Sizing agent-containing carbon fiber bundle, carbon fiber-reinforced composite material, and pressure container

Abstract

The purpose of the present invention is to provide a carbon fiber bundle which, when used in a carbon fiber-reinforced composite material, enables carbon fiber tensile strength to be efficiently exhibited.　Provided is a sizing agent-containing carbon fiber bundle, wherein: a strand strength (strand strength A') evaluated on the basis of JIS R7608 (2007) is not less than 5.9 GPa; a strand strength (strand strength B') evaluated with the resin in the formula in JIS R7608 (2007) changed to "Araldite (registered trademark)" LY1564 SP CI / "Baxxodur (registered trademark)" EC331 is not less than 5.7 GPa; the ratio of the strand strength B' to the strand strength A' is not less than 90%; monofilament diameter is not less than 5.1 µm but less than 6.0 µm; and interface shear strength is not more than 16 MPa.

Description

Carbon fiber bundle containing sizing agent, carbon fiber reinforced composite material and pressure vessel

[0001] The present invention relates to a carbon fiber bundle containing a sizing agent that is suitable for use in aircraft, automobile, and ship components, as well as in sports applications such as golf shafts and fishing rods, and other general industrial applications, and particularly to a carbon fiber bundle containing a sizing agent that is excellent in strength development when made into a carbon fiber reinforced composite material, a carbon fiber reinforced composite material, and a pressure vessel.

[0002] Polyacrylonitrile (hereinafter sometimes abbreviated as "PAN")-based carbon fibers have higher specific strength and specific modulus than other fibers, and therefore are being widely used as reinforcing fibers for composite materials in a wide range of applications, including not only traditional sports and aerospace applications but also general industrial applications such as automobiles, civil engineering and construction, pressure vessels, and wind turbine blades, and there is a strong demand for even higher performance. In particular, there is a growing demand for higher strength in compressed hydrogen gas containers that can be filled with hydrogen gas for fuel cells, as these containers are required to operate at higher pressures than conventional compressed natural gas containers.

[0003] Improving the mechanical properties of carbon fibers contributes to weight reduction of components such as pressure vessels, so it is important to improve their mechanical properties, such as tensile strength and tensile modulus. In particular, even higher strength is required for automotive pressure vessels. To increase the strength of CFRP tanks, it is important not only to increase the strand tensile strength of the carbon fibers used, but also to improve how efficiently the mechanical properties of carbon fibers can be expressed when used as reinforcing fibers for composite materials.

[0004] Several proposals have been made to date with the aim of improving strength development when a carbon fiber reinforced composite material is made. Patent Documents 1 to 4 propose improving moldability when a carbon fiber reinforced composite material is made by preventing thread breakage and improving the openability of carbon fiber bundles and resin impregnation when molding the carbon fiber reinforced composite material, thereby improving strength development by eliminating unimpregnated and excess resin portions. Patent Document 1 proposes a technology in which a sizing agent is applied to the inner layer portions of the carbon fiber bundles and then gas is blown onto the carbon fiber bundles to remove the sizing agent from the outer layer portions of the carbon fiber bundles, thereby achieving both abrasion resistance, thread breakage resistance, and resin impregnation properties.

[0005] Patent Document 2 proposes a technique for improving moldability when forming a composite material by entangling carbon fiber precursor fiber bundles to make them less susceptible to fiber breakage when opened to form a composite material. Patent Document 3 proposes a technique for improving resin impregnation by reducing the fiber diameter per single fiber constituting the carbon fiber bundle and forming grooves of a specific depth in the fiber axial direction on the surface of the single fiber. Furthermore, Patent Document 4 proposes a technique for forming a homogeneous molded product by flattening the shape of the carbon fiber bundle to improve openability during molding.

[0006] Patent Documents 5 to 7 propose improving the mechanical properties of carbon fiber bundles. Patent Document 5 proposes that the 0° tensile strength of a carbon fiber reinforced composite material be easily exhibited by controlling the crystal structure in the carbon fiber to a preferred state through the firing conditions in the flame retardant and carbonization process. Patent Documents 6 and 7 propose a technique of electrolytically oxidizing the surface layer of a carbon fiber bundle obtained from a precursor fiber bundle whose density has been increased by dry and wet spinning in an electrolyte aqueous solution containing nitrate ions as an essential component.

[0007] Furthermore, Patent Document 8 proposes a technique for suppressing a decrease in mechanical properties from the time when carbon fiber bundles are processed into a prepreg form until the time when they are processed into a final molded product, in which excess epoxy groups contained in a sizing agent are hydrolyzed either before or after the application of the sizing agent to the carbon fiber bundles, or both.

[0008] Patent Document 9 proposes a technology for obtaining a carbon fiber bundle that can produce a carbon fiber reinforced composite material with excellent stability of thread shape during composite material molding and high tensile strength, by increasing the number of filaments to improve production efficiency, while also uniforming heat treatment, improving the fracture toughness of single fibers, and controlling the entanglement of fiber bundles.

[0009] Japanese Patent No. 6543309, Japanese Patent Laid-Open No. 2020-059937, Japanese Patent No. 4533518, Japanese Patent Laid-Open No. 2002-294568, Japanese Patent No. 7239401, Japanese Patent Publication No. 5-4463, Japanese Patent Publication No. 4-9227, Japanese Patent No. 6051987, Japanese Patent No. 6575696

[0010] However, the techniques of Patent Documents 1 to 4 are merely techniques for improving the moldability of carbon fiber bundles, and if good moldability has already been established, improvements in mechanical properties cannot be expected. Patent Document 1 proposes a technique for adhering a sizing agent to the inside of a fiber bundle and a technique for improving uneven adhesion inside and outside the bundle, but none of the patent documents mentions optimizing the adhesiveness at the interface between the carbon fiber and the resin. Patent Document 4 shows that flattening a carbon fiber bundle in a resin-impregnated state has the effect of suppressing the rate of decrease in ring tensile strength relative to the strength of the resin-impregnated strand, but its purpose is to improve performance by obtaining a homogeneous molded body, and there is no mention of optimizing the adhesiveness at the interface between the carbon fiber and the resin, and the level of strength achieved is insufficient.

[0011] Furthermore, the technology of Patent Document 5 claims that the 0° tensile strength of the carbon fiber reinforced composite material is high relative to the strength of a resin-impregnated strand of carbon fiber bundles, but the absolute value of the strength is not sufficient. In the technologies of Patent Documents 6 and 7, although an improvement in strand strength is observed before and after nitric acid treatment for both types of resin, post-treatment of carbon fibers with a small single fiber fineness, including nitric acid treatment, drying, and inactivation in a nitrogen atmosphere at 700°C for several minutes, is required, which results in a decrease in quality due to the generation of fluff, and there are also problems in terms of productivity and cost due to the post-treatment.

[0012] The technology of Patent Document 8 is intended to suppress the decrease in strength that occurs from processing into a prepreg form until processing into a final molded product, but is not intended to improve strength.

[0013] The technology of Patent Document 9 succeeds in improving the 0° tensile strength of a carbon fiber reinforced composite material by improving the fracture toughness and moldability of the carbon fiber bundles, but does not mention the adhesion at the interface between the carbon fiber and the resin, and does not achieve further strength enhancement that can be achieved by optimizing not only the adhesion at the interface between the carbon fiber and the resin but also the adhesion at the interface between the carbon fiber and the resin.

[0014] Furthermore, as a method for evaluating the strength of resin-impregnated strands, an evaluation method based on a resin composition and technique in accordance with JIS R7608 (2007) is advantageous in that test specimens can be easily prepared and stable test results can be obtained, but the resin has fewer functional groups than practical resins used in carbon fiber reinforced composite materials, and often has poor adhesion to carbon fiber bundles. As a result, a discrepancy may occur between the resin-impregnated strand strength specified in JIS R7608 (2007) and the 0° tensile strength of carbon fiber reinforced composite materials using practical resins.

[0015] Since the 0° tensile strength of a carbon fiber reinforced composite material is dominant in determining the pressure resistance of a pressure vessel, the discrepancy between the resin-impregnated strand strength specified in JIS R7608 (2007) and the 0° tensile strength of a carbon fiber reinforced composite material using a practical resin poses an issue when designing a pressure vessel.

[0016] On the other hand, even if the resin composition specified in JIS R7608 (2007) is simply changed to a practical resin, there is a problem that impregnation of the carbon fiber bundle with the resin becomes insufficient in some cases, for example, when the original viscosity of the resin is high or when the reactivity of the resin is high and the viscosity tends to increase during the resin impregnation, resulting in a large variability in the evaluation results and making it impossible to perform an appropriate evaluation.

[0017] Therefore, an object of the present invention is to find an evaluation method using a resin composition that reflects the strength exhibited when made into a carbon fiber reinforced composite material, and to provide a carbon fiber bundle that can efficiently exhibit tensile strength when made into a carbon fiber reinforced composite material.

[0018] In order to achieve the above object, the present invention has the following configuration: (1) A carbon fiber bundle to which a sizing agent has been applied, wherein the strand strength (strand strength A') evaluated according to JIS R7608 (2007) using the following resin formulation A is 5.9 GPa or more, and the strand strength (strand strength B') evaluated according to JIS R7608 (2007) using the following resin formulation B is 5.7 GPa or more, the ratio of the strand strength B' to the strand strength A' is 90% or more, the single fiber diameter is 5.1 or more and less than 6.0 μm, and the interfacial shear strength is 16 MPa or less, and the carbon fiber bundle contains a sizing agent. Resin formulation A: "Celloxide (registered trademark)" 2021P / boron trifluoride monoethylamine / acetone = 100 / 3 / 4 (parts by mass) is used, and the curing conditions are atmospheric pressure, a temperature of 125°C, and a time of 30 minutes. Resin formulation B: "Araldite" (registered trademark) LY1564 SP CI / "Baxxodur" (registered trademark) EC331 = 100 / 35 (parts by mass), and curing conditions are normal pressure, 80°C, 120 minutes of curing, followed by 110°C, 240 minutes of curing. (2) The carbon fiber bundle according to (1), in which the number of filaments constituting the carbon fiber bundle is 24,000 or more. (3) The carbon fiber bundle according to (1) or (2), in which the strand strength B' is 6.0 GPa or more. (4) The carbon fiber bundle according to (1) or (2), in which the sizing agent contains at least one component containing an epoxy group, and the sizing agent eluted by immersing the carbon fiber bundle in an N,N-dimethylformamide solvent and subjecting it to ultrasonic treatment satisfies the relationship of the following formula 1, where X meq. / g is the epoxy value of the sizing agent eluted, and Y % by mass is the adhesion ratio of the sizing agent applied to the carbon fiber bundle.

[0019] 0.1 meq. / g≦X×Y≦0.68 meq. / g Formula 1 (5) The carbon fiber bundle according to (1) or (2), which has a drape value of 18 cm or less. (6) The carbon fiber bundle according to (5), which has a drape value of 4 cm or more and 10 cm or less. (7) A carbon fiber reinforced composite material using the carbon fiber bundle according to (1) or (2). (8) A pressure vessel using the carbon fiber bundle according to (1) or (2).

[0020] By using carbon fiber bundles containing the sizing agent of the present invention, the tensile strength of carbon fiber reinforced composite materials can be efficiently improved.

[0021] Fig. 1 is a diagram showing a method for preparing a sample used for measuring the drape value. Fig. 2 is a diagram showing a method for measuring the drape value. Fig. 3 is a schematic diagram of an apparatus for performing a pressure test on a pressure vessel.

[0022] The carbon fiber bundle containing the sizing agent of the present invention has a strand strength (hereinafter, the strand strength with this resin formulation A may be referred to as "strand strength A'") of 5.9 GPa or more, preferably 6.3 GPa or more and 8.5 GPa or less, evaluated using the resin formulation A described below, which is a combination of resins described in JIS R7608 (2007), in accordance with the tensile test method for resin-impregnated strands described in JIS R7608 (2007).

[0023] Resin formulation A: "Celloxide (registered trademark)" 2021P / boron trifluoride monoethylamine / acetone = 100 / 3 / 4 (parts by mass) was used, and the curing conditions were atmospheric pressure and 30 minutes in an oven set at a temperature of 125°C.

[0024] Note that "Celloxide (registered trademark)" 2021P is an epoxy resin containing 97% by mass or more of (3',4'-epoxycyclohexane)methyl-3,4-epoxycyclohexylcarboxylate, having an epoxy equivalent of 130 g / eq and a viscosity at 25°C of 240 mPa·s, and an equivalent product may also be used.

[0025] The strand strength A' is an index showing the resistance to breakage when a load is applied to the carbon fiber, and is an index showing the strength of the carbon fiber bundle itself containing a sizing agent. If the strand strength A' is 5.9 GPa or more, the strength of the carbon fiber reinforced composite material when made into a carbon fiber reinforced composite material is likely to be increased. The higher the strand strength A', the more preferable it is, but if the strand strength A' is 6.2 GPa or more, a carbon fiber reinforced composite material that can withstand practical use is likely to be obtained, and 8.5 GPa is often sufficient.

[0026] The strand strength A' can be controlled by manufacturing the carbon fiber according to the manufacturing method described below.

[0027] The carbon fiber bundle containing the sizing agent of the present invention has a strand strength evaluated in accordance with the tensile test of a resin-impregnated strand described in JIS R7608 (2007) using resin formulation B described below (hereinafter, the strand strength with resin formulation B may be referred to as "strand strength B'") of 5.7 GPa or more, preferably 6.0 GPa or more and 7.8 GPa or less, and more preferably 6.5 GPa or more and 7.8 GPa or less.

[0028] Resin formulation B: "Araldite (registered trademark)" LY1564 SP CI / "Baxodur (registered trademark)" EC331 = 100 / 35 (parts by mass) was used, and the curing conditions were atmospheric pressure, 80°C, and 120 minutes, followed by atmospheric pressure, 110°C, and 240 minutes.

[0029] Note that, instead of "Araldite (registered trademark)" LY1564 SP CI, an epoxy resin containing 80 mass % of 2,2'-[(1-methylethylidene)bis(4,1-phenyleneoxymethylene)]bisoxirane and 20 mass % of 1,4-bis(2,3-epoxypropoxy)butane may be used. Also, instead of "Baxodur (registered trademark)" EC331, 2,2'-dimethyl-4,4'-methylenebis(cyclohexylamine) may be used.

[0030] Resin formulation B is a practical resin for filament winding, and has a viscosity suitable for preparing strand test pieces by the impregnation method described in JIS R7608 (2007). Furthermore, Resin formulation B has more functional groups than the resin composition described in JIS R7608 (2007), and has high adhesion to carbon fibers. Therefore, it was discovered that strand strength B' in Resin formulation B can be used as an index that represents, in a model manner, the strength of a carbon fiber reinforced composite material when the carbon fiber bundle is made into a carbon fiber reinforced composite material.

[0031] If the strand strength B' is 5.7 GPa or more, the strength of the carbon fiber reinforced composite material can be increased when it is actually made into a carbon fiber reinforced composite material. Also, if the strand strength B' is 6.0 GPa or more, the carbon fiber reinforced composite material is likely to be practically usable, and if it is 6.5 GPa or more, the amount of carbon fiber used in the carbon fiber reinforced composite material can be effectively reduced, which is expected to reduce the weight of the carbon fiber reinforced composite material, but 7.8 GPa is sufficient in many cases.

[0032] The strand strength B' can be controlled by producing a carbon fiber bundle containing a sizing agent according to the method for producing a carbon fiber bundle containing a sizing agent described below.

[0033] In the carbon fiber bundle containing the sizing agent of the present invention, the ratio of strand strength B' to strand strength A' (hereinafter also referred to as "strength utilization rate") is 90% or more, preferably 93% or more, and more preferably 95% to 99%. The strength utilization rate is an index of strength development when the carbon fiber bundle is made into a carbon fiber reinforced composite material. If the strength utilization rate is 90% or more, it is easy to increase the strength when actually made into a carbon fiber reinforced composite material, and if it is 95% or more, the mechanical properties of the carbon fiber can be efficiently developed when made into a carbon fiber reinforced composite material. The closer to 100% the strength utilization rate is, the more preferable, but in many cases, 99% is sufficient for a carbon fiber reinforced composite material.

[0034] The carbon fiber bundle containing the sizing agent of the present invention has an interfacial shear strength of 16 MPa or less, preferably 10 MPa to 16 MPa, more preferably 12 MPa to 16 MPa. When a tensile load is applied to a carbon fiber reinforced composite material, the load is transmitted to the fibers by shear forces generated at the interface. Therefore, controlling the interfacial shear strength is important for increasing the tensile strength of the carbon fiber reinforced composite material. The interfacial shear strength is an index representing the adhesion between the carbon fiber contained in the carbon fiber bundle and the resin when the carbon fiber reinforced composite material is formed. If the adhesion between the carbon fiber and the resin is low, delamination may occur at the interface between the carbon fiber and the resin, leading to fracture of the entire carbon fiber reinforced composite material. If the adhesion between the carbon fiber and the resin is 10 MPa or more, it is expected that delamination at the interface between the carbon fiber and the resin will be suppressed in practical use when the carbon fiber reinforced composite material is formed. If the adhesion between the carbon fiber and the resin is too high, stress concentration is likely to occur at the fracture initiation point when the carbon fiber reinforced composite material is formed, leading to fracture of the entire carbon fiber reinforced composite material. Therefore, it is preferable to set the interfacial shear strength to 16 MPa or less.

[0035] The single fiber diameter of the carbon fiber bundle containing the sizing agent of the present invention is 5.1 μm or more and less than 6.0 μm, preferably 5.1 μm or more and 5.8 μm or less, and more preferably 5.2 μm or more and 5.8 μm or less. Because the breaking load per single fiber is determined by the strand strength and the cross-sectional area of ​​the single fiber, the single fiber diameter affects the breaking load per single fiber. Furthermore, the larger the single fiber diameter, the less fuzzing due to abrasion during processing tends to occur, which affects the quality. A single fiber diameter of 5.2 μm or more tends to improve the quality when producing carbon fiber or when making it into a carbon fiber reinforced composite material. If the single fiber diameter is too large, there is a possibility that the reaction within the single fiber may become non-uniform during the baking process, so a single fiber diameter of less than 6.0 μm is preferred.

[0036] The carbon fiber bundle containing the sizing agent of the present invention is expected to have improved tensile strength when made into a carbon fiber reinforced composite material, when all of the strand strength A' in resin formulation A, the strand strength B' in resin formulation B, the ratio of strand strength B' to strand strength A', the single fiber diameter, and the interfacial shear strength satisfy the above-mentioned ranges.

[0037] The carbon fiber bundle containing a sizing agent of the present invention preferably contains at least one component containing an epoxy group in the sizing agent, and when the epoxy value of the sizing agent eluted by immersing the carbon fiber bundle containing a sizing agent in an N,N-dimethylformamide solvent and subjecting it to ultrasonic treatment is X meq. / g, and the content ratio of the sizing agent contained in the carbon fiber bundle containing a sizing agent is Y mass %, X and Y preferably satisfy the relationship of the following formula 1, and more preferably satisfy the relationship of the following formula 2: 0.10 meq. / g≦X×Y≦0.68 meq. / g Formula 1 0.10 meq. / g≦X×Y≦0.40 meq. / g Formula 2.

[0038] The epoxy value is an index showing the amount of epoxy groups contained per 1 g of sizing agent, and the larger the epoxy value, the more epoxy groups contained per 1 g of sizing agent. The content of the sizing agent is the total mass of the sizing agent eluted by immersing a carbon fiber bundle containing the sizing agent in N,N-dimethylformamide and subjecting it to ultrasonic treatment, expressed as a percentage (mass%) with the mass of the carbon fiber bundle containing the sizing agent being 100 mass%.

[0039] Therefore, X × Y in Formulas 1 and 2 is an index representing the amount of epoxy groups contained in the carbon fiber bundle containing a sizing agent, and when X × Y is large, it is easy to increase the adhesion at the interface between the carbon fiber contained in the carbon fiber bundle containing a sizing agent and the resin that constitutes the carbon fiber reinforced composite material. If the adhesion between the carbon fiber and the resin is low, peeling occurs at the interface between the carbon fiber and the resin, leading to breakage of the entire carbon fiber reinforced composite material, which is not preferable, while on the other hand, if the adhesion between the carbon fiber and the resin is too high, stress concentration is likely to occur at the break initiation point when the carbon fiber is made into a carbon fiber reinforced composite material, leading to breakage of the entire carbon fiber reinforced composite material, which is not preferable.

[0040] By controlling X×Y within the range of formula 1, it is easy to increase the strength of the carbon fiber reinforced composite material when it is actually made into a carbon fiber reinforced composite material. Furthermore, by controlling X×Y within the range of formula 2, it is easy to make a carbon fiber reinforced composite material that can withstand practical use.

[0041] The carbon fiber bundle containing the sizing agent of the present invention preferably has a drape value of 18 cm or less, more preferably 4 cm or more and 16 cm or less, and even more preferably 4 cm or more and 10 cm or less. The drape value is an index representing the hardness of the carbon fiber bundle, and the larger the drape value, the harder the carbon fiber bundle.

[0042] If the drape value is less than 4 cm, the fiber bundle is soft and is therefore likely to bend or twist in a guide such as a comb that aligns the yarns drawn from a bobbin during the production of a composite material. If bending or twisting occurs, the affected portion becomes difficult to open, resulting in uneven opening, which is undesirable. Furthermore, if the drape value is greater than 18 cm, the fiber bundle is stiff and may be prone to fuzzing when it comes into contact with a guide such as a comb and deforms. A drape value of 4 cm or more and 10 cm or less is preferable because it can suppress both uneven opening and fuzzing when it comes into contact with a guide.

[0043] The carbon fiber bundle containing the sizing agent of the present invention preferably has 24,000 or more filaments, more preferably 36,000 or more filaments. When producing a composite material by filament winding, productivity depends on the yarn speed and the number of filaments, so a large number of filaments allows for efficient production of the composite material. A filament number of 24,000 or more is satisfactory from the viewpoint of productivity. There is no particular upper limit on the number of filaments, but the greater the number of filaments, the more likely it is that variations in basis weight will occur due to uneven drawing inside and outside the yarn bundle during the drawing process. Therefore, the number of filaments is preferably 48,000 or less.

[0044] Next, a method for producing a carbon fiber precursor fiber bundle suitable for obtaining a carbon fiber bundle containing the sizing agent of the present invention will be described.

[0045] The carbon fiber precursor fiber bundle can be obtained by spinning a spinning solution of a polyacrylonitrile copolymer. The polyacrylonitrile copolymer is not limited to a homopolymer obtained from acrylonitrile alone, but may contain other monomers in addition to acrylonitrile as the main component. Specifically, the polyacrylonitrile copolymer preferably contains 90 to 100% by mass of acrylonitrile and less than 10% by mass of a copolymerizable monomer.

[0046] Examples of monomers copolymerizable with acrylonitrile that can be used include acrylic acid, methacrylic acid, itaconic acid, and their alkali metal salts, ammonium salts, and lower alkyl esters, acrylamide, and derivatives thereof, allylsulfonic acid, methallylsulfonic acid, and their salts or alkyl esters.

[0047] The polyacrylonitrile copolymer is dissolved in a solvent in which the polyacrylonitrile copolymer is soluble, such as dimethyl sulfoxide, dimethylformamide, dimethylacetamide, nitric acid, an aqueous zinc chloride solution, or an aqueous sodium rhodanide solution, to prepare a spinning solution. When solution polymerization is used to produce the polyacrylonitrile copolymer, it is preferable to use the same solvent for polymerization as the spinning solvent, as this eliminates the need for a step of separating the obtained polyacrylonitrile copolymer and redissolving it in the spinning solvent.

[0048] When producing a carbon fiber precursor fiber bundle, either a dry / wet spinning method or a wet spinning method may be used as the spinning method. The spinning process includes a coagulation process in which a spinning dope is discharged from a spinneret into a coagulation bath and spun, a water washing process in which the coagulated fiber obtained in the coagulation process is washed in a water bath, a water bath drawing process in which the fiber obtained in the water washing process is drawn in a water bath, and a dry heat treatment process in which the fiber obtained in the water bath drawing process is dry heat treated. If necessary, a steam drawing process in which the fiber obtained in the dry heat treatment process is steam drawn may also be included. Furthermore, if necessary, it is preferable to include a doubling process so that the number of filaments matches that of the carbon fiber bundle. The order of each process can be appropriately changed.

[0049] The spinning dope is prepared by dissolving the polyacrylonitrile polymer in a solvent in which polyacrylonitrile is soluble, such as dimethyl sulfoxide, dimethylformamide, or dimethylacetamide.

[0050] The coagulation bath preferably contains the solvent used for the spinning solution, such as dimethyl sulfoxide, dimethylformamide, or dimethylacetamide, and a coagulation-promoting component. The coagulation-promoting component may be one that does not dissolve the polyacrylonitrile polymer and is compatible with the solvent used for the spinning solution. Specifically, it is preferable to use water as the coagulation-promoting component.

[0051] The washing step is performed by introducing the fibers obtained in the spinning step into a washing bath to further remove the organic solvent from the coagulated fiber bundle. In order to improve the fiber passing property in the washing step, drawing may be performed in the washing step.

[0052] The water bath stretching step can usually be carried out in a single or multiple water baths whose temperature is controlled at 30 to 98° C. The stretching ratio in the water bath stretching step is preferably set to 2 to 6 times.

[0053] The oil application step is a step in which an oil is applied after the in-bath drawing step in order to prevent adhesion between fibers. The oil used in this step is preferably an oil containing silicone as its main component. If the oil does not contain silicone, it will not be possible to suppress interfiber adhesion during the flame-proofing step, resulting in reduced strand strength. Furthermore, it is preferable to use a silicone oil containing a modified silicone such as an amino-modified silicone, which has high heat resistance. Other silicone oils include epoxy-modified and alkylene oxide-modified silicones.

[0054] The drying step can be carried out by a known method. From the viewpoint of improving productivity and the degree of crystal orientation, it is preferable to stretch the film in a heating medium after the drying step. As the heating medium, for example, pressurized steam or superheated steam is preferably used in terms of operational stability and cost.

[0055] After the drying step, a hot stretching step or a steam stretching step may be added.

[0056] Next, a method for producing a carbon fiber bundle containing a sizing agent of the present invention will be described. In the method for producing a carbon fiber bundle containing a sizing agent of the present invention, for example, the carbon fiber precursor fiber bundle produced by the method described above is subjected to a flame retardation step of flame retarding in an oxidizing atmosphere at a temperature of 200 to 300°C, a preliminary carbonization step of preliminary carbonization in an inert atmosphere at a maximum temperature of 500 to 1,200°C, and then a carbonization step of carbonization in an inert atmosphere at a maximum temperature of 1,200 to 2,000°C, to produce a carbon fiber bundle.

[0057] In order to increase the strength of carbon fiber, in the flame-resistant process, the obtained flame-resistant fiber has a wavelength of 1,370 cm in the infrared spectrum. －１ The peak intensity at 1,453 cm －１ The ratio of the peak intensities of the two peaks is in the range of 0.60 to 0.75, and the peak intensity of the two peaks is 1,370 cm in the infrared spectrum. －１ The peak intensity at 1,254 cm －１ It is preferable to control the ratio of the peak intensities of the 1,453 cm peak in the infrared spectrum to the 1,453 cm peak in the infrared spectrum so as to be in the range of 0.50 to 0.65. －１ The peak at 1,370 cm is derived from alkenes and decreases as the flame resistance increases. －１ and 1,254 cm －１ The peak at 1,370 cm is a peak derived from the flame-resistant structure, and increases as the flame resistance progresses. －１ The peak intensity at 1,254 cm －１ The peak intensity ratio decreases as the flame-proofing process progresses, and the decrease is particularly large in the initial stage. However, depending on the flame-proofing conditions, the peak intensity ratio may not become 0.65 or less even if the time is increased.

[0058] In order to achieve a ratio of these two peak intensities within a target range, conditions should basically be set by focusing mainly on the following: a small amount of copolymerization component contained in the polyacrylonitrile polymer constituting the precursor fiber, a high degree of crystalline orientation of the precursor fiber, a small single fiber fineness of the precursor fiber, and a higher flameproofing temperature in the latter half. －１ The peak intensity at 1,453 cm －１ a first flame-proofing step of flame-proofing the fiber for 8 to 40 minutes until the ratio of the peak intensities of the fibers obtained by the first flame-proofing step is in the range of 0.80 to 1.05; －１ The peak intensity at 1,453 cm －１ The ratio of the peak intensities is in the range of 0.60 to 0.75, and the peak intensity at 1,370 cm in the infrared spectrum is －１ The peak intensity at 1,254 cm －１ The second flameproofing step is preferably carried out in two stages, in which the flameproofing is carried out for 5 to 40 minutes, preferably 5 to 30 minutes, until the peak intensity ratio reaches the range of 0.50 to 0.65.

[0059] The flame-stabilizing temperature in the first flame-stabilizing step is preferably set to 200 to 250°C, more preferably 230 to 250°C, in order to control the infrared spectrum within the above-mentioned range.

[0060] The second flame-stabilizing step is preferably performed at a higher flame-stabilizing temperature than the first flame-stabilizing step. In order to shorten the flame-stabilizing time in the second flame-stabilizing step, the flame-stabilizing temperature may be adjusted to a higher temperature, but the appropriate flame-stabilizing temperature depends on the characteristics of the precursor fiber. The flame-stabilizing temperature is preferably set to 250 to 300°C, more preferably 260 to 290°C, in order to control the infrared spectrum within the above-mentioned range. The flame-stabilizing temperature does not need to be constant, and may be set in multiple stages. In order to increase the strand strength of the resulting carbon fiber, it is preferable to set the flame-stabilizing temperature high and the flame-stabilizing time short.

[0061] In the present invention, flame retardation refers to heat treatment of the precursor fiber at 200 to 310° C. in an oxygen-containing atmosphere.

[0062] The flame-stabilizing time referred to here means the time the fiber remains in the flame-stabilizing furnace. The flame-stabilized fiber refers to the fiber after the flame-stabilizing step and before the preliminary carbonization step. The peak intensity referred to here means the absorbance at each wavelength after baseline correction of the infrared spectrum obtained by sampling a small amount of the flame-stabilized fiber and measuring the spectrum, without any particular peak division. The sample concentration when measuring the infrared spectrum is diluted with KBr to 0.67% by mass. In this way, the infrared spectrum is measured every time the flame-stabilizing condition settings are changed, and the conditions are examined according to the preferred manufacturing method described below. By appropriately controlling the infrared spectrum peak intensity ratio of the flame-stabilized fiber, the strand strength of the resulting carbon fiber can be controlled.

[0063] Air is preferably used as the oxidizing atmosphere in the flame-proofing treatment. In the present invention, the preliminary carbonization treatment and the carbonization treatment are carried out in an inert atmosphere. Examples of gases used in the inert atmosphere include nitrogen, argon, and xenon, and from an economical viewpoint, nitrogen is preferably used.

[0064] The obtained carbon fiber bundles can be subjected to electrolytic treatment for surface modification, because electrolytic treatment can optimize the adhesion between the carbon fiber and the carbon fiber matrix in the obtained fiber-reinforced composite material.

[0065] After the electrolytic treatment, the carbon fiber bundles are subjected to a sizing treatment to impart bundling properties. A sizing agent that is compatible with the matrix resin can be selected appropriately depending on the type of resin used, but it is important to control the adhesion between the carbon fiber and the resin to simultaneously suppress interfacial delamination and mitigate stress concentration when the carbon fiber reinforced composite material is made, and to achieve good mechanical properties.

[0066] For this purpose, it is preferable to optimize the electrolysis conditions, such as the type and concentration of the electrolyte, the deposition ratio of the sizing agent, or control the amount of functional groups contained in the sizing agent. When the sizing agent contains epoxy groups, it is preferable to hydrolyze the epoxy groups in advance before applying the sizing agent, and also to adjust the amount of epoxy groups by subjecting the carbon fiber bundle after applying the sizing agent to an aging treatment at constant temperature and humidity to hydrolyze the epoxy groups.

[0067] The carbon fiber bundle containing the sizing agent of the present invention is preferably used as a reinforcing fiber for a carbon fiber reinforced composite material. Members using such carbon fiber reinforced composite materials can be used in many fields, such as aerospace, automobiles, railway vehicles, ships, civil engineering and construction, and sporting goods. In particular, they can be suitably used as hollow containers such as pressure vessels, and cylindrical members.

[0068] A known method can be used to produce a carbon fiber reinforced composite material using a carbon fiber bundle containing the sizing agent of the present invention. In particular, when producing hollow containers such as pressure vessels and cylinders, it is preferable to apply a molding method using filament winding or a towpreg in which fibers are pre-impregnated with a resin.

[0069] The methods for measuring various physical property values ​​used in the examples of the present invention are as follows. In the items of the measurement methods and in the tables of the results, for carbon fiber bundles not containing a sizing agent among the comparative examples, "carbon fiber bundles containing a sizing agent" will be read as "carbon fiber bundles."

[0070] <Infrared Spectral Intensity Ratio> After freeze-pulverization, 2 mg of the flame-resistant fiber to be measured was precisely weighed and sampled, which was then thoroughly mixed with 300 mg of KBr, placed in a molding jig, and pressed at 40 MPa for 2 minutes using a press to prepare a tablet for measurement. This tablet was set in a Fourier transform infrared spectrophotometer, and the 1,000 to 2,000 cm －１ The spectrum is measured in the range of 1,700 to 2,000 cm. －１This was done by subtracting the minimum value in the range from each intensity so that the minimum value in the range would be 0. The Paragon 1000 manufactured by PerkinElmer was used as the Fourier transform infrared spectrophotometer. The peak intensity ratio was calculated using the peak intensities at each wavenumber obtained in this way.

[0071] <Total Fineness> A 10 m length of the carbon fiber bundle containing the sizing agent to be measured was sampled, and bone dried at 120°C for 2 hours. The mass (unit: grams) measured after that was divided by 10 to determine the total fineness (unit: g / m), which is the mass per 1 m.

[0072] <Evaluation of specific gravity of carbon fiber single fiber> A 1 m sample is taken from the carbon fiber bundle containing the sizing agent to be measured, and the specific gravity is measured by the Archimedes method using o-dichloroethylene as the specific gravity liquid. The measurement is carried out on three samples. The average value is used as the measured value.

[0073] <Single fiber diameter> The single fiber diameter was calculated from the total fineness (g / m) and specific gravity obtained by the above method and the number of filaments in the carbon fiber bundle used for the measurement. The unit of the single fiber diameter was μm.

[0074] <Strand strength and strength utilization rate of carbon fiber bundle containing sizing agent> Strand strength The strand strength of the carbon fiber bundle containing a sizing agent was determined using each resin formulation (resin formulation A, resin formulation B) in accordance with the resin-impregnated strand strength test method of JIS-R-7608 (2007). The curing conditions were as shown for each resin formulation. Ten strands of the carbon fiber bundle containing a sizing agent were measured, and the average values ​​(rounded to the first decimal place in GPa) were taken as strand strengths A' and B', respectively. Strength utilization rate The strength utilization rate was determined using the following formula from the strand strengths A' and B' obtained above. Strength utilization rate (%) = (strand strength B' / strand strength A') × 100 The strength utilization rate was determined to two significant digits.

[0075] <Measurement of the content ratio Y (Sz content ratio) of sizing agent in carbon fiber bundle containing sizing agent> A carbon fiber bundle containing 2.0±0.5 g of sizing agent was weighed (W １) (read to four decimal places), and then place in an electric furnace (capacity 120 cm) set to a temperature of 450°C in a nitrogen gas flow of 50 ml / min. ３ ) for 15 minutes to completely decompose the sizing agent. Then, the carbon fiber bundle was transferred to a container in a dry nitrogen gas flow of 20 liters / minute, and cooled for 15 minutes, after which the carbon fiber bundle was weighed (W ２ ) (read to four decimal places) and W １ -W ２ The content of the sizing agent in the carbon fiber bundle containing the sizing agent is calculated by the following formula. １ The content ratio Y (mass%) of the sizing agent was calculated by dividing the total weight of the sizing-agent-containing carbon fiber bundle by 100 mass% (rounded to two decimal places). The measurement was carried out twice, and the average value was taken as the content ratio Y (mass%) of the sizing agent.

[0076] <Measurement of Epoxy Value X> 30 g of carbon fiber bundles containing a sizing agent were immersed in 150 ml of N,N-dimethylformamide solvent at 25°C, and subjected to ultrasonic treatment three times for 30 minutes at a frequency of 40 kHz. The sizing agent solution eluted from the fibers was analyzed to determine the epoxy value X. When the sizing agent was eluted from the carbon fiber bundles containing the sizing agent, the amount of sizing agent remaining in the carbon fibers was set to 0.20 mass% or less. The epoxy groups in the eluted sizing agent solution were ring-opened with hydrochloric acid, and the epoxy value X (meq. / g) was determined by acid-base titration.

[0077] <Measurement of Drape Value> As shown in Figure 1, a 50 cm-cut carbon fiber bundle 2 containing a sizing agent was hung with a weight 3 under a load of 0.0375 [g / tex] in an atmosphere at 25°C and left for 30 minutes or more to remove twisting. A 30 cm-long portion was sampled from the center, and as shown in Figure 2, the carbon fiber bundle 2 containing a sizing agent was placed on a rectangular horizontal stand 4 with a 90° angle so that 25 cm of the carbon fiber bundle protruded from the horizontal stand 4 while being supported to prevent bending. The carbon fiber bundle 2 containing a sizing agent on the horizontal stand 4 was then fixed with tape. The support for the carbon fiber bundle 2 containing a sizing agent protruding from the horizontal stand 4 was then removed, allowing it to hang down. After 1 second, the horizontal distance L from the fulcrum was measured. The measurement was performed five times, and the arithmetic average of the measurements was taken as the drape value.

[0078] <Measurement of Interfacial Shear Strength (IFSS)> The interfacial shear strength is measured according to the following steps (1) to (4).

[0079] (1) Preparation of Resin 100 parts by mass of bisphenol A epoxy compound "jER (registered trademark)" 828 (manufactured by Mitsubishi Chemical Corporation) and 14.5 parts by mass of metaphenylenediamine (manufactured by Sigma-Aldrich Japan Co., Ltd.) were placed in a container. Thereafter, the mixture was heated at a temperature of 75°C for 15 minutes to reduce the viscosity of the jER828 and dissolve the metaphenylenediamine. Thereafter, the two mixtures were thoroughly mixed and subjected to vacuum degassing at a temperature of 80°C for approximately 15 minutes.

[0080] (2) Fixing the carbon fiber monofilament in a dedicated mold: One monofilament was extracted from a carbon fiber bundle containing a sizing agent, and both ends were fixed with adhesive while applying a constant tension of 4.0±2.0 g to the monofilament in the longitudinal direction of a dumbbell-shaped mold. Then, to remove moisture adhering to the carbon fiber monofilament and the mold, the mold was vacuum-dried at a temperature of 80°C for 30 minutes or more. The dumbbell-shaped mold used was made of silicone rubber, and the casting part had a central width of 5 mm, a length of 25 mm, both end widths of 10 mm, and an overall length of 150 mm.

[0081] (3) From resin casting to curing The resin prepared in the above procedure (1) was poured into the mold after vacuum drying in the above procedure (2), and using an oven, the temperature was increased to 75°C at a rate of 1.5°C / min and held for 2 hours, then increased to 125°C at a rate of 1.5°C / min and held for 2 hours, and then decreased to 30°C at a rate of 2.5°C / min. The mold was then demolded to obtain a test piece.

[0082] (4) Measurement of Interfacial Shear Strength: A tensile force was applied to the test piece obtained by the procedure in (3) above in the fiber axis direction (longitudinal direction) of the carbon fiber monofilament to generate a strain of 12%, and then the number N (number of breaks) of monofilament breaks within a 22 mm range at the center of the test piece was measured using a polarizing microscope. Next, the average broken fiber length la was calculated using the formula: la (μm) = 22 × 1,000 (μm) / N (number of breaks). Next, the critical fiber length lc was calculated from the average broken fiber length la using the formula: lc (μm) = (4 / 3) × la (μm). Using the strand strength A' obtained by the above method and the carbon fiber monofilament diameter d, the interfacial shear strength, which is an index of the adhesive strength at the interface between the carbon fiber and the resin, was calculated using the following formula. The measurement was performed five times, and the arithmetic average was used as the test result. Interfacial shear strength (MPa) = strand strength A' (MPa) x d (µm) / (2 x lc) (µm).

[0083] <Processability of carbon fiber bundle containing sizing agent> An example is shown for the case of 24,000 filaments. Correspondence for other filament numbers is shown later, with the number of filaments being N. Two metal bars (made of stainless steel) with a diameter of 50 mm and a surface roughness Rmax of 0.3 μm were arranged 150 mm apart, and in the vertical direction so that the carbon fiber bundle passed while contacting each metal bar at an angle of 0.3925π (rad) ± 0.04π (rad), for a total of 0.785π (rad). Then, a carbon fiber bundle containing a sizing agent and having 24,000 filaments was hung on the metal bars, and the unwinding tension from the package was set to 1600 g. The bundle was pulled by a drive roll at 4 m / min to pass the metal bar, and the number of fluffs was counted for one minute after passing the second metal bar, to determine the processability.

[0084] Number of process fluffs of carbon fiber bundle (pieces / m) = Number of counted fluffs (pieces) / 4 (m) A: Number of process fluffs is 4.9 pieces / m or less B: Number of process fluffs is more than 4.9 pieces / m and 7.0 pieces / m or less C: Number of process fluffs is more than 7.0 pieces / m When the number of filaments in the carbon fiber bundle to be measured is N (N is a natural number), the release tension was set to 1,600 × N / 24,000 g, and the counted number of process fluffs was divided by √(N / 24,000) to determine the processability after aligning the evaluation criteria. For example, when the number of filaments in the carbon fiber bundle to be measured is 36,000, the release tension was set to 2,400 g, and the counted number of process fluffs was divided by √1.5 to determine the processability. Note that the measurement conditions other than the unwinding tension are the same as when the number of filaments is 24,000. A and B are preferred results in the present invention, with A being the more preferred result.

[0085] <Pressure resistance of pressure vessel> A sample pressure vessel was placed in a pressure vessel hydraulic burst test device shown in Figure 3, and water was pumped in and pressurized using a hydraulic pump to measure the burst pressure when the vessel burst. Measurements were performed three times, and the arithmetic mean values ​​were used to evaluate pressure resistance performance according to the following criteria. S, A, B, or C are preferred ranges in the present invention, with S, A, or B being more preferred. Note that "-" indicates a missing value. S: Burst pressure of 107 MPa or more A: Burst pressure of 99 MPa or more but less than 107 MPa B: Burst pressure of 91 MPa or more but less than 99 MPa C: Burst pressure of 86 MPa or more but less than 91 MPa D: Burst pressure less than 86 MPa

[0086] Reference Example 1-1: Method for Producing Carbon Fiber Bundles I A copolymer of acrylonitrile and itaconic acid was dissolved in dimethyl sulfoxide to prepare a spinning solution. The resulting spinning solution was extruded into air through a spinneret with 6,000 holes and introduced into a coagulation bath of an aqueous solution of dimethyl sulfoxide via a dry-wet spinning method to obtain a coagulated fiber bundle. This fiber bundle was then washed with water at 30 to 98°C and stretched by a conventional method. Subsequently, an amino-modified silicone-based silicone oil was applied to the fiber bundle after water bath stretching, and the fiber bundle was subjected to a drying and densification treatment using a heated roller at 160°C. The fiber bundle then had 12,000 filaments and was then stretched 3.7 times in pressurized steam, resulting in a total draw ratio of 13 times, yielding a polyacrylonitrile-based precursor fiber bundle with a single fiber fineness of 0.7 dtex.

[0087] Next, the polyacrylonitrile precursor fiber bundles obtained as necessary were doubling up to obtain the number of filaments shown in Table 1, and then treated in the following calcination step to obtain carbon fiber bundles.

[0088] The first flame-stabilizing step was carried out under conditions of a flame-stabilizing temperature of 240°C and a flame-stabilizing time of 36 minutes, and the second flame-stabilizing step was carried out under conditions of a flame-stabilizing temperature of 250°C and a flame-stabilizing time of 37 minutes, and the carbon fiber precursor fiber bundle was subjected to a flame-stabilizing treatment while being stretched at a draw ratio of 1 in an oven in an air atmosphere, to obtain a flame-stabilized fiber.

[0089] 1,370 cm in the infrared spectrum of the fiber after the first flame retardant treatment －１ The peak intensity at 1,453 cm －１ The ratio of the peak intensities at 1,370 cm in the infrared spectrum of the fiber after the second flameproofing step was 0.87. －１ The peak intensity at 1,453 cm －１ The ratio of the peak intensities is 0.63 and 1,370 cm －１ The peak intensity at 1,254 cm －１ The peak intensity ratio was 0.60.

[0090] The obtained flame-resistant fiber was subjected to a pre-carbonization treatment in a nitrogen atmosphere at a maximum temperature of 900°C and a draw ratio of 0.96 to obtain a pre-carbonized fiber. The obtained pre-carbonized fiber was subjected to a carbonization treatment in a nitrogen atmosphere at a maximum temperature of 1,500°C and a draw ratio of 0.950.

[0091] Subsequently, the carbon fiber bundle was subjected to electrolytic surface treatment using an aqueous sulfuric acid solution as an electrolyte, washed with water, and dried to obtain a carbon fiber bundle containing no sizing agent. The carbon fiber bundle obtained by carbon fiber bundle manufacturing method I is referred to as carbon fiber I in the tables for convenience.

[0092] [Reference Example 1-2] Carbon fiber bundle manufacturing methods II to IV Using carbon fiber bundle manufacturing method I as a base, carbon fiber bundles containing no sizing agent were obtained by changing the flame retardant treatment, pre-carbonization, and carbonization conditions shown in Table 1. The manufacturing methods for each carbon fiber are designated manufacturing methods II to IV, and, as with manufacturing method I, the obtained carbon fiber bundles are conveniently referred to as carbon fibers II to IV in the table.

[0093]

[0094] Reference Example 2-1: Production of sizing agents i to iii Ethylene oxide was added to bisphenol A in the presence of a potassium hydroxide catalyst, followed by removal of the catalyst to obtain an ethylene oxide (2 moles) adduct of bisphenol A. 2 moles of the ethylene oxide adduct of bisphenol A, 1.5 moles of maleic acid, and 0.5 moles of sebacic acid were charged into a 1 L flask equipped with a stirrer, stirring blade, nitrogen seal, and rectification column. While blowing nitrogen into the liquid, the mixture was heated and stirred at 160°C for 4 hours, and the resulting water was distilled off to obtain 2 parts by mass of a condensate of an unsaturated dibasic acid and an alkylene oxide adduct of bisphenols. This was followed by preparation of an aqueous dispersion emulsion consisting of 2 parts by mass of "jER (registered trademark)" 828 (manufactured by Mitsubishi Chemical Corporation), 1 part by mass of polyoxyethylene (70 moles) styrenated (5 moles) cumylphenol, and 95 parts by mass of distilled water, to obtain sizing agent i. Sizing agent i was heat-treated under the conditions shown in Table 2 to obtain sizing agents ii and iii.

[0095] Reference Example 2-2 Sizing Agent iv Bisphenol A ethylene oxide 10 mol adduct represented by the following formula was used as sizing agent iv.

[0096]

[0097]

[0098] [Examples 1 to 14, Comparative Examples 1 to 7] Carbon fiber bundles I to IV containing no sizing agent obtained in Reference Example 1 were impregnated with sizing agents i to iv obtained in Reference Example 2 after adjusting the concentrations of the aqueous sizing agents so as to achieve the combinations and content ratios of the sizing agents shown in Table 3. Thereafter, a heat treatment was performed at a temperature of 210°C for 75 seconds to obtain carbon fiber bundles containing a sizing agent.

[0099] The physical properties of the obtained carbon fiber bundles are summarized in Table 3. For Comparative Example 1 to which no sizing agent was applied, fluffing and misalignment occurred when measuring the strand strength, resulting in a strand strength A' of 5.7 GPa, which was lower than the level when a sizing agent was applied to carbon fiber bundle I. Furthermore, for Comparative Example 1 to which no sizing agent was applied, and Examples 5, 8, 11, and 14 to which an epoxy group-free sizing agent iv was used, the epoxy value was not measured.

[0100] Next, "Araldite (registered trademark)" LY1564 SP CI and "Baxodur (registered trademark)" EC331 were mixed in a ratio of 100:35 (parts by mass) to prepare a resin composition B corresponding to resin formulation B.

[0101] A 7.5 L polyethylene liner was placed in a filament winding molding device, and the resin composition B, which had been uniformly mixed in advance at 25°C, was impregnated into the sized carbon fiber bundles while being fed so that the amount of the resin composition B applied relative to the total mass of the carbon fiber bundles and the resin composition B was 22 to 28 mass %.

[0102] First, hoop layers forming an angle of +89° with respect to the axial direction of the liner and hoop layers forming an angle of −89° with respect to the axial direction of the liner were alternately formed and wound to form a first layer having a thickness of 1.4 mm.

[0103] Next, a helical layer was wound at an angle of ±20° with respect to the axial direction of the liner to a thickness of 2.2 mm to form a second layer.

[0104] Furthermore, a hoop layer forming an angle of +89° with respect to the axial direction of the liner and a hoop layer forming an angle of −89° with respect to the axial direction of the liner were alternately formed, and the resulting third layer was wound to a thickness of 0.6 mm, thereby obtaining an intermediate body consisting of the first to third layers.

[0105] As described above, the carbon fiber bundle containing the sizing agent impregnated with resin composition B was wound around a 7.5 L polyethylene liner to form an intermediate, which was then rotated at a speed of 7 rpm and held for 15 minutes in an environment of 20°C. The intermediate was heated at a temperature of 80°C for 120 minutes and then at a temperature of 110°C for 240 minutes to cure mixture B, thereby obtaining a pressure vessel for pressure resistance testing.

[0106] In Examples 4 and 5, carbon fiber bundles were produced using the same carbon fiber bundle manufacturing method I as in Comparative Examples 2 and 3, and although strand strength A' was equivalent, strand strength B' and the pressure resistance of the pressure vessel were improved. This shows that by optimizing the adhesion at the interface between the carbon fiber and the resin using a sizing agent, the tensile strength of the carbon fiber can be efficiently expressed and the pressure resistance of the pressure vessel can be increased to a high level.

[0107] In Example 8, carbon fiber bundles were produced using the same carbon fiber bundle manufacturing method II as in Comparative Example 5, and although strand strength A' was equivalent, strand strength B' and the pressure resistance of the pressure vessel were improved. This shows that by optimizing the adhesion at the interface between the carbon fiber and the resin using a sizing agent, the tensile strength of the carbon fiber can be efficiently expressed and the pressure resistance of the pressure vessel can be increased to a high level.

[0108] In Example 11, carbon fiber bundles were produced using the same carbon fiber bundle manufacturing method III as in Comparative Example 6, and although strand strength A' was equivalent, strand strength B' and the pressure resistance of the pressure vessel were improved. This shows that by optimizing the adhesion at the interface between the carbon fiber and the resin using a sizing agent, the tensile strength of the carbon fiber can be efficiently expressed and the pressure resistance of the pressure vessel can be increased to a high level.

[0109] In Example 14, carbon fiber bundles were produced using the same carbon fiber bundle manufacturing method IV as in Comparative Example 7, and although strand strength A' was equivalent, strand strength B' and the pressure resistance of the pressure vessel were improved. This shows that by optimizing the adhesion at the interface between the carbon fiber and the resin using a sizing agent, the tensile strength of the carbon fiber can be efficiently expressed and the pressure resistance of the pressure vessel can be increased to a high level.

[0110] [Examples 15 to 18] The carbon fiber bundles of Comparative Examples 3, 5, 6, and 7 were left standing in a constant temperature and humidity environment of 60°C and 90% relative humidity for 200 hours to undergo aging treatment, thereby obtaining the carbon fiber bundles of Examples 15 to 18. Thereafter, pressure vessels for pressure tests were obtained in the same manner as in Comparative Examples 3, 5, 6, and 7. The physical properties of the obtained carbon fiber bundles are summarized in Table 4. Compared to before the aging treatment, the strand strength B' was improved, and the pressure resistance of the pressure vessel was also improved. In other words, this shows that by optimizing the adhesion at the interface between the carbon fiber and the resin, the tensile strength of the carbon fiber can be efficiently expressed, and the pressure resistance of the pressure vessel can be increased to a high level.

[0111]

[0112]

[0113] 1: Fixing bar 2: Carbon fiber bundle 3: Weight 4: Horizontal platform 5: Compressed air line 6: Pressure booster 7: Water pressure pump 8: Liquid supply hose 9: Fixing mechanism 10: Pressure vessel 11: Safety cover 12: Data logger

Claims

1. A carbon fiber bundle containing a sizing agent, the strand strength (strand strength A') evaluated based on JIS R7608 (2007) using the following resin formulation A is 5.9 GPa or more, the strand strength (strand strength B') evaluated based on JIS R7608 (2007) using the following resin formulation B is 5.7 GPa or more, the ratio of the strand strength B' to the strand strength A' is 90% or more, the single fiber diameter is 5.1 or more and less than 6.0 μm, and the interface shear strength is 16 MPa or less. Resin formulation A: "Celloxide (registered trademark)" 2021P / boron trifluoride monoethylamine / acetone = 100 / 3 / 4 (parts by mass) is used, and the curing conditions are normal pressure, temperature 125 ° C, and time 30 minutes. Resin formulation B: "Araldite" (registered trademark) LY1564 SP CI / "Baxodur" (registered trademark) EC331 = 100 / 35 (parts by mass) was used, and the curing conditions were normal pressure, temperature 80°C, and curing time 120 minutes, followed by temperature 110°C and time 240 minutes.

2. A carbon fiber bundle containing a sizing agent according to claim 1, wherein the number of filaments constituting the carbon fiber bundle containing a sizing agent is 24,000 or more.

3. A carbon fiber bundle containing the sizing agent according to claim 1 or 2, wherein the strand strength B' is 6.0 GPa or more.

4. A carbon fiber bundle containing a sizing agent according to claim 1 or 2, wherein the sizing agent contains at least one component containing an epoxy group, and when the epoxy value of the sizing agent eluted by immersing a carbon fiber bundle containing the sizing agent in an N,N-dimethylformamide solvent and subjecting it to ultrasonic treatment is X meq. / g, and the content of the sizing agent contained in the carbon fiber bundle containing the sizing agent is Y mass %, X and Y satisfy the relationship of the following formula 1. 0.1 meq. / g≦X×Y≦0.68 meq. / g... formula 1 5. A carbon fiber bundle containing the sizing agent according to claim 1 or 2, which has a drape value of 18 cm or less.

6. A carbon fiber bundle containing the sizing agent according to claim 5, which has a drape value of 4 cm or more and 10 cm or less.

7. A carbon fiber reinforced composite material using a carbon fiber bundle containing the sizing agent according to claim 1 or 2.

8. A pressure vessel using a carbon fiber bundle containing the sizing agent according to claim 1 or 2.

9. A carbon fiber bundle containing a sizing agent according to claim 1 or 2, wherein the number of filaments constituting the carbon fiber bundle containing a sizing agent is 36,000 or more.

10. A carbon fiber bundle containing a sizing agent according to claim 1 or 2, wherein the diameter of the single fiber constituting the carbon fiber bundle containing a sizing agent is 5.8 μm or less.

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