Carbon fiber bundle, method for producing same, towpreg, laminate, carbon fiber-reinforced composite material, rotating electric machine protective ring, and rotating electric machine

Abstract

In order to provide: a carbon fiber bundle having a high bundle strength, which is required when stably and annularly laminating a carbon fiber bundle impregnated with a matrix resin while applying a high tension to the carbon fiber bundle, said carbon fiber bundle being of low thickness and having a low thickness variation coefficient; and a method for producing said carbon fiber bundle, the carbon fiber bundle according to the present invention has, in a carbon fiber bundle having a test length of 500 mm, a bundle strength of 1.8‒3.0 GPa, a bundle-strength Weibull shape coefficient of 14‒30, a thickness of 0.05‒0.11 mm, and a thickness variation coefficient of 7.0% or less, the carbon fiber bundle being substantially twist-free.

Description

Carbon fiber bundle, method for manufacturing the same, towpreg, laminate, carbon fiber reinforced composite material, rotating electric machine protective ring and rotating electric machine

[0001] This invention relates to carbon fiber bundles, methods for producing the same, towpregs, laminates, carbon fiber reinforced composite materials, rotating electric machine protective rings, and rotating electric machines.

[0002] Due to their extremely high specific strength and specific modulus, carbon fiber bundles have been widely used in various industrial fields as reinforcing fibers in composite materials in recent years. In particular, in fields where weight reduction is important, the replacement of conventional metal materials with carbon fiber reinforced composite materials is accelerating. Among these, in sports and general industrial applications, carbon fiber bundles are laminated in a ring shape with high tensile strength applied, from the perspective of suppressing deformation under load. In recent years, in order to improve the performance of rotating electric machines and enable high-speed rotation, they are also used as ring-shaped materials that cover the outer surface of permanent magnets placed on the outer circumference of rotating members, in order to suppress the detachment of permanent magnets placed on the outer circumference and damage to the rotor.

[0003] On the other hand, there are various methods for producing carbon fiber reinforced composite materials using carbon fiber bundles. When obtaining a cyclic laminate, for example, methods include laminating and molding a cyclic structure using a prepreg pre-impregnated with a solid matrix resin or a toupreg pre-impregnated with a liquid matrix resin, or filament winding, a method in which a cyclic structure is laminated and molded while impregnating with a liquid matrix resin. Hereafter, "lamination" mainly refers to lamination in a cyclic shape.

[0004] To produce carbon fiber reinforced composite materials for large components such as pressure vessel components, automobile components, or housings, techniques have been proposed to impart entanglement or twist to precursor fiber bundles, with the aim of obtaining carbon fiber bundles exhibiting high tensile modulus and uniform physical properties between individual fibers (Patent Documents 1-3). In addition, from the viewpoint of quality, techniques have been proposed to control the conditions for imparting entanglement to solidified fiber bundles (Patent Document 4). Furthermore, techniques have been proposed to increase the strand tensile strength of carbon fiber bundles by controlling the structure of flame-resistant fibers (flame-resistant structure) (Patent Documents 5 and 6).

[0005] Furthermore, regarding carbon fiber bundles for filament winding, a technique has been proposed to control the flattening ratio by controlling the temperature of the hot roller and the contact time with the carbon fiber bundle in the post-processing step (Patent Document 7).

[0006] Japanese Patent Publication No. 2014-141761, Japanese Patent Publication No. 2014-141762, Japanese Patent Publication No. 2014-159665, Japanese Patent Publication No. 2020-59937, International Publication No. 2016 / 068034, Japanese Patent Publication No. 2010-510406, Japanese Patent Publication No. 2011-252264

[0007] In methods of laminating materials such as carbon fiber prepregs and towpregs in a ring shape, there was a problem that the material would break when high tension was applied to form a specific shape. To address this problem, Patent Document 1 discloses that the bundle strength of a carbon fiber bundle with a test length of 10 m is 1.9 to 4.0 GPa. While it is expected that the high bundle strength will reduce material breakage when high tension is applied, on the other hand, a problem was considered in that the thickness of the carbon fiber bundle inevitably becomes large due to the strong entanglement or twisting applied in the specific examples. Patent Document 2 discloses carbon fiber bundles with a bundle strength of up to 1.8 GPa at a test length of 10 m, but it was considered that there was still a problem in stably exhibiting the bundle strength of the carbon fiber bundle. Patent Document 3 discloses that by controlling the entanglement state, the bundle strength at a test length of 10 m can be 1.9 to 4.0 GPa. However, the mechanism is not clear, leaving room for further improvement. Furthermore, there is no concept of controlling the thickness of the carbon fiber bundle, and it does not satisfy the requirements regarding the thickness of the carbon fiber bundle and its coefficient of variation. On the other hand, Patent Document 4 discloses a precursor fiber bundle that achieves both quality and convergence by applying entanglement while controlling the moisture content and tension of the carbon fiber precursor fiber bundle. However, the entanglement is weak, and there is no concept of increasing the bundle strength. In other words, Patent Documents 1 to 4 do not allow for both reducing the thickness of the carbon fiber bundle and increasing the bundle strength. In addition, while the technologies in Patent Documents 5 and 6 can increase the tensile strength of the carbon fiber bundle, they do not provide a way to control the thickness of the carbon fiber bundle or the coefficient of variation of the thickness of the carbon fiber bundle. According to the technology described in Patent Document 7, the flattening ratio of the carbon fiber bundle is controlled by controlling the contact time between the surface temperature of the hot roller and the carbon fiber bundle in the post-processing step, but the variation in flattening ratio was not at a satisfactory level.

[0008] To solve the aforementioned problems, the present invention aims to provide a carbon fiber bundle and a method for manufacturing the same that has the high bundle strength required when stably laminating a carbon fiber bundle impregnated with a matrix resin (referred to as a resin-impregnated carbon fiber bundle in this invention) in a ring shape while applying high tension, and that enables weight reduction of the laminate obtained by laminating the resin-impregnated carbon fiber bundles, and that allows for the production of a smooth laminate without thickness fluctuations.

[0009] The present invention, which solves the above problems, has the following configuration: 1. A substantially untwisted carbon fiber bundle having a bundle strength of 1.8 to 3.0 GPa, a Weibull shape factor of the bundle strength of 14 to 30, a thickness of 0.05 to 0.110 mm, and a coefficient of variation of thickness of 7.0% or less in a carbon fiber bundle with a test length of 500 mm. 2. The carbon fiber bundle according to 1 above, having a filament count of 6,000 to 24,000. 3. The carbon fiber bundle according to 1 or 2 above, having a bundle strength of 2.3 to 3.0 GPa in a carbon fiber bundle with a test length of 500 mm. 4. The carbon fiber bundle according to any one of 1 to 3 above, having a single fiber diameter of 5.0 to 6.0 μm. 5. The carbon fiber bundle according to any one of 1 to 4 above, having a strand tensile strength of 6.7 to 9.0 GPa. 6. The carbon fiber bundle according to any one of 1 to 5 above, having a strand tensile modulus of elasticity of 280 to 380 GPa. 7. Density is 1.84 g / cm³ ３ The carbon fiber bundle described in any of 1 to 6 above, which is as follows: 8. The carbon fiber bundle described in any of 1 to 7 above, wherein the number of unraveled fibers is 20 or less per 100m. 9. The carbon fiber bundle described in any of 1 to 8 above, wherein the carbon fiber bundle is for use as a rotating electric machine protection ring. 10. A fluid entanglement treatment step performed after the solidification step of the polyacrylonitrile carbon fiber precursor fiber bundle and before the water bath stretching step, wherein the applied tension is 2.0 to 5.0 mN / dtex and the fluid discharge pressure is 0.2 to 0.4 MPa, and the polyacrylonitrile carbon fiber precursor fiber bundle is measured at 1,370 cm⁻¹ in the infrared spectrum. －１ 1,453 cm⁻¹ relative to the peak intensity －１A first flame-retardant treatment step involves flame-retardant treatment for 8 to 25 minutes until the ratio of peak intensities is in the range of 0.98 to 1.10, and the fiber bundle obtained in the first flame-retardant treatment step is subjected to infrared spectroscopy at 1,370 cm⁻¹. －１ 1,453 cm⁻¹ relative to the peak intensity －１ The ratio of peak intensities is in the range of 0.70 to 0.75, and the infrared spectrum is 1,370 cm⁻¹. －１ 1,254 cm⁻¹ relative to the peak intensity －１ A method for producing a substantially twistless carbon fiber bundle, comprising: a second flame-retardant step of flame-retardantizing for 5 to 14 minutes until the ratio of peak intensities is in the range of 0.50 to 0.65; a pre-carbonization step of pre-carbonizing the fiber bundle obtained in the second flame-retardant step in an inert atmosphere with a maximum temperature of 600 to 800°C and a draw ratio of 1.00 to 1.25; a carbonization step of carbonizing the fiber bundle obtained in the pre-carbonization step in an inert atmosphere with a maximum temperature of 1,350 to 2,000°C; a step of electrolytically surface-treating the fiber bundle obtained in the carbonization step to obtain a carbon fiber bundle; and a step of impregnating the carbon fiber bundle with a sizing agent, and then contacting the carbon fiber bundle impregnated with the sizing agent with a contact drying means at a surface temperature of 100 to 180°C for 30 to 50 seconds. 11. A tow preg using the carbon fiber bundle described in any of 1 to 9 above. 12. A laminate using the tow preg described in 11 above. 13. A carbon fiber reinforced composite material obtained by molding the laminate described in 12 above. 14. A rotating electric machine protective ring obtained by laminating and molding the toupreg described in 11 above in an annular shape. 15. A rotating electric machine using the rotating electric machine protective ring described in 14 above.

[0010] According to the present invention, when resin-impregnated carbon fiber bundles are laminated in a ring shape, high tension can be stably applied, and a smooth laminate with no thickness variation can be obtained.

[0011] This is a schematic diagram of the manufacturing process for an annular laminate obtained by applying high tension, according to an embodiment of the present invention.

[0012] The carbon fiber bundle of the present invention has a bundle strength of 1.8 to 3.0 GPa at a test length of 500 mm, preferably 2.3 to 3.0 GPa, more preferably 2.5 to 3.0 GPa, and even more preferably 2.6 to 3.0 GPa. The bundle strength of the carbon fiber bundle refers to the tensile strength when the carbon fiber bundle is subjected to a bundle tensile test without impregnation with matrix resin. A high bundle strength of the carbon fiber bundle makes it less likely to break even when high tension is applied to the carbon fiber bundle when laminating resin-impregnated carbon fiber bundles, thereby improving processability. It should be noted that this bundle strength is not a parameter directly related to the strand tensile strength described later, and the key point is to evaluate the long region of 500 mm in test length, assuming a lamination process of resin-impregnated carbon fiber bundles. It is known that the bundle strength of a carbon fiber bundle decreases as the test length increases, because defects that govern the bundle strength tend to be statistically included within the range of the test length. It is known that the influence of large defects appearing in this long test length on the strand tensile strength is infrequent and not fundamental. A bundle strength of 1.8 GPa or higher at a test length of 500 mm allows for high tension to be imparted when laminating resin-impregnated carbon fiber bundles, while a bundle strength of 3.0 GPa is sufficient. The bundle strength of the carbon fiber bundle is a value evaluated by bundle testing using a Tensilon universal material tester, as described in the Examples section under "Bundle Strength of Carbon Fiber Bundles and its Weibull Shape Factor." If equivalent results can be obtained, equipment and conditions other than those described in that section may be used. To increase the bundle strength at a test length of 500 mm, it is advisable to use the carbon fiber bundle manufacturing method of the present invention, which will be described later.

[0013] The carbon fiber bundle of the present invention has a Weibull shape factor of 14 to 30 for bundle strength at a test length of 500 mm, preferably 20 to 28. The Weibull shape factor of bundle strength is calculated as an index indicating the narrowness of the distribution by Weibull plotting the bundle strength distribution when bundle strength is evaluated multiple times. A larger Weibull shape factor indicates a narrower distribution of bundle strength. A Weibull shape factor of 14 or higher for the bundle strength of a carbon fiber bundle ensures that the frequency of carbon fiber bundle breakage is sufficiently low even when resin-impregnated carbon fiber bundles are continuously laminated in a ring. If the Weibull shape factor of the bundle strength of a carbon fiber bundle is 30 or lower, the set tension during lamination can be sufficiently high, and resin-impregnated carbon fiber bundles can be stably laminated in a ring, thereby improving processability. The Weibull shape factor of the bundle strength of a carbon fiber bundle is the value evaluated in the bundle test described in "Bundle Strength of Carbon Fiber Bundles and Their Weibull Shape Factor" in the Examples section, and if equivalent results can be obtained, equipment and conditions other than those described in that section may be used. A Weibull plot is created by arranging 50 bundle strength points obtained from bundle tensile tests in order of strength. The slope of this plot, obtained by linear approximation using the least squares method, is determined and used as the Weibull shape coefficient. The rank method used to determine the cumulative fracture probability in the Weibull plot is the symmetric sample cumulative distribution method. To control the Weibull shape coefficient of the bundle strength of a 500 mm test length, it is preferable to use the carbon fiber bundle manufacturing method of the present invention, which will be described later.

[0014] The carbon fiber bundle of the present invention has a thickness of 0.05 to 0.110 mm, preferably 0.05 to 0.105 mm, and more preferably 0.05 to 0.100 mm. When the thickness of the carbon fiber bundle is 0.110 mm or less, a thin, lightweight carbon fiber reinforced composite material can be produced. While a smaller carbon fiber bundle thickness is preferable, if it is less than 0.05 mm, gaps may form within the carbon fiber bundle, which may reduce the quality of the carbon fiber reinforced composite material and decrease its mechanical properties. The thickness of the carbon fiber bundle and its coefficient of variation are determined by the method described in the Examples section under "<Thickness of Carbon Fiber Bundle and its Coefficient of Variation>". To keep the thickness of the carbon fiber bundle within the above range, it is necessary to control the surface temperature and processing time using a contact drying means in the post-processing step described later.

[0015] The carbon fiber bundle of the present invention has a coefficient of variation of thickness of 7.0% or less, preferably 6.5% or less, and more preferably 6.0% or less. When the coefficient of variation of the thickness of the carbon fiber bundle is small, a smooth resin-impregnated carbon fiber bundle can be obtained, and the effect of suppressing deformation of the member is large. If the coefficient of variation of the thickness of the carbon fiber bundle exceeds 7.0%, even when the thickness of the carbon fiber bundle is small, the number of gap cracks that occur between the carbon fiber bundles increases, and the smoothness of the resin-impregnated carbon fiber bundle is greatly reduced. In other words, in addition to the thickness of the carbon fiber bundle being small, it is important that the coefficient of variation of the thickness of the carbon fiber bundle is 7.0% or less. The coefficient of variation of the thickness of the carbon fiber bundle can be controlled not only by reducing the thickness of the carbon fiber bundle itself, but also by reducing the number of unraveled fibers as described later, adjusting the surface temperature and processing time by a contact drying means, and uniformly performing fluid entanglement treatment on the fiber bundle.

[0016] The carbon fiber bundles of the present invention are substantially untwisted. Being substantially untwisted means that the carbon fiber bundles are either completely untwisted, or, if twisted, have 0.5 turns or less per meter. When the carbon fiber bundles are untwisted, they exhibit excellent smoothness when used as reinforcing fibers for carbon fiber reinforced composite materials, resulting in resin-impregnated carbon fiber bundles.

[0017] The carbon fiber bundle of the present invention preferably has 6,000 to 24,000 filaments, and more preferably 6,000 to 12,000 filaments. The number of filaments refers to the number of single fibers contained in the carbon fiber bundle. If the number of filaments is 6,000 or more, the number of gap cracks that occur between carbon fiber bundles when laminating resin-impregnated carbon fiber bundles is reduced, and a resin-impregnated carbon fiber bundle of good quality can be obtained. If the number of filaments is 24,000 or less, the thickness of the carbon fiber bundle can be kept small, and a resin-impregnated carbon fiber bundle with a small thickness can be obtained. The number of filaments can be arbitrarily determined during the manufacturing process of the polyacrylonitrile-based carbon fiber precursor fiber bundle.

[0018] The carbon fiber bundle of the present invention preferably has a single fiber diameter of 5.0 to 6.0 μm, more preferably 5.0 to 5.8 μm, and even more preferably 5.0 to 5.5 μm. The single fiber diameter of the carbon fiber bundle is evaluated by the method described in the Examples section under <Single Fiber Diameter of Carbon Fiber Bundle>. If the cross-sectional shape of the single fiber is not a perfect circle, the equivalent diameter is used as a substitute. That is, the equivalent diameter refers to the diameter of a perfect circle having a cross-sectional area equal to the measured cross-sectional area of ​​the single fiber. In the process of manufacturing carbon fiber reinforced composite materials, the impregnation of the matrix resin into the carbon fiber bundle depends on the single fiber diameter; therefore, a larger single fiber diameter improves the impregnation of the resin, allowing for efficient manufacturing of composite materials. Furthermore, the single fiber diameter affects the breaking load per single fiber, which is determined from the strand tensile strength and the single fiber cross-sectional area. In addition, a larger single fiber diameter tends to reduce fuzzing due to friction during the process, thus affecting the quality. If the single fiber diameter is 5.0 μm or larger, the quality of the carbon fiber bundle will be good, resulting in less unraveling and generally better smoothness when the carbon fiber bundle is impregnated with resin. If the single fiber diameter is too large, the reaction within the single fiber may become non-uniform during the flame-retardant process, which can reduce the bundle strength. Therefore, it is preferable that the diameter be 6.0 μm or less, and more preferably 5.8 μm or less. The single fiber diameter can be controlled by the amount of carbon fiber precursor fiber bundle discharged from the spinneret during spinning and the stretch ratio during each process.

[0019] The carbon fiber bundle of the present invention preferably has a strand tensile strength of 6.7 to 9.0 GPa, more preferably 7.0 to 8.6 GPa, and even more preferably 7.5 to 8.4 GPa. The strand tensile strength of the carbon fiber bundle is precisely the resin-impregnated strand tensile strength, which affects the tensile strength of the carbon fiber reinforced composite material and is determined by the method described in <Strand Tensile Test of Carbon Fiber Bundle> in the Examples section. When the strand tensile strength of the carbon fiber bundle is 6.7 GPa or more, the tensile strength of the carbon fiber reinforced composite material of the present invention can be sufficiently maintained, and the carbon fiber reinforced composite material can be designed to be lightweight. Although the higher the strand tensile strength, the better, from the perspective of increasing the tensile strength of the carbon fiber reinforced composite material, 9.0 GPa is sufficient. To increase the strand tensile strength, it is preferable to use the method for manufacturing the carbon fiber bundle of the present invention described below.

[0020] The carbon fiber bundle of the present invention preferably has a strand tensile modulus of 280 to 380 GPa, more preferably 290 to 370 GPa, and even more preferably 300 to 360 GPa. The strand tensile modulus of the carbon fiber bundle is precisely the resin-impregnated strand tensile modulus, which affects the tensile modulus of the carbon fiber reinforced composite material and is determined by the method described in <Strand Tensile Test of Carbon Fiber Bundle> in the Examples section. When the strand tensile modulus of the carbon fiber bundle is 280 GPa or more, the tensile modulus of the carbon fiber reinforced composite material can be increased, and the carbon fiber reinforced composite material can be designed to be thin and lightweight. Also, although the higher the strand tensile modulus, the better, from the perspective of the single fiber compressive strength, it is preferably controlled so that the upper limit is 380 GPa.

[0021] The carbon fiber constituting the carbon fiber bundle of the present invention preferably has a density of 1.84 g / cm ３ or less, more preferably 1.82 g / cm ３ or less, and even more preferably 1.79 g / cm ３ or less. The lower the density, the better the specific strength and specific modulus, so that the carbon fiber reinforced composite material can be efficiently produced. When the density of the carbon fiber is 1.84 g / cm ３The following conditions may make it efficient to produce carbon fiber reinforced composite materials. There is no particular limit to the lower density, but from the perspective of the manufacturing process for obtaining carbon fiber bundles, 1.70 g / cm³ is desirable. ３ The above is preferable. The density used in the present invention can be evaluated by the method described in the Examples section under <Density of carbon fibers>. The density of carbon fibers can be controlled to the above range by the stretching ratio of the pre-carbonization process, the maximum temperature of the carbonization process, etc.

[0022] The carbon fiber bundle of the present invention preferably has a number of unraveled bristles of 20 fibers / 100m or less, more preferably 16 fibers / 100m or less, and even more preferably 9 fibers / 100m or less. If the number of unraveled bristles in the carbon fiber bundle is high, the coefficient of variation of the thickness of the carbon fiber bundle tends to increase due to an increase in the breakage of single fibers within the carbon fiber bundle. Also, if the number of unraveled bristles in the carbon fiber bundle is high, snagging occurs when the carbon fiber bundle is pulled out, which tends to increase the number of bristle defects. If the number of unraveled bristles in the carbon fiber bundle is 20 fibers / 100m or less, the coefficient of variation of the thickness of the carbon fiber bundle tends to be low. As a lower limit, it is particularly preferable to have 0 fibers / 100m or more, but in reality, 1 fiber / 100m or more is sufficiently preferable. The number of unraveled bristles is measured by the method described in the Examples section under <Number of Unraveled Bristles>. The number of unraveled fibers per 100m of carbon fiber bundle can be controlled within the above range by the pre-carbonization process and the stretching ratio of the carbonization process, which will be described later.

[0023] Next, the method for producing carbon fiber bundles according to the present invention will be described.

[0024] In a method for producing carbon fiber bundles, carbon fiber bundles are obtained by subjecting a carbon fiber precursor fiber bundle that has undergone fluid entanglement treatment to a flame-retardant step, a pre-carbonization step, and a carbonization step.

[0025] In the present invention, the carbon fiber precursor fiber bundle generally comprises a polymerization step of polymerizing acrylonitrile to obtain a polyacrylonitrile-based polymer as a spinning solution, a coagulation step of spinning by discharging from a spinneret by a wet spinning method or a dry-wet spinning method, a water washing step of washing the fiber obtained in the spinning step in a water bath, a water bath stretching step of stretching the fiber obtained in the water washing step in a water bath, and a dry heat treatment step of dry heat-treating the fiber obtained in the water bath stretching step. If necessary, it further comprises a steam stretching step of steam stretching the fiber obtained in the dry heat treatment step. Further, after the water bath stretching step, it is preferable to apply an oil agent composed of silicone or the like to the yarn for the purpose of preventing adhesion between single fibers.

[0026] The polyacrylonitrile-based polymer may be not only a homopolymer obtained only from acrylonitrile, but also a copolymerized product using other monomers in addition to acrylonitrile as a main component or a mixture thereof. Specifically, the polyacrylonitrile-based polymer preferably contains 98 to 99.9% by mass of a structure derived from acrylonitrile and 0.1 to 2% by mass of a structure derived from a copolymerizable monomer.

[0027] Examples of the monomer copolymerizable with acrylonitrile include acrylic acid, methacrylic acid, itaconic acid and their alkali metal salts, ammonium salts and lower alkyl esters, acrylamide and its derivatives, allylsulfonic acid, methallylsulfonic acid and their salts or alkyl esters.

[0028] The above-mentioned polyacrylonitrile-based polymer is dissolved in a solvent in which the polyacrylonitrile-based polymer is soluble, such as dimethyl sulfoxide, dimethylformamide, dimethylacetamide, nitric acid, zinc chloride aqueous solution, rhodansoda aqueous solution, etc., to obtain a spinning solution. When solution polymerization is used in the production of the polyacrylonitrile-based polymer, it is preferable to use the same solvent for polymerization and spinning, because the step of separating the obtained polyacrylonitrile-based polymer and redissolving it in the solvent for spinning becomes unnecessary.

[0029] In the method for producing a carbon fiber bundle according to the present invention, after the coagulation step of the carbon fiber precursor fiber bundle and before the water bath drawing step, a fluid entanglement treatment is performed. By performing the fluid entanglement treatment immediately after the coagulation step, when the fiber bundle subjected to the entanglement treatment passes through the subsequent steps, it comes into contact with many rollers, and it is considered that the degree of entanglement formation becomes uniform in the longitudinal direction and the cross-sectional direction of the fiber bundle. As a result, not only is it easy to increase the bundle strength of the carbon fiber bundle, which is important for the lamination process in a state where high tension is applied, but the Weibull shape factor is likely to increase, and furthermore, it becomes easier to control the thickness of the yarn bundle.

[0030] As the fluid used for the fluid entanglement treatment, either a gas or a liquid can be used, but air or nitrogen is preferable because they are inexpensive. In the fluid entanglement treatment, it is preferable to spray the fluid onto the fiber bundle using a nozzle. The shape of the nozzle for spraying the fluid is not particularly limited, but it is preferable to use a nozzle having 2 to 8 ejection holes. The arrangement of the ejection holes is not particularly limited, but when the traveling fiber bundle is viewed from the side, an even number of ejection holes are arranged so as to sandwich the fiber bundle from above and below such that the angle formed by the longitudinal direction of the fiber bundle and the direction in which the fluid is ejected is in the range of 88° to 90° (±2° with respect to 90°), and each ejection hole is preferably arranged at a position facing so as to form a pair of 2 holes sandwiching the fiber bundle.

[0031] The fluid entanglement treatment in the present invention is performed by setting the discharge pressure of the fluid to 0.20 to 0.40 MPa with respect to the fiber bundle with a tension of 2.0 to 5.0 mN / dtex. Further, preferably, the tension is 2.0 to 4.5 mN / dtex and the discharge pressure is 0.25 to 0.35 MPa. Also, the fiber bundle during the fluid entanglement treatment is preferably substantially untwisted. Here, substantially untwisted means that even if there is twist, it is 1 turn or less per 1 m of the fiber bundle.

[0032] If the tension applied to the fiber bundle during fluid entanglement treatment is higher than 5.0 mN / dtex, the rotational motion of the individual fibers may be suppressed, and thus the formation of entanglement may also be suppressed. On the other hand, if the tension is lowered below 2.0 mN / dtex, the rotational motion of the individual fibers constituting the fiber bundle is promoted, making entanglement easier to form, but the fiber bundle may come into contact with the nozzle, causing yarn damage, which may lead to a deterioration in quality and a decrease in strand strength. In addition, excessive rotational motion of the fiber bundle may result in uneven entanglement formation in the longitudinal direction of the fiber bundle, creating areas with a low degree of entanglement. If the fluid discharge pressure during fluid entanglement treatment is higher than 0.40 MPa, the fluid may cause yarn damage, which may lead to a deterioration in quality and a decrease in strand strength, as well as excessive entanglement, which may reduce the expandability of the carbon fiber bundle and increase the thickness of the yarn bundle. On the other hand, if the pressure is lowered below 0.20 MPa, the rotational motion of the individual fibers may be suppressed, and entanglement formation may be suppressed. It is best to set the tension of the fiber bundle and the fluid discharge pressure during the fluid entanglement process while considering the balance of the above factors.

[0033] In the present invention, the flame-retardant process refers to heat-treating the carbon fiber precursor fiber bundle at 200 to 400°C in an oxygen atmosphere with an oxygen concentration of ±5% by mass of the air. The total processing time for the flame-retardant process can be appropriately selected from a range of preferably 13 to 39 minutes. These preferred ranges for processing time and flame-retardant temperature vary depending on the characteristics of the carbon fiber precursor fiber bundle and the copolymerization composition of the polyacrylonitrile polymer.

[0034] To increase the strand tensile strength in strand tensile tests of carbon fiber bundles, in particular, when subjecting carbon fiber precursor bundles to the flame-retardant process, the flame-retardant fibers obtained after the flame-retardant process should have an infrared spectrum of 1,370 cm⁻¹. －１ 1,453 cm⁻¹ relative to the peak intensity －１ The ratio of peak intensities is in the range of 0.70 to 0.75, and the infrared spectrum is at 1,370 cm⁻¹. －１ 1,254 cm⁻¹ relative to the peak intensity －１ The ratio of the peak intensities is controlled to be in the range of 0.50 to 0.65. In the infrared spectrum, 1,453 cm⁻¹ －１The peak is of alkene origin, and its peak intensity decreases as flame resistance progresses. 1,370 cm －１ The peak was 1,254 cm. －１ The peaks are thought to originate from the flame-retardant structure (which is considered to be the naphthyridine ring and the hydride naphthyridine ring structure, respectively), and the peak intensity increases as flame retardant treatment progresses. In the flame retardant treatment process, it is common practice to reduce the peaks originating from polyacrylonitrile as much as possible to increase the carbonization yield, but in this invention, the conditions of the flame retardant treatment process are set to intentionally leave a large amount of alkenes. It is thought that subjecting flame-retardant fibers having such a structure to the preliminary carbonization process has the effect of increasing the strand tensile strength of the resulting carbon fiber bundle. Furthermore, 1,254 cm －１ The peak is frequently observed in areas where flame resistance is insufficient, and it is thought that a high proportion of this structure reduces the tensile strength of the resulting carbon fiber strands, therefore, 1,370 cm －１ 1,254 cm⁻¹ relative to the peak intensity －１ The peak intensity ratio is set within the above range. This peak intensity ratio decreases as flame resistance progresses, with a particularly large decrease in the initial stages. However, depending on the flame resistance conditions, the peak intensity ratio may not fall below 0.65 even if the time is increased, so it is advisable to adjust the conditions.

[0035] To achieve both of these peak intensity ratios within the desired range, the basic approach is to focus on setting conditions by reducing the amount of copolymer components in the polyacrylonitrile polymer constituting the carbon fiber precursor fiber bundle, increasing the degree of crystal orientation of the carbon fiber precursor fiber bundle, reducing the fineness of the carbon fiber precursor fiber bundle, and increasing the flame-retardant temperature in the latter half of the overall flame-retardant process.

[0036] In the flame-retardant treatment process, the infrared spectrum at 1,370 cm⁻¹ －１ 1,453 cm⁻¹ relative to the peak intensity －１ The material is heat-treated until the ratio of its peak intensity is in the range of 0.98 to 1.10 (first flame-retardant treatment step).

[0037] Next, preferably at a temperature higher than the first flame-retardant step, the infrared spectrum at 1,370 cm⁻¹ is measured. －１ 1,453 cm⁻¹ relative to the peak intensity －１ The ratio of peak intensities is in the range of 0.70 to 0.75, and the infrared spectrum is 1,370 cm⁻¹. －１ 1,254 cm⁻¹ relative to the peak intensity －１ It is preferable to perform heat treatment (second flame-retardant step) for 5 to 14 minutes, preferably 5 to 10 minutes, until the ratio of the peak intensities is in the range of 0.50 to 0.65. In order to shorten the flame-retardant step, the flame-retardant temperature can be adjusted to be higher, but the appropriate flame-retardant temperature depends on the properties of the polyacrylonitrile precursor fiber bundle. It is preferable to set the fiber bundle center temperature to preferably 280 to 310°C, more preferably 280 to 300°C, and even more preferably 280 to 285°C in order to control the infrared spectrum within the range described above. The flame-retardant temperature does not need to be constant, and a multi-stage temperature setting is also acceptable.

[0038] In order to increase the shear modulus of the resulting carbon fiber, it is generally preferable to use a high flame-retardant temperature and a short flame-retardant time in both the first and second flame-retardant processes. In the first flame-retardant process, it is preferable to use a flame-retardant temperature such that the flame-retardant time is 8 to 25 minutes, preferably 8 to 15 minutes, and the peak intensity ratio falls within the range described above.

[0039] The flame-retardant time described herein refers to the time the fiber bundles remain in each flame-retardant furnace when the first and second flame-retardant processes are carried out in separate flame-retardant furnaces. The flame-retardant fiber bundle refers to the fiber bundle after the flame-retardant process and before the preliminary carbonization process. The peak intensity described herein refers to the absorbance at each wavelength after baseline correction of the infrared spectrum obtained by sampling a small amount of the fiber bundle obtained in the first flame-retardant process or the flame-retardant fiber obtained in the second flame-retardant process; no special operations such as peak splitting are performed. The peak intensity of the infrared spectrum is measured using the method described in the Examples section under <Infrared Spectrum Intensity Ratio>. At this time, the concentration of flame-retardant fiber in the sample is diluted with potassium bromide (KBr) to 0.67% by mass before measurement. In this way, the infrared spectrum should be measured each time the flame-retardant conditions are changed, and the polymerization, spinning, and flame-retardant conditions should be examined according to the preferred manufacturing method described later. By appropriately controlling the infrared spectral peak intensity ratio of flame-resistant fibers, the nonlinearity of the resulting stress-strain curve of carbon fibers can be controlled.

[0040] The amount of copolymer component in the polyacrylonitrile polymer is preferably 0.1 to 2% by mass, and more preferably 0.1 to 1% by mass. Adding the copolymer component has the effect of promoting the flame-retardant reaction, but the effect is difficult to obtain if the copolymer amount is less than 0.1% by mass. Furthermore, if the copolymer amount exceeds 2% by mass, the flame-retardant treatment of the surface layer of the single fiber is preferentially promoted, and the flame-retardant treatment inside the flame-retardant yarn becomes insufficient, so the above range of infrared spectral peak intensity ratio is often not met.

[0041] In the pre-carbonization step, which pre-carbonizes the fiber bundles obtained in the flame-retardant process, the obtained flame-retardant fiber bundles are heat-treated in an inert atmosphere at a maximum temperature of 600 to 800°C. If the maximum temperature of the pre-carbonization is 600°C or higher, the pre-carbonized fiber bundles can be carbonized in the subsequent carbonization step without breaking due to thermal decomposition. There is no particular upper limit to the maximum temperature of the pre-carbonization, but it is preferable to keep it below 800°C in order to keep it below the carbonization temperature in the subsequent carbonization step.

[0042] In the present invention, the elongation ratio in the pre-carbonization process is 1.00 to 1.25, preferably 1.10 to 1.20. Generally, a higher elongation ratio in the pre-carbonization process improves the strand tensile strength and tensile modulus of the carbon fibers, but it also makes the fibers more prone to fuzzing. An elongation ratio in the range of 1.00 to 1.25 is sufficient to achieve both the strand tensile strength and tensile modulus of the carbon fiber bundle and the quality of the carbon fiber bundle.

[0043] In the present invention, in the carbonization step of carbonizing a pre-carbonized fiber bundle, the obtained pre-carbonized fiber bundle is heat-treated in an inert atmosphere at a maximum temperature of 1,350 to 2,000°C, preferably 1,400 to 1,900°C. Generally, the higher the maximum temperature of the carbonization step, the larger the crystallite size and the more uniform the orientation, so when a strand tensile test is performed, the strand modulus of the carbon fiber bundle improves and the strand tensile strength decreases. A carbonization temperature of 1,350°C is sufficient to allow carbonization to proceed sufficiently and increase the crystallite size, while a temperature of 2,000°C or lower is sufficient to maintain the strand tensile strength of the carbon fiber bundle.

[0044] In the present invention, the tension applied to the fiber bundle in the carbonization process is preferably 3.0 to 8.0 mN / dtex, more preferably 3.5 to 7.5 mN / dtex, and even more preferably 3.5 to 6.0 mN / dtex. By carbonizing the fiber bundle while applying tension in the carbonization process, the orientation of the crystallites can be aligned, and the initial modulus of elasticity in the strand tensile test of the carbon fiber bundle is improved. If the tension applied to the fiber bundle in the carbonization process is 3.0 mN / dtex or higher, the initial modulus of elasticity in the strand tensile test of the carbon fiber bundle is sufficiently expressed, and if it is 8.0 mN / dtex or lower, the generation of fluff in the carbonization process can be suppressed even when a substantially untwisted fiber bundle is used.

[0045] In the carbonization process, it is preferable to apply tension while maintaining the maximum temperature and residence time at the maximum temperature. If the maximum temperature in the carbonization process is low, or if the residence time at the maximum temperature is short, the initial modulus of elasticity in the strand tensile test of the carbon fiber bundle will be insufficient. To satisfy this initial modulus of elasticity, it is effective to increase the tension applied to the fiber bundle in the carbonization process, but this can cause fuzz to form and wrap around rollers, significantly reducing productivity, so it is preferable to keep it within the range described above. On the other hand, if the tension is too low, the initial modulus of elasticity in the strand tensile test of the carbon fiber bundle will be insufficient. Even if measures are taken to increase the maximum temperature or residence time at the maximum temperature in the carbonization process to compensate for and satisfy this low initial modulus of elasticity, the strand tensile strength of the carbon fiber bundle may decrease, so it is preferable to control the tension within the range described above. The tension in the carbonization process is measured by clamping the moving fiber bundle with a tension meter immediately after it leaves the heating furnace of the carbonization process. This tension can be adjusted by controlling the speed of the rollers before and after the carbonization process.

[0046] Carbon fiber bundles are obtained by electrolytic surface treatment of the fiber bundles obtained in the carbonization process. This treatment involves oxidation and the introduction of oxygen-containing functional groups. As methods for electrolytic surface treatment in the present invention, gas-phase oxidation, liquid-phase oxidation, and liquid-phase electrolytic oxidation can be used, but liquid-phase electrolytic oxidation is preferably used from the viewpoint of high productivity and uniform treatment. In the present invention, there are no particular restrictions on the method of liquid-phase electrolytic oxidation, and any known method may be used.

[0047] After the electrolytic treatment, a sizing treatment is performed to impart bundleability to the resulting carbon fiber bundle by impregnating it with a sizing agent. It is preferable to impregnate the carbon fiber bundle with the sizing agent by continuously immersing the carbon fibers in a sizing bath. Depending on the type of matrix resin used in the composite material, a sizing agent with good compatibility with the matrix resin can be appropriately selected. In order to achieve both abrasion resistance and resin impregnation, it is preferable that the amount of sizing agent adhering to the carbon fiber bundle is 0.5 to 2.0% by mass, when the entire carbon fiber bundle including the sizing agent is considered to be 100% by mass.

[0048] Carbon fibers impregnated with such sizing agent are dried using a contact drying method at a surface temperature of 100 to 180°C, preferably 100 to 160°C. The method of drying using the contact drying method is not particularly limited, but it is preferable to use a heated roller (e.g., a hot roller) to maintain high processability. If the surface temperature of the contact drying method is less than 100°C, the sizing agent applied to the carbon fiber bundle will not dry sufficiently, resulting in an increased thickness of the carbon fiber bundle. If the surface temperature of the contact drying method exceeds 180°C, the sizing agent applied to the carbon fiber bundle may decompose, worsening the bundleability, which may degrade the quality of the carbon fiber bundle itself. In addition, fuzzy fibers may wrap around the roller during carbon fiber bundle production, increasing the number of untangled fibers and increasing the coefficient of variation of the carbon fiber bundle thickness. If the surface temperature of the contact drying method is between 100 and 180°C, the thickness of the carbon fiber bundle can be controlled to be small, and the coefficient of variation of the carbon fiber bundle thickness can also be controlled to be small.

[0049] The contact time in such a contact-type drying means is 30 to 50 seconds, preferably 30 to 45 seconds. If the contact time in the contact-type drying means is less than 30 seconds, the sizing agent applied to the carbon fiber bundle will not dry sufficiently, resulting in an increased thickness of the carbon fiber bundle. If the contact time in the contact-type drying means exceeds 50 seconds, the sizing agent applied to the carbon fiber bundle may decompose, worsening its ability to bundle, which can degrade the quality of the carbon fiber bundle itself. This can also lead to fuzzy wrapping around the rollers during carbon fiber bundle manufacturing, increasing the number of untangled fuzzy fibers and increasing the coefficient of variation of the carbon fiber bundle thickness. If the contact time in the contact-type drying means is 30 to 50 seconds, the thickness of the carbon fiber bundle can be controlled to be small, and the coefficient of variation of the carbon fiber bundle thickness can also be controlled to be small.

[0050] The carbon fiber bundle thus obtained can stably impart high tension when resin-impregnated carbon fiber bundles are laminated in a ring shape, and a smooth laminate with no thickness variation can be obtained. Therefore, it can be suitably used in sports applications such as golf shafts and fishing rods, as well as in other general industrial applications such as rotating electric machine protection rings that can be used to protect the rotors of rotating electric machines such as generators and electric motors, and is particularly suitable for use in rotating electric machine protection rings as described later.

[0051] The towpreg of the present invention is a towpreg containing the above-mentioned carbon fiber bundle. The manufacturing process of the towpreg of the present invention can utilize known methods. For example, using a towpreg manufacturing apparatus equipped with a creel, kiss roll, nip roll, and winder, an epoxy resin composition adjusted to a temperature of 60°C is applied to one side of the obtained carbon fiber bundle so that the amount applied is 22 to 28% by mass relative to the total mass of the towpreg, and then passed through a nip roll to impregnate the carbon fiber bundle with the epoxy resin composition, thereby obtaining a towpreg. At this time, the towpreg bobbin should be cylindrical with an initial tension of 600 to 1,000 gf and a winding ratio of 6 to 10, and 2,300 m should be wound onto a paper tube to form a winding width of 230 to 260 mm.

[0052] The laminate of the present invention is a laminate using the above-described towpreg. The manufacturing process of the laminate of the present invention can utilize known methods. For example, the laminate can be obtained by laminating the obtained towpreg onto a rigid tool using the tape placement method, or by winding it at a predetermined angle with respect to the core material axis using the tape winding method.

[0053] The carbon fiber reinforced composite material of the present invention is a carbon fiber reinforced composite material obtained by molding the above-mentioned laminate. The manufacturing process of the carbon fiber reinforced composite material of the present invention can utilize known methods. For example, a fiber reinforced composite material having an arbitrary shape can be obtained by sealing a laminate obtained by the tape placement method with a flexible film, degassing the space between a rigid tool and the flexible film by vacuum pumping, and then heating and pressurizing it after placing it in an autoclave. Alternatively, a hollow tubular fiber reinforced composite material can be obtained by heating and curing a laminate obtained by the tape winding method in an oven. When curing, a heat-shrinkable tape may be wrapped around the surface of the material wound around the core. When a heat-shrinkable tape is wrapped around the surface of the material wound around the core, pressure is applied as the tape shrinks during curing, improving the surface quality of the resulting hollow tubular fiber reinforced composite material and suppressing the formation of voids inside.

[0054] The rotating electric machine protection ring of the present invention is a rotating electric machine protection ring obtained by laminating the above-mentioned tow preg in an annular shape and forming it. The manufacturing process of the rotating electric machine protection ring of the present invention can utilize known methods. For example, the tension applied to the tow preg is increased as it passes from a bobbin on which the tow preg is wound, through a predetermined path using a drive roll and a nip roll, and then wound onto an annular core at high tension via a touch roll to form an annular laminate, which is then heat-cured to form a rotating electric machine protection ring.

[0055] The rotating electric machine of the present invention is a rotating electric machine that includes the rotating electric machine protection ring described above. The rotating electric machine of the present invention may further include a rotor, a rotating electric machine protection ring, and a stator on the outside of the rotating electric machine protection ring. As described above, the rotating electric machine protection ring is manufactured by forming a laminate in which a tow preg is wound in an annular manner around a core material such as a rotor. Forming is performed by heating or by heating and pressurizing. As a result, the rotating electric machine protection ring is mounted around the rotor. The smaller the air gap between the rotor and the stator, the higher the magnetic flux density can be, and consequently, the power density of the rotating electric machine can be improved. The rotating electric machine protection ring described in the present invention can suppress magnet levitation at high speed rotation even if it is thin, and its high surface smoothness contributes to reducing the air gap.

[0056] The upper and lower limits of the numerical ranges described above can be combined in any way.

[0057] The methods for measuring various physical properties used in this invention are as follows.

[0058] <Strand Tensile Test of Carbon Fiber Bundles> The strand tensile strength of a carbon fiber bundle is determined according to JIS R7608 (2008) "Strand Test Method". Seven strands are measured, and the arithmetic mean of the measurement results is taken as the strand strength, strand modulus, and initial modulus of elasticity of the carbon fiber bundle in the strand tensile test. At this time, the strand modulus is measured in the strain range of 0.1 to 0.6%. Strain is measured using an extensometer. The test specimens used for measurement were prepared by impregnating a carbon fiber bundle with the following resin composition and curing it under heat treatment conditions of 130°C for 35 minutes.

[0059] [Resin composition] 3,4-Epoxycyclohexylmethyl-3,4-Epoxy-cyclohexane-carboxylate (100 parts by mass) Boron trifluoride monoethylamine (3 parts by mass) Acetone (4 parts by mass).

[0060] As the above 3,4-epoxycyclohexylmethyl-3,4-epoxy-cyclohexane-carboxylate, Celoxide P2021P (manufactured by Daicel Corporation) <Bundle strength of carbon fiber bundles and its Weibull shape coefficient> The bundle strength of carbon fiber bundles was measured using a Tensilon universal material tester RTC-1210A (manufactured by A&D Company, Limited), with a chuck distance of 500 mm, a crosshead speed of 100 mm / min, and a sample size of n=50. The Weibull shape coefficient was determined from the slope when the 50 bundle strength points obtained from the bundle tensile test were plotted in order of strength using the Weibull method and the resulting plot was linearly approximated using the least squares method. The rank method used to determine the cumulative fracture probability in the Weibull plot was the symmetric sample cumulative distribution method.

[0061] <Thickness of carbon fiber bundle and its coefficient of variation> 0.9 × 10⁻⁶ －４ A load of mN / dtex is applied to align the carbon fiber bundle, and the thickness is measured using a micrometer along a line segment that passes through the center of the circumscribed circle in the cross-section of the carbon fiber bundle and is perpendicular to the long side within that cross-section. The thickness of the above line segment is measured at 20 points at 3m intervals in the longitudinal direction, and the average value of the 20 points is taken as the thickness of the carbon fiber bundle, and the standard deviation of the 20 points is used as the standard deviation of the thickness of the carbon fiber bundle. The coefficient of variation of the thickness of the carbon fiber bundle is the ratio of the carbon fiber bundle thickness and the standard deviation of the thickness, expressed as a percentage. ([Standard Deviation] / [Mean Value] × 100) <Single Fiber Diameter of Carbon Fiber Bundle> The cross-section of a single fiber of the carbon fiber bundle to be evaluated is observed with a scanning electron microscope, and the cross-sectional area is evaluated. The diameter of a perfect circle with the same cross-sectional area as this cross-sectional area is calculated and taken as the single fiber diameter. In these examples and comparative examples, a scanning electron microscope (SEM) "S-4800" manufactured by Hitachi High-Technologies Corporation was used, and the acceleration voltage was set to 5 keV.

[0062] <Density of carbon fiber> Density of carbon fiber (g / cm³) ３ The density is calculated using the Archimedes method with o-dichlorobenzene as the specific gravity solution. Three samples are used for the measurement, and the arithmetic mean is taken as the density of the carbon fiber.

[0063] <Number of Unpacked Fuzz> A bobbin of carbon fiber bundles is placed on a creel, and a 100m length is drawn from it by a roller rotating at a speed of 2m / min under a tension of 1.6mN / dtex and wound up by a winder. At this time, the aggregated fuzz and pilling that occur between the creel and the roller, as defined below, are counted for 50 minutes, and the sum of these numbers is taken as the number of unpacked fuzz. However, if the length of the carbon fiber bundle is less than 100m, it is calculated using the following formula. However, from the viewpoint of accuracy of the number of unpacked fuzz, the length of the carbon fiber bundle must be 30m or more.

[0064] Number of loosened fibers (fibers / 100m) = Number of fibers counted (clumps of fibers + pills) (fibers) / Measured length (m) × 100 Clumps of fibers: Broken carbon fiber single fibers that protrude 5 mm or more from the carbon fiber bundle are called fibers, and there are three or more of these fibers within a bundle length of 10 mm. Pills: Broken carbon fiber single fibers that protrude from the carbon fiber bundle and become entangled, forming a mass with a diameter of 5 mm or more. Here, the diameter of a pill is the length of the longest line segment from end to end of the pill.

[0065] <Infrared Spectrum Intensity Ratio> After freeze-grinding the flame-resistant fiber to be used for measurement, 2 mg is accurately weighed and taken, and this is thoroughly mixed with 300 mg of KBr. The mixture is placed in a molding jig and pressurized at 40 MPa for 2 minutes using a press to produce a measurement tablet. This tablet is set in a Fourier transform infrared spectrophotometer and measured at 1,000 to 2,000 cm⁻¹. －１ The absorption spectrum is measured within this range. The background correction is 1,700–2,000 cm⁻¹. －１ The procedure is performed by subtracting the measured minimum value of the spectrum within the specified range from each intensity, until the minimum value becomes 0. In this example and comparative example, a PerkinElmer Paragon 1000 was used as the Fourier transform infrared spectrophotometer.

[0066] <Processability in High-Tensile Lamination of Resin-Impregnated Carbon Fiber Bundles> The processability in the fabrication of the annular laminate described below was evaluated. When resin-impregnated carbon fiber bundles are laminated in an annular shape under high tension, insufficient bundle strength leads to tow preg rupture, resulting in poor operability. Tow preg rupture includes not only a state where the bundle is completely separated at the rupture point, but also a state where the carbon fiber bundle bearing the stress is partially broken, preventing sufficient tension from being applied to the carbon fiber bundle. Furthermore, insufficient bundle strength can lead to single-fiber rupture in the tow preg, causing carbon fiber fuzz to wrap around the roll. If the wrapping around the roll worsens, it can lead to tow preg rupture, requiring the roll to be cleaned beforehand, thus worsening operability. Therefore, in the fabrication of annular laminates, it is desirable to suppress not only tow preg rupture but also the wrapping of carbon fiber fuzz around the roll to reduce the frequency of cleaning. Therefore, processability was evaluated based on the need for cleaning and the frequency of tow preg breakage after producing five annular laminates with 15 layers, and this is shown in Table 4 as processability during molding. The need for cleaning was determined by whether or not carbon fiber fluff was wrapped around the various rolls used in the manufacturing of the laminate. S: Tow preg did not break, and no fluff was wrapped around the rolls (no cleaning required) A: Tow preg did not break, but fluff was wrapped around the rolls (cleaning required) B: Tow preg broke once C: Tow preg broke two or more times.

[0067] <Quality of Annular Laminates> If the quality of the laminate is insufficient, dimensional errors are likely to occur when the number of layers is increased, which reduces the degree of freedom in terms of mechanical properties and use as a component. Therefore, even when laminating under high tension, it is important that the resulting laminate has good quality and a smooth surface. To evaluate the quality of the laminate, the smoothness of the laminate was used as an indicator by winding one full turn of tow preg around the core 5 described later and measuring the variation in thickness in the circumferential direction. A high level of smoothness in the laminate means that the error in thickness of the laminate at any multiple locations is small. In the fabrication of the annular laminate described later, the annular body obtained with one full turn of tow preg around the core 5 was measured at 1 cm intervals in the circumferential direction, starting from an arbitrary point, and the coefficient of variation of the thickness was measured and evaluated as follows, and shown as surface irregularities in Table 4. S: The coefficient of variation of the thickness of the annular body is less than 15%. A: The coefficient of variation of the thickness of the annular body is 15% or more and less than 19%. B: The coefficient of variation of the thickness of the annular body is 19% or more and less than 20%. C: The coefficient of variation of the thickness of the annular body is 20% or more and less. The present invention will be further described in detail by the examples.

[0068] (Example 1) A polyacrylonitrile copolymer copolymerized with itaconic acid was polymerized by solution polymerization using dimethyl sulfoxide as the solvent to produce a polyacrylonitrile copolymer and obtain a spinning stock. The obtained spinning solution was discharged into the air from a spinneret and introduced into a coagulation bath consisting of an aqueous solution of dimethyl sulfoxide by a wet-dry spinning method to obtain a coagulated yarn. After fluid entanglement treatment was applied to this coagulated yarn under the conditions shown in Table 1, it was washed with water by a conventional method and stretched 3.5 times in two hot water baths. Next, an amino-modified silicone-based silicone oil was applied to the fiber bundle after water bath stretching, and a drying and densification treatment was performed using a heated roller at 160°C. Two yarns were then combined to form a bundle of 12,000 single fibers, which was then stretched 3.7 times in pressurized steam to achieve a total stretching ratio of 13 times, yielding a polyacrylonitrile-based precursor fiber bundle with a crystal orientation of 93%, a single fiber fineness of 0.75 dtex, and 12,000 single fibers. Next, using the flame-retardant temperature and flame-retardant time conditions of Reference Example 1 shown in Table 1, the carbon fiber precursor fiber bundle was subjected to flame-retardant treatment while being stretched at a stretching ratio of 1 in an oven with an air atmosphere, yielding the flame-retardant fiber bundle shown in Table 1.

[0069]

[0070] In Table 1, the flame-retardant treatment process in the "first furnace" corresponds to the first flame-retardant treatment process, and the flame-retardant treatment process in the "second furnace" corresponds to the second flame-retardant treatment process.

[0071] The obtained flame-resistant fiber bundles were run in a nitrogen atmosphere with a temperature range of 300 to 800°C (i.e., a maximum temperature of 800°C), and the stretch ratio was controlled to obtain pre-carbonized fiber bundles. The obtained pre-carbonized fiber bundles were run in a nitrogen atmosphere, and the carbonization treatment was performed by controlling the maximum temperature and tension. The conditions for the pre-carbonization treatment and the carbonization treatment are summarized in Table 2.

[0072]

[0073] The obtained carbon fiber bundles were subjected to electrolytic surface treatment, then impregnated with a sizing agent, and contact-dried to obtain the final carbon fiber bundles. The amount of sizing agent adhering to the carbon fiber bundles was adjusted to 1.2% by mass. The resulting carbon fiber bundles had 12,000 filaments, a single fiber diameter of 5.3 μm, and a density of 1.82 g / cm³. ３ The strand tensile strength was 7.9 GPa, and the strand tensile modulus was 287 GPa, indicating high mechanical properties. Furthermore, the bundle strength of the carbon fiber bundle with a test length of 500 mm was 2.1 GPa, and the Weibull shape coefficient of the bundle strength of the carbon fiber bundle with a test length of 500 mm was 17, indicating high bundle strength and a narrow distribution of bundle strength. In addition, the thickness of the carbon fiber bundle was 0.092 mm, and the coefficient of variation of the thickness of the carbon fiber bundle was 5.8%, indicating small variation in thickness. Moreover, the quality of the carbon fiber bundle was good, with a detachable fuzzy count of 1 fuzz per 100 m. The above results are summarized in Table 3.

[0074]

[0075] Furthermore, using this carbon fiber bundle, toupreg was prepared with the resin composition shown below. Using a toupreg manufacturing apparatus equipped with a creel, kiss roll, nip roll, and winder, the resin composition, adjusted to a temperature of 60°C, was applied to one side of the obtained carbon fiber bundle so that the amount applied was 22 to 28% by mass relative to the total mass of the toupreg. Then, it was passed through the nip roll to impregnate the carbon fiber bundle with the resin composition, thereby obtaining toupreg. At this time, the toupreg bobbin was wound onto a paper tube with an initial tension of 600 to 1,000 gf, a winding ratio of 6 to 10, and a cylindrical shape with a winding width of 230 to 260 mm. The fiber volume fraction in the toupreg was 63%. The resin composition is as follows.

[0076] [Resin Composition] Epoxy resin: ・Liquid bisphenol A type epoxy resin ("jER®" 828: manufactured by Mitsubishi Chemical Corporation): 20 parts by mass ・Triglycidyl-m-aminophenol ("Araldite®" MY0600: manufactured by Huntsman Advanced Materials Co., Ltd.): 50 parts by mass ・Phenol novolac type epoxy ("jER®" 154: manufactured by Mitsubishi Chemical Corporation): 30 parts by mass Curing agent: ・Dicyandiamide (manufactured by Mitsubishi Chemical Corporation): 6 parts by mass Curing accelerator: ・3-(3,4-dichlorophenyl)-1,1-dimethylurea (manufactured by Hodogaya Chemical Co., Ltd.): 3 parts by mass.

[0077] An annular laminate was fabricated using the tow preg obtained in this way. The outline of the fabrication process is shown in Figure 1. The tow preg was wound from the bobbin 1 through a predetermined path by a drive roll 2 and a nip roll 3, increasing the tension applied to the tow preg as it passed through the touch roll 4 and was wound onto the core 5 at high tension to obtain the laminate 6. A metal mandrel with a diameter of 130 mm and a height of 15 mm was used as the core 5. The touch roll 4 was positioned near the core 5, and the tow preg traveled on the touch roll 4, passing through the starting point of the winding, and was wound onto the core 5. The touch roll 4 and the laminate wound on the core 5 were positioned so that there was a very narrow gap (1 mm). The core 5 was rotated in the direction of arrow 7. The unwinding speed of the tow preg from the bobbin 1 was 5 m / min, the distance 8 of the path between the nip roll 3 and the touch roll 4 was 500 mm, and a tensile stress of 1.8 GPa was applied to the tow preg located in the above section. The dimensions of the laminate 6 obtained in this way were approximately the same as those of the core 5, with a diameter of 130 mm, due to the thinness of the laminate 6. No thread breakage or entanglement with the roll occurred during the fabrication of the laminate, indicating good processability. Furthermore, the obtained laminate was of high quality. The processability and quality of the annular laminate are shown in Table 4.

[0078]

[0079] (Examples 2-9) Except for the conditions summarized in Tables 1 and 2, carbon fiber bundles were obtained in the same manner as in Example 1, and various evaluations were performed. The results are summarized in Tables 3 and 4. Carbon fiber bundles were obtained that had high mechanical properties, good quality, high bundle strength, a narrow distribution of bundle strength, small thickness, and small variation in thickness. The processability of the annular laminates fabricated in the same manner as in Example 1 using the obtained carbon fiber bundles was good, and the resulting laminates were of high quality. The processability and quality of the laminates are shown in Table 4.

[0080] (Comparative Examples 1-2) Except for the conditions summarized in Tables 1 and 2, carbon fiber bundles were obtained in the same manner as in Example 1, and various evaluations were performed. The fluid entanglement treatment was carried out under the same conditions as in Example 1, after applying an amino-modified silicone-based silicone oil to the fiber bundles after water bath stretching, as shown in Reference Example 5 in Table 1. The results are summarized in Tables 3 and 4, and the bundle strength and distribution of bundle strength of the carbon fiber bundles, as well as the thickness of the carbon fiber bundles and the coefficient of variation of thickness, did not satisfy all the requirements of the present invention. The processability and quality of the annular laminates made in the same manner as in Example 1 using the obtained carbon fiber bundles are shown in Table 4, and it was not possible to achieve both processability and quality.

[0081] (Comparative Examples 3-13) Except for the conditions summarized in Tables 1 and 2, carbon fiber bundles were obtained in the same manner as in Example 1, and various evaluations were performed. The results are summarized in Tables 3 and 4, and the bundle strength and distribution of bundle strength of the carbon fiber bundles, as well as the thickness of the carbon fiber bundles and the coefficient of variation of thickness, did not satisfy all the requirements of the present invention. The processability and quality of the annular laminates prepared in the same manner as in Example 1 using the obtained carbon fiber bundles are shown in Table 4, and it was not possible to achieve both processability and quality.

[0082] 1. Bobbin 2. Drive roll 3. Nip roll 4. Touch roll 5. Core 6. Laminate 7. Core rotation direction 8. Distance of the path between the nip roll and the touch roll

Claims

1. A carbon fiber bundle with a length of 500 mm, having a bundle strength of 1.8 to 3.0 GPa, a Weibull shape factor of the bundle strength of 14 to 30, a thickness of 0.05 to 0.110 mm, and a coefficient of variation of thickness of 7.0% or less, and being substantially untwisted.

2. The carbon fiber bundle according to claim 1, wherein the number of filaments is 6,000 to 24,000.

3. The carbon fiber bundle according to claim 1 or 2, wherein the bundle strength of the carbon fiber bundle with a test length of 500 mm is 2.3 to 3.0 GPa.

4. The carbon fiber bundle according to claim 1 or 2, wherein the single fiber diameter is 5.0 to 6.0 μm.

5. The carbon fiber bundle according to claim 1 or 2, wherein the strand tensile strength is 6.7 to 9.0 GPa.

6. The carbon fiber bundle according to claim 1 or 2, wherein the strand tensile modulus is 280 to 380 GPa.

7. Density is 1.84 g / cm³ ３ The carbon fiber bundle according to claim 1 or 2, wherein the carbon fiber bundle is as follows:

8. The carbon fiber bundle according to claim 1 or 2, wherein the number of unfurled hairs is 20 or less per 100m.

9. The carbon fiber bundle according to claim 1 or 2, wherein the carbon fiber bundle is for use as a rotating electric machine protection ring.

10. A fluid entanglement treatment step is performed after the solidification step of the polyacrylonitrile carbon fiber precursor fiber bundle and before the water bath stretching step, in which the fiber bundle is subjected to a tension of 2.0 to 5.0 mN / dtex and the fluid discharge pressure is 0.2 to 0.4 MPa, and the polyacrylonitrile carbon fiber precursor fiber bundle is subjected to an infrared spectrum at 1,370 cm⁻¹. －１ 1,453 cm⁻¹ relative to the peak intensity －１ A first flame-retardant treatment step involves flame-retardant treatment for 8 to 25 minutes until the ratio of peak intensities is in the range of 0.98 to 1.10, and the fiber bundle obtained in the first flame-retardant treatment step is subjected to infrared spectroscopy at 1,370 cm⁻¹. －１ 1,453 cm⁻¹ relative to the peak intensity －１ The ratio of peak intensities is in the range of 0.70 to 0.75, and the infrared spectrum is 1,370 cm⁻¹. －１ 1,254 cm⁻¹ relative to the peak intensity －１ A method for producing substantially untwisted carbon fiber bundles, comprising: a second flame-retardant step of flame-retardantizing for 5 to 14 minutes until the ratio of peak intensities is in the range of 0.50 to 0.65; a pre-carbonization step of pre-carbonizing the fiber bundles obtained in the second flame-retardant step in an inert atmosphere with a maximum temperature of 600 to 800°C and a draw ratio of 1.00 to 1.25; a carbonization step of carbonizing the fiber bundles obtained in the pre-carbonization step in an inert atmosphere with a maximum temperature of 1,350 to 2,000°C; a step of electrolytically surface-treating the fiber bundles obtained in the carbonization step to obtain carbon fiber bundles; and a step of impregnating the carbon fiber bundles with a sizing agent and then contacting the carbon fiber bundles impregnated with the sizing agent with a contact drying means at a surface temperature of 100 to 180°C for 30 to 50 seconds.

11. A towpreg using a carbon fiber bundle according to claim 1 or 2.

12. A laminate using the toupreg described in claim 11.

13. A carbon fiber reinforced composite material obtained by molding the laminate according to claim 12.

14. A rotating electric machine protection ring obtained by stacking the towpreg described in claim 11 in an annular shape and forming it.

15. A rotating electric machine using the rotating electric machine protection ring described in claim 14.

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