JP2000248432A - Production of chopped carbon fiber strand and chopped carbon fiber strand - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently produce a chopped carbon fiber strand which has a high bulk density, an excellent compounding property, and is suitable for carbon fiber-reinforced composite materials. SOLUTION: This method for producing a chopped carbon fiber strand comprises subjecting a polyacrylonitrile-based fiber bundle comprising 30,000 to 350,000 filaments in a substantially non-twisted state to a flame-proofing treatment, a carbonization treatment and a surface treatment to convert the fiber bundle into a carbon fiber bundle, and then continuously subjecting the carbon fiber bundle to a sizing treatment and a cutting treatment. Therein, the carbon fiber bundle has a bundling ability having a fiber-interlaced value (CF value) of 10-70 1/m by a hook drop method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a carbon fiber chopped strand having a high bulk density suitable for producing a carbon fiber reinforced resin using a thermoplastic resin as a matrix, and a carbon fiber chopped strand produced thereby. It is about.

[0002]

2. Description of the Related Art Conventionally, carbon fiber chopped strands are:
After converting the polyacrylonitrile-based fiber bundle to a flame-resistant treatment, a carbonization treatment, and a surface treatment to convert it to a carbon fiber bundle,
It has been manufactured by a carbon fiber chopped strand manufacturing apparatus different from the carbon fiber manufacturing apparatus, using as it is or after sizing processing, a material once wound up or shaken down into a can or the like as a starting material. That is, a carbon fiber bundle wound on a bobbin or shaken off by a can is drawn out and subjected to a cutting process or a sizing process and a cutting process.

[0003] Carbon fiber reinforced resins have been used for premium applications such as aircraft and sports because they have much better strength, rigidity and dimensional stability than non-reinforced resins. In recent years, demand has been expanding to general industrial uses such as construction, civil engineering, and energy, and the demand for carbon fiber has not only been reduced in performance but also in price.

However, in the conventional method of manufacturing a carbon fiber chopped strand, after a carbon fiber bundle is manufactured, it is once wound around a bobbin or shaken down into a can, and then further fed to a carbon fiber chopped strand manufacturing apparatus. And the carbon fiber bundle must be drawn out again, and the number of steps is increased, so that it has been difficult to reduce the production cost.

Japanese Patent Application Laid-Open No. 49-53922 discloses a production method for glass fiber chopped strands, in which a spun glass fiber is directly treated with a coating agent and cut without being wound up.

In the case of producing such glass fiber chopped strands, the method of producing glass fiber is a simple process of spinning molten glass, and the spinning process is performed in units of one yarn. It was relatively easy to directly connect the manufacturing process with the coating agent treatment and cutting process.

However, in the production of chopped carbon fiber strands, the method for producing carbon fibers is a combination of a flame-retardant treatment, a carbonization treatment and a surface treatment of a polyacrylic fiber bundle and a plurality of complicated steps. In order to reduce the production cost of carbon fiber, it is necessary to treat a large number of filaments of a polyacrylonitrile fiber bundle composed of a large number of filaments in a substantially untwisted state with a large number of filaments. It was not easy to directly connect the manufacturing process with the sizing and cutting processes.
In particular, when the untwisted thick yarn carbon fiber is subjected to sizing treatment and cutting treatment as it is, there is a problem that the carbon fiber yarn cannot obtain a chopped strand having a high bulk density. Therefore, as proposed in Japanese Patent Application Laid-Open No. 2-129229, a conventional method for producing a carbon fiber chopped strand in which a carbon fiber bundle wound around a bobbin or the like is drawn out, and then subjected to a sizing treatment and a cutting treatment is used. In drawing out a fiber bundle, it has been usual to increase the sizing ability by giving a twist to a yarn to produce a carbon fiber chopped strand having a high bulk density.

However, in the production method in which the carbon fiber production step and the cutting step are directly connected, it is not easy to give a twist to the non-twisted yarn in the middle of the step, so that it is difficult to obtain a carbon fiber chopped strand having a high bulk density. It was difficult.

[0009]

SUMMARY OF THE INVENTION In view of the background of the prior art, an object of the present invention is to provide a carbon fiber chopped strand having a high bulk density and excellent compoundability and suitable for a carbon fiber reinforced composite material. And a method for efficiently producing such a carbon fiber chopped strand.

[0010]

The present invention employs the following means in order to solve the above-mentioned problems. That is, the method for producing a carbon fiber chopped strand of the present invention comprises a step of subjecting a polyacrylonitrile-based fiber bundle composed of 30,000 to 350,000 filaments to a flame-resistant treatment, After performing the treatment and the surface treatment to convert the carbon fiber bundle into a carbon fiber bundle, the sizing process and the cutting process are continuously performed without winding once, thereby producing the carbon fiber chopped strand. The fiber entanglement value (CF value) in the hook drop method is 10 to 70.
It has a convergence in the range of (1 / m). Further, the carbon fiber chopped strand of the present invention is a carbon fiber chopped strand produced by such a production method, and the bulk density of the chopped strand is 0.4 g / ml or more. is there.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The object of the present invention is to provide a carbon fiber bundle having a high bulk density and excellent compounding properties which is suitable for a carbon fiber reinforced composite material. When the convergence was specified and applied to the manufacturing process, it was surprisingly sought to solve such a problem at once.

In the present invention, the polyacrylonitrile fiber bundle has 30,000 to 350,000 filaments, and more preferably 50,000 to 200,000 filaments.
What consists of 000 filaments is used. That is, when the number of filaments constituting the polyacryloniloryl-based fiber bundle is less than 30,000, the efficiency in converting to carbon fiber by performing the oxidizing treatment, the carbonizing treatment, and the surface treatment is reduced. This is because it is difficult to produce low-cost chopped strands.
If the number of filaments is more than 350,000, it tends to be difficult to produce chopped strands having good convergence.

In the present invention, when the polyacrylonitrile-based fiber bundle is converted into a carbon fiber bundle by a flame-proofing treatment, a carbonization treatment, and a surface treatment, the polyacrylonitrile-based fiber bundle is supplied in a substantially untwisted state. You. That is, when the polyacrylonitrile fiber bundle of the thick yarn having 30,000 to 350,000 filaments is twisted in the state of being twisted, the yarn density becomes uneven, and it is difficult to control the heat of the oxidation reaction. And it tends to be difficult to achieve stable flame resistance.

In the present invention, the convergence of the carbon fiber bundle before continuous sizing and cutting is 10 to 70 (1 / m), more preferably 20 to 50 (1 / m) in terms of fiber entanglement value. ). If the fiber entanglement value is less than 10, the convergence of the carbon fiber bundle is too low, and it tends to be difficult to obtain a carbon fiber chopped strand having a high bulk density. In the subsequent sizing step, it becomes difficult to impregnate the inside of the fiber bundle with the sizing agent, and therefore, it tends to be difficult to obtain a carbon fiber chopped strand having a high bulk density.

In the present invention, the convergence is 10 to 70 (1/1) as the fiber entanglement value (CF value) in the hook drop method.
m) As a method for obtaining a carbon fiber bundle in the range, a carbon entangled fiber bundle having a fiber entanglement value in the range of 20 to 100 (1 / m), more preferably 30 to 90 (1 / m) is carbonized. , Surface treatment method and fiber entanglement value is 20-100
(1 / m), more preferably 30 to 90 (1 / m).
A method of subjecting the polyacrylonitrile-based fiber bundle in the range of m) to oxidization treatment, carbonization treatment, surface treatment, or the like can be employed.

In the present invention, the fiber entanglement value is 20 to 10
Examples of a method for obtaining a flame-resistant fiber in the range of 0 (1 / m) include a method of flame-proofing a polyacrylonitrile-based fiber bundle having a fiber entanglement value of 20 to 100 (1 / m),
A method of performing air entanglement treatment on the oxidized fiber bundle can be employed.

In the present invention, the fiber entanglement value is 20 to 10
As a method for obtaining a polyacrylonitrile-based fiber bundle in the range of 0 (1 / m), there are a coagulation bath when spinning the polyacrylonitrile-based fiber bundle and a filament constituting the fiber bundle by a flow of a bath solution in a washing bath. And a method of performing air entanglement treatment on the polyacrylonitrile fiber bundle.

In the present invention, the air entanglement treatment means a treatment of blowing a fluid such as air at a high speed from a direction perpendicular to the fiber bundle.

In the present invention, the oxidizing treatment is carried out when the polyacrylonitrile fiber bundle density on the roll is 3 to 10 KD / mm.
, More preferably in the range of 4 to 8 KD / mm. That is, when the fiber bundle density on a roll is less than 3 KD / mm, the efficiency of the oxidizing treatment is low, and it is difficult to obtain a low-cost carbon fiber chopped strand. Also, 10K
If it is larger than D / mm, it is difficult to control the heat of reaction for flame resistance, and stable flame resistance cannot be obtained.

In the present invention, the carbonization treatment is carried out at a density of the oxidized fiber bundle on a roll in the range of 3 KD / mm to 20 KD / mm, more preferably in the range of 4 to 20 KD / mm. That is, when the density of the oxidized fiber bundle on the roll is smaller than 3 KD / mm, the efficiency of carbonization treatment is low, and it becomes difficult to obtain a low-cost carbon fiber chopped strand.
If it is larger than KD / mm, it becomes difficult for exhaust gas generated by carbonization to escape from the fiber bundle, and the strength of the carbon fiber tends to be low.

In the present invention, the surface treatment is carried out by a usual method such as oxidizing with a nascent oxygen generated by electrolysis of water using a carbon fiber bundle as an anode in an aqueous solution of an acid or alkali.

In the present invention, a carbon fiber chopped strand may be produced by continuously carbonizing, sizing, and cutting the oxidized fiber bundle one yarn at a time as it is. Thread, 60,000
It is more preferable to produce a thicker carbon fiber chopped strand by performing carbonization treatment, sizing treatment, and cutting treatment after forming an oxidized fiber bundle composed of 1 to 350,000 filaments. This is because the thickness of the yarn suitable for the step of subjecting the polyacrylonitrile-based fiber bundle to flame-proofing does not always match the thickness of the yarn suitable for the carbonizing step or the cutting step. In other words, the cutting process is less problematic to perform with a thick yarn than the flame-resistant treatment process and the carbonization treatment process,
By using as thick a thread as possible, there is an advantage that the number of cutting devices can be reduced and the efficiency of the cutting process can be increased accordingly.

In the present invention, a carbon fiber chopped strand may be produced by continuously treating a yarn converted into a carbon fiber bundle one by one with a sizing agent and a cutting treatment. And 60, 0
After forming a carbon fiber bundle composed of 00 to 350,000 filaments, it is more preferable to perform a sizing treatment and a cutting treatment to produce a thicker carbon fiber chopped strand. This point is similar to the case of the above-mentioned flame-resistant fiber bundle, and the thickness of the yarn suitable for the step of converting the polyacrylonitrile-based fiber bundle into a carbon fiber bundle by performing a flame-resistant treatment, a carbonization treatment, and a surface treatment, and the chopped strand This is because the optimum thicknesses do not always match, and similarly, the efficiency of the cutting step can be increased.

In the present invention, a chopped strand may be manufactured by performing a drying process after the sizing process and then performing a cutting process. However, the cutting process is performed after the sizing process, and then the drying process is performed.
It is more preferred to produce chopped strands.

This is because when the cutting treatment is performed after drying, the chopped strands are broken by the shearing force at the time of cutting and the convergence is reduced, whereas when the cutting treatment is performed in a wet state with a sizing agent, This is because the carbon fiber bundle has a high convergence and the carbon fiber bundle is flexible, so that the chopped strand is hard to be broken by the shearing force during cutting.

In the present invention, when the cutting treatment is performed after the sizing agent treatment, and then the drying treatment is performed, the drying method is usually performed with hot air or radiant heat. It is more preferable to perform while giving. This is because when drying while applying vibration, the drying efficiency is greatly improved, and drying can be performed in a short time. Such vibration conditions include a frequency of 1 to 3
A range of 0 cycle / second and an amplitude of 3 to 10 mm is preferable. The drying temperature is preferably a temperature at which the sizing agent does not decompose, and a temperature condition in the range of 130 to 250C is preferably employed.

As the sizing agent in the present invention, any of a thermosetting resin and a thermoplastic resin may be used as long as it can impart convergence. For example, urethane resin, epoxy resin, urethane-modified epoxy resin, epoxy-modified urethane resin, polyester resin, polyamide resin, polycarbonate resin, polyimide resin, polyetherimide resin, bismaleide resin, polysulfone resin and the like can be used. The resin is used alone, in a mixture, or in a form in which an additive is added thereto. Such a method for applying the sizing agent may be any of a dip method in which the traveling carbon fiber bundle is immersed in a solution or dispersion of the sizing agent, a kiss roll method in which the sizing agent adheres to the roller surface, or a guide lubrication method. Schemes can also be used. Further, the amount of the sizing agent attached is preferably in the range of 1 to 10%, more preferably 2 to 6%.

For the cutting process in the present invention, a roving cutter, a guillotine cutter, an EC cutter or the like is used. A roving cutter is a cutter roll with a plurality of blades mounted on a roll, a rubber-coated anvil roll pressed against the cutter roll for cutting, and an anvil roll that supplies a fiber bundle to the cutting section. It consists of a nip roll applied.

The chopped carbon fiber strand obtained by the production method of the present invention is characterized by having a high bulk density of 0.40 g / ml or more, preferably 0.45 g / ml or more.

This is a method of producing a carbon fiber reinforced resin using a thermoplastic resin as a matrix by using a carbon fiber chopped strand. In the method, the chopped strand is supplied to an extruder, kneaded with a molten resin, and pelletized. Usually, the pellets are injection-molded into a molded product. In order to quantitatively and stably supply the chopped strands to the extruder in the pelletizing step, the bulk density of the chopped strands is 0.40 g /. It is preferably at least 0.4 ml / ml, more preferably at least 0.45 g / ml. That is, if the chopped strand has a low bulk density of less than 0.4 g / ml, in the pelletizing step, the chopped strand is put into a hopper and fed to the extruder continuously and automatically by a screw filter or the like. However, at that time, since the chopped strand is subjected to a shearing force, the chopped strand is easily defibrated, fiber balls are generated, the fluidity is reduced, and the chopped strand cannot be transferred to the extruder.

[0031]

The present invention will be described in more detail with reference to the following examples.

In the present invention, the convergence of the fiber bundle is defined by the entanglement value (CF value) by the hook drop method. The method of measuring the entanglement value by the hook drop method is as follows.

That is, the fiber bundle is hung with a weight of 200 g. The fiber bundle is pierced with a hook having a weight of 10 g, and the falling distance is measured. Measured 50 times, 10 from the largest value to the largest, 1 from the smallest value to the smallest
An average value of the remaining 30 values excluding 0 is defined as X (cm), and a confounding value (CF value) is obtained from the following equation.

CF value = 100 / X (1 / m) When the fiber bundle is a polyacrylonitrile-based fiber bundle having crimps, the crimp is removed and the measurement is performed by the hook drop method. In the method of removing the crimp, the fiber bundle is pulled by hand and stretched, and an iron of about 120 degrees is pressed for about 15 seconds.

In the case of a carbon fiber bundle, when measured in a state where the sizing agent is not adhered, the yarn is soaked that it is difficult to obtain a stable value. % Is measured in the state of being adhered. <Composition of the sizing agent> Bisphenol A type epoxy resin 74 Wt% (EP834 type manufactured by Yuka Shell Epoxy Co., Ltd. = 39 Wt%, EP1001 type = 35 Wt%) Pentaerythritol tetraolate (oil agent) 6 Wt% Tribenzylated phenyl PEG (nonionic emulsifier) 20 Wt% <Sizing method> After immersing the carbon fiber bundle in a 3 Wt% aqueous dispersion of the above sizing composition, it is dried with hot air at 180 to 190 ° C for 10 to 20 minutes to reduce the moisture content to 0.1% or less. Adjust to

In the present invention, the bulk density of the carbon fiber chopped strand is measured by the following method. About 200 ml of carbon fiber chopped strand is placed in a 500 ml measuring cylinder, and the measuring cylinder is moved from a height of 3 cm to 1 m.
After dropping 0 times, the volume (V ml) of the carbon fiber chopped strand in the measuring cylinder is read. Weight of carbon fiber chopped strand in measuring cylinder (W
g) is measured. The bulk density is determined in W / V (g / ml). Example 1 Acrylonitrile 96.4 mol%, methyl acrylate 3
A 20% by weight solution of a polyacrylonitrile-based polymer in dimethyl sulfoxide (DMSO) copolymerized with 0.6% by mole of ammonium itaconate and 0.6% by mole of ammonium itaconate was added at 30 ° C. and 60% of D
Spinning was carried out from a die having 70,000 holes in an aqueous MSO solution. The fiber bundle is drawn in hot water. After washing with water, a process oil was applied, dried and densified, a finishing oil was applied, and a crimp was applied to obtain a polyacrylonitrile fiber bundle having 70,000 filaments and 1.5 d single denier 1.5 denier.

The fiber entanglement value of this polyacrylonitrile fiber bundle was 16 (1 / m). The polyacrylonitrile-based fiber bundle is subjected to a flame-proof treatment in a heated air at 220 to 230 ° C. at a fiber bundle density of 7 KD / mm on a roll for 120 minutes in a non-twist state, an air entangling treatment to the flame-resistant fiber bundle, a maximum temperature of 1400 ° C. Carbonization and surface treatment in a nitrogen atmosphere
A sizing agent treatment, a cutting treatment and a drying treatment were successively performed to obtain a carbon fiber chopped strand having a cut length of about 6 mm.

Here, the air entanglement treatment for the oxidized fiber bundle is performed by forming a hole having a diameter of 2 mm for blowing high-pressure air into the fiber bundle.
The oxidized fiber bundle is passed through a ring-shaped treatment device arranged at intervals of 60 degrees in the degree direction at a pressure of 0.8 kgf / mm ^2.
Was performed by blowing air.

The fiber entanglement values before and after the air entanglement treatment were 18 and 65 (1 / m), respectively.

The fiber entanglement value of the obtained carbon fiber bundle was 25 (1 / m), and the strand strength was 360 kgf / m.
m ² , and strand elastic modulus were 23, 5 tf / mm ² . The sizing process involves passing the carbon fiber bundle through water in which the urethane resin is finely dispersed to reduce the urethane resin by about 3%.
Attached. For the cutting process, a cartridge cutter was used. Drying was carried out using a vibratory drier, with a vibration
The test was performed in 190 ° C. hot air for 4 minutes while giving a vibration having a cycle / second and an amplitude of 5 mm.

The bulk density of the obtained chopped carbon fiber strand was 0.49 g / ml. When this chopped strand was compounded with a nylon resin using an extruder having a hopper capacity of 300 L, the fluidity in the hopper was good. Example 2 The same polyacrylonitrile-based fiber bundle obtained in Example 1 was subjected to an air-entanglement treatment at an air pressure of 1.0 kgf / mm ² to obtain a polyacrylonitrile-based fiber having a fiber entanglement value of 60 (1 / m). A carbon fiber chopped strand was produced in the same manner as in Example 1 except that the fiber bundle was used and the air entanglement treatment was not performed on the flame-resistant fiber bundle.

The bulk density of the obtained chopped carbon fiber strand was 0.45 g / ml. Comparative Example 1 The same polyacrylonitrile-based fiber bundle obtained in Example 1 was twisted for 5 turns per 1 m, and subjected to oxidization treatment under the same conditions as in Example 1. Was broken, so that a carbon fiber bundle could not be obtained. Comparative Example 2 A chopped strand was obtained in the same manner as in Example 1 except that the air-entangled treatment was not performed on the oxidized fiber bundle.

The bulk density of the obtained chopped strand was as low as 0.34. When this chopped strand was compounded into nylon resin using an extruder with a hopper capacity of 300 L, the flowability was poor, causing blockage,
A stable process was not possible. The fiber entanglement value of the carbon fiber bundle was 8 (1 / m). Comparative Example 3 A chopped strand was obtained in the same manner as in Example 2, except that the air pressure when air-treating the polyacrylonitrile fiber bundle was changed to 2.5 kgf / mm ² .

The bulk density of the obtained chopped strand was as low as 0.37. Upon examination, it was confirmed that the penetration of the sizing agent into the carbon fiber bundle was insufficient. The entanglement values of the polyacrylonitrile fiber bundle, the oxidized fiber bundle, and the carbon fiber bundle after the air treatment are respectively
110, 120 and 75 (1 / m). Example 3 After converting into a carbon fiber bundle in the same manner as in Example 1, about 3% of the same sizing agent as in Example 1 was applied and dried, followed by cutting to obtain a chopped strand.

The bulk density of the obtained chopped strand was 0.42. Example 4 Acrylonitrile 97.6 mol%, methyl acrylate 2
A 20% by weight solution of a polyacrylonitrile-based polymer copolymerized with 0.4% by mole of ammonium itaconate and 0.4% by mole of ammonium itaconate was added at 30 ° C. and 60% D
It was spun from a die having 50,000 holes into an aqueous MSO solution. The fiber bundle is drawn in hot water. After washing with water, a process oil was applied, dried and densified, a finishing oil was applied, and a crimp was applied to obtain a polyacrylonitrile fiber bundle having 50,000 filaments and 1.5 d single yarn denier.

The fiber entanglement value of this polyacrylonitrile fiber bundle was 15 (1 / m). The polyacrylonitrile-based fiber bundle is rolled in a heated air at 220 to 230 ° C at a density of 5 KD / mm.
20 minutes of non-twisting in a non-twisted state, flame proofing treatment, air entanglement treatment on the fiber proofing fiber bundle, carbonization treatment in nitrogen atmosphere at a maximum temperature of 1400 ° C, surface treatment, sizing agent treatment, cutting treatment and drying treatment continuously As a result, a carbon fiber chopped strand having a cut length of about 6 mm was obtained.

Here, the air entanglement treatment for the oxidized fiber bundle is carried out in the same manner as in Example 1 by using an air pressure of 1.5 kgf.
/ Mm ² . The fiber entanglement value before and after the air entanglement process is
They were 20 and 85 (1 / m), respectively.

The fiber entanglement value of the obtained carbon fiber bundle was 45 (1 / m), and the strand strength was 380 kgf / m.
m ² , and strand elastic modulus were 24.0 tf / mm ² . The sizing process involves passing the carbon fiber bundle through water in which the urethane resin is finely dispersed to reduce the urethane resin by about 3%.
Attached. For the cutting process, a cartridge cutter was used. Drying was carried out using a vibratory drier and at a vibration frequency of 16
The test was carried out in 190 ° C. hot air for 3 minutes while giving a vibration having a cycle / second and an amplitude of 5 mm.

The bulk density of the obtained chopped carbon fiber strand was 0.53 g / ml. Example 5 Using the same polyacrylonitrile-based fiber bundle as in Example 3, the polyacrylonitrile-based fiber bundle was subjected to air treatment at an air pressure of 1.0 kgf / mm ² in the same manner as in Example 2, and then subjected to Example 3. The sizing agent treatment, the cutting treatment, and the drying treatment were performed in the same manner as in Example 3 in a state where the carbon fiber bundle was converted into a carbon fiber bundle in the same manner as in Example 3 and two carbon fiber bundles were combined into 100,000 carbon fiber bundles. I got a chopped strand.

The bulk density of the obtained chopped strand was 0.44 g / ml. Example 6 A polyacrylonitrile-based fiber bundle having 35,000 filaments was obtained in the same manner as in Example 3 except that the number of holes in the die was changed to 35,000. This polyacrylonitrile-based fiber bundle was converted into a flame-resistant fiber bundle in the same manner as in Example 3, except that the density of the polyacrylonitrile-based fiber bundle on the roll was 3, 5 KD / mm. Was combined into two bundles to obtain 70,000 flame-retardant fiber bundles, which were entangled at an air pressure of 1.2 kgf / mm ² , and then chopped strands were obtained in the same manner as in Example 3.

[0051] The bulk density of the obtained chopped strand was 0.51 g / ml. Example 7 A polyacrylonitrile fiber bundle having 140,000 filaments was obtained in the same manner as in Example 1 except that two yarns were combined in the middle of the yarn production. Using the present polyacrylonitrile-based fiber bundle, a polyacrylonitrile-based fiber bundle on a roll was converted to an oxidized fiber bundle in the same manner as in Example 1 at a density of 7 KD / mm. Air treatment was performed at 0 kgf / mm ² , and the subsequent steps were performed in the same manner as in Example 1 to obtain a chopped strand.

The bulk density of the obtained chopped strand was 0.44 g / ml. The fiber entanglement values before and after the air treatment of the oxidized fiber bundle were 20, 60 (1/1), respectively.
m). The fiber entanglement value of the carbon fiber bundle was 22. Example 8 A chopped strand was produced in the same manner as in Example 7, except that the drying treatment after cutting was not performed by using the vibration drying method. Since the vibration drying method was not used, it took 8 minutes at 190 ° C. to dry.

The bulk density of the obtained chopped strand was 0.40 g / ml. Example 9 A polyacrylonitrile fiber bundle having 210,000 filaments was obtained in the same manner as in Example 7, except that three yarns were combined in the middle of the yarn production. Using the present polyacrylonitrile-based fiber bundle, the density of the polyacrylonitrile-based fiber bundle on the roll is 9 KD / mm at 300 to 210 ° C.
For 5 minutes in a non-twisted state to convert the fiber bundle into a flame-resistant fiber bundle, and in the same manner as in Example 1, an air pressure of 1.5 kgf /
Air treatment was performed using mm ² , and the subsequent steps were performed in the same manner as in Example 1 to obtain a chopped strand.

The bulk density of the obtained chopped strand was 0.41 g / ml. The fiber entanglement value of the carbon fiber bundle was 18 (1 / m).

[0055]

According to the present invention, a polyacrylonitrile fiber bundle which has been converted into a carbon fiber bundle by a flame-proofing treatment, a carbonization treatment and a surface treatment is directly sized and cut without being wound up. Processing,
A carbon fiber chopped strand having a high bulk density and excellent compounding properties can be efficiently produced and provided.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4L037 AT03 CS03 CT30 FA02 FA03 FA06 PA55 PC05 PF18 PF41 PF52 PF57 PS02 UA12 4L038 AA28 BA37 BB03 BB08 CA06 DA10

Claims (12)

[Claims] 1. A polyacrylonitrile-based fiber bundle composed of 30,000 to 350,000 filaments is subjected to an oxidizing treatment, a carbonizing treatment and a surface treatment in a substantially non-twisted state to obtain a carbon fiber. After being converted into a fiber bundle, the carbon fiber bundle is subjected to a sizing process and a cutting process without being wound once, thereby producing a carbon fiber chopped strand. 10 to 70 in CF value)
A method for producing a carbon fiber chopped strand, having a convergence in the range of (1 / m). 2. The oxidized fiber bundle subjected to the carbonization treatment has a fiber entanglement value (CF value) of 20 to 20 in a hook drop method.
The method for producing a carbon fiber chopped strand according to claim 1, wherein the carbon fiber has a convergence in the range of 100 (1 / m). 3. The polyacrylonitrile fiber bundle has a fiber entanglement value (CF value) of 20 to 1 in a hook drop method.
The method for producing a chopped carbon fiber strand according to claim 1 or 2, having a convergence in the range of 00 (1 / m). 4. A method according to claim 1, wherein a plurality of yarns of the oxidized fiber bundle are combined to form a yarn.
The method for producing a chopped carbon fiber strand according to any one of claims 1 to 3, wherein the carbonized fiber bundle is continuously carbonized after being made into an oxidized fiber bundle composed of 0000 to 350,000 filaments. 5. A carbon fiber bundle composed of 60,000 to 350,000 filaments, which is combined with a plurality of yarns converted into the carbon fiber bundle, and then continuously treated with a sizing agent. And performing a cutting process.
5. The method for producing a carbon fiber chopped strand according to any one of 4. 6. The fiber entanglement value (CF value) is 20 (1/1).
The carbon fiber chopped according to any one of claims 2 to 5, wherein the oxidized fiber bundle, which is less than m), is subjected to an air entanglement treatment to control the fiber entanglement value in a range of 20 to 100 (1 / m). Strand manufacturing method. 7. The acrylonitrile-based fiber bundle is subjected to an air entanglement treatment on a fiber bundle having a fiber entanglement value (CF value) of less than 20 (1 / m), and the fiber entanglement value (CF value) is reduced to 20.
The method for producing a carbon fiber chopped strand according to any one of claims 3 to 6, wherein the carbon fiber chopped strand is controlled to a range of from 100 to 1 / m. 8. The process for producing a chopped carbon fiber strand according to claim 1, wherein the oxidizing treatment is carried out at a polyacrylonitrile fiber bundle density of 3 to 10 KD / mm on a roller. Method. 9. The method for producing a carbon fiber chopped strand according to claim 1, wherein the carbonizing treatment is performed at a density of the oxidized fiber bundle on the roller of 3 to 20 KD / mm. 10. The method for producing a chopped carbon fiber strand according to claim 1, wherein a drying process is performed after the cutting process. 11. The method for producing a carbon fiber chopped strand according to claim 10, wherein said drying treatment is performed by a vibration drying method. 12. A carbon fiber chopped strand produced by the production method according to any one of claims 1 to 11, wherein the chopped strand has a bulk density of 0.1.
A carbon fiber chopped strand of 4 g / ml or more.