Method for manufacturing carbon fiber bundle

Abstract

To provide a method for producing a carbon fiber bundle capable of producing a carbon fiber bundle hardly contaminating a flameproofing furnace and having excellent physical properties.SOLUTION: The method can produce a carbon fiber bundle hardly contaminating a flameproofing furnace and having excellent physical properties by adding a silicone oil agent having a finger touch drying time of less than 40 minutes at 250°C to a precursor fiber bundle of carbon fibers and then polymerizing a silicone in the silicone oil agent to a higher molecular weight, followed by subjecting the precursor fiber bundle to flame-resistant treatment.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a carbon fiber bundle. In particular, the present invention relates to a method for manufacturing a carbon fiber bundle including a step of subjecting a precursor fiber bundle of carbon fiber to a flame retardant treatment by a predetermined method.

Background Art

[0002] Carbon fibers have excellent specific strength and specific modulus of elasticity, and are widely industrially used in aerospace applications, sports applications, general industrial applications, etc. as reinforcing fibers for composite materials with resins, taking advantage of their light weight and excellent mechanical properties.

[0003] As a method for manufacturing carbon fibers, a method is generally used in which a precursor fiber bundle is converted into a flame retardant fiber bundle by heating in an oxidizing atmosphere at 200 to 300°C and then carbonized in an inert atmosphere. During these heat treatments at high temperatures, fusion occurs between the single fibers of the precursor fiber bundle, and during these processes, abrasion due to friction between the fibers and between the fibers and the manufacturing apparatus occurs, resulting in a problem of deteriorating the quality and grade of the obtained carbon fibers.

[0004] Therefore, in the flame-resistant treatment process, in order to prevent the fusion between single fibers caused by the large amount of heat generation associated with heat treatment and oxidation reaction, and to prevent damage due to rubbing during the process, an oil agent is applied to the precursor fiber bundle. As this oil agent, silicone oil agents are widely used. However, when using a silicone oil agent, in the flame-resistant treatment process, a part of the silicone is thermally decomposed to generate fine dust such as silicon oxide. This fine dust volatilizes in the flame-resistant furnace and contaminates the flame-resistant furnace, so it is necessary to frequently clean the flame-resistant furnace, which significantly reduces productivity. In addition, when this fine dust contaminates the fiber bundle, it reduces the strength of the carbon fiber bundle. Furthermore, the openability of the fiber bundle is inhibited by the silicone oil agent applied to the fiber bundle, or the gelled silicone oil agent adheres to the conveying rollers and guides in the flame-resistant treatment process and carbonization process, and the precursor fiber or flame-resistant fiber bundle winds around, resulting in process failures, which may lead to a decrease in operability and a decrease in the strength of the obtained carbon fiber. Also, the silicone oil agent penetrates into the single fiber of the precursor fiber bundle, and voids are formed in the single fiber surface layer and inside, which may conversely reduce the strength of the obtained carbon fiber bundle.

[0005] Various measures have been taken to prevent the fusion between single fibers and damage due to rubbing, while suppressing the decrease in operability and the strength of the carbon fiber bundle caused by the silicone oil agent. As a method for suppressing the decrease in operability caused by the silicone oil agent, for example, Patent Document 1 discloses using a silicone oil agent with a specific composition that is difficult to gel. Patent Document 2 discloses setting the proportion of the modified silicone oil agent that is easy to gel to a specific amount. Also, Patent Document 3 proposes a method for preventing a decrease in the openability of the fiber bundle by using a treatment oil agent with low viscosity. However, in such treatment oil agents, since the oil agent easily penetrates into the single fiber of the precursor fiber, the strength of the obtained carbon fiber is not sufficient.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] An object of the present invention is to provide a method for producing a carbon fiber bundle capable of preventing damage due to fusion and rubbing between single fibers in a flame-retardant treatment step and a carbonization step, and producing a carbon fiber bundle having excellent physical properties.

Means for Solving the Problems

[0008] The present inventors have found that in the flame-retardant treatment step in the production of a carbon fiber bundle, the above problems can be solved by applying a silicone oil agent that increases the molecular weight of the precursor fiber bundle by predetermined heating and then performing the flame-retardant treatment, and have completed the present invention.

[0009] The present invention for solving the above problems is as described below.

[0010] 〔1〕 The following steps (b) to (e): (b) An oil agent application step of applying a silicone oil agent to a precursor fiber bundle to obtain an oil agent-attached precursor fiber bundle, (d) A flame-retardant treatment step of subjecting the oil agent-attached precursor fiber bundle to a flame-retardant treatment to obtain a flame-retardant fiber bundle, (e) A carbonization step of carbonizing the flame-retardant fiber bundle, A method for producing a carbon fiber bundle having: Characterized in that the finger-touch drying time of the silicone oil agent at 250 ° C is less than 40 minutes.

[0011] The invention described in [1] is a method for producing carbon fibers, which comprises applying a predetermined silicone oil agent to a precursor fiber bundle of carbon fibers, heating the fiber bundle to polymerize the silicone, and then performing a flame retardant treatment. The touch-dry time of the silicone oil agent used in this method at 250°C is less than 40 minutes, so that the silicone in the silicone oil agent quickly polymerizes and gels. The polymerized silicone is less likely to be thermally decomposed into silicon oxide in the flame retardant step. In addition, the gelled silicone due to polymerization is less likely to penetrate into the individual fibers of the precursor fiber bundle.

[0012] [2] Before the oil agent application step, (a) A preheating step of preheating the precursor fiber bundle at 200 to 250°C, The method for producing a carbon fiber bundle according to [1], further comprising this step.

[0013] [3] After the oil agent application step and before the flame retardant step, (c) A heating step of heating the oil agent-attached precursor fiber bundle at 150 to 200°C, The method for producing a carbon fiber bundle according to [1] or [2], further comprising this step.

[0014] [4] The method for producing a carbon fiber bundle according to any one of [1] to [3], wherein the silicone oil agent is a silicone oil agent containing amino-modified silicone with a reactive end.

[0015] [5] The method for producing a carbon fiber bundle according to any one of [1] to [4], wherein the silicone oil agent is an oil-in-water emulsion.

[0016] [6] The method for producing a carbon fiber bundle according to any one of [1] to [5], wherein the silicone oil agent contains a polyoxyalkylene alkyl ether composed of a polyoxyalkylene containing both ethylene oxide units and propylene oxide units and an alkyl group, and the ethylene oxide unit number / propylene oxide unit number of the polyoxyalkylene alkyl ether is 2 to 20. [Advantages of the Invention]

[0017] According to the method for producing a carbon fiber bundle of the present invention, after applying a predetermined silicone oil agent to the precursor fiber bundle, the silicone in the silicone oil agent is quickly polymerized and gelled, so that damage due to fusion and abrasion between single fibers in the flame resistance step and the carbonization step can be prevented, while it is difficult to contaminate the flame resistance furnace, and a carbon fiber bundle with excellent physical properties can be obtained.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, the method for producing carbon fiber of the present invention will be described in detail. In the present invention, the touch-dry time means the touch-dry time measured by the test method described below. Also, the touch-dry time means the time required for the silicone oil agent to reach the touch-dry state, and does not mean the actual drying time of the present invention.

[0019] The method for producing a carbon fiber bundle of the present invention includes the following steps (b) to (e): (b) An oil application step of applying a predetermined silicone oil agent to the precursor fiber bundle to obtain an oil-coated precursor fiber bundle, (d) A flame resistance step of subjecting the oil-coated precursor fiber bundle to a flame resistance treatment to obtain a flame-resistant fiber bundle, (e) A carbonization step of carbonizing the flame-resistant fiber bundle, and has. Before the oil application step of (b) above, (a) A preheating step of preheating the precursor fiber bundle at 200 to 250 ° C., It is preferably provided. After the oil application step of (b) above and before the flame resistance step of (d) above, (c) A heating step of heating the oil-coated precursor fiber at 150 to 200 ° C., It is preferably provided.

[0020] In the present invention, the (b) oil application step is a step of applying a silicone oil to the precursor fiber bundle to obtain an oil-attached precursor fiber bundle. The adhesion amount of the silicone oil to the precursor fiber is preferably 0.01 to 5.0% by mass, more preferably 0.05 to 1.5% by mass. In the present invention, the adhesion amount of the silicone oil refers to the amount of the active ingredient of the silicone oil attached to the precursor fiber, and the active ingredient of the oil refers to the residue (solid content) (%) when the oil is heated at 105°C for 3 hours. The adhesion amount of the silicone oil can be changed by adjusting the silicone concentration in the oil bath and the viscosity of the oil bath. Further, after applying the silicone oil, the adhesion amount of the silicone oil can be adjusted by adjusting the amount of squeezing out the excess silicone oil.

[0021] The method for applying the silicone oil to the precursor fiber bundle is not particularly limited, and known methods such as a dipping method, a roller dipping method, and a spraying method can be used. Among them, the dipping method and the roller dipping method are preferably used because it is easy to uniformly apply the silicone oil. The liquid temperature of the silicone oil bath is preferably in the range of 10 to 50°C in order to suppress fluctuations in the concentration of the silicone oil due to evaporation of the solvent and destruction of the emulsion. The amount of the active ingredient in the silicone oil bath is preferably 0.5 to 40% by mass, more preferably 1.5 to 30. Usually, a silicone oil containing 5 to 70% by mass of the active ingredient is appropriately diluted with water to adjust the silicone content.

[0022] The silicone oil used in the present invention is a silicone oil having a touch-dry time at 250°C of less than 40 minutes. The touch-dry time at 250°C is preferably 38 minutes or less. After touch-drying, the silicone oil becomes a state in which the silicone is polymerized and uniformly gelled, and it becomes difficult to penetrate into the fiber bundle. By using a silicone oil agent with a finger-touch drying time of less than 40 minutes at 250°C, the silicone in the silicone oil agent crosslinks and gels rapidly, so that it is possible to suppress the excessive penetration of the silicone oil agent into the precursor fiber bundle. When the finger-touch drying time at 250°C exceeds 40 minutes, the oil agent easily penetrates into the single fibers of the precursor fiber, so that the strength of the obtained carbon fiber decreases. On the other hand, the finger-touch drying time preferably exceeds 5 minutes. If it is 5 minutes or less, the gelation of the silicone oil agent may be completed before the water has sufficiently evaporated.

[0023] The silicone contained in the silicone oil agent used in the present invention is an organopolysiloxane, and may be a modified product, branched product, partially crosslinked product, copolymer with other molecules, etc. thereof. Specifically, dimethyl silicone, phenylmethyl silicone, methylhydrogen siloxane, alkyl aralkyl modified silicone, fluorine modified silicone, amino modified silicone, amino modified polyether modified silicone, amide modified silicone, and terminal reactive silicone thereof; silicone wax, silicone resin, silicone resin oil, silicone elastomer, stearoxymethyl polysiloxane, aminomethylaminopropyl siloxane·dimethylsiloxane copolymer are exemplified. Among these, amino modified silicone, amino modified polyether modified silicone, amide modified silicone, and terminal reactive silicone thereof are preferable, and amino modified silicone which is terminal reactive is particularly preferable. Examples of such silicone oil agents include the silicone oil agents disclosed in JP-A-2002-129016 and JP-A-2005-298689.

[0024] The form of the silicone oil agent is not particularly limited, but from the viewpoint of handleability, it is preferable to use water as a solvent, and it is preferably an oil-in-water emulsion. As the surfactant used for forming the emulsion, it is preferable that it has high dilution stability in the silicone oil agent bath and can be quickly demulsified after being adhered to the fiber. Although not particularly limited, it preferably contains a nonionic surfactant. As the nonionic surfactant, it is preferably a polyoxyalkylene alkyl ether. As the polyoxyalkylene alkyl ether, it is preferably an ether compound composed of polyoxyalkylene containing ethylene oxide units and / or propylene oxide units as repeating units and an alkyl group, and it is particularly preferably an ether compound composed of polyoxyalkylene containing both ethylene oxide units and propylene oxide units and an alkyl group. The number of carbon atoms of the alkyl chain of the polyoxyalkylene alkyl ether is preferably 5 to 15, more preferably 10 to 15. Also, the number of ethylene oxide units of the polyoxyalkylene alkyl ether is preferably 1 to 100, more preferably 1 to 50, and even more preferably 1 to 20. The number of propylene oxide units is preferably 1 to 100, more preferably 1 to 50, and particularly preferably 1 to 20. The ethylene oxide unit number / propylene oxide unit number is preferably 1 to 50, more preferably 2 to 20. By using such a polyoxyalkylene alkyl ether as a surfactant, a silicone oil agent with a finger-touch drying time of less than 40 minutes can be obtained.

[0025] The content of the surfactant may be appropriately adjusted according to the content of silicone and the like, but it is usually 1 to 50 parts by mass per 100 parts by mass of silicone, and more preferably 5 to 40 parts by mass. The method for producing the emulsion is not particularly limited, and a known method can be used. For example, the method disclosed in JP-A-2002-129016 (particularly paragraphs 0028 to 0034 and 0041) can be mentioned.

[0026] As the precursor fiber bundle used in the production method of the present invention, various precursor fiber bundles such as polyacrylonitrile, pitch, rayon (cellulose), etc. can be used. A polyacrylonitrile fiber bundle, which is likely to obtain the desired high-strength carbon fiber, can be preferably used. As the polyacrylonitrile fiber bundle, a monomer containing acrylonitrile preferably in an amount of 90% by mass or more, more preferably 95% by mass or more, and other monomers in an amount of 10% by mass or less is spun from a spinning solution prepared by homopolymerization or copolymerization. Examples of other monomers include itaconic acid, (meth)acrylic acid ester, etc. The precursor fiber can be obtained by subjecting the raw fiber after spinning to water washing, drying, and stretching treatment.

[0027] The number of filaments of the precursor fiber bundle used in the present invention is preferably 1000 to 100000, more preferably 3000 to 50000. Also, from the viewpoint of production efficiency, 12000 or more is preferable, and 24000 or more is more preferable. Further, the number of filaments per unit width is preferably 5000 filaments / mm or less, more preferably 3000 filaments / mm or less. When it exceeds 5000 filaments / mm, the variation in the adhesion amount of the silicone oil agent tends to increase.

[0028] The (d) flame-retardant treatment step in the present invention is a flame-retardant treatment step of subjecting the oil agent-attached precursor fiber bundle with the silicone oil agent attached thereto to obtain a flame-retardant fiber bundle. In the present invention, at least by the heat treatment in the flame-retardant treatment step, the silicone of the silicone oil agent is crosslinked and polymerized (gelled). Since the silicone in the silicone oil agent gels rapidly, it is possible to suppress the excessive penetration of the silicone oil agent into the inside of the precursor fiber bundle, and high-strength carbon fiber can be obtained. In the present invention, the oil agent-attached precursor fiber is preferably heat-treated before the flame-retardant treatment step, and more preferably by a heating step (c) of providing an independent heat treatment furnace after the application of the silicone oil agent and before the flame-retardant treatment step and heating the oil agent-attached precursor fiber at 150 to 200°C.

[0029] The heating time at 150 to 200 °C is preferably 10 to 1000 seconds, more preferably 50 to 200 seconds, and even more preferably 100 to 200 seconds. In the present invention, the touch-dry time of the silicone oil agent used is defined, but it is not always necessary to perform the heat treatment until it reaches the touch-dry state.

[0030] Also, it is preferable to provide a preheating step (a) of preheating the precursor fiber bundle to 200 to 250 °C in advance before applying the oil agent, and then applying the silicone oil agent to the preheated precursor fiber bundle. By preheating the precursor fiber before applying the oil agent, the voids present on the surface of the single fiber of the precursor fiber can be reduced, so that the penetration of the silicone oil agent into the inside of the precursor fiber bundle can be more suppressed, and higher-strength carbon fibers can be obtained. In the present invention, the treatment time of the preheating step is preferably 10 to 1000 seconds, and more preferably 100 to 300 seconds. In the present invention, such preheat treatment is preferably carried out until the water vapor adsorption amount (humidity 90%) of the precursor fiber after treatment becomes 10 cc / g or less, and more preferably until it becomes 5 to 8.5 cc / g, from the viewpoint of the strength of the obtained carbon fiber. The water vapor adsorption amount at 90% humidity represents the state of the pores on the surface of the precursor fiber, and the lower the adsorption amount, the fewer the voids on the surface of the single fiber of the precursor fiber. These (a) preheating step and (c) heating step may be used in combination. Alternatively, without providing an independent heat treatment furnace after applying the silicone oil agent, heat treatment may be carried out by setting the temperature of the first-stage flame resistance furnace in the multi-stage flame resistance process to 150 to 200 °C.

[0031] Flame resistance can be carried out under known conditions. For example, when PAN-based fibers are used as precursor fibers, they are subjected to a flame resistance treatment at 200 to 260 °C in heated air with a draw ratio in the range of 0.85 to 1.15 for 10 to 100 minutes. By this flame resistance treatment, a cyclization reaction occurs in the fiber, and flame-resistant fibers with an increased oxygen bond amount are obtained. The flame resistance treatment may be carried out with a temperature gradient to gradually increase the treatment temperature.

[0032] According to the manufacturing method of the present invention, the silicone oil agent is rapidly gelled by being heated after the application of the silicone oil agent. That is, since the flame resistance improvement process is performed after the silicone is polymerized, it is possible to suppress the thermal decomposition of the silicone into silicon oxide in the flame resistance improvement process. As a result, the volatilization of silicon oxide in the flame resistance furnace is suppressed. Further, since the silicone oil agent is rapidly gelled, it is possible to prevent the silicone oil agent from staying on the surface of the single fiber and penetrating into the inside of the single fiber. In addition, the adhesion spots of the oil agent on the surface of the single fiber are suppressed, and it becomes easier to uniformly apply. As a result, during the flame resistance improvement process, it is possible to suppress the cutting of the single fiber due to rubbing or the like.

[0033] (e) The carbonization step in the present invention is a carbonization step in which the flame-resistant fiber bundle is heated to 300°C or higher in an inert atmosphere for carbonization. As the carbonization conditions, conventionally known conditions can be adopted. For example, a method of performing a first carbonization treatment at 300 to 800°C in a nitrogen atmosphere and then a second carbonization at 800 to 1600°C is exemplified. When a higher elastic modulus is required, a graphitization treatment may be performed at 2000 to 3000°C.

[0034] According to the manufacturing method of the present invention described above, the cutting of the single filament is suppressed, and the Fuzz described later can be made 40 μg / m or less. As a result, it is possible to manufacture a carbon fiber bundle having a high strength such that the strength of the epoxy resin-impregnated strand is preferably 6000 Mpa or more according to JIS R-7601.

Examples

[0035] Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited to the examples. The components and test methods used in the present examples and comparative examples will be described below.

[0036] 〔Finger-touch drying test〕 Place 2.0 g of the silicone oil agent in an oven at 250°C and let it stand. Take out the sample every 5 minutes, and touch and then separate a stainless steel rod from it. The heating time at 250°C required until the sample no longer adheres to the stainless steel rod is defined as the touch-dry time.

[0037] 〔OCU (Oil agent adhesion amount)〕 Using a Soxhlet extraction method with a mixed solution of ethanol and benzene as the solvent, the oil agent was extracted from the acrylic precursor, and then the solution containing the oil agent was dried. The solid content obtained was weighed to determine the amount. The precursor fiber bundle was dried at 70°C for 1 hour and approximately 5 g was measured (let the mass at this time be M1). Based on the Soxhlet extraction method with a mixed solution of ethanol and benzene as the solvent, it was refluxed for 4 hours to extract the oil agent adhering to the precursor fiber bundle by solvent extraction. After extraction, the precursor fiber bundle was removed, the solvent was concentrated, the extract was transferred to a weighing bottle (let the tare weight be M2), dried at 105°C for 2.5 hours, and then the amount of the extract (M3) was measured. The adhesion amount of the oil agent was determined by the following formula. Oil agent adhesion amount [M (mass%)] = (M3 - M2) / M1 × 100

[0038] 〔Number of rubbing times until the flame-resistant fiber bundle is cut〕 The flame-resistant fiber bundle was cut into a length of 1.0 m. Three stainless steel needles (diameter 2 mm) were arranged at intervals of 2 cm so that their surfaces passed while the carbon fiber bundle contacted at a contact angle of 135°. The cut carbon fiber bundle was passed through the stainless steel needles in a zigzag manner, and while applying a tension of 1.0 g / Tex to the flame-resistant fiber bundle, a reciprocating motion was performed with a width of 3 cm until the fiber bundle was cut by rubbing (reciprocating rubbing times: 200 times / min). The number of reciprocations until cutting was counted. The rubbing property of the flame-resistant fiber bundle was evaluated in the following three levels according to the number of reciprocations until cutting. ○: More than 2500 times △: 1500 - 2500 times ×: Less than 1500 times

[0039] 〔Number of single-filament cuts of carbonized fiber〕 The carbonized fiber was cut to 1.0 m, spread out, and the number of single fibers cut (the number of single-fiber breaks) was counted visually. The state of single-fiber breaks in the carbonized fiber was evaluated in the following three levels. ○: Less than 100 count / m △: 100 - 200 count / m ×: More than 200 count / m

[0040] 〔Water vapor adsorption amount of precursor fiber〕 The pore state on the surface of the precursor fiber before sizing treatment was evaluated by the water vapor adsorption amount. The water vapor adsorption amount of the precursor fiber was measured using a fully automatic gas adsorption apparatus "AUTOSORB-1" manufactured by Yuasa Ionics Co., Ltd. under the following conditions for a sample cut to about 15 cm in length (about 0.3 g). The value of the water vapor adsorption amount at 90% humidity is the value obtained at the point where the relative pressure (P / Po) is 0.9. Adsorbed gas: H20 Dead volume: He Adsorption temperature: 293K Measurement range: Relative pressure (P / Po) = 0 - 1.0 P: Measurement pressure, Po: Saturated vapor pressure of H2O

[0041] 〔Carbon fiber strength〕 In accordance with JIS R-7601, the strength of the epoxy resin-impregnated strand was measured, and the average value of 5 measurement times was shown.

[0042] 〔Fuzz〕 Five chromium-plated stainless steel bars with a diameter of 2 mm were arranged in a zigzag pattern at 15 mm intervals, and the surface of the bars was passed through while the carbon fiber bundle was in contact with a contact angle of 120°. The carbon fiber bundle was rubbed in a zigzag pattern between these stainless steel bars. The carbon fiber bundle after rubbing was sandwiched between two urethane sponges (bottom surface 32 mm × 64 mm, height 10 mm, weight about 0.25 g), and a 125 g weight was placed so that the entire surface of the urethane sponge was loaded. The weight of the fuzz adhering to the sponge when the carbon fiber bundle was passed through at a speed of 15 m / min for 2 minutes was defined as the rubbing fuzz amount.

[0043] ​ (Production of Precursor Fiber Bundle) A spinning dope prepared by dissolving 7% by mass of an acrylonitrile copolymer consisting of 95% by mass of acrylonitrile, 4% by mass of methyl acrylate, and 1% by mass of itaconic acid in an aqueous zinc chloride solution was extruded through a spinneret into a 25% by mass aqueous zinc chloride solution (coagulating liquid) to continuously obtain a coagulated fiber bundle. This coagulated fiber bundle was washed with water, stretched, oiled, dried and densified, and post-stretched to obtain a precursor fiber bundle having a filament fineness of 0.7 dtex and 24,000 filaments.

[0044] (Production of Silicone Oil Agent) Silicone Oil Agent A: 15% by mass of an amino-modified silicone oil having a kinematic viscosity of 1000 mm 2 / s and an amine number of 0.3, 3% by mass of polyoxypropylene polyoxyethylene tridecyl ether (the number of carbon atoms in the alkyl chain, ethylene oxide units, and propylene oxide units are as described in Table 1) as a surfactant, and 82% by mass of ion-exchanged water were added, and stirred using a homogenizer to adjust an O / W type emulsion to obtain Silicone Oil Agent A. The touch-dry time of this Silicone Oil Agent A at 250 °C was 35 minutes.

[0045] Silicone Oil Agents B to G: An O / W type emulsion was adjusted in the same manner as Silicone Oil Agent A except that the type of surfactant was changed as described in Table 1 to obtain a silicone oil agent. The touch-dry time of this silicone oil agent at 250 °C is as described in Table 1.

[0046]

Table 1

[0047] (Example 1) A precursor fiber bundle was immersed in a silicone oil bath filled with a silicone oil agent solution (silicone oil agent A) containing silicone oil at a concentration of 15% by mass to apply the oil agent. Then, after heating at 150°C for 180 seconds, while stretching at 1.0 times, a flame-retardant treatment was performed at 240 - 250°C for 1 hour to obtain a flame-retardant fiber bundle. Next, a carbonization treatment was performed at 300 - 1200°C in a nitrogen atmosphere to obtain a carbonized fiber bundle. The obtained carbonized fiber bundle was surface-treated using an aqueous ammonium sulfate solution as an electrolyte, a sizing agent (epoxy resin) was added and applied, and then dried to obtain a carbon fiber bundle. When the number of rubbing times until the obtained flame-retardant fiber bundle was cut was measured, it exceeded 2500 times. The single-filament break count of the obtained carbonized fiber bundle was less than 100 count / m. Also, the strength of the carbon fiber bundle was 6200 MPa. The fuzz was 33 μg / m.

[0048] (Examples 2 - 4, Comparative Examples 1 - 5) Carbon fiber bundles were produced in the same manner as in Example 1 except that the type of the oil agent and the amount of oil agent adhesion were changed as shown in Table 2. The results are shown in Table 2. In all of Examples 1 - 4 using a silicone oil agent with a finger-touch drying time of 35 minutes, there was little damage to the short fibers in the flame-retardant process and the carbonization process, and high-strength and high-quality carbon fibers were obtained.

[0049] (Example 5) The precursor fiber bundle was preheated in air at 220°C for 180 seconds. Then, the preheated precursor fiber bundle was put into a silicone oil bath filled with a silicone oil agent solution (silicone oil agent A) containing silicone oil at a concentration of 15% by mass to apply the oil agent. The amount of oil agent adhesion was 0.4% by mass as silicone. Then it was heated at 150°C for 90 seconds. Thereafter, while stretching this oil-agent-attached precursor fiber bundle, a flame-retardant treatment was performed at 240 - 250°C for 1 hour to obtain a flame-retardant fiber bundle. Next, a carbonization treatment was performed at 300 - 1200°C in a nitrogen atmosphere to obtain a carbon fiber bundle. When the number of rubbing times until the obtained flame-retardant fiber bundle was cut was measured, it exceeded 2500 times. The number of single filaments cut per unit length of the obtained carbon fiber bundle was less than 100 count / m. Also, the strength of the carbon fiber bundle was 6150 MPa.

[0050] (Examples 6 - 15) Carbon fiber bundles were produced in the same manner as in Example 5, except that the preheating temperature, preheating time, heat treatment temperature, and type of sizing agent of the precursor fiber bundle were changed as described in Table 3. The results are shown in Table 3.

[0051] (Example 16) Carbon fiber bundles were produced in the same manner as in Example 5, except that no pre - heat treatment of the precursor fiber bundle was performed. The results are shown in Table 3.

[0052] [Table 2]

[0053] [Table 3]

Claims

1. The following steps (a) to (e): (a) A preheating step of preheating a precursor fiber bundle at 200 to 250°C; (b) An oil application step of applying a silicone oil agent to the precursor fiber bundle to obtain an oil-applied precursor fiber bundle; (c) A heating step of heating the oil-applied precursor fiber bundle at 150 to 200°C for 10 to 1000 seconds to crosslink the silicone in the silicone oil agent attached to the oil-applied precursor fiber bundle; (d) A flameproofing step of subjecting the oil-applied precursor fiber bundle to a flameproofing treatment to obtain a flameproofed fiber bundle; (e) A carbonization step of carbonizing the flameproofed fiber bundle, which is a method for producing a carbon fiber bundle, characterized in that the finger-touch drying time of the silicone oil agent at 250°C is less than 40 minutes.

2. The method for producing a carbon fiber bundle according to Claim 1, wherein the silicone oil agent is a silicone oil agent containing an amino-modified silicone having a reactive terminal.

3. The method for producing a carbon fiber bundle according to Claim 1 or 2, wherein the silicone oil agent is a water-in-oil emulsion.

4. The method for producing a carbon fiber bundle according to any one of Claims 1 to 3, wherein the silicone oil agent contains a polyoxyalkylene alkyl ether composed of a polyoxyalkylene containing both ethylene oxide units and propylene oxide units and an alkyl group, and the ethylene oxide unit number / propylene oxide unit number of the polyoxyalkylene alkyl ether is 2 to 20.

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