Classifications

• • D—TEXTILES; PAPER
  • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
  • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
  • D06M15/00—Treating fibres, threads, yarns, fabrics, or fibrous goods made from such materials, with macromolecular compounds; Such treatment combined with mechanical treatment
  • D06M15/19—Treating fibres, threads, yarns, fabrics, or fibrous goods made from such materials, with macromolecular compounds; Such treatment combined with mechanical treatment with synthetic macromolecular compounds
  • D06M15/37—Macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
  • D06M15/55—Epoxy resins
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
  • B29B15/00—Pretreatment of the material to be shaped, not covered by groups B29B7/00 - B29B13/00
  • B29B15/08—Pretreatment of the material to be shaped, not covered by groups B29B7/00 - B29B13/00 of reinforcements or fillers
  • B29B15/10—Coating or impregnating independently of the moulding or shaping step
  • B29B15/12—Coating or impregnating independently of the moulding or shaping step of reinforcements of indefinite length
  • B29B15/14—Coating or impregnating independently of the moulding or shaping step of reinforcements of indefinite length of filaments or wires
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/04—Reinforcing macromolecular compounds with loose or coherent fibrous material
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/04—Reinforcing macromolecular compounds with loose or coherent fibrous material
  • C08J5/0405—Reinforcing macromolecular compounds with loose or coherent fibrous material with inorganic fibres
  • C08J5/042—Reinforcing macromolecular compounds with loose or coherent fibrous material with inorganic fibres with carbon fibres
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/04—Reinforcing macromolecular compounds with loose or coherent fibrous material
  • C08J5/06—Reinforcing macromolecular compounds with loose or coherent fibrous material using pretreated fibrous materials
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/24—Impregnating materials with prepolymers which can be polymerised in situ, e.g. manufacture of prepregs
  • C08J5/241—Impregnating materials with prepolymers which can be polymerised in situ, e.g. manufacture of prepregs using inorganic fibres
  • C08J5/243—Impregnating materials with prepolymers which can be polymerised in situ, e.g. manufacture of prepregs using inorganic fibres using carbon fibres
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/24—Impregnating materials with prepolymers which can be polymerised in situ, e.g. manufacture of prepregs
  • C08J5/248—Impregnating materials with prepolymers which can be polymerised in situ, e.g. manufacture of prepregs using pre-treated fibres
• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
  • D01F9/00—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments
  • D01F9/08—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments of inorganic material
  • D01F9/12—Carbon filaments; Apparatus specially adapted for the manufacture thereof
  • D01F9/14—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments
  • D01F9/20—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products
  • D01F9/21—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products from macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • D01F9/22—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products from macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds from polyacrylonitriles
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2363/00—Characterised by the use of epoxy resins; Derivatives of epoxy resins
• • D—TEXTILES; PAPER
  • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
  • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
  • D06M2101/00—Chemical constitution of the fibres, threads, yarns, fabrics or fibrous goods made from such materials, to be treated
  • D06M2101/40—Fibres of carbon
• • D—TEXTILES; PAPER
  • D10—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
  • D10B—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
  • D10B2101/00—Inorganic fibres
  • D10B2101/10—Inorganic fibres based on non-oxides other than metals
  • D10B2101/12—Carbon; Pitch

Definitions

• the present invention relates to carbon fiber bundles that are 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.
• PAN Polyacrylonitrile
• carbon fiber composite materials In order to improve the tensile strength of carbon fiber reinforced composite materials (hereinafter sometimes simply referred to as "carbon fiber composite materials"), in addition to simply increasing the strand strength of the carbon fiber itself, one approach is to improve how efficiently the mechanical properties of the carbon fiber can be expressed when it is used as a reinforcing fiber for composite materials (i.e., the strength utilization rate).
• Patent documents 1 and 2 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.
• Patent document 3 also proposes a technique of preventing fuzzing and thread breakage when molded by filament winding by increasing the strand strength and thread breakage limit tension, and improving the expression of tensile strength in the resulting cylinder.
• Patent document 4 improves the impact resistance, tensile strength, and compressive strength of a carbon fiber composite material by adjusting the rigidity modulus of the rubber-like flat part above the glass transition point.
• Patent document 5 improves the interlaminar toughness and compressive strength under high temperature conditions of a carbon fiber composite material by adjusting the rigidity modulus of the rubber-like flat part above the glass transition point.
• Patent document 6 improves the compressive strength of a carbon fiber composite material by adjusting the compressive yield stress of a resin cured product.
• Patent documents 7 to 10 propose preventing yarn breakage and improving the openability and resin impregnation of carbon fiber bundles when forming a carbon fiber composite material to improve moldability when forming the carbon fiber composite material, and improving strength development by eliminating unimpregnated and excess resin portions.
• Patent document 7 proposes a technique for achieving both abrasion resistance, yarn breakage, and resin impregnation by attaching a sizing agent to the inner layer of the carbon fiber bundle and then blowing gas to remove the sizing agent from the outer layer of the carbon fiber bundle.
• Patent document 8 proposes a technique for improving moldability when forming a composite material by adding entanglement to the carbon fiber precursor fiber bundle to make it less likely to break when opening the fiber to form a composite material.
• Patent document 9 proposes a technique for improving resin impregnation by reducing the fiber diameter per single fiber constituting the carbon fiber bundle and forming a groove of a specific depth in the fiber axis direction on the surface of the single fiber.
• Patent document 10 also proposes a technique for forming a homogeneous molded body by flattening the shape of the carbon fiber bundle to improve openability during molding.
• the 0° tensile strength of a carbon fiber composite material is easily expressed 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 Document 12 proposes a technique for suppressing the deterioration of mechanical properties from processing carbon fiber bundles into a prepreg form to processing them into a final molded product, in which excess epoxy groups contained in the sizing agent are hydrolyzed either before or after applying the sizing agent to the carbon fiber bundle, or both.
• Patent Documents 1 and 2 Although the strand strength is improved before and after the nitric acid treatment for both types of resin, the post-treatment of the fine carbon fiber requires nitric acid treatment, drying, and inactivation in a nitrogen atmosphere at 700°C for several minutes, which leads to problems in terms of quality deterioration due to the generation of fluff, and productivity and cost due to the post-treatment.
• the same resin as that used for strand evaluation is used to measure the tensile strength of the cylinder formed by filament winding, so the presence or absence of strength reduction due to yarn damage in the filament winding molding process can be evaluated, but the improvement of the strength utilization rate due to the difference in resin is insufficient.
• Patent Documents 4 to 6 the mechanical properties of the epoxy resin cured material are designed to maximize the mechanical properties of existing carbon fibers, but since it is limited to a resin with a specific composition, it is not a technology that can be applied to carbon fiber composite materials for a wide range of applications.
• the technologies of Patent Documents 7 to 10 are merely technologies that improve the moldability of carbon fiber bundles, and if good moldability has already been established, improvement of the mechanical properties cannot be expected.
• Patent Documents 8 and 9 the diameter of the single fibers that make up the carbon fiber bundle is small, so there are problems with the productivity of the carbon fiber bundle itself and the deterioration of quality due to the generation of fluff during processing.
• Patent Document 10 the base resin and hardener described in the resin-impregnated strand strength test method of JIS R7608 (2007) are used as the matrix resin when making a carbon fiber composite material, and this is a technology that suppresses the decrease in strength when the test specimen is made into a cylindrical shape.
• the technology in Patent Document 11 claims that the 0° tensile strength of the carbon fiber composite material is high compared to the strength of the resin-impregnated strand of the carbon fiber bundle, but the absolute value of the strength is not sufficient.
• the technology in Patent Document 12 suppresses the decrease in strength that occurs from processing into a prepreg form to processing into a final molded product, but does not improve strength.
• the evaluation method based on the resin composition and method specified in JIS R7608 (2007) is excellent in that test specimens can be easily prepared and stable test results can be obtained, but compared to practical resins used in carbon fiber composite materials, it has fewer functional groups and often has poor adhesion to carbon fiber bundles. For this reason, there may be a discrepancy between the resin-impregnated strand strength specified in JIS R7608 (2007) and the 0° tensile strength of carbon fiber composite materials using practical resins.
• the present invention aims to find an evaluation method using a resin composition that reflects the strength exhibited when made into a carbon fiber composite material, and to provide a carbon fiber bundle that can efficiently exhibit tensile strength when made into a carbon fiber composite material by optimally designing the carbon fiber bundle manufacturing method, the interfacial adhesion between the carbon fiber bundle and the resin, or both.
• the present invention comprises the following configuration.
• a carbon fiber bundle to which a sizing agent has been applied, the strand strength (strand strength A') evaluated based on JIS R7608 (2007) using the following resin formulation A is 5.0 GPa or more and 6.0 GPa or less, the strand strength (strand strength B') evaluated based on JIS R7608 (2007) using the following resin formulation B is 4.7 GPa or more and 5.5 GPa or less, a ratio of the strand strength B' to the strand strength A' is 85% or more, and a single fiber diameter is 6.0 ⁇ m or more.
• a carbon fiber bundle according to (1) in which the product Ex d/W of the ratio d/W of the single fiber diameter d to the loop width W just before breakage evaluated by the single fiber loop method and the strand elastic modulus E is 12.6 GPa or more.
• the tensile strength of carbon fiber reinforced composite materials can be efficiently improved.
• FIG. 1 is a diagram showing a method for preparing a sample used to measure 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 carrying out a pressure test on a pressure vessel.
• the carbon fiber bundle of the present invention has a strand strength 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).
• the strand strength with this resin formulation A may be referred to as "strand strength A'", of 5.0 GPa or more and 6.0 GPa or less, preferably 5.5 GPa or more and 6.0 GPa or less, and more preferably 5.7 GPa or more and 6.0 GPa or less.
• Strand strength A' is an index showing the resistance of carbon fibers to breakage when a load is applied, and is an index showing the strength of the carbon fiber bundle itself. If strand strength A' is 5.0 GPa or more, it is easy to increase the strength when made into a carbon fiber composite material. The higher the strand strength, the better, but if strand strength A' is preferably 5.5 GPa or more, and more preferably 5.7 GPa or more, it is easy to make a carbon fiber composite material that is extremely excellent for practical use. Strand strength A' can be controlled by manufacturing according to the carbon fiber manufacturing method described below.
• the carbon fiber bundle of the present invention has a strand strength evaluated according to 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 4.7 GPa or more and 5.5 GPa or less, preferably 4.9 GPa or more and 5.5 GPa or less.
• Resin formula B is a practical resin for filament winding (towpreg) by the dry method, and has a viscosity suitable for preparing strand test pieces by the impregnation method described in JIS R7608 (2007).
• resin formula A which is a combination of resins described in JIS R7608 (2007), resin formula B has more functional groups and has high adhesion to carbon fiber bundles, so strand strength B' is an index that represents the strength of a carbon fiber bundle when it is made into a carbon fiber composite material. If strand strength B' is 4.7 GPa or more, it is easy to increase the strength when it is actually made into a carbon fiber composite material.
• Strand strength B' is 4.9 GPa or more, it is easy to make a carbon fiber composite material that is extremely excellent in practical use.
• Strand strength B' can be controlled by improving the density of the carbon fiber precursor fiber bundle according to the carbon fiber manufacturing method described later, adjusting the interfacial adhesion between the carbon fiber and the resin, or both.
• the carbon fiber bundle of the present invention has a ratio of strand strength B' to strand strength A' (strand strength B'/strand strength A'; hereinafter, sometimes referred to as "strength utilization rate ⁇ ") of 85% or more, and preferably 88% or more.
• the strength utilization rate ⁇ is an index of strength expression when a carbon fiber bundle is made into a carbon fiber composite material. If the strength utilization rate ⁇ is 85% or more, the mechanical properties of the carbon fiber can be efficiently expressed when made into a carbon fiber composite material. The closer to 100% the strength utilization rate ⁇ is, the more preferable, but in many cases, 88% or more is sufficient for a carbon fiber composite material.
• the single fiber diameter of the carbon fiber bundle of the present invention is 6.0 ⁇ m or more, preferably 6.6 ⁇ m or more, and more preferably 6.8 ⁇ m or more.
• the breaking load per single fiber is determined by the strand strength and the cross-sectional area of the single fiber, so the single fiber diameter affects the breaking load per single fiber.
• the larger the single fiber diameter the less fuzzing due to abrasion during the process tends to occur, which affects the quality. If the single fiber diameter is 6.6 ⁇ m or more, the quality is likely to be good when producing carbon fiber or when making it into a carbon fiber composite material.
• the single fiber diameter is too large, there is a possibility that the reaction will become uneven within the single yarn during the baking process, so a single fiber diameter of 6.8 ⁇ m or more is sufficient, and a single fiber diameter of 8.0 ⁇ m or less is preferable.
• the carbon fiber bundle of the present invention satisfies the ranges described above for strand strength, strength utilization rate ⁇ , and single fiber diameter in resin formulations A and B, and therefore can achieve improved tensile strength and pressure resistance as a pressure vessel when made into a carbon fiber composite material.
• the carbon fiber bundle of the present invention preferably has a product Ex ⁇ d/W of the ratio d/W of the single fiber diameter (d, in ⁇ m; for convenience, sometimes referred to as "single fiber diameter d") to the loop width just before breakage evaluated by the single fiber loop method (W, in ⁇ m; for convenience, sometimes referred to as "loop width W just before breakage evaluated by the single fiber loop method") and the strand modulus (E, in GPa) of 12.6 GPa or more.
• this strand modulus (for convenience, sometimes referred to as “strand modulus E") is determined by the method described in the Examples section using the resin formulation A described above. There is no particular upper limit to this product Ex ⁇ d/W, and the higher the better, but it is practical to keep it at 14 GPa or less.
• the single fiber loop method is a method for investigating the relationship between the strain applied to a single fiber by deforming the single fiber into a loop and the fracture behavior such as single fiber breakage and buckling.
• a compressive strain is applied to the inside of the single fiber and a tensile strain is applied to the outside. Since compressive buckling occurs before tensile failure, the single fiber loop method has been used in many cases as a test method for the single fiber compressive strength of carbon fiber bundles. However, by evaluating the fracture strain, it is possible to evaluate the achievable bending strength of the carbon fiber bundle.
• d/W is a value proportional to the strain
• the product of this value and the strand modulus E can be said to be a value equivalent to the strength.
• the tensile strength of a composite material may not increase simply by increasing the strand strength of a carbon fiber bundle, the tensile strength of the composite material can be effectively increased by increasing the E ⁇ d/W.
• E ⁇ d/W There is no particular restriction on the upper limit of E ⁇ d/W, but it is sufficient to set the upper limit of E ⁇ d/W at 19.0 GPa. Note that such parameters can be controlled by improving the denseness of the carbon fiber precursor fiber bundle according to the manufacturing method of the carbon fiber bundle of the present invention described later.
• the sizing agent-containing carbon fiber bundle of the present invention preferably has a strand strength of 4.8 GPa or more and 5.5 GPa or less, more preferably a lower limit of 5.0 GPa or more, and even more preferably a lower limit of 5.2 GPa or more, as evaluated in accordance with the tensile test of a resin-impregnated strand described in JIS R7608 (2007) using resin formulation C described below (hereinafter, the strand strength using resin formulation C may be referred to as "strand strength C'").
• Resin formula C is a practical resin for filament winding using the wet method, and has a viscosity suitable for preparing strand test pieces using the impregnation method described in JIS R7608 (2007). Furthermore, compared to resin formula A, which is a combination of resins described in JIS R7608 (2007), resin formula C has more functional groups and has stronger adhesion to carbon fiber bundles. Therefore, it was found that strand strength C' can be used as an index that represents, in model form, the strength of a carbon fiber bundle when it is made into a carbon fiber composite material.
• the strand strength C' is 4.8 GPa or more, it is easy to increase the strength when it is actually made into a carbon fiber composite material. Also, if the strand strength C' is 5.0 GPa or more, it is easy to make a carbon fiber composite material that is extremely excellent for practical use, and 5.5 GPa is often sufficient.
• the strand strength C' can be controlled by improving the density of the carbon fiber precursor fiber bundles according to the carbon fiber manufacturing method described below, by adjusting the interfacial adhesion between the carbon fiber and the resin, or by both.
• the carbon fiber bundle of the present invention preferably has a ratio of strand strength C' to strand strength A' (strand strength C'/strand strength A'; hereinafter, sometimes referred to as "strength utilization rate ⁇ ") of 85% or more, more preferably 88% or more.
• the strength utilization rate ⁇ is an index of strength expression when a carbon fiber bundle is made into a carbon fiber composite material. If the strength utilization rate ⁇ is 85% or more, the mechanical properties of the carbon fiber can be efficiently expressed when made into a carbon fiber composite material. The closer the strength utilization rate ⁇ is to 100%, the more preferable, but in many cases, 88% or more is sufficient as a carbon fiber composite material.
• the carbon fiber bundle of the present invention preferably has an interfacial shear strength of 16 MPa or less, and more preferably 12 MPa or more and 16 MPa or less.
• the interfacial shear strength is an index that indicates the adhesiveness with the resin when the carbon fiber is made into a carbon fiber composite material. If the adhesiveness between the carbon fiber and the resin is low, peeling may occur at the interface between the carbon fiber and the resin, which may lead to the breakage of the entire carbon fiber composite material. If the adhesiveness is 12 MPa or more, preferably 14 MPa or more, peeling at the interface can be expected to be suppressed in practical use when the carbon fiber composite material is made into a carbon fiber composite material.
• the interfacial shear strength 16 MPa or less, as this makes it easier to increase strand strength B', strand strength C', or the strength when actually made into a carbon fiber reinforced composite material.
• the carbon fiber bundle has a single fiber diameter of 6.6 ⁇ m or more, a strand strength A' of 5.0 GPa to 6.0 GPa, a strand strength C' of 4.8 GPa to 5.5 GPa, a strength utilization rate ⁇ of 85% to 100%, and an interfacial shear strength of 16 MPa or less.
• the cross-sectional shape of the constituent single yarn is close to a perfect circle and that the surface irregularities are small.
• the circularity of the carbon fiber precursor fiber bundle is preferably in the range of 0.80 to 0.99, more preferably in the range of 0.90 to 0.99.
• the surface area ratio of the carbon fiber precursor fiber bundle is preferably in the range of 1.00 to 1.08, more preferably in the range of 1.00 to 1.05. If the cross-sectional shape of the single yarn in the precursor fiber bundle is far from a perfect circle, stress concentration occurs when stress is applied as a carbon fiber bundle, increasing the possibility of breakage.
• the surface area ratio is preferably 1.08 or less, and for the same reason, the circularity is preferably 0.80 or more.
• Such circularity and surface area ratio can be measured by the method described below and can be controlled by the spinning conditions.
• the spinning solution which is kept at a higher temperature than the coagulation bath, is discharged from a spinneret into the air, and then introduced into a coagulation bath kept at a relatively low temperature.
• the polymer concentration, the solvent concentration of the coagulation bath, and the temperature are set, and the resulting coagulated yarn is stretched, washed with water, treated with an oil agent, steam stretched, etc.
• the carbon fiber bundle of the present invention preferably has a circularity in the range of 0.80 to 0.99, and preferably has a surface area ratio in the range of 1.00 to 1.08.
• the sizing agent used in the carbon fiber bundle of the present invention preferably contains at least one component containing an epoxy group, and the epoxy value of the sizing agent eluted by immersing the carbon fiber bundle in N,N-dimethylformamide and subjecting it to ultrasonic treatment is X meq./g, and the adhesion ratio of the sizing agent applied to the carbon fiber bundle, Y mass %, preferably satisfies the relationship of the following formula 1, and more preferably satisfies the relationship of the following formula 2.
• the epoxy value is an index that indicates the amount of epoxy groups contained per gram of sizing agent; the higher the epoxy value, the more epoxy groups are contained per gram of sizing agent.
• the sizing adhesion ratio is expressed as a percentage (mass%) of the total mass of sizing agent dissolved when the mass of the carbon fiber bundle immersed in N,N-dimethylformamide and ultrasonically treated is taken as 100 mass%.
• X ⁇ Y in formulas 1 and 2 is an index that represents the amount of epoxy groups contained per unit mass of the carbon fiber bundle, i.e., 1 g, and the larger X ⁇ Y, the easier it is to increase the interfacial adhesion between the carbon fiber bundle and the resin. If the adhesion between the carbon fiber and the resin is low, peeling will occur at the interface between the carbon fiber and the resin, leading to breakage of the entire carbon fiber composite material, which is undesirable, while if the adhesion between the carbon fiber and the resin is too high, stress concentration is likely to occur at the breakage initiation point when the carbon fiber composite material is made, which is undesirable because it will lead to breakage of the entire carbon fiber composite material.
• the drape value of the carbon fiber bundle of the present invention is preferably greater than 0 cm and less than 18 cm, more preferably greater than 4 cm and less than 16 cm, and even more preferably greater than 4 cm and less than 10 cm.
• the drape value is an index that represents the hardness of the carbon fiber bundle, and the higher the drape value, the harder the carbon fiber bundle is.
• the fiber bundle is soft and is prone to bending and twisting when it is exposed to a guide such as a comb that is used to align the yarn pulled out from the bobbin during the production of composite materials. If bending or twisting occurs, it becomes difficult to open that part, which is undesirable as it will cause uneven opening. Also, if the drape value is more than 18 cm, the fiber bundle is hard 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 as it can suppress both uneven opening and fuzzing when it comes into contact with a guide.
• the carbon fiber bundle of the present invention preferably has a filament count of 12,000 or more, and more preferably 24,000 or more.
• productivity depends on the yarn speed and the number of filaments, so a large number of filaments allows the composite material to be manufactured efficiently.
• a filament count of 12,000 or more is satisfactory from the standpoint of productivity.
• the number of filaments is preferably 36,000 or less.
• the carbon fiber precursor fiber bundle of the present invention can be obtained by spinning a spinning solution of a polyacrylonitrile copolymer.
• the polyacrylonitrile copolymer is not limited to a homopolymer obtained only from acrylonitrile, but may also contain other monomers in addition to the main component acrylonitrile.
• the polyacrylonitrile copolymer preferably contains 90 to 100% by mass of acrylonitrile and less than 10% by mass of a copolymerizable monomer.
• Examples of monomers that can be used as copolymerizable monomers with acrylonitrile include acrylic acid, methacrylic acid, itaconic acid and their alkali metal salts, ammonium salts and lower alkyl esters, acrylamide and its derivatives, allylsulfonic acid, methallylsulfonic acid and their salts or alkyl esters, etc.
• the polyacrylonitrile copolymer described above 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 obtain a spinning solution.
• 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.
• the spinning process includes a spinning process in which a spinning solution is discharged from a spinneret into a coagulation bath by the dry-wet spinning method and spun, a water washing process in which the fiber obtained in the spinning 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, and may include a steam drawing process in which the fiber obtained in the dry heat treatment process is steam drawn.
• the spinning solution is obtained by dissolving the polyacrylonitrile-based polymer described above in a solvent in which polyacrylonitrile is soluble, such as dimethyl sulfoxide, dimethylformamide, and dimethylacetamide.
• the coagulation bath preferably contains a solvent such as dimethyl sulfoxide, dimethylformamide, or dimethylacetamide used as the solvent for the spinning solution, 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 in the spinning solution. Specifically, it is preferable to use water as the coagulation-promoting component.
• the swelling degree of the coagulated yarn spun from the acrylic polymer solution (hereinafter referred to as “coagulated yarn swelling degree” or simply “swelling degree”) is preferably controlled to less than 120%, and more preferably less than 110%. If the swelling degree is less than 3%, it takes time to remove the solvent in the water washing process, so the lower limit is about 3%. It is more preferable to control the swelling degree to 3 to 120%, as this balances the tensile strength and processability of the carbon fiber.
• the swelling degree of the coagulated yarn is an index that reflects the density of the carbon fiber precursor fiber bundle, and the denser the carbon fiber precursor fiber bundle, the easier it is to improve the density of the obtained carbon fiber bundle.
• the swelling degree of the coagulated yarn can be reduced by reducing the tension in the coagulation process.
• the friction per single yarn can be reduced by increasing the number of single fibers discharged from the coagulation bath, by using free rollers instead of fixed guides, or by finishing the surfaces of the fixed guides and free rollers with a matte finish;
• the viscosity of the coagulation bath liquid can be reduced by adjusting the composition and temperature of the coagulation bath, or by changing the yarn path in the coagulation bath or by rectifying the flow, thereby reducing the fluid resistance that the single yarn experiences from the coagulation bath liquid, and thus the coagulated yarn tension can be reduced.
• the PAN-based polymer solution is introduced into a coagulation bath liquid and coagulated, and then the process goes through a water washing step, a stretching step, a step of applying an oil agent, and a drying step to obtain a carbon fiber precursor fiber bundle.
• the water washing process is carried out for the purpose of introducing the coagulated fiber bundle that has been through the air retention process into a water washing bath and further removing the organic solvent from the coagulated fiber bundle.
• the fiber may be stretched 1 to 1.5 times during the water washing process.
• the stretching process can usually be carried out in a single or multiple stretching baths whose temperatures are adjusted to 30 to 98°C. Stretching in the bath during the stretching process is called in-bath stretching, and the stretching ratio is called the in-bath stretching ratio.
• the in-bath stretching ratio is preferably set to 2 to 2.8 times. If the total stretching ratio before the oil application process exceeds 3 times, the density of the surface layer decreases, and the oil will more easily penetrate into the fibers.
• the total stretching ratio before the oil application process is the product of the stretching ratio in the water washing process and the in-bath stretching ratio.
• the oil application process is a process in which an oil is applied after the bath drawing process in order to prevent adhesion between the fibers. It is preferable to use an oil whose main component is silicone as the oil used in this process. If the oil does not contain silicone, it will not be possible to suppress interfiber adhesion during the flame-proofing process, and strand strength will decrease. It is also preferable to use a silicone oil that contains modified silicone, such as amino-modified silicone, which has high heat resistance. Other silicone oils include silicones modified with epoxy or alkylene oxide.
• a publicly known method can be used for the drying process. From the viewpoint of improving productivity and the degree of crystal orientation, it is preferable to perform stretching in a heating medium after the drying process.
• a heating medium for example, pressurized steam or superheated steam is preferably used in terms of operational stability and cost.
• a dry heat stretching process or a steam stretching process may be added.
• a method for producing a carbon fiber bundle of the present invention will be described.
• a carbon fiber precursor fiber bundle produced by the method described above is subjected to a flame retardant process in an oxidizing atmosphere at a temperature of 200 to 300°C, a preliminary carbonization process in an inert atmosphere at a maximum temperature of 500 to 1,200°C, and then a carbonization process in an inert atmosphere at a maximum temperature of 1,200 to 2,000°C, to produce a carbon fiber bundle.
• Air is preferably used as the oxidizing atmosphere in the flame-resistant treatment.
• the preliminary carbonization treatment and the carbonization treatment are carried out in an inert atmosphere.
• gases used in the inert atmosphere include nitrogen, argon, and xenon, and from an economical point of view, nitrogen is preferably used.
• the obtained carbon fiber bundles can be electrolytically treated to modify their surface. This is because electrolytic treatment can optimize the adhesion to the carbon fiber matrix in the resulting fiber-reinforced composite material.
• a sizing treatment is performed to impart bundling properties to the carbon fiber bundles.
• a sizing agent that is compatible with the matrix resin can be appropriately selected depending on the type of resin used, but it is important to control the adhesion in order to simultaneously suppress interfacial peeling between the carbon fiber and resin and alleviate stress concentration when the carbon fiber composite material is made, and to express good mechanical properties.
• the electrolytic treatment conditions such as the type and concentration of the electrolyte, the deposition rate of the sizing agent, and control the amount of functional groups contained in the sizing agent.
• the sizing agent contains epoxy groups, it is preferable to adjust the amount of epoxy groups by hydrolyzing the epoxy groups beforehand or after applying the sizing agent to the carbon fiber bundle.
• the carbon fiber reinforced composite material using the carbon fiber bundles of the present invention can be produced by known methods and can be used in many fields such as aerospace, automobiles, railway vehicles, ships, civil engineering and construction, and sporting goods. In particular, it can be used favorably for producing hollow containers such as pressure vessels, and cylinders.
• ⁇ Coagulated thread tension> The coagulated yarn tension was measured at the point where the yarn exited the coagulation bath during the coagulation process. The tension was calculated by measuring the load by clamping the running yarn using a tensiometer and dividing the load by the fineness (dtex) of the yarn at the measurement point.
• S Swelling degree is 3% or more and less than 110%.
• A Swelling degree is 110% or more and less than 120%.
• B Swelling degree is 120% or more and less than 150%.
• C Swelling degree is less than 3% or 150% or more.
• Total fineness> A 10 m length of the carbon fiber bundle to be measured was sampled and completely dried at 120° C. for 2 hours. The measured mass (unit: g) was then divided by 10 to obtain the total fineness (unit: g/m), which is the mass per 1 m.
• ⁇ Density> The carbon fiber bundle to be measured was dried at 120°C for 2 hours before the measurement.
• a dry automatic density meter was used to measure the density, with nitrogen as the measurement medium, a 10 cc type sample container, and the amount of sample adjusted to 3 to 6 cc in volume. The measurement was performed three times, and the average value was used. In this measurement, an Accupyc 1330 type dry automatic density meter manufactured by Shimadzu Corporation was used.
• the single fiber diameter d was measured in ⁇ m.
• strand strength and strand elastic modulus of carbon fiber bundle were determined using each resin formulation (resin formulation A, resin formulation B, resin formulation C, resin formulation D) in accordance with the resin impregnated strand strength test method of JIS R7608 (2007).
• the curing conditions were as shown in each resin formulation, and resin formulation B, resin formulation C, and resin formulation D were used instead of resin formulation A, and resin formulation B and resin formulation D were heated to 60°C during impregnation.
• Ten strands of the carbon fiber bundle were measured, and the average values were taken as the strand strength and strand modulus.
• the strand modulus was measured in a strain range of 0.1 to 0.6%.
• the measurement result of resin formulation A was used for the strand modulus (strand modulus E) in the single fiber loop test described later.
• ⁇ Single fiber loop test> A single fiber with a length of about 10 cm was placed on a slide glass, and 1 to 2 drops of glycerin were dropped on the center of the single fiber, and both ends of the single fiber were lightly twisted in the circumferential direction of the fiber to make one loop in the center of the single fiber, and a cover glass was placed on it. This was placed on the stage of the microscope, and video recording was started under conditions of a total magnification of 100 times and a frame rate of 15 frames/second. While adjusting the stage each time so that the loop did not fall out of the field of view, both ends of the looped fiber were pressed toward the slide glass with fingers while pulling at a constant speed in the opposite direction, and distortion was applied until the single fiber broke.
• the frame immediately before the break was identified by frame-by-frame advance, and the width W of the loop immediately before the break was measured by image analysis.
• the single fiber diameter d was divided by the width W of the loop to calculate d/W.
• the measurement was performed 20 times, the average value of d/W was calculated, and the average value of d/W was multiplied by the strand elastic modulus to calculate E ⁇ d/W.
• the interfacial shear strength was measured according to the following steps (1) to (4).
• the interfacial shear strength which is an index of the adhesive strength of the carbon fiber and resin interface, was calculated by the following formula. The measurement was performed five times, and the arithmetic average was taken as the test result.
• Interfacial shear strength (MPa) strand strength A' (MPa) x single fiber diameter d ( ⁇ m) / (2 x lc) ( ⁇ m).
• ⁇ Circularity> The carbon fiber precursor fiber bundle or the carbon fiber bundle was cut perpendicular to the fiber axis with a razor, and the cross-sectional shape of the single fiber was observed using an optical microscope. The measurement magnification was set to 200 to 400 times so that the thinnest single fiber was observed to be about 1 mm.
• the cross-sectional area and circumference of the single fiber were obtained by image analysis of the obtained image, and the cross-sectional diameter (fiber diameter) of the single fiber when assumed to be a perfect circle was calculated from the cross-sectional area to the nearest 0.1 ⁇ m, and the circularity was calculated using the following formula.
• Probe Silicon cantilever (Seiko Instruments, DF-20) Measurement mode: Dynamic Force Mode (DFM) Scanning speed: 1.5Hz Scanning range: 3 ⁇ m x 3 ⁇ m Resolution: 256 pixels x 256 pixels Taking into account the curvature of the fiber cross section, the obtained measured image was fitted by determining a linear plane from all the image data using the least squares method using the attached software, and a linear slope correction was performed to correct the in-plane slope, followed by a secondary slope correction to correct the quadratic curve in the same manner. After that, a surface roughness analysis was performed using the attached software, and the surface area ratio to a surface assumed to be smooth was calculated. The measurement was performed five times in total, once for each single yarn, by randomly sampling five different single yarns, and the arithmetic average value was taken as the surface area ratio.
• DFM Dynamic Force Mode
• the sizing agent attachment amount is divided by W 1 to convert it to mass% when the entire sizing-containing carbon fiber bundle is taken as 100 mass% (rounded off to the third decimal place), which is the attachment ratio (mass%) of the attached sizing agent.
• the measurement is performed twice, and the average value is taken as the attachment ratio (mass%) of the sizing agent.
• the epoxy value was determined by immersing 30 g of a sample in 150 ml of N,N-dimethylformamide at 25° C. and subjecting the sample to ultrasonic treatment at a frequency of 40 kHz for 30 minutes three times, and analyzing the sizing agent solution eluted from the fibers.
• the amount of sizing agent remaining in the carbon fibers is 0.20 mass% or less.
• the epoxy group is opened with hydrochloric acid using the eluted sizing agent solution, and the epoxy value is determined by acid-base titration.
• a weight 3 was hung from a carbon fiber bundle 2 cut to 50 cm under a load of 0.0375 [g/tex] in an atmosphere at a temperature of 25 ° C., and the bundle was left for 30 minutes or more to remove twisting.
• a portion of the bundle 2 with a length of 30 cm from the center was sampled, and as shown in Fig. 2, the carbon fiber bundle 2 was placed on a rectangular horizontal stand 4 with a 90 ° angle so that the carbon fiber bundle 2 protruded 25 cm from the horizontal stand 4 while being supported so as not to break, and the carbon fiber bundle 2 on the horizontal stand 4 was fixed with tape.
• Two metal bars (made of stainless steel) with a diameter of 50 mm and a surface roughness Rmax of 0.3 ⁇ m are arranged vertically at intervals of 150 mm so that the carbon fiber bundle passes while contacting each metal bar at an angle of 0.3925 ⁇ (rad) ⁇ 0.04 ⁇ (rad), a total of 0.785 ⁇ (rad).
• a carbon fiber bundle with 12,000 filaments is hung on the metal bars, the unwinding tension from the package is set to 800 g, and the metal bars are passed by being pulled at 4 m/min by a driving roll, and the number of fuzz in one minute after passing the second metal bar is counted to determine the process passability.
• A Burst pressure of 75 MPa or more.
• B Burst pressure of 70 MPa or more but less than 75 MPa.
• C Burst pressure less than 70 MPa.
• Example 1 A copolymer of acrylonitrile and itaconic acid was dissolved in dimethyl sulfoxide to prepare a spinning solution.
• the obtained spinning solution was once extruded into the air from a spinneret with 3,000 holes, and mixed with 80% by mass of dimethyl sulfoxide and 20% by mass of water as a coagulation accelerator (hereinafter, the mass ratio of components other than the coagulation accelerator in the coagulation bath solution is also referred to as the "coagulation bath concentration”) and introduced into the coagulation bath solution whose temperature was controlled at -5°C to obtain a coagulated yarn.
• This process for obtaining a coagulated yarn is abbreviated as the "coagulation process”.
• the coagulated yarn was introduced into a water washing bath and washed, and then in the drawing process, bath drawing was performed in warm water at 90°C.
• the total draw ratio was 2.3 times.
• an amino-modified silicone-based silicone oil was applied to this fiber bundle.
• a drying process was performed using a heated roller at 180°C, and the number of single fibers was reduced to 12,000, and then the bundle was drawn 5 times in pressurized steam, resulting in a total draw ratio of 12 times for spinning, and a polyacrylonitrile-based precursor fiber bundle with a single fiber fineness of 1.1 dtex was obtained.
• the resulting polyacrylonitrile precursor fiber bundle was treated in the following firing process to produce a carbon fiber bundle.
• the resulting polyacrylonitrile precursor fiber bundle was flame-retardant treated in air at a temperature of 200 to 300°C to obtain a flame-retardant fiber bundle.
• the flame-retardant fiber bundle obtained in the flame-retardant process was pre-carbonized in a nitrogen atmosphere at a maximum temperature of 800°C in the pre-carbonization process to obtain a pre-carbonized fiber bundle.
• the pre-carbonized fiber bundle obtained in the pre-carbonization process was carbonized in a nitrogen atmosphere at a maximum temperature of 1,300°C in the carbonization process.
• the surface was electrolytically treated using an aqueous sulfuric acid solution as the electrolyte, washed with water, dried, and then sizing agent i was applied to obtain a carbon fiber bundle.
• mixture B adjusted to a temperature of 60°C was applied to one side of the obtained carbon fiber bundle so that the amount applied to the total mass of the towpreg was 22 to 28 mass%, and then the bundle was passed through a nip roll to impregnate the inside of the carbon fiber bundle with mixture B to obtain a towpreg.
• the towpreg bobbin was wound up to 2,300 m on a paper tube so that the initial tension was 600 to 1,000 gf, the wind ratio was 6 to 10, and the winding width was 230 to 260 mm.
• a 7.5 L polyethylene liner was placed in a filament winding molding device, and the towpreg was wound around the entire liner to produce a pressure vessel.
• a hoop layer at an angle of +89° to the axial direction of the liner and a hoop layer at an angle of -89° to the axial direction of the liner were wound to a thickness of 1.4 mm.
• a helical layer at an angle of +20° to the axial direction of the liner and a helical layer at an angle of -20° to the axial direction of the liner were wound to a thickness of 2.2 mm.
• a hoop layer at an angle of +89° to the axial direction of the liner and a hoop layer at an angle of -89° to the axial direction of the liner were wound to a thickness of 0.6 mm to obtain an intermediate body.
• the intermediate body was rotated in a curing oven and cured at 130°C for 90 minutes to obtain a pressure vessel for pressure resistance testing.
• Tables 2 and 3 The results are summarized in Tables 2 and 3.
• Example 2 A carbon fiber bundle having a sizing agent applied thereto was obtained in the same manner as in Example 1, except that the content of dimethyl sulfoxide in the coagulation bath was 79% by mass (coagulation bath concentration: 79% by mass). The results are shown in Tables 2 and 3.
• Example 1 A carbon fiber bundle to which a sizing agent was applied was obtained in the same manner as in Example 1, except that the temperature of the coagulation bath in the coagulation step was 5°C, and the free roller at the exit of the coagulation step was replaced with a fixed guide to increase the frictional resistance (coagulated yarn tension) received by the coagulated yarn.
• the coagulated yarn tension increased, and the swelling degree of the coagulated yarn increased, and the denseness of the obtained precursor fiber bundle was insufficient.
• the strand strength A' was 5.5 GPa, and the strand strength B' was 4.5 GPa.
• the decrease in strand strength when resin formulation B was used was large, and the strength utilization rate ⁇ was low at 82%.
• the results are summarized in Tables 2 and 3.
• the pressure resistance of the obtained pressure vessel was also inferior to that of Example 1.
• Example 3 A carbon fiber bundle to which a sizing agent was applied was obtained in the same manner as in Example 1, except that the number of holes in the spinneret was 6,000 and the amount of dimethyl sulfoxide in the coagulation bath was 82% by mass. At this time, the strand strength A' was 5.5 GPa, the strand strength B' was 4.9 GPa, and the strength utilization rate ⁇ was 89%. Compared with Comparative Example 1, the strand strength B' and the pressure resistance of the pressure vessel were improved in Example 3, in which the denseness of the precursor fiber bundle was good. On the other hand, focusing on the strand strength A', both Example 3 and Comparative Example 1 were equivalent to 5.5 GPa, and the result did not reflect the improvement in the pressure resistance of the pressure vessel. The results are summarized in Tables 2 and 3.
• Example 4 A carbon fiber bundle to which a sizing agent was applied was obtained in the same manner as in Example 1, except that the number of holes in the spinneret was 6,000. The number of holes in the spinneret was increased, and the frictional resistance borne by each solidified yarn was reduced, so that the swelling degree was judged to be better than in Example 1, suggesting that a dense structure was formed.
• the strand strength A' was 5.7 GPa
• the strand strength B' was 5.0 GPa
• the strength utilization rate ⁇ was 88%
• the strand strength was improved when the resin formulation B was used compared to Example 1, so that the strength utilization rate ⁇ was also higher.
• Tables 2 and 3 The results are summarized in Tables 2 and 3.
• Example 5 A carbon fiber bundle to which a sizing agent was applied was obtained in the same manner as in Example 4, except that the adhesion ratio of the sizing agent was changed so that the interfacial shear strength was 14 MPa. At this time, the strand strength A' was 5.7 GPa, the strand strength B' was 5.2 GPa, and the strength utilization rate was 91%. In addition, the pressure resistance of the pressure vessel was improved compared to Example 1 and Comparative Example 1. The results are summarized in Tables 2 and 3.
• an amino-modified silicone-based silicone oil was applied to the fiber bundle after the water bath stretching, and a drying and densification treatment was performed using a heating roller at 160 ° C., and the number of filaments was increased to 12,000.
• the fiber bundle was then stretched 5 times in pressurized steam to obtain a polyacrylonitrile-based precursor fiber bundle with a single fiber fineness of 1.1 dtex at a total stretch ratio of 12 times.
• the polyacrylonitrile precursor fiber bundles obtained were bundled as necessary to obtain the number of filaments shown in Table 3, and were then processed in the following flame retardant process, preliminary carbonization process, and baking process to produce carbon fiber bundles.
• the resulting polyacrylonitrile precursor fiber bundle was flame-retardant treated in air at a temperature of 200 to 300°C to obtain a flame-retardant fiber bundle.
• the flame-retardant fiber bundle obtained in the flame-retardant process was pre-carbonized in a nitrogen atmosphere at a maximum temperature of 800°C in the pre-carbonization process to obtain a pre-carbonized fiber bundle.
• the pre-carbonized fiber bundle obtained in the pre-carbonization process was carbonized in a nitrogen atmosphere at a maximum temperature of 1,300°C in the carbonization process.
• Examples 6 to 15, Comparative Examples 4 and 5, Reference Examples 1 to 25 As shown in Table 5, sizing agent i, sizing agent ii, sizing agent iii, or sizing agent iv was applied to carbon fiber bundle I, carbon fiber bundle II, carbon fiber bundle III, or carbon fiber bundle IV. Then, a heat treatment was performed at a temperature of 210° C. for 75 seconds to obtain a carbon fiber bundle to which a sizing agent was applied (however, in Reference Example 1, no sizing agent was applied).
• a 7.5 L polyethylene liner was placed in a filament winding molding device, and the carbon fiber bundle to which the sizing was applied was impregnated with mixture C, which had been uniformly mixed at 25°C in advance, so that the amount of mixture C impregnated was 22 to 28% by mass relative to the total mass of the carbon fiber bundle and mixture C, while being fed.
• a hoop layer at an angle of +89° to the axial direction of the liner and a hoop layer at an angle of -89° to the axial direction of the liner were wound to a thickness of 1.4 mm.
• a helical layer at an angle of +20° to the axial direction of the liner and a helical layer at an angle of -20° to the axial direction of the liner were wound to a thickness of 2.2 mm.
• a hoop layer at an angle of +89° to the axial direction of the liner and a hoop layer at an angle of -89° to the axial direction of the liner were wound to a thickness of 0.6 mm to obtain an intermediate.
• the intermediate was rotated at a speed of 7 rpm and held in a 20°C environment for 15 minutes.
• the intermediate was heated at 80°C for 120 minutes, then at 110°C for 240 minutes to harden mixture C and obtain a pressure vessel for pressure resistance testing.
• Reference Example 8 which satisfies Formula 1, also showed an improvement in process passability compared to Reference Example 11.
• the spinning conditions for carbon fiber bundles II and IV were changed so that the degree of solidified yarn swelling during spinning of the carbon fiber precursor fiber bundle was in a more preferable range, and the strand strength C' was improved in Examples 6 to 11 using carbon fiber bundle II compared to Reference Examples 1 to 17 using carbon fiber bundle I.
• Example 7 used sizing agent i in both cases, and the adhesion ratio of the sizing agent was the same, but both the strand strength C' and the pressure resistance of the pressure vessel were improved.
• Example 7 in which the adhesion ratio of the sizing agent or the epoxy value was further changed from Example 9 using carbon fiber bundle II, which has a degree of solidified yarn swelling in the preferable range, to control the interfacial shear strength, both the strand strength C' and the pressure resistance of the pressure vessel were improved, and a carbon fiber bundle particularly preferable for pressure vessel applications was obtained by appropriately controlling both the degree of solidified yarn swelling and the interfacial shear strength.
• Comparative Example 4 had a strand strength A' of 5.7 GPa, which was equal to or greater than those of Examples 7, 9, 10, and 11, but did not satisfy formula 1 due to a large Sz agent adhesion ratio, and had low strand strength B' or C' due to high interfacial shear strength, resulting in a low pressure resistance value for the pressure vessel. From this, it can be said that strand strength A' does not necessarily reflect the pressure resistance of the pressure vessel, and that it is important to improve strand strength B' or C' by appropriately controlling either or both of the degree of swelling of the coagulated yarn and the interfacial shear strength in order to increase the pressure resistance of the pressure vessel.
• Examples 16 to 17, Reference Examples 26 to 27 The carbon fiber bundles of Example 9, Comparative Example 5, Reference Example 11, and Reference Example 22 were stored in a constant temperature and humidity environment of 60° C. and 90% relative humidity for 200 hours to perform aging treatment, and carbon fiber bundles of Examples 16, 17, Reference Examples 26, and 27 corresponding to the respective Examples, Comparative Examples, and Reference Examples were obtained. Thereafter, pressure vessels for pressure resistance tests were obtained in the same manner as in the corresponding Example 9, Comparative Example 5, Reference Example 11, or Reference Example 22. Details are summarized in Table 6. No change was observed in strand strength A' before and after aging treatment.
• the strand strength (strand strength D') of the carbon fiber bundles of Examples 1, 3, 5, 7, 9, 10, 11, and 16, Comparative Examples 1 and 4, and Reference Examples 8, 11, 13, 17, and 26 was evaluated based on JIS R7608 (2007) using the following resin formulation D.
• the resin formulation D was heated to 60°C during impregnation. Details are shown in Table 7.
• resin formulation D is a practical resin for towpregs.
• the carbon fiber bundle of the present invention also exhibited a higher strand strength D' compared to the carbon fiber bundle of the comparative example when resin composition D was used.
• Fixing bar 2 Carbon fiber bundle 3: Weight 4: Horizontal stand 5: Factory compressed air line 6: Pressure booster 7: Water pressure pump 8: Liquid supply hose 9: Fixing mechanism 10: Safety cover 11: Pressure vessel 12: Data logger

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Materials Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Health & Medical Sciences (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Textile Engineering (AREA)
• General Chemical & Material Sciences (AREA)
• Inorganic Chemistry (AREA)
• Mechanical Engineering (AREA)
• Reinforced Plastic Materials (AREA)

Priority Applications (4)

Applications Claiming Priority (4)

Publications (1)

Family

ID=90830712

Family Applications (1)

Country Status (5)

Cited By (2)

Families Citing this family (1)

Citations (17)

• 2023
  • 2023-10-10 WO PCT/JP2023/036704 patent/WO2024090196A1/ja not_active Ceased
  • 2023-10-10 CN CN202380058524.3A patent/CN119677902A/zh active Pending
  • 2023-10-10 KR KR1020257000557A patent/KR20250088700A/ko active Pending
  • 2023-10-10 JP JP2023562842A patent/JPWO2024090196A1/ja active Pending
  • 2023-10-10 EP EP23882405.6A patent/EP4570974A1/en active Pending

Patent Citations (18)

Also Published As

Similar Documents

Legal Events