Unidirectional prepregs, carbon fiber reinforced composite materials, carbon fiber reinforced composite tubular bodies, and yacht masts

Abstract

To provide a unidirectional prepreg which is excellent in lamination workability by effectively suppressing warpage, even when a twisted yarn having the large number of twisting is untwisted and is formed into a prepreg.SOLUTION: A unidirectional prepreg contains a carbon fiber and a matrix resin, and has a warpage amount when a prepreg that has an average value of a spiral pitch of a fiber axis of the carbon fiber of 7.00 cm or less and satisfies (i) and / or (ii) is cut into a square of 13 cm and cured in a single layer of 4.0 mm or less. (i) A carbon fiber in which a spiral direction of the fiber axis is a direction of a right-handed screw, and a carbon fiber in which a spiral direction of the fiber axis is a direction of a left-handed screw are mixed. (ii) The carbon fiber has an average value of a single fiber diameter of 6.0 μm or less, and a fluctuation width of the fiber axis when the single fiber is observed in a range of a straight line distance of 1 mm from the side face of less than 3.0 μm.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a unidirectional prepreg with little warping even when untwisted yarn is used.

Background Art

[0002] Carbon fibers with low specific gravity and excellent mechanical properties have been increasingly used in recent years, and the required levels are diversifying and becoming more sophisticated accordingly. The forms for using carbon fibers vary depending on the application, and they are used in various forms from continuous fibers to discontinuous fibers. Among them, prepreg is one of the typical forms of use. Typically, a unidirectional prepreg, which is a sheet-like base material in which carbon fibers are arranged in one direction and impregnated with resin, exhibits excellent mechanical properties in the orientation direction of the carbon fibers.

[0003] A wide variety of carbon fibers are used for prepregs regardless of their types. Carbon fibers used for unidirectional prepregs are preferably twisted as little as possible from the viewpoints of spreadability and resin impregnability. For example, Patent Document 1 discloses a method for producing a prepreg using a carbon fiber bundle wound so that the number of twists per meter is 1 or less. Patent Document 2 also stipulates that the twist mark of the carbon fiber bundle should be 0.2 turns / m or less prior to prepreg formation. For the same reason, when using carbon fibers produced in a twisted state, so-called twisted yarns, it is common to perform an "untwisting treatment" prior to prepreg formation and use them as untwisted yarns from which the twist has been removed. For example, Patent Document 3 discloses a technique using a roller with a special shape to reduce twist unevenness and untwisting unevenness in the untwisting treatment.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 书2

[0005] However, conventional technologies have the following challenges:

[0006] Patent documents 1 and 2 propose methods for reducing the number of twists and unevenness of twists in carbon fiber bundles prior to prepreg formation. However, the present inventors have found that when the number of twists is increased in twisted yarn, even if the number of twists and unevenness are controlled to the range described in Patent documents 1 and 2 by performing an untwisting treatment prior to prepreg formation, the resulting unidirectional prepreg may have warping, which can impair lamination workability.

[0007] Furthermore, while Patent Document 3 discloses a method for obtaining carbon fiber bundles with less uneven twisting and untwisting, it does not focus on the warping of the unidirectional prepreg observed by the inventors when the aforementioned twisted yarn with a high number of twists is untwisted and made into a prepreg, and the resulting deterioration of lamination workability, nor is it recognized as a problem.

[0008] Twisted yarn has advantages that untwisted yarn does not, such as superior convergence as a carbon fiber bundle. While these advantages increase with increasing twist count, there is sometimes a trade-off with the lamination workability of the resulting unidirectional prepreg. Therefore, the problem that this invention aims to solve is to propose a method that can maintain lamination workability by effectively suppressing warping of the prepreg, even when twisted yarn with a high twist count is untwisted to form a unidirectional prepreg. [Means for solving the problem]

[0009] To achieve the above objective, the unidirectional prepreg of the present invention has the following configurations 1 to 7. 1. A unidirectional prepreg containing carbon fibers and a matrix resin, wherein the average value of the helical pitch of the fiber axes of the carbon fibers is 7.00 cm or less, and the warpage amount when the prepreg is cut out into a 13 cm square in length and width and cured in a single layer is 4.0 mm or less. (i) Carbon fibers with a right-handed helical direction of the fiber axis and carbon fibers with a left-handed helical direction of the fiber axis are mixed. (ii) The carbon fibers have an average single fiber diameter of 6.0 μm or less, and the fluctuation width of the fiber axis when the single fiber is observed from the side within a range of a straight-line distance of 1 mm is less than 3.0 μm. 2. When the number of twists of a carbon fiber bundle composed of single fibers with a right-handed helical direction of the fiber axis before untwisting is A (turns / m), the number of twists of a carbon fiber bundle composed of single fibers with a left-handed helical direction of the fiber axis before untwisting is B (turns / m), and the abundance ratio of the carbon fiber bundle composed of single fibers with a right-handed helical direction of the fiber axis is f A , when the average value of the single fiber diameter of these carbon fibers is d (μm), the unidirectional prepreg according to 1 above that satisfies formula (1). d 6 ÷10 5 ×|A×f A - B×(1 - f A )| ≦ 5.5 ··· Formula (1) (The ratio f A refers to the ratio N A calculated when the number of carbon fiber bundles composed of single fibers with a right-handed helical direction of the fiber axis is N B (pieces), and the number of carbon fiber bundles composed of single fibers with a left-handed helical direction of the fiber axis is N A (pieces), and is N A / (N B + N 3. Let A (turns / m) be the number of twists a carbon fiber bundle consisting of single fibers satisfying (i) above and whose fiber axis helical direction is oriented in the direction of a right-hand thread, B (turns / m) be the number of twists a carbon fiber bundle consisting of single fibers whose fiber axis helical direction is oriented in the direction of a left-hand thread, and f be the ratio of carbon fiber bundles consisting of single fibers whose fiber axis helical direction is oriented in the direction of a right-hand thread. A The unidirectional prepreg described in 1 or 2 above, wherein the average value of the single fiber diameter of these carbon fibers is d (μm), and equation (2) is satisfied. C × (d 2 ÷24-1)-4 ≦ 0...Equation (2) (However, C = |A×f A -B×(1-f A )|is) (ratio f A N is the number of carbon fiber bundles consisting of single fibers whose fiber axis helical direction is in the direction of a right-hand screw. A (Number of strands) N is the number of carbon fiber bundles consisting of single fibers whose fiber axis spirals in the direction of a left-hand thread. B The ratio N calculated when (this is the book) A / (N A +N B (This refers to) 4. The number of carbon fiber bundles consisting of single fibers that satisfy (i) above and whose fiber axis helical direction is in the direction of a right-hand thread is N. A (Number of strands) N is the number of carbon fiber bundles consisting of single fibers whose fiber axis spirals in the direction of a left-hand thread. B When (book), ratio N A / (N A +N B A unidirectional prepreg according to any of the above 1 to 3, wherein the ratio is 0.4 to 0.6. 5. Let α (cm) be the average helical pitch of the carbon fiber axis, and N be the number of single fibers contained in the carbon fiber bundle. α (This refers to a unidirectional prepreg according to any of the above 1 to 4, wherein the average value of the single fiber diameter of the carbon fiber is d (μm), and equation (3) is satisfied. 1.0 ≤ d 2 ×N α ÷(α 2 ×10 4 ) ≦ 4.0...Equation (3) 6. Carbon fiber basis weight: 250g / m 2 The above is a one-way prepreg as described in any of items 1 to 5 above. 7. A unidirectional prepreg according to any of items 1 to 6 above, wherein the average helical pitch of the carbon fiber axis is 6.00 cm or less.

[0010] Furthermore, the carbon fiber reinforced composite material of the present invention has the following components 8 to 9. 8. A carbon fiber reinforced composite material obtained by laminating one-way prepregs as described in any of items 1 to 7 above. 9. A carbon fiber reinforced composite material as described in 8 above, satisfying equations (4) and (5), where X is the tensile modulus and Y is the 0° compressive strength. X≧150...Formula (4) Y×X ≧320...Equation (5) Furthermore, the tubular body of the present invention is made of the carbon fiber reinforced composite material described in item 9 above, and the yacht mast of the present invention is made using the above-described tubular body. [Effects of the Invention]

[0011] The unidirectional prepreg of the present invention is a prepreg with excellent lamination workability because warping is effectively suppressed even when twisted yarn with a high number of twists is untwisted and made into a prepreg. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a schematic diagram illustrating a method for evaluating the fluctuation range of the fiber axis. [Figure 2] Figure 2 is a schematic diagram illustrating a method for evaluating the helical pitch of a single carbon fiber. [Figure 3] Figure 3 is a schematic diagram illustrating the method for evaluating the amount of warping. [Figure 4] Figure 4 is a schematic diagram illustrating a specific example of warping. [Modes for carrying out the invention]

[0013] In this invention, the term "carbon fiber" is used in a broad sense, including carbon fiber bundles and single carbon fibers. A carbon fiber bundle refers to a bundle of multiple single carbon fibers (for clarity, a single carbon fiber may also be simply called a "single fiber").

[0014] The unidirectional prepreg of the present invention is obtained by arranging multiple carbon fibers in one direction and impregnating them with a matrix resin. Specifically, the average helical pitch of the carbon fiber axis is 7.00 cm or less, and satisfies (i) and / or (ii), and the amount of warping when the prepreg is cut into a 13 cm x 13 cm square and cured as a single layer is 4.0 mm or less. (i) A mixture of carbon fibers in which the helical direction of the fiber axis is oriented in the direction of a right-hand thread, and carbon fibers in which the helical direction of the fiber axis is oriented in the direction of a left-hand thread. (ii) The average single fiber diameter of the carbon fiber is 6.0 μm or less, and the fluctuation width of the fiber axis when the single fiber is observed from the side within a straight-line distance of 1 mm is less than 3.0 μm. In this invention, the helical pitch of the carbon fiber axis is a morphological characteristic of the fiber axis that correlates with the twist strength of the twisted yarn. That is, twisted yarn is obtained by processing a carbon fiber bundle while it is twisted, and the twisted shape may be retained in the carbon fiber bundle obtained in this way.

[0015] Here, "a state in which the twist shape is maintained" refers to a state in which the twist does not come out of the carbon fiber bundle even when the carbon fiber bundle is cut to form a free end. In contrast, if a carbon fiber bundle obtained without any twisting during the manufacturing process is forcibly twisted and then cut at an arbitrary point to form a free end, the fiber axis of the single fibers constituting the carbon fiber bundle is originally straight, so the twist will naturally dissipate from the free end in order due to the high rigidity of the carbon fibers. Carbon fiber bundles in which the twist shape is maintained are particularly likely to be obtained when the twist has been applied during the carbonization process.

[0016] When a single fiber is taken from a carbon fiber bundle that maintains this twisted shape and observed, the fiber axis of the single fiber forms a "helical" shape. In this invention, helical pitch refers to the distance traveled in the axial direction of the fiber while this helix completes one rotation. The average value of this helical pitch refers to the average value of the helical pitch obtained by taking multiple single carbon fibers from a unidirectional prepreg and evaluating them, and the detailed evaluation method will be described later.

[0017] An average helical pitch of 7.00 cm or less indicates that the carbon fiber bundles were processed with sufficient twist during manufacturing. In particular, the improved stress transfer between individual fibers due to the twist can suppress single fiber breakage during the carbonization process. By applying high tension during the carbonization process, the degree of crystal orientation can be effectively increased, or high-quality carbon fiber bundles can be obtained by using moderate tension. An average helical pitch of 6.00 cm or less is preferable. Furthermore, from the viewpoint of avoiding a complicated twisting process during carbon fiber manufacturing, an average helical pitch of 0.50 cm or more is preferable.

[0018] The helical direction of a fiber axis can be either right-hand or left-hand, depending on the direction of the twist applied to the carbon fiber bundle during the manufacturing process. The common technical terms "Z-twist" and "S-twist," which describe the direction of twist, correspond to right-hand and left-hand threads, respectively, in terms of the helical direction of a single fiber. In other words, Z-twisted yarn is made from single fibers whose fiber axis helical direction is oriented in the direction of a right-hand thread, while S-twisted yarn is made from single fibers whose fiber axis helical direction is oriented in the direction of a left-hand thread.

[0019] As a result of diligent research into controlling the warping of the aforementioned unidirectional prepreg, the inventors have found that a unidirectional prepreg with less warping can be obtained if at least one of the following conditions is met: using a mixture of carbon fibers with a right-hand thread direction for the fiber axis helix, and carbon fibers with a left-hand thread direction for the fiber axis helix, or if the average single fiber diameter of the carbon fibers is 6.0 μm or less, and the fluctuation width of the fiber axis when observed from the side of a single fiber at a straight-line distance of 1 mm is less than 3.0 μm.

[0020] Observations have revealed that the unidirectional prepreg warps in the helical direction of the fiber axis. In the unidirectional prepreg, the individual carbon fibers are constrained by the resin, so instead of the individual fibers moving independently, they move in a coordinated manner as a single sheet, resulting in warping in the aforementioned direction. Furthermore, it is hypothesized that when carbon fibers with a right-hand thread orientation and carbon fibers with a left-hand thread orientation are mixed, the forces trying to warp in opposite directions cancel each other out through the resin, suppressing overall warping.

[0021] Whether carbon fibers with a right-hand helical direction and carbon fibers with a left-hand helical direction are mixed, or whether the average single fiber diameter of the carbon fibers is 6.0 μm or less and the fluctuation width is less than 3.0 μm, can be easily confirmed by observing the carbon fiber bundles being fed during the prepreg stage. If the prepreg has already been formed, it can be confirmed by removing the matrix resin from the unidirectional prepreg using a known method, randomly sampling single carbon fibers from the remaining carbon fiber bundle assembly, and observing them. Methods for removing the matrix resin include burning it off and elution using a solvent. The helical direction of the fiber axis, the average single fiber diameter, and the fluctuation width can be evaluated using the methods described later.

[0022] The measurement of fluctuation width in this invention is evaluated by observing a single carbon fiber in an environment free from stresses other than gravity, from a direction perpendicular to the fiber axis direction. In a fiber exhibiting three-dimensional fluctuation, the fiber axis direction and the direction perpendicular to it are defined as follows: In the projection image of a single carbon fiber placed on a horizontal plane, a straight line connecting two points 1,000 μm apart is defined as the virtual fiber axis at the observation point, and the vertical direction is defined as the direction perpendicular to the fiber axis direction. In other words, the fluctuation width is approximately measured in the projection image.

[0023] As shown in Figure 1, the fluctuation range is defined as the residual ΔY (μm) obtained by subtracting the minimum value Ymin (μm) from the maximum value Ymax (μm) of the Y coordinate values ​​through which the center of the thickness direction of the single fiber passes, when point A is arbitrarily selected as the center in the thickness direction of the observed single fiber and point B is the center of the thickness direction of the single fiber located 1 mm away in a straight line from point A, and point B is set as the origin in the XY coordinate system, i.e., X=0 μm, Y=0 μm, and point B is a point on the X axis, i.e., X=0 μm, Y=1,000 μm. The fluctuation range is measured on 50 randomly selected independent single fibers, and the average value is adopted. By adopting the average value of 50 single fibers, it is possible to identify slight differences that affect the warping of the unidirectional prepreg.

[0024] The average value of the single fiber diameter and the fluctuation width of the carbon fiber can be interpreted as parameters indicating the strength of the twist of the carbon fiber used in the unidirectional prepreg, with larger average values ​​of the single fiber diameter and fluctuation width indicating stronger twist. By setting the average value of the single fiber diameter of the carbon fiber to 6.0 μm or less and the fluctuation width to less than 3.0 μm, warping of the unidirectional prepreg can be suppressed. Preferably, the average value of the single fiber diameter is 5.8 μm or less. Furthermore, from the viewpoint of stability in the carbon fiber manufacturing process, it is preferable that the average value of the single fiber diameter be 4.5 μm or more. Preferably, the fluctuation width is less than 2.7 μm, and more preferably less than 2.3 μm. Furthermore, from the viewpoint of suppressing single fiber breakage in the carbonization process by improving stress transmission between single fibers due to twisting, it is preferable that the fluctuation width be 1.5 μm or more.

[0025] The inventors of this invention have discovered that when using twisted yarn with a high twist count in a unidirectional prepreg, even if the twist is seemingly eliminated by the untwisting process, warping may become apparent in the unidirectional prepreg obtained after prepreg formation. Furthermore, it was found that the warping of the unidirectional prepreg can lead to a significant decrease in lamination workability during the lamination process, as the space between the prepregs that have been laminated may lift and the relative positional relationship may shift. In some cases, the warping may also spread to the composite material obtained by lamination and curing, depending on the lamination configuration.

[0026] The warping of unidirectional prepregs that causes such problems is easily affected by the viscoelasticity of the uncured matrix resin and the rigidity of the release paper or release film. Even if it appears fine before lamination begins, the problem may become apparent as soon as the prepreg is peeled off the release paper or release film during lamination.

[0027] To quantify this potential warping, the inventors developed a method of cutting the prepreg into 13cm x 13cm squares, curing it in a single layer, and then quantifying the amount of warping. If the amount of warping when the prepreg is cut into 13cm x 13cm squares and cured in a single layer is 4.0mm or less, the prepreg will exhibit less apparent warping when the uncured prepreg is peeled off the release paper or release film. It is more preferable that the amount of warping be 3.0mm or less, and even more preferable that it be 2.0mm or less.

[0028] In the present invention, a specific method for obtaining a unidirectional prepreg obtained by mixing carbon fibers whose fiber axis helical direction is oriented in the direction of a right-hand thread and carbon fibers whose fiber axis helical direction is oriented in the direction of a left-hand thread is to determine the number of carbon fiber bundles consisting of single fibers whose fiber axis helical direction is oriented in the direction of a right-hand thread. A (Number of strands) N is the number of carbon fiber bundles consisting of single fibers whose fiber axis spirals in the direction of a left-hand thread. B When (book), ratio N A / (N A +N B It is preferable to mix them so that the ratio is 0.4 to 0.6.

[0029] In this invention, for simplicity, such a ratio is referred to as ratio f A It is also written as follows: such ratio f A This is calculated based on the number of carbon fiber bundles. For example, ratio f A A ratio of 0.4 means that the prepreg is made in a ratio of 6 carbon fiber bundles, each consisting of a single fiber with a left-hand thread orientation, for every 4 carbon fiber bundles, each consisting of a single fiber with a left-hand thread orientation.

[0030] This ratio can be determined by observing the carbon fiber bundles being fed during the prepreg stage, using the method described below. If a unidirectional prepreg is already formed, the matrix resin is removed from the unidirectional prepreg using a known method to extract an assembly of carbon fiber bundles. Three single fibers are then taken from each individually identified carbon fiber bundle, and the helical direction of the fiber axis is observed for all the taken single fibers using the method described below. The method for removing the matrix resin can be the method described above. The results of this observation are compiled using the method described below, and the carbon fiber bundles consisting of single fibers with a right-hand thread helical direction and the carbon fiber bundles consisting of single fibers with a left-hand thread helical direction are found to have the above ratio f A This allows you to verify whether it is a unidirectional prepreg that has been mixed together.

[0031] In the present invention, a specific method for obtaining a unidirectional prepreg obtained by mixing carbon fibers whose fiber axis helical direction is in the direction of a right-hand thread and carbon fibers whose fiber axis helical direction is in the direction of a left-hand thread is as follows: A (turns / m) is the number of twists that the carbon fiber bundle consisting of single fibers whose fiber axis helical direction is in the direction of a right-hand thread had before untwisting, B (turns / m) is the number of twists that the carbon fiber bundle consisting of single fibers whose fiber axis helical direction is in the direction of a left-hand thread had before untwisting, and f is the ratio of carbon fiber bundles consisting of single fibers whose fiber axis helical direction is in the direction of a right-hand thread. A When the average single fiber diameter of these carbon fibers is d (μm), it is preferable to mix them in such a way that equation (1) is satisfied. d 6 ÷10 5×|A×f A -B×(1-f A )| ≦ 5.5 ···Equation (1).

[0032] Although equation (1) is an empirical formula obtained experimentally by the inventors and is not rigorously supported by physical forces, the inventors' findings indicate that by controlling the process to satisfy equation (1), it is possible to effectively suppress the warping of a unidirectional prepreg when a twisted yarn with a high twist count is untwisted and converted into a prepreg.

[0033] In equation (1), d 6 ÷10 5 The part becomes smaller as the average diameter of the single carbon fiber decreases. Also, |A×f A -B×(1-f A The part in parentheses )| represents the way the right-hand and left-hand threads cancel each other out when a carbon fiber bundle consisting of single fibers with a right-hand thread direction and a carbon fiber bundle consisting of single fibers with a left-hand thread direction are mixed, using the ratio of the number of carbon fiber bundles f A It can be said that this is expressed using a compound rule.

[0034] Here, the symbol "|" means taking the absolute value. Therefore, the left side of equation (1) becomes smaller as the average diameter of the carbon fiber single fibers decreases, and becomes smaller as the right-hand and left-hand threads cancel each other out. When this left side is 5.5 or less, it is preferable because the warping of the unidirectional prepreg is effectively suppressed. It is even more preferable when this left side is 4.0 or less in terms of more effectively controlling the warping of the unidirectional prepreg. As will be described later, the number of twists can be calculated from the helical pitch.

[0035] In the present invention, a specific method for obtaining a unidirectional prepreg obtained by mixing carbon fibers whose fiber axis helical direction is oriented in the direction of a right-hand thread and carbon fibers whose fiber axis helical direction is oriented in the direction of a left-hand thread is as follows: A (turns / m) is the number of twists that a carbon fiber bundle consisting of single fibers whose fiber axis helical direction is oriented in the direction of a right-hand thread had before untwisting; B (turns / m) is the number of twists that a carbon fiber bundle consisting of single fibers whose fiber axis helical direction is oriented in the direction of a left-hand thread had before untwisting; and f is the ratio of carbon fiber bundles consisting of single fibers whose fiber axis helical direction is oriented in the direction of a right-hand thread. A When the average single fiber diameter of these carbon fibers is d (μm), it is preferable to mix them in such a way that equation (2) is satisfied. C × (d 2 ÷24-1)-4 ≦ 0...Equation (2) (However, C = |A×f A -B×(1-f A )|is).

[0036] Although equation (2) is an empirical formula obtained experimentally by the inventors and is not rigorously supported by physical forces, the inventors' findings indicate that by controlling the process to satisfy equation (2), it is possible to effectively suppress the warping of a unidirectional prepreg when a twisted yarn with a high twist count is untwisted and converted into a prepreg.

[0037] In equation (2), C represents the way the right-hand and left-hand threads cancel each other out when carbon fiber bundles consisting of single fibers with the helical direction of the fiber axis in the direction of a right-hand thread are mixed with carbon fiber bundles consisting of single fibers with the helical direction of the fiber axis in the direction of a left-hand thread, as expressed by the ratio of the number of carbon fiber bundles f. A This is expressed using a composite rule. Therefore, the left side of equation (2) becomes smaller as the average single fiber diameter of the carbon fiber decreases, and becomes smaller as the right-hand and left-hand threads cancel each other out. When this left side is 0 or less, it is preferable because the warping of the unidirectional prepreg is effectively suppressed. It is even more preferable when this left side is -2 or less in terms of more effectively controlling the warping of the unidirectional prepreg. As will be described later, the number of twists can be calculated from the average value of the helical pitch.

[0038] In the present invention, a specific method for obtaining a unidirectional prepreg that satisfies at least one of the following conditions: a mixture of carbon fibers with a right-hand thread helical direction and single fibers with a left-hand thread helical direction, or the average diameter of the single carbon fibers being 6.0 μm or less, and the fluctuation width of the fiber axis when the single fiber is observed from the side at a straight-line distance of 1 mm being less than 3.0 μm, is as follows: the average helical pitch of the carbon fiber axis is α (cm), and the number of single fibers contained in the carbon fiber bundle is N. α (This) When the average value of the single fiber diameter of the carbon fiber is d (μm), it is preferable that equation (3) is satisfied. 1.0 ≤ d 2 ×N α ÷(α 2 ×10 4 ) ≦ 4.0...Equation (3) Although equation (3) is an empirical formula obtained experimentally by the inventors and is not rigorously supported by physical principles, the inventors' research shows that by controlling the process to satisfy equation (3), warping of the unidirectional prepreg can be effectively suppressed when a twisted yarn with a high twist count is untwisted and converted into a prepreg. Equation (3) can be interpreted as a formula indicating the twist strength of the carbon fibers used in the unidirectional prepreg, showing excellent convergence when it is 1.0 or higher, and suppressing warping when it is 4.0 or lower. Furthermore, a value of 2.5 or lower is more preferable from the viewpoint of more effectively controlling the warping of the unidirectional prepreg.

[0039] In equation (3), d 2 The part becomes smaller as the average diameter of the carbon fiber single fibers decreases. In other words, it indicates that the smaller the diameter of the carbon fiber single fibers, the weaker the twist. Also, in equation (3), N α The part becomes smaller as the number of single fibers decreases. In other words, it indicates that the fewer the number of single carbon fibers, the weaker the twist. Furthermore, in equation (3), 1 / (α 2 ×10 4 The part in parentheses becomes larger as the helical pitch decreases. In other words, a smaller helical pitch in carbon fiber indicates a stronger twist.

[0040] The number of single fibers in a carbon fiber bundle can be determined by observing the fed carbon fiber bundle using the method described below, if the carbon fiber bundle is at the prepreg stage. If it is already a unidirectional prepreg, the matrix resin is removed from the unidirectional prepreg to extract the carbon fiber bundle aggregate, and the number of single fibers in each carbon fiber bundle, which has been visually identified, can be determined by observing the method described below.

[0041] The unidirectional prepreg of the present invention has a carbon fiber basis weight of 250 g / m². 2 The above is preferable. When the basis weight of the carbon fibers increases, that is, when the thickness of the carbon fiber layer increases, the second moment of area of ​​the unidirectional prepreg increases, making the prepreg less prone to warping. Also, it is preferable that the carbon fiber bundles overlap to some extent, as this allows for uniform warping suppression. Increasing the basis weight of the carbon fibers makes it easier to ensure overlap between the carbon fiber bundles. When the overlap between the carbon fiber bundles is sufficient, it is less likely that low-rigidity matrix resin-rich regions will form between the carbon fiber bundles, making it less likely for localized bending to occur at such locations, and the unidirectional prepreg is less likely to crack even if there is a large difference in the average value of the helical pitch of adjacent carbon fiber bundles. The basis weight of the carbon fibers is 300 g / m 2 It is more preferable that the above conditions are met.

[0042] The carbon fiber reinforced composite material of the present invention is preferably a carbon fiber reinforced composite material formed by laminating the unidirectional prepreg of the present invention. By laminating the unidirectional prepreg of the present invention, it is possible to obtain a carbon fiber reinforced composite material with excellent mechanical properties and quality, taking advantage of the benefits of twisted yarn.

[0043] The carbon fiber reinforced composite material of the present invention preferably satisfies equations (4) and (5), where X is the tensile modulus (GPa) and Y is the 0° compressive strength (GPa). X≧150...Formula (4) Y×X ≧320...Equation (5) Carbon fiber reinforced composite materials satisfying equations (4) and (5) can achieve both high rigidity and compressive strength, making them suitable for applications where strong bending forces are applied. In equation (4), X is preferably less than 400 (GPa) because excessively high X values ​​may lead to a decrease in tensile strength and the formation of fuzz. Similarly, in equation (5), Y × X is preferably 500 (GPa) from the viewpoint of maintaining an appropriate range for the tensile modulus. 2 It is preferable that it be less than ).

[0044] The tubular body of the present invention is made of a carbon fiber reinforced composite material that satisfies formulas (4) and (5). Because the tubular body is made of a carbon fiber reinforced composite material that satisfies formulas (4) and (5), it is resistant to bending and breaking, regardless of the direction from which strong bending forces are applied.

[0045] The yacht mast of the present invention is made using the carbon fiber reinforced composite tubular body of the present invention. By using the tubular body of the present invention, it is possible to make a yacht mast that is lightweight, highly rigid, and resistant to bending and breakage even when strong bending forces are applied, thereby greatly contributing to the stabilization of the yacht's center of gravity and improvement of its aerodynamic performance.

[0046] The twisted yarn used in the unidirectional prepreg of the present invention can be obtained, for example, by the method described in Japanese Patent Application Publication No. 2014-141761 or the method described in International Publication No. 2019 / 203088. The degree of crystal orientation may be effectively increased by passing the yarn through a carbonization process while applying high tension in the twisted state, or a high-quality carbon fiber bundle may be obtained with less breakage of single fibers by applying twist but with moderate tension. The important point is that by adopting the configuration of the unidirectional prepreg of the present invention, when a twisted yarn with a strong twist is untwisted and used, the warping of the unidirectional prepreg can be effectively suppressed, and a unidirectional prepreg with excellent lamination workability can be obtained. It should be noted that the unidirectional prepreg of the present invention must contain carbon fiber bundles in which the twisted form is maintained, but it may also contain untwisted carbon fiber bundles. There is no clear standard for the content of untwisted carbon fiber bundles, but a guideline is to limit it to about 50% of the number of fiber bundles relative to the twisted yarn.

[0047] The methods for measuring the various physical properties described herein are as follows:

[0048] <Average single fiber diameter of carbon fiber> The carbon fiber is evaluated by observing individual fibers using a scanning electron microscope (SEM). Fifty individual fibers are evaluated, and their average value is taken as the average fiber diameter. In the examples and comparative examples of this invention, observation was performed using a scanning electron microscope (SEM) "S-4800" manufactured by Hitachi High-Technologies Corporation.

[0049] <Number of individual fibers in a carbon fiber bundle> The carbon fiber bundles are evaluated by observing them with a scanning electron microscope (SEM). Three carbon fiber bundles are evaluated, and the average value is taken as the number of individual fibers contained in the carbon fiber bundle. If the carbon fiber bundles are at the prepreg stage, they can be identified by observing the carbon fiber bundles being fed. The number of individual fibers is determined in units of 1,000. If the carbon fiber bundles have already been prepregized and it is difficult to obtain the carbon fiber bundles before manufacturing the unidirectional prepreg, a square of 13 cm in the fiber orientation direction and 13 cm in the direction perpendicular to it is cut from the prepreg, the matrix resin is burned off in an electric furnace with a nitrogen atmosphere set to a temperature of 450°C, and then the individual carbon fiber bundles can be identified by visually inspecting the remaining aggregate of carbon fiber bundles. In the examples and comparative examples of the present invention, observation was performed using a scanning electron microscope (SEM) "S-4800" manufactured by Hitachi High-Technologies Corporation.

[0050] <Tensile modulus of carbon fiber> The tensile modulus of carbon fiber is determined according to the resin-impregnated strand test method of JIS R7608:2004, following the procedure below. However, if the carbon fiber is twisted, it is evaluated after untwisting by applying the same number of reverse twists as the number of twists. The resin formulation used is "Celoxide (registered trademark)" 2021P (manufactured by Daicel Chemical Industries, Ltd.) / boron trifluoride monoethylamine (manufactured by Tokyo Chemical Industry Co., Ltd.) / acetone = 100 / 3 / 4 (parts by mass), and the curing conditions are normal pressure, temperature 125°C, and time 30 minutes. Ten strands of carbon fiber are measured, and the average value is taken as the tensile modulus. The strain range when calculating the tensile modulus is 0.1 to 0.6%.

[0051] <Number of twists in carbon fiber bundles> The twist count (turns / m) of a carbon fiber bundle is calculated by pulling out 1m of the carbon fiber bundle to be measured, twisting one end with the longitudinal direction of the fiber bundle as the axis of rotation, and dividing the number of twists until the twist is completely eliminated by 1. The number of twists is counted as 360 degrees as one rotation. Whether the twist has been completely eliminated is determined by visual inspection, and if it is difficult to track visually, a thin, rigid needle such as a culture needle with a stalk is inserted into the carbon fiber bundle and traced along the longitudinal direction of the carbon fiber bundle to identify any remaining slight twists and make fine adjustments. The measurement is performed three times, and the average value is taken as the twist count of the carbon fiber bundle. If it is difficult to evaluate the twist count of a carbon fiber bundle before manufacturing a unidirectional prepreg, such as when it has already been prepregized, it can be estimated from the helical pitch (cm) of the carbon fiber axis, as described later.

[0052] Specifically, dividing 100 cm by the helical pitch (cm) allows for an approximate calculation of the twist count (turns / m). In fact, according to the inventors' studies, when a carbon fiber bundle with a twist count of 45 turns / m was untwisted and then made into a prepreg, and the carbon fibers were extracted from the unidirectional prepreg by a burning method, and the helical pitch was evaluated using the method described later, and the twist count was calculated, the first time the result was exactly 45.0 turns / m, the second time 46.9 turns / m, and the third time 45.7 turns / m. From these results, it can be seen that when calculating the twist count from the helical pitch, although there is an error of about ±1 turn / m, the twist count that the twisted yarn originally had can be evaluated with a reasonable degree of accuracy, even after untwisting.

[0053] <Helical pitch of the fiber axis of a single carbon fiber> Cut a single carbon fiber to be measured to a length of 10 ± 0.5 cm and place it on a sheet of copy paper laid on a horizontal table. If the single fiber sticks to the copy paper due to static electricity, remove the static charge using a general method. If the single fiber sticks to the copy paper when the copy paper with the single fiber on it is turned upside down and does not separate, static charge removal is insufficient, so remove the static charge further. Visually observe the single fiber from a direction normal to the fiber and parallel to the paper surface, and measure the distance between the points where the single fiber contacts the copy paper. For example, when the helical pitch is 3.0 cm, contact with the copy paper occurs at three points, A, B, and C, as illustrated in Figure 2. In this case, measure the distances AB and BC, and take their average value (3.0 cm) as the helical pitch of the fiber axis of the single carbon fiber.

[0054] Individual values ​​are read to the first decimal place, i.e., the 1mm digit. When calculating the average, if digits beyond the second decimal place appear, the value is retained up to the second decimal place. For example, averaging 2.2cm, 2.3cm, and 2.2cm results in 2.23333...cm, but the average is rounded to the third decimal place to obtain 2.23cm. The helical pitch of the fiber axis of a single carbon fiber is evaluated once for each single fiber being evaluated.

[0055] <Average value of the helical pitch of the fiber axis of carbon fiber> Fifty single fibers are randomly selected from the carbon fiber bundle used in the unidirectional prepreg. If it is difficult to obtain the carbon fiber bundle before the unidirectional prepreg was manufactured, as the prepreg has already been formed, a 13 cm square is cut from the prepreg in the direction of fiber orientation and another 13 cm square perpendicular to it. After burning off the matrix resin in an electric furnace with a nitrogen atmosphere set to 450°C, fifty single fibers are randomly selected from the remaining carbon fiber bundle. The helical pitch of the fiber axis of the obtained single fibers is evaluated using the method described above, and the average value of the fiber axis pitch of the carbon fibers is calculated by averaging the evaluated values ​​of the helical pitch. The average value of the helical pitch is rounded to two decimal places.

[0056] <Variation of the fiber axis fluctuation of carbon fiber> First, 50 single fibers are randomly selected from the carbon fiber bundle used in the unidirectional prepreg. If it is difficult to obtain the carbon fiber bundle before the unidirectional prepreg is manufactured, since it has already been prepregized, a rectangle measuring 1 cm in the fiber orientation direction and 13 cm in the direction perpendicular to it is cut from the prepreg, the matrix resin is burned off in an electric furnace with a nitrogen atmosphere set to 450°C, the remaining carbon fiber bundle is placed in a 50 mL glass container with a lid, and the single fibers are thoroughly mixed by shaking it up and down 50 times, and then 50 single carbon fibers are randomly selected from it.

[0057] Next, a single carbon fiber to be evaluated, 1-5 mm in length, is placed on a sheet of copy paper. If the single fiber sticks to the copy paper due to static electricity, it should be discharged using a general method before proceeding. The fiber is observed from the vertical direction of the paper using an optical microscope, and an image is acquired. The magnification of the optical microscope's objective lens is set to 10x. The image is saved in JPG format with a width of 2592 pixels and a height of 1944 pixels.

[0058] The acquired image is loaded into the open-source image processing software "ImageJ". An arbitrary point on the fiber axis is designated as point A, and a point on the fiber axis 1,000 μm away from point A is designated as point B. Next, "Bilinear Interpolation" is selected as the interpolation algorithm for rotation, and the image is rotated so that points A and B are horizontal. After binarization, skeletonization is performed to extract the fiber axis as a curve with a width of 1 pixel. At this time, if there is dirt or other debris attached to the fiber surface, the fiber axis may appear to branch upwards, but side chains other than the fiber axis are ignored.

[0059] Finally, the residual ΔY (μm) obtained by subtracting the minimum value Ymin from the maximum value Ymax among the Y coordinates through which the fiber axis passes between points A and B is read and is taken as the fluctuation width of the evaluated single fiber. The fluctuation widths evaluated for 50 different single fibers are averaged and adopted as the fluctuation width in this invention.

[0060] In this embodiment, a Leica Microsystems DM2700M upright microscope was used as the optical microscope.

[0061] <Helical direction of the fiber axis of carbon fiber> In the aforementioned method for measuring helical pitch, the helical direction of the carbon fiber axis is identified by visual observation from the fiber axis direction rather than the normal direction of the single fiber. A right-hand thread is the direction in which, when rotated clockwise, progresses toward the back of the clock face, and is also called a Z-winding. A left-hand thread is the opposite and is also called an S-winding.

[0062] <Determination of whether carbon fibers with different helical directions of the fiber axis are mixed in a unidirectional prepreg> At the stage of converting carbon fiber bundles into prepregs, this can be easily confirmed by observing the carbon fiber bundles being fed. Specifically, when the fed carbon fiber bundles are cut to form free ends, the twist is restored in the direction of the twist that the carbon fiber bundle originally held, starting from the free ends. If the direction of this restored twist is the Z-twist direction, the helical direction of the fiber axis is oriented like a right-hand thread, and if it is the S-twist direction, the helical direction of the fiber axis is oriented like a left-hand thread. Therefore, by arbitrarily checking a few to all of the fed carbon fiber bundles, and observing carbon fiber bundles with right-hand threads and carbon fiber bundles with left-hand threads, it can be determined that the prepreg is a unidirectional prepreg consisting of a mixture of carbon fibers with right-hand threads and carbon fibers with left-hand threads.

[0063] On the other hand, if the material has already been made into a prepreg, it can be confirmed whether carbon fibers with different helical directions are mixed together as follows. First, a 13 cm square is cut from the unidirectional prepreg in the direction of fiber orientation and another 13 cm square perpendicular to it. After burning off the matrix resin in an electric furnace with a nitrogen atmosphere set to 450°C, 50 single fibers are randomly selected from the remaining aggregate of carbon fiber bundles. Next, the helical direction of the fiber axis is evaluated using the method described above. Taking experimental errors into consideration, when it is confirmed that there are three or more single fibers with a right-hand helical direction and three or more single fibers with a left-hand helical direction, it is determined that the material is a unidirectional prepreg consisting of a mixture of carbon fibers with a right-hand helical direction and carbon fibers with a left-hand helical direction.

[0064] <The relative abundance of carbon fiber bundles consisting of single fibers whose fiber axis helical direction is in the direction of a right-hand screw> A > At the stage of prepreging carbon fiber bundles, the abundance ratio f can be determined by checking the number of carbon fiber bundles with the fiber axis helical direction in the direction of a right-hand thread and the number of carbon fiber bundles with the fiber axis helical direction in the direction of a left-hand thread for the total number of carbon fiber bundles being fed. A It is possible to identify this.

[0065] If a unidirectional prepreg is already in the state, first, a 13 cm square is cut from the unidirectional prepreg in the direction of fiber orientation and another 13 cm square perpendicular to it. After burning off the matrix resin in an electric furnace with a nitrogen atmosphere set to 450°C, the remaining carbon fiber bundles are visually inspected to identify the individual carbon fiber bundles. Next, three single fibers are taken from each carbon fiber bundle, and the helical direction of the fiber axis is evaluated using the method described above. For a given carbon fiber bundle, the helical direction of the entire carbon fiber bundle is determined by majority vote based on the evaluation results of the helical direction of the fiber axis of the three single fibers taken from that carbon fiber bundle.

[0066] For example, if the evaluation results of the helical direction of the fiber axes of three single fibers taken from a carbon fiber bundle are right-hand thread, right-hand thread, and left-hand thread, then it is determined that the carbon fiber bundle consists of single fibers whose fiber axes have a right-hand helical direction (i.e., a carbon fiber bundle consisting of single fibers whose fiber axes have a right-hand helical direction). A carbon fiber bundle with a basis weight of 1.5 g / m was used to create a carbon fiber with a basis weight of 300 g / m. 2 In the case of a unidirectional prepreg, a width of 13 cm contains an average of 26 carbon fiber bundles. Therefore, if we take three single fibers from each carbon fiber bundle, we will be observing a total of 3 × 26 = 78 single fibers.

[0067] Here, N is the number of carbon fiber bundles consisting of single fibers whose fiber axis helical direction is in the direction of a right-hand screw. A (Number of strands) N is the number of carbon fiber bundles consisting of single fibers whose fiber axis spirals in the direction of a left-hand thread. B (Book) and ratio N A / (N A +N B ) is calculated, and this is used as the ratio of carbon fiber bundles consisting of single fibers whose fiber axis helical direction is in the direction of a right-hand screw. A Let's assume that.

[0068] <Average helical pitch of carbon fiber bundles consisting of single fibers with a right-hand thread orientation, and average helical pitch of carbon fiber bundles consisting of single fibers with a left-hand thread orientation> The relative abundance of carbon fiber bundles consisting of single fibers whose fiber axis helical direction is oriented in the direction of a right-hand screw thread f AIn the evaluation method, the helical pitch of the fiber axis of three single fibers taken from each carbon fiber bundle is evaluated using the method described above. For carbon fiber bundles consisting of single fibers with a right-hand thread direction and carbon fiber bundles consisting of single fibers with a left-hand thread direction, the evaluation values ​​of the helical pitch of the single fibers belonging to each bundle are averaged to calculate the average helical pitch of carbon fiber bundles consisting of single fibers with a right-hand thread direction and the average helical pitch of carbon fiber bundles consisting of single fibers with a left-hand thread direction. The average helical pitch is rounded to two decimal places.

[0069] <Convergence of carbon fiber bundles> The carbon fiber bundle to be evaluated is grasped separately by the right and left hands at a distance of 30 cm in the direction of the fiber axis. After bringing the distance between the gripping points of the right and left hands to 20 cm, the hands are moved up and down vertically multiple times while visually observing the fiber bundle. To keep the vertical height of the gripping points of the right and left hands constant, the vertical movement of both hands is performed at the same time. The vertical movement distance is 10 cm, and this is repeated 20 times at a speed of one back-and-forth motion per second.

[0070] In this test, if the fiber bundle spreads out into single fiber units, the convergence is considered poor (B). As this is a sensory evaluation, a strict line is difficult to draw, but if any part of the fiber bundle spreads out by 5 cm or more perpendicular to the fiber axis, it will be considered to have spread out into single fiber units. In all other cases, the convergence is judged to be good (A). The evaluation will be conducted indoors with as little wind as possible, and the central part of the fiber bundle will be suspended by gravity.

[0071] <Quality of carbon fiber bundles> The quality of the carbon fiber bundle is evaluated as follows: First, the number of broken single fibers visible on the outside of a 3.0m carbon fiber bundle with residual twist after carbonization is counted. The measurement is performed three times, and the number of broken carbon fiber bundles is defined by the following formula based on the total count from the three measurements.

[0072] Number of carbon fiber bundle fractures (pieces / m) = Total count of fractures in all single fibers over 3 cycles (pieces) / 3.0 / 3 Based on the number of carbon fiber bundle fractures obtained in this way, the quality is judged from A to C. A: Less than 3 pieces / m B: 3 pieces / m or more, less than 6 pieces / m C: 6 pieces / m or more.

[0073] <Amount of warping when a unidirectional prepreg is cured in a single layer> The unidirectional prepreg to be evaluated is cut with a cutter or similar tool into a square with dimensions of 13 cm in the direction of the fiber axis and 13 cm perpendicular to the fiber axis. This square is then sandwiched between a stainless steel tool plate and a 13 cm square aluminum pressure plate. After bagging with bag film and sealant, it is cured in an autoclave. The curing reaction is carried out by holding the autoclave at 130°C for 2 hours, then raising the temperature to 180°C and holding it for another 2 hours. The cured material consisting of one layer of unidirectional prepreg is removed, placed on a flat surface, and the amount of warping is measured.

[0074] Specifically, as shown in Figure 3, the amount of warping is measured by pressing any vertex of a square-shaped cured material onto a table with a fingertip, and measuring the distance between the vertex at the diagonal and the top surface of the table. This operation is performed for each of the four vertices, and the maximum distance is taken as the amount of warping. The amount of warping is measured on both sides of the cured material, which consists of one layer of unidirectional prepreg, and the average value is taken as the final amount of warping. The cured material is prepared with N=1. 。

[0075] <Lamination workability of unidirectional prepregs> The unidirectional prepreg to be evaluated is cut to the same size as the warp amount evaluation, and six layers are laminated in a 0° / 90° / 0° / 90° / 0° / 90° pattern. During this lamination process, materials that can be easily laminated without peeling between plies without the need to place weights are rated as "A" for good workability, "D" for poor workability where plies tend to peel unless weights are placed after each layer, "B" for almost no impact on workability where peeling may occur after 10 minutes without weights, but does not immediately peel, and materials that do not fall into any of categories A, C, or D, and "C" for relatively poor workability where peeling may occur within 5 minutes without weights. The evaluation is conducted at room temperature of 25±5℃, and the unidirectional prepreg is evaluated after being allowed to acclimate to this room temperature for 12 hours. The evaluation is performed twice, and the lower score is adopted.

[0076] <Tensile modulus of carbon fiber reinforced composite materials> Multiple sheets of the unidirectional prepreg to be evaluated are laminated with the fiber direction aligned in one direction, and the resin is cured by processing at a temperature of 130°C and a pressure of 0.3 MPa for 2 hours to obtain a laminated board (fiber-reinforced composite material) with a thickness of 1 mm. From this laminated board, rectangular test specimens with a thickness of 1 mm, a width of 15 mm, and a length of 250 mm are cut out. Reinforcement plates are fixed to both ends of the test specimen in the longitudinal direction (56 mm from each end) with adhesive or the like.

[0077] In accordance with ASTM D3039 (2008), the tensile modulus was measured for a given number of test specimens at a tensile speed of 2.0 mm / min, and the obtained tensile modulus was converted to that for a fiber volume fraction of 60%. The measurement was performed for n=6, and the average value was taken as the tensile modulus of the carbon fiber reinforced composite material in this invention.

[0078] <Compressive strength of carbon fiber reinforced composite materials at 0°> Multiple sheets of the unidirectional prepreg to be evaluated are laminated with the fiber direction aligned in one direction, and the resin is cured by processing at a temperature of 130°C and a pressure of 0.3 MPa for 2 hours to obtain a laminated board (fiber-reinforced composite material) with a thickness of 1 mm. From this laminated board, a rectangular test piece with a thickness of 1 mm, a width of 12.7 mm, a length of 80 mm, and a gauge section length of 5 mm is cut out. Reinforcement plates are fixed to both ends of the test piece in the longitudinal direction (37.5 mm from each end) with adhesive or the like.

[0079] In accordance with ASTM D695 (1996), the compressive strength of a given number of test specimens was measured under a strain rate of 1.27 mm / min, and the obtained compressive strength was converted to that for a fiber volume fraction of 60%. Measurements were taken with n=6, and the average value was taken as the 0° compressive strength of the carbon fiber reinforced composite material in this invention. [Examples]

[0080] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

[0081] Examples 1 to 19, Comparative Examples 1 to 7, and Reference Examples 1 and 2 described below were carried out using the methods described in the following comprehensive Examples 1 to 4 and 5, under the conditions listed in Table 1.

[0082] [Comprehensive Example 1] In the comprehensive example described in Table 2019 / 244830, flame-resistant fiber bundles were obtained in the same manner, except that eight carbon fiber precursor fiber bundles were bonded together to obtain 24,000 single fibers prior to obtaining the flame-resistant fiber bundles, and the oven conditions were set to an air atmosphere of 230-270°C.

[0083] [Comprehensive Example 2] In the comprehensive example described in Table 2019 / 244830, flame-resistant fiber bundles were obtained in the same manner as described above, except that the single fiber fineness of the carbon fiber precursor fiber bundles was set to 0.8 dtex, and eight carbon fiber precursor fiber bundles were bonded together to obtain 24,000 single fibers prior to obtaining the flame-resistant fiber bundles.

[0084] [Comprehensive Example 3] Flame-resistant fiber bundles were obtained in the same manner as in the comprehensive examples described in Table 2019 / 244830, except that the single fiber fineness of the carbon fiber precursor fiber bundle was set to 0.8 dtex.

[0085] [Comprehensive Example 4] Flame-resistant fiber bundles were obtained in the same manner as the comprehensive examples described in Table 2019 / 244830.

[0086] [Comprehensive Example 5] An epoxy resin composition was prepared by applying 50 parts by mass of N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenylmethane ("Araldite®" MY720, manufactured by Huntsman Advanced Materials Co., Ltd.), 50 parts by mass of bisphenol A type epoxy resin ("jER®" 825, manufactured by Mitsubishi Chemical Corporation), 40 parts by mass of 3,3'-diaminodiphenyl sulfone (3,3'-DDS, manufactured by Mitsui Chemicals Fine Co., Ltd.), and 10 parts by mass of polyethersulfone (PES5003P, manufactured by Sumitomo Chemical Co., Ltd.) onto release paper using a reverse roll coater to produce a resin film. A bundle of carbon fibers aligned in one direction was sandwiched between the resin films from both the top and bottom, and impregnated with resin by heating and pressurizing, resulting in a carbon fiber basis weight of 300 g / m². 2 A unidirectional prepreg with a carbon fiber content of 65% by mass was obtained.

[0087] [Comprehensive Example 6] An epoxy resin composition was prepared by coating a release paper with 50 parts by mass of triglycidyl-m-aminophenol ("Araldite®" MY0600, manufactured by Huntsman Advanced Materials Co., Ltd.), 20 parts by mass of liquid bisphenol A type epoxy resin ("jER®" 828, manufactured by Mitsubishi Chemical Corporation), 30 parts by mass of phenol novolac type epoxy ("jER®" 154, manufactured by Mitsubishi Chemical Corporation), 6 parts by mass of dicyandiamide (manufactured by Mitsubishi Chemical Corporation), and 3 parts by mass of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (manufactured by Hodogaya Chemical Co., Ltd.) using a reverse roll coater to produce a resin film. A bundle of carbon fibers aligned in one direction was sandwiched between the resin films from both the top and bottom, and impregnated with resin by heating and pressurizing, resulting in a carbon fiber basis weight of 300 g / m². 2 A unidirectional prepreg with a carbon fiber content of 65% by mass was obtained.

[0088] [Example 1] The flame-resistant fiber bundles obtained in Comprehensive Example 1 were subjected to a twisting treatment to produce twisted flame-resistant fiber bundles with a Z twist of 45 turns / m and twisted flame-resistant fiber bundles with a S twist of 45 turns / m. Each twisted flame-resistant fiber bundle was subjected to a pre-carbonization treatment in a nitrogen atmosphere at a temperature of 300-800°C with a draw ratio of 0.97 to obtain pre-carbonized fiber bundles with Z twist and S twist, respectively. Next, these pre-carbonized fiber bundles were subjected to a carbonization treatment in a nitrogen atmosphere at a temperature of 1,000-1,800°C under the tensions shown in Table 1 while appropriately adjusting the draw ratio, to obtain carbon fiber bundles with excellent convergence and quality, having the single fiber fineness, tensile modulus, average helical pitch, and single fiber fluctuation width shown in Table 1.

[0089] Carbon fiber bundles with Z-twist and carbon fiber bundles with S-twist were untwisted to an untwisted state, and then prepregized according to Comprehensive Example 5. During prepregization, carbon fiber bundles with Z-twist and carbon fiber bundles with S-twist were arranged in a 1:1 ratio by number, alternating as much as possible. The average values ​​of various helical pitches obtained by analyzing the unidirectional prepreg, and the abundance of carbon fiber bundles consisting of carbon fibers whose fiber axis helical direction is in the direction of a right-hand thread f A The warping and lamination workability of the unidirectional prepreg were as shown in Table 2.

[0090] [Example 2] Except for setting the number of twists for the Z-twist to 25 turns / m and the number of twists for the S-twist to 25 turns / m, and fine-tuning the draw ratio and tension during the carbonization treatment, the same procedure as in Example 1 was followed to obtain a carbon fiber bundle with excellent convergence and quality, exhibiting the single fiber fineness, tensile modulus, average helical pitch, and single fiber fluctuation width shown in Table 1. Next, a unidirectional prepreg was prepared in the same manner as in Example 1. The analysis results of the carbon fiber bundle constituting the unidirectional prepreg and the unidirectional prepreg are shown in Table 2.

[0091] [Example 3] A carbon fiber bundle with excellent convergence and quality was obtained in the same manner as in Example 1, except that the number of twists for the Z-twist was set to 15 turns / m and the number of twists for the S-twist was set to 15 turns / m, and the stretch ratio and tension in the carbonization treatment were finely adjusted. The single fiber fineness, tensile modulus, average values ​​of helical pitch and single fiber fluctuation width are shown in Table 1. Next, a unidirectional prepreg was prepared in the same manner as in Example 1, except that the carbon fiber bundles with Z-twist and carbon fiber bundles with S-twist were arranged in a ratio of 3:7 by the number of fibers in the [ZSSZSSZSSS] arrangement (meaning that the carbon fiber bundles with different twist directions are arranged in the width direction of the unidirectional prepreg from one end to the other). The analysis results of the carbon fiber bundles constituting the unidirectional prepreg and the unidirectional prepreg are shown in Table 2.

[0092] [Example 4] Except for setting the number of twists for the Z-twist to 45 turns / m and the number of twists for the S-twist to 30 turns / m, the same procedure as in Example 3 was followed to obtain carbon fiber bundles with excellent convergence and quality, exhibiting the single fiber fineness, tensile modulus, average helical pitch, and single fiber fluctuation width shown in Table 1. Next, a unidirectional prepreg was prepared in the same procedure as in Example 1, except that the carbon fiber bundles with Z-twist and carbon fiber bundles with S-twist were arranged in a [ZSZSS] pattern in a ratio of 2:3 by number. The analysis results of the carbon fiber bundles constituting the unidirectional prepreg and the unidirectional prepreg are shown in Table 2.

[0093] [Example 5] Except for setting the number of twists for the Z-twist to 45 turns / m and the number of twists for the S-twist to 25 turns / m, the same procedure as in Example 3 was used to obtain carbon fiber bundles with excellent convergence and quality, having the single fiber fineness, tensile modulus, average helical pitch, and single fiber fluctuation width shown in Table 1. Next, a unidirectional prepreg was prepared in the same procedure as in Example 1, except that the carbon fiber bundles with Z-twist and carbon fiber bundles with S-twist were arranged in a ratio of 3:7 by number in the pattern [ZSSZSSZSSS]. The analysis results of the carbon fiber bundles constituting the unidirectional prepreg and the unidirectional prepreg are shown in Table 2.

[0094] [Example 6] Except for setting the number of twists for the Z-twist to 25 turns / m and the number of twists for the S-twist to 25 turns / m, the same procedure as in Example 1 was followed to obtain carbon fiber bundles with excellent convergence and quality, exhibiting the single fiber fineness, tensile modulus, average helical pitch, and single fiber fluctuation width shown in Table 1. Next, a unidirectional prepreg was prepared in the same procedure as in Example 1, except that the carbon fiber bundles with Z-twist and carbon fiber bundles with S-twist were arranged in a [ZSZSZ] pattern in a ratio of 3:2 by number. The analysis results of the carbon fiber bundles constituting the unidirectional prepreg and the unidirectional prepreg are shown in Table 2.

[0095] [Example 7] The flame-resistant fiber bundles obtained in Comprehensive Example 2 were subjected to a twisting treatment to produce twisted flame-resistant fiber bundles with a Z twist of 30 turns / m and twisted flame-resistant fiber bundles with a S twist of 30 turns / m. Each twisted flame-resistant fiber bundle was subjected to a pre-carbonization treatment in a nitrogen atmosphere at a temperature of 300-800°C with a draw ratio of 0.97 to obtain pre-carbonized fiber bundles with Z twist and S twist, respectively. Next, these pre-carbonized fiber bundles were subjected to a carbonization treatment in a nitrogen atmosphere at a temperature of 1,000-1,800°C under the tensions shown in Table 1 while appropriately adjusting the draw ratio, to obtain carbon fiber bundles with excellent convergence and quality, having the single fiber fineness, tensile modulus, average helical pitch, and single fiber fluctuation width shown in Table 1.

[0096] Carbon fiber bundles with Z-twist and carbon fiber bundles with S-twist were untwisted to an untwisted state, and then prepreged according to Comprehensive Example 5. During prepreg formation, carbon fiber bundles with Z-twist and carbon fiber bundles with S-twist were arranged in a 1:1 ratio by number, alternating as much as possible. The analysis results of the carbon fiber bundles constituting the unidirectional prepreg and the unidirectional prepreg are shown in Table 2.

[0097] [Example 8] Except for setting the number of twists in the Z-twist to 15 turns / m and the number of twists in the S-twist to 30 turns / m, and fine-tuning the stretch ratio and tension in the carbonization treatment, carbon fiber bundles with excellent convergence and quality, exhibiting the single fiber fineness, tensile modulus, average helical pitch, and single fiber fluctuation width shown in Table 1 were obtained in the same manner as in Example 7. Next, a unidirectional prepreg was prepared in the same manner as in Example 7, except that the carbon fiber bundles with Z-twist and carbon fiber bundles with S-twist were arranged in a [ZSZSZ] pattern in a ratio of 3:2 by number. The analysis results of the carbon fiber bundles constituting the unidirectional prepreg and the unidirectional prepreg are shown in Table 2.

[0098] [Example 9] Except for setting the number of twists for the Z-twist to 75 turns / m and the number of twists for the S-twist to 50 turns / m, and fine-tuning the draw ratio and tension during the carbonization treatment, carbon fiber bundles with excellent convergence and quality, exhibiting the single fiber fineness, tensile modulus, average helical pitch, and single fiber fluctuation width shown in Table 1 were obtained in the same manner as in Example 7. Next, a unidirectional prepreg was prepared in the same manner as in Example 7, except that the carbon fiber bundles with Z-twist and carbon fiber bundles with S-twist were arranged in a [ZSZSS] pattern in a ratio of 2:3 by number. The analysis results of the carbon fiber bundles constituting the unidirectional prepreg and the unidirectional prepreg are shown in Table 2.

[0099] [Example 10] Except for setting the number of twists for the Z-twist to 75 turns / m and the number of twists for the S-twist to 15 turns / m, and fine-tuning the draw ratio and tension during the carbonization treatment, a carbon fiber bundle with excellent convergence and quality was obtained, having the single fiber fineness, tensile modulus, average helical pitch, and single fiber fluctuation width shown in Table 1, in the same manner as in Example 7. Next, a unidirectional prepreg was prepared in the same manner as in Example 7, except that the carbon fiber bundles with Z-twist and carbon fiber bundles with S-twist were arranged in a [ZSSSS] pattern in a ratio of 1:4 by number. The analysis results of the carbon fiber bundles constituting the unidirectional prepreg and the unidirectional prepreg are shown in Table 2.

[0100] [Example 11] Except for setting the number of twists for the Z-twist to 45 turns / m and the number of twists for the S-twist to 15 turns / m, and fine-tuning the stretch ratio and tension during the carbonization treatment, a carbon fiber bundle with excellent convergence and quality, exhibiting the single fiber fineness, tensile modulus, average helical pitch, and single fiber fluctuation width shown in Table 1 was obtained in the same manner as in Example 7. Next, a unidirectional prepreg was prepared in the same manner as in Example 7, except that the carbon fiber bundles with Z-twist and carbon fiber bundles with S-twist were arranged in a [ZSZSZ] pattern in a ratio of 3:2 by number. The analysis results of the carbon fiber bundles constituting the unidirectional prepreg and the unidirectional prepreg are shown in Table 2.

[0101] [Example 12] The basis weight of the carbon fiber in the unidirectional prepreg is 200 g / m².2 Carbon fiber bundles and unidirectional prepregs were prepared in the same manner as in Example 1, except for the following: The carbon fiber bundles constituting the unidirectional prepreg and the analysis results of the unidirectional prepreg are shown in Table 2. Note that the basis weight was 200 g / m². 2 Because the fibers were small, there were sparse gaps between adjacent carbon fiber bundles, and the overlap between adjacent carbon fiber bundles was insufficient. As a result, although overall warping was suppressed, the unidirectional prepreg was prone to bending between adjacent carbon fibers, and the lamination workability was rated as a lower level B.

[0102] [Example 13] The flame-resistant fiber bundles obtained in Comprehensive Example 2 were subjected to a twisting treatment to produce twisted flame-resistant fiber bundles with a Z twist of 45 turns / m and twisted flame-resistant fiber bundles with an S twist of 35 turns / m. Each twisted flame-resistant fiber bundle was subjected to a pre-carbonization treatment in a nitrogen atmosphere at a temperature of 300-800°C with a draw ratio of 0.97 to obtain pre-carbonized fiber bundles with Z twist and S twist, respectively. Next, these pre-carbonized fiber bundles were subjected to a carbonization treatment in a nitrogen atmosphere at a temperature of 1,000-1,800°C while appropriately adjusting the draw ratio and tension to obtain carbon fiber bundles with excellent convergence and quality, having the single fiber fineness, tensile modulus, average helical pitch, and single fiber fluctuation width shown in Table 1.

[0103] Carbon fiber bundles with Z-twist and carbon fiber bundles with S-twist were untwisted to an untwisted state, and then prepregized according to Comprehensive Example 5. During prepregization, the carbon fiber bundles with Z-twist and carbon fiber bundles with S-twist were arranged in a ratio of 7:3 by number, in the pattern [ZZSZZSZZZS]. The analysis results of the carbon fiber bundles constituting the unidirectional prepreg and the unidirectional prepreg are shown in Table 2.

[0104] [Example 14] Except for performing the carbonization treatment in a nitrogen atmosphere at a temperature of 1,000 to 1,400°C while appropriately adjusting the stretch ratio and tension, a carbon fiber bundle with excellent convergence and quality was obtained in the same manner as in Example 1, having the single fiber diameter, tensile modulus, average helical pitch, and single fiber fluctuation width shown in Table 1. It was then made into a prepreg in the same manner as in Example 1. The analysis results of the carbon fiber bundle constituting the unidirectional prepreg and the unidirectional prepreg are shown in Table 2.

[0105] [Example 15] Except for fine-tuning the stretch ratio and tension during the carbonization process, the procedure was the same as in Example 2 to obtain carbon fiber bundles with excellent convergence and quality, possessing the single fiber fineness, tensile modulus, average helical pitch, and single fiber fluctuation width shown in Table 1. Next, the carbon fiber bundles with Z-twist and the carbon fiber bundles with S-twist were untwisted to an untwisted state, and then prepreged according to Comprehensive Example 6. During prepreging, the carbon fiber bundles with Z-twist and the carbon fiber bundles with S-twist were arranged in a 1:1 ratio by number, alternating as much as possible. The analysis results of the carbon fiber bundles constituting the unidirectional prepreg and the unidirectional prepreg are shown in Table 2.

[0106] [Example 16] The flame-resistant fiber bundles obtained in Comprehensive Example 2 were subjected to a twisting treatment to create twisted flame-resistant fiber bundles with a Z twist of 15 turns / m. These twisted flame-resistant fiber bundles were subjected to a pre-carbonization treatment in a nitrogen atmosphere at a temperature of 300-800°C with a draw ratio of 0.97 to obtain Z-twisted pre-carbonized fiber bundles. Next, these pre-carbonized fiber bundles were subjected to a carbonization treatment in a nitrogen atmosphere at a temperature of 1,000-1,800°C while appropriately adjusting the draw ratio and tension to obtain carbon fiber bundles with excellent convergence and quality, having the single fiber fineness, tensile modulus, average helical pitch, and single fiber fluctuation width shown in Table 1.

[0107] Carbon fiber bundles with Z-twist were untwisted to an untwisted state, and then prepreged according to Comprehensive Example 5. The analysis results of the carbon fiber bundles constituting the unidirectional prepreg and the unidirectional prepreg are shown in Table 2.

[0108] [Example 17] The flame-resistant fiber bundles obtained in Comprehensive Example 3 were subjected to a twisting treatment to create twisted flame-resistant fiber bundles with a Z twist of 20 turns / m. These twisted flame-resistant fiber bundles were subjected to a pre-carbonization treatment in a nitrogen atmosphere at a temperature of 300-800°C with a draw ratio of 0.97 to obtain Z-twisted pre-carbonized fiber bundles. Next, these pre-carbonized fiber bundles were subjected to a carbonization treatment in a nitrogen atmosphere at a temperature of 1,000-1,800°C while appropriately adjusting the draw ratio and tension to obtain carbon fiber bundles with excellent convergence and quality, having the single fiber fineness, tensile modulus, average helical pitch, and single fiber fluctuation width shown in Table 1.

[0109] Carbon fiber bundles with Z-twist were untwisted to an untwisted state, and then prepreged according to Comprehensive Example 5. The analysis results of the carbon fiber bundles constituting the unidirectional prepreg and the unidirectional prepreg are shown in Table 2.

[0110] [Example 18] Except for setting the number of Z twists to 25 turns / m, the carbon fiber bundles with excellent convergence and quality were obtained in the same manner as in Example 17, having the single fiber fineness, tensile modulus, average helical pitch, and single fiber fluctuation width shown in Table 1. Next, a unidirectional prepreg was prepared in the same manner as in Example 17. The carbon fiber bundles constituting the unidirectional prepreg and the analysis results of the unidirectional prepreg are shown in Table 2.

[0111] [Example 19] Except for setting the number of Z twists to 30 turns / m, the carbon fiber bundles with excellent convergence and quality were obtained in the same manner as in Example 17, having the single fiber fineness, tensile modulus, average helical pitch, and single fiber fluctuation width shown in Table 1. Next, a unidirectional prepreg was prepared in the same manner as in Example 17. The carbon fiber bundles constituting the unidirectional prepreg and the analysis results of the unidirectional prepreg are shown in Table 2.

[0112] [Example 20] In the same manner as in Example 18, carbon fiber bundles with excellent convergence and quality were obtained, having the average values ​​of single fiber fineness, tensile modulus, helical pitch, and single fiber fluctuation width shown in Table 1. Next, the Z-twisted carbon fiber bundles were untwisted to an untwisted state, and then prepreged according to Comprehensive Example 6. The analysis results of the carbon fiber bundles constituting the unidirectional prepreg and the unidirectional prepreg are shown in Table 2.

[0113] [Comparative Example 1] The flame-resistant fiber bundle obtained in Comprehensive Example 1 was subjected to a twisting treatment to create a twisted flame-resistant fiber bundle with a Z twist of 35 turns / m. This twisted flame-resistant fiber bundle was subjected to a pre-carbonization treatment in a nitrogen atmosphere at a temperature of 300-800°C with a draw ratio of 0.97 to obtain a Z-twisted pre-carbonized fiber bundle. Next, this pre-carbonized fiber bundle was subjected to a carbonization treatment in a nitrogen atmosphere at a temperature of 1,000-1,800°C while appropriately adjusting the draw ratio and tension to obtain a carbon fiber bundle with excellent convergence and quality, having the single fiber fineness, tensile modulus, average helical pitch, and single fiber fluctuation width shown in Table 3.

[0114] After untwisting the Z-twisted carbon fiber bundles to an untwisted state, they were made into a prepreg according to Comprehensive Example 5. The analysis results of the carbon fiber bundles constituting the unidirectional prepreg and the unidirectional prepreg are shown in Table 4.

[0115] [Comparative Example 2] Except for setting the number of Z twists to 20 turns / m, the carbon fiber bundles with excellent convergence and quality were obtained in the same manner as in Comparative Example 1, having the single fiber fineness, tensile modulus, average helical pitch, and single fiber fluctuation width shown in Table 3. Next, a unidirectional prepreg was prepared in the same manner as in Comparative Example 1. The carbon fiber bundles constituting the unidirectional prepreg and the analysis results of the unidirectional prepreg are shown in Table 4.

[0116] [Comparative Example 3] The flame-resistant fiber bundles obtained in Comprehensive Example 2 were subjected to a twisting treatment to create twisted flame-resistant fiber bundles with a Z twist of 25 turns / m. These twisted flame-resistant fiber bundles were subjected to a pre-carbonization treatment in a nitrogen atmosphere at a temperature of 300-800°C with a draw ratio of 0.97 to obtain Z-twisted pre-carbonized fiber bundles. Next, these pre-carbonized fiber bundles were subjected to a carbonization treatment in a nitrogen atmosphere at a temperature of 1,000-1,800°C while appropriately adjusting the draw ratio and tension to obtain carbon fiber bundles with excellent convergence and quality, having the single fiber fineness, tensile modulus, average helical pitch, and single fiber fluctuation width shown in Table 3.

[0117] After untwisting the Z-twisted carbon fiber bundles to an untwisted state, they were made into a prepreg according to Comprehensive Example 5. The analysis results of the carbon fiber bundles constituting the unidirectional prepreg and the unidirectional prepreg are shown in Table 4.

[0118] [Comparative Example 4] Except for setting the number of Z twists to 45 turns / m, the carbon fiber bundles with excellent convergence and quality were obtained in the same manner as in Comparative Example 3, having the single fiber fineness, tensile modulus, average helical pitch, and single fiber fluctuation width shown in Table 3. Next, a unidirectional prepreg was prepared in the same manner as in Comparative Example 3. The carbon fiber bundles constituting the unidirectional prepreg and the analysis results of the unidirectional prepreg are shown in Table 4.

[0119] [Comparative Example 5] The flame-resistant fiber bundles obtained in Comprehensive Example 4 were subjected to a twisting treatment to create twisted flame-resistant fiber bundles with a Z twist of 5 turns / m. These twisted flame-resistant fiber bundles were subjected to a pre-carbonization treatment in a nitrogen atmosphere at a temperature of 300-800°C with a draw ratio of 0.97 to obtain Z-twisted pre-carbonized fiber bundles. Next, these pre-carbonized fiber bundles were subjected to a carbonization treatment in a nitrogen atmosphere at a temperature of 1,000-1,900°C while appropriately adjusting the draw ratio and tension to obtain carbon fiber bundles having the single fiber fineness, tensile modulus, average helical pitch, and single fiber fluctuation width shown in Table 3. The obtained carbon fiber bundles had excellent convergence properties, but their quality was poor.

[0120] Carbon fiber bundles with Z-twist were untwisted to an untwisted state and then prepreged according to Comprehensive Example 5. The analysis results of the carbon fiber bundles constituting the unidirectional prepreg and the unidirectional prepreg are shown in Table 4. Although there were no problems with lamination workability, the quality of the unidirectional prepreg was also reduced due to the poor quality of the carbon fiber bundles.

[0121] [Comparative Example 6] Except for setting the number of Z twists to 10 turns / m, carbon fiber bundles with the average values ​​of single fiber fineness, tensile modulus, helical pitch, and single fiber fluctuation width shown in Table 3 were obtained in the same manner as in Comparative Example 5. The obtained carbon fiber bundles had excellent convergence, but the quality was somewhat poor. Next, a unidirectional prepreg was prepared in the same manner as in Comparative Example 5. The analysis results of the carbon fiber bundles constituting the unidirectional prepreg and the unidirectional prepreg are shown in Table 4. There were no problems with lamination workability, but because the quality of the carbon fiber bundles was somewhat poor, the quality of the unidirectional prepreg was also somewhat reduced.

[0122] [Comparative Example 7] Except for setting the number of Z twists to 5 turns / m, carbon fiber bundles with the average values ​​of single fiber fineness, tensile modulus, helical pitch, and single fiber fluctuation width shown in Table 3 were obtained in the same manner as in Example 17. The obtained carbon fiber bundles had excellent convergence but poor quality. Next, a unidirectional prepreg was prepared in the same manner as in Example 17. The analysis results of the carbon fiber bundles constituting the unidirectional prepreg and the unidirectional prepreg are shown in Table 4. There were no problems with lamination workability, but the quality of the unidirectional prepreg was also reduced due to the poor quality of the carbon fiber bundles.

[0123] [Comparative Example 8] The flame-resistant fiber bundles obtained in Comprehensive Example 3 were subjected to a twisting treatment to impart a Z-twist of 45 turns / m to produce twisted flame-resistant fiber bundles. These twisted flame-resistant fiber bundles were subjected to a pre-carbonization treatment in a nitrogen atmosphere at a temperature of 300-800°C with a draw ratio of 0.97 to obtain Z-twisted pre-carbonized fiber bundles. Next, these pre-carbonized fiber bundles were subjected to a carbonization treatment in a nitrogen atmosphere at a temperature of 1,000-1,400°C while appropriately adjusting the draw ratio and tension to obtain carbon fiber bundles with excellent convergence and quality, having the single fiber fineness, tensile modulus, average helical pitch, and single fiber fluctuation width shown in Table 3.

[0124] After untwisting the Z-twisted carbon fiber bundles to an untwisted state, they were made into a prepreg according to Comprehensive Example 5. The analysis results of the carbon fiber bundles constituting the unidirectional prepreg and the unidirectional prepreg are shown in Table 4.

[0125] [Comparative Example 9] Except for performing the carbonization treatment in a nitrogen atmosphere at a temperature of 1,000 to 1,400°C while appropriately adjusting the stretch ratio and tension, a carbon fiber bundle with excellent convergence and quality was obtained in the same manner as in Comparative Example 1, having the single fiber fineness, tensile modulus, average values ​​of helical pitch, and single fiber fluctuation width shown in Table 3.

[0126] After untwisting the Z-twisted carbon fiber bundles to an untwisted state, they were made into a prepreg according to Comprehensive Example 6. The analysis results of the carbon fiber bundles constituting the unidirectional prepreg and the unidirectional prepreg are shown in Table 4.

[0127] [Reference example 1] Commercially available high modulus carbon fiber "Torayca®" M40JB-12,000 (Toray Industries, Inc.) was prepared as a prepreg according to Comprehensive Example 5. The carbon fiber bundles constituting the unidirectional prepreg and the analysis results of the unidirectional prepreg are shown in Table 4.

[0128] [Reference example 2] Commercially available high modulus carbon fiber "Torayca®" T700SC-24,000 (Toray Industries, Inc.) was prepared as a prepreg according to Comprehensive Example 5. The carbon fiber bundles constituting the unidirectional prepreg and the analysis results of the unidirectional prepreg are shown in Table 4.

[0129] [Example 21] The evaluation results for the tensile modulus and 0° compressive strength of the carbon fiber reinforced composite material obtained by laminating and curing the unidirectional prepreg of Example 15 are shown in Table 5, and both equations (4) and (5) were satisfied. Furthermore, the lamination workability of the unidirectional prepreg was good, and there were no particular problems in the preparation of the test specimens.

[0130] [Example 22] The evaluation results for the tensile modulus and 0° compressive strength of the carbon fiber reinforced composite material obtained by laminating and curing the unidirectional prepreg of Example 20 are shown in Table 5, and both equations (4) and (5) were satisfied. Furthermore, the lamination workability of the unidirectional prepreg was good, and there were no particular problems in the preparation of the test specimens.

[0131] [Comparative Example 10] The evaluation results for the tensile modulus and 0° compressive strength of the carbon fiber reinforced composite material obtained by laminating and curing the unidirectional prepreg of Comparative Example 9 are shown in Table 5, and equations (4) and (5) were not satisfied. Furthermore, the lamination workability of the unidirectional prepreg was poor, and care had to be taken during the preparation of the test specimens to ensure that the relative positions of the prepregs did not shift.

[0132] [Reference example 3] The evaluation results for the tensile modulus and 0° compressive strength of the carbon fiber reinforced composite material obtained by prepregizing commercially available high modulus carbon fiber "Torayca®" M40JB-12,000 (Toray Industries, Inc.) according to Comprehensive Example 6, followed by lamination and curing, are shown in Table 5, and equation (5) was not satisfied.

[0133] [Table 1]

[0134] [Table 2]

[0135] [Table 3]

[0136] [Table 4]

[0137] [Table 5] [Industrial applicability]

[0138] According to the present invention, even when a twisted yarn with a high number of twists is untwisted and made into a prepreg, warping is effectively suppressed, thereby obtaining a unidirectional prepreg with excellent lamination workability. [Explanation of symbols]

[0139] 1: Single carbon fiber 2: Copy paper A: Contact point A B: Contact point B C: Contact point C 3: Unidirectional prepreg cured in a single layer 4: The top surface of a flat table D: Any vertex D E: Vertex E located at the diagonal of any given vertex. F: Distance between the top surface of the flat platform and vertex E (amount of curvature) 5: Weight

Claims

1. A unidirectional prepreg comprising carbon fibers and a matrix resin, wherein the average helical pitch of the fiber axes of the carbon fibers is 7.00 cm or less, and satisfies (i) and / or (ii), and the amount of warping when the prepreg is cut into a 13 cm x 13 cm square, cured in a single layer by holding at 130°C for 2 hours in an autoclave, and then raising the temperature to 180°C and holding for another 2 hours, is 4.0 mm or less. (i) A mixture of carbon fibers in which the helical direction of the fiber axis is oriented in the direction of a right-hand thread, and carbon fibers in which the helical direction of the fiber axis is oriented in the direction of a left-hand thread. (ii) The carbon fiber has an average single fiber diameter of 6.0 μm or less, and the fluctuation width of the fiber axis when observed from the side within a straight-line distance of 1 mm is less than 3.0 μm.

2. The number of twists in a carbon fiber bundle consisting of single fibers satisfying (i) above, where the helical direction of the fiber axis is oriented in the direction of a right-hand thread, is A (turns / m), the number of twists in a carbon fiber bundle consisting of single fibers where the helical direction of the fiber axis is oriented in the direction of a left-hand thread, is B (turns / m), and the ratio of carbon fiber bundles consisting of single fibers where the helical direction of the fiber axis is oriented in the direction of a right-hand thread is f. Ａ The unidirectional prepreg according to claim 1, wherein when the average value of the single fiber diameter of these carbon fibers is d (μm), the formula (1) is satisfied. d ６ ÷10 ５ ×|A×f Ａ -B×(1-f) Ａ )| ≦ 5.5 ・・・Form (1) (Ratio f Ａ is the number of carbon fiber bundles composed of single fibers with the helical direction of the fiber axis being the right-handed direction, denoted as N Ａ (number of bundles), and the number of carbon fiber bundles composed of single fibers with the helical direction of the fiber axis being the left-handed direction is N Ｂ (number of bundles). When calculated, the ratio N Ａ / (N Ａ + N Ｂ ).)

3. The number of twists in a carbon fiber bundle consisting of single fibers satisfying (i) above, where the helical direction of the fiber axis is oriented in the direction of a right-hand thread, is A (turns / m), the number of twists in a carbon fiber bundle consisting of single fibers where the helical direction of the fiber axis is oriented in the direction of a left-hand thread, is B (turns / m), and the ratio of carbon fiber bundles consisting of single fibers where the helical direction of the fiber axis is oriented in the direction of a right-hand thread is f. Ａ The unidirectional prepreg according to claim 1 or 2, wherein when the average value of the single fiber diameters of these carbon fibers is d (μm), the formula (2) is satisfied. C×(d) ２ ÷24-1)-4 ≦ 0 ・・・Formula (2) (However, C = |A × f Ａ -B × (1 - f Ａ ) | is) (ratio f Ａ N is the number of carbon fiber bundles consisting of single fibers whose fiber axis helical direction is in the direction of a right-hand screw. Ａ (Number of strands), the number of carbon fiber bundles consisting of single fibers whose fiber axis spirals in the direction of a left-hand thread, N Ｂ The ratio N calculated when (book) is used. Ａ / (N Ａ +N Ｂ (This refers to)

4. The number of carbon fiber bundles consisting of single fibers that satisfy (i) above and whose fiber axis helical direction is in the direction of a right-hand screw is N. Ａ (Number of strands), the number of carbon fiber bundles consisting of single fibers whose fiber axis spirals in the direction of a left-hand thread, N Ｂ When (book), ratio N Ａ / (N Ａ +N Ｂ The unidirectional prepreg according to claim 1 or 2, wherein the ratio is 0.4 to 0.

6.

5. α (cm) is the average helical pitch of the carbon fiber axis, and N is the number of single fibers contained in the carbon fiber bundle. α (This refers to the unidirectional prepreg according to claim 1, wherein when the average value of the single fiber diameter of the carbon fiber is d (μm), the formula (3) is satisfied. 1.0 ≤ d ２ × N α ÷ (α ２ × 10 ４ ) ≤ 4.0 ··· Equation (3)

6. The basis weight of the carbon fiber is 250 g / m ２ The above describes the unidirectional prepreg according to claim 1 or 2.

7. The unidirectional prepreg according to claim 1 or 2, wherein the average value of the helical pitch of the fiber axes of the carbon fibers is 6.00 cm or less.

8. A carbon fiber reinforced composite material obtained by laminating unidirectional prepregs according to claim 1 or 2.

9. The carbon fiber reinforced composite material according to claim 8, wherein the tensile modulus is X (GPa) and the 0° compressive strength is Y (GPa), and the equations (4) and (5) are satisfied. X≧150...Formula (4) Y×X ≧320...Formula (5)

10. A tubular body made of carbon fiber reinforced composite material, comprising the carbon fiber reinforced composite material described in claim 9.

11. A yacht mast comprising a tubular body made of carbon fiber reinforced composite material as described in claim 10.

Images