JP4979478B2 - Acrylonitrile-based carbon fiber precursor fiber bundle, carbon fiber bundle using the same, and method for producing the same - Google Patents

Description

  The present invention relates to an acrylonitrile-based carbon fiber precursor fiber bundle (hereinafter sometimes referred to as a precursor), which is a precursor of a carbon fiber bundle used as a reinforcing fiber material in various composite materials, and a method for producing the same, and The present invention relates to a carbon fiber bundle using the precursor and a method for producing the same.

  Carbon fibers have excellent specific strength and specific elastic modulus compared to other fibers, and are frequently used as reinforcing materials when obtaining composite materials due to their light weight and excellent mechanical properties. In particular, it is used as a carbon fiber reinforced composite material in fields such as various sports equipment and aerospace applications, and in recent years, there is an increasing demand for industrial applications. Therefore, in order to improve production efficiency, “addition of spinning equipment and firing equipment”, “multifilamentation of fiber bundles (increase in the number of monofilaments constituting the fiber bundle)”, “speeding up spinning speed and firing speed”, “one Responses such as “increase in the amount of windings” are essential.

In order for a carbon fiber reinforced composite material to exhibit stable physical properties, the structure and physical properties must be stable between the fiber bundles of the carbon fibers and in the longitudinal direction of the fiber. To that end, the precursor that is the precursor is required. The structure between the fiber bundles and in the fiber longitudinal direction needs to be stable. However, in response to the above-mentioned “increase in spinning speed and firing speed” and “increase in the amount of winding once”, structural spots and physical spots in the longitudinal direction of the fiber become very large, and the precursor structure becomes the longitudinal direction of the fiber. There may be a problem that the direction is not uniform.
In particular, the crystal structure derived from polyacrylonitrile (100) reflection is empirically found to be very effective for the physical properties of the carbon fiber, and unless the crystal structure is uniformly controlled, large spots are generated in the physical properties of the carbon fiber. It will be. The (100) indicates a crystal orientation (the same applies hereinafter).
When carbon fiber is used as a composite material, very long ones are required, so if there are uneven spots in the longitudinal direction of the fiber, the physical properties of the composite material using the carbon fiber will be fatally affected. There is a fear.

Therefore, control of the crystal structure of the precursor is very important in order to stably develop the carbon fiber properties. In patent document 1, when manufacturing a precursor, the crystal size of a precursor is controlled and the carbon fiber is strengthened by optimizing the distribution of the draw ratio in the drawing step performed before and after drying densification. Proposed method.
Patent Document 2 proposes a method of manufacturing ultrafine fibers with few birefringence spots by laser stretching PET (polyethylene terephthalate) or PP (polypropylene).
Patent Document 3 proposes a method of obtaining a fiber having a stable fineness by setting the actual draw ratio of poly (trimethylene terephthalate) within 10% of the predicted draw ratio.
JP 2004-183194 A JP 2003-166115 A Japanese translation of PCT publication No. 2003-526023

Patent Document 1 does not mention between the fiber bundles of the precursor and the unevenness in the fiber longitudinal direction, and the structure unevenness in the longitudinal direction of the fiber of the precursor is reduced by actually spinning under the conditions described in the document. Difficult to do.
In the method of stretching using the laser of Patent Document 2, there is a possibility that a portion where the laser hits reliably and a portion where it is difficult to hit due to the multifilament formation, thereby causing stretch spots, which is not suitable for multifilament formation.
In the method of Patent Document 3, the fineness is stabilized, but the structural spots in the fiber longitudinal direction may increase conversely. In addition, in the case of multifilamentation, if the same drawing cannot be applied to all filaments, a part of the filaments may break due to slight fluctuations in manufacturing conditions, which may cause a new problem of fluff generation. .

Thus, in order to stabilize the physical properties of the carbon fiber and further stabilize the physical properties of the composite material using the carbon fiber, a precursor having a small crystal structure spot in the fiber longitudinal direction is desired.
The present invention has been made in view of the above circumstances, and is a precursor in which crystal structure unevenness in the fiber longitudinal direction is reduced while being a multifilament (aggregate of long-fiber monofilaments), a method for producing the same, and the precursor An object of the present invention is to provide a carbon fiber bundle and a method for producing the same.

  In order to solve the above problems, an acrylonitrile-based carbon fiber precursor fiber bundle according to the present invention is a polyacrylonitrile-based carbon fiber precursor fiber bundle, which is 2θ of X-ray diffraction in a direction perpendicular to the longitudinal direction of the fiber bundle. When the measurement is performed, the average half-value width of the diffraction intensity peak corresponding to the polyacrylonitrile (100) reflection in the vicinity of 2θ = 17 ° is 0.60 ° or less, and the CV value obtained by the following formula (1) is 2 It is characterized by the following.

  In the above 2θ measurement, β measurement of X-ray diffraction was performed at an angle at which the diffraction intensity peak corresponding to polyacrylonitrile (100) reflection becomes the maximum intensity, and the half-value width of the diffraction intensity peak was defined as B (unit: °). In this case, the value of the degree of crystal orientation calculated using the following mathematical formula (2) is preferably 90% or more.

  When a diffraction intensity peak obtained by performing the β measurement of the X-ray diffraction is fitted by a least square method as a combined function of a Lorentz function and a Gauss function, a Gaussian with respect to the total of the Lorentz function area and the Gauss function area is obtained. The crystallization index represented by the area ratio of the function is preferably 0.15 or more.

  The present invention includes a spinning process for spinning a spinning stock solution containing an acrylonitrile-based polymer to obtain a coagulated yarn, a wet heat stretching process for stretching the coagulated yarn by wet heat, and a dry densification for drying and densifying the wet heat stretched fiber bundle. A process, and a steam stretching process for stretching the dried and densified fiber bundle by a steam stretching method, P is a stretching ratio in the steam stretching process, and Q is a maximum stretching ratio at which breakage occurs due to steam stretching. Provided is a method for producing an acrylonitrile-based carbon fiber precursor fiber bundle, wherein the steam pressure in the steam stretching step is set so as to satisfy the following mathematical formula (3).

It is preferable that the draw ratio P in the steam drawing step is 3 to 4 times.
It is preferable that the temperature of the fiber bundle immediately before coming into contact with the pressurized steam in the steam stretching step is 80 ° C. or higher and 120 ° C. or lower.
The present invention provides a carbon fiber bundle obtained by firing the acrylonitrile-based carbon fiber precursor fiber bundle of the present invention.
The present invention provides a process for producing an acrylonitrile-based carbon fiber precursor fiber bundle by the method of the present invention and a process for firing the obtained acrylonitrile-based carbon fiber precursor fiber bundle. Provide a method.

According to the present invention, an acrylonitrile-based carbon fiber precursor fiber bundle excellent in the uniformity of the crystal structure in the fiber longitudinal direction can be obtained.
The carbon fiber obtained by firing the acrylonitrile-based carbon fiber precursor fiber bundle of the present invention has small physical properties in the fiber longitudinal direction and excellent physical property stability.

[1] “Half-width of diffraction intensity peak corresponding to polyacrylonitrile (100) reflection” in the present invention is a value obtained by the following method.
That is, a fiber bundle to be measured is cut into a fiber length of 5 cm at an arbitrary position, aligned so that the fiber axes are exactly parallel, and then the width in the direction perpendicular to the longitudinal direction of the fiber is 1 mm. And a fiber bundle having a uniform thickness in a direction perpendicular to both the width direction and the longitudinal direction of the fiber. A sample fiber bundle to be measured is obtained by impregnating both ends of the fiber bundle with a vinyl acetate / methanol solution and fixing the fiber bundle so as not to lose its shape.
The sample fiber bundle is fixed to a wide-angle X-ray diffraction sample stage, and the diffraction intensity is measured by a transmission method to obtain a diffraction intensity profile (vertical axis: diffraction intensity, horizontal axis: 2θ (unit: °). A diffraction intensity peak in the vicinity of 2θ = 17 ° corresponding to polyacrylonitrile (100) reflection is detected, and the true half-value width is calculated from the half-value width (apparent half-value width) β _E of the peak using the following formula (4). Obtain β ₀ .

In Equation (4), β ₀ is a true half width (unit: °), β _E is an apparent half width (unit: °), and β ₁ is a device constant.
In this specification, a CuKα ray (using Ni filter) X-ray generator (trade name: Ru-200B, rotating anti-cathode X-ray generator) manufactured by Rigaku Corporation is used as an X-ray source, and the measurement of the diffraction intensity profile is Detection was performed with a scintillation counter using a Rigaku goniometer. The output was 40 kV-100 mA. The apparatus constant β ₁ is 0.57 ° (1.05 × 10 ⁻² rad).

The “average value of the half width of the diffraction intensity peak corresponding to the polyacrylonitrile (100) reflection” in the present invention is an average value of a plurality of sample fiber bundles collected at different positions in the fiber longitudinal direction. That is, when producing sample fiber bundles, 10 sample fiber bundles are collected at intervals of 0.1 m, 10 at 1 m intervals, and 10 at 10 m intervals in the longitudinal direction of the fiber bundle to be measured. Then, the 30 sample fiber bundles are measured by the above-described method, and an average value of the half width (true half width β ₀ ) is calculated from these measurement results.
In addition, when there are too many filaments constituting the fiber bundle to be measured and XRD measurement cannot be performed at once, the filaments are divided into appropriate numbers within the range of 2 to 3000, and The diffraction intensity profile is measured by the method to find the half width, and the average value of these is calculated.

[2] The CV value (unit:%) in the present invention is a value that represents the degree of crystal size unevenness in the longitudinal direction of the fiber bundle, and is a value obtained by the following method.
First, by the method described in [1], the “half-value width (true half-value width β ₀ ) of diffraction intensity peak corresponding to polyacrylonitrile (100) reflection” is obtained for the 30 sample fiber bundles. The average value (unit: °) and standard deviation of the half-value width (true half-value width β ₀ ) and the standard deviation are obtained from the individual measurement results, and the CV value is obtained by the equation (1).
If there are too many filaments constituting the fiber bundle to be measured and XRD measurement cannot be performed at once, the filaments are divided in the same manner as in the above [1], and each of them is measured by the above method. Then, the half width (true half width β ₀ ) is obtained, and the CV value is obtained using the average value and the standard deviation.

[3] The “degree of crystal orientation” in the present invention is a value obtained by the following method.
First, a sample fiber bundle for measurement is prepared in the same manner as in [1], and β measurement of X-ray diffraction is performed on the sample fiber bundle. X-ray diffraction β measurement is a method of measuring diffraction intensity while rotating a sample fiber bundle 360 ° on a plane perpendicular to X-rays. Specifically, first, 2θ measurement in the direction perpendicular to the fiber direction is performed on the acrylonitrile-based carbon fiber precursor fiber bundle to obtain a diffraction profile in the vicinity of 2θ = 17 ° corresponding to polyacrylonitrile (100) reflection. Then, the scintillation counter is fixed at an angle position of 2θ, which is the highest peak intensity in the profile, and then the holder fixing the sample fiber bundle is rotated 360 ° on a plane perpendicular to the incident X-ray. While measuring the diffraction intensity. The full width at half maximum B (unit: °) of the diffraction intensity peak is obtained, and the degree of crystal orientation (unit:%) is obtained from the mathematical formula (2). The half-value width B here is a true half-value width, and is obtained by the above mathematical formula (4).
The crystal orientation degree is measured by taking 10 sample fiber bundles at intervals of 0.1 m, 10 pieces at 1 m intervals, and 10 sample fiber bundles at 10 m intervals in the longitudinal direction of the fiber bundle to be measured. The degree of crystal orientation is determined for each bundle, and the average value thereof is calculated. This average value is defined as the “crystal orientation degree” in the present invention.
In addition, when the number of filaments constituting the fiber bundle to be measured is too large, it is divided in the same manner as in the above [1], and the degree of crystal orientation is obtained for each by the above method, and the average value thereof is calculated. And

In this specification, the apparatus used for the measurement of “degree of crystal orientation” is the same as the measuring apparatus described in [1] above, and the output is 40 kV-100 mA. The device constant β ₁ is the same as [1] above.

[4] The “crystallization index” in the present invention is a value determined by the following method.
First, a sample fiber bundle for measurement is prepared in the same manner as in [1], and β measurement of X-ray diffraction is performed on the sample fiber bundle in the same manner as in [3].
The obtained diffraction intensity peak corresponding to polyacrylonitrile (100) reflection having a peak top in the vicinity of β = 180 ° is a mixture of crystal part and amorphous part diffraction.
This diffraction intensity peak is assumed to be a composite function of a Gaussian function, which is a typical diffraction pattern of a crystal part, and a Lorentz function, which is a typical diffraction pattern of an amorphous part. The crystallization index that is an index of the degree of crystal orientation is calculated. A higher value means higher crystallinity.
Specifically, the diffraction intensity peak is cut out in a section of β = 90 to 270 °, and fitting is performed by the least square method so that the values of all the positions, intensities, and widths of the respective functions are changed. Then, the area of each function is calculated for the cut out section, and the ratio of the area of the Gaussian function to the sum of the areas of both is defined as the crystallization index.
The analysis of the crystallization index was performed using a diffraction profile of β measurement measured to determine the degree of crystal orientation. That is, the crystallization index was determined for each of the 30 sample fiber bundles, and the average value thereof was calculated. This average value is taken as the value of “crystallization index” in the present invention.
In addition, when the number of filaments constituting the fiber bundle to be measured is too large, it is divided in the same manner as in the above [1], and the crystallization index is obtained by the above method for each, and the average value thereof is calculated. And

<Manufacturing method>
Hereinafter, the manufacturing method of the acrylonitrile-type carbon fiber precursor fiber bundle (precursor) of this invention is demonstrated.
[Spinning process]
First, a spinning solution containing an acrylonitrile polymer is discharged into a spinning bath to obtain a coagulated yarn.

  As the acrylonitrile-based polymer, homopolymers of acrylonitrile and / or copolymers with other monomers can be used. In the case of a copolymer, the content of a structural unit derived from acrylonitrile is preferably 90% by mass or more among all the structural units constituting the copolymer for the purpose of good carbonization. The mass% or more is more preferable.

Other monomers that can be copolymerized with acrylonitrile are not particularly limited. For example, acrylic acid esters represented by methyl acrylate and ethyl acrylate; methacrylic acid represented by methyl methacrylate and ethyl methacrylate Esters; unsaturated monomers represented by acrylic acid, methacrylic acid, maleic acid, itaconic acid, acrylamide, styrene, vinyltoluene, etc .; methallylsulfonic acid, allylsulfonic acid, styrenesulfonic acid, and alkali metal salts thereof Is mentioned. These may be one kind or a combination of two or more kinds.
As another monomer copolymerizable with acrylonitrile, a monomer having a carboxylic acid group or acrylamide is preferably used for the purpose of promoting the cyclization reaction in the carbonization step. As the monomer having a carboxylic acid group, methacrylic acid and itaconic acid are preferable. From the viewpoint of improving solubility in a solvent, it is preferable that 1% by mass or more of a structural unit derived from acrylamide is included in all the structural units constituting the acrylonitrile-based polymer, and 1.5% by mass or more is more preferable. preferable.

The acrylonitrile-based polymer can be obtained by a known polymerization method such as solution polymerization or suspension polymerization. It is preferable to subject the reaction product containing the acrylonitrile-based polymer obtained by polymerization to a treatment that removes unreacted monomers, polymerization catalyst residues, and other impurities as much as possible.
Further, from the viewpoints of stretchability when spinning, performance of carbon fiber, and the like, the degree of polymerization of the acrylonitrile-based polymer is preferably 1.0 or higher, more preferably 1.4 or higher, as the intrinsic viscosity [η]. However, those having a limiting viscosity [η] not exceeding 2.0 are usually used.

The above acrylonitrile-based polymer is dissolved in a solvent to obtain a spinning dope. As the solvent, organic solvents such as dimethylacetamide, dimethylsulfoxide, dimethylformamide, and aqueous solutions of inorganic compounds such as zinc chloride and sodium thiocyanate can be used. An organic solvent is preferable in that the fiber to be produced does not contain a metal and the process is simplified. Of the organic solvents, it is more preferable to use dimethylacetamide as a solvent in that a coagulated yarn having high density can be obtained.
When the spinning dope is spun, in order to obtain a dense coagulated yarn, the concentration of the acrylonitrile polymer in the spinning dope is preferably 17% by mass or more, and more preferably 19% by mass or more. The upper limit of the acrylonitrile-based polymer concentration depends on the degree of polymerization of the acrylonitrile-based polymer to be used, but in order to obtain a spinning dope having an appropriate viscosity and fluidity, a range not exceeding 25% by mass is usually preferred.

The spinning method for spinning the spinning dope to obtain a coagulated yarn may be a wet spinning method or a dry wet spinning method. Usually, a wet spinning method is used for higher productivity.
In the spinning process in the wet spinning method, first, the spinning solution is discharged into a coagulation bath from a nozzle hole having a circular cross section to obtain a coagulated yarn. Although there is no restriction | limiting in particular about the number of nozzle holes, Generally the nozzle which has 2000-50000 holes is used. If the diameter of the nozzle hole is too large, coagulation spots are generated inside and outside the fiber when discharged into the coagulation bath, and if it is too small, the coagulation bath runs out with only a little stretching. .10 mm is preferable, and 0.45 to 0.80 mm is more preferable.
For the coagulation bath, an aqueous solution containing a solvent used in the spinning dope is preferably used. The concentration of the solvent in the coagulation bath is adjusted so that the spinning dope discharged from the nozzle hole becomes a coagulated yarn having a desired fiber diameter. The concentration of the solvent depends on the type of the solvent to be used. For example, when dimethylacetamide is used, 50 to 80% by mass is preferable, and 60 to 70% by mass is more preferable.
If the temperature of the spinning dope immediately before being discharged into the coagulation bath is too high, the polymers cross-link to each other to induce high-temperature gelation, and if it is too low, the viscosity increases and spinning becomes impossible. More preferably, it is 50-70 degreeC.
The temperature of the coagulation bath is preferably lower from the viewpoint of the density of the coagulated yarn. However, in the case of wet spinning, if the temperature of the coagulation bath is lowered too much, the take-up speed of the coagulated yarn is lowered and the overall productivity is lowered, so that it is usually 50 ° C. or less, more preferably 20 ° C. The temperature is in the range of 40 ° C. or lower.

[Wet heat stretching process]
Next, the coagulated yarn is stretched by wet heat. Specifically, the coagulated yarn is drawn in a drawing bath. The coagulated yarn is introduced into the drawing bath in the form of a fiber bundle in which a plurality of single yarns (filaments) are assembled. The number of single yarns constituting one fiber bundle is not particularly limited, but is preferably 1000 to 50000, and more preferably 3000 to 25000.
Water is mainly used for the stretching bath. It is effective to set the temperature of the drawing bath as high as possible as long as the single yarns of the coagulated yarn are not fused to each other. From this viewpoint, the temperature of the stretching bath is preferably 60 ° C. or higher. In the case of multistage stretching, the final bath is preferably 90 ° C. or higher. There is no particular upper limit on the temperature of the stretching bath.
The wet heat draw ratio is determined as the ratio of the roll speed at which drying densification is performed after wet heat draw to the roll speed at which the coagulated yarn is taken up. If the wet heat draw ratio is too high, the internal structure of the fiber tends to be destroyed. This destruction causes a defect of the carbon fiber and causes a decrease in the carbon fiber performance. In order to prevent such destruction of the fiber internal structure, it is preferable to reduce the wet heat draw ratio. In that case, in order not to reduce the productivity, it is necessary to increase the draw ratio after the drying and densification, so that the passability of the spinning process is deteriorated, and the spinning speed is decreased for the stability of the spinning process. On the other hand, productivity may be reduced. For these reasons, the wet heat draw ratio is preferably 1.5 to 6 times, and more preferably 2 to 5 times.

[Oil agent treatment process]
The fiber bundle after wet heat drawing may be washed as necessary and then subjected to an oil agent treatment by a known method. For example, the fiber bundle is immersed in an aqueous solution containing an oil agent to bring the fiber surface into contact with the oil agent. Although the kind of oil agent is not specifically limited, Amino silicone type surfactant is used suitably.

[Drying densification process]
Thereafter, the fiber bundle is heated and dried and densified. The drying densification temperature is selected from temperatures exceeding the glass transition temperature of the fiber. Substantially, the glass transition temperature may change due to the state of the fiber bundle itself changing from a water-containing state to a dry state, so that the fiber bundle is brought into contact with a heating roller having a temperature of about 100 to 200 ° C. Dry densification is preferably performed.

[Steam stretching process]
In the present invention, a steam stretching method of stretching in pressurized steam is used as the stretching method after drying and densification. The steam stretching method is preferable in that the movable state of the molecular chain in the fiber can be increased due to the plasticizing effect of water.
The draw ratio P in the steam drawing step is determined as the ratio of the speeds of the rolls before and after the steam drawing machine. The total draw ratio obtained by combining the draw ratio in the wet heat draw process and the draw ratio P in the steam draw process is obtained by multiplying the values of both draw ratios.
If the total draw ratio is too low, the orientation of the fiber bundle becomes insufficient and the performance of the carbon fiber bundle may be deteriorated. On the other hand, if it is too high, yarn breakage tends to occur, which is not preferable in production. From these viewpoints, the total draw ratio is preferably 5 to 20 times, and more preferably 7 to 15 times.
The stretching ratio P in the steam stretching process is preferably set according to the stretching ratio in the wet heat stretching process so that the total stretching ratio is in a preferable range. The draw ratio P in the steam drawing step is, for example, preferably in the range of 2 to 5 times, more preferably in the range of 3 to 4 times.

By varying the steam pressure in the steam drawing step, the maximum draw ratio Q at which the fiber bundle breaks due to steam drawing changes. That is, when the fiber bundle after drying and densification is stretched in pressurized steam at a constant pressure, if the stretch ratio is increased, the fiber bundle breaks when a certain stretch ratio is reached. The draw ratio when such breakage occurs is referred to as the maximum draw ratio Q. If the steam pressure is too high or too low, the maximum draw ratio Q becomes small.
In the present invention, the draw ratio P (that is, the set draw ratio P) actually performed in the steam drawing step is smaller than 0.4 times the maximum draw ratio Q (that is, P / Q <0.4). It is preferable to set the steam pressure so as to be, more preferably 0.35 times or less.
If P / Q is 0.4 or more, spots with different fiber plasticization states depending on the location of the fiber bundle, and as a result, stretch spots may occur, resulting in structural spots in the fiber longitudinal direction.
On the other hand, if the P / Q is too low, the orientation state in the fiber becomes insufficient, and there is a possibility that the graphite structure will not be sufficiently developed when the carbon fiber is fired later. Is preferably set to be 1 or more, and more preferably, P / Q is 0.2 or more.
Also, if the steam pressure is too low, the plasticizing effect of water cannot be fully utilized, and if it is too high, the steam properties become unstable, so that the steam pressure is 170 kPa to 350 kPa for smooth stretching. It is preferable that it is 250 kPa or more and 300 kPa or less. When the steam pressure is less than 170 kPa or more than 350 kPa, the maximum draw ratio Q is remarkably lowered, so that stretch spots are likely to occur in the fiber longitudinal direction.

The temperature of the fiber bundle immediately before contacting with the pressurized steam is preferably 80 ° C. or higher and 120 ° C. or lower, more preferably 90 ° C. or higher and 100 ° C. or lower. Therefore, after the drying densification step, the fiber bundle is cooled by air cooling, for example, as necessary.
If the temperature of the fiber bundle immediately before coming into contact with the pressurized steam is less than 80 ° C., a desired stretched state may not be obtained because the fiber bundle is stretched before the temperature is fully raised in the steam stretching machine. On the other hand, if the temperature exceeds 120 ° C., the temperature of the fiber bundle is too high, and water that causes a plasticizing effect in the steam drawing machine may not sufficiently diffuse into the fiber.
Thus, the acrylonitrile-based carbon fiber precursor fiber bundle (precursor) of the present invention is obtained.

[Carbon fiber bundle and method for producing the same]
A carbon fiber bundle is obtained by baking the obtained precursor by a well-known method. As the firing method, for example, a method of performing flameproofing treatment, pre-carbonization treatment, and carbonization treatment in this order can be used.
The flameproofing treatment is a treatment of heating in an oxidizing atmosphere of 200 to 300 ° C. under tension or stretching conditions until the density is preferably 1.25 g / cm ³ or more, more preferably 1.32 g / cm ³ or more. The method is preferred. If the flameproofing treatment is insufficient, adhesion between single yarns is likely to occur during the precarbonization treatment thereafter. As the oxidizing atmosphere, known oxidizing atmospheres such as air, oxygen and nitrogen dioxide can be adopted, but air is preferable from the viewpoint of economy.

As the pre-carbonization treatment, in an inert atmosphere having a maximum temperature of 550 to 800 ° C., under tension, in a temperature range of 300 to 500 ° C., the heating rate is 500 ° C./min or less, preferably 300 ° C./min or less. A method of heat treatment is preferred for improving the mechanical properties of the carbon fiber bundle. As the inert atmosphere, a known inert atmosphere such as nitrogen, argon, or helium can be adopted, but nitrogen is desirable from the viewpoint of economy.
As the carbonization treatment, in an inert atmosphere of 1200 to 1800 ° C., in a temperature range of 1000 to 1200 ° C., a method of performing a heat treatment at a heating rate of 500 ° C./min or less, preferably 300 ° C./min or less, It is preferable for improving the mechanical properties of the carbon fiber bundle. As the inert atmosphere, a known inert atmosphere such as nitrogen, argon or helium can be adopted, but nitrogen is desirable from the viewpoint of economy.

The carbon fiber bundle thus obtained is subjected to an electrolytic oxidation treatment in a known electrolyte solution or an oxidation treatment in a gas phase or a liquid phase, whereby the affinity between the carbon fiber bundle and the matrix resin in the composite material is increased. It is preferable to improve adhesiveness.
Furthermore, a sizing agent can be provided by a known method as necessary.

[Acrylonitrile-based carbon fiber precursor fiber bundle]
According to the production method of the present invention, an acrylonitrile-based carbon fiber precursor fiber bundle (precursor) having excellent crystal structure uniformity in the fiber longitudinal direction can be obtained. For example, when the X-ray diffraction analysis is performed on the fiber bundle, the average half-value width of the diffraction intensity peak corresponding to polyacrylonitrile (100) reflection is 0.60 ° or less, and the mathematical formula (1) A precursor having a required CV value of 2.0 or less is obtained.
The half-value width of the diffraction intensity peak corresponding to the polyacrylonitrile (100) reflection obtained by X-ray diffraction varies depending on the crystal size, and the smaller this value, the better the crystal growth and the larger the crystal produced. Represents. In particular, it has been empirically found that the crystal structure involved in polyacrylonitrile (100) reflection has a great influence on the physical properties of carbon fibers. It is preferable that the half-value width is 0.60 or less in that the graphite-derived crystal grows smoothly during the flameproofing reaction. The lower limit of the half-value width of the diffraction intensity peak is not particularly limited, but is, for example, 0.40 or more.
The CV value obtained by the formula (1) varies depending on the variation in crystal size (crystal size spot), and the smaller this value, the smaller the crystal size spot in the fiber longitudinal direction. Although the lower limit of this CV value is not specifically limited, For example, it is 0.5 or more.

Moreover, according to this invention, the crystal orientation degree calculated | required by the said Numerical formula (2) as high as 90% or more can be obtained, and an acrylonitrile-type carbon fiber precursor fiber bundle can be obtained. The higher the value of the degree of crystal orientation,
This means that the graphite crystal grows easily. The upper limit of the degree of crystal orientation is not particularly limited and may be 100%, but is usually 95% or less.
Furthermore, according to the present invention, an acrylonitrile-based carbon fiber precursor fiber bundle having a crystallization index determined by the above method of 0.15 or more can be obtained. It represents that there are many crystal parts which are easy to form a graphite structure, so that the value of this crystallization index | exponent is large. The upper limit value of the crystallization index is not particularly limited, but is, for example, 0.4 or less.

  The acrylonitrile-based carbon fiber precursor fiber bundle (precursor) of the present invention has a very small difference in crystal structure in the fiber longitudinal direction. Therefore, the carbon fiber bundle obtained by firing the precursor can exhibit stable physical properties.

Hereinafter, the present invention will be described more specifically with reference to examples. In addition, this invention is not limited by these Examples.
Example 1
An acrylonitrile-based polymer (intrinsic viscosity [η] = 1.7) copolymerized with 96% by mass of acrylonitrile, 1% by mass of methacrylic acid and 3% by mass of acrylamide is dissolved in dimethylacetamide to prepare a stock solution for spinning (polymer concentration: 21 Mass%, temperature: 60 ° C.). This spinning dope was discharged into a dimethylacetamide aqueous solution having a temperature of 38 ° C. and a concentration of 67% by mass using a die having a nozzle hole with a diameter of 0.060 mm and a number of holes of 3000 to obtain a coagulated yarn. The coagulated yarn was first stretched in warm water at 65 ° C., and then wet-heat stretched by a multi-stage stretching method in which it was stretched in warm water at 95 ° C. The wet heat draw ratio was 3.4 times. Next, the fiber bundle after wet heat drawing was immersed in an aqueous solution containing 1% by mass of an aminosilicone-based oil agent and subjected to an oil agent treatment, and then contacted with a heating roller at 180 ° C. to be densified. Subsequently, the acrylonitrile-based carbon fiber precursor fiber bundle was obtained by drawing in a steam drawing machine having a steam pressure of 300 kPa. The draw ratio P in this steam drawing step was 3.0 times, and the temperature of the fiber bundle immediately before being introduced into the steam drawing machine was around 100 ° C.
Further, the maximum draw ratio Q at which the fiber bundle breaks when steam drawing was performed under the same conditions and the draw ratio was increased was 8.7 times. That is, P / Q is about 0.35. The total draw ratio of the wet heat draw ratio and the steam draw ratio P is determined by 3.4 × 3, and is about 10 times.
About the obtained acrylonitrile-based carbon fiber precursor fiber bundle, the average value of the half-value width of the diffraction intensity peak corresponding to polyacrylonitrile (100) reflection (hereinafter referred to as the average half-value width), the CV value, and the degree of crystal orientation (hereinafter, Simply called the degree of orientation), and the crystallization index was measured and calculated. The results are shown in Table 1. Table 1 also shows the main manufacturing conditions.

(Comparative Examples 1-3)
As shown in Table 1, an acrylonitrile-based carbon fiber precursor fiber bundle was produced in the same manner as in Example 1 except that the steam pressure in the steam stretching step was changed. With the change in steam pressure, the maximum draw ratio was as shown in Table 1.
About the obtained acrylonitrile-type carbon fiber precursor fiber bundle, it carried out similarly to Example 1, and calculated | required each physical-property value. The results are shown in Table 1.

  As shown in Table 1, in Example 1 in which the ratio (P / Q) of the steam draw ratio P to the maximum draw ratio Q is 0.35, Comparative Example 1 in which the value of P / Q is greater than 0.4 Compared to ˜3, the average width at half maximum and the degree of orientation were almost the same, but the CV value indicating the degree of crystal size spots was significantly reduced. The crystallization index was 0.187.

Claims (8)

Diffraction corresponding to polyacrylonitrile (100) reflection in the vicinity of 2θ = 17 ° when a polyacrylonitrile-based carbon fiber precursor fiber bundle is subjected to 2θ measurement of X-ray diffraction in a direction perpendicular to the longitudinal direction of the fiber bundle. A carbon fiber precursor fiber bundle having an average half-width of an intensity peak of 0.60 ° or less and a CV value obtained by the following mathematical formula (1) of 2 or less.

The β measurement of X-ray diffraction is performed at an angle at which the diffraction intensity peak corresponding to the polyacrylonitrile (100) reflection becomes the highest intensity in the 2θ measurement according to claim 1, and the half-value width of the diffraction intensity peak is expressed as B (unit: ° ), The carbon fiber precursor fiber bundle according to claim 1, wherein the value of crystal orientation calculated using the following mathematical formula (2) is 90% or more.

  When the diffraction intensity peak obtained by performing β measurement of X-ray diffraction according to claim 2 is fitted by a least square method as a composite function of a Lorentz function and a Gauss function, the area of the Lorentz function and the area of the Gauss function are calculated. The carbon fiber precursor fiber bundle according to claim 1 or 2, wherein a crystallization index represented by an area ratio of a Gaussian function to a total is 0.15 or more. A spinning process for spinning a spinning stock solution containing an acrylonitrile-based polymer to obtain a coagulated yarn, a wet heat stretching process for stretching the coagulated thread by wet heat, a dry densification process for drying and densifying the wet and heat stretched fiber bundle, and drying A steam stretching step of stretching the densified fiber bundle by a steam stretching method,
A carbon fiber precursor fiber bundle in which the steam pressure in the steam stretching process is set so as to satisfy the following formula (3), where P is the stretch ratio in the steam stretching process and Q is the maximum stretch ratio at which breakage occurs due to steam stretching. Manufacturing method.

The manufacturing method of the carbon fiber precursor fiber bundle of Claim 4 whose draw ratio P in the said steam extending process is 3 times or more and 4 times or less. The method for producing a carbon fiber precursor fiber bundle according to claim 4 or 5, wherein the temperature of the fiber bundle immediately before contacting with the pressurized steam in the steam stretching step is 80 ° C or higher and 120 ° C or lower.   The carbon fiber bundle obtained by baking the carbon fiber precursor fiber bundle as described in any one of Claims 1-3. The manufacturing method of a carbon fiber bundle which has the process of manufacturing a carbon fiber precursor fiber bundle by the method as described in any one of Claims 4-6, and the process of baking the obtained carbon fiber precursor fiber bundle.