Manufacturing method of carbon fiber bundle

Abstract

In order to provide a method for suppressing the generation of fluff during conveying by a drive roller when producing a carbon fiber bundle having a high total fineness, a high elastic modulus, and a large yarn width with twisting added, provided is a method for manufacturing a carbon fiber bundle, the method comprising: performing a flame retardant treatment for heat-treating a polyacrylonitrile-based carbon fiber precursor fiber bundle in an oxidizing atmosphere at 200-300°C to obtain a flame retardant fiber bundle; then performing a pre-carbonization treatment for heat-treating the flame retardant fiber bundle in an inert atmosphere, in which the maximum temperature is controlled to be 500-1200°C, to obtain a pre-carbonized fiber bundle; and then performing a carbonization treatment for heat-treating the pre-carbonized fiber bundle in an inert atmosphere, in which the maximum temperature is controlled to be 1200-3000°C, to obtain a carbon fiber bundle, wherein the fiber bundle is moved in contact with the drive roller before and after the carbonization treatment, the obtained carbon fiber bundle has a total fineness A of 6000-40000 dtex and a maximum twist angle B of 1-10°, the tension C of the fiber bundle in the carbonization treatment is 50-500 N / bundle, and the diameter D of the drive roller before and after the carbonization treatment is 200-1000 mm.

Description

[Technical field]

[0001] The present invention relates to a method for producing high-quality carbon fiber bundles having a high elastic modulus and excellent productivity. [Background technology]

[0002] One of the features of polyacrylonitrile carbon fibers is their high elastic modulus, and in order to increase the elastic modulus even more than that of general-purpose products while also improving productivity, studies are being conducted to increase the total fineness of the carbon fiber bundles (Patent Document 1).The proposed carbon fiber bundles with a large total fineness and high elastic modulus have a large yarn width (thickness) when twisted.

[0003] Here, the carbon fiber bundle is industrially manufactured through a flame-retardant process in which a polyacrylonitrile-based carbon fiber precursor fiber bundle is converted into a flame-retardant fiber in an oxidizing atmosphere at 200 to 300 ° C, a pre-carbonization process in which the fiber bundle is pre-carbonized in an inert atmosphere at 500 to 1200 ° C, and a carbonization process in which the fiber bundle is carbonized in an inert atmosphere at 1200 to 3000 ° C. Among them, in order to increase the elastic modulus of the carbon fiber bundle, it has been promoted to impart high tension in the carbonization process. Specifically, for example, Patent Document 2 proposes imparting high tension in the carbonization process during the manufacture of the carbon fiber bundle. Patent Document 3 proposes imparting high tension in the carbonization process while adding twist during the manufacture of the carbon fiber bundle.

[0004] Furthermore, the manufacturing equipment used in producing carbon fiber bundles includes drive rollers for transporting the fiber bundles, and examples are known in which the roller diameter is increased to 60 mm or more (Patent Document 4). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2019 / 244830 [Patent Document 2] JP 2014-141762 A [Patent Document 3] JP 2014-141761 A [Patent Document 4] Japanese Patent Application Publication No. 49-92327 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the conventional techniques have the following problems.

[0007] Unlike polyacrylonitrile-based carbon fiber precursor fiber bundles and flame-resistant fibers, the fiber bundles transported to the carbonization process have a small breaking strain due to the treatment up to the preliminary carbonization process. Therefore, when the total fineness is increased while twisting is added and carbonization treatment is performed at high tension as described in Patent Document 1, fluff occurs even in front of the rollers outside the carbonization furnace due to the tension in the carbonization furnace. That is, a new problem occurs in that fluff increases not only in the carbonization furnace but also during transport with rollers outside the carbonization furnace. In Patent Documents 2 and 3, since the total fineness essential from the viewpoint of productivity was low, no particular problem occurred with normal roller transport, and no consideration was given to the problem when the total fineness was increased. Patent Document 4 describes that the physical properties improve as the roller diameter is increased in the flame-resistant process, but even in the examples, it only shows an embodiment in which a roller with a diameter of 159 mm is used at most. And there is no description of a carbonization process with a small breaking strain, nor any suggestion of applying high tension, and no attention was paid to the quality.

[0008] Therefore, an object of the present invention is to provide a method for suppressing the generation of fuzz on a fiber bundle during transport by a drive roller when producing a carbon fiber bundle with a large total fineness, high elastic modulus, and large yarn width through the addition of twist. [Means for solving the problem]

[0009] In order to achieve the above object, the method for producing a carbon fiber bundle of the present invention has any one of the following features. (1) A method for producing a carbon fiber bundle, comprising the steps of: (1) subjecting a polyacrylonitrile-based carbon fiber precursor fiber bundle to a flame-retardant treatment in an oxidizing atmosphere at 200 to 300°C to obtain a flame-retardant fiber bundle; (2) subjecting the flame-retardant fiber bundle to a pre-carbonization treatment in an inert atmosphere controlled so that the maximum temperature is 500 to 1200°C to obtain a pre-carbonized fiber bundle; and (3) subjecting the pre-carbonized fiber bundle to a carbonization treatment in an inert atmosphere controlled so that the maximum temperature is 1200 to 3000°C to obtain a carbon fiber bundle, wherein the fiber bundle runs while being in contact with a drive roller before and after the carbonization treatment, the carbon fiber bundle has a total fineness A of 6000 to 40000 dtex, a maximum twist angle B of 1 to 10°, a tension C of the fiber bundle in the carbonization treatment of 50 to 500 N / bundle, and a diameter D of the drive roller before and after the carbonization treatment of 200 to 1000 mm. (2) A method for producing a carbon fiber bundle, comprising the steps of: subjecting a polyacrylonitrile-based carbon fiber precursor fiber bundle to a flame-retardant treatment by heat-treating the bundle in an oxidizing atmosphere at 200 to 300°C to obtain a flame-retardant fiber bundle; subjecting the flame-retardant fiber bundle to a pre-carbonization treatment by heat-treating the bundle in an inert atmosphere at 500 to 1200°C to obtain a pre-carbonized fiber bundle; and then subjecting the pre-carbonized fiber bundle to a carbonization treatment by heat-treating the bundle in an inert atmosphere at 1200 to 3000°C to obtain a carbon fiber bundle, wherein the fiber bundle runs while being in contact with a drive roller before and after the carbonization treatment, the carbon fiber bundle has a total fineness A of 6000 to 40000 dtex, a maximum twist angle B of 1 to 10°, a tension C of the fiber bundle in the carbonization treatment of 50 to 500 N / bundle, and a diameter D of the drive roller before and after the carbonization treatment of 200 to 1000 mm.

[0010] In these manufacturing methods, it is preferable that the total fineness A of the carbon fiber bundle, the maximum twist angle B of the carbon fiber bundle, the tension C of the fiber bundle in the carbonization treatment, and the diameter D of the drive roller satisfy formula (1). D>C / 2+(A 0.5 ×B) / 10...Equation (1) Moreover, the fiber bundle passing through the driving roller after the carbonization treatment preferably has an elongation of 0.5 to 3.0%. Effect of the Invention

[0011] According to the method for producing carbon fiber bundles of the present invention, carbon fiber bundles having a high elastic modulus can be obtained with high quality and high productivity. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present invention achieves the production of carbon fiber bundles by carrying out a flame retardant treatment in which a polyacrylonitrile-based carbon fiber precursor fiber bundle is heat-treated in an oxidizing atmosphere at 200 to 300°C to obtain a flame retardant fiber bundle, a pre-carbonization treatment in which the flame retardant fiber bundle is heat-treated in an inert atmosphere at 500 to 1200°C to obtain a pre-carbonized fiber bundle, and then a carbonization treatment in which the pre-carbonized fiber bundle is heat-treated in an inert atmosphere at 1200 to 3000°C to obtain a carbon fiber bundle, by focusing on the carbonization step in which a fiber bundle having a small breaking strain is treated. This achieves the production of a high-quality carbon fiber bundle having a high elastic modulus with high productivity.

[0013] In the method for producing carbon fiber bundles of the present invention, the total fineness A of the carbon fiber bundles obtained is 6000 to 40000 dtex, preferably 8000 to 35000 dtex, and more preferably 10000 to 30000 dtex. The total fineness of the carbon fiber bundles is related to the productivity of the carbon fiber bundles, so the larger the better. In addition, the total fineness of the carbon fiber bundles is indicated in basis weight (g / m) in the catalog, so it can be easily known by converting it to dtex. The carbon fiber bundles change in mass during the carbonization process, so the total fineness changes during the process, but the change in mass after leaving the carbonization furnace is small, and the total fineness of the carbon fiber bundles can be considered to be the total fineness immediately after leaving the carbonization furnace. In other words, if the total fineness of the carbon fiber bundles is 6000 dtex or more, it can be said that the productivity of the carbon fiber bundles is high. If the total fineness of the carbon fiber bundles is 40000 dtex or less, the quality of the carbon fiber bundles is at a satisfactory level. It is important to note that the greater the total fineness of the carbon fiber bundle, the thicker the bundle will be on the roller (more details will be given later). The total fineness of the carbon fiber bundle can be evaluated by converting it into the mass per 10 m. To control the total fineness of the carbon fiber bundle, it is sufficient to adjust the single fiber fineness and the number of filaments.

[0014] The number of filaments per one carbon fiber bundle is preferably 10,000 to 80,000, and more preferably 20,000 to 50,000. When the number of filaments in the carbon fiber bundle is 10,000 or more, the productivity of the carbon fiber bundle can be said to be high. When the number of filaments in the carbon fiber bundle is 80,000 or less, the quality of the carbon fiber bundle is at a satisfactory level.

[0015] In the method for producing a carbon fiber bundle of the present invention, the maximum twist angle B of the obtained carbon fiber bundle is 1 to 10°, preferably 2 to 9°, and more preferably 3 to 8°. When the carbon fiber bundle is twisted, the twist angle at the center in the radial direction of the fiber bundle is close to 0°, and the outermost layer has the maximum twist angle. The fact that the carbon fiber bundle has a twist means that it has high bundling ability, and it is sufficient to adjust the maximum twist angle. If the maximum twist angle of the carbon fiber bundle is 1° or more, the bundling ability is satisfactory, and if it is 10° or less, tension is easily applied during the carbonization treatment. The larger the maximum twist angle of the carbon fiber bundle, the more likely the cross section of the carbon fiber bundle is to change from flat to circular, and it is also necessary to note that the thickness of the bundle on the roller increases (details will be described later). In order to make the carbon fiber bundle twisted, the fiber bundle is twisted before the carbonization process. The maximum twist angle is determined based on the basis weight y (g / m) and density d (g / cm 3 ), and the number of twists T (turns / m), are used to calculate the following formula (2).

[0016] Twisting angle (°)=arctan{(0.01×y / π / d) 0.5 ×10 -6 ×π×T} (2) The method of giving a twist to the fiber bundle can be selected from known methods. Specifically, the twist can be controlled by a method in which the fiber bundle is once wound around a bobbin, and then the bobbin is rotated in a plane perpendicular to the unwinding direction when the fiber bundle is unwound, or a method in which a rotating roller or belt is brought into contact with the running fiber without being wound around a bobbin to give a twist. In other words, the maximum twist angle can also be evaluated from the basis weight, density, and number of twists.

[0017] In the method for producing carbon fiber bundles of the present invention, the tension C in the carbonization treatment is 50 to 500 N / bundle, preferably 100 to 450 N / bundle, and more preferably 150 to 400 N / bundle. The tension in the carbonization treatment is an important factor that determines the elastic modulus of the carbon fiber bundle, and if the tension is 50 N / bundle or more, the elastic modulus is satisfactory, and if it is 500 N / bundle or less, the quality of the carbon fiber bundle is satisfactory. The tension in the carbonization treatment can be adjusted by changing the roller speed (draw ratio) before and after the treatment, and can be evaluated with a tensiometer or the like.

[0018] In the method for producing a carbon fiber bundle of the present invention, the fiber bundle runs while contacting the driving roller before and after the carbonization treatment, and the diameter D of the driving roller before and after the carbonization treatment is 200 to 1000 mm, preferably 250 to 800 mm, and more preferably 270 to 600 mm. In the present invention, a high tension is applied to a thick carbon fiber bundle in the carbonization treatment, and the thick carbon fiber bundle has a large difference in circumferential length between the inside of the carbon fiber bundle (the side in contact with the driving roller) and the outside of the carbon fiber bundle (the side farthest from the driving roller) on the driving roller, and distortion occurs even without tension. Therefore, the larger the curvature radius of the driving roller is, that is, the smaller the diameter of the driving roller is, the more likely it is that distortion will occur in the carbon fiber bundle and fluff will occur. However, if the diameter of the driving roller is 200 mm or more, fluffing of the carbon fiber bundle is easily suppressed, and if it is 1000 mm, the effect of suppressing fluff is often saturated.

[0019] In the method for producing a carbon fiber bundle of the present invention, a preferable point is that when the total fineness A, the maximum twist angle B, and the tension C of the fiber bundle in the carbonization treatment are within specific ranges as described above, the diameter D of the drive roller before and after the carbonization treatment satisfies the relationship of formula (1). D>C / 2+(A 0.5 ×B) / 10...Equation (1) The strain due to the difference in circumferential length associated with the tension in the carbonization process and the thickness of the carbon fiber bundle is related to the way in which fuzz appears in the carbon fiber bundle, but this formula was derived from an empirical understanding that by increasing the diameter of the drive roller, the effect of the difference in circumferential length of the carbon fiber bundle is alleviated, making it difficult for fuzz to appear in the carbon fiber bundle. Therefore, it is preferable to adjust the diameter of the drive roller according to conditions A, B, and C. In the present invention, the drive roller before and after the carbonization process refers to the drive roller with which the fiber bundle entering and leaving the carbonization furnace comes into contact at a position closest to the carbonization furnace before and after the carbonization furnace.

[0020] In the method for producing a carbon fiber bundle of the present invention, the number of drive rollers before and after the carbonization treatment is preferably 1 to 10. If the number of drive rollers is 1 or more, the fiber bundle can be transported, and if the number is 10 or less, the increase in fuzz at each drive roller can be suppressed. The "drive rollers before and after the carbonization treatment" specified in the present invention refers only to the drive roller closest to the carbonization furnace, among the preferably 1 to 10 drive rollers before and after the carbonization treatment. However, the diameter of the other drive rollers is also preferably 200 to 1000 mm.

[0021] In the method for producing a carbon fiber bundle of the present invention, the elongation of the fiber bundle passing through the driving roller after the carbonization treatment is preferably 0.5 to 3.0%, more preferably 0.5 to 2.0%. The lower the elongation of the fiber bundle passing through the driving roller, the easier it is to obtain the effect of suppressing the generation of fluff by the driving roller by adjusting the diameter of the driving roller. If the elongation of the fiber bundle is 0.5% or more, it is often industrially valuable because it has high strength, and if it is 3.0% or less, it is often industrially valuable because it means that the elastic modulus is high. The elongation of the fiber bundle can be adjusted by the maximum temperature and tension C of the carbonization furnace. In addition, the elongation of the fiber bundle can be evaluated by a tensile test of a single fiber, and the details will be described later. As the fiber bundle passing through the driving roller after the carbonization treatment, the fiber bundle present on the driving roller after the carbonization treatment may be sampled as it is, or the fiber bundle may be subjected to subsequent surface treatment, sizing agent application treatment, etc., because the elongation does not change, and the finally obtained carbon fiber bundle may be used as it is. The standard elongation of carbon fiber bundles is approximately 0.7 to 2.2%, as indicated by the catalog values ​​of each company.

[0022] Another suitable method for producing carbon fiber bundles will now be described.

[0023] The carbon fiber precursor fiber bundle that is the basis of the carbon fiber bundle of the present invention can be obtained by spinning a spinning solution of a polyacrylonitrile copolymer. The obtained spinning solution is spun by a wet spinning method or a dry-wet spinning method to produce a carbon fiber precursor fiber. Specifically, the spinning solution is introduced into a coagulation bath to coagulate, and the obtained coagulated fiber is passed through a water washing step, a bath drawing step, an oil application step, and a drying step to obtain a carbon fiber precursor fiber. In addition, a dry heat drawing step or a steam drawing step may be added to the above steps.

[0024] The obtained carbon fiber precursor fiber bundle is usually in the form of a continuous fiber. The number of filaments per one thread is preferably 10,000 to 80,000, and more preferably 20,000 to 50,000. In the present invention, the carbon fiber precursor fiber bundle may be doubling as necessary to adjust the number of filaments per one thread of the obtained carbon fiber bundle.

[0025] In the method for producing a carbon fiber bundle of the present invention, the above-mentioned carbon fiber precursor fiber bundle is subjected to a flame retardant treatment, and then a preliminary carbonization treatment and a carbonization treatment are carried out in this order.

[0026] The flame-retardant treatment of the carbon fiber precursor fiber bundle is carried out in an oxidizing atmosphere such as air, preferably at a temperature range of 200 to 300° C. The carbon fiber precursor fiber bundle is flame-retardant treated within this temperature range to become a flame-retardant fiber bundle.

[0027] In the present invention, following the flame-retardant treatment, the flame-retardant fiber bundle is subjected to a preliminary carbonization treatment. In the preliminary carbonization treatment, the flame-retardant fiber bundle obtained by the flame-retardant treatment is carbonized to a density of 1.5 to 1.8 g / cm in an inert atmosphere controlled so that the maximum temperature is within the range of 500 to 1200°C. 3 It is preferable to heat treat the fiber bundle until the fiber bundle reaches a temperature of 1200°C. The flame-resistant fiber bundle is pre-carbonized to obtain a pre-carbonized fiber. The maximum temperature of the inert atmosphere is preferably less than 1200°C.

[0028] Furthermore, following the pre-carbonization treatment, the pre-carbonized fiber is carbonized. The carbonization treatment is performed in an inert atmosphere controlled so that the maximum temperature of the pre-carbonized fiber obtained by the pre-carbonization treatment is within a range of 1200 to 3000°C. The maximum temperature in the carbonization treatment is preferably higher from the viewpoint of increasing the elastic modulus of the obtained carbon fiber bundle, and if the maximum temperature is 1200°C or higher, a carbon fiber bundle with a high elastic modulus suitable for applications in which rigidity is important as a carbon fiber reinforced composite material can be obtained. The maximum temperature in the carbonization treatment is preferably 1500°C or higher. On the other hand, if the maximum temperature in the carbonization treatment is too high, the quality may be easily reduced.

[0029] In the present invention, preferred examples of the inert gas used in the inert atmosphere include nitrogen, argon, and xenon, and from the economical viewpoint, nitrogen is preferably used.

[0030] The carbon fiber bundle obtained by the above-mentioned production method may be further subjected to an additional graphitization treatment in an inert atmosphere up to a maximum of 3000° C., and the elastic modulus of the carbon fiber bundle may be appropriately adjusted depending on the application.

[0031] The carbon fiber bundle obtained as described above is preferably subjected to a surface treatment after carbonization to introduce a functional group containing an oxygen atom in order to improve the adhesive strength between the carbon fiber bundle and the matrix. As the surface treatment method, gas phase oxidation, liquid phase oxidation, and liquid phase electrolytic oxidation are used, but liquid phase electrolytic oxidation is preferably used from the viewpoint of high productivity and uniform treatment. In the present invention, there is no particular restriction on the method of liquid phase electrolytic oxidation, and it may be performed by a known method.

[0032] The methods for measuring the various physical properties described in this specification are as follows. Unless otherwise specified, evaluation was performed with a measurement number of n=1.

[0033] <Maximum twist angle> The maximum twist angle is determined by the weight y (g / m) and density d (g / cm 3 ) and the number of twists T (turns / m), calculated using the following formula (2).

[0034] Twisting angle (°)=arctan{(0.01×y / π / d) 0.5 ×10 -6 ×π×T} (2) <Total fineness> A 10 m length of the fiber bundle to be measured is sampled and completely dried. The measured mass is then multiplied by 1000 to obtain the total fineness, which is the mass per 10,000 m.

[0035] <Elongation of fiber bundle> A fiber bundle of about 20 cm is divided into approximately four equal parts, and single fibers are sampled in order from each of the four bundles. A total of 15 single fibers are sampled, but each bundle is sampled as evenly as possible. Each sampled single fiber is fixed to a 50 mm perforated mount. A fast-curing epoxy adhesive, "Araldite (registered trademark)" manufactured by Nichiban Co., Ltd., is used for fixing, and after application, the material is left to harden at room temperature for 24 hours. The mount with the single fibers fixed is attached to a tensile test device, and a tensile test is performed at each gauge length of 50 mm, with a strain rate of 4% / min and 15 samples. The elongation (%) of each single fiber is averaged to obtain the elongation of the fiber bundle.

[0036] In this example, a tensile tester "Tensilon RTF-1210" manufactured by A&D Co., Ltd. was used as the tensile tester.

[0037] <Number of fluffs in carbon fiber bundle> Only the fuzz generated on the drive rollers is evaluated. In particular, of the drive rollers before and after the carbonization furnace, the fuzz generated on the drive roller after the carbonization furnace is evaluated and used as a representative of both. The number of fuzz on the carbon fiber bundle is counted on both the inlet and outlet sides of the group of drive rollers after the carbonization furnace. To make the fuzz easier to see, the number of fuzz per meter is calculated by counting the fuzz for 10 m while shining a spotlight on the area and dividing by 10. To exclude fuzz generated during the carbonization process, the number of fuzz on the inlet side is subtracted from the number of fuzz on the outlet side to obtain the final fuzz count. EXAMPLES

[0038] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these.

[0039] Examples 1 to 9, Comparative Examples 1 to 8, and Reference Examples 1 to 3 described below were carried out under the conditions described in Table 1 in the implementation methods described in the following comprehensive examples.

[0040] [Comprehensive Example] A polyacrylonitrile copolymer was polymerized by a solution polymerization method using dimethyl sulfoxide as a solvent to obtain a spinning solution. Next, the obtained spinning solution was once discharged from a spinneret into the air, and then introduced into a coagulation bath to obtain a coagulated fiber bundle by a dry-wet spinning method. The coagulated fiber bundle was then washed with water, stretched in the bath, given a silicone oil agent, dried, and stretched in pressurized steam to obtain a carbon fiber precursor fiber bundle with a single fiber fineness of 1.1 dtex.

[0041] The obtained carbon fiber precursor fiber bundle was doubling and wound up so that the total fineness was the value shown in Table 1, and the bobbin was rotated, and while adding twist to the twist angle shown in Table 1, it was flame-retarded in an oven at 230 to 280 ° C in an air atmosphere to convert it into a flame-retarded fiber bundle. The obtained flame-retarded fiber bundle was pre-carbonized in a nitrogen atmosphere with a maximum temperature of 800 ° C to obtain a pre-carbonized fiber bundle. Next, the pre-carbonized fiber bundle was carbonized in a nitrogen atmosphere with a maximum temperature of 1800 ° C at the load shown in Table 1 to obtain a carbon fiber bundle. At that time, there were eight driving rollers before and after the carbonization treatment, and the diameters of all the rollers were the values ​​shown in Table 1. Table 1 lists the elongation of the fiber bundle passing through the driving roller after the carbonization treatment, the evaluation results of the obtained carbon fiber bundle, and the calculation results of the right side of the formula (1).

[0042] In Reference Examples 1 to 3, any one of the total fineness, maximum twist angle, and load is outside the range of the present invention. In such cases, the number of fluffs in the carbon fiber bundle does not increase, and therefore the conditions are such that the problems of the present invention do not arise.

[0043] [Table 1]

[0044] In addition, as Reference Examples 4 to 12, a flame-retardant fiber bundle (elongation: 4.0%) was obtained by doubling yarns in the above [Comprehensive Examples] so that the total fineness was 26,000 dtex, and the number of fuzz was evaluated at room temperature using the flame-retardant fiber bundle at the twist angle, load, and roller diameter shown in Table 2 (pre-carbonization treatment and carbonization treatment were not performed). The results are shown in Table 2. In these flame-retardant fiber bundles, the influence of the roller diameter is small, and the effect of the present invention is not exhibited.

[0045] [Table 2] [Industrial Applicability]

[0046] The method for producing a carbon fiber bundle of the present invention can produce a high-quality carbon fiber bundle having a high elastic modulus with high productivity. By using the carbon fiber bundle of the present invention, a carbon fiber reinforced composite material having a high elastic modulus can be produced with high productivity.

Claims

1. A method for producing a carbon fiber bundle, comprising the steps of: subjecting a polyacrylonitrile-based carbon fiber precursor fiber bundle to a flame-retardant treatment in an oxidizing atmosphere at 200 to 300° C. to obtain a flame-retardant fiber bundle; subjecting the flame-retardant fiber bundle to a pre-carbonization treatment in an inert atmosphere controlled so that the maximum temperature is 500 to 1200° C. to obtain a pre-carbonized fiber bundle; and then subjecting the pre-carbonized fiber bundle to a carbonization treatment in an inert atmosphere controlled so that the maximum temperature is 1200 to 3000° C. to obtain a carbon fiber bundle, wherein the fiber bundle runs while being in contact with a drive roller before and after the carbonization treatment, the carbon fiber bundle has a total fineness A of 6000 to 40000 dtex, a maximum twist angle B of 1 to 10°, a tension C of the fiber bundle in the carbonization treatment of 50 to 500 N / bundle, and a diameter D of the drive roller before and after the carbonization treatment of 200 to 1000 mm.

2. A method for producing a carbon fiber bundle, comprising the steps of: subjecting a polyacrylonitrile-based carbon fiber precursor fiber bundle to a flame-retardant treatment in an oxidizing atmosphere at 200 to 300°C to obtain a flame-retardant fiber bundle; subjecting the flame-retardant fiber bundle to a pre-carbonization treatment in an inert atmosphere at 500 to 1200°C to obtain a pre-carbonized fiber bundle; and then subjecting the pre-carbonized fiber bundle to a carbonization treatment in an inert atmosphere at 1200 to 3000°C to obtain a carbon fiber bundle, wherein the fiber bundle runs while in contact with a drive roller before and after the carbonization treatment, the carbon fiber bundle has a total fineness A of 6000 to 40000 dtex, a maximum twist angle B of 1 to 10°, a tension C of the fiber bundle in the carbonization treatment of 50 to 500 N / bundle, and a diameter D of the drive roller before and after the carbonization treatment of 200 to 1000 mm.

3. 3. The method for producing a carbon fiber bundle according to claim 1 or 2, wherein a total fineness A of the carbon fiber bundle, a maximum twist angle B of the carbon fiber bundle, a tension C of the fiber bundle in the carbonization treatment, and a diameter D of the drive roller satisfy formula (1). D>C / 2+(A ０．５ ×B) / 10 ……Formula (1)

4. The method for producing a carbon fiber bundle according to any one of claims 1 to 3, wherein the fiber bundle passing through the drive roller after the carbonization treatment has an elongation of 0.5 to 3.0%.

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