Carbon fiber bundle, prepreg, and carbon fiber reinforced composite material

Abstract

To provide carbon fiber bundles that satisfy high levels of tensile elasticity, strength, and adhesiveness.SOLUTION: Carbon fiber bundles that satisfy all of the following (i) to (iv). (i) Composed of single fibers with an average fiber axis fluctuation width of 1.2 μm or more. (ii) The crystal size Lc, evaluated by bulk measurement of the entire fiber bundle, is 3.0 nm or less, and the crystal orientation π002 satisfies the following equation. π002>4.0×Lc+73.2...Equation (1). (iii) The average O / C ratio of the single fiber surface in the fiber bundle is 0.08 or greater. (iv) The average value of the fiber axis spiral pitch of the single fiber is 3.8 cm or greater.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a carbon fiber bundle having a surface structure advantageous for adhesion to a matrix resin and exhibiting high physical properties of a composite material because of its high elastic modulus and high strength.

Background Art

[0002] Carbon fibers are lightweight and excellent in strength and elastic modulus. Therefore, as composite materials combined with various matrix resins, they are used in many fields such as aircraft members, spacecraft members, automobile members, ship members, civil engineering and construction materials, and sports goods.

[0003] In recent years, the scope of its application has been expanding. In industrial applications, while maintaining the high mechanical properties of carbon fibers, the same economy as current materials such as metal materials and glass fiber reinforced composite materials is required. To meet this need, not only the cost reduction of expensive carbon fibers but also the weight reduction of structural members (reduction in the amount of members used) by further improving the mechanical properties of carbon fibers, and the reduction in the amount of carbon fibers used accompanying the weight reduction are desired.

[0004] In order to reduce the amount of carbon fibers used as described above, it is most effective to improve the tensile elastic modulus of carbon fibers that governs the rigidity of carbon fiber reinforced composite materials, and it is also important to achieve both the strength of carbon fibers and the adhesive strength to matrix resins.

[0005] In Patent Document 1, when surface-treating a high elastic modulus fiber with advanced graphitization, since the surface is inert, it is necessary to enhance the electrolytic treatment. However, it is mentioned that the introduction of oxygen functional groups increases the surface fragile layer, which is accompanied by a decrease in strength. Therefore, a technique is proposed in which, by performing two-stage electrolytic treatment with different electrolytes, a large number of oxygen functional groups with high adhesiveness to the matrix resin are introduced onto the surface of the carbon fiber, while suppressing the increase in the surface fragile layer, thereby increasing the adhesive strength without reducing the strength. In Patent Document 2, although it is pitch-based carbon fiber, by controlling the active surface area of the carbon fiber, the adhesive strength is efficiently improved without excessively increasing the surface oxygen molecule concentration. Thereby, a technique for obtaining high elastic modulus and high adhesion carbon fiber while suppressing a decrease in strength is proposed.

[0006] On the other hand, it is known that increasing the drawing tension in the carbonization process is effective in improving the orientation degree π 002 of the obtained carbon fiber bundle. However, simply increasing the drawing tension induces the generation of fluff and thread breakage, inevitably leading to a decrease in operability and a decrease in the quality of the obtained carbon fiber bundle. In Patent Document 3, by increasing the molecular weight of the polyacrylonitrile polymer, and in Patent Documents 4 to 6, by adding entanglement or twist to the fiber bundle in the carbonization process, a technique is proposed to suppress the generation of fluff even at high drawing tensions and increase the orientation degree π 002 of the obtained carbon fiber bundle.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] However, the background art has the following problems.

[0009] Patent Document 1 can treat intermediate modulus carbon fibers before and after with an elastic modulus of 350 tf / mm to have high strength and high adhesion by dividing the electrolysis treatment into two different stages of electrolytic solutions. However, when obtaining carbon fibers with an even higher elastic modulus, there is a high possibility that a decrease in strength is inevitable, the process is complicated, and productivity is low, resulting in an increase in cost, which has also been a problem. 2 Further, according to Patent Document 2, by controlling the surface oxygen molecule concentration of oxidized fibers, the active surface area of the obtained carbon fibers is increased, and high-adhesion carbon fibers can be obtained even with low electric field treatment. However, the tensile strength of the untreated carbon fibers is as low as 3.5 GPa, which is not satisfactory in terms of physical properties.

[0010] In the invention described in Patent Document 3, by increasing the molecular weight of the polyacrylonitrile polymer, the carbonization drawability is improved, and the tensile elastic modulus is improved. However, the single fiber strength is not satisfactory, and further, since the processability of the precursor fiber decreases, the cost increases, which has been a problem.

[0011] In the inventions described in Patent Documents 4 to 6, by imparting entanglement or twist to the fiber bundle in the carbonization process, the carbonization drawability can be enhanced, and the tensile elastic modulus can be improved without increasing the heat treatment temperature. Therefore, since the crystallite size L in the carbon fibers could be suppressed, it was advantageous for achieving both strength, adhesiveness, and tensile elastic modulus. However, in the electrolysis treatment carried out to enhance the adhesiveness, uneven treatment was likely to occur in the twisted fiber bundle, and there was a problem that it was difficult to effectively enhance the adhesiveness.

[0012] In the inventions described in Patent Documents 4 to 6, by imparting entanglement or twist to the fiber bundle in the carbonization process, the carbonization drawability can be enhanced, and the tensile elastic modulus can be improved without increasing the heat treatment temperature. Therefore, since the crystallite size L in the carbon fibers could be suppressed, it was advantageous for achieving both strength, adhesiveness, and tensile elastic modulus. However, in the electrolysis treatment carried out to enhance the adhesiveness, uneven treatment was likely to occur in the twisted fiber bundle, and there was a problem that it was difficult to effectively enhance the adhesiveness. c was suppressed, which was advantageous for achieving both strength, adhesiveness, and tensile elastic modulus. However, in the electrolysis treatment carried out to enhance the adhesiveness, uneven treatment was likely to occur in the twisted fiber bundle, and there was a problem that it was difficult to effectively enhance the adhesiveness.

[0013] That is, improvement in the physical properties of carbon fiber reinforced composite materials by increasing the high elastic modulus of carbon fibers has been studied. However, it has been difficult to achieve both the strength of carbon fibers and the adhesiveness with the matrix resin, and the improvement in the physical properties of carbon fiber reinforced composite materials has been limited. Therefore, the problem to be solved by the present invention is to obtain a carbon fiber bundle that satisfies high levels of tensile elastic modulus, strength, and adhesiveness.

Means for Solving the Problems

[0014] The present invention for solving the above problems is as follows. (1) A carbon fiber bundle that satisfies all of the following (i) to (iv). (i) It is composed of single fibers with an average value of the fluctuation width of the fiber axis of 1.2 μm or more. (ii) The crystallite size L c evaluated by bulk measurement of the entire fiber bundle is 3.0 nm or less, and the crystal orientation degree π 002 satisfies the following equation. π 002 > 4.0 × L c + 73.2 ··· Equation (1) (iii) The O / C on the average single fiber surface in the yarn bundle is 0.08 or more. (iv) The average value of the helix pitch of the fiber axis of the single fiber is 3.8 cm or more. (2) The carbon fiber bundle according to (1), wherein the crystal orientation degree π 002 is higher than 85.5%. (3) The carbon fiber bundle according to (1) or (2), having a tensile elastic modulus of 320 GPa or more. (4) The carbon fiber bundle according to any one of (1) to (3), having a tensile strength of 4.8 GPa or more. (5) The carbon fiber bundle according to any one of (1) to (4), having 12,000 or more filaments. (6) The carbon fiber bundle according to any one of (1) to (5), wherein the N / C on the average single fiber surface in the yarn bundle is 0.04 or less. (7) The carbon fiber bundle according to any one of (1) to (6), having a twist number of 4 turns / m or less. (8) A prepreg containing the carbon fiber bundle according to any one of (1) to (7) and a matrix resin. (9) The carbon fiber reinforced composite material containing the carbon fiber bundle according to any one of (1) to (7) and the matrix resin. (10) The carbon fiber reinforced composite material according to (9), wherein the carbon fiber bundle is composed of single fibers having an average value of the fluctuation width of the fiber axis of 1.4 μm or more, and the mass content rate of the carbon fiber is 60 mass% or more. (11) An injection molded product made of the carbon fiber reinforced composite material according to (9). (12) A drawn molded product made of the carbon fiber reinforced composite material according to (9) or (10). (13) A prepreg molded product made of the carbon fiber reinforced composite material according to (9) or (10). [Effect of the Invention]

[0015] According to the present invention, it is possible to obtain a carbon fiber bundle having a surface structure advantageous for adhesiveness to a matrix resin, having a high elastic modulus and high strength, and suitable for obtaining a composite having high physical properties. [Brief Description of the Drawings]

[0016]

Figure 1

Figure 2

[0017] Hereinafter, embodiments for carrying out the present invention will be described.

[0018] The average value of the fluctuation width of the fiber axis of the single fibers constituting the carbon fiber bundle of the present invention is 1.2 μm or more. The fluctuation width of the fiber axis means that, as shown in FIG. 1, one point on the fiber axis of the observed single fiber is arbitrarily selected as point A, and one point on the fiber axis 1 mm away from the straight line distance from there is taken as point B. When point A is the origin in the XY coordinate system, that is, the point where X = 0 μm and Y = 0 μm, and point B is the point on the X axis, that is, X = 1,000 μm and Y = 0 μm, among the Y coordinate values through which the fiber axis passes, the maximum value Y max(μm) to the minimum value Y min It is defined as the residual ΔY (μm) obtained by subtracting (μm). The method for evaluating the average value of the fluctuation width in the present invention will be described later.

[0019] The fluctuation width can be interpreted as a parameter indicating the strength of the twist of the carbon fiber, and the larger the fluctuation width, the stronger the twist. By setting the average value of the fluctuation width to 1.2 μm or more, single fiber breakage during the carbonization process can be suppressed by improving stress transfer between single fibers due to twisting, and sufficient drawing tension can be imparted.

[0020] The average value of the fluctuation width is preferably 1.4 μm or more, more preferably 1.6 μm or more. There is no particular limitation on the upper limit of the average value of the fluctuation width, but from the perspective of the manufacturing process for obtaining the carbon fiber bundle, the upper limit is 80.0 μm. The average value of the fluctuation width can be controlled by imparting bending to the fiber bundle in the steps of the flame retardant treatment and the preliminary carbonization treatment, and the carbonization treatment step described later. In particular, it is preferable from the perspective of ease of imparting bending to impart bending to the fiber bundle in the carbonization treatment step where the treatment temperature is the highest.

[0021] As a method for imparting bending, known methods can be adopted, such as twisting the fiber bundle or knitting the fiber bundles together in a three-ply or four-ply shape like a braid. Among them, in particular, it is preferable from an industrial perspective to adopt twisting that can be handled with simple equipment. Also, increasing the single fiber diameter is effective in increasing the average value of the fluctuation width.

[0022] The carbon fiber bundle of the present invention has a crystallite size L c obtained by bulk measurement of the entire fiber bundle, which is 3.0 nm or less, and the crystal orientation degree π 002 satisfies the formula (1). π 002 > 4.0 × L c + 73.2 ··· formula (1).

[0023] The crystallite size L c and the crystal orientation degree π 002It is an index representing the thickness in the c-axis direction of crystallites present in carbon fibers and the orientation angle with respect to the fiber axis of the crystallites, and is measured by wide-angle X-ray diffraction. The detailed measurement method will be described later.

[0024] Generally, the larger the crystallite size L c is, the more likely the adhesiveness between the carbon fiber and the matrix resin decreases. Therefore, by setting the crystallite size L c to 3.0 nm or less, a decrease in adhesive strength can be suppressed.

[0025] The crystallite size L c is preferably 1.9 nm or more. When the crystallite size L c is 1.9 nm or more, the stress burden inside the carbon fiber is effectively carried out, so it is easy to increase the tensile modulus. Also, the higher the relative crystallinity degree π c with respect to the crystallite size L 002 is, the more effectively the tensile modulus can be increased while suppressing a decrease in adhesive strength. The crystallite size L c is more preferably 2.2 nm or more.

[0026] If no tension is applied in the carbonization process, although there may be a case where a carbon fiber bundle having a shape similar to a twist habit locally is obtained due to the shrinkage of the fiber bundle, the carbon fiber bundle thus obtained has a crystallite size L c and a degree of orientation π 002 that tend to be low and cannot be said to be industrially useful. The carbon fiber bundle satisfying formula (1) can easily increase the rigidity of the carbon fiber reinforced composite material and can meet the needs in industrial applications and the like where future growth is expected.

[0027] The carbon fiber bundle of the present invention has an O / C of 0.08 or more on the average single fiber surface in the tow. O / C is an index representing the surface oxygen concentration (atomic ratio) of the carbon fiber and is measured by X-ray photoelectron spectroscopy (ESCA). The detailed measurement method will be described later. In the following, the O / C on the average single fiber surface in the tow may also be simply referred to as O / C.

[0028] Generally, since the surface of carbon fiber has low activity, in the surface treatment process, oxygen functional groups are imparted to increase O / C. In addition to suppressing uneven adhesion of the sizing agent, the adhesiveness with the matrix resin is improved. Here, an important point is to increase the O / C of the average single fiber surface in the tow. In the case of a tow in which the fibers are highly intertwined like entanglement or twisting, it has been found by the study of the present inventors that the single fibers in the central part are not sufficiently treated compared to the single fibers arranged in the surface layer, resulting in low adhesion. It is significant to increase the O / C not only of the single fibers arranged in the surface layer but also of the single fibers in the central part to increase the above average O / C. The O / C of the average single fiber surface is preferably 0.10 or more, more preferably 0.12 or more, and even more preferably 0.14 or more. Also, the O / C of the average single fiber surface is preferably 0.40 or less. By setting the O / C of the average single fiber surface to 0.40 or less, it becomes easier to suppress a decrease in the strength of the carbon fiber.

[0029] As a method for increasing the O / C of the average single fiber surface, known methods such as lowering the temperature of the carbonization process, applying a high voltage in the electrolytic solution, or using sulfuric acid in the electrolytic solution can be adopted. In addition, it is also effective to add a step of removing twist immediately after the carbonization process. However, it is required to set the conditions so that the O / C increases not only in the single fibers arranged in the surface layer but also in the single fibers in the central part.

[0030] The single fiber constituting the carbon fiber tow of the present invention has an average value of the helix pitch of the fiber axis of 3.8 cm or more. In the present invention, the helix pitch of the fiber axis of the single fiber is a morphological feature that serves as an index of the twist number of the twisted yarn. That is, the twisted yarn is obtained by treating the carbon fiber tow in a twisted state when manufacturing the carbon fiber tow, and the twisted form may be retained in the thus obtained carbon fiber tow.

[0031] Here, a state in which the twist form 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 in the manufacturing process is forcibly twisted and then cut at an arbitrary location to form a free end, the fiber axes of the single fibers constituting the carbon fiber bundle are originally straight, and the twist is naturally released sequentially from the free end due to the high rigidity of the carbon fiber. A carbon fiber bundle in which the twist form is maintained is easily obtained, particularly when the carbon fiber bundle has been subjected to a state in which twisting has been added in the carbonization process.

[0032] When a single fiber is taken out from a carbon fiber bundle that maintains such a twisted form and observed, the fiber axis of the single fiber forms a "helical" shape. In the present invention, the helical pitch refers to the distance in the fiber axial direction that this helix travels for one full turn. The average value of the helical pitch refers to the average value of the helical pitch obtained by taking out and evaluating a plurality of single carbon fiber fibers, and a detailed evaluation method will be described later.

[0033] By setting the average helical pitch to 3.8 cm or more, excessive entanglement of single fibers within the carbon fiber bundle can be suppressed, thereby reducing uneven treatment within the yarn bundle during the surface treatment process. Furthermore, in order to obtain carbon fiber with a small helical pitch, a large number of twists per unit length of the yarn bundle must be added, which requires a slower production speed. From the viewpoint of productivity, a helical pitch of 3.8 cm or more is preferable. The average helical pitch is preferably 15.0 cm or less. If the helical pitch is 15.0 cm or less, the twist improves stress transmission between the single fibers, suppressing single fiber breakage during the carbonization process and making it easier to apply sufficient drawing tension.

[0034] The carbon fiber bundle of the present invention has a crystal orientation degree of π 002 is preferably higher than 85.5%, more preferably higher than 86.0%, and even more preferably higher than 86.5%. 002 When the degree of crystal orientation π is high, the stress-bearing capacity in the fiber axis direction increases, making it easier to increase the tensile modulus of the carbon fiber. 002 is preferably lower than 95.0%.002 When it exceeds 95.0%, the stress burden in the fiber axis direction becomes too large, and thread breakage may occur during the carbonization process.

[0035] Crystal orientation degree π 002 can be controlled by the drawing tension in addition to the temperature and time in the carbonization process. However, if the drawing tension in the carbonization process is increased too much, fiber breakage may increase, causing winding around the roller, or the entire fiber bundle may break, rendering the process inoperable. In the conventional method for manufacturing carbon fiber bundles, there was a limit to the achievable drawing tension. On the other hand, according to the preferred manufacturing method of the present invention described later, it is possible to apply a high drawing tension while suppressing fiber breakage.

[0036] The carbon fiber bundle of the present invention preferably has a tensile modulus of 320 GPa or more, more preferably 330 GPa or more, and even more preferably 340 GPa or more. The higher the tensile modulus of the carbon fiber, the greater the reinforcing effect of the carbon fiber when used as a carbon fiber reinforced composite material, and it is easier to obtain a high-rigidity carbon fiber reinforced composite material. Furthermore, in order to satisfy the required properties with a small amount of members, it can be made lightweight and low-cost. The tensile modulus is preferably 450 GPa or less. If the tensile modulus is increased above 450 GPa, thread breakage during the carbonization process or a decrease in the tensile strength of the carbon fiber bundle may occur.

[0037] If no tension is applied during the carbonization process, although a carbon fiber bundle having a shape similar to a twist habit locally may be obtained due to the contraction of the fiber bundle, the carbon fiber bundle thus obtained tends to have a low tensile modulus and cannot be said to be industrially useful.

[0038] The tensile modulus of the carbon fiber bundle can be measured according to the tensile test of the resin-impregnated strand described in JIS R7608 (2004). When the carbon fiber bundle has a twist, the untwisted one with the same number of twists applied in the reverse method is used for measurement. Such a tensile modulus can be controlled by known methods such as the tension and the maximum temperature in the carbonization process.

[0039] The carbon fiber bundle of the present invention preferably has a tensile strength of 4.8 GPa or more. From the viewpoint of increasing the tensile elongation of the obtained carbon fiber reinforced composite material, it is preferable to increase the tensile strength of the carbon fiber bundle. Further, even if the single fiber compressive strength of the carbon fiber bundle is high, if the tensile strength is low, when a bending deformation is applied to the obtained carbon fiber reinforced composite material, the outer side of the bending where the tensile load acts may trigger final fracture. Also, the tensile strength of the carbon fiber bundle is preferably 9.0 GPa or less. When such tensile strength exceeds 9.0 GPa, the difference from the single fiber compressive strength tends to be large, and the physical property balance as a carbon fiber reinforced composite material tends to be disrupted. The tensile strength of the carbon fiber bundle can be evaluated by the strand tensile test described later. To make such tensile strength within the above range, it is important to carbonize while controlling the crystallite size L c is important.

[0040] The carbon fiber bundle of the present invention preferably has 12,000 or more filaments, and more preferably 24,000 or more filaments. If the number of twists is the same, the larger the number of filaments, the larger the distance between the central axis of the twist and the outer periphery of the fiber bundle. Therefore, the twist is likely to be stable, and the handleability and high-order processability are likely to be enhanced. In addition, even when a high tension is applied in the carbonization process, it is easy to suppress the generation of fluff and breakage, and the tensile elastic modulus can be effectively increased.

[0041] The number of filaments can be calculated from the density and basis weight of the fiber bundle and the average diameter of the single fiber. There is no particular limitation on the upper limit of the number of filaments, and it may be set according to the intended use. However, for the convenience of the manufacturing process for obtaining carbon fibers, the upper limit is generally about 250,000.

[0042] The carbon fiber bundle of the present invention preferably has an N / C of 0.04 or less, more preferably 0.03 or less, and even more preferably 0.02 or less on the average single fiber surface in the tow. N / C is an index representing the surface nitrogen concentration (atomic ratio) of carbon fiber and is measured by ESCA. The detailed measurement method will be described later. In the following, the N / C on the average single fiber surface in the tow may sometimes be simply referred to as N / C.

[0043] In the surface treatment step, either an alkaline electrolytic solution or an acidic electrolytic solution can be used. However, when a compound containing an amino group is used as the alkaline electrolytic solution, nitrogen functional groups are secondarily introduced onto the carbon fiber surface, increasing the N / C, so it cannot be said to be a preferable electrolytic solution.

[0044] Also, as described in Japanese Patent Application Laid-Open No. 2015-67910 (Patent Document 5), it is known that when an alkaline electrolytic solution containing ammonium ions is used, it is easy to introduce polar nitrogen functional groups onto the surface of carbon fiber. On the other hand, it has been experimentally found that in order to increase O / C at a low voltage to suppress a decrease in strength, it is preferable to use an acidic electrolytic solution. Based on such findings, if the N / C is lowered, the adhesiveness can be efficiently increased while suppressing the voltage applied to the carbon fiber bundle during electrolytic surface treatment. As a method for suppressing N / C, a known method such as using sulfuric acid in the electrolytic solution can be adopted.

[0045] The carbon fiber bundle of the present invention preferably has a twist number of 4 turns / m or less, more preferably 3 turns / m or less, even more preferably 2 turns / m or less, and particularly preferably 1 turn / m or less. In order to increase the drawing tension, it is important that the fiber bundle is twisted in the carbonization treatment step. However, when it is combined with the matrix resin, it is preferable that the twist number is small also from the viewpoints of resin impregnation property and spreadability of the tow. The twist of the carbon fiber bundle can be untwisted and controlled by applying a twist in the opposite direction after the carbonization treatment or after the surface treatment step.

[0046] The prepreg of the present invention is a prepreg containing the above carbon fiber bundle and matrix resin. The matrix resin includes thermoplastic resins and thermosetting resins, and thermosetting resins are preferred from the viewpoint of resin impregnation properties. The matrix resin is not particularly limited as long as it is a thermosetting resin, and examples thereof include epoxy resins, vinyl ester resins, phenolic resins, benzoxazine resins, bismaleimide resins, cyanate ester resins, polyimide resins, and the like. Among them, epoxy resins are preferred from the viewpoints of excellent handleability and curability in the state before curing.

[0047] Examples of the epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, biphenyl type epoxy resin, naphthalene type epoxy resin, novolac type epoxy resin, epoxy resin having a fluorene skeleton, epoxy resin using a copolymer of a phenol compound and dicyclopentadiene as a raw material, glycidyl ether type epoxy resins such as diglycidyl resorcinol, tetrakis(glycidyloxyphenyl)ethane, and tris(glycidyloxyphenyl)methane, and glycidyl amine type epoxy resins such as tetraglycidyl diaminodiphenylmethane, triglycidyl aminophenol, triglycidyl aminocresol, and tetraglycidyl xylylenediamine. These epoxy resins may be used alone or in combination of multiple types.

[0048] The curing agent for the epoxy resin is not particularly limited as long as it can cure the epoxy resin, and examples thereof include amines such as aromatic amines and alicyclic amines, acid anhydrides, polyaminoamides, organic acid hydrazides, and isocyanates. Amine curing agents are preferred because the resulting resin cured products have excellent mechanical properties and heat resistance. As the amine curing agent, diamino diphenyl sulfone and diamino diphenyl methane which are aromatic amines, dicyandiamide or its derivatives which are aliphatic amines, hydrazide compounds, etc. can be used.

[0049] Further, the curing agent may be used in combination with a curing accelerator. Examples of the curing accelerator to be combined include ureas, imidazoles, Lewis acid catalysts, etc. Among them, a urea compound is preferably used in view of the balance between storage stability and catalytic ability. Examples of such urea compounds include N,N-dimethyl-N'-(3,4-dichlorophenyl)urea, toluene bis(dimethylurea), 4,4'-methylenebis(phenyldimethylurea), 3-phenyl-1,1-dimethylurea, etc. which can be used.

[0050] There are prepregs containing carbon fiber bundles and thermosetting resins. Such prepregs can be obtained by impregnating carbon fiber bundles with a thermosetting resin. Examples of the impregnation method include the wet method and the hot melt method (dry method).

[0051] The wet method is a method in which a carbon fiber bundle is immersed in a solution in which a thermosetting resin is dissolved in a solvent such as methyl ethyl ketone or methanol, then the carbon fiber bundle is pulled up, and the solvent is evaporated from the carbon fiber bundle using an oven or the like to impregnate the carbon fiber bundle with an epoxy resin composition. The hot melt method is a method in which a thermosetting resin whose viscosity has been lowered by heating is directly impregnated into a carbon fiber bundle, or a film in which a thermosetting resin is coated on a release paper or the like is prepared, and then the film is overlapped from both sides or one side of the carbon fiber bundle and heated and pressed to impregnate the carbon fiber bundle with the resin. Here, only one carbon fiber bundle may be used, or a plurality of carbon fiber bundles may be aligned and used.

[0052] The carbon fiber reinforced composite material of the present invention is a composite material containing the above carbon fiber bundle and a matrix resin. As the matrix resin, a cured product of a thermosetting resin, a thermoplastic resin, or a mixture thereof can be used. When using a thermosetting resin, the carbon fiber reinforced composite material may be produced via the prepreg described above. The types of the thermosetting resin and the thermoplastic resin are not particularly limited, and the thermosetting resin can be appropriately combined and used together with a curing agent or the like from those described above.

[0053] The carbon fiber reinforced composite material of the present invention contains a carbon fiber bundle composed of single fibers having an average value of the fluctuation width of the fiber axis of 1.4 μm or more, and preferably has a carbon fiber mass content of 60% by mass or more. According to the studies of the present inventors, in a carbon fiber reinforced composite material containing carbon fibers with high adhesiveness to the matrix resin, the toughness tends to be improved. However, in a carbon fiber reinforced composite material containing a carbon fiber bundle composed of single fibers having an average value of the fluctuation width of the fiber axis of 1.4 μm or more, the single fibers are likely to be intertwined. Furthermore, it has been found that when the mass content of carbon fibers in the carbon fiber reinforced composite material is 60% by mass or more, the contact frequency between the single fibers increases, and thus the toughness tends to be more easily improved. The average value of such a fluctuation width of the fiber axis is more preferably 1.6 μm or more, and the mass content of carbon fibers is more preferably 65% by mass or more. There is no particular limitation on the upper limit of the average value of the fluctuation width, but from the viewpoint of the manufacturing process for obtaining the carbon fiber bundle, it is preferably 80.0 μm or less. Also, from the viewpoint of the impregnation property of the matrix resin, the mass content of carbon fibers is preferably 80% by mass or less.

[0054] The injection molded article of the present invention is an injection molded article containing the above carbon fiber reinforced composite material.

[0055] The drawn molded article of the present invention is a drawn molded article containing the above carbon fiber reinforced composite material.

[0056] The prepreg molded article of the present invention is produced via the above prepreg, and is a prepreg molded article containing the above carbon fiber reinforced composite material.

Examples

[0057] Next, the present invention will be specifically described by way of examples, but the present invention is not limited by these examples.

[0058] The measurement methods for various physical property values described in this specification are as follows.

[0059] <Measurement method for average value of fluctuation width> The single fiber of carbon fiber to be measured was set to a length of 1 to 5 mm and placed on copy paper laid on a horizontal table. When the single fiber adhered to the copy paper due to the influence of static electricity, it was carried out after eliminating static electricity by a general method. The paper surface was observed using an optical microscope from the vertical direction, and an image was obtained. The magnification of the objective lens of the optical microscope was set to 10 times. The image was saved in the jpg format of 2,592 pixels in width × 1,944 pixels in height. At this time, when imaging a scale of 1,000 μm in actual size, the imaging range was set so that the scale corresponded to 2,320 to 2,340 pixels. The obtained image was loaded into the open-source image processing software "ImageJ (Image J)". An arbitrary point on the fiber axis was set as point A, and a point on the fiber axis 1,000 μm away from point A was set as point B. Next, "Bilinear Interpolation" was selected as the interpolation algorithm during rotation, and the image was rotated so that points A and B were horizontal. After performing binarization processing, skeletonization was carried out, and the fiber axis was extracted as a curve with a width of 1 pixel. At this time, if dust or the like adhered to the fiber surface, the fiber axis might branch, but side chains other than the fiber axis were ignored. When point A was the origin in the XY coordinate system, that is, the point where X = 0 μm and Y = 0 μm, and point B was the point on the X axis, that is, X = 1,000 μm and Y = 0 μm, the residual ΔY (μm) obtained by subtracting the minimum value Ymin from the maximum value Ymax of the Y coordinates through which the fiber axis passed between points A and B was read and used as the fluctuation width of the measured single fiber. The average of the fluctuation widths measured for 10 different single fibers was adopted as the average value of the fluctuation width in the present invention. In this example, an upright microscope "DM2700M" manufactured by Leica Microsystems GmbH was used as the optical microscope.

[0060] <Helical pitch of the fiber axis of the single fiber> Cut out a single fiber of the carbon fiber to be measured to a length of 10 ± 0.5 cm and place it statically on the copy paper laid on a horizontal table. If the single fiber adheres to the copy paper due to the influence of static electricity, perform the operation after removing the static electricity by a general method. If the single fiber adheres to the copy paper and does not separate when the copy paper with the single fiber is turned upside down, it means that the static electricity removal is insufficient, so remove the static electricity additionally. Observe visually from the direction normal to the single 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 helix pitch is 3.0 cm, as illustrated in Fig. 2, the contact with the copy paper is made at three points, namely contact points A, B, and C. Therefore, in this case, measure the distances A - B and B - C, and take the average value (3.0 cm) as the helix pitch of the fiber axis of the single fiber.

[0061] Read the individual values to the first decimal place, that is, to the digit of 1 mm. When calculating the average value, if digits below the second decimal place appear, retain them up to the second decimal place. The evaluation of the helix pitch of the fiber axis of the single fiber is performed once for the single fiber to be evaluated.

[0062] <Crystallite size L of carbon fiber bundle c and crystal orientation degree π 002 > Align the carbon fiber bundles to be measured, and use a collodion - alcohol solution to solidify them to prepare a measurement sample in the form of a quadrangular prism with a length of 4 cm and a length of 1 mm for each side at the bottom in both the vertical and horizontal directions. For the prepared measurement sample, perform the measurement using a wide - angle X - ray diffractometer under the following conditions.

[0063] 1. Measurement of crystallite size L c · X - ray source: CuKα ray (tube voltage 40 kV, tube current 30 mA) · Detector: Goniometer + Monochromator + Scintillation counter · Scanning range: 2θ = 10~40° · Scanning mode: Step scan, step unit 0.02°, counting time 2 s.

[0064] In the obtained diffraction pattern, for the crystal peak appearing around 2θ = 25 to 26°, the full width at half maximum is determined, and from this value, the crystal grain size L is calculated by the following Scherrer's formula. c is calculated. The crystal grain size L c (nm) = Kλ / β0cosθ B However, K: 1.0, λ: 0.15418 nm (wavelength of X-ray) β0: (β E 2 - β1 2 ) 1 / 2 β E : apparent full width at half maximum (measured value) rad, β1: 1.046×10 -2 rad θ B : Bragg diffraction angle.

[0065] 2. Measurement of crystal orientation degree π 002 is measured It is calculated and obtained using the following formula from the full width at half maximum of the intensity distribution obtained by scanning the above-mentioned crystal peak in the circumferential direction. π 002 = (180 - H) / 180 However, H: apparent full width at half maximum (deg)

[0066] For the target carbon fiber bundle, the above measurement is performed 3 times, and the arithmetic mean is taken as the crystal grain size L c and crystal orientation degree π 002 of the carbon fiber.

[0067] In the examples and comparative examples described later, XRD - 6100 manufactured by Shimadzu Corporation is used as the above wide - angle X - ray diffractometer.

[0068] <O / C and N / C of carbon fiber> In this example, the O / C and N / C of the carbon fiber were measured by X - ray photoelectron spectroscopy according to the following procedure. First, the carbon fiber was cut into 20 mm, evenly spread and arranged on a copper sample support table to a thickness of 10 - 20 μm, and then AlKα was used as the X - ray source.1、2 Using this, the inside of the sample chamber was maintained at 1×10 -8 Torr, and X-ray photoelectron spectroscopy was performed with the photoelectron emission angle set at 45°. Twenty measurement points were randomly selected from the expanded carbon fibers, and measurements were taken. As the correction value for the peak associated with charging during measurement, the binding energy value of the main peak of C 1S was adjusted to 285 eV. The C 1S peak area was determined by drawing a straight baseline in the range of binding energy values from 275 to 290 eV. The O 1s peak area was determined by drawing a straight baseline in the range of binding energy from 525 to 540 eV. The N 1s peak area was determined by drawing a straight baseline in the range of binding energy from 395 to 410 eV. Here, O / C and N / C can be calculated as atomic ratios using the sensitivity correction value specific to the apparatus from the ratio of the above O 1s or N 1s peak area to the C 1S peak area. The average O / C and N / C in the tow were obtained by calculating the average values of O / C and N / C at the above 20 points. As the X-ray photoelectron spectroscopy apparatus, ESCA-1600 manufactured by ULVAC-PHI, Inc. was used.

[0069] <Tensile Strength and Tensile Elastic Modulus of Carbon Fiber Tow> The tensile elastic modulus of the carbon fiber tow was determined according to the resin-impregnated strand test method of JIS R7608 (2004) following the procedure below. However, when the carbon fiber tow had twist, it was untwisted by applying the same number of reverse twists as the number of twists and then evaluated. As the resin formulation, “Celloxide (registered trademark)” 2021P (manufactured by Daicel Corporation) / boron trifluoride monoethylamine (manufactured by Tokyo Chemical Industry Co., Ltd.) / acetone = 100 / 3 / 4 (parts by mass) was used, and as the curing conditions, normal pressure, a temperature of 125 °C, and a time of 30 minutes were used. Ten strands of the carbon fiber tow were measured, and the average values were taken as the tensile strength and the tensile elastic modulus, respectively. The strain range for calculating the tensile elastic modulus was set at 0.1 to 0.6%.

[0070] <Mass content of carbon fiber in carbon fiber reinforced composite material> After measuring the mass of a carbon fiber reinforced composite material cut into any size, the mass content of carbon fiber is determined by measuring the mass of the carbon fiber obtained by putting it into an electric furnace in a nitrogen atmosphere set at a temperature of 450°C to burn off the matrix resin.

[0071] <90-degree bending strength of unidirectional composite> The 90-degree bending strength of the unidirectional composite was determined according to ASTM D790-03 (2017) following the steps below. The unidirectional composite was cut with a cutter to a width of 15 mm, a length of 50 mm, and a thickness of 2 mm. The six test pieces obtained were measured, and the average value was taken as the 90-degree bending strength (90FS in the table). The fiber axis direction was made to be the width direction of the test piece.

[0072] <Interlaminar toughness value [G1c] of unidirectional composite> The interlaminar toughness value [G1c] of the unidirectional composite was determined according to JIS K7086 (1993) following the steps below. The composite for interlaminar toughness evaluation produced according to the following [Manufacturing example of composite for interlaminar toughness evaluation] was cut to a width of 20 mm and a length of 200 mm. An aluminum block was adhered perpendicularly to the fiber direction at the end where the film was inserted. A double-cantilever beam test was carried out using an Instron universal testing machine (manufactured by Instron Corporation) to measure the fracture toughness value. Such fracture toughness values were measured for six samples, and the average value was determined as the interlaminar toughness value [G1c].

[0073] [Manufacturing example of unidirectional prepreg] First, 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 4,4’-diaminodiphenyl sulfone (4,4’-DDS, manufactured by Mitsui Chemicals, Inc.), 10 parts by mass of polyethersulfone (PES5003P, manufactured by Sumitomo Chemical Co., Ltd.), and 20 parts by mass of nylon 12 particles (SP-10, manufactured by Toray Industries, Inc., shape: true sphere) were blended to form an uncured epoxy resin composition. The composition was applied onto a release paper using a reverse roll coater to produce a resin film. Next, a carbon fiber bundle aligned in one direction was sandwiched between the resin films from both the upper and lower surfaces, and heated and pressurized to impregnate the resin, obtaining a unidirectional prepreg with a carbon fiber areal density of 190 g / m 2 and a carbon fiber content of 65% by mass.

[0074] [Manufacturing Example of Unidirectional Composite] The unidirectional prepreg produced in the above [Manufacturing Example of Unidirectional Prepreg] was cut out with a cutter into a square shape with a length of 13 cm in the fiber axis direction and a width of 13 cm in the direction perpendicular to the fiber axis. It was sandwiched between a SUS tool plate and an aluminum pressure plate in the shape of a 13 cm square, bagged using a bag film and a sealant, and then heated to 180 °C in an autoclave and cured for 2 hours to obtain a unidirectional composite with a width of 13 cm, a length of 13 cm, and a thickness of approximately 1 mm.

[0075] [Manufacturing Example of Composite for Interlaminar Toughness Evaluation] The fiber directions of the unidirectional prepregs produced in the above [Manufacturing Example of Unidirectional Prepreg] were aligned, and 13 plies were laminated to produce two laminates. “Toylon®” E (manufactured by Toray Industries, Inc.) was sandwiched between the laminates at a position 40 mm from the end along the fiber direction, and heated to 180 °C in an autoclave and cured for 2 hours to obtain a composite for interlaminar toughness evaluation with a thickness of 3 mm.

[0076] (Example 1) The single-fiber fineness of 0.8 dtex polyacrylonitrile-based carbon fiber precursor fiber bundles obtained by a known method were combined into yarns to make the number of single fibers 24,000, and heat-treated in an oven at 230 - 280 °C in an air atmosphere to convert them into flame-resistant fiber bundles. Next, the obtained flame-resistant fiber bundles were subjected to a twisting process to impart a twist of 15 turns / m, and pre-carbonization treatment was performed in a nitrogen atmosphere at a temperature of 300 - 800 °C to obtain pre-carbonized fiber bundles. Subsequently, such pre-carbonized fiber bundles were carbonized at the maximum carbonization temperature shown in Table 1 and at a draw ratio of 1.02, and then electrolytic surface treatment was performed using an aqueous sulfuric acid solution as the electrolyte, followed by washing with water and drying in hot air to obtain carbon fiber bundles.

[0077] After the obtained carbon fiber bundles were untwisted to a state without residual twist, unidirectional composites were obtained according to the unidirectional prepreg production example and the unidirectional composite production example. The analysis results of the carbon fiber bundles and the unidirectional composites were as shown in Table 1.

[0078] (Example 2) Carbon fiber bundles and unidirectional composites shown in Table 1 were obtained in the same manner as in Example 1, except that the amount of electricity during electrolytic surface treatment was 90 C / g. The analysis results of the carbon fiber bundles and the unidirectional composites were as shown in Table 1.

[0079] (Example 3) Carbon fiber bundles and unidirectional composites shown in Table 1 were obtained in the same manner as in Example 1, except that when combining the polyacrylonitrile-based carbon fiber precursor fiber bundles into yarns, the number of single fibers was 12,000, the twist number of the flame-resistant fiber bundles was 25 turns / m, and the amount of electricity during electrolytic surface treatment was 25 C / g. The analysis results of the carbon fiber bundles and the unidirectional composites were as shown in Table 1.

[0080] (Example 4) The single fiber fineness of the polyacrylonitrile-based carbon fiber precursor fiber bundle was set to 1.1 dtex, the twist number of the flame-resistant fiber bundle was set to 25 turns / m, and the carbon fiber bundle and unidirectional composite shown in Table 1 were obtained in the same manner as in Example 1 except that the amount of electricity during electrolytic surface treatment was set to 30 C / g. The results of analyzing the carbon fiber bundle and unidirectional composite were as shown in Table 1.

[0081] (Example 5) The carbon fiber bundle and unidirectional composite shown in Table 1 were obtained in the same manner as in Example 1 except that the electrolytic solution during electrolytic surface treatment was an aqueous ammonium bicarbonate salt solution and the amount of electricity was set to 80 C / g. The results of analyzing the carbon fiber bundle and unidirectional composite were as shown in Table 1.

[0082] (Example 6) The carbon fiber bundle and unidirectional composite shown in Table 1 were obtained in the same manner as in Example 5 except that the amount of electricity during electrolytic surface treatment was set to 150 C / g. The results of analyzing the carbon fiber bundle and unidirectional composite were as shown in Table 1.

[0083] (Example 7) The carbon fiber bundle and unidirectional composite shown in Table 1 were obtained in the same manner as in Example 5 except that the amount of electricity during electrolytic surface treatment was set to 300 C / g. The results of analyzing the carbon fiber bundle and unidirectional composite were as shown in Table 1.

[0084] (Example 8) The carbon fiber bundle and unidirectional composite shown in Table 1 were obtained in the same manner as in Example 1 except that the maximum carbonization temperature was set to 1,600 °C. The results of analyzing the carbon fiber bundle and unidirectional composite were as shown in Table 1.

[0085] (Example 9) The carbon fiber bundle and unidirectional composite shown in Table 1 were obtained in the same manner as in Example 8 except that the amount of electricity during electrolytic surface treatment was set to 90 C / g. The results of analyzing the carbon fiber bundle and unidirectional composite were as shown in Table 1.

[0086] (Example 10) The electrolyte during electrolytic surface treatment was an aqueous ammonium bicarbonate solution, and a carbon fiber bundle and a unidirectional composite shown in Table 1 were obtained in the same manner as in Example 8 except that the amount of electricity was 80 C / g. The results of analyzing the carbon fiber bundle and the unidirectional composite were as shown in Table 1.

[0087] (Example 11) A carbon fiber bundle and a unidirectional composite shown in Table 1 were obtained in the same manner as in Example 10 except that the amount of electricity during electrolytic surface treatment was 150 C / g. The results of analyzing the carbon fiber bundle and the unidirectional composite were as shown in Table 1.

[0088] (Example 12) A carbon fiber bundle and a unidirectional composite shown in Table 1 were obtained in the same manner as in Example 10 except that the amount of electricity during electrolytic surface treatment was 300 C / g. The results of analyzing the carbon fiber bundle and the unidirectional composite were as shown in Table 1.

[0089] (Example 13) A carbon fiber bundle and a unidirectional composite shown in Table 1 were obtained in the same manner as in Example 1 except that the maximum carbonization temperature was 1,400 °C. The results of analyzing the carbon fiber bundle and the unidirectional composite were as shown in Table 1.

[0090] (Example 14) A carbon fiber bundle and a unidirectional composite shown in Table 1 were obtained in the same manner as in Example 13 except that the amount of electricity during electrolytic surface treatment was 90 C / g. The results of analyzing the carbon fiber bundle and the unidirectional composite were as shown in Table 1.

[0091] (Example 15) The electrolyte during electrolytic surface treatment was an aqueous ammonium bicarbonate solution, and a carbon fiber bundle and a unidirectional composite shown in Table 1 were obtained in the same manner as in Example 13 except that the amount of electricity was 80 C / g. The results of analyzing the carbon fiber bundle and the unidirectional composite were as shown in Table 1.

[0092] (Example 16) A carbon fiber bundle and a unidirectional composite shown in Table 1 were obtained in the same manner as in Example 15, except that the amount of electricity during electrolytic surface treatment was 150 C / g. The results of analyzing the carbon fiber bundle and the unidirectional composite were as shown in Table 1.

[0093] (Example 17) A carbon fiber bundle and a unidirectional composite shown in Table 1 were obtained in the same manner as in Example 15, except that the amount of electricity during electrolytic surface treatment was 300 C / g. The results of analyzing the carbon fiber bundle and the unidirectional composite were as shown in Table 1.

[0094] (Example 18) A carbon fiber bundle and a unidirectional composite shown in Table 1 were obtained in the same manner as in Example 1, except that the single fiber fineness of the polyacrylonitrile-based carbon fiber precursor fiber bundle was 1.1 dtex, the twist number of the flame-resistant fiber bundle was 10 turns / m, and the carbonization draw ratio was 0.98. When the twist number of the flame-resistant fiber bundle was 10 turns / m and the carbonization draw ratio was 1.02, fluff occurred in the carbonization process and the processability was not stable. Therefore, the draw ratio was lowered in this example. The results of analyzing the carbon fiber bundle and the unidirectional composite were as shown in Table 1.

[0095] (Example 19) A carbon fiber bundle and a unidirectional composite shown in Table 1 were obtained in the same manner as in Example 1, except that the amount of electricity during electrolytic surface treatment was 25 C / g. The results of analyzing the carbon fiber bundle and the unidirectional composite were as shown in Table 1.

[0096] (Example 20) A carbon fiber bundle and a unidirectional composite shown in Table 1 were obtained in the same manner as in Example 1, except that the maximum carbonization temperature was 1,700 °C and the amount of electricity during electrolytic surface treatment was 15 C / g. The results of analyzing the carbon fiber bundle and the unidirectional composite were as shown in Table 1.

[0097] (Example 21) A carbon fiber bundle and a unidirectional composite shown in Table 1 were obtained in the same manner as in Example 20, except that the amount of electricity during the electrolytic surface treatment was 45 C / g. The results of analyzing the carbon fiber bundle and the unidirectional composite were as shown in Table 1.

[0098] (Example 22) A carbon fiber bundle and a unidirectional composite shown in Table 1 were obtained in the same manner as in Example 4, except that the step of untwisting the obtained carbon fiber bundle to a state without remaining twist was carried out before the electrolytic surface treatment using an aqueous sulfuric acid solution as the electrolyte, rather than after the electrolytic surface treatment using an aqueous sulfuric acid solution as the electrolyte. The results of analyzing the carbon fiber bundle and the unidirectional composite were as shown in Table 1.

[0099] (Comparative Example 1) A carbon fiber bundle and a unidirectional composite shown in Table 2 were obtained in the same manner as in Example 3, except that the number of turns of the flame-retardant fiber bundle was 0 turns / m, the maximum carbonization temperature was 2,300 °C, the draw ratio was 0.96, and the amount of electricity during the electrolytic surface treatment was 0 C / g. The results of analyzing the carbon fiber bundle and the unidirectional composite were as shown in Table 2.

[0100] (Comparative Example 2) A carbon fiber bundle and a unidirectional composite shown in Table 2 were obtained in the same manner as in Comparative Example 1, except that the amount of electricity during the electrolytic surface treatment was 50 C / g. The results of analyzing the carbon fiber bundle and the unidirectional composite were as shown in Table 2.

[0101] (Comparative Example 3) A carbon fiber bundle and a unidirectional composite shown in Table 2 were obtained in the same manner as in Comparative Example 1, except that the amount of electricity during the electrolytic surface treatment was 200 C / g. The results of analyzing the carbon fiber bundle and the unidirectional composite were as shown in Table 2.

[0102] (Comparative Example 4) The carbonization maximum temperature was set at 1,400 °C, the draw ratio was set such that the amount of electricity during electrolytic surface treatment was 40 C / g, and the electrolytic solution was an aqueous ammonium bicarbonate salt solution. Otherwise, the carbon fiber bundles and unidirectional composites shown in Table 2 were obtained in the same manner as in Comparative Example 1. The results of analyzing the carbon fiber bundles and unidirectional composites were as shown in Table 2.

[0103] (Comparative Example 5) The carbon fiber bundles and unidirectional composites shown in Table 2 were obtained in the same manner as in Comparative Example 4, except that the amount of electricity during electrolytic surface treatment was set at 80 C / g. The results of analyzing the carbon fiber bundles and unidirectional composites were as shown in Table 2.

[0104] (Comparative Example 6) The carbon fiber bundles and unidirectional composites shown in Table 2 were obtained in the same manner as in Comparative Example 4, except that the amount of electricity during electrolytic surface treatment was set at 120 C / g. The results of analyzing the carbon fiber bundles and unidirectional composites were as shown in Table 2.

[0105] (Comparative Example 7) The carbon fiber bundles and unidirectional composites shown in Table 2 were obtained in the same manner as in Comparative Example 4, except that the amount of electricity during electrolytic surface treatment was set at 400 C / g. The results of analyzing the carbon fiber bundles and unidirectional composites were as shown in Table 2.

[0106] (Comparative Example 8) The carbon fiber bundles and unidirectional composites shown in Table 2 were obtained in the same manner as in Example 3, except that the single fiber fineness of the polyacrylonitrile-based carbon fiber precursor fiber bundle was set at 1.1 dtex, the twist number of the flame-resistant fiber bundle was set at 100 turns / m, the carbonization maximum temperature was set at 1,900 °C, and the amount of electricity during electrolytic surface treatment was set at 10 C / g. The results of analyzing the carbon fiber bundles and unidirectional composites were as shown in Table 2.

[0107] (Comparative Example 9) When carbonization treatment was carried out in the same manner as in Example 1, except that the number of single fibers was set at 6,000 and the twist number of the flame-resistant fiber bundle was set at 10 turns / m when combining the polyacrylonitrile-based carbon fiber precursor fiber bundles, the fiber bundle broke and no carbon fiber bundle could be obtained.

[0108] (Comparative Example 10) When combining the polyacrylonitrile-based carbon fiber precursor fiber bundles, the number of single fibers was 12,000, the twist number of the flame-resistant fiber bundle was 0 turns / m, the carbonization draw ratio was 0.96, and the amount of electricity during electrolytic surface treatment was 10 C / g. Otherwise, it was the same as in Example 1, and the carbon fiber bundle and the unidirectional composite shown in Table 2 were obtained. The results of analyzing the carbon fiber bundle and the unidirectional composite were as shown in Table 2.

[0109] (Comparative Example 11) When combining the polyacrylonitrile-based carbon fiber precursor fiber bundles, the number of single fibers was 24,000, and the amount of electricity during electrolytic surface treatment was 10 C / g. Otherwise, it was the same as in Comparative Example 4, and the carbon fiber bundle and the unidirectional composite shown in Table 2 were obtained. The results of analyzing the carbon fiber bundle and the unidirectional composite were as shown in Table 2.

[0110] (Example 23) The carbon fiber bundle obtained in Example 19 was untwisted to a state without remaining twist, and then an interlaminar toughness evaluation composite was obtained according to the unidirectional prepreg production example and the composite production example for interlaminar toughness evaluation. The results of evaluating the interlaminar toughness value were as shown in Table 3.

[0111] (Example 24) The carbon fiber bundle obtained in Example 20 was untwisted to a state without remaining twist, and then an interlaminar toughness evaluation composite was obtained according to the unidirectional prepreg production example and the composite production example for interlaminar toughness evaluation. The results of evaluating the interlaminar toughness value were as shown in Table 3.

[0112] (Example 25) The carbon fiber bundle obtained in Example 21 was untwisted to a state without remaining twist, and then an interlaminar toughness evaluation composite was obtained according to the unidirectional prepreg production example and the composite production example for interlaminar toughness evaluation. The results of evaluating the interlaminar toughness value were as shown in Table 3.

[0113] (Comparative Example 12) The carbon fiber bundle obtained in Comparative Example 11 was untwisted to a state without remaining twist, and then a composite for interlaminar toughness evaluation was obtained according to the unidirectional prepreg production example and the composite production example for interlaminar toughness evaluation. The results of evaluating the interlaminar toughness values were as shown in Table 3.

[0114]

Table 1

[0115]

Table 2

[0116]

Table 3

Industrial Applicability

[0117] The carbon fiber bundle of the present invention has a surface structure advantageous for adhesion to a matrix resin while having a high elastic modulus and high strength. Therefore, a composite having high physical properties can be obtained.

Explanation of Signs

[0118] 1: Single fiber of carbon fiber 2: Copy paper A: Contact point A B: Contact point B C: Contact point C

Claims

1. A carbon fiber bundle that satisfies all of the following (i) to (iv). (i) It is composed of single fibers with an average value of the fluctuation width of the fiber axis of 1.2 μm or more. (ii) The crystallite size L evaluated by bulk measurement of the entire fiber bundle ｃ is 3.0 nm or less, and the crystal orientation degree π ００２ satisfies the formula (1). π ００２ > 4.0 × L ｃ + 73.2... Equation (1) (iii) O / C of the average single fiber surface in the yarn bundle is 0.08 or more. (iv) The average value of the helix pitch of the fiber axis of the single fiber is 3.8 cm or more.

2. Crystal orientation degree π ００２ The carbon fiber bundle according to claim 1, wherein ００２ is higher than 85.5%.

3. The carbon fiber bundle according to Claim 1 or 2, having a tensile modulus of 320 GPa or more.

4. The carbon fiber bundle according to Claim 1 or 2, having a tensile strength of 4.8 GPa or more.

5. The carbon fiber bundle according to Claim 1 or 2, having 12,000 or more filaments.

6. The carbon fiber bundle according to Claim 1 or 2, wherein N / C of the average single fiber surface in the yarn bundle is 0.04 or less.

7. The carbon fiber bundle according to Claim 1 or 2, having a twist number of 4 turns / m or less.

8. A prepreg containing the carbon fiber bundle according to Claim 1 or 2 and a matrix resin.

9. A carbon fiber reinforced composite material containing the carbon fiber bundle according to Claim 1 or 2 and a matrix resin.

10. The carbon fiber bundle is composed of single fibers with an average value of the fluctuation width of the fiber axis of 1.4 μm or more, 2]]The carbon fiber reinforced composite material according to Claim 9, wherein the mass content rate of the carbon fiber is 60% by mass or more.

11. An injection molded article made of the carbon fiber reinforced composite material according to Claim 9.

12. An extrusion molded article made of the carbon fiber reinforced composite material according to Claim 10.

13. A prepreg molded article made of the carbon fiber reinforced composite material according to Claim 10.

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