JP5313797B2 - Acrylonitrile-based precursor fiber bundle for carbon fiber, method for producing the same, and carbon fiber bundle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acrylonitrile-based precursor fiber bundle for carbon fibers, giving a carbon fiber bundle having good resin impregnation property and openability and high bulkiness, and having excellent bundling property and processability of a baking process; a method for producing the precursor fiber bundle; and a carbon fiber bundle. <P>SOLUTION: There are provided the acrylonitrile-based precursor fiber bundle for carbon fibers composed of single fibers having an average surface roughness (Ra) of 36-55 nm, a maximum peak-to-valley difference (P-V) of 170-270 nm and a surface area ratio (Sratio) of 1.18-1.25; the method for producing the precursor fiber bundle; and the carbon fiber bundle produced by flame-proofing treatment and carbonization treatment of the acrylonitrile-based precursor fiber bundle for carbon fiber. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an acrylonitrile-based precursor fiber bundle for carbon fibers suitable for producing a carbon fiber bundle used as a reinforcing material for a fiber-reinforced composite material, a method for producing the same, and a carbon fiber bundle.

Precursor fiber bundles used in the production of carbon fiber bundles are high so that the fiber bundles are not scattered in the firing process, and the single fibers constituting the fiber bundles are not entangled with adjacent fiber bundles or wound around rollers. Convergence is required.
The carbon fiber bundle is usually impregnated with a matrix resin and molded as a composite material and used for various applications. However, the carbon fiber bundle obtained from the precursor fiber having high sizing property has a problem that the matrix resin is difficult to be impregnated due to its high sizing property. If the matrix resin is difficult to be impregnated, the basic characteristics of the resulting composite material are not sufficiently exhibited.

Further, the carbon fiber fabric obtained by weaving the carbon fiber bundle needs to be a fabric with as few openings as possible so that resin voids (voids) do not occur when the matrix resin is impregnated. For this reason, some opening process is often performed during or after weaving.
However, the carbon fiber bundle obtained from the precursor fiber bundle having high converging property has a problem that it is difficult to open due to its high converging property. Furthermore, since the carbon fiber woven fabric is required to have a uniform weave with little open space, a bulky carbon fiber bundle is required.

Conventionally, as a method for improving the basic characteristics of a composite material, a surface form of a carbon fiber bundle, a method for improving characteristics of a matrix resin, and the like have been studied.
For example, Patent Document 1 discloses an acrylonitrile-based fiber bundle in which wrinkles having a height of 0.5 to 1.0 μm that are continuous in the longitudinal direction of the fiber bundle are present on the surface of the fiber bundle. According to the acrylonitrile-based fiber bundle, the wrinkles present on the surface of the fiber bundle have excellent convergence and good spreadability.

Patent Document 2 discloses a precursor fiber bundle having a roughening degree of 2.0 to 3.0. According to the precursor fiber bundle, by defining the roughening degree, the precursor fiber bundle itself has sufficient performance without exhibiting phenomena such as fusion and sticking between the fiber bundles in the firing step. A carbon fiber bundle that can be exhibited is obtained.
Patent Document 3 discloses a precursor fiber bundle that is a non-circular shape having a rotational symmetry angle θ in which the fiber cross-sectional shape is defined by θ = 360 ° / n (n is an integer of 1 to 10). ing. According to the precursor fiber bundle, the basic characteristics of the composite material can be improved by specifying the cross-sectional shape.

Japanese Patent No. 38084633 JP 59-130320 A JP-A-3-185121

However, the precursor fiber bundles described in Patent Documents 1 and 2 do not always satisfy the convergence. Moreover, the passability in the firing step may be reduced.
Moreover, it was difficult for the precursor fiber bundle described in Patent Document 3 to simultaneously satisfy the permeability in the firing step and the resin impregnation property and the fiber opening property of the obtained carbon fiber bundle.

  The present invention has been made in view of the above circumstances, and has good resin impregnation and spreadability, can obtain a bulky carbon fiber bundle, has excellent bundling properties, and has good firing process passability. An object of the present invention is to provide an acrylonitrile-based precursor fiber bundle, a method for producing the same, and a carbon fiber bundle.

As a result of intensive studies, the inventors of the present invention have improved the convergence of the precursor fiber bundle and the ability to pass through the firing process by controlling the surface form of the single fiber constituting the precursor fiber bundle to have a specific uneven shape. In addition, the present inventors have found that a carbon fiber bundle having good resin impregnation properties and fiber opening properties can be obtained, and the present invention has been completed.
That is, the acrylonitrile-based precursor fiber bundle for carbon fiber of the present invention comprises an acrylonitrile-based polymer containing 95% by mass or more of acrylonitrile units and 0.5 to 4% by mass of acrylamide units, and has an average surface roughness of the surface. (Ra) is 36 to 55 nm, the maximum height difference (P-V) is 170 to 270 nm, and the surface area ratio (Sratio) is 1.18 to 1.25.

Moreover, the manufacturing method of the acrylonitrile type | system | group precursor fiber bundle for carbon fibers of this invention is 95 mass% or more in the 1st coagulation bath which consists of organic-solvent aqueous solution of 55-68 mass% of organic solvent concentration, and the temperature of 33-40 degreeC. A spinning stock solution comprising an organic solvent solution of an acrylonitrile polymer containing acrylonitrile units of 0.5 to 4% by mass is discharged into a coagulated yarn, and the coagulated yarn is spun from the first coagulation bath. A step of drawing at a rate of 0.8 times or less of the discharge line speed of the stock solution, and subsequently, the coagulated yarn is placed in a second coagulation bath comprising an organic solvent aqueous solution having an organic solvent concentration of 55 to 68% by mass and a temperature of 33 to 40 ° C. Stretching the fiber bundle 1.5 to 2 times to form a bundle in a swollen state, applying the heat-stretched fiber bundle 3 times or more to the stretched fiber bundle, Oil processing When, after drying the fiber bundle which has been hydrogenated oil processed, characterized in that a step of performing a steam drawing of 1.5 to 2.5 times the fiber bundle.
Furthermore, it is preferable that the swelling degree of the wet-heat-stretched fiber bundle is 90% by mass or less.

  In addition, the carbon fiber bundle of the present invention is obtained by making the acrylonitrile-based precursor fiber bundle for carbon fiber flameproof and carbonized.

  According to the present invention, an acrylonitrile-based precursor fiber bundle for carbon fibers that has a good resin impregnation property and spreadability, can obtain a bulky carbon fiber bundle, has excellent converging properties, and has good firing process passability. And a manufacturing method thereof, and a carbon fiber bundle can be provided.

Hereinafter, the present invention will be described in detail.
The acrylonitrile-based precursor fiber bundle for carbon fibers of the present invention (hereinafter referred to as “precursor fiber bundle”) is a tow obtained by bundling a plurality of single fibers of an acrylonitrile-based polymer.
As the acrylonitrile polymer, an acrylonitrile polymer containing 95% by mass or more of acrylonitrile units and 0.5 to 4% by mass of acrylamide units is used. When the acrylamide unit exceeds 4% by mass, strength development of the carbon fiber bundle obtained by firing the precursor fiber bundle of the present invention is lowered. On the other hand, if the acrylamide unit is less than 0.5% by mass, the solubility of the acrylonitrile-based polymer in the organic solvent solution is lowered, and the coagulation speed when discharged into the coagulation bath through the spinneret is increased, and the spinning is performed. Stability is reduced. As a result, it becomes difficult to control the surface form of the single fiber, and it becomes difficult to obtain a single fiber having a specific uneven shape.

  Acrylonitrile polymers are acrylonitrile and acrylamide, and monomers that can be copolymerized with these monomers as needed, redox polymerization in aqueous solution, suspension polymerization in heterogeneous system, emulsification using dispersant It can be obtained by polymerization, such as by polymerization.

Examples of monomers that can be copolymerized with acrylonitrile and acrylamide include (meth) acrylic such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, and hexyl (meth) acrylate. Acid 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, methacrylamide, styrene , Α-methylstyrene, vinyl acetate; polymerizable unsaturated monomer containing a sulfone group such as sodium styrenesulfonate sodium allylsulfonate, β-styrenesulfonate sodium, methallylsulfonate sodium; 2-vinylpyridine, 2 -Methyl-5-vinylpi Examples thereof include polymerizable unsaturated monomers containing a pyridine group such as lysine.
Among these, acids such as (meth) acrylic acid, itaconic acid, crotonic acid, and salts thereof are particularly flame-resistant when firing a precursor fiber bundle obtained by spinning the obtained acrylonitrile-based polymer. It is preferably used in that the firing rate of the is increased.

  The single fiber constituting the precursor fiber bundle of the present invention has an average surface roughness (Ra) of 36 to 55 nm, a maximum height difference (P-V) of 170 to 270 nm, and a surface area ratio (Sratio) of 1.18. ~ 1.25.

  When the average surface roughness (Ra) of the single fiber is less than 36 nm, the bulkiness of the carbon fiber bundle obtained by firing the precursor fiber bundle is insufficient, and the resin impregnation property, the fiber opening property, and the carbon fiber fabric (cross) Covering performance when using the On the other hand, when the average surface roughness (Ra) of the single fiber exceeds 55 nm, the surface area of the precursor fiber bundle increases, and static electricity is likely to be generated. There is a possibility that it will be easy to disperse and the baking process passability will deteriorate. Moreover, it exists in the tendency for the strand strength of the carbon fiber bundle obtained to fall.

  When the maximum height difference (P-V) of the single fibers is less than 170 nm, the bulkiness of the obtained carbon fiber bundle is insufficient, and the resin impregnation property, the fiber opening property and the covering property when made into a cloth are deteriorated. On the other hand, when the maximum height difference (P-V) of the single fiber exceeds 270 nm, the strength of the precursor fiber bundle decreases, and the spinning stability tends to decrease.

  When the surface area ratio (Sratio) of the single fiber is less than 1.18, it becomes difficult to reach a level that sufficiently satisfies the converging property of the precursor fiber bundle and the passability of the firing process. On the other hand, when the surface area ratio (Sratio) of the single fiber exceeds 1.25, the surface area of the precursor fiber bundle is increased and static electricity is easily generated, the convergence is lowered, and the precursor fiber bundle is reduced in the firing step. There is a possibility that it will be easy to disperse and the baking process passability will deteriorate. Moreover, it exists in the tendency for the strand strength of the carbon fiber bundle obtained to fall.

The average surface roughness (Ra), maximum height difference (PV), and surface area ratio (Sratio) of single fibers are values measured using a scanning probe microscope and are defined as follows.
The average surface roughness (Ra) is a three-dimensional extension of the centerline average roughness defined in JIS B0601 so that it can be applied to the measurement surface. The absolute value of the deviation from the reference surface to the specified surface Is an average value.
The maximum height difference (P−V) is a difference between the maximum value Zmax and the minimum value Zmin of the Z data in the cross-sectional profile in the direction perpendicular to the Z fiber axis. Note that the Z data is height data based on XY axis coordinate positions and Z axis height data measured by a scanning probe microscope.
The surface area ratio (Sratio) is the ratio (S ₁ / S ₀ ) of the actual surface area S ₁ to the area S ₀ when the designated surface is assumed to be ideally flat.

The average surface roughness (Ra), maximum height difference (PV), and surface area ratio (Sratio) of single fibers can be measured as follows.
Collect several single fibers and place them on a sample table to fix both ends to make a measurement sample. Measurement is performed in a shape measurement mode using a cantilever with a scanning probe microscope. A measurement image is obtained by scanning a range of 1 to 3 μm as a range in which the influence of the curved surface of the single fiber is as small as possible and reflecting the fiber surface shape. The obtained measurement image is subjected to data processing to obtain an image obtained by fitting the curved surface of the single fiber to a plane. The shape parameter of the fiber surface is obtained from the surface roughness analysis of the flattened image.
The measurement is carried out by measuring the shape of 10 single yarns per sample with a scanning probe microscope, obtaining the shape parameters for each measurement image by the method described above, and calculating the average value of the average surface roughness (Ra) and the maximum height difference of the sample. (PV), surface area ratio (Sratio).

  Since the precursor fiber bundle of the present invention has the above-described specific uneven shape on the surface of the single fiber, it has excellent convergence and good firing process passability. The carbon fiber bundle obtained by firing the precursor fiber bundle is bulky and has good resin impregnation and fiber opening properties.

Next, the manufacturing method of the precursor fiber bundle of this invention is demonstrated.
The precursor fiber bundle of the present invention composed of single fibers having the specific uneven shape described above can be produced, for example, as follows.
First, a spinning stock solution composed of an organic solvent solution of acrylonitrile-based polymer containing 95% by mass or more of acrylonitrile units and 0.5 to 4% by mass of acrylamide units is passed through a spinneret, and the organic solvent concentration is 55 to 68% by mass. The coagulated yarn is discharged into a first coagulation bath made of an organic solvent aqueous solution at a temperature of 33 to 40 ° C. to obtain a coagulated yarn. Take over at the take-off speed.
Next, the coagulated yarn was stretched 1.5 to 2 times in a second coagulation bath composed of an organic solvent aqueous solution having an organic solvent concentration of 55 to 68% by mass and a temperature of 33 to 40 ° C. To do.

Subsequently, the stretched and swollen fiber bundle is subjected to wet heat stretching three times or more.
Next, after adding the silicone oil adjusted to a concentration of 0.4 to 1.5% by mass to the fiber bundle that has been wet-heat-stretched, and performing the oil addition treatment, the fiber bundle subjected to the oil addition treatment is dried, Steam stretching is performed 1.5 to 2.5 times with a steam stretching machine.
The moisture content of the fiber bundle is adjusted with a touch roll, and then the yarn is entangled by blowing air onto the yarn to obtain a precursor fiber bundle.

Examples of the organic solvent for the acrylonitrile polymer used in the spinning dope include dimethylacetamide, dimethylsulfoxide, dimethylformamide, and the like. Among these, dimethylacetamide is preferably used because it hardly deteriorates in properties due to hydrolysis of the solvent and gives good spinnability.
As the organic solvent used for the first coagulation bath and the second coagulation bath, it is preferable to use the same solvent as the organic solvent used for the spinning dope.

  The concentration of the acrylonitrile polymer in the spinning dope is preferably 18 to 26% by mass, and more preferably 20 to 22% by mass. When the concentration of the acrylonitrile-based polymer is 18% by mass or more, a precursor fiber bundle having a dense fiber interior is obtained, and a carbon fiber bundle having high mechanical strength is easily obtained. On the other hand, when the concentration of the acrylonitrile-based polymer is 26% by mass or less, the viscosity of the spinning dope becomes appropriate and the spinning stability becomes good.

 Here, the organic solvent concentrations of the first coagulation bath and the second coagulation bath are made the same, the temperatures of the first coagulation bath and the second coagulation bath are made the same, and further, the organic solvent of the spinning stock solution and the first coagulation bath are used. By taking measures such as making the organic solvent used and the organic solvent used in the second coagulation bath the same, the preparation of the first coagulation bath and the second coagulation bath is facilitated, and there are also advantages in terms of solvent recovery. .

  And a spinning stock solution comprising a dimethylacetamide solution of an acrylonitrile-based polymer, a first coagulation bath comprising a dimethylacetamide aqueous solution, and a second coagulation bath comprising a dimethylacetamide aqueous solution having the same temperature and composition as the first coagulation bath. When used, it is possible to easily produce single fibers having an average surface roughness (Ra) of 36 to 55 nm, a maximum height difference (P-V) of 170 to 270 nm, and a surface area ratio (Sratio) of 1.18 to 1.25. It becomes like this.

  Moreover, if the organic solvent density | concentration of a 1st coagulation bath and a 2nd coagulation bath is in the said range, the average surface roughness (Ra), the maximum height difference (PV), and the surface area ratio (Sratio) of a single fiber will be set. Easy to adjust. Specifically, the values of the average surface roughness (Ra), the maximum height difference (PV), and the surface area ratio (Sratio) are increased by lowering the organic solvent concentration in the first coagulation bath and the second coagulation bath. A single fiber is obtained. On the other hand, by increasing the concentration of the organic solvent in the first coagulation bath and the second coagulation bath, single fibers having small average surface roughness (Ra), maximum height difference (PV), and surface area ratio (Sratio) are obtained. can get.

  In addition, when the temperature of the first coagulation bath and the second coagulation bath is less than 33 ° C., the coagulated yarn is difficult to coagulate, and it is necessary to reduce the take-up speed of the coagulated yarn, which decreases productivity. On the other hand, when the temperature of the first coagulation bath and the second coagulation bath exceeds 40 ° C., the coagulated yarns are easily fused.

Further, the take-up speed of the coagulated yarn from the first coagulation bath is 0.8 times or less of the discharge linear speed of the stock solution from the nozzle hole of the spinneret (the take-up speed of the coagulated yarn / the stock solution from the nozzle hole). If the discharge linear velocity is less than 0.8), good spinnability can be maintained. The lower limit of the take-up speed is not particularly limited, but is preferably 0.4 times or more of the discharge linear speed.
For the spinneret for extruding the spinning dope, acrylonitrile polymer single fibers of about 1.08 denier (1.2 dTex), which is a general thickness of acrylonitrile polymer single fibers, are produced. A spinneret having a nozzle hole having a diameter of 15 to 100 μm can be used.

In such a precursor fiber bundle manufacturing method, the concentration of the organic solvent in the liquid contained in the coagulated yarn of the coagulated yarn pulled up from the first coagulation bath exceeds the concentration of the organic solvent in the first coagulation bath. Therefore, only the surface of the coagulated yarn becomes a coagulated yarn in a semi-solidified state, and the coagulated yarn has good stretchability in the second coagulation bath in the next step.
Further, 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 this coagulated yarn can be drawn in the second coagulation bath as in the above method. By adopting a means for stretching at, solidification of the coagulated yarn can be promoted, and temperature control in the stretching process is facilitated.

  If the draw ratio in the second coagulation bath is lower than 1.5 times, uniformly oriented fibers cannot be obtained, and if it is higher than 2.0 times, single fiber breakage is likely to occur, and spinning stability is improved. In addition, the stretchability in the subsequent wet heat stretching process deteriorates.

  The wet heat drawing after the drawing step in the second coagulation bath is for further enhancing the fiber orientation. This wet heat stretching is performed by stretching a fiber bundle in a swollen state (swelling fiber bundle) that has been stretched in the second coagulation bath while being washed with water, or by stretching in hot water. Among them, it is preferable to perform stretching in hot water from the viewpoint of high productivity. In addition, when the draw ratio in this wet heat drawing process is made lower than 3 times, the improvement of fiber orientation becomes insufficient. The upper limit of the draw ratio in the wet heat drawing step is not particularly limited, but is preferably 5 times or less.

The swelling degree of the wet and heat-stretched fiber bundle (before drying) is preferably 90% by mass or less. When the degree of swelling of the wet and heat-stretched fiber bundle is 90% by mass or less, it becomes easy to obtain fibers that are uniformly oriented to the inside of the fiber.
The degree of swelling of the wet-heat-stretched fiber bundle can be adjusted by adjusting the take-up speed of the coagulated yarn from the first coagulation bath. That is, by lowering the value of “coagulated yarn take-off speed / spinning solution discharge linear velocity from nozzle hole”, coagulation of the coagulated yarn in the first coagulation bath can be made uniform. By stretching in the two coagulation bath, the fiber can be uniformly oriented to the inside of the fiber, and the swelling degree of the wet and heat-stretched fiber bundle can be easily adjusted to 90% by mass or less.
On the other hand, if the value of “coagulated yarn take-up speed / spinning solution discharge linear velocity from nozzle hole” is increased, coagulation and stretching of the coagulated yarn in the first coagulation bath are likely to occur simultaneously. As a result, coagulation of the coagulated yarn in the first coagulation bath becomes uneven. Therefore, even if this is stretched in the second coagulation bath, the wet-heat-stretched fiber bundle has a high degree of swelling, making it difficult to obtain fibers that are uniformly oriented to the inside of the fiber.

The degree of swelling of the wet-heat-stretched fiber bundle is determined by the mass w ₁ of the wet-heat-stretched fiber bundle after removing the adhering liquid adhering to the wet-heat-stretched fiber bundle by a centrifuge (3000 rpm, 15 minutes). Is measured with a hot air drier at 105 ° C. for 2 hours, and the mass w ₀ is measured and can be determined by the following equation.
Swelling degree (mass%) = (w ₁ −w ₀ ) / w ₀ × 100

A general silicone-based oil agent or a low silicone oil agent can be used for the oil addition treatment for the fiber bundle that has been subjected to wet heat drawing. The method of the oil addition treatment is not particularly limited, and examples thereof include a method of diving a fiber bundle that has been wet-heat drawn in an oil bath.
The silicone-based oil used for the oiling treatment is used after being adjusted to a concentration of 0.4 to 1.5% by mass. If the concentration is less than 0.4% by mass, the fiber bundle may not be sufficiently converged in the drying step and the subsequent firing step, and the process passability may be impaired. On the other hand, if the concentration exceeds 1.5% by mass, fusion or adhesion between single fibers occurs, fuzz and single yarn breakage are induced, and the quality and quality of the obtained carbon fiber bundle are likely to be deteriorated.

  The fiber bundle that has been oiled is densified by drying. At the time of drying, it is preferable that the temperature be higher than the glass transition temperature of the precursor fiber bundle, and it is preferable that the temperature is substantially brought into contact with a hot roll at 100 to 200 ° C. for drying.

The steam drawing after drying is for obtaining a precursor fiber bundle and a carbon fiber bundle having high mechanical strength. This steam stretching is performed using a known steam stretching machine.
If the draw ratio of the steam drawing is lower than 1.5 times, the effect of the steam drawing cannot be sufficiently obtained, and the mechanical strength of the precursor fiber bundle or the carbon fiber bundle is likely to be lowered, and more than 2.5 times. If it is increased, the spinning stability tends to be impaired. Therefore, the steam draw ratio is in the range of 1.5 to 2.5 times in consideration of the draw ratio (solvent draw ratio) in the second coagulation bath before drying and densification and the balance with the wet heat draw ratio. It is important to set within.

A carbon fiber bundle can be produced by firing the precursor fiber bundle thus obtained by a known method. Examples of the firing method include a method of performing flameproofing treatment and carbonization treatment in this order.
In the flameproofing treatment, the precursor fiber bundle is put into a hot air circulation type flameproofing furnace at 230 to 260 ° C. in the air and treated for 30 to 60 minutes to obtain a flameproof fiber bundle.
In the carbonization treatment, the flame-resistant fiber bundle is treated in a nitrogen atmosphere at a maximum temperature of about 800 ° C. for 1 to 2 minutes, and further in the same atmosphere in a high-temperature heat treatment furnace having a maximum temperature of 1000 to 2000 ° C. for about 1 to 2 minutes. A carbon fiber bundle is obtained by processing.
For the purpose of developing the strength of the fiber-reinforced composite material, the carbon fiber bundle surface may be subjected to electrolytic treatment after carbonization treatment as necessary to give a carbon fiber sizing agent.

The carbon fiber bundle thus obtained is obtained by firing the precursor fiber bundle of the present invention, so that it is bulky and has excellent resin impregnation and fiber opening properties.
The carbon fiber bundle of the present invention is molded as a fiber reinforced composite material by impregnating a matrix resin by a conventional method. Although it does not restrict | limit especially as a matrix resin, For example, an epoxy resin, a phenol resin, a polyester resin, a polycarbonate resin, a polyamide resin, a polypropylene resin, an ABS resin etc. are mentioned.

According to the present invention, since a carbon fiber bundle can be sufficiently impregnated with a matrix resin, a fiber-reinforced composite material that can sufficiently exhibit basic characteristics can be obtained.
Moreover, since the carbon fiber bundle of the present invention is bulky, a carbon fiber woven fabric having a uniform weave with few voids can be obtained. Further, since the carbon fiber woven fabric is obtained from a carbon fiber bundle having a good opening property, resin voids are hardly generated even when impregnated with a matrix resin.

Hereinafter, the present invention will be described in detail with reference to examples. However, the present invention is not limited to these.
Various measurement and evaluation methods are as follows.

<Measurement of average surface roughness (Ra), maximum height difference (PV), surface area ratio (Sratio)>
Both ends of the single fiber of the precursor fiber bundle are fixed with a carbon paste on a metal sample stage for SPA400 (20 mm diameter) attached to a scanning probe microscope (Eployd Service, “KY10200167”), and the following conditions The measurement was performed.

(Scanning probe microscope measurement conditions)
Apparatus: manufactured by SII Nano Technology, "SPI4000 probe station, SPA400 (unit)"
Scanning mode: Dynamic force mode (DFM) (shape image measurement),
Probe: "SI-DF-20", manufactured by SII Nano Technology,
Scanning range: 2 μm × 2 μm,
Rotation: 90 ° (scan in the direction perpendicular to the fiber axis direction),
Scanning speed: 1.0 Hz
Number of pixels: 512 × 512,
Measurement environment: room temperature, in air.

  One image was obtained for one single fiber under the above conditions, and the obtained image was subjected to image analysis under the following conditions using image analysis software (SPIWin) attached to a scanning probe microscope.

(Image analysis conditions)
The obtained shape image was subjected to “flat processing”, “median 8 processing”, and “third-order tilt correction” to obtain an image obtained by fitting the curved surface to a plane. The average surface roughness (Ra) from the surface roughness analysis of the flattened image, the maximum height difference (PV) from the cross-sectional profile in the direction perpendicular to the fiber axis of the flattened image, and the surface of the flattened image The surface area ratio (Sratio) was determined from the roughness analysis.
Measurement is carried out by measuring the shape of 10 single yarns per sample with a scanning probe microscope, and obtaining the average surface roughness (Ra), maximum height difference (PV), and surface area ratio (Sratio) for each measurement image. The average value was defined as the average surface roughness (Ra), the maximum height difference (PV), and the surface area ratio (Sratio).
The “flat processing”, “median 8 processing”, and “cubic tilt correction” are as follows.

(Flat processing)
This is a process for removing distortion and undulation in the Z-axis direction that appeared in image data due to lift, vibration, scanner creep, and the like. Data distortion due to device factors in SPM measurement can be removed.
(Median 8 processing)
In the 3 × 3 window (matrix) centered on the data point S to be processed, the calculation is performed between S and D1 to D8, and the Z data of S is replaced. Filter effects such as smoothing and noise removal can be obtained.
The median 8 processing can be performed by calculating the median value of 9 points of Z data of S and D1 to D8 and replacing S.
(Cubic tilt correction)
The tilt correction is to correct a tilt by obtaining and fitting a curved surface from all data of the processing target image by least square approximation. (Primary), (Secondary), and (Cubic) indicate the degree of the curved surface to be fitted. In the cubic, the cubic surface is fitted. The cubic tilt correction process eliminates the curvature of the data fibers and makes a flat image.

<Measurement of swelling degree>
The adhering liquid adhering to the wet-heat-stretched fiber bundle was removed using a centrifuge at 3000 rpm for 15 minutes, and the mass w ₁ of the wet-heat-stretched fiber bundle was measured. Next, the mass w ₀ after drying the wet-heat-stretched fiber bundle with a hot air dryer at 105 ° C. for 2 hours was measured, and the degree of swelling was determined by the following equation.
Swelling degree (mass%) = (w ₁ −w ₀ ) / w ₀ × 100

<Evaluation of spinning stability>
The spinning state in the first coagulation bath was visually observed.

<Evaluation of convergence>
The precursor fiber bundle was visually observed and evaluated according to the following evaluation criteria.
○: The bundle is not scattered.
Δ: The bundles are slightly scattered.
X: The bundle is scattered.

<Evaluation of baking process passability>
The permeability at the time of firing the precursor fiber bundle was visually observed and evaluated according to the following evaluation criteria.
○: The single fibers are not separated and the fiber bundles can be fired without being entangled.
(Triangle | delta): The single fiber was scattered a little and the adjacent fiber bundles were slightly entangled.
X: Single fibers were scattered and adjacent fiber bundles were entangled.

<Evaluation of 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, and evaluated according to the following evaluation criteria.
○: The mass ratio of the glycidyl ether sucked up is 3% by mass or more.
X: The mass ratio of the glycidyl ether sucked up is less than 3% by mass.

<Evaluation of spreadability>
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 and evaluated according to the following evaluation criteria. .
○: Tow width is 2 mm or more.
X: Tow width is less than 2 mm.

[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.
This acrylonitrile-based polymer was dissolved in dimethylacetamide to prepare a 21% by mass spinning solution.

This spinning dope 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 65% by mass and a temperature of 35 ° C. to obtain coagulated yarn. The yarn was taken up at a take-up speed of 0.6 times the discharge linear speed of the spinning dope.
The coagulated yarn was subsequently introduced into a second coagulation bath composed of an aqueous dimethylacetamide solution having a concentration of 65% by mass and a temperature of 35 ° C., and stretched 1.8 times in the bath.
Subsequently, the stretched fiber bundle (swelling fiber bundle) was wet-heat-stretched 3.5 times simultaneously with water washing.
Thereafter, an aminosilicone-based oil adjusted to a concentration of 1.1% by mass was added to the fiber bundle that had been wet-heat drawn.
Next, the fiber bundle that had been subjected to the oil addition treatment was dried using a hot roll, and steam-stretched 2.1 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 3% by mass of water per fiber. Subsequently, the fiber bundle was entangled with air having an air pressure of 280 kPa and wound with a winder to obtain an acrylonitrile-based precursor fiber bundle for carbon fibers having a single fiber fineness of 1.2 dtex.

When spinning the spinning dope, no fluff was generated and the spinning stability was very good.
The degree of swelling of the wet heat-stretched fiber bundle, and the average surface roughness (Ra), maximum height difference (P-V), and surface area ratio (Sratio) of the obtained precursor fiber bundle were measured to evaluate the convergence. . The results are shown in Table 1.

Further, the obtained precursor fiber bundle was treated in air in a hot air circulation type flameproof furnace at 230 to 260 ° C. for 50 minutes to form a flameproof fiber bundle, and then the flameproof fiber bundle was heated to a maximum temperature of 780 in a nitrogen atmosphere. Treated for 1.5 minutes at ℃, and further treated for about 1.5 minutes in a high-temperature heat treatment furnace with the maximum temperature of 1300 ℃ under the same atmosphere, and then electrolyzed in aqueous ammonium bicarbonate solution at 0.4 Amin / m To obtain a carbon fiber bundle.
The passability of the precursor fiber bundle through the firing process, and the resin impregnation property and fiber opening property of the obtained carbon fiber bundle were evaluated. The results are shown in Table 1.

[Example 2]
It is discharged into a first coagulation bath made of a dimethylacetamide aqueous solution having a concentration of 56% by mass and a temperature of 34 ° C. to form a coagulated yarn, and this coagulated yarn is 0.6 times the discharge linear velocity of the spinning dope from the first coagulation bath. It was picked up at the pick-up speed.
The coagulated yarn was subsequently introduced into a second coagulation bath composed of an aqueous dimethylacetamide solution having a concentration of 56% by mass and a temperature of 34 ° C., and stretched 1.9 times in the bath.
Next, the stretched fiber bundle (swelled fiber bundle) was subjected to wet heat stretching 3.3 times at the same time as washing with water, and steam stretched 2.1 times with a steam stretching machine. In the same manner as in Example 1, a precursor fiber bundle having a single fiber fineness of 1.2 dtex was obtained.
When spinning the spinning dope, no fluff was generated and the spinning stability was very good.
The degree of swelling of the wet heat-stretched fiber bundle, and the average surface roughness (Ra), maximum height difference (P-V), and surface area ratio (Sratio) of the obtained precursor fiber bundle were measured to evaluate the convergence. . The results are shown in Table 1.

[Example 3]
It is discharged into a first coagulation bath comprising a dimethylacetamide aqueous solution having a concentration of 67% by mass and a temperature of 34 ° C. to obtain a coagulated yarn, and this coagulated yarn is 0.6 times the discharge linear velocity of the spinning dope from the first coagulation bath. It was picked up at the pick-up speed.
The coagulated yarn was subsequently introduced into a second coagulation bath composed of an aqueous dimethylacetamide solution having a concentration of 67% by mass and a temperature of 34 ° C., and stretched 1.9 times in the bath.
Next, the stretched fiber bundle (swelled fiber bundle) was subjected to wet heat stretching 3.3 times at the same time as washing with water, and steam stretched 2.1 times with a steam stretching machine. In the same manner as in Example 1, a precursor fiber bundle having a single fiber fineness of 1.2 dtex was obtained.
When spinning the spinning dope, no fluff was generated and the spinning stability was very good.
The degree of swelling of the wet heat-stretched fiber bundle, and the average surface roughness (Ra), maximum height difference (P-V), and surface area ratio (Sratio) of the obtained precursor fiber bundle were measured to evaluate the convergence. . The results are shown in Table 1.

[Example 4]
It is discharged into a first coagulation bath made of a dimethylacetamide aqueous solution having a concentration of 56% by mass and a temperature of 38 ° C. to form a coagulated yarn, and this coagulated yarn is 0.6 times the discharge linear velocity of the spinning dope from the first coagulation bath. It was picked up at the pick-up speed.
The coagulated yarn was subsequently introduced into a second coagulation bath composed of an aqueous dimethylacetamide solution having a concentration of 56 mass% and a temperature of 38 ° C., and stretched 1.7 times in the bath.
Subsequently, the stretched fiber bundle (swelled fiber bundle) was subjected to wet heat stretching 3.3 times at the same time as washing with water and steam stretched 2.4 times with a steam stretching machine. In the same manner as in Example 1, a precursor fiber bundle having a single fiber fineness of 1.2 dtex was obtained.
When spinning the spinning dope, no fluff was generated and the spinning stability was very good.
The degree of swelling of the wet heat-stretched fiber bundle, and the average surface roughness (Ra), maximum height difference (P-V), and surface area ratio (Sratio) of the obtained precursor fiber bundle were measured to evaluate the convergence. . The results are shown in Table 1.

[Example 5]
A coagulated yarn is discharged into a first coagulation bath comprising a dimethylacetamide aqueous solution having a concentration of 67% by mass and a temperature of 38 ° C., and this coagulated yarn is 0.6 times the discharge linear velocity of the spinning dope from the first coagulation bath. It was picked up at the pick-up speed.
The coagulated yarn was subsequently introduced into a second coagulation bath composed of a dimethylacetamide aqueous solution having a concentration of 67% by mass and a temperature of 38 ° C., and stretched 1.7 times in the bath.
Subsequently, the stretched fiber bundle (swelled fiber bundle) was subjected to wet heat stretching 3.3 times at the same time as washing with water and steam stretched 2.4 times with a steam stretching machine. In the same manner as in Example 1, a precursor fiber bundle having a single fiber fineness of 1.2 dtex was obtained.
When spinning the spinning dope, no fluff was generated and the spinning stability was very good.
The degree of swelling of the wet heat-stretched fiber bundle, and the average surface roughness (Ra), maximum height difference (P-V), and surface area ratio (Sratio) of the obtained precursor fiber bundle were measured to evaluate the convergence. . The results are shown in Table 1.

[Comparative Example 1]
Acrylonitrile, methyl acrylate and methacrylic acid were copolymerized by aqueous suspension polymerization in the presence of ammonium persulfate-ammonium hydrogen sulfite and iron sulfate, and acrylonitrile unit / methyl acrylate unit / methacrylic acid unit = 96/3/1 ( A precursor fiber bundle having a single fiber fineness of 1.2 dtex was obtained in the same manner as in Example 1 except that an acrylonitrile-based polymer comprising (mass ratio) was used.
The obtained precursor fiber bundle was slightly scattered and inferior in convergence.
The degree of swelling of the wet-heat-stretched fiber bundle, and the average surface roughness (Ra), maximum height difference (PV), and surface area ratio (Sratio) of the obtained precursor fiber bundle were measured. The results are shown in Table 1.

Further, this precursor fiber bundle was fired in the same manner as in Example 1. However, in the firing process, the single fibers constituting the fiber bundle were slightly dispersed, and the adjacent fiber bundles were slightly entangled with each other. Inferior to
The obtained carbon fiber bundle was evaluated for resin impregnation property and fiber opening property. The results are shown in Table 1.

[Comparative Example 2]
A precursor fiber bundle having a single fiber fineness of 1.2 dtex was produced in the same manner as in Example 1 except that the second coagulation bath was bypassed and 1.8-fold drawing was performed by air drawing (cold drawing). The spinning stability was poor, it was difficult to spin, and a precursor fiber bundle could not be obtained.

[Comparative Example 3]
A precursor fiber bundle having a single fiber fineness of 1.2 dtex was obtained in the same manner as in Example 1 except that the wet heat draw ratio was changed to 2.3 times and the steam draw ratio was changed to 3.2 times.
When spinning the spinning dope, no fluff was produced, and spinning stability comparable to that of Example 1 was obtained.
The degree of swelling of the wet heat-stretched fiber bundle, and the average surface roughness (Ra), maximum height difference (P-V), and surface area ratio (Sratio) of the obtained precursor fiber bundle were measured to evaluate the convergence. . The results are shown in Table 1.

Further, this precursor fiber bundle was fired in the same manner as in Example 1. However, in the firing process, the single fibers constituting the fiber bundle were slightly dispersed, and the adjacent fiber bundles were slightly entangled with each other. Inferior to
The obtained carbon fiber bundle was evaluated for resin impregnation property and fiber opening property. The results are shown in Table 1.

[Comparative Example 4]
A precursor fiber bundle having a single fiber fineness of 1.2 dtex was obtained in the same manner as in Example 1 except that the draw ratio in the bath in the second coagulation bath was changed to 2.2 times, but the spinning dope was spun. In some cases, some fluff was generated and the spinning stability was poor.
The degree of swelling of the wet heat-stretched fiber bundle, and the average surface roughness (Ra), maximum height difference (P-V), and surface area ratio (Sratio) of the obtained precursor fiber bundle were measured to evaluate the convergence. . The results are shown in Table 1.

Further, this precursor fiber bundle was fired in the same manner as in Example 1. However, in the firing process, the process passability during firing was inferior, such as fuzz entangled with adjacent fibers.
The obtained carbon fiber bundle was evaluated for resin impregnation property and fiber opening property. The results are shown in Table 1.

[Comparative Example 5]
A precursor fiber bundle was produced in the same manner as in Example 1 except that a dimethylacetamide aqueous solution having a concentration of 50% by mass and a temperature of 30 ° C. was used as the first coagulation bath and the second coagulation bath, but the spinning stability was poor. It was difficult to spin, and a precursor fiber bundle could not be obtained.

From the results shown in Table 1, the precursor fiber bundles obtained in the respective examples were able to produce carbon fiber bundles that were excellent in bundling property, good in firing process passability, and good in resin impregnation and spreadability. .
On the other hand, the precursor fiber bundle obtained in Comparative Examples 1 and 4 has an average surface roughness (Ra) of more than 55 nm, a maximum height difference (PV) of more than 270 nm, and a surface area ratio (Sratio) of more than 1.25. It was comprised from the single fiber which is. The precursor fiber bundle was inferior to the precursor fiber bundle obtained in Example 1 in the bundling property and the firing process passability.
The precursor fiber bundle obtained in Comparative Example 3 has an average surface roughness (Ra) of less than 36 nm, a maximum height difference (P-V) of less than 170 nm, and a surface area ratio (Sratio) of less than 1.18. It was composed of monofilament. The precursor fiber bundle was inferior in the firing process passability as compared with the precursor fiber bundle obtained in Example 1. Furthermore, the carbon fiber bundle obtained by firing the precursor fiber bundle of Comparative Example 3 was inferior in resin impregnation property and fiber opening property.
Further, in Comparative Examples 2 and 5, the spinning stability was poor and the precursor fiber bundle was not obtained, so the bundling property, the firing process passability, the resin impregnation property of the carbon fiber bundle, and the fiber opening property could not be evaluated. It was.

Claims (4)

It is composed of an acrylonitrile polymer containing 95% by mass or more of acrylonitrile units and 0.5 to 4% by mass of acrylamide units, and has an average surface roughness (Ra) of 36 to 55 nm and a maximum height difference (PV). Is an acrylonitrile-based precursor fiber bundle for carbon fibers, which is composed of single fibers having a surface area ratio (Sratio) of 1.18 to 1.25. An acrylonitrile system containing 95% by mass or more of acrylonitrile units and 0.5 to 4% by mass of acrylamide units in a first coagulation bath comprising an organic solvent aqueous solution having an organic solvent concentration of 55 to 68% by mass and a temperature of 33 to 40 ° C. A step of discharging a spinning stock solution composed of an organic solvent solution of a polymer into a coagulated yarn, and drawing the coagulated yarn from the first coagulation bath at a rate of 0.8 times or less of the discharge linear velocity of the spinning stock solution;
Subsequently, the coagulated yarn is stretched 1.5 to 2 times in a second coagulation bath made of an organic solvent aqueous solution having an organic solvent concentration of 55 to 68% by mass and a temperature of 33 to 40 ° C. And a process of
After the stretched and swollen fiber bundle has been subjected to wet heat stretching three times or more, the wet heat stretched fiber bundle is subjected to an oil treatment, and the oil treated fiber bundle is dried, A method for producing an acrylonitrile-based precursor fiber bundle for carbon fibers, the method comprising a step of performing 1.5 to 2.5 times steam drawing.   The method for producing an acrylonitrile-based precursor fiber bundle for carbon fibers according to claim 2, wherein the swelling degree of the wet-heat-stretched fiber bundle is 90% by mass or less.   A carbon fiber bundle obtained by flameproofing and carbonizing the acrylonitrile-based precursor fiber bundle for carbon fibers according to claim 1.