Carbon fiber bundle

Abstract

Provided is a carbon fiber bundle with total fineness of 2 g / m or more. The variation rate of the fiber bundle thickness in the width direction of the fiber bundle is 30% or less. Provided is a method for producing carbon fiber bundles, involving: applying a sizing agent to a carbonized fiber bundle; drying same; subsequently bringing one surface and the opposite surface of the widthwise surfaces of the carbonized fiber bundle alternatively into contact with two or more parallel bars and passing the carbonized fiber bundle through the bars; and winding the carbonized fiber bundle around a bobbin.

Description

[Technical Field]

[0001] The present invention relates to a carbon fiber bundle that is easy to handle during advanced processing even when the carbon fiber bundle has a large total fineness, and from which a molded product in which the carbon fibers are uniformly distributed can be obtained. This application claims priority based on Japanese Patent Application No. 2021-052932, filed on March 26, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] Carbon fiber, with its excellent specific strength and specific modulus, is widely used in a variety of applications, from sports and leisure goods to aerospace. In addition to sports applications such as golf club shafts and fishing rods, and aircraft applications, it is also being expanded to general industrial applications such as wind turbine components for power generation, automobile components, CNG tanks, earthquake reinforcement of buildings, and ship components, which require carbon fiber bundles with a large mass per unit length (total fineness).

[0003] When carbon fiber bundles with a large total fineness are processed into prepregs by the drum winding method or when various composite materials are molded by the filament winding method or the like, resin is applied to the carbon fiber bundles using the touch roll method. However, with conventional techniques, the molded product has parts with high fiber content and parts with low fiber content, and the parts with low fiber content can sometimes become the starting point of early breakage.

[0004] One of the causes is thought to be uneven thickness in the width direction of carbon fiber bundles with a large total fineness. During the carbon fiber precursor fiber bundle production process, carbon fiber bundles with a large total fineness must have their width restricted by width restricting guides or the like to prevent adjacent fiber bundles from coming into contact with each other and becoming tangled or stuck together during processes such as the baking process and sizing agent application process. When passing through the width restricting guides, the fiber bundles are pushed from both sides, which makes thickness unevenness likely to occur. Furthermore, when winding the carbon fiber bundle, the width is narrowed by a concavely curved guide, which tends to result in uneven thickness.

[0005] Patent Document 1 discloses a method for producing a wide carbon fiber bundle with a large total fineness, in which the variation rate of the yarn width of the carbon fiber bundle during unwinding is small, the yarn width is uniform, and the total fineness is large, by twisting the fiber bundle by 90 degrees at the traverse location when winding the bundle and then twisting it back, and winding it around a concavely curved guide.

[0006] Patent Document 2 discloses a method for reducing fluctuations in yarn width when winding a bundle of 36,000 carbon fibers by using a guide that stabilizes the yarn path.

[0007] Patent Document 3 discloses a carbon fiber bundle in which 24,000 fiber bundles are calcined, impregnated with a sizing agent, and then brought into contact with a heat roller having a surface temperature of 120 to 140°C for 15 to 30 seconds, resulting in a fiber bundle cross-section with an aspect ratio (ratio of width to thickness of the carbon fiber bundle) of 40 to 90 and a drape value (softness of the carbon fiber bundle) of 50 to 100 mm. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-11830 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-154000 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-252264 Summary of the Invention [Problem to be solved by the invention]

[0009] However, in Patent Document 1, the thickness variation rate was large, as shown in the comparative example of the present application. Patent Documents 2 and 3 do not describe the rate of variation in the thickness of the carbon fiber bundles, and the thickness is not controlled. In the sizing agent application process, the film passes through a comb guide, is dried, and is wound up while the thickness still fluctuates greatly, so the thickness still fluctuates greatly.

[0010] The present invention aims to solve the conventional problems and to provide a carbon fiber bundle that is easy to handle during advanced processing, has uniformly distributed carbon fibers, and allows the production of a molded product with a uniform fiber content, even when the carbon fiber bundle has a large total fineness. [Means for solving the problem]

[0011] The carbon fiber bundle of the present invention has the following characteristics. [1] A carbon fiber bundle having a total fineness of 2 g / m or more, and a variation in thickness of the fiber bundle in the width direction of the fiber bundle of 30% or less. [2] The carbon fiber bundle according to [1], wherein the number of single fibers is 20,000 or more. [3] The carbon fiber bundle according to [1] or [2], wherein the average thickness of the fiber bundle is 0.18 to 0.28 mm. [4] The carbon fiber bundle according to any one of [1] to [3], wherein the variation rate of the width of the fiber bundle in the length direction of the fiber bundle is 13% or less. [5] The carbon fiber bundle according to any one of [1] to [4], wherein the width of the fiber bundle is 13 to 18 mm. [6] The carbon fiber bundle according to any one of [1] to [5], wherein the flatness (width / average thickness) of the fiber bundle is 60 to 70. [7] The carbon fiber bundle according to any one of [1] to [6], which has a cantilever value of 210 to 250 mm and an adhesion of 0.18 m or less. [8] The carbon fiber bundle according to any one of [1] to [7], wherein the amount of the sizing agent attached is 0 to 20% by mass. [9] The carbon fiber bundle according to any one of [1] to [8], wherein the coefficient of dynamic friction between fibers is 0.2 or less.

[10] The carbon fiber bundle according to any one of [1] to [9], wherein the fiber-metal dynamic friction coefficient is 0.18 or less.

[11] A method for producing a carbon fiber bundle, comprising: passing a carbonized fiber bundle through an averaging member having two or more parallel rods arranged between a sizing agent dryer and a winder or a feeding device, while bringing a surface A of the carbonized fiber bundle and a surface B opposite to the surface A into contact with the rods at least once each.

[12] The method for producing a carbon fiber bundle according to

[11] , wherein the distance between adjacent parallel rods is 15 to 50 mm.

[13] The method for producing a carbon fiber bundle according to

[11] or

[12] , wherein, in the passing, the carbonized fiber bundle is passed in contact with the parallel rods in a state where the surface direction of the carbon fiber bundle in contact with the roller immediately preceding the parallel rods is twisted by 90°.

[14] The method for producing a carbon fiber bundle according to any one of

[11] to

[13] , wherein the carbonized fiber bundle is passed so that the maximum width of the carbonized fiber bundle in contact with the parallel rod is 5 to 20% wider than the width of the carbonized fiber bundle in contact with the roller immediately preceding the parallel rod.

[15] The manufacturing method according to

[13] or

[14] , wherein the roller is located upstream of the parallel rods in the running direction of the carbonized fiber bundle, and the length direction of the roller and the length direction of the parallel rods are approximately perpendicular to each other.

[16] The manufacturing method according to any one of

[13] to

[15] , wherein the distance from the center of the roller to the center of the parallel rods is preferably 200 to 1500 mm, more preferably 500 to 1000 mm, at the shortest point.

[17] The method for producing a carbon fiber bundle according to any one of

[11] to

[16] , wherein, in the passing, the carbonized fiber bundle is flat, and one surface A of the carbonized fiber bundle is brought into contact with the parallel rod located upstream in the running direction of the carbonized fiber bundle, and then the other surface B of the carbonized fiber bundle is brought into contact with the parallel rod located downstream in the running direction of the carbonized fiber bundle, and the carbonized fiber bundle is passed through the averaging member.

[18] The method for producing a carbon fiber bundle according to any one of

[11] to

[17] , comprising changing the direction of the plane of the carbonized fiber bundle around the length direction of the carbonized fiber bundle as an axis before the passing.

[19] The manufacturing method according to

[18] , wherein, in changing the orientation of the face, it is preferable to tilt the face of the carbonized fiber bundle in the width direction within a range of 30° to 150° around the length direction of the carbonized fiber bundle as an axis; it is more preferable to tilt the face of the carbonized fiber bundle in the width direction within a range of 45° to 135° around the length direction of the carbonized fiber bundle as an axis; it is even more preferable to tilt the face of the carbonized fiber bundle in the width direction within a range of 60° to 120° around the length direction of the carbonized fiber bundle as an axis; and it is particularly preferable to tilt the face of the carbonized fiber bundle in the width direction at approximately 90° around the length direction of the carbonized fiber bundle as an axis.

[20] The manufacturing method described in

[18] or

[19] , wherein the changing of the orientation of the faces is carried out between a roller located upstream of the two or more parallel rods in the running direction of the carbonized fiber bundle and a parallel rod located most upstream among the two or more parallel rods.

[21] The method for producing the carbon fiber bundle according to any one of

[11] to

[20] , which is the method for producing the carbon fiber bundle according to any one of [1] to

[10] .

[0012] The carbon fiber bundle of the present invention also has the following features. [1a] A method for producing a carbon fiber bundle, comprising: contacting one surface A of a carbonized fiber bundle with a first rod; and contacting the other surface B of the carbonized fiber bundle with a second rod. [2a] The manufacturing method according to [1a], which comprises changing the orientation of the plane of the carbonized fiber bundle around the longitudinal direction of the carbonized fiber bundle as an axis. [3a] The manufacturing method according to [2a], wherein, in changing the orientation of the face, it is preferable to tilt the face of the carbonized fiber bundle in the width direction within a range of 30° to 150° with the length direction of the carbonized fiber bundle as an axis; it is more preferable to tilt the face of the carbonized fiber bundle in the width direction within a range of 45° to 135° with the length direction of the carbonized fiber bundle as an axis; it is even more preferable to tilt the face of the carbonized fiber bundle in the width direction within a range of 60° to 120° with the length direction of the carbonized fiber bundle as an axis; and it is particularly preferable to tilt the face of the carbonized fiber bundle in the width direction at approximately 90° with the length direction of the carbonized fiber bundle as an axis. [4a] The manufacturing method according to [2a] or [3a], wherein the steps of changing the orientation of the surface; contacting the first rod; and contacting the second rod are carried out in this order. [5a] The manufacturing method according to any one of [2a] to [4a], wherein the steps of changing the orientation of the face; bringing the carbon fiber bundle into contact with the first rod; and bringing the carbon fiber bundle into contact with the second rod are carried out in this order, so that the width of the carbon fiber bundle after these steps is in the range of 105 to 120% of 100% of the width of the carbon fiber bundle before these steps. [6a] The method for producing the carbon fiber bundle according to any one of [1a] to [5a], which is a method for producing the carbon fiber bundle according to any one of [1] to

[10] . [Effects of the Invention]

[0013] The carbon fiber bundle of the present invention, even if it has a large total fineness, is easy to handle during advanced processing, and a molded product in which the carbon fibers are uniformly distributed can be obtained. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 10 is a diagram showing a method for calculating the rate of variation in the thickness of a carbon fiber bundle. [Figure 2] FIG. 1 is a diagram showing an example of an apparatus used to measure the fiber-to-fiber kinetic friction coefficient of a carbon fiber bundle and the fiber-to-metal kinetic friction coefficient. [Figure 3] FIG. 1 is a diagram showing an example of an averaging member used to produce the carbon fiber bundle of the present invention. [Figure 4] FIG. 1 is a perspective view showing an example of a state in which the carbonized fiber bundle of the present invention passes through parallel rods. [Figure 5] FIG. 2 is a top view showing an example of a state in which the carbonized fiber bundle of the present invention passes through parallel rods. [Figure 6] FIG. 10 is a diagram showing an example of the location of an averaging member of the present invention. [Figure 7] FIG. 1 is a diagram showing an example of a winder of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] The carbon fiber bundle of the present invention is a carbon fiber bundle having a total fineness of 2 g / m or more and a variation rate of the thickness of the fiber bundle in the width direction of the fiber bundle of 30% or less.

[0016] The carbon fiber bundle of the present invention has a total fineness of 2.0 g / m or more. Since the productivity of carbon fiber bundles depends on the total fineness of the carbon fiber bundles, a large mass per unit length of the carbon fiber bundles allows for efficient production of carbon fiber bundles. The total fineness is more preferably 2.5 g / m or more, and most preferably 3 g / m or more. A total fineness of 2.0 g / m is 20,000 dtex.

[0017] The variation rate of the thickness of the carbon fiber bundle in the width direction of the fiber bundle of the present invention (hereinafter, "the variation rate of the thickness of the carbon fiber bundle in the width direction of the fiber bundle" may be simply referred to as "the variation rate of thickness") can be measured by the method described below. The carbon fiber bundle of the present invention preferably has a thickness variation rate of 30% or less. By setting the thickness variation rate of the carbon fiber bundle to 30% or less, a molded product in which the carbon fibers are uniformly distributed can be produced. The thickness variation rate of the carbon fiber bundle is more preferably 20% or less, and even more preferably 15% or less.

[0018] The carbon fiber bundle of the present invention preferably has 20,000 or more single fibers. The greater the number of single fibers, the higher the productivity, which is preferable. Also, the greater the number of single fibers, the greater the thickness variation rate, which makes it easier to apply the method for producing a carbon fiber bundle of the present invention. From these viewpoints, the number of single fibers is more preferably 30,000 or more, and even more preferably 40,000 or more.

[0019] The carbon fiber bundle of the present invention preferably has an average thickness of 0.18 to 0.28 mm. If the average thickness of the fiber bundle is 0.18 mm or more, the width of the carbon fiber bundle having a large total fineness will not become too large, and handling will tend to be good, and if it is 0.28 mm or less, the thickness variation rate will tend to be small. From these viewpoints, the average thickness of the fiber bundle is more preferably 0.20 to 0.27 mm, and even more preferably 0.21 to 0.25 mm.

[0020] The carbon fiber bundle of the present invention preferably has a fiber bundle width variation rate of 13% or less in the length direction of the fiber bundle. When the fiber bundle width variation rate is 13% or less, a molded product in which the carbon fibers are uniformly distributed can be easily produced. The thickness variation rate of the carbon fiber bundle is more preferably 12% or less, and even more preferably 11% or less. The variation rate of the width of the carbon fiber bundle in the length direction of the fiber bundle of the present invention can be measured by the method described below.

[0021] (Method for measuring the average thickness of carbon fiber bundles, thickness variation rate, carbon fiber width, and width variation rate) Measurements were performed at room temperature of 25°C and 50% humidity. The carbon fiber bundle was placed under a tension of 0.40 cN / tex and brought into contact with a 60 mm diameter free-rotating roller at a wrap angle θ = π (rad) at a speed of 10 m / min. A two-dimensional line laser displacement meter was installed at the midpoint of the wrap angle of the rotating roller to simultaneously acquire displacement data in a line at equal intervals of 0.1 mm in the width direction of the carbon fiber bundle. The average and standard deviation of the displacements were calculated (Figure 1), excluding measurement points on both ends of the line where the displacement was 5% or less of the maximum value (Figure 1). The rate of variation was calculated from the ratio of the two. The average displacement was taken as the average thickness. The width of the range over which the average thickness and standard deviation were calculated was recorded as the width of the fiber bundle. The average of the rate of variation obtained from 300 measurements at 2 cm intervals in the longitudinal direction of the carbon fiber bundle was taken as the "rate of variation in thickness in the width direction of the carbon fiber bundle" of the carbon fiber bundle being measured. In addition, the average value and standard deviation of the widths of the 300 fiber bundles obtained at the same time are calculated, and the ratio of the two is defined as the "rate of variation in width in the length direction of the carbon fiber bundle" of the carbon fiber bundle to be measured, and the average value of the widths of the fiber bundles is defined as the width of the carbon fiber.

[0022] The carbon fiber bundle of the present invention preferably has a width of 13 to 18 mm. If the width of the carbon fiber is 13 mm or more, the thickness will not become too large and the thickness variation rate will be small, and if it is 18 mm or less, the fiber bundle will not break and will be easy to handle. From these viewpoints, the width of the carbon fiber bundle is more preferably 13.5 to 16.5 mm, and even more preferably 14 to 17 mm.

[0023] The carbon fiber bundle of the present invention preferably has a flatness (width / average thickness) of 60-70. If the flatness of the carbon fiber bundle is 60 or more, the thickness of the carbon fiber bundle becomes too large, and if it is 70 or less, the width does not become too wide, and handling tends to be good. From these viewpoints, the flatness is more preferably 61 to 69, and further preferably 62 to 68.

[0024] The carbon fiber bundle of the present invention preferably has a cantilever value of 210 to 250 mm. If the cantilever value is 210 mm or more, the concentration of the carbon fiber bundle traveling along the yarn path during advanced processing can be ensured, and the generation of fuzz along the yarn path from the creel containing the carbon fiber bundle to the resin impregnation step can be prevented when the carbon fiber bundle is impregnated with resin. If the cantilever value is 250 mm or less, good opening between the carbon fiber filaments can be ensured during advanced processing. A cantilever value of 220 mm or more and 240 mm or less is more preferable. The cantilever value of the carbon fiber bundle can be measured by the method described below.

[0025] (Method for measuring cantilever value of carbon fiber bundle) Measurements are performed at room temperature of 25°C and humidity of 50%. Approximately 1 m of carbon fiber bundle is unwound from a carbon fiber bundle package without tension and cut out. To eliminate the influence of the winding tendency of the cut carbon fiber bundle, one end of the carbon fiber bundle is fixed, and a 13 mg / tex weight is attached to the other end. The bundle is then hung vertically for 30 minutes, after which the weight is removed and a 30 cm length is cut out, excluding the end, to serve as the test carbon fiber bundle. A measurement table has a horizontal plane and a slope with a 45-degree inclination angle that slopes downward from one end (straight) of the horizontal plane. The test carbon fiber bundle is placed on the horizontal plane without twisting or disorder, and the end (straight) of the test carbon fiber bundle is aligned with the boundary line between the slope and the horizontal plane. A metal pressure plate is placed on the test carbon fiber bundle, and the end (straight) of the pressure plate is aligned with the boundary line. Next, the presser plate is moved horizontally toward the slope at a speed of 0.5 cm / sec, and when the end of the test carbon fiber bundle comes into contact with the slope, the movement of the presser plate is stopped, and the shortest distance between the point where the end of the carbon fiber bundle comes into contact with the slope and the boundary line is measured. The measurement is carried out once for each of five test carbon fiber bundles, and the simple average of the obtained values ​​is taken as the cantilever value of the carbon fiber bundle.

[0026] The carbon fiber bundle of the present invention preferably has an adhesion of 0.18 m or less. If the stickiness is 0.18 m or less, the concentration of the carbon fiber bundles running through the yarn path during advanced processing can be ensured, and the generation of fuzz can be prevented in the yarn path from the creel containing the carbon fiber bundles to the resin impregnation step when the carbon fiber bundles are impregnated with a matrix resin. The stickiness is more preferably 0.16 m or less. The adhesiveness of the carbon fiber bundles can be measured by the method described below.

[0027] (Method for measuring adhesion of carbon fiber bundles) The measurement is performed in a windless environment at a room temperature of 25°C and humidity of 50%. A spool with a diameter of 20 to 25 cm around which a carbon fiber bundle is wound is held horizontally, and the carbon fiber bundle is unwound without tension. The carbon fiber bundle is then cut at a position 10 cm below the height of the center of the spool's axis. Next, the spool is held vertically without vibration, with the direction in which the carbon fiber bundle is obliquely wound around the spool moving upward from the point where contact between the unwound fiber bundle and the spool begins. After holding the carbon fiber bundle for 10 minutes, the carbon fiber bundle is cut at a position 10 cm from the point where contact with the spool begins, and the length of the carbon fiber bundle that has peeled off from the spool is measured. The measurement is performed three times, and the simple average of the obtained values ​​is used as the measurement value of the adhesion of the carbon fiber bundle.

[0028] The carbon fiber bundle of the present invention preferably has an amount of sizing agent attached thereto of 0 to 20% by mass. If the amount of the sizing agent applied is 20% by mass or less, the fiber bundles are less likely to stick together, and the thickness variation rate can be easily reduced. From this viewpoint, the amount of the sizing agent attached is more preferably 15% by mass or less, further preferably 10% by mass or less, and most preferably 5% by mass or less. The lower limit is preferably 0% by mass from the viewpoint of thickness unevenness, but is more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, in order to make the carbon fiber bundles cohesive and easy to handle.

[0029] The carbon fiber bundle of the present invention preferably has an inter-fiber dynamic friction coefficient of 0.2 or less. If the inter-fiber kinetic friction coefficient is 0.2 or less, the frictional force between the single yarns is reduced, thereby suppressing the generation of fluff due to rubbing between carbon fiber filaments and preventing a phenomenon called ringing, in which fluff surrounds the bobbin and makes it impossible to unwind the carbon fiber bundle. A coefficient of 0.17 or less is more preferable. The inter-fiber dynamic friction coefficient can be measured by the method described below.

[0030] (Method for measuring the coefficient of dynamic friction between fibers) An example of a measurement device is shown in Figure 2. The carbon fiber bundle 1 to be measured is tightly wound around a 30 mm diameter drive roller 1 equipped with a heater, with a helix angle in the range of 0.1 to 0.5 mm to ensure a uniform thickness, and then secured in place. With the drive roller 1 stopped, the carbon fiber bundle 2 to be measured is positioned at a wrap angle θ = π (rad) in the yarn path shown in Figure 2. The surface temperature of the drive roller 1 is set to 30°C. A weight 4 (T1 = 0.53 g / tex) is attached to one end of the carbon fiber bundle 2 placed in the yarn path, and a spring balance 5 is attached to the opposite end. The drive roller 1 is rotated at a speed of 60 rpm, and the median value T2 (g) indicated by the spring balance 5 after one minute is read. The measurement is performed twice, and the inter-fiber kinetic friction coefficient is calculated from the average of the obtained T2 values. Coefficient of kinetic friction between fibers = π -1 ln((average value of T2) / (T1 × total fineness))

[0031] The carbon fiber bundle of the present invention preferably has a fiber-metal dynamic friction coefficient of 0.18 or less. If the coefficient of dynamic friction between the fibers and metal is 0.18 or less, the friction force between the metal guide and the carbon fiber filaments is reduced, thereby improving abrasion resistance. A coefficient of dynamic friction between the fibers and metal of 0.16 or less is more preferable. The fiber-metal dynamic friction coefficient can be measured by the method described below.

[0032] (Method for measuring the coefficient of dynamic friction between fibers and metals) An example of a measuring device is shown in Figure 2. With a 30 mm diameter drive roller 1 equipped with a heating device stopped, the carbon fiber bundle 2 to be measured is positioned in the yarn path shown in Figure 2 so that the wrap angle θ = π (rad). Note that, unlike the above-described method for measuring the fiber-metal kinetic friction coefficient, the carbon fiber bundle 2 to be measured is simply placed on the drive roller 1, without being wrapped around the carbon fiber bundle 1. The drive roller 1 is a metal roller (material: S45C-H, mesh 400 matte finish) with a surface temperature of 30°C. A weight 4 (T3 = 0.53 g / tex) is attached to one end of the carbon fiber bundle placed in the yarn path, and a spring balance 5 is attached to the opposite end. The drive roller 1 is rotated at 60 rpm, and the median value T4 (g) of the spring balance readings is read after 5 minutes. The measurement is performed twice, and the fiber-metal kinetic friction coefficient is calculated from the average of the obtained T4 values. Coefficient of kinetic friction between fiber and metal = π -1 ln((average value of T4) / (T3 × total fineness))

[0033] (Method of manufacturing carbon fiber bundles) The method for producing the carbon fiber bundle of the present invention is not particularly limited, and it can be produced, for example, by a method including the following steps (a) to (i). (a) A step of spinning a spinning dope and coagulating it to obtain a coagulated thread. (b) A process of washing and stretching the coagulated yarn to obtain a precursor yarn. (c) Precursor process: A process in which an oil is applied to the yarn, and then the yarn is dried and densified to obtain a precursor fiber bundle. (d) A step of subjecting the precursor fiber bundle to a flame-retardant treatment to obtain a flame-retardant fiber bundle. (e) A step of carbonizing the flame-retardant fiber bundle to obtain a carbonized fiber bundle. (f) A step of subjecting the carbonized fiber bundle to a surface oxidation treatment. (g) A step of applying a sizing agent to the carbonized fiber bundle after the surface oxidation treatment. (h) A step of homogenizing the carbonized fiber bundle after applying the sizing agent. (i) A winding process in which carbon fiber bundles are obtained by winding the fibers onto a bobbin.

[0034] 6 and 7 show general process diagrams for the transition to the process of applying a sizing agent to a carbonized fiber bundle, and the averaging member of the present invention is placed in the area indicated by the dashed line A in FIG.

[0035] In step (a), the spinning dope is spun and coagulated to obtain a coagulated thread. The spinning dope used in step (a) is not particularly limited. From the viewpoint of manifesting mechanical properties such as strength of the carbon fiber, it is preferably an organic solvent solution of an acrylonitrile copolymer. The acrylonitrile copolymer is a polymer having 90% by mass or more of repeating units derived from acrylonitrile, and preferably a copolymer having 95% by mass or more of repeating units derived from acrylonitrile.

[0036] In the acrylonitrile copolymer, examples of repeating units derived from units other than acrylonitrile (hereinafter referred to as "copolymerization components") include acrylic acid, methacrylic acid, itaconic acid, acrylic acid derivatives such as methyl acrylate, methacrylic acid derivatives such as methyl methacrylate, acrylamide derivatives such as acrylamide, methacrylamide, N-methylolacrylamide, N,N-dimethylacrylamide, and vinyl monomers such as vinyl acetate. The copolymerization components may be one type or two or more types. As the copolymerization component, a vinyl monomer having one or more carboxy groups is preferred.

[0037] The polymerization method for producing the acrylonitrile copolymer is not particularly limited, and examples thereof include solution polymerization in an organic solvent that dissolves the acrylonitrile copolymer, and precipitation polymerization in water.

[0038] Examples of organic solvents used in the spinning dope include polar organic solvents such as dimethylacetamide, dimethyl sulfoxide, and dimethylformamide. The spinning dope obtained using these polar organic solvents does not contain metal elements, so the metal element content of the resulting carbon fiber bundle can be reduced. The solid content of the spinning dope is preferably 20% by mass or more.

[0039] The spinning method may be either wet spinning or dry-wet spinning. For example, in wet spinning, filaments are spun from a spinneret with many nozzles into a temperature-controlled coagulation liquid, where they are coagulated, and the resulting filaments are collected and taken up as a coagulated yarn. The coagulation liquid may be a known one, such as a mixed solution of a polar organic solvent and water used in a spinning dope.

[0040] In step (b), the coagulated yarn obtained in step (a) is washed and stretched to obtain a precursor yarn. Any known washing method can be used as long as it can remove the solvent from the coagulated yarn. Before washing the coagulated yarn, the fibers can be stretched in air or in an aqueous solvent solution with a lower solvent concentration and higher temperature than the coagulation liquid to form a denser fibril structure. Furthermore, after washing the coagulated yarn, the fibers can be stretched in hot water to further enhance the orientation of the acrylonitrile copolymer in the fibers.

[0041] In step (c), an oil is applied to the precursor fiber obtained in step (b), and the precursor fiber bundle is obtained by drying and densifying. Any known oil can be used as the oil, and examples of such oils include oils made of silicone compounds such as silicone oil.

[0042] The method of drying and densifying the precursor process yarn to which the oil agent is attached may be dried by a known drying method to densify the yarn, and there is no particular limitation.

[0043] If necessary, the dried and densified fibers may be stretched 1.8 to 6 times in pressurized steam at 130 to 200°C, between heated rollers, or on a heated plate to further improve the orientation and densify the precursor fiber bundles.

[0044] In step (d), the precursor fiber bundle obtained in step (c) is subjected to a flame retardant treatment to obtain a flame retardant fiber bundle. For example, the flame-resistant treatment may involve passing the fibers through a hot air oven set to gradually increase the temperature from 220 to 260°C for 30 to 100 minutes. The fibers may be stretched during the flame-resistant treatment. Appropriate stretching during the flame-resistant treatment can maintain or improve the orientation of the fibril structure forming the fibers, making it easier to obtain a carbon fiber bundle with excellent mechanical properties. The density of the single fibers constituting the flame-resistant fiber bundle can be set to 1.33 to 1.40 g / cm. 3 It is preferable to set the following.

[0045] In step (e), the flame-resistant fiber bundle obtained in step (d) is carbonized to obtain a carbonized fiber bundle. Examples of the carbonization treatment include a first carbonization treatment in which the fiber bundle is heated in an inert atmosphere such as nitrogen at a maximum temperature of 600°C to 800°C, and a second carbonization treatment in which the fiber bundle is heated in an inert atmosphere such as nitrogen at a maximum temperature of 1200°C to 2000°C.

[0046] The treatment time for the first carbonization treatment is preferably 1 to 3 minutes. In the first carbonization treatment, it is preferable to carry out an elongation operation of 1% to 5% in order to promote regular orientation of the carbon structure.

[0047] The treatment time in the second carbonization treatment is preferably 1.3 to 5 minutes. The strength and elastic modulus of the carbon fiber bundle can be controlled by the temperature and treatment time in the second carbonization treatment. Since the second carbonization treatment causes significant shrinkage in the fibers, it is preferable to set the elongation rate to -5% to -2%. After the second carbonization treatment, an additional third carbonization treatment may be performed as needed.

[0048] In step (f), the carbonized fiber bundle obtained in step (e) is subjected to a surface oxidation treatment. Known methods can be used for the surface oxidation treatment, and examples include electrolytic oxidation, chemical oxidation, and air oxidation. Among these, electrolytic oxidation is preferred.

[0049] In step (g), a sizing agent is applied to the carbonized fiber bundle obtained in step (f). A solution of a sizing agent dissolved in an organic solvent or an emulsion of a sizing agent dispersed in water with an emulsifier or the like is applied to the carbonized fiber bundle, and then the bundle is dried, thereby applying the sizing agent to the carbonized fiber bundle. Before and after applying the sizing agent, it is preferable to separate adjacent carbonized fiber bundles with a comb guide or the like to prevent them from sticking together.

[0050] The sizing agent is selected so that the inter-fiber kinetic friction coefficient is 0.20 or less and the fiber-metal kinetic friction coefficient is 0.18 or less, as measured by the method described in the specification. There are no particular limitations on the sizing agent as long as it has an inter-fiber kinetic friction coefficient of 0.20 or less and a fiber-metal kinetic friction coefficient of 0.18 or less.

[0051] The amount of sizing agent attached to the carbon fiber bundle can be adjusted by adjusting the concentration of the sizing agent in the solution or emulsion, or by adjusting the amount of squeezing after applying the solution or emulsion. The amount of sizing agent attached to the carbon fiber bundle is preferably 0.4 to 2.0% of the total mass of the carbon fiber bundle to which the sizing agent is attached. The drying method after applying the solution or emulsion is not particularly limited, and can be performed using, for example, hot air, a hot plate, a heated roller, an infrared heater, or the like.

[0052] In step (h), before the carbonized fiber bundle obtained in step (g) is wound up, the width of the carbonized fiber bundle is expanded using an averaging member for the carbonized fiber bundle to make the thickness of the fiber bundle uniform. The averaging member preferably applies an external force to the fiber bundle to widen the fiber bundle and loosen the single fibers to make them easier to move. Means for applying an external force to the single fibers include friction between the fibers and a metal member, airflow, vibration, etc., but friction with a metal member is preferred because it can be achieved with a simple device. When producing a large number of carbon fiber bundles, it is preferable to spread them in a direction that avoids contact with adjacent fiber bundles. The averaging member constantly applies a physical external force to the single fibers that make up the running fiber bundle, causing the single fibers to change position within the fiber bundle, resulting in a carbon fiber bundle with good cantilever value and adhesion.

[0053] The averaging member used to produce the carbon fiber bundle of the present invention may be any means that constantly applies a physical external force to the single fibers, and it is sufficient if the averaging member can avoid contact between adjacently running carbonized fiber bundles, while shifting the positions of the single fibers constituting the carbonized fiber bundle with respect to each other by the physical external force, thereby making the distribution uniform.

[0054] The shape of the equalizing member that applies an external force to the single fibers by friction between the fibers and the metal member is not particularly limited. Parallel bar guides, comb guides, etc. can be used as equalizing members, but it is preferable to use parallel bar guides that can efficiently apply an external force to the single fibers and that allow the applied external force to be adjusted. Figure 3 shows an example of a parallel bar guide. The parallel bar guide preferably has a smooth surface and is made up of two straight bars that are held in parallel.

[0055] In the method for producing a carbon fiber bundle of the present invention, an averaging member having two or more parallel rods is arranged between a sizing agent dryer and a traverse guide device or a feeding device, and surface A of the carbonized fiber bundle and surface B opposite surface A are each brought into contact with the rods at least once. This spreads the fiber bundles in the width direction, making it easier to loosen the individual fibers that are stuck together. The rods may have parallel surfaces that come into contact with the carbonized fiber bundles. The shape of the rods is not particularly limited, and may be round, square, or the like, but if the surface that comes into contact with the carbonized fiber bundles has corners, fluffing is likely to occur, so it is preferable that the rods have curved surfaces so that the contact occurs on the surfaces. Since the fiber bundle is loosened by each of surface A and surface B coming into contact with the rod once, it is easy to reduce the rate of variation in thickness. From the viewpoint of loosening the fiber bundles, it is preferable that the first rod contacts with surface A and the second rod contacts with surface B, in the order of surface A, surface B, surface A, surface B alternately.

[0056] In the method for producing a carbon fiber bundle of the present invention, the distance between adjacent parallel rods is preferably 15 to 50 mm. If the distance between adjacent parallel rods is 15 mm or more, the carbonized fiber bundle can be easily passed through, and if it is 50 mm or less, the effect of widening the width is easily achieved. From these viewpoints, the distance between adjacent parallel bars is more preferably 17 to 45 mm, and even more preferably 19 to 40 mm.

[0057] In the method for producing a carbon fiber bundle of the present invention, it is preferable that the carbonized fiber bundle is passed in contact with the parallel rods in a state in which the surface direction of the carbon fiber bundle in contact with the roller immediately preceding the parallel rods is twisted by 90°. By twisting the carbonized fiber bundle by 90°, an external force is applied to the carbonized fiber bundle, which makes it easier to widen the width of the carbonized fiber bundle. In addition, when multiple carbonized fiber bundles run side by side, they do not come into contact with adjacent carbonized fiber bundles, which is preferable because it does not take up space.

[0058] In the method for producing a carbon fiber bundle of the present invention, the maximum width of the carbonized fiber bundle in contact with the parallel rod is preferably 5 to 20% wider than the width of the carbonized fiber bundle in contact with the roller immediately before the parallel rod. Furthermore, although it is preferable that the rod is fixed, the rod may be rotated if there is resistance in the rod that makes the surface speed of the rod slower than the speed of the fiber bundle so that frictional force is generated between the carbon fiber bundles and an external force is applied.

[0059] In the winding process of step (i), the carbon fiber bundle is wound around a winding core while being traversed to obtain a spool of the carbon fiber bundle. The method for winding the carbon fiber bundle may be any method that can wind the carbon fiber bundle around the spool without twisting, etc. There is a recessed free roll guide 11 just before the traverse, which narrows the fiber bundle, but the presence of the averaging member of the present invention prevents thickness unevenness from occurring. In addition to being wound onto a spool, the cable may also be placed in a packaging box or the like. [Example]

[0060] The present invention will be specifically described below with reference to examples, but the following examples are not intended to limit the scope of the present invention.

[0061] (Method for measuring the amount of abrasion fluff) The carbon fiber bundle was unwound from the bobbin at an unwinding tension of 0.40 cN / tex and a running speed of the carbon fiber bundle of 20 m / min, and was brought into contact with a fixed metal rod (material: SUS304, chrome-plated and mirror-finished) with a diameter of 8 mm at a wrap angle of 15° via a roller, and rubbed. After the carbon fiber bundle had traveled 500 m, the running was stopped, and the fluff deposited on the stainless steel rod was collected and its mass was measured. The measurement was performed three times, and the simple average of the obtained values ​​was taken as the amount of rubbed fluff.

[0062] [Examples 1 to 10] (Manufacturing of carbon fiber bundles) A precursor fiber bundle having a single fiber fineness of 1.33 dtex and 50,000 single fibers was flame-resistant for 66 minutes in heated air at 240°C to 260°C in a hot air circulation flame-resistant furnace at an elongation rate of -3.9%, to obtain a flame-resistant fiber bundle. The bundle was then subjected to a pre-carbonization treatment for approximately 1.5 minutes in a heat treatment furnace at a maximum temperature of 700°C in a nitrogen atmosphere at an elongation rate of 1.5%, and then to a carbonization treatment for approximately 1.5 minutes in a heat treatment furnace at a maximum temperature of 1350°C in a nitrogen atmosphere at an elongation rate of -4.5%, to obtain a carbonized fiber bundle.

[0063] The carbonized fiber bundle was then run through a 5% by mass aqueous solution of ammonium bicarbonate, and an electric current was applied between the carbonized fiber bundle as the anode and the counter electrode so that the amount of electricity was 30 coulombs per 1 g of the carbonized fiber bundle. The bundle was then washed with warm water at 90°C and dried. The bundle was then immersed in an aqueous dispersion containing 6.0% of a sizing agent whose main component was bisphenol A epoxy resin. The bundle was then passed through nip rollers and then brought into contact with a roller heated to 150°C for 30 seconds to dry the bundle and obtain a carbonized fiber bundle with 1.6 wt% of the sizing agent attached to the carbon fiber bundle.

[0064] The carbonized fiber bundle coated with the sizing agent was subjected to an averaging process. The averaging member consisted of two parallel rods, each 5 mm in diameter and 30 mm center-to-center, arranged parallel to each other. The parallel rods were positioned perpendicular to the plane of the fiber bundle's width. The angle of the parallel rods was adjusted so that the gap between the rods was 0 mm when viewed from the direction of travel of the carbonized fiber bundle. The carbonized fiber bundle was twisted 90° in the axial direction by the parallel rods, and the width direction of the fiber bundle was made vertical. The carbonized fiber bundle was then passed through the parallel rods in contact with them. After that, the bundle was twisted back 90° using a horizontal roller, and the carbon fiber bundle was wound onto 10 spools.

[0065] The carbon fiber bundle obtained in this manner was subjected to various evaluations. To measure the thickness of the carbon fiber bundle, a two-dimensional laser displacement meter (Keyence Corporation, sensor head LJ-V7080, controller LJ-V7000) was used to simultaneously obtain thickness data in a line in the width direction of the carbon fiber bundle. The results are shown in Table 1. In the example, the variation rate of the thickness of the carbon fiber bundle was less than half of that in the comparative example, which was a conventional process without the parallel rods serving as averaging members, and the result was good. Furthermore, the cantilever value and adhesion were lower than those of the comparative example, indicating that the fiber bundles were loosened. The carbon fiber bundles obtained in these examples have a small variation rate in the thickness of the fiber bundle in the width direction of the fiber bundle, so that a constant amount of resin can be applied to a unit amount of carbon fiber by the touch roll method, resulting in a uniform fiber content in the molded product.

[0066] [Comparative Examples 1 to 4] A carbon fiber bundle was obtained in the same manner as in Example 1, except that the carbon fiber bundle was wound around four spools in the winding section without being subjected to a process for homogenizing the carbon fiber bundle after the sizing process. The results of various evaluations are shown in Table 1. The obtained carbon fiber bundle had a rate of variation in thickness of the carbon fiber bundle of more than 35%, which was poor.

[0067] [Table 1] [Industrial Applicability]

[0068] The carbon fiber bundle of the present invention, even if it has a large total fineness, is easy to handle during advanced processing, and a molded product in which the carbon fibers are uniformly distributed can be obtained. [Explanation of symbols]

[0069] 1: Drive roller 2: Carbon fiber bundle 3:Free roller 4: Weight 5: Spring balance 6: Parallel bars (averaging members) 7: Carbonized fiber bundle 8: Sizing bath 9: Dryer 10: Winder 11: Freeroll A: Location of averaging members

Claims

1. A carbon fiber bundle having a total fineness of 2 g / m or more, a variation rate of the thickness of the fiber bundle in the width direction of the fiber bundle of 30% or less, and a width of the fiber bundle of 13 to 18 mm.

2. A carbon fiber bundle having a total fineness of 2 g / m or more, wherein the variation rate of the thickness of the fiber bundle in the width direction of the fiber bundle is 30% or less, and the flatness of the fiber bundle (width / average thickness) is 60 to 70.

3. 3. The carbon fiber bundle according to claim 1, wherein the number of single fibers is 20,000 or more.

4. A carbon fiber bundle having 20,000 or more single fibers, a variation rate of the thickness of the fiber bundle in the width direction of the fiber bundle of 30% or less, and a width of the fiber bundle of 13 to 18 mm.

5. A carbon fiber bundle having 20,000 or more single fibers, a variation rate of the thickness of the fiber bundle in the width direction of the fiber bundle of 30% or less, and a flatness of the fiber bundle (width / average thickness) of 60 to 70.

6. The carbon fiber bundle according to any one of claims 1 to 5, wherein the average thickness of the fiber bundle is 0.18 to 0.28 mm.

7. The carbon fiber bundle according to any one of claims 1 to 6, wherein the variation rate of the width of the fiber bundle in the length direction of the fiber bundle is 13% or less.

8. The carbon fiber bundle according to any one of claims 1 to 7, wherein the cantilever value is 210 to 250 mm and the adhesion is 0.18 m or less.

9. The carbon fiber bundle according to any one of claims 1 to 8, wherein the amount of sizing agent attached is 0 to 20 mass%.

10. The carbon fiber bundle according to any one of claims 1 to 9, wherein the inter-fiber dynamic friction coefficient is 0.2 or less.

11. The carbon fiber bundle according to any one of claims 1 to 10, wherein the fiber-metal dynamic friction coefficient is 0.18 or less.

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