the surface portion of a single fiber to create a region having lower crystallinity than the central portion of the single fiber.

However, there is no mention of the improvement of the torsional strength, and conversely, the incorporation of a different element may cause a decrease in the torsional strength.
JP-B-52-24130 JP-A-11-217734 JP-A-2000-160436 JP-A-9-170170

  It is an object of the present invention to provide a carbon fiber bundle, a precursor fiber thereof, and a method for producing the same, which can realize excellent characteristics in various composite materials according to applications.

  Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have reached the present invention.

  According to the present invention, there is provided a carbon fiber bundle comprising at least 70% by mass of a single fiber of a carbon fiber having a ratio of a single fiber torsional strength (GPa) to a single fiber torsional elasticity (GPa) of 0.1 or more. Is done.

  The carbon fiber bundle preferably contains 90% by mass or more of carbon fiber single fibers having a ratio of single fiber torsional strength (GPa) to single fiber torsional elasticity (GPa) of 0.09 or more.

  According to the present invention, there is provided an acrylonitrile-based precursor fiber for carbon fiber, wherein the total draw ratio and the crystal domain size obtained from the (100) reflection of polyacrylonitrile satisfy the following formula.

A spinning step of spinning an undiluted spinning solution containing a solvent and an acrylonitrile-based polymer dissolved in the solvent according to the present invention to obtain a coagulated yarn, a wet heat drawing step of wet-heat drawing the coagulated yarn, and an oil agent for treating the drawn yarn with an oil solution In the method for producing an acrylonitrile-based precursor fiber for carbon fiber, comprising a treatment step, a dry-densification step of drying and densifying the oil-treated yarn,
A method for producing an acrylonitrile-based precursor fiber for carbon fiber, characterized in that the value of the wet heat draw ratio is not more than the draw ratio at which the swelling degree of the wet heat drawn yarn reaches the maximum value or reaches saturation.

According to the present invention, a spinning step of spinning an undiluted spinning solution containing a solvent and an acrylonitrile-based polymer dissolved in the solvent to obtain a coagulated yarn, a wet heat drawing step of wet-heat drawing the coagulated yarn, and treating the drawn yarn with an oil agent An oil agent treatment step, a method for producing an acrylonitrile-based precursor fiber for carbon fiber having a dry densification step of drying and densifying the oil-treated yarn,
A method for producing an acrylonitrile-based precursor fiber for carbon fiber, characterized in that the value of the wet heat drawing ratio is equal to or less than the drawing ratio at which the average pore radius of the wet heat drawn yarn reaches the maximum value or saturation.

According to the present invention, a spinning step of spinning an undiluted spinning solution containing a solvent and an acrylonitrile-based polymer dissolved in the solvent to obtain a coagulated yarn, a wet heat drawing step of wet-heat drawing the coagulated yarn, and treating the drawn yarn with an oil agent An oil agent treatment step, a method for producing an acrylonitrile-based precursor fiber for carbon fiber having a dry densification step of drying and densifying the oil-treated yarn,
A method for producing an acrylonitrile-based precursor fiber for carbon fiber, characterized in that the value of the wet heat draw ratio is not more than the draw ratio at which the degree of fiber orientation immediately after dry densification reaches the maximum value or reaches saturation.

  In the method for producing an acrylonitrile-based precursor fiber for carbon fiber, it is preferable that the solvent is dimethylacetamide or dimethylformamide, and that the wet heat drawn yarn swelling degree when performing the wet heat drawing is 120% or less.

  According to the present invention, a carbon fiber bundle capable of realizing excellent properties in various composite materials according to the application and a precursor fiber suitable for the production thereof are provided, and furthermore, the precursor fiber is suitably produced. A possible manufacturing method is provided.

  The carbon fiber bundle of the present invention is a carbon fiber single fiber having a ratio of single fiber torsional strength to single fiber torsional elasticity (single fiber torsional strength (GPa) / single fiber torsional elastic modulus (GPa)) of 0.1 or more. Is 70 mass% or more.

  When the ratio of the single fibers having the ratio of 0.1 or more is less than 70%, the ratio of the carbon fiber single fibers having a low torsional strength to the torsional elasticity increases, and in the case of a composite material, the ratio of the single fibers to the complex stress increases. The strength is significantly reduced. From the same viewpoint, it is preferable that the short fiber of the carbon fiber having the above ratio of 0.09 or more contains 90% by mass or more. The larger the ratio of single fiber torsion strength (GPa) / single fiber torsional modulus (GPa) is 0.1 or more, the more preferable.

  Further, the present invention is an acrylonitrile-based precursor fiber for carbon fiber, wherein the total draw ratio and the crystal region size obtained from the (100) reflection of polyacrylonitrile satisfy the following expression. The total draw ratio referred to herein is a value obtained by multiplying a draw ratio for drawing a coagulated yarn before dry densification and a draw ratio after dry densification. The same applies to the value divided by.

  The acrylonitrile-based precursor fiber for carbon fiber can be suitably obtained by the production method of the present invention described below, and the carbon fiber of the present invention described above by firing the acrylonitrile-based precursor fiber for carbon fiber of the present invention. A bundle can be suitably obtained. When the above formula is satisfied, the carbon fiber bundle of the present invention can be suitably obtained, and the crystal region in the fiber, or the interface between the crystal region and the amorphous region is prevented from being broken by drawing, and graphite is fired during firing. It is possible to prevent the occurrence of defects in the crystal network plane and the vicinity thereof to significantly lower the carbon fiber performance.

  Hereinafter, the method for producing the carbon fiber bundle and the acrylonitrile-based precursor fiber for carbon fiber of the present invention will be described in detail.

  As the acrylonitrile-based polymer used for the acrylonitrile-based precursor fiber for carbon fiber of the present invention, a homopolymer of acrylonitrile and / or a copolymer with another monomer can be used. In this case, the acrylonitrile composition in the copolymer is preferably 90% by mass or more for the purpose of satisfactorily carbonizing the carbon fiber. Acrylonitrile is more preferably 95% by mass or more for the purpose of improving quality and performance.

  The copolymerization component monomer of the acrylonitrile-based polymer is not particularly limited. For example, methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, Acrylic esters such as hydroxypropyl acrylate; methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, n-hexyl methacrylate, cyclohexyl methacrylate, lauryl methacrylate, 2-methacrylic acid 2- Methacrylic esters represented by hydroxyethyl, hydroxypropyl methacrylate, diethylaminoethyl methacrylate, etc .; acrylic acid, methacrylic acid, maleic acid, itaconic acid, acrylamide, N-methyl Unsaturated monomers such as acrylacrylamide, diacetone acrylamide, styrene, vinyltoluene, vinyl acetate, vinyl chloride, vinylidene chloride, vinyl bromide, vinylidene bromide, vinyl fluoride and vinylidene fluoride; p-sulfophenyl methallyl ether , Methallylsulfonic acid, allylsulfonic acid, styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, and alkali metal salts thereof.

  As the copolymer component monomer of the acrylonitrile-based polymer, it is preferable to use a monomer having a carboxylic acid group or an acrylamide-based monomer for the purpose of promoting the cyclization reaction in the carbonization step. As such a monomer having a carboxylic acid group, methacrylic acid and itaconic acid are preferred. Acrylamide is preferably used as the acrylamide monomer. From the viewpoint of improving the solubility in a solvent and improving the denseness of the coagulated yarn, it is preferable that acrylamide is contained in the copolymer in an amount of 1% by mass or more. Therefore, in this case, the preferred range of acrylonitrile is necessarily 99% by mass or less. Regarding the denseness of the coagulated yarn, in particular, irrespective of wet spinning or dry-wet spinning, the coagulated yarn did not generate voids under almost all possible coagulation bath conditions, so it was determined according to the variety. It is possible to realize excellent carbon fibers under any coagulation bath conditions. The upper limit of the acrylamide content is not particularly limited, but is preferably less than 4% by mass.

  As a polymerization method of the acrylonitrile polymer used as a raw material, any of known polymerization methods such as solution polymerization and suspension polymerization can be employed. It is preferable to remove the unreacted monomer, polymerization catalyst residue, and other impurities from the polymerized copolymer as much as possible. Further, from the viewpoints of elongation in precursor fiber spinning and performance development of carbon fiber, the degree of polymerization of the copolymer is preferably such that the intrinsic viscosity [η] is 1.0 or more, particularly 1.4 or more. Is preferred. If the degree of polymerization is high, dissolution in a solvent or spinning tends to be difficult, so that the intrinsic viscosity [η] in a range not exceeding 4.0 is preferably used.

  Next, the acrylonitrile-based copolymer, preferably the above-mentioned copolymer that has been subjected to the impurity removal treatment, is dissolved in a solvent to obtain a spinning solution. As the solvent, an organic solvent such as dimethylacetamide, dimethylsulfoxide and dimethylformamide, and an aqueous solution of an inorganic compound such as zinc chloride and sodium thiocyanate can be used. Organic solvents are preferred because they do not contain metal in the fiber to be produced and the process is simplified. Among them, dimethylacetamide or dimethylformamide is more preferably used as the solvent, since the coagulated yarn and the wet heat drawn yarn have high densities.

  In order to obtain a dense coagulated yarn at the time of spinning, it is preferable to use a polymer solution having a polymer concentration of a certain level or more as a spinning solution. Specifically, the polymer concentration in the spinning dope is preferably in the range of 17% by mass or more, more preferably 19% by mass or more. Although it depends on the degree of polymerization of the polymer used, the polymer concentration is preferably in the range not exceeding 25% by mass in order to have appropriate viscosity and fluidity.

  The spinning method of the acrylonitrile-based precursor fiber for carbon fiber is preferably a wet spinning method or a dry-wet spinning method, but may be a dry spinning method. The wet spinning method and the dry-wet spinning method can be used depending on the application.

  In the spinning step, first, the spinning solution is discharged from a nozzle hole into a coagulation bath to form a coagulated yarn. Although the shape of the nozzle hole is not limited, a circular shape is generally used. The coagulation bath is first set to a condition having a sufficient margin for taking out the coagulated yarn to be produced. Then, the concentration and the temperature of the solvent contained in the coagulation bath are set so that the cross-sectional shape of the coagulated yarn becomes a shape corresponding to the use of the carbon fiber, such as a circle, a bean shape, and an oval shape.

  For the coagulation bath, an aqueous solution containing the solvent used for the spinning solution is preferably used. The concentration of the contained solvent is adjusted so that the spinning dope discharged from the nozzle hole becomes a coagulated yarn having a desired fiber diameter. Although it depends on the type of solvent used, for example, when dimethylacetamide or dimethylformamide is used, the concentration is preferably selected from 50 to 80% by mass.

  The temperature of the coagulation bath is preferably lower from the viewpoint of the denseness of the coagulated yarn. However, in the case of wet spinning, taking into account that when the temperature of the coagulation bath is lowered, the take-up speed of the coagulated yarn is reduced, and overall productivity is reduced, it is usually preferably 50 ° C. or lower, more preferably 20 ° C. or higher. Select in the range below 40 ° C.

  The coagulated yarn is subsequently subjected to wet heat drawing. The term “wet heat drawing” as used in the present invention refers to drawing in which the coagulated yarn is dried and densified. Accordingly, the wet heat draw ratio is defined by the ratio of the roll speed for performing dry densification to the roll speed for drawing the coagulated yarn, and the wet heat drawn yarn refers to the yarn immediately before dry densification. As the wet heat stretching method, stretching in the air, stretching in a liquid medium such as water, a solvent / water mixture, or glycerin and stretching in pressurized or normal pressure steam are combined in any order. Good. A relaxation step may be included on the way. However, it is preferable that the stretching ratio in warm water accounts for half or more from the viewpoint of completing the washing of the solvent contained before the drying and densification. For example, when the wet heat stretching ratio is 3 times, stretching in warm water is preferably 1.7 (= √3) times or more. Further, it is effective to make the hot water temperature as high as possible within a range in which the single yarns do not fuse together. From this viewpoint, the temperature of the stretching bath is preferably set to a high temperature of 70 ° C. or higher. In the case of multi-stage stretching of warm water, the final bath is preferably heated to a high temperature of 90 ° C. or higher. Prior to the wet heat stretching, the solvent may be washed in warm water. The present inventors have found that the swelling degree of the wet heat drawn yarn increases as the wet heat drawing ratio increases, and that the swelling degree becomes maximum or saturated at a certain drawing ratio. The inventors have also found that the average pore radius of the wet-heat drawn yarn and the fiber orientation degree of the yarn immediately after dry densification have the same relationship. These are such that when the wet heat draw ratio becomes a certain value or more, the degree of swelling and the average pore radius of the wet heat drawn yarn hardly change or become small, and it seems that the denseness is improved, but in reality, the drawing in which the orientation is not improved is performed. Indicating that the internal structure of the fiber had been destroyed. This destruction causes a defect of the carbon fiber and causes a decrease in performance. In particular, this remarkably appears in torsional physical properties, and greatly reduces torsional strength with respect to torsional elasticity. In addition, the yarn immediately after dry densification is a yarn at a stage where the wet heat drawn yarn is subjected to an oil agent application described later and a subsequent dry densification treatment, and thereafter is not drawn.

  In order to prevent such a phenomenon, at least one of the degree of wet-heat drawn yarn swelling, the average pore radius, and the degree of orientation immediately after dry densification is not more than the draw ratio at which the value reaches the maximum value or saturation. It is effective to select a suitable wet heat stretching ratio.

  The wet heat draw ratio at which the wet heat drawn yarn swelling degree, the average pore radius, and the fiber orientation degree of the yarn immediately after dry densification reach the maximum value or saturation, naturally depends on the conditions such as the polymer composition, spinning solution solvent, and spin bath conditions. Therefore, the present invention can be achieved by setting the wet heat stretching ratio after obtaining the maximum value of the above values or the wet heat stretching ratio reaching the saturation for each condition. It is preferable to measure each value of the wet heat stretch ratio at which the maximum value of each of the above values or the saturation is reached is 0.2 to 0.8 times. If the ratio is larger than 0.8, it may not be possible to accurately determine the maximum heat draw ratio or the wet heat draw ratio that reaches saturation. When it is smaller than 0.2 times, the number of measurement points increases and the measurement becomes complicated. The saturation point is defined as a point at which the absolute value of the gradient of the line connecting the measurement points when the horizontal axis represents the wet heat draw ratio and the vertical axis represents the measured value is 1/10 or less of the maximum gradient. .

  If the wet heat draw ratio is set to a lower value, the draw ratio after drying and densification needs to be increased, and the spinning process passability tends to be relatively poor. Therefore, for stable production, it may be necessary to lower the productivity such as reducing the spinning speed. From such a viewpoint, the wet heat stretching ratio is preferably 1.5 times or more.

  By setting the draw ratio before drying and densification in this way, the acrylonitrile-based precursor fiber for carbon fiber and carbon fiber of the present invention can be obtained, and the polymer composition, spinning solution solvent, wet or dry-wet, etc. It is possible to obtain carbon fibers capable of realizing excellent composite material characteristics irrespective of conditions such as spinning method, spinning bath conditions, fiber cross-sectional shape, single yarn fineness and total fineness.

  After wet heat drawing and washing, the fiber surface is subjected to an oil treatment by a known method. The type of the oil agent is not particularly limited, but an aminosilicone-based surfactant is preferably used. After this oil agent treatment, dry densification is performed. The temperature of this dry densification is chosen to be above the glass transition temperature of the fiber. The glass transition temperature may vary depending on the fact that the state of the fiber itself changes substantially from a water-containing state to a dry state, and a method using a heating roller having a temperature of about 100 to 200 ° C is preferable.

  After the drying and densification, it is preferable to provide a post-stretching step in which the precursor fiber has a desired fiber diameter by drawing again. After this, various methods can be used as long as the state of the fiber itself is not significantly changed, such as dry heat drawing using a high-temperature heating roller or a hot plate, or steam drawing by pressurized steam. It is also possible to carry out in multiple stages. The stretching ratio of the post-stretching step itself is the stretching performed before the dry densification and the post-stretching step performed after the dry densification, and as a whole, the post-stretching is performed so as to achieve a predetermined stretching ratio. The stretching ratio in the process is selected.

  The total draw ratio of the draw ratio before and after the dry densification is preferably 6 times or more, more preferably 8 times or more, from the viewpoint of obtaining carbon fibers having excellent fiber orientation and excellent performance. It is preferably 20 times or less, more preferably 15 times or less, from the viewpoint of favorably preventing yarn breakage and achieving excellent productivity.

  As described above, a spinning step of spinning a spinning stock solution containing a solvent and an acrylonitrile-based copolymer dissolved in the solvent to obtain a coagulated yarn, a wet-heat drawing step of wet-heat-drawing the coagulated yarn, and treating the drawn yarn with an oil agent In the method for producing an acrylonitrile-based precursor fiber for carbon fiber, which has a dry densification step of drying and densifying the oil-treated yarn, the wet heat drawing ratio is in the above-mentioned range, whereby an excellent carbon fiber An acrylonitrile-based precursor fiber can be obtained.

  This precursor fiber is fired by a known technique such as a flame-proofing step and a carbonization step, so that an acrylonitrile-based carbon fiber can be obtained.

  Hereinafter, the present invention will be described more specifically with reference to examples. The following embodiments are examples of the best embodiment of the present invention, but the present invention is not limited to these embodiments.

  Various physical properties of acrylonitrile-based precursor fiber and carbon fiber for carbon fiber used in describing the present invention, specifically, “swelling degree”, “average pore radius”, “degree of orientation”, “crystal” With respect to the “region size”, “strand strength, elastic modulus” and “torsion strength, elastic modulus”, evaluation methods thereof will be described in advance. In the examples, unless otherwise specified, the various physical property values and indices described are values measured and evaluated by the methods described herein. Normally, a plurality of samples are evaluated and the average value is adopted. Further, “%” and “parts” used in the description of the content rate, the concentration, and the blending amount represent mass% and mass parts, respectively.

(B) "Swelling degree"
The mass (W) of the swollen yarn after removing adhering water using a centrifugal dehydrator (at 1800 revolutions per minute for 10 minutes), washing it with boiling water and drying it at 80 ° C. for 16 hours with a hot air drier Is the value obtained by the following equation from the mass (Wo).

(B) “Average pore radius”
The yarn coming out of the stretching bath is collected and immersed sequentially in a solution in which the concentration of t-butanol is increased in seven stages with a mixed solution of t-butanol and deionized water, so that the fiber structure is not changed. Replace all the liquid inside with t-butanol. This is dried under vacuum (3 Pa or less) for 24 hours while cooling it to -20 ° C or less. About 0.2 g of the dried sample is precisely weighed and placed in a dilatometer. Next, the inside of the container is evacuated (7 Pa or less) using a mercury injection device, and then filled with mercury. Then, the measurement is performed using a porosimeter. The pressure is applied up to 400 MPa. Then, the pore radius r is calculated by the following equation. The average pore radius was a pore radius obtained from the pressure at the time when half of the total amount of mercury injected was injected.

(C) "Degree of orientation"
Hundreds of carbon fibers are hardened with a vinyl acetate / methanol solution to prepare a sample having a width of about 0.5 mm, and the sample is rotated by 360 ° on a plane perpendicular to X-rays to obtain the highest intensity in (002) reflection. Was calculated from the half width of the profile in the meridian direction including the following formula using the following formula. As the X-ray source, a CuKα ray (using a Ni filter) X-ray generator manufactured by Rigaku Corporation was used, and the output was 40 kV-100 mA.

(D) “Crystal region size”
The precursor fiber was cut into a length of 50 mm, 30 mg was precisely weighed and collected so that the sample fiber axes were exactly parallel to each other. Then, the thickness of 1 mm width was uniform using a jig for sample adjustment. The fiber bundle was prepared. The fiber sample bundle was impregnated with a vinyl acetate / methanol solution so as to be fixed so as not to lose its shape, and then fixed to a wide-angle X-ray diffraction sample table. As the X-ray source, a CuKα ray (using a Ni filter) X-ray generator manufactured by Rigaku Corporation is used, and a goniometer also manufactured by Rigaku Corporation is used. Was detected by a scintillation counter. The output was measured at 40 kV-100 mA. The crystal region size La was determined from the half width at the diffraction peak using the following equation (2).

(Where K is the Scherrer constant of 0.9, λ is the wavelength of the X-ray used (1.5418 ° because CuKα rays are used here), θ is the Bragg diffraction angle, and β ₀ is the true half-value width. , Β ₀ = β _E −β ₁ (β _E is an apparent half width, β ₁ is a device constant, and is 1.05 × 10 ⁻² rad here.)
(E) "Strand strength and elastic modulus"
It was measured by the method described in JIS R-7601. The strand was prepared by mixing “Epicoat 828 (trade name)” (manufactured by Yuka Shell Co., Ltd.) (100 parts), methylnadic anhydride (90 parts), dibenzylmethylamine (2 parts), and acetone (50 parts). After the resin was impregnated with the carbon fiber, it was kept at 50 ° C. for 1 hour, heated from 50 ° C. to 130 ° C. for 1 hour, and kept at 130 ° C. for 2 hours to cure.

(F) "Torsion strength and elastic modulus of single fiber"
Both ends of a single fiber sample having a length of about 2 mm were fixed to a mount, and one end of the mount was attached to a metal hook of a single fiber torsion test device, and a metal hook was suspended from the other end of the mount, and a groove was formed. The rotating cylinder is set at 8 mg / rotation at a constant speed, and the strain and the stress when the single fiber breaks are detected to determine the torsional strength (GPa) and torsional elasticity of the single fiber. The rate (GPa) was determined.

  The number of single fiber samples was 25 to 30, and the ratio of the single fiber torsional strength to the single fiber torsional modulus was calculated for each sample, and the ratio of single fibers having this ratio of 0.1 or more was calculated.

Examples 1 and 2, Comparative Examples 1 and 2
An acrylic copolymer copolymerized with 96% acrylonitrile, 1% methacrylic acid, and 3% acrylamide was dissolved in dimethylacetamide to prepare a spinning stock solution (polymer concentration 21%, stock solution temperature 60 ° C). This spinning stock solution was discharged into an aqueous solution of dimethylacetamide having a temperature of 40 ° C. and a concentration of 65% using a die having a diameter of 0.075 mm and a number of holes of 6000 to form a coagulated yarn.

  This coagulated yarn is stretched at a draw ratio of 0.5, such as 1.0 times, 1.5 times, and 2.0 times, at 70 ° C, 90 ° C under all 12 conditions up to 6.0 times. , 95 ° C. in three stages of hot water. At 6.5 times or more, the fiber was broken and could not be drawn stably. The swelling degree and the average pore radius of the wet heat drawn yarn are summarized in Table 1, and graphs are shown in FIGS. As a result, the swelling degree was maximum at a wet heat stretching ratio of 4.0, and the average pore radius was maximum at a stretching ratio of 4.5. Subsequently, the wet-heat drawn yarn under each condition was immersed in a 1% aqueous solution of an aminosilicone oil agent, and dried and densified with a heating roller at 180 ° C. When the degree of orientation of the dried and densified yarn was measured, the results were as shown in Table 1 and FIG. 3, and it was found that the degree of orientation of the dried and densified yarn reached saturation at a draw ratio of 4.5.

  From the above results, those in which the wet heat stretching ratio was set to 2, 3, 5, and 6 times were designated as Examples 1 and 2 and Comparative Examples 1 and 2, respectively. After each of the above-mentioned dry densifications, it is stretched in a pressurized steam of 0.25 MPa so that the stretching ratio becomes 12 times in total, and the single yarn fineness is 1.2 dtex, the total fineness is 7200 dtex, and the cross-sectional shape is substantially circular. An acrylonitrile-based precursor fiber was obtained. In Example 1, although there is no practical problem at all, the yarn before drawing in the pressurized steam becomes wide, and the ends of the yarn are broken and the yarn is sometimes rubbed due to rubbing with the drawing machine. Was done. The crystal region sizes of the acrylonitrile-based precursor fibers of Examples 1 and 2 and Comparative Examples 1 and 2 are as shown in Table 2. FIG. 4 shows the relationship between the crystal region size and the total stretching ratio.

The obtained precursor fiber was subjected to heat treatment at 230 to 260 ° C. in air so as to have a density of 1.35 g / cm ² to obtain a flame-resistant fiber. Subsequently, the fibers were finally treated at a maximum temperature of 1300 ° C. in a nitrogen atmosphere, and then subjected to electrolytic treatment in nitric acid to obtain carbon fibers. Table 3 summarizes the results of the strand strength, elastic modulus, torsional strength, and elastic modulus.

  In the examples, carbon fibers excellent in tensile strength and torsion properties were obtained. In addition, in comparison between Example 1 and Example 2, although the strength of Example 1 was slightly higher, the spinning stability of the precursor fiber was slightly inferior to Example 2 as described above.

Example 3, Comparative Example 3
The same spinning dope as in Example 1 was discharged into a dimethylacetamide aqueous solution having a temperature of 35 ° C. and a concentration of 60% using a die having a diameter of 0.075 mm and a number of holes of 3,000 to obtain a coagulated yarn.

  This coagulated yarn is stretched by 0.5 times in the same manner as in the previous example, and stretched in hot water in three stages of 70 ° C., 90 ° C., and 95 ° C. under all 12 conditions up to 6.0 times. Then, the wet heat drawn yarn under each condition was immersed in a 1% aqueous solution of an aminosilicone-based oil agent, and dried and densified with a heating roller at 180 ° C. When each data was taken, the maximum point of the degree of swelling, the maximum point of the average pore radius, and the saturation point of the degree of orientation of the dried and densified yarn were 5.0 times, 5.5 times and 5.5 times the wet heat draw ratio, respectively. It was twice. From these results, those with the wet heat stretching ratio set to 3.0 times and 6.0 times were designated as Example 3 and Comparative Example 3, respectively. Subsequently, the acrylonitrile-based precursor fiber having a single-fiber fineness of 1.2 dtex, a total fineness of 3600 dtex and a cross-sectional shape of empty bean is drawn by applying a draw ratio of 10 times in a pressurized steam of 0.25 MPa. Obtained. Table 2 shows the crystal region size of the obtained acrylonitrile-based precursor fiber. FIG. 4 shows the relationship between the crystal region size and the total stretching ratio.

  Firing and electrolytic treatment were performed under the same conditions as in Example 1 to obtain carbon fibers. Table 3 shows the results of the strand strength, elastic modulus, torsional strength, and elastic modulus. In the examples, carbon fibers excellent in tensile strength and torsion properties were obtained.

Example 4, Comparative Example 4
The same spinning dope as in Example 1 was discharged into a dimethylacetamide aqueous solution having a temperature of 35 ° C. and a concentration of 65% using a ferrule having a diameter of 0.075 mm and a number of holes of 6000 to obtain a coagulated yarn.

  This coagulated yarn is stretched by 0.5 times in the same manner as in the previous example, and stretched in hot water in three stages of 70 ° C., 90 ° C., and 95 ° C. under all 12 conditions up to 6.0 times. Then, the wet heat drawn yarn under each condition was immersed in a 1% aqueous solution of an aminosilicone-based oil agent, and dried and densified with a heating roller at 180 ° C. When each data was taken, the maximum point of the degree of swelling, the maximum point of the average pore radius, and the saturation point of the degree of orientation of the dried and densified yarn were 4.0 times, 4.5 times and 4.5 times the wet heat draw ratio, respectively. It was twice. From these results, those in which the wet heat stretching ratio was set to 3.0 times and 5.0 times were designated as Example 4 and Comparative Example 4, respectively. Subsequently, it is stretched in a pressurized steam of 0.25 MPa so that the stretching ratio becomes a total of 10 times, and an acrylonitrile-based precursor fiber having a single-fiber fineness of 0.8 dtex, a total fineness of 4800 dtex, and a substantially circular cross section is obtained. Obtained. Table 2 shows the crystal region size of the obtained acrylonitrile-based precursor fiber. FIG. 4 shows the relationship between the crystal region size and the total stretching ratio.

The obtained precursor fiber was subjected to heat treatment at 230 to 260 ° C. in air so as to have a density of 1.35 g / cm ² to obtain a flame-resistant fiber. Subsequently, the fibers were finally treated at a maximum temperature of 1400 ° C. in a nitrogen atmosphere, and then subjected to electrolytic treatment in nitric acid to obtain carbon fibers. Table 3 summarizes the results of the strand strength, elastic modulus, torsional strength, and elastic modulus. In the examples, carbon fibers excellent in tensile strength and torsion properties were obtained.

Example 5, Comparative Example 5
The same spinning dope as in Example 1 was discharged into the air once using a die having a diameter of 0.15 mm and a number of holes of 1500, and allowed to pass through the air having a diameter of about 5 mm. It was led to an aqueous solution to obtain a coagulated yarn.

  This coagulated yarn is stretched by 0.5 times in the same manner as in the previous example, and stretched in hot water in three stages of 70 ° C., 90 ° C., and 95 ° C. under all 12 conditions up to 6.0 times. Then, the wet heat drawn yarn under each condition was immersed in a 1% aqueous solution of an aminosilicone-based oil agent, and dried and densified with a heating roller at 180 ° C. When each data was taken, the maximum point of the degree of swelling, the maximum point of the average pore radius, and the saturation point of the orientation degree of the dried and densified yarn were all 4.0 times the wet heat draw ratio. From these results, those in which the wet heat stretching ratio was set to 3.0 times and 5.0 times were designated as Example 5 and Comparative Example 5, respectively. After the four yarns are joined, they are stretched in a pressurized steam of 0.25 MPa so that the draw ratio becomes 10 times in total, and an acrylonitrile-based fiber having a single-fiber fineness of 1.2 dtex, a total fineness of 7200 dtex, and a substantially circular cross section is used. A precursor fiber was obtained. Table 2 shows the crystal region size of the obtained acrylonitrile-based precursor fiber. FIG. 4 shows the relationship between the crystal region size and the total stretching ratio.

  The obtained precursor fiber was fired and electrolyzed under the same conditions as in Example 1 to obtain a carbon fiber. Table 3 summarizes the results of the strand strength, elastic modulus, torsional strength, and elastic modulus. In the examples, carbon fibers excellent in tensile strength and torsion properties were obtained.

Example 6, Comparative Example 6
An acrylic copolymer copolymerized with 98% acrylonitrile and 2% methacrylic acid was dissolved in dimethylformamide to prepare a spinning stock solution (polymer concentration 23%, stock solution temperature 60 ° C). This spinning stock solution was discharged into an aqueous solution of dimethylformamide having a temperature of 30 ° C. and a concentration of 50% using a die having a diameter of 0.075 mm and a number of holes of 6000 to obtain a coagulated yarn.

  This coagulated yarn is stretched by 0.5 times in the same manner as in the previous example, and stretched in hot water in three stages of 70 ° C., 90 ° C., and 95 ° C. under all 12 conditions up to 6.0 times. Then, the wet heat drawn yarn under each condition was immersed in a 1% aqueous solution of an aminosilicone-based oil agent, and dried and densified with a heating roller at 180 ° C. When each data was taken, the maximum point of the degree of swelling, the maximum point of the average pore radius, and the saturation point of the degree of orientation of the dried and densified yarn were all 3.5 times the wet heat draw ratio. From these results, those in which the wet heat stretching ratio was set to 2.0 times and 5.0 times were designated as Example 6 and Comparative Example 6, respectively. Subsequently, it is stretched in a pressurized steam of 0.25 MPa so that the stretching ratio becomes a total of 10 times, and an acrylonitrile-based precursor fiber having a single-fiber fineness of 0.8 dtex, a total fineness of 4800 dtex, and a substantially circular cross section is obtained. Obtained. Table 2 shows the crystal region size of the obtained acrylonitrile-based precursor fiber. FIG. 4 shows the relationship between the crystal region size and the total stretching ratio.

  The obtained precursor fiber was fired and electrolyzed under the same conditions as in Example 1 to obtain a carbon fiber. Table 3 summarizes the results of the strand strength, elastic modulus, torsional strength, and elastic modulus. In the examples, carbon fibers excellent in tensile strength and torsion properties were obtained.

Example 7, Comparative Example 7
The same spinning dope as in Example 1 was discharged into a dimethylacetamide aqueous solution having a temperature of 35 ° C. and a concentration of 65% using a die having a diameter of 0.045 mm and a number of holes of 6000, to obtain a coagulated yarn.

  This coagulated yarn is similarly stretched by a factor of 0.5, and subjected to wet heat stretching in three stages of 70 ° C., 90 ° C. and 95 ° C. in all 12 conditions up to 6.0 times, followed by The wet-heat drawn yarn under each condition was immersed in a 1.5% aqueous solution of an aminosilicone oil agent, and dried and densified with a heating roller at 180 ° C. When each data was taken, the maximum point of the degree of swelling, the maximum point of the average pore radius, and the saturation point of the degree of orientation of the dried and densified yarn were 3.5 times, 3.5 times and 4.0 times the wet heat draw ratio, respectively. It was twice. From these results, those in which the wet heat stretching ratio was set to 2.5 times and 5.0 times were designated as Example 7 and Comparative Example 7, respectively. Subsequently, the acrylonitrile-based precursor fiber having a single fiber fineness of 1.2 dtex, a total fineness of 7200 dtex, and a cross-sectional shape of bean-bean-shaped is drawn by applying a drawing ratio of 7 times between hot rolls heated to 180 ° C. Got. Table 2 shows the crystal region size of the obtained acrylonitrile-based precursor fiber. FIG. 4 shows the relationship between the crystal region size and the total stretching ratio.

  The obtained precursor fiber was fired and electrolyzed under the same conditions as in Example 4 to obtain a carbon fiber. Table 3 summarizes the results of the strand strength, elastic modulus, torsional strength, and elastic modulus. In the examples, carbon fibers excellent in tensile strength and torsion properties were obtained.

It is a graph which shows the relationship between wet heat drawing ratio and wet heat drawn yarn swelling degree in an Example. It is a graph which shows the relationship between wet heat draw ratio and an average pore radius in an Example. It is a graph which shows the relationship between wet heat stretching ratio and orientation degree in an Example. 4 is a graph showing a relationship between a total stretching ratio and a crystal region size in Examples.

Claims (7)

  A carbon fiber bundle comprising 70% by mass or more of carbon fiber single fibers having a ratio of single fiber torsional strength (GPa) to single fiber torsional elasticity (GPa) of 0.1 or more.   2. The carbon fiber bundle according to claim 1, wherein the carbon fiber bundle contains 90% by mass or more of carbon fiber single fibers having a ratio of single fiber torsional strength (GPa) to single fiber torsional elasticity (GPa) of 0.09 or more. 3. An acrylonitrile-based precursor fiber for carbon fiber, wherein a total draw ratio and a crystal region size obtained from (100) reflection of polyacrylonitrile satisfy the following expression.

A spinning step of spinning a stock spinning solution containing a solvent and an acrylonitrile-based polymer dissolved in the solvent to obtain a coagulated yarn, a wet heat drawing step of wet and heat drawing the coagulated yarn, an oil treatment step of oil treating the drawn yarn, A method for producing an acrylonitrile-based precursor fiber for carbon fiber, comprising a dry densification step of drying and densifying the oil-treated yarn,
A method for producing an acrylonitrile-based precursor fiber for carbon fiber, wherein the value of the wet heat draw ratio is not more than the draw ratio at which the wet heat drawn yarn swelling reaches the maximum value or saturation. A spinning step of spinning a stock spinning solution containing a solvent and an acrylonitrile-based polymer dissolved in the solvent to obtain a coagulated yarn, a wet heat drawing step of wet and heat drawing the coagulated yarn, an oil treatment step of oil treating the drawn yarn, A method for producing an acrylonitrile-based precursor fiber for carbon fiber, comprising a dry densification step of drying and densifying the oil-treated yarn,
A method for producing an acrylonitrile-based precursor fiber for carbon fiber, wherein the value of the wet heat draw ratio is not more than the draw ratio at which the average pore radius of the wet heat drawn yarn reaches the maximum value or saturation. A spinning step of spinning a stock spinning solution containing a solvent and an acrylonitrile-based polymer dissolved in the solvent to obtain a coagulated yarn, a wet heat drawing step of wet and heat drawing the coagulated yarn, an oil treatment step of oil treating the drawn yarn, A method for producing an acrylonitrile-based precursor fiber for carbon fiber, comprising a dry densification step of drying and densifying the oil-treated yarn,
A method for producing an acrylonitrile precursor fiber for carbon fiber, wherein the value of the wet heat draw ratio is not more than the draw ratio at which the fiber orientation degree immediately after dry densification reaches the maximum value or reaches saturation.   The carbon fiber according to any one of claims 4 to 6, wherein the solvent is dimethylacetamide or dimethylformamide, and the wet heat drawn yarn swelling degree when performing the wet heat drawing is 120% or less. A method for producing an acrylonitrile-based precursor fiber.

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