JP5313788B2 - Carbon fiber precursor fiber bundle and method for producing the same - Google Patents

Description

  The present invention relates to a carbon fiber precursor fiber bundle suitably used for the production of a carbon fiber bundle used as a reinforcing material for a fiber reinforced composite material, and a method for producing the same.

  Carbon fiber, glass fiber, aramid fiber, etc. are used for the fiber reinforced composite material. Among them, carbon fiber is excellent in specific strength, specific elastic modulus, heat resistance, chemical resistance, etc., and is used as a reinforcing material for fiber reinforced composite materials for aircraft applications, sports applications such as golf shafts and fishing rods, and general industrial applications. Yes. The fiber reinforced composite material using carbon fiber is manufactured as follows, for example.

  First, a precursor fiber bundle composed of a single fiber of a polyacrylonitrile-based polymer is fired at a temperature of 200 to 300 ° C. in an oxidizing gas such as air in a firing process (flame resistance process) to form a flame resistant fiber bundle. obtain. Next, in the carbonization step, the flame resistant fiber bundle is carbonized at a temperature of 300 to 2000 ° C. in an inert atmosphere to obtain a carbon fiber bundle. Then, the obtained carbon fiber bundle is processed into a woven fabric or the like as necessary, and then impregnated with a synthetic resin and molded into a predetermined shape to obtain a fiber-reinforced composite material.

  In the precursor fiber bundle used for the production of the carbon fiber bundle, the fiber bundle is scattered in the firing step, so that the single fiber constituting the fiber bundle is not entangled with the adjacent fiber bundle or wound around the roller. High convergence is required. However, the carbon fiber bundle obtained from the precursor fiber bundle having a high bundling property has a problem that the resin is difficult to be impregnated due to its high bundling property.

  In addition, the carbon fiber fabric obtained by weaving the carbon fiber bundle needs to be a fabric having as small an opening as possible so that a resin void does not occur when the resin is impregnated. For this purpose, some opening process is performed during or after weaving. However, the carbon fiber bundle obtained from the precursor fiber bundle having high bundling property has a problem that it is difficult to open due to its high bundling property. In addition, since the carbon fiber fabric is required to have a uniform weave having a small mesh opening, a bulky carbon fiber bundle is required.

  As a method for improving these problems, in Patent Document 1, the ratio of the major axis to the minor axis (major axis / minor axis) of the cross section of the single fiber of the acrylonitrile-based polymer is 1.05 to 1.6, Carbon that has good resin impregnation and spreadability when calcined into carbon fiber by forming a carbon fiber precursor fiber bundle having an Si amount measured by ICP emission analysis in the range of 500 to 4000 ppm. A fiber precursor fiber bundle is disclosed.

JP 2002-20927 A

However, although the carbon fiber precursor fiber bundle obtained in the example of Patent Document 1 has good spreadability and strength, the resin impregnation property is only 5.1 or less, and there is room for improvement. There is.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a carbon fiber precursor fiber bundle capable of producing a carbon fiber bundle having good resin impregnation property and spreadability and high strength, and a method for producing the same. To do.

  In order to solve the above-mentioned problems, the carbon fiber precursor fiber bundle of the present invention is a carbon fiber precursor fiber bundle made of an acrylonitrile-based polymer, and the ratio of the major axis to the minor axis of the single fiber (major axis / short axis). Diameter) is 1.35 to 1.5, the maximum height (Ry) of the surface of the single fiber is 0.42 to 0.6 μm, and Ry / (major axis / minor axis) is 0.31 μm. That's it.

The acrylonitrile-based polymer preferably contains 0.5 to 4% by mass of acrylamide monomer units.
The center line average roughness (Ra) of the surface of the single fiber is preferably 0.07 to 0.15 μm, and Ra / (major axis / minor axis) is preferably 0.05 μm or more.
It is preferable that the surface of the single fiber has wrinkles, the local summit spacing (S) is 0.7 to 1.0 μm, and S / (major axis / minor axis) is 0.5 μm or more.
The total fineness of the fiber bundle is preferably 15000 dtex or less.

  Moreover, the manufacturing method of the carbon fiber precursor fiber bundle of this invention is the organic solvent density | concentration of 52-58 mass%, temperature 30 which consists of the organic solvent solution of the acrylonitrile type | system | group polymer containing 95 mass% or more of acrylonitrile units. The coagulated yarn is discharged into a first coagulation bath composed of an organic solvent aqueous solution at ˜50 ° C. to obtain coagulated yarn, and the coagulated yarn is taken out from the first coagulation bath at a take-off speed of 0.8 times or less of the spinning solution discharge linear velocity. And a step of stretching the solidified yarn by 2.6 to 3.5 times in a second coagulation bath composed of an organic solvent aqueous solution having an organic solvent concentration of 60 to 70% by mass and a temperature of 30 to 50 ° C. And a step of performing wet heat stretching 3 times or more to the swollen fiber bundle that has been stretched in the second coagulation bath, and 0.4 to 1 to the fiber bundle after the wet heat stretching. .Silicon oil adjusted to 5% by mass And performing hydrogenated oil processing, after the hydrogenated oil processing, after drying the fiber bundle, and a step of performing steam drawing of 1.2 to 4 times.

The acrylonitrile-based polymer preferably contains 0.5 to 4% by mass of acrylamide monomer units.
The total fineness of the obtained carbon fiber precursor fiber bundle is preferably 15000 dtex or less.

  According to the present invention, a carbon fiber precursor fiber bundle capable of producing a carbon fiber bundle having good resin impregnation property and spreadability and high strength is obtained.

It is sectional drawing of the single fiber surface of a carbon fiber precursor fiber bundle explaining centerline average roughness (Ra). It is sectional drawing of the single fiber surface of a carbon fiber precursor fiber bundle explaining the maximum height (Ry). It is sectional drawing of the single fiber surface of a carbon fiber precursor fiber bundle explaining the space | interval (S) of a local peak.

Hereinafter, the present invention will be described in detail.
The carbon fiber precursor fiber bundle of the present invention is a tow obtained by bundling a plurality of acrylonitrile polymer single fibers (hereinafter sometimes simply referred to as fibers).
As the acrylonitrile-based polymer, a polymer containing 95% by mass or more of an acrylonitrile unit is preferable in terms of strength development of a carbon fiber bundle obtained by firing a carbon fiber precursor fiber bundle. An acrylonitrile polymer is a polymer of acrylonitrile and a monomer that can be copolymerized with it by redox polymerization in an aqueous solution, suspension polymerization in a heterogeneous system, emulsion polymerization using a dispersing agent, or the like. Can be obtained.

Examples of monomers that can be copolymerized with acrylonitrile include (meth) acrylic acid such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, and hexyl (meth) acrylate. Esters; vinyl halides such as vinyl chloride, vinyl bromide, vinylidene chloride; acids such as (meth) acrylic acid, itaconic acid, crotonic acid and their salts; maleic imide, phenylmaleimide, (meth) acrylamide, Styrene, α-methylstyrene, vinyl acetate; polymerizable unsaturated monomer containing a sulfo group such as sodium styrene sulfonate, sodium allyl sulfonate, sodium β-styrene sulfonate, sodium methallyl sulfonate; 2-vinylpyridine 2-methyl-5-vinylpyridine pyri Examples thereof include polymerizable unsaturated monomers containing a gin group. These may use any 1 type and may use 2 or more types.
In order to ensure the denseness of solidification during the production of the carbon fiber precursor fiber bundle, the acrylonitrile-based polymer preferably includes an acrylamide monomer unit. The content of the acrylamide monomer unit is preferably 0.5 to 4% by mass, and more preferably 1 to 3.5% by mass. When the acrylamide monomer unit is less than 0.5% by mass, the effect on the denseness of solidification is insufficient, and it becomes difficult to obtain high-strength carbon fibers. On the other hand, if it exceeds 4% by mass, the cost of the polymer is remarkably increased.

  The ratio (major axis / minor axis) of the major axis to the minor axis of the cross section of the single fiber of the acrylonitrile polymer in the present invention is 1.35 to 1.5, preferably 1.36 to 1.49. . If the ratio of major axis / minor axis is within the above range, it is possible to simultaneously satisfy the firing processability of the precursor fiber bundle and the resin impregnation property and fiber opening property of the carbon fiber bundle obtained therefrom. When the major axis / minor axis ratio is less than 1.35, the voids between the single fibers are reduced, and the resin impregnation property and the fiber opening property of the obtained carbon fiber bundle tend to be insufficient. When the major axis / minor axis ratio exceeds 1.5, the convergence of the fiber bundle decreases, and the firing process passability deteriorates. Moreover, it exists in the tendency for strand strength to fall.

(Measurement method of ratio of major axis to minor axis (major axis / minor axis) of fiber cross section of single fiber)
In the present invention, the ratio of the major axis to the minor axis (major axis / minor axis) of the cross section of the single fiber is a value determined as follows.
After passing a bundle of single fibers for measurement through a tube made of vinyl chloride resin having an inner diameter of 1 mm, a sample is prepared by cutting the bundle with a knife.
Next, the sample was bonded to an SEM sample stage so that the cross section of the single fiber faced upward, and Au was sputtered to a thickness of about 10 nm, and then a scanning electron microscope (manufactured by PHILIPS, product name: XL20). ) Under the conditions of an acceleration voltage of 7.00 kV and a working distance of 31 mm, the major axis and minor axis of the cross section of the single fiber are measured, and the major axis / minor axis ratio is determined by dividing the major axis by the minor axis.
Similarly, the ratio of the major axis / minor axis is obtained for all the single fibers passed through the tube, and the average value is defined as the ratio of the major axis to the minor axis of the single fiber (major axis / minor axis).

The Si content of the carbon fiber precursor fiber bundle of the present invention is preferably in the range of 500 to 4000 ppm, and more preferably in the range of 1000 to 3000 ppm. If the amount of Si is within the above range, it is possible to satisfy both the passability of the precursor fiber bundle through the firing step and the resin impregnation property and the fiber opening property of the carbon fiber bundle obtained therefrom. If the amount of Si is less than 500 ppm, the fiber bundle's convergence may be lowered, and the firing process passability may be deteriorated. Moreover, the strand strength of the obtained carbon fiber bundle may be lowered. When the amount of Si exceeds 4000 ppm, a large amount of silica is scattered during firing of the precursor fiber bundle, and firing stability is deteriorated. Further, the obtained carbon fiber bundle is less likely to be separated, and the resin impregnation property and the fiber opening property are deteriorated.
The amount of Si is derived from the silicon-based oil used when producing the carbon fiber precursor fiber bundle. The amount of Si can be measured using an ICP emission analyzer.

  The single fiber strength of the acrylonitrile-based polymer in the present invention is preferably 5.0 cN / dtex or more, more preferably 6.5 cN / dtex or more, and still more preferably 7.0 cN / dtex or more. If the single fiber strength is less than 5.0 cN / dtex, the generation of fluff due to single yarn breakage in the firing process increases, and the firing processability deteriorates.

  The single fiber strength of the acrylonitrile-based polymer in the present specification is determined by using a single fiber automatic tensile strength / elongation measuring machine (product name: UTM II-20, manufactured by Orientec Co., Ltd.), and using the single fiber attached to the mount as a load cell. It is a value calculated | required by mounting | wearing the chuck | zipper of this and performing a tensile test at a speed | rate of 20.0 mm / min, and measuring a strong elongation.

The carbon fiber precursor fiber bundle of the present invention preferably has wrinkles extending in the longitudinal direction of the fiber bundle on the surface of the single fiber. Due to the presence of such wrinkles, the carbon fiber precursor fiber bundle of the present invention has good sizing properties, and at the same time, the resulting carbon fiber bundle has good resin impregnation properties and fiber opening properties.
The wrinkle depth is defined by the following centerline average roughness (Ra), maximum height (Ry) and local summit spacing (S).

1 to 3 are diagrams schematically showing a cross-sectional shape of a single fiber surface in a cross section perpendicular to a fiber length direction of single fibers constituting a carbon fiber precursor fiber bundle.
The centerline average roughness (Ra) of the surface of the single fiber is, as shown in FIG. 1, extracted from the roughness curve by the reference length L in the direction of the centerline m, and measured from the centerline m of the extracted portion. The absolute values of the deviations up to are totaled and averaged. The center line average roughness (Ra) is measured by using a laser microscope.
As shown in FIG. 2, the maximum height (Ry) of the surface of the single fiber is extracted by a reference length L in the direction of the center line m from the roughness curve, and the highest peak line and center line in the extracted part The total value (Rp + Rv) of the distance Rp to m and the distance Rv between the lowest valley line and the center line m. The maximum height (Ry) is measured by using a laser microscope.
The local summit interval (S) is a parameter that defines the interval between the wrinkles. As shown in FIG. 3, the reference length L is extracted from the roughness curve in the direction of the center line m and adjacent to the extracted portion. It is the average value S of the distances S1, S2, S3,. The local summit spacing (S) is measured by using a laser microscope.

The maximum height (Ry) is 0.42 to 0.6 μm, preferably 0.42 to 0.56 μm. When the maximum height (Ry) is less than 0.42 μm, the resin impregnation property and the fiber opening property of the obtained carbon fiber bundle are deteriorated, and the bulkiness is insufficient. When the maximum height (Ry) exceeds 0.6 μm, the surface area of the fiber bundle increases, and static electricity is likely to be generated, thereby reducing the convergence of the fiber bundle. Further, the strand strength of the obtained carbon fiber bundle is lowered.
Ry / (major axis / minor axis) is 0.31 μm or more. If it is smaller than 0.31 μm, the wrinkles on the fiber surface are relatively small compared to the cross-sectional shape (major axis / minor axis) of the fiber, and the resin impregnation property and fiber opening property of the resulting carbon fiber bundle are deteriorated.
That is, the cross-sectional shape of the fiber becomes a flattened ellipse as the value of the major axis / minor axis increases. In order to obtain good resin impregnation property and spreadability, the value of Ry / (major axis / minor axis) needs to be equal to or greater than a predetermined value, depending on the degree of flatness of the ellipse in the fiber cross section. It means that the wrinkle height of a certain level or more is necessary, and the flatter the ellipse becomes, the larger the wrinkle height becomes.

The center line average roughness (Ra) is preferably 0.07 to 0.15 μm, more preferably 0.07 to 0.13 μm, and still more preferably 0.08 to 0.12 μm. When the center line average roughness (Ra) is less than 0.07 μm, the resin impregnation property and fiber opening property of the obtained carbon fiber bundle are deteriorated, and the bulkiness is insufficient. When the center line average roughness (Ra) exceeds 0.15 μm, the surface area of the fiber bundle is increased, and static electricity is likely to be generated, thereby reducing the convergence of the fiber bundle. Further, the strand strength of the obtained carbon fiber bundle is lowered.
Further, Ra / (major axis / minor axis) is preferably 0.05 μm or more. If it is smaller than 0.05 μm, the wrinkles on the fiber surface are relatively small compared to the cross-sectional shape (major axis / minor axis) of the fiber, and the resin impregnation property and the fiber opening property of the resulting carbon fiber bundle are deteriorated.
That is, in order to obtain good resin impregnation property and spreadability, the value of Ra / (major axis / minor axis) is preferably equal to or greater than a predetermined value depending on the degree of flattening of the ellipse in the fiber cross section. Thus, it is preferable that the wrinkle roughness is large to some extent, and the more flat the ellipse is, the more preferable wrinkle roughness is.

The distance (S) between the local peaks is preferably 0.7 to 1.0 μm, and more preferably 0.7 to 0.9 μm. If the distance (S) between the local peaks is less than 0.7 μm, the resin impregnation property and the fiber opening property of the obtained carbon fiber bundle will be insufficient. When the distance (S) between the local peaks exceeds 1.0 μm, the surface area of the fiber bundle increases, and static electricity is likely to be generated, thereby reducing the convergence of the fiber bundle. Further, the strand strength of the obtained carbon fiber bundle is lowered.
Further, S / (major axis / minor axis) is preferably 0.5 μm or more. If it is smaller than 0.5 μm, the wrinkles on the fiber surface are relatively small compared to the cross-sectional shape (major axis / minor axis) of the fiber, and the resin impregnation property and the fiber opening property of the obtained carbon fiber bundle are deteriorated.
That is, in order to obtain good resin impregnation and spreadability, the value of S / (major axis / minor axis) is preferably equal to or greater than a predetermined value depending on the degree of flattening of the ellipse in the fiber cross section. Thus, it is preferable that the wrinkle interval is large to some extent, and the more flat the ellipse is, the larger the preferable wrinkle interval is.

  The number of single fibers of the acrylonitrile polymer constituting the carbon fiber precursor fiber bundle of the present invention is preferably 12000 or less, more preferably 6000 or less, and further preferably 3000 or less. When the number of single fibers exceeds 12,000, tow handling and tow volume increase and the drying load increases, so that the spinning speed cannot be increased. Moreover, it becomes difficult to give uniform entanglement, and as a result, the permeability in a baking process deteriorates.

The total fineness of the carbon fiber precursor fiber bundle of the present invention is preferably 15000 dtex or less. More preferably, it is 10,000 dtex or less. If the total fineness exceeds 15000 dtex, the drying load increases and it is difficult to increase the spinning speed, which is not preferable.
The lower limit of the total fineness is not particularly limited, but is preferably 1000 dtex or more, more preferably 3000 dtex or more in terms of ensuring productivity.

Next, the manufacturing method of the carbon fiber precursor fiber bundle of this invention is demonstrated.
[1] First, a spinning solution comprising an organic solvent solution of an acrylonitrile polymer containing 95% by mass or more of an acrylonitrile unit is passed through a spinneret into a first coagulation bath at a constant linear velocity (spinning solution discharge linear velocity). To form a coagulated yarn, and the coagulated yarn is taken out from the first coagulation bath at a constant speed (take-off speed).
Examples of the organic solvent used for the spinning dope include dimethylacetamide, dimethylsulfoxide, dimethylformamide, and the like. Among them, dimethylacetamide is preferably used because it is less deteriorated due to hydrolysis of the solvent and gives good spinnability.
The concentration of the acrylonitrile polymer in the spinning dope is preferably 10 to 40% by mass, and more preferably 15 to 25% by mass. Within the above range, good spinnability is easily obtained.

  The spinneret for extruding the spinning dope is used for producing an acrylonitrile polymer single fiber of about 1.0 denier (1.1 dtex), which is a general thickness of a single fiber of an acrylonitrile polymer. A spinneret having a nozzle hole having a hole diameter of 15 to 100 μm can be preferably used. The number of nozzle holes is the same as the number of single fibers constituting the carbon fiber precursor fiber bundle to be obtained.

The first coagulation bath is composed of an organic solvent aqueous solution having an organic solvent concentration of 52 to 58 mass% and a temperature of 30 to 50 ° C. Examples of the organic solvent for the first coagulation bath include the same organic solvents used for the spinning dope. The organic solvent used for the spinning dope and the organic solvent for the first coagulation bath may be the same or different. The same is preferable so as not to complicate the solvent recovery step.
When the organic solvent concentration in the first coagulation bath is low, the value of the major axis / minor axis of the cross section of the fiber tends to increase, and when the organic solvent concentration is increased, the major axis / minor axis approaches 1. In the present invention, it is preferable that the concentration of the organic solvent in the first coagulation bath is 52 to 58% by mass in order to set the long axis / short axis value of the cross section of the fiber to a range of 1.35 to 1.5.
When the temperature of the first coagulation bath is within the above range, macrovoids are hardly observed in the obtained coagulated yarn, and the strength of the finally obtained carbon fiber bundle is improved. A more preferable temperature of the first coagulation bath is 20 to 40 ° C.

  The speed at which the coagulated yarn is taken out from the first coagulation bath (take-up speed) is 0.8 times or less of the linear velocity (spinning solution discharge linear velocity) when the spinning stock solution is discharged into the first coagulation bath through the spinneret. To do. That is, the value of “take-off speed / spinning stock solution discharge linear speed” is 0.8 or less, and good spinnability can be maintained within this range. The lower limit of “take-off speed / spinning solution discharge linear speed” is not particularly limited, but is preferably 0.4 or more in order to increase the spinning speed and improve productivity.

  The coagulated yarn pulled up from the first coagulation bath in this step contains an organic solvent derived from the first coagulation bath and the spinning dope and water derived from the first coagulation bath, and is contained in the liquid contained in the coagulated yarn. The concentration of the organic solvent exceeds the concentration of the organic solvent in the first coagulation bath. For this reason, the coagulated yarn is in a semi-solidified state in which only the surface is coagulated, and good stretchability in the second coagulation bath in the next step can be obtained.

  The fibers constituting the carbon fiber precursor fiber bundle preferably have a uniform surface layer portion and fiber interior. In this step, if the “take-off speed / spinning solution discharge linear speed” at the time of producing the coagulated yarn in the first coagulation bath is low, coagulation of the coagulated yarn formed in the first coagulation bath tends to be uniform, It is easy to obtain a fiber in which the surface layer portion and the inside of the fiber are uniformly oriented. On the other hand, if the “take-off speed / spinning solution discharge linear speed” is too high, coagulation and stretching of the coagulated yarn in the first coagulation bath occur at the same time, and coagulation of the coagulated yarn formed in the first coagulation bath does not occur. It becomes uniform. Therefore, even if this is stretched in the second coagulation bath, it is difficult to form a fiber that is uniformly oriented to the inside of the fiber.

[2] Next, the coagulated yarn taken from the first coagulation bath is stretched 2.6 to 3.5 times in the second coagulation bath. The second coagulation bath is composed of an organic solvent aqueous solution having an organic solvent concentration of 60 to 70% by mass and a temperature of 30 to 50 ° C.
Examples of the organic solvent for the second coagulation bath include the same organic solvents used for the spinning dope. The organic solvent for the spinning dope or the first coagulation bath and the organic solvent for the second coagulation bath may be the same or different. The same is preferable so as not to complicate the solvent recovery step.
In the present invention, the organic solvent concentration in the second coagulation bath is set higher than the organic solvent concentration in the first coagulation bath. By increasing the concentration of the organic solvent in the second coagulation bath, the draw ratio in the second coagulation bath can be increased and wrinkles can be deepened. By setting the organic solvent concentration and temperature of the second coagulation bath in the above ranges, stretching of 2.6 to 3.5 times can be stably performed while preventing the occurrence of single fiber breakage.
If the draw ratio in the second coagulation bath is lower than 2.6 times, wrinkles are difficult to deepen, and if it is higher than 3.5 times, single fiber breakage is likely to occur, and spinning stability decreases. Moreover, the stretchability in the subsequent wet heat stretching step is deteriorated.

In addition, the coagulated yarn in the swollen state containing the coagulation liquid drawn out from the first coagulation bath can be drawn in the air, but is drawn in the second coagulation bath as in this step. As a result, solidification of the coagulated yarn can be promoted, and temperature control during stretching becomes easy.
A carbon fiber precursor having a maximum height (Ry) of 0.42 to 0.6 μm and a Ry / (major axis / minor axis) of 0.31 μm or more by stretching in the second coagulation bath under the above conditions. A fiber bundle can be obtained.

[3] Subsequently, wet heat drawing is performed on the fiber bundle in a swollen state after drawing in the second coagulation bath. Thereby, the orientation of the fiber can be further increased. Specifically, the wet heat stretching is performed by stretching a swollen fiber bundle in a swollen state after stretching in the second coagulation bath while being subjected to water washing or stretching in hot water. Drawing at the same time as washing with water is preferable from the viewpoint of simplification and efficiency of the spinning process, and drawing in hot water is preferable from the viewpoint of productivity.
The draw ratio in the wet heat drawing needs to be 2.5 times or more, and more preferably 3 times or more. If it is lower than 2.5 times, the effect of increasing the fiber orientation tends to be insufficient. The upper limit of the draw ratio is not particularly limited, but is preferably 4 times or less from the viewpoint of the stability of the spinning process.

[4] Next, a silicon oil additive is added to the fiber bundle that has been subjected to wet heat drawing. As the silicon-based oil, a general silicon-based oil such as an aminosilicon-based oil can be used. The silicon-based oil agent is prepared to a concentration of 0.4 to 1.5% by mass and used. If the concentration of the silicone-based oil is less than 0.4% by mass, the amount of oil attached to the fiber is not preferable because it is too small, and if it exceeds 1.5% by mass, the amount of oil is too large. A more preferable range of the concentration of the silicone-based oil is 0.8 to 1.5 mass.

[5] Next, the fiber bundle that has been subjected to the silicon oil addition process is dried and further stretched 1.2 to 4 times with a steam stretching machine. By carrying out the steam stretching, stretching at a high magnification can be stably performed, and troubles in the manufacturing process due to generation of static electricity can be suppressed. The draw ratio of steam drawing is 1.2 times or more, preferably 1.5 times or more.
If dry heat drawing is performed instead of steam drawing, the wrinkles become too deep, the surface area of the fiber bundle increases, and static electricity is likely to be generated, thereby reducing the convergence of the fiber bundle. Further, the strand strength of the obtained carbon fiber bundle is lowered.

[6] Next, the moisture content of the fiber bundle subjected to the steam drawing is adjusted with a touch roll as necessary, and then entangled with air by a known method to obtain a carbon fiber precursor. Obtain a fiber bundle. In the present invention, the entanglement treatment is not essential, but by providing entanglement between the filaments of the carbon fiber precursor fiber bundle, it is possible to obtain a fiber bundle that imparts convergence and maintains the form of one tow. . In addition, the fiber bundle can be made difficult to disperse and the baking process passage property can be improved.

The moisture content of the fiber bundle before being entangled is preferably 15% by mass or less, more preferably 10% by mass or less, and further preferably 3 to 5% by mass. When the moisture content exceeds 15% by mass, it becomes difficult for the single fibers to be entangled when the fiber bundle is entangled by blowing air.
The moisture content in this specification is the moisture content (mass%) = (w−) by the mass w of the fiber bundle in a wet state and the mass w 0 after drying this with a hot air dryer at 105 ° C. for 2 hours. It is a numerical value obtained by w0) × 100 / w0.

The entanglement degree in the carbon fiber precursor fiber bundle subjected to the entanglement treatment is preferably in the range of 5 to 20 pieces / m, and more preferably in the range of 10 to 14 pieces / m. If the degree of entanglement is less than 5 / m, the effect of improving the passability of the firing process by imparting entanglement and making it difficult to disperse the fiber bundle cannot be obtained. When the entanglement degree exceeds 20 pcs / m, the resin impregnation property and the fiber opening property of the obtained carbon fiber bundle are deteriorated.
The entanglement degree of the carbon fiber precursor fiber bundle in the present specification is a parameter indicating how many times one single fiber in the fiber bundle is entangled between the adjacent single fibers and 1 m. The degree of entanglement is measured by the hook drop method.

Hereinafter, the present invention will be described in detail with reference to examples.
Each measurement in this example was performed by the following method.
(Si amount)
First, a sample is placed in a Teflon (registered trademark) sealed container, and after acid decomposition with sulfuric acid and then nitric acid, an ICP emission analyzer (manufactured by Jarrel Ash, product name: IRIS-AP) is used as a constant volume. It was measured.
(Entanglement)
A fiber bundle of carbon fiber precursor in a dry state was prepared, the fiber bundle was attached to the upper part of the drooping device, and a weight was attached and suspended 1 m below from the upper gripping part. The weight load used here was 1/5 of the denier number. A hook was inserted so as to divide the fiber bundle into two at a point 1 cm below the upper grip of the fiber bundle, and the hook was lowered at a speed of 2 cm / S. The lowering distance L (mm) of the hook to the point where the hook stopped due to the entanglement of the fiber bundle was obtained, and the degree of entanglement was calculated by the following equation. The number of tests was N = 50, and the average value was obtained up to one decimal place.
Degree of confounding = 1000 / L
The hook used here is a needle having a diameter of 0.5 mm to 1.0 mm, and the surface is smoothly finished.

(Wrinkle shape)
A fiber bundle of a carbon fiber precursor in a dry state is attached to a slide glass, and Ra, Ry, and S are measured in a direction perpendicular to the fiber axis direction using a laser microscope (manufactured by Lasertec Corporation, product name: VL2000). did. The measurement was performed on 10 fibers arbitrarily selected from the single fibers constituting the fiber bundle, and the average value was obtained. Ra / (major axis / minor axis), Ry / (major axis / minor axis), S / (major axis / minor axis) were calculated from the average values of Ra, Ry, and S obtained and the measurement results of the cross-sectional shape.
(Total fineness)
First, the carbon fiber precursor fiber bundle was cut accurately from the bobbin so as not to be twisted by 1 m in the longitudinal direction in an atmosphere having a temperature of 23 ± 5 ° C. and a relative humidity of 60 ± 20%, thereby obtaining a first sample. Next, the second sample is accurately cut in the same manner at a position 50 m away along the length direction of the fiber bundle from the first sample cut as described above. A sample was cut.
The collected 20 samples were dried in a dryer at 105 ° C. for 1 hour, the post-drying mass (unit: g) of each sample having a length of 1 m was measured with an electronic balance, and the average value of all data (M. Unit: g / m) was determined. Using the obtained average value (M), the total fineness of the carbon fiber precursor fiber bundle was determined by the following equation.
Total fineness (dtex) of carbon fiber precursor fiber bundle = M (g / m) × 10000 (m)

A method for evaluating a carbon fiber bundle obtained by firing an acrylonitrile fiber bundle (carbon fiber precursor fiber bundle) is as follows.
(Resin impregnation)
The carbon fiber bundle was cut about 20 cm, immersed in about 3 cm in glycidyl ether, and left for 15 minutes. After taking out from glycidyl ether, it was allowed to stand for 3 minutes, cut off from the bottom at 3.5 cm, and the length and mass of the remaining carbon fiber bundle were measured. The mass ratio of glycidyl ether sucked up from the basis weight of the carbon fiber bundle was calculated and used as an index for resin impregnation.
(Opening property)
The tow width when the carbon fiber bundle was run on a metal roll at a running speed of 1 m / min under a tension of 0.06 g / single fiber was used as an index of the spreadability.
(Strand strength of carbon fiber)
It measured according to JIS-7601.

[Example 1]
Acrylonitrile, acrylamide and methacrylic acid were copolymerized by aqueous suspension polymerization in the presence of ammonium persulfate-ammonium hydrogen sulfite and iron sulfate, and acrylonitrile unit / acrylamide unit / methacrylic acid unit = 96/3/1 (mass ratio) An acrylonitrile-based polymer was obtained. The acrylonitrile-based polymer was dissolved in dimethylacetamide to prepare a spinning dope having a polymer concentration of 21% by mass.

  The spinning solution is passed through a spinneret having a pore number of 3000 and a pore diameter of 75 μm and discharged into a first coagulation bath made of a dimethylacetamide aqueous solution having a concentration of 55% by mass and a temperature of 30 ° C. to obtain a coagulated yarn. The yarn was taken up at a take-up speed of 0.8 times the spinning solution discharge linear speed. The coagulated yarn was subsequently introduced into a second coagulation bath composed of an aqueous dimethylacetamide solution having a concentration of 60% by mass and a temperature of 30 ° C., and stretched 2.8 times in the bath.

  Subsequently, the fiber bundle was wet-stretched 3 times at the same time as being washed with water, and an aminosilicone oil prepared to 1.5% by mass was added thereto. The fiber bundle was dried using a hot roll and stretched 1.9 times with a steam stretching machine. Thereafter, the moisture content of the fiber bundle was adjusted with a touch roll, and the fiber bundle contained 5% by mass of water per fiber. Next, the fiber bundle is entangled with air having an air pressure of 405 kPa and wound on a bobbin with a winder to obtain an acrylonitrile fiber bundle having a single fiber fineness of 1.1 dtex (1.0 denier) and a total fineness of 3300 dtex. It was. Table 1 shows the main manufacturing conditions.

About the obtained acrylonitrile fiber bundle, cross-sectional shape, Si amount, single fiber strength, entanglement degree, and wrinkle shape were measured. The results are shown in Table 2.
Further, the acrylonitrile fiber bundle was treated in a hot air circulation type flameproofing furnace at 230 to 260 ° C in air for 50 minutes to form a flameproofed fiber bundle, and then the flameproof fiber bundle was 1 at a maximum temperature of 780 ° C in a nitrogen atmosphere. After 5 minutes of treatment and further treatment in a high-temperature heat treatment furnace with a maximum temperature of 1300 ° C. for about 1.5 minutes in the same atmosphere, electrolytic treatment was performed at 0.4 Amin / m in an aqueous solution of ammonium bicarbonate to obtain carbon. A fiber bundle was obtained. The obtained carbon fiber bundle was evaluated for resin impregnation property, fiber opening property and strand strength. The results are shown in Table 3.

[Examples 2-6, Comparative Examples 1-11]
In Example 1, one of the organic solvent concentration of the first coagulation bath, the organic solvent concentration of the second coagulation bath, the draw ratio in the second coagulation bath, the draw ratio in the wet heat drawing, and the draw ratio by the steam drawing machine An acrylonitrile fiber bundle was obtained in the same manner as in Example 1 except that the above was changed as shown in Table 1. The single fiber fineness of the obtained acrylonitrile fiber bundle was 1.1 dtex, and the total fineness was 3300 dtex.
In Comparative Examples 2, 3, and 12, yarn breakage occurred in the second coagulation bath, and thus an acrylonitrile fiber bundle could not be produced.
The obtained acrylonitrile fiber bundle was measured in the same manner as in Example 1. The results are shown in Table 2.
Further, the same evaluation as in Example 1 was performed on the carbon fiber bundle obtained by firing the acrylonitrile fiber bundle in the same manner as in Example 1. The results are shown in Table 3.

As shown in the results of Table 3, the ratio of the major axis to the minor axis (major axis / minor axis) in the fiber cross section of the single fiber is 1.35 to 1.5, and the maximum height of the surface of the single fiber ( Ry) is 0.42 to 0.6 μm, and Ry / (major axis / minor axis) is 0.31 μm or more, and the acrylonitrile fiber bundles of Examples 1 to 6 are produced using this carbon fiber. All of the resin impregnation property, fiber opening property, and strength of the fiber bundle were good.
In contrast, the acrylonitrile fiber bundles obtained in Comparative Examples 1, 5, and 9 having a high organic solvent concentration of 60% by mass in the first coagulation bath have a single fiber major axis / minor axis ratio of 1.32. Was less than 0.42 and Ry / (major axis / minor axis) was less than 0.31, and the carbon fiber bundle obtained from the acrylonitrile fiber bundle was inferior in resin impregnation property and fiber opening property.
Further, in Comparative Example 4 where the organic solvent concentration of the first coagulation bath is 70% by mass, the ratio of major axis / minor axis is 1.02, Ry is 0.20, and Ry / (major axis / minor axis) is 0.20. And the resin impregnation property, opening property, and strength were all inferior.
In Comparative Examples 6, 8, and 11, where the organic solvent concentration of the first coagulation bath is as low as 50% by mass, the major axis / minor axis ratio is as large as 1.52, 1, 53, and 1, 52, respectively. Is less than 0.42, the wrinkles are shallow, and Ry / (major axis / minor axis) is as small as less than 0.31, so the carbon fiber bundle obtained from the acrylonitrile fiber bundle was inferior in resin impregnation and strength.
In Comparative Example 7, where the organic solvent concentration of the first coagulation bath is 40 mass%, which is even lower, Ry / (major axis / minor axis) is 0.38, which is equivalent to the example, but the major axis / minor axis ratio is 1. Since 72 and Ry were as large as 0.65, the resin impregnation property and the fiber opening property were good, but the strength was significantly inferior. Also, the convergence was poor.
In Comparative Example 10 where the organic solvent concentration of the second coagulation bath was as high as 75% by mass, the ratio of major axis / minor axis was 1.42, which was the same as that of the example, but Ry was as small as 0.36 and wrinkles were observed. Since it was shallow and Ry / (major axis / minor axis) was as small as 0.25, the resin impregnation property and the fiber opening property were inferior.
In Comparative Examples 2 and 12, where the organic solvent concentration of the second coagulation bath is as low as 55% by mass, and in Comparative Example 3 where the draw ratio in the second coagulation bath is as high as 4 times, yarn breakage occurs in the second coagulation bath. However, an acrylonitrile fiber bundle could not be produced.

Claims (8)

A carbon fiber precursor fiber bundle made of an acrylonitrile polymer,
The ratio (major axis / minor axis) of the major axis and the minor axis of the cross section of the single fiber constituting the carbon fiber precursor fiber bundle is 1.35 to 1.5,
The maximum height (Ry) of the surface of the single fiber is 0.42 to 0.6 μm,
A carbon fiber precursor fiber bundle in which Ry / (major axis / minor axis) is 0.31 μm or more. The carbon fiber precursor fiber bundle according to claim 1, wherein the acrylonitrile-based polymer contains 0.5 to 4% by mass of an acrylamide monomer unit. The center line average roughness (Ra) of the surface of the single fiber is 0.07 to 0.15 μm,
The carbon fiber precursor fiber bundle according to claim 1 or 2, wherein Ra / (major axis / minor axis) is 0.05 µm or more. The surface of the single fiber has wrinkles, and the local summit interval (S) is 0.7 to 1.0 μm.
The carbon fiber precursor fiber bundle according to claim 1, wherein S / (major axis / minor axis) is 0.5 μm or more. The carbon fiber precursor fiber bundle according to any one of claims 1 to 4, wherein the total fineness of the fiber bundle is 15000 dtex or less. A spinning stock solution comprising an organic solvent solution of an acrylonitrile polymer containing 95% by mass or more of an acrylonitrile unit is placed in a first coagulation bath comprising an organic solvent aqueous solution having an organic solvent concentration of 52 to 58% by mass and a temperature of 30 to 50 ° C. A step of discharging into a coagulated yarn and taking the coagulated yarn from the first coagulation bath at a take-off speed of 0.8 times or less of the spinning solution discharge linear velocity;
A step of subjecting the coagulated yarn to 2.6 to 3.5 times stretching in a second coagulation bath composed of an organic solvent aqueous solution having an organic solvent concentration of 60 to 70% by mass and a temperature of 30 to 50 ° C;
A step of performing wet heat stretching three times or more on the swollen fiber bundle that has been stretched in the second coagulation bath;
A step of performing an oil addition treatment of the silicon-based oil adjusted to 0.4 to 1.5% by mass with respect to the fiber bundle after the wet heat drawing,
A method of producing a carbon fiber precursor fiber bundle having a step of subjecting the fiber bundle to a 1.2 to 4 times steam drawing after the oiling treatment. The method for producing a carbon fiber precursor fiber bundle according to claim 6, wherein the acrylonitrile-based polymer contains 0.5 to 4% by mass of an acrylamide monomer unit. The method for producing a carbon fiber precursor fiber bundle according to any one of claims 6 and 7, wherein the total fineness of the obtained carbon fiber precursor fiber bundle is 15000 dtex or less.

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