JP2023133739A - carbon fiber bundle - Google Patents

Abstract

To provide a carbon fiber bundle with a small tow width variation even in the carbon fiber bundle having a large filament diameter, and with a good handling property during high-order processing.SOLUTION: The carbon fiber bundle has a single fiber diameter of 8 μm or more and an average tearable distance of 550 to 800 mm. Preferably, a degree of interlace per 1 mm thickness of the carbon fiber bundle is 150/m or more, the number of single fibers is 12,000 or more, an average tow width of the carbon fiber bundle is 4 to 20 mm, and a tow width variation rate is 20% or less.SELECTED DRAWING: Figure 4

Description

The present invention relates to a carbon fiber bundle that has excellent bundling and opening properties even if the diameter of the single fibers is large.

Carbon fiber has excellent specific strength and specific modulus, so it is widely used in everything from sports and leisure goods to aerospace applications. In addition to sports applications such as golf club shafts and fishing rods, and aircraft applications, the development of so-called general industrial applications such as power generation wind turbine components, automobile components, CNG tanks, seismic reinforcement of buildings, and ship components is progressing, and the overall fineness is increasing. Large carbon fiber bundles are required.

A carbon fiber bundle is an assembly of several thousand to tens of thousands of carbon fiber single fibers each having a diameter of several microns. Carbon fiber bundles are generally used by being unwound from a package (spool) that is wound into a cylindrical shape on a winding core while being traversed. When winding up, convergence is required, and when forming a molded product of a carbon fiber bundle and resin, spreadability is required to ensure uniform resin impregnation. Among carbon fiber bundles with a large total fineness, carbon fiber bundles with a filament diameter exceeding 8 μm have excellent resin impregnation properties and the compressive strength of the resulting molded product. Fiber bundles are required. On the other hand, when carbon fibers with a large filament diameter are unwound from the spool, if the cohesiveness is poor, some carbon fibers will come loose from the carbon fiber bundle and stick to the spool side, causing fuzz. In some cases, the width of the carbon fiber bundle was unstable.

In order to improve the handling properties of carbon fiber bundles during high-level processing, it is common to add a sizing agent to the carbon fiber bundles. The sizing agent brings the filaments into close contact with each other, allowing the carbon fiber bundle to have convergence. Increasing the amount of sizing agent will improve the convergence of the carbon fiber bundle, but if there is too much sizing agent, the spreadability of the carbon fiber bundle will generally decrease, so it is difficult to achieve both convergence and spreadability. It was difficult. In particular, in the case of carbon fiber bundles with large filament diameters, it is more difficult to achieve both convergence and spreadability than with carbon fiber bundles with small filament diameters.

Patent Document 1 describes that due to the semi-permanent twist of the carbon fiber bundle, the fiber bundle converges on its own without unraveling, improving the handling properties of the fiber bundle. In addition, even if fuzz is generated due to breakage at the filament level when carbon fiber bundles are subjected to high-order processing, the carbon fiber bundles have semi-permanent twists, so they are difficult to grow into long fuzz, and are handled during high-order processing. It is said to increase sex.

Japanese Patent Application Publication No. 2019-151956

However, the spreadability of twisted carbon fiber bundles is suppressed, and if a method is used to untwist the fibers prior to opening, untwisting not only generates fuzz but also causes the fibers to be encapsulated by the twisting. There is a problem in that the fuzz that has been kept is released and becomes visible on the surface of the carbon fiber bundle.

SUMMARY OF THE INVENTION An object of the present invention is to solve the conventional problems and provide a carbon fiber bundle that exhibits less variation in width and excellent spreadability even when the diameter of single fibers is large.

The carbon fiber bundle of the present invention has the following characteristics.
[1] A carbon fiber bundle whose single fibers have a diameter of 8 μm or more and an average tearable distance of 550 to 800 mm.
[2] The carbon fiber bundle according to [1], wherein the degree of entanglement per mm of thickness of the fiber bundle is 150 times/m or more; [3] The carbon fiber bundle according to [1] or [2], wherein the number of single fibers is 12,000 or more. carbon fiber bundle.
[4] The carbon fiber bundle according to [1] to [3], wherein the average tow width of the carbon fiber bundle of 2000 m is 4 to 20 mm, and the tow width variation rate is 20% or less.
[5] The carbon fiber bundle according to [1] to [4], which has a strand strength of 3.0 to 5.0 GPa and a strand elastic modulus of 230 to 280 GPa.
[6] The carbon fiber bundle according to [1] to [5], wherein the resin backflow magnification during drawing is 1.0 to 4.5 times.
[7] The carbon fiber bundle according to [1] to [6], wherein the amount of fluff generated when the carbon fiber bundle is unwound is 0.1 g/m or less.

The carbon fiber bundle of the present invention exhibits little variation in width even if the diameter of the single fibers is large, and has excellent spreadability.

FIG. 2 is an overall view of the interlacing device. FIG. 3 is a cross-sectional view of the sealing chamber of the entangling device. FIG. 3 is a cross-sectional view of the compressed air outlet of the entangling device. It is a figure which shows the measuring method of the average tearable distance. FIG. 3 is a diagram showing an example of a device used to measure the tow width variation rate of a carbon fiber bundle. It is a figure showing an outline of a process of winding up a carbon fiber bundle around a winding core.

The carbon fiber bundle of the present invention has a single fiber diameter of 8 μm or more and an average tearable distance of 400 to 800 mm.
The diameter of the single fiber is more preferably 8.5 μm or more, and even more preferably 9 μm or more.
In the present invention, the diameter of a carbon fiber single fiber is the diameter of a perfect circle having the same area as the area of the cross section perpendicular to the fiber axis of the single fiber.
If the diameter of the single fiber is 8 μm or more, excellent resin impregnation properties can be obtained, and the larger the diameter of the single fiber, the stronger the resistance to bending of the single fiber itself and the ability to maintain a straight state, which increases the compressive strength of the composite. You can expect improved effects. There is no particular upper limit for the diameter of a single fiber, but the larger the diameter of a single fiber, the more difficult it becomes to pass through rolls with a small radius during high-order processing without causing breakage of the single fiber, so realistically it is 15 μm. That's about it.

The average tearable distance can be measured by the method described below. The average tearable distance of the carbon fiber bundle of the present invention is preferably 550 mm or more, more preferably 600 mm or more, and even more preferably 700 mm or more.
If the average tearable distance is 400 mm or more, sufficient spreadability can be ensured when performing high-order processing on the carbon fiber bundle unwound from the spool, and if it is 800 mm or less, the carbon fiber bundle can be unwound from the spool. Since the necessary convergence can be ensured, the generation of fuzz during high-order processing is suppressed.

The carbon fiber bundle of the present invention preferably has a degree of entanglement of 150 times/m or more per 1 mm of thickness of the fiber bundle. If the degree of entanglement per 1 mm of the thickness of the fiber bundle is 150 times/m or more, the tow width fluctuation rate will be low and the fibers can be opened stably during high-order processing. The degree of entanglement per 1 mm thickness of the fiber bundle is more preferably 200 times/m or more.
The degree of entanglement per 1 mm thickness of the fiber bundle can be measured by the method described below.

In the carbon fiber bundle of the present invention, the number of single fibers is preferably 12,000 or more, more preferably 24,000 or more.
If the number of single fibers is 12,000 or more, production efficiency is good and it is easy to keep the price down.
The upper limit of the number of single fibers is preferably 100,000 or less, more preferably 80,000 or less, and even more preferably 60,000 or less. When the number is 100,000 or less, the handleability and resin impregnation properties when forming a resin-impregnated molded article will be good. To make a fiber bundle of 12,000 or more fibers, it may be spun from one spinning nozzle, or it may be spun from a plurality of spinning nozzles and combined.
There is no particular restriction on the location where the yarns are interlaced as long as they are not intertwined, but in order to improve the cohesiveness of the fiber bundles, it may be in the spinning bath or on the first or second roll after coming out of the spinning bath. It is preferable to double the threads.

In the carbon fiber bundle of the present invention, the average tow width of 2000 m of carbon fiber bundles is preferably 4 to 20 mm, and the tow width fluctuation rate is preferably 20% or less.
More preferably, the average tow width is 5 to 18 mm. If the average tow width of 2000 m of carbon fiber bundles is 4 mm or more, the fibers can be opened sufficiently in the subsequent process to obtain a prepreg with a thin basis weight, and if it is 20 mm or less, the tow form will change significantly. Since the thread can be wound onto the spool without any trouble, it is possible to suppress the occurrence of thread breakage when the thread is released.
The toe width variation rate is more preferably 18% or less. If the tow width variation rate is 20% or less, the resin content ratio can be adjusted with high precision during resin impregnation processing such as filament winding.
The tow width variation rate of the carbon fiber bundle can be measured by the method described below. Here, the tow width refers to the width of the carbon fiber bundle.

<Cross-sectional shape of single fiber of carbon fiber bundle>
Although the cross-sectional shape of the single fibers of the carbon fiber bundle of the present invention is not particularly limited, it is preferable that the circularity is 0.9 or less. In the present invention, roundness is a value determined by the following formula (1), and S and L are obtained by observing a cross section perpendicular to the fiber axis of a single fiber using an SEM with a resolution of 5 to 10 nm. These are the cross-sectional area and circumference of a single fiber obtained by image analysis of the obtained image.
Roundness = 4πS/L ² ...(1)

However, if the roundness is too small, the fiber content of the prepreg produced from the carbon fiber bundle cannot be increased, and the elastic modulus of the composite material is limited to a low value. Therefore, the circularity of the single fibers constituting the carbon fiber bundle is preferably 0.7 or more, more preferably 0.75 or more, and even more preferably 0.8 or more.

The strand strength of the carbon fiber bundle is preferably 3.0 GPa or more, more preferably 3.3 GPa or more. If the strand strength is 3.0 GPa or more, sufficient elongation can be obtained when formed into a molded product.
Strand strength is measured in accordance with JIS R 7608:2007.

The strand elastic modulus of the carbon fiber bundle is preferably 230 GPa or more, more preferably 235 GPa or more. If the strand elastic modulus is 230 GPa or more, sufficient rigidity can be obtained when the strand is made into a composite.
The strand elastic modulus can be controlled by adjusting the heating temperature and the like when carbonizing the flame-resistant fiber bundle by heating it.
Strand elastic modulus is measured in accordance with JIS R 7608:2007A method.

The carbon fiber bundle of the present invention preferably has a resin backflow ratio of 1.0 to 4.5 times during drawing.
If the resin backflow magnification during pultrusion is 1.0 times or more, voids contained in the pultruded product can be suppressed, and if the resin backflow magnification is 4.5 times or less, the drawing resistance can be suppressed. A pultruded product can be obtained with high productivity.
From these viewpoints, the resin backflow magnification is more preferably 1.1 to 4.0 times, and even more preferably 1.2 to 3.5 times.

In the carbon fiber bundle of the present invention, it is preferable that the amount of fuzz generated when the carbon fiber bundle is unwound is 0.1 g/m or less.
If the amount of fluff generated during unwinding of the carbon fiber bundle is 0.1 g/m or less, it is possible to prevent fluff from being mixed into the prepreg, thereby making it possible to obtain a high-quality prepreg.

(Method for manufacturing carbon fiber bundle)
The method for manufacturing the carbon fiber bundle of the present invention is not particularly limited, and, for example, the carbon fiber bundle can be manufactured by a method including the following steps (a) to (h) in order.
(a) Step of spinning and coagulating the spinning dope to obtain a coagulated thread.
(b) A step of washing and stretching the coagulated thread to obtain a processed thread.
(c) Step of attaching an oil to the process yarn, drying and densifying it, and imparting entanglement to obtain a precursor fiber bundle.
(d) A step of flame-proofing the precursor fiber bundle to obtain a flame-resistant fiber bundle.
(e) Carbonizing the flame-resistant fiber bundle to obtain a carbon fiber bundle.
(f) Process of subjecting the carbon fiber bundle to surface oxidation treatment (g) Process of applying a sizing agent to the carbon fiber bundle after surface oxidation treatment (h) Winding process

In step (a), the spinning stock solution is spun and coagulated to obtain a coagulated thread.
The spinning stock solution used in step (a) is not particularly limited, but is preferably an organic solvent solution of an acrylonitrile copolymer from the viewpoint of developing mechanical properties such as strength of carbon fibers. The acrylonitrile copolymer is a copolymer having 96% by mass or more of repeating units derived from acrylonitrile, and preferably a copolymer having 97% by mass or more of repeating units derived from acrylonitrile.

In the case of an acrylonitrile copolymer, repeating units derived from sources other than acrylonitrile (hereinafter referred to as "copolymerization components") include, for example, acrylic acid; methacrylic acid; itaconic acid; acrylic acid derivatives such as methyl acrylate; Examples include methacrylic acid derivatives such as methyl acid; acrylamide derivatives such as acrylamide, methacrylamide, N-methylol-acrylamide, and N,N-dimethylacrylamide; and vinyl polymerizable monomers such as vinyl acetate. The number of copolymerization components may be one, or two or more. As the copolymerization component, a vinyl polymerizable monomer having one or more carboxy groups is preferred.

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, aqueous precipitation polymerization in an aqueous solution of acrylonitrile (and copolymerization component), etc. .
Examples of the organic solvent used in the spinning dope include polar organic solvents such as dimethylacetamide, dimethylsulfoxide, and dimethylformamide. Since the spinning dope obtained using these polar organic solvents does not contain metal elements, the content of metal elements in the resulting carbon fiber bundle can be reduced.
The solid content concentration of the spinning dope is preferably 20% by mass or more.

The spinning method may be either wet spinning or wet/dry spinning.
For example, in wet-dry spinning, a spinning stock solution is spun into the air from a spinneret with many discharge holes, and then introduced into a temperature-controlled coagulation solution and coagulated, and a large number of filaments formed are collected. Take it off as a coagulated thread.
As the coagulating solution, a known solution such as a mixed solution of a polar organic solvent and water used in the spinning dope can be used.

In step (b), the coagulated thread obtained in step (a) is washed and stretched to obtain a process thread.
The washing method may be any method as long as it can remove the solvent from the coagulated thread, and any known method can be used.
Before washing the coagulated threads, a more dense fibril structure can be formed by stretching the fibers in air or in an aqueous solution with a lower solvent concentration and higher temperature than the coagulating solution. can.
In addition, after washing the coagulated threads, the orientation of the acrylonitrile copolymer in the fibers can be further enhanced by stretching the fibers in hot water, and by slightly relaxing the fibers, it is also possible to remove the distortion caused by the stretching. .

In step (c), an oil agent is applied to the process yarn obtained in step (b), the yarn is dried and densified, and entangled to obtain a precursor fiber bundle.
Known oils can be used, and examples include oils made of silicone compounds such as silicone oil.
The method of drying and densification is not particularly limited, as long as the process yarn to which the oil agent has been adhered is dried by a known drying method.
The fibers after drying and densification are stretched 1.8 to 6 times in pressurized steam at 130 to 200°C, or between heating rolls or on a heating plate, as necessary, to change the orientation of the acrylonitrile copolymer. Further improvements and refinements may be made.
Furthermore, an interlacing device blows air onto the process yarn to impart entanglement. Although there are no particular restrictions on the entangling device, it is preferable to use one that blows air onto the process yarn from above and below, since this tends to result in uniform entangling.

In step (d), the precursor fiber bundle obtained in step (c) is flame-resistant treated to obtain a flame-resistant fiber bundle.
As the flameproofing treatment, for example, there is a method in which the material is passed through a hot air oven set to gradually increase the temperature in an air atmosphere of 220 to 260° C. for 30 to 100 minutes.
The fibers may be elongated during the flameproofing treatment. By performing appropriate elongation during the flameproofing treatment, the orientation of the fibril structure forming the fibers can be maintained or improved, making it easier to obtain carbon fiber bundles with excellent mechanical properties.
The density of the single fibers constituting the flame-resistant fiber bundle is preferably 1.33 to 1.37 g/cm ³ .

In step (e), the flame-resistant fiber bundle obtained in step (d) is carbonized to obtain a carbon fiber bundle.
Examples of the carbonization treatment include a first carbonization treatment in which the maximum temperature is 600°C to 800°C in an inert atmosphere such as nitrogen, and a first carbonization treatment in which the maximum temperature is 1200°C to 2000°C in an inert atmosphere such as nitrogen. A treatment including a second carbonization treatment in which heat treatment is performed at a temperature of 0.degree.
The treatment time of the first carbonization treatment is preferably 1 to 3 minutes. In the first carbonization treatment, it is preferable to perform an elongation operation because it is easy to maintain the orientation of the fibril structure.
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.
In the second carbonization treatment, large shrinkage occurs in the fiber bundle, so it is preferable to set the elongation rate to -5% to -2%.
After the second carbonization treatment, a third carbonization treatment may be additionally performed as necessary.

In step (f), the carbon fiber bundle obtained in step (e) is subjected to surface oxidation treatment. Known methods can be used for surface oxidation treatment, such as electrolytic oxidation, chemical oxidation, air oxidation, and the like. Among these, electrolytic oxidation is preferred.

In step (g), a sizing agent is applied to the carbon fiber bundle obtained in step (f). The sizing agent can be applied to the carbon fiber bundle by applying a solution in which the sizing agent is dissolved in an organic solvent or an emulsion in which the sizing agent is dispersed in water using an emulsifier or the like to the carbon fiber bundle and then drying the carbon fiber bundle.
As the sizing agent, a known sizing agent can be used. It is preferable to use the epoxy resin in the form of an emulsion.
The amount of the 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 the sizing agent attached to the carbon fiber bundle is preferably 0.4 to 2.0% by mass. 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.

In the winding process of step (h), the carbon fiber bundle is traversed and wound onto a winding core to obtain a spool of the carbon fiber bundle. FIG. 6 schematically shows an example of the process of winding the carbon fiber bundle onto the winding core 31a while performing traverse. The distance between the first upper fixed guide roll 32 and the second upper fixed guide roll 33 is preferably 200 mm or less so that the carbon fiber bundle is not twisted. The carbon fiber bundle 35 is twisted by 90 degrees between the upper second guide roll 33 and the traverse guide group 34, so that the wide surface of the carbon fiber bundle is parallel to the paper plane of FIG. In this case, it is preferable to arrange the carbon fiber bundles at a distance of 1000 mm or more to prevent bending or the like. By reciprocating the traverse guide group 34 in the thickness direction of the paper in FIG. 6, the position at which the carbon fiber bundle is wound onto the spool 31 is controlled. The method for winding up the carbon fiber bundle may be any method as long as it can wind up the carbon fiber bundle onto the spool without twisting or the like.

In any of the above steps (a) to (h), operations can be performed to control the average tearable distance of the carbon fiber bundle, the degree of entanglement per 1 mm thickness of the carbon fiber bundle, and the rate of variation in the tow width of the carbon fiber bundle.
For example, at the end of step (c) or before introducing the precursor fiber bundle into the flameproofing furnace in step (d), a fluid such as air may be sprayed onto the precursor fiber bundle and the flow rate of the fluid may be adjusted. The degree of entanglement per 1 mm thickness of the carbon fiber bundle can be controlled.
Moreover, the degree of entanglement per 1 mm thickness of the carbon fiber bundle can also be controlled by adjusting the amount of the sizing agent applied in step (g).

EXAMPLES Hereinafter, the present invention will be specifically described with reference to Examples, but the following Examples do not limit the scope of the present invention. Various calculations and measurement methods in Examples were as follows.

(Method for calculating the diameter of a carbon fiber single fiber)
The cross-sectional area of one carbon fiber filament was calculated from the density of the carbon fibers constituting the carbon fiber bundle (g/cm ³ ), the mass per meter of carbon fiber bundle (g/m), and the number of filaments in the carbon fiber bundle. . The diameter of a perfect circle having an area equal to the cross-sectional area was calculated and used as the diameter of a single carbon fiber.

(Measurement method of average tearable distance)
The carbon fiber bundle was cut to a length of 1160 mm, and one end of the carbon fiber bundle was fixed with adhesive tape on a horizontal table so that it would not move (this point is referred to as fixing point A). One end of the unfixed fiber bundle is divided into two parts with a finger, and one part is fixed to the table with adhesive tape in a taut state so that it does not move (this point is referred to as fixing point B).
Move the other half of the two halves using fixed point A as a fulcrum and move them along the table so that there is no slack, stop them at a straight-line distance of 500 mm from fixed point B, and fix them on the table with adhesive tape so that they do not move. (This point is called fixed point C). Visually observe the area surrounded by fixed points A, B, and C, find the farthest intersecting point from fixed point A, and measure the distance projected on the straight line connected between fixed points A and B with a minimum scale of 1 mm. Read with a ruler to determine the distance that can be torn apart. The arithmetic mean value of the measurements obtained by repeating the above operation 30 times is defined as the average tearable distance.
In this measurement method, the intertwined point furthest from the fixed point A is the point where the straight line distance from the fixed point A is the furthest and three or more filaments without slack are intertwined.

(Method for measuring degree of entanglement per 1 mm thickness of fiber bundle)
a) A 1.4 m long carbon fiber bundle was unwound from the spool at the lowest possible tension without twisting and was used as a sample. One end of the sample is attached to the upper grip of the hanging device so as not to disturb the shape of the sample, and a weight is suspended 1 m below the upper grip to suspend the sample in the vertical direction. The load of the weight is the load (mN) obtained by multiplying the tex number of the sample by 17.64, and the upper limit is 980 mN.
b) Measure the thickness of the sample at a position 5 cm below the upper grip using a dial thickness gauge (manufactured by Mitutoyo Co., Ltd., code No. 7321).
c) Insert one end of a hook with a diameter of 0.5 mm and a smooth surface so as to divide the fiber bundle into two equal parts 10 cm below the upper gripping part of the sample, and then insert the other end of the hook. A load (mN) with a lower limit of 19.6 and an upper limit of 98, which is the value obtained by dividing the tex number of the sample by the number of filaments multiplied by 88.2, is attached to the sample, and the hook is lowered to allow it to fall naturally.
d) Measure the descending distance (m) of the hook from the starting point where one end of the hook is inserted to the point where the hook stops due to the entanglement of the thread, and place the hook insertion position approximately 10 mm apart from the hook stopping position. Re-insert the needle in the lower part of the tube and measure the descending distance in sequence.
e) When the hook reaches the hanging position of the weight 1m below, prepare the unmeasured sample in the same way as in a) above without measuring the descending distance, and remove the hook from b) by the same operation. The descending distance of the hook was measured 50 times in total, the average value was determined, and the number of descending times required for the hook to descend by 1 m was calculated as the reciprocal of the descending distance, which was defined as the degree of entanglement.
f) The degree of entanglement determined in e) above was divided by the thickness (mm) of the carbon fiber bundle calculated as the average thickness of the sample to calculate the degree of entanglement per 1 mm of the thickness of the fiber bundle.

(Method for measuring average tow width and tow width variation rate of carbon fiber bundle)
Using the apparatus shown in FIG. 5, the carbon fiber bundle is pulled out from the unwinding spool 13 at a speed of 50 m/min with the godet roll 18 while controlling the unwinding tension to 20 N with the unwinding dancer roll 17A. The film was wound onto the take-up spool 16 while controlling the winding tension to 20N using the winding spool 17B. During that time, the width of the carbon fiber bundle (tow width) was measured over a fiber bundle length of 1000 m using a tow width sensor 15 (CCD transmission type digital laser sensor, manufactured by Keyence Corporation, sensor head: IG-028). . The distance between the rolls before and after the location where the sensor is installed is set so that the carbon fiber bundle (tow) does not tilt or twist. The average toe width and the coefficient of variation of the tow width were determined from the 60,000 tow width data obtained with a data sampling interval of 20 ms. The coefficient of variation of the tow width was defined as the tow width variation rate.

(Evaluation method of resin backflow rate during pultrusion molding)
As an index for evaluating the handling of carbon fiber bundles during high-order processing, we evaluated the resin backflow rate during pultrusion molding. Ten carbon fiber bundles were used, and the epoxy resin composition contained 7 parts by mass of DY9577 (boron trichloride amine complex, manufactured by Huntsman Japan Co., Ltd.) and 100 parts by mass of CY184 (alicyclic epoxy resin, manufactured by Huntsman Japan Co., Ltd.). A mixture of parts by weight was used. The pultrusion molding conditions were such that the diameter of the pultrusion mold was 6 mm, the mold temperature was 190° C., the tow tension was 1500 cN, and the drawing speed was 0.25 m/min to obtain a pultrusion molded product. During pultrusion, when the carbon fiber bundle impregnated with the epoxy resin composition enters the mold, the mass of the epoxy resin composition overflowing from the entrance of the mold to obtain a pultrusion molded product with a length of 1 m. was defined as the resin backflow amount, and the backflow magnification was calculated by dividing the resin backflow amount by the mass of the resin in the pultrusion molded product having a length of 1 m.

(Method for evaluating the amount of fuzz generated during prepreg production)
As an index for evaluating the handleability of carbon fiber bundles during high-order processing, we evaluated the amount of fuzz that accumulated on the eyelet guide when producing prepregs in which carbon fibers were aligned in one direction. Pull out 55 carbon fiber bundles for 1000 m, measure the amount of fluff (g) accumulated on the eyelet guide, and divide by the length of the carbon fiber bundle (=1000) and the number of carbon fiber bundles (=55). The amount of fluff (g) generated per meter of the book was determined.

(Method for measuring strand physical properties)
The strand strength and strand elastic modulus of the carbon fiber bundle were measured in accordance with JIS R 7608:2007. Note that the strand elastic modulus was calculated using method A of the same method.

(Example 1)
A precursor fiber bundle with a single fiber fineness of 2.5 dtex, roundness of 0.86, 24,000 single fibers, and a total fineness of 60,000 dtex was passed through an interlacing device and air was blown to perform interlacing treatment between multiple single fibers. .
The interlacing device shown in FIGS. 1 to 3 was one in which the space through which the precursor fiber bundle passed had a round cross-section, and the portion that came into contact with the precursor fiber bundle was plated. The size of the round cross section of the entangling device was 16 mm in diameter, and the flow rate of compressed air blown onto the process yarn was 500 NL/min. Compressed air was blown out toward the process yarn from one outlet at the top and one at the bottom.
The width of the fiber bundle at the time of introduction into the entangling device was 18 mm, the moisture content was 3%, the processing speed was 90 m/min, and the outside temperature was 25°C.

The thus-entangled precursor fiber bundles are subjected to flame-retardant treatment in heated air at 240°C to 260°C for 70 minutes at an elongation rate of +2.0% in a hot air circulation flame-retardant furnace to create flame-retardant fibers. After obtaining the bundle, a pre-carbonization treatment was performed for 1.5 minutes at an elongation rate of 3.0% in a heat treatment furnace with a maximum temperature of 660°C under a nitrogen atmosphere, and then under a nitrogen atmosphere with a maximum temperature of 1350°C. Carbonization treatment was carried out for 1.5 minutes at an elongation rate of -4.5% in a heat treatment furnace at .degree. C. to obtain a carbonized fiber bundle.

Next, the carbonized fiber bundle was run in an aqueous solution of 5% by mass of ammonium bicarbonate, and the carbonized fiber bundle was used as an anode to conduct an electric current treatment between it and a counter electrode so that the amount of electricity was 30 coulombs per 1 g of the carbonized fiber bundle. After that, it was washed with 90°C warm water and dried. Next, it was immersed in an aqueous dispersion containing 6.0% by mass of a sizing agent containing bisphenol A type epoxy resin as a main component. Next, after passing through a nip roll, the moisture was dried by contacting with a roll heated to 150°C for 30 seconds, and the sizing agent-attached carbon fiber bundle, to which 1.2% by mass of sizing agent was attached to the carbon fibers, was obtained. Obtained.

The obtained carbon fiber bundle was wound around a paper core (paper tube) using a KTW-C type winder (trade name) manufactured by Kozu Seisakusho. A paper tube with a diameter of 82 mm and a length of 280 mm was used, and the traverse width was 254 mm. The carbon fiber bundle was fed to the winding section at a speed of 11 m/min, and the carbon fiber bundle was wound around the paper tube for 2000 m.

Various evaluations of the carbon fiber bundle thus obtained were performed. The tow width stability when the obtained carbon fiber bundle was unwound was high, and the handleability during high-order processing was also good. The results are shown in Table 1.

(Example 2)
A carbon fiber bundle was obtained in the same manner as in Example 1, except that the flow rate of compressed air supplied to the entangling device was 300 NL/min. The tow width stability when the obtained carbon fiber bundle was unwound was high, and the handleability during high-order processing was also good. The evaluation results are shown in Table 1.

(Example 3)
A carbon fiber bundle was obtained in the same manner as in Example 1, except that the flow rate of compressed air supplied to the entangling device was 200 NL/min. The tow width stability when the obtained carbon fiber bundle was unwound was high, and the handleability during high-order processing was also good. The evaluation results are shown in Table 1.

(Example 4)
A carbon fiber bundle was obtained in the same manner as in Example 1, except that the flow rate of compressed air supplied to the entangling device was 100 NL/min. The tow width stability when the obtained carbon fiber bundle was unwound was high, and the handleability during high-order processing was also good. The evaluation results are shown in Table 1.

(Comparative example 1)
A carbon fiber bundle was obtained in the same manner as in Example 1, except that the flow rate of compressed air supplied to the entangling device was 50 NL/min. The tow width stability when the obtained carbon fiber bundle was unwound was low, and the handleability during high-order processing was also poor. The evaluation results are shown in Table 1.

(Comparative example 2)
A carbon fiber bundle was obtained in the same manner as in Example 1, except that the flow rate of compressed air supplied to the entangling device was 550 NL/min. The tow width stability when the obtained carbon fiber bundle was unwound was low, and the handleability during high-order processing was also poor. The evaluation results are shown in Table 1.

(Comparative example 3)
The interlacing device used had a space through which the precursor fibers passed and had a flat rectangular cross-section, and the portions that came into contact with the precursor fiber bundles were plated. The hole diameter, pitch, height (length in the short side direction of the flat rectangular cross-sectional shape), and width (dimension in the long side direction of the flat rectangular cross-sectional shape) of the air blowing holes of the interlacing device are φ0.75, respectively. Carbon fiber bundles were obtained in the same manner as in Example 1, except that the lengths were 1.35 mm, 2.5 mm, and 20 mm, and the flow rate of compressed air supplied to the entangling device was 200 NL/min. The tow width stability when the obtained carbon fiber bundle was unwound was low, and the handleability during high-order processing was also poor. The evaluation results are shown in Table 1.

(Reference example 1)
Various evaluations were performed on carbon fiber bundle Pyrofil TRW40-50L (filament fineness 0.75 dtex, number of filaments 50,000, sizing agent: K, sizing agent adhesion amount: 1.4%) manufactured by Mitsubishi Chemical Corporation. The evaluation results are shown in Table 1.

1: Entanglement imparting device 2: Fiber bundle travel path 3: Fluid injection chamber 3a: Inner wall surface 3b: Fluid injection hole 4: Seal chamber 4a: Housing 4b: Labyrinth seal structure 5: Seal chamber 5a: Housing 5b: Labyrinth seal Structure 6: Ejector 6a: Fluid inlet F: Carbon fiber precursor fiber bundle 7: Carbon fiber bundle 8: Fixing point A
9: Fixed point B
10: Fixed point C
11: Intertwining point 12: Tearing distance 13: Unwinding spool 14: Carbon fiber bundle 15: Tow width sensor 16: Winding spool 17A: Unwinding dancer roll 17B: Winding dancer roll 18: Godet roll 19: Spool 19a: Winding Core 20: Upper first fixed guide roll 21: Upper second fixed guide roll
22: Traverse guide group 23: Carbon fiber bundle

Claims (7)

A carbon fiber bundle whose single fibers have a diameter of 8 μm or more and an average tearable distance of 550 to 800 mm. The carbon fiber bundle according to claim 1, wherein the degree of entanglement per 1 mm of thickness of the carbon fiber bundle is 150 times/m or more. The carbon fiber bundle according to claim 1 or 2, wherein the number of single fibers is 12,000 or more. The carbon fiber bundle according to any one of claims 1 to 3, wherein the carbon fiber bundle has an average tow width of 4 to 20 mm and a tow width fluctuation rate of 20% or less. The carbon fiber bundle according to any one of claims 1 to 4, having a strand strength of 3.0 to 5.0 GPa and a strand elastic modulus of 230 to 280 GPa. The carbon fiber bundle according to any one of claims 1 to 5, wherein the resin backflow magnification during drawing is 1.0 to 4.5 times. The carbon fiber bundle according to any one of claims 1 to 6, wherein the amount of fuzz generated when the carbon fiber bundle is unwound is 0.1 g/m or less.

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