JP5434187B2 - Polyacrylonitrile-based continuous carbon fiber bundle and method for producing the same - Google Patents

Description

  The present invention relates to a polyacrylonitrile-based continuous carbon fiber bundle and a method for producing the same, and a method for producing a precursor fiber for polyacrylonitrile-based carbon fiber for producing the continuous carbon fiber bundle.

Carbon fiber has higher specific strength and specific modulus than other fibers, so as a reinforcing fiber for composite materials, in addition to conventional sports and aerospace applications, automobiles, civil engineering / architecture, pressure vessels and Widely deployed in general industrial applications such as windmill blades, it is desired to improve the reliability of the material by improving the impact resistance of the composite material. In particular, in aeronautical applications, glass fibers may be attached to the surface of carbon fiber composite material to protect the aircraft from impacts caused by dredging and tools, but the specific gravity of glass fiber is as heavy as 2.2 g / cm ^3. Further weight reduction and high performance as a material are desired.

  Among the carbon fibers, the most widely used polyacrylonitrile (hereinafter sometimes referred to as PAN) carbon fiber is a precursor obtained by wet-spinning, dry-spinning or dry-wet spinning of a PAN-based polymer solution. After obtaining the body fiber, it is heated in an oxidizing atmosphere at a temperature of 200-400 ° C. to convert to a flame-resistant fiber, which is heated in an inert atmosphere at a temperature of at least 1,100 ° C. By industrializing, it is manufactured industrially.

  Conventionally, by lowering the maximum temperature in carbonization treatment (hereinafter sometimes abbreviated as carbonization temperature) to 1000 ° C. or less, the tensile modulus is usually 200 GPa or more at a carbonization temperature of 1100 ° C. or more. A technique for obtaining physical properties with a tensile elastic modulus of 176 GPa or more by making the carbon fiber into a fiber with insufficient carbonization in which carbonization is interrupted before the tensile elastic modulus is improved (see Patent Document 1). A technique (see Patent Document 2) for obtaining physical properties of a tensile elastic modulus of 127 to 176 GPa has been proposed. However, these proposals have insufficient carbonization, and therefore have a low specific gravity and a large amount of highly hydrophilic functional groups. Therefore, the saturated water absorption is large, and there is a problem in performance when a composite material is obtained. It was fatal for aircraft use.

  In order to reduce the saturated water absorption rate to a level where there is no problem, it is necessary to increase the carbonization temperature. However, when a conventionally known PAN-based precursor fiber is used, a tensile modulus other than the carbonization temperature is used. Even when the firing tension that greatly contributes to the tension is in an unstrained state, the tensile elastic modulus was 180 to 220 GPa (see Patent Document 3).

  There has been a proposal that the tensile modulus is 34 to 98 GPa by using a precursor material other than PAN, specifically, an aromatic sulfonic acid derivative (see Patent Document 4). Therefore, not only the fiber axis direction but also the unnecessary direction is strengthened, and the cost performance is lowered.

  In addition, a material using an isotropic pitch widely used other than PAN as a precursor material has been proposed (see Patent Document 5). However, in this proposal, the raw material is isotropic. The degree of crystal orientation of the carbon fiber is as low as around 60%, and it is strengthened not only in the fiber axis direction but also in an unnecessary direction, and the cost performance is lowered. In addition, the element ratio obtained from elemental analysis is 99% or more carbon, and since there are few nitrogen atoms, the compression strength is improved due to the disorder of the structure due to the presence of nitrogen atoms, and the adhesive strength control range with the resin for composite materials The required material properties could not be obtained. Moreover, since PAN is excellent in stability of supply and raw material characteristics with respect to pitch, pitch raw materials could not be used for aircraft applications. Furthermore, due to the instability of raw materials and spinning process and the firing in a special flame-resistant atmosphere, pitch-based carbon fibers have a large single fiber strength distribution compared to low elastic modulus carbon fibers, which makes the composite material reliable. It was lacking.

  Some organic fibers other than carbon fibers satisfy a tensile modulus of 70 to 140 GPa, but carbon fibers are most suitable because of their structural and physical stability and high compressive strength.

  In view of the above-mentioned problems of the prior art, the present inventors have reached the present invention as a result of intensive studies on obtaining high-performance carbon fibers and obtaining them efficiently with high productivity.

JP 61-9717 A JP-A 62-265329 JP-A-2005-256221 Japanese Patent Laid-Open No. 06-173122 Japanese Patent No. 3090868

  Therefore, an object of the present invention is a low tensile elastic modulus useful as a surface layer material for improving the impact resistance of the carbon fiber composite material of the aircraft primary structure material, which has a high elongation at break and a low saturated water absorption rate. Another object of the present invention is to provide a PAN-based continuous carbon fiber bundle having a small amount of nitrogen atoms and a graphite fine crystal structure having a specific orientation structure.

  Another object of the present invention is to provide a method capable of stably producing a high-quality PAN-based continuous carbon fiber bundle in a large amount.

  In order to achieve the above object, the PAN-based continuous carbon fiber bundle of the present invention has the following configuration.

  That is, the polyacrylonitrile-based continuous carbon fiber bundle of the present invention has a strand tensile modulus of 70 to 140 GPa, a break elongation of 1.3 to 3%, and a saturated water absorption of 0 to 0.4% by weight. A polyacrylonitrile-based continuous carbon fiber bundle having a nitrogen content of 1 to 5% obtained from elemental analysis and a C-axis crystallite size of 1.3 to 3 obtained from a 002 diffraction line by X-ray diffraction measurement It is a polyacrylonitrile-based continuous carbon fiber bundle having a crystal orientation degree of 2.0 to 80% and a 002 plane crystal orientation of 75 to 80%.

  According to a preferred embodiment of the polyacrylonitrile-based continuous carbon fiber bundle of the present invention, the surface area ratio of the single fibers constituting the PAN-based continuous carbon fiber bundle is 1.02 to 1.2.

  According to a preferred embodiment of the polyacrylonitrile-based continuous carbon fiber bundle of the present invention, the ratio of the major axis to the minor axis (major axis / minor axis) of the fiber cross section of the single fiber constituting the PAN-based continuous carbon fiber bundle is 1. It is 05-1.6.

  According to a preferred embodiment of the polyacrylonitrile-based continuous carbon fiber bundle of the present invention, the number of filaments of the PAN-based continuous carbon fiber bundle is 1000 to 6000, and the single fiber diameter is 7 to 11 μm.

According to a preferred aspect of the polyacrylonitrile-based continuous carbon fiber bundle of the present invention, the Weibull shape factor m ″ of the single fiber tensile strength of the PAN-based continuous carbon fiber bundle is 7-10, The square R ^{2 of the} correlation coefficient is 0.92-1.

  Moreover, the manufacturing method of the precursor fiber bundle for polyacrylonitrile-based carbon fibers has a weight average molecular weight Mw of 100,000 to 1,000,000 and a polydispersity Mz / Mw (Mz represents a Z average molecular weight). A polymer solution prepared by dissolving a polyacrylonitrile polymer of 7 to 6 in a solvent to a polymer concentration of 6 to 25% by weight is transferred from the spinneret having an average pore diameter of 0.10 to 0.26 mm. The spun draft of the coalesced solution is controlled so that the spinning draft is in the range of 12 to 50, and the single fiber fineness of the coagulated yarn is 1.4 to 2.3 dtex. A polyacrylonitrile-based carbon fiber precursor obtained by obtaining a coagulated yarn and then drawing the coagulated yarn at a draw ratio of 1 to 1.9 to obtain a drawn yarn having a single fiber fineness of 1.2 to 1.8 dtex. It is a manufacturing method of a body fiber bundle.

  According to a preferred embodiment of the method for producing a precursor fiber bundle for polyacrylonitrile-based carbon fiber of the present invention, the take-up speed of the coagulated yarn is 20 to 200 m / min.

  Moreover, the manufacturing method of the polyacrylonitrile type | system | group continuous carbon fiber bundle of this invention is 200-300 degreeC, using the precursor fiber for PAN type carbon fibers obtained by the manufacturing method of the precursor fiber bundle for said PAN type carbon fibers. Flameproofing treatment in air at a temperature, followed by preliminary carbonization treatment in an inert atmosphere at a temperature of 300 to 800 ° C., and then carbonization treatment in an inert atmosphere at a temperature of 1,100 to 3,000 ° C., This is a method for producing a polyacrylonitrile-based continuous carbon fiber bundle having a maximum tension of 10 to 100 mg per single fiber.

  According to the present invention, it is useful as a surface layer material for improving the impact resistance of the carbon fiber composite material of the aircraft primary structure material, has a low tensile elastic modulus, high tensile / compression / bending fracture elongation, and saturated water absorption. A PAN-based continuous carbon fiber bundle having a low rate and a graphite fine crystal structure having a specific orientation structure can be obtained. In addition, such a PAN-based continuous carbon fiber bundle can be stably produced in a large amount.

  First, a production method suitable for obtaining the PAN-based continuous carbon fiber bundle of the present invention will be described.

  Carbon fibers are broadly divided into those using PAN as a raw material and those using pitch as a raw material. From the viewpoint of quality stability of raw materials and reduction of manufacturing energy of raw materials, PAN may be used as raw materials. preferable. The present inventors have already proposed a technique for producing a carbon fiber precursor fiber that gives excellent spinnability by using a PAN-based polymer having a specific molecular weight distribution (Japanese Patent Application No. 2007-269822). However, by applying this proposed technique, the PAN-based continuous carbon fiber bundle of the present invention can be suitably obtained.

  Specifically, a specific PAN-based polymer solution is controlled to a specific range within a spinning draft described later, and the single fiber fineness of the coagulated yarn is controlled within a specific range so that productivity is not impaired. The present inventors have found that a precursor fiber for carbon fiber having a low degree of orientation could be produced, and reached the present invention. Specifically, in the present invention, by using a specific PAN-based polymer solution and setting the spinning draft within a specific range, stretching can be almost completed without molecular orientation at the initial stage of the spinning process. It is possible to produce a PAN-based carbon fiber precursor fiber having a low orientation degree without fuzzing with high productivity. As a result, a carbon fiber having a low tensile elastic modulus, a high elongation at break and a low saturated water absorption can be obtained.

  The method for producing a precursor fiber bundle for a PAN-based carbon fiber according to the present invention and the method for producing a precursor fiber bundle for a polyacrylonitrile-based carbon fiber have a weight average molecular weight Mw of 100,000 to 1,000,000, and polydispersity A polymer solution obtained by dissolving a polyacrylonitrile polymer having Mz / Mw (Mz represents a Z average molecular weight) of 2.7 to 6 in a solvent to a polymer concentration of 6 to 25% by weight, From a spinneret having an average pore diameter of 0.10 to 0.26 mm, the winding and discharging of the polymer solution are controlled so that the spinning draft of the polymer solution is in the range of 12 to 50, and spinning, dry and wet spinning, and drying are performed. A coagulated yarn having a single fiber fineness of 1.4 to 2.3 dtex was obtained, and the coagulated yarn was drawn at a draw ratio of 1 to 1.9 times to obtain a single fiber fineness of 1.2 to 1.8 dtex. It is characterized by using the drawn yarn.

  First, the PAN polymer suitably used in the present invention will be described. The PAN-based polymer used in the present invention has a weight average molecular weight Mw of 100,000 to 1,000,000, preferably 200,000 to 650,000, more preferably 300 to 500,000. The PAN-based polymer has a polydispersity Mz / Mw represented by a ratio of the Z average molecular weight Mz to Mw of 2.7 to 6, preferably 3 to 6, more preferably 4 to 6 It is.

  In the present invention, the above various average molecular weights are measured by a gel permeation chromatograph (hereinafter abbreviated as GPC) method, and are obtained as polystyrene converted values.

  The polydispersity Mz / Mw has the following meaning. That is, the number average molecular weight (hereinafter abbreviated as Mn) is sensitively influenced by the low molecular weight substance contained in the polymer compound. On the other hand, Mw is sensitively influenced by the high molecular weight substance, and Mz is more sensitively influenced by the high molecular weight substance. Therefore, the spread of the molecular weight distribution can be evaluated by using Mw / Mn as the molecular weight distribution and Mz / Mw as the polydispersity. When the molecular weight distribution Mw / Mn is 1, it is monodispersed, and as the molecular weight distribution increases, the molecular weight distribution becomes broader around the low molecular weight side, whereas as the polydispersity Mz / Mw increases, the molecular weight The distribution is broad around the high molecular weight side.

  As described above, since the molecular weight distribution Mw / Mn and the polydispersity Mz / Mw are different, even if Mw / Mn is large, Mz / Mw is not necessarily 2.7 or more.

  By using the PAN-based polymer as described above, a mechanism capable of producing a high-quality carbon fiber precursor fiber with less fuzz while achieving both improvement in productivity and stabilization is not necessarily clear. It is not a translation, but it is thought as follows. When the PAN-based polymer is stretched and deformed immediately after the mouthpiece hole, the ultrahigh molecular weight substance and the high molecular weight substance are entangled, and the molecular chain between the entanglement is tensioned around the ultrahigh molecular weight substance, resulting in a rapid increase in elongational viscosity. That is, strain hardening occurs. As the PAN polymer solution is thinned, the elongational viscosity of the thinned portion is increased and the flow is stabilized, so that the spinning speed can be increased, the spinning draft rate can be increased, and the spinning speed can be increased. By using a solution in which a PAN-based polymer as described above is dissolved in a solvent, the yarn will not break even if the yarn is wound at a high speed of 20000 mm / min, and the length of the yarn cannot be measured. Can do.

  The higher the polydispersity Mz / Mw, the better. When Mz / Mw is less than 2.7, the strain hardening is weak and the discharge stability of the PAN polymer is insufficiently improved. Further, when the weight average molecular weight Mw is less than 100,000, the strength of the precursor fiber is insufficient, and when Mw is more than 1,000,000, ejection becomes difficult.

  Further, the smaller the molecular weight distribution Mw / Mn, the smaller the content of low molecular components that are likely to be structural defects of the carbon fiber. Therefore, the smaller the Mw / Mn is, the smaller the Mw / Mw is. That is, even if it is broad on both the high molecular weight side and the low molecular weight side, there is little decrease in ejection stability, but the low molecular weight side is preferably as sharp as possible, and Mz / Mw is higher than Mw / Mn. It is preferably 1.5 times or more, and more preferably 1.8 times or more. According to the study by the present inventors, in radical polymerization such as aqueous suspension or solution method, which is usually performed in the polymerization of acrylonitrile (hereinafter abbreviated as AN), the molecular weight distribution is on the low molecular weight side. Since the skirt is pulled, Mw / Mn is larger than Mz / Mw. Therefore, when performing polymerization under special conditions such as the type and ratio of the polymerization initiator and sequential addition, or when using general radical polymerization, there is a method of mixing two or more PAN-based polymers. The method of mixing is simple. The smaller the number of types to be mixed, the easier and the two types are often sufficient from the viewpoint of ejection stability.

  In the measurement of GPC method, in order to accurately measure even the high molecular weight, dilute the elution time to the extent that it does not depend on the dilution concentration (that is, the viscosity change is small), and increase the injection amount as much as possible to obtain detection sensitivity. And the solvent flow rate and column selection should be made to accommodate a wide molecular weight distribution. The exclusion limit molecular weight of the column is at least 10 million or more, and is set so that the peak does not tail. Usually, the dilution concentration is 0.1 wt / vol%, the injection volume is measured under two conditions of 20 μL and 200 μL, and if the data are different, the data of the injection volume of 200 μL is taken.

  The PAN polymer used in the present invention can be obtained by a method of mixing two kinds of polyacrylonitrile polymers (referred to as component A and component B) having different weight average molecular weights Mw. In the present invention, mixing means to finally obtain a mixture of the A component and the B component, and a specific mixing method will be described later, but is not limited to mixing each single component.

  First, two types of polyacrylonitrile polymers to be mixed will be described. When a polyacrylonitrile polymer having a large weight average molecular weight Mw is A component and a polyacrylonitrile polymer having a small weight average molecular weight Mw is B component, the Mw of the A component is preferably 1,000,000 to 15 million, more preferably Is 1 million to 5 million, and the Mw of the B component is preferably 150,000 to 1 million. This is a preferred embodiment because the polydispersity Mz / Mw of the mixed polymer tends to increase as the difference between the Mw of the A component and the B component increases, but when the Mw of the A component is greater than 15 million, A The productivity of the component may decrease, and when the Mw of the B component is less than 150,000, the strength of the precursor fiber may be insufficient. Therefore, the polydispersity Mz / Mw is preferably 6 or less. .

  In the PAN-based polymer used in the present invention, specifically, the weight average molecular weight ratio of the above component A and component B is preferably 2 to 45, more preferably 4 to 20, Preferably it is 5-15.

  Moreover, it is preferable that the weight ratio of A component / B component is 0.001-0.3, More preferably, it is 0.005-0.2, More preferably, it is 0.01-0.1. . When the weight ratio of the A component and the B component is less than 0.001, strain hardening may be insufficient, and when it is greater than 0.3, the discharge viscosity of the polymer solution may increase so that the discharge may become difficult.

  Mw and weight ratio are measured by dividing the peak of the molecular weight distribution measured by GPC into shoulders and peak parts and calculating the Mw and peak area ratio of each peak.

  The component A preferably used in the present invention desirably has compatibility with PAN, and is preferably a PAN-based polymer from the viewpoint of compatibility. As the composition, AN is preferably 93 to 100 mol%, and copolymerization may be carried out if the monomer copolymerizable with AN is 7 mol% or less, but the chain transfer constant of the copolymerization component is smaller than AN. When it is difficult to obtain the required Mw, it is preferable to reduce the amount of the copolymer component as much as possible.

  Examples of monomers copolymerizable with AN include acrylic acid, methacrylic acid, itaconic acid and their alkali metal salts, ammonium salts and lower alkyl esters, acrylamide and its derivatives, allyl sulfonic acid, methallyl sulfonic acid and Those salts or alkyl esters can be used.

  The polymerization method for producing the PAN-based polymer as component A can be selected from a solution polymerization method, a suspension polymerization method, an emulsion polymerization method, etc., and the purpose of uniformly polymerizing AN and copolymer components It is preferable to use a solution polymerization method. In the case of polymerizing using the solution polymerization method, as the solvent, for example, a solvent in which PAN is soluble, such as an aqueous zinc chloride solution, dimethyl sulfoxide, dimethylformamide, and dimethylacetamide, is preferably used. If it is difficult to obtain the required Mw, a solvent having a large chain transfer constant, that is, a solution polymerization method using a zinc chloride aqueous solution or a suspension polymerization method using water is also preferably used.

  As the composition of the PAN-based polymer, which is the B component suitably used in the present invention, AN is preferably 93 to 100 mol%, and a monomer copolymerizable with AN is copolymerized if it is 7 mol% or less. However, as the amount of the copolymerization component increases, molecular breakage due to thermal decomposition at the copolymerization portion becomes more prominent in the flameproofing step, and the tensile strength of the resulting carbon fiber decreases.

  Examples of the monomer copolymerizable with AN include, for example, acrylic acid, methacrylic acid, itaconic acid and alkali metal salts thereof, ammonium salts and lower alkyl esters, acrylamide and derivatives thereof, allyl, from the viewpoint of promoting flame resistance. Sulfonic acid, methallylsulfonic acid and their salts or alkyl esters can be used. In addition, as a monomer that cannot be copolymerized, it contributes to the formation of a crosslinked structure. As a monomer that forms a crosslinked structure by a covalent bond, a plurality of carbon-carbons such as a (meth) acryloyl group are used. A monomer having a double bond, a monomer having a hydroxyl group at a terminal, a monomer having a hydroxyl group, a monomer having a carboxylic acid group Examples thereof include a mixture of divalent or higher valent metal ions and a mixture of monomers each having a carboxylic acid group and an amino group. If it has a cross-linked structure, the spinning tension is high, particularly when the spinning draft is high, and it becomes impossible to obtain a precursor fiber having a low degree of crystal orientation that is required because the degree of crystal orientation increases.

  Next, the PAN polymer solution used in the present invention will be described. The polymer concentration of the PAN-based polymer solution is in the range of 6 to 25% by weight, preferably in the range of 15 to 25% by weight, more preferably 17 to 23% by weight, and most preferably 19 to 21%. % By weight. If the polymer concentration is less than 6% by weight, the difference between the fiber diameter at the initial stage of solidification and the fiber diameter after solidification becomes large, and voids may be generated inside, so that fibers with a dense structure may not be obtained. Even if the single fiber fineness of the yarn is lowered, the effect of forming a fiber having a dense structure may be difficult to exhibit, and the effect is particularly high when the polymer concentration is 15% by weight or more. On the other hand, when the polymer concentration exceeds 25% by weight, the viscosity increases, it is difficult to increase the winding speed of the coagulated yarn, and spinning becomes difficult. The polymer concentration of the polymer solution that is the spinning solution can be adjusted by the amount of the solvent used.

  In the present invention, the polymer concentration of the polymer solution is the weight percent of the PAN polymer contained in the PAN polymer solution. Specifically, after weighing the PAN-based polymer solution, the PAN-based polymer solution that does not dissolve the PAN-based polymer and is compatible with the solvent used for the PAN-based polymer solution is used. After removing the solvent, the PAN-based polymer is weighed. The polymer concentration is calculated by dividing the weight of the PAN polymer after desolvation by the weight of the PAN polymer solution before desolvation.

  The viscosity of the PAN polymer solution at a temperature of 45 ° C. is preferably in the range of 15 to 100 Pa · s, more preferably 20 to 80 Pa · s. When the viscosity of the PAN-based polymer solution is less than 15 Pa · s, the shape of the spun yarn is lowered, and therefore the speed at which the yarn taken out from the spinneret is taken up, that is, the spinnability tends to be lowered. Further, when the viscosity of the PAN-based polymer solution exceeds 100 Pa · s, since the entanglement is large, the molecular orientation proceeds at the time of spinning draft, and it becomes difficult to obtain a precursor fiber having a low degree of orientation. The viscosity of the PAN-based polymer solution can be controlled by the amount of charged polymerization initiator and chain transfer agent at the time of manufacturing the PAN-based polymer.

  In the present invention, the viscosity of the PAN-based polymer solution at a temperature of 45 ° C. can be measured with a B-type viscometer. Specifically, the PAN-based polymer solution placed in a beaker is immersed in a hot water bath adjusted to a temperature of 45 ° C. to adjust the temperature, and as a B-type viscometer, for example, B8L manufactured by Tokyo Keiki Co., Ltd. Using a viscometer, rotor No. 4 is used, and the viscosity of the PAN polymer solution is in the range of 0 to 100 Pa · s. p. m. Measure with

  Next, the manufacturing method of the precursor fiber bundle for PAN-type carbon fibers of this invention is demonstrated.

  From the viewpoint of obtaining high-strength carbon fibers before spinning the PAN-based polymer solution, the PAN-based polymer solution is passed through, for example, a filter having an aperture of 1 μm or less, and in the PAN-based polymer raw material and each step. It is preferable to remove the mixed impurities.

  In the present invention, a precursor fiber bundle for carbon fibers can be produced by spinning using the above-described PAN-based polymer solution as a spinning solution by a dry and wet spinning method. The dry-wet spinning method is a spinning method in which a polymer solution is once discharged into the air from a die and then introduced into a coagulation bath to coagulate.

  In the method for producing a precursor fiber bundle for a PAN-based carbon fiber of the present invention, the spinning draft of the polymer solution containing the PAN-based polymer is preferably in the range of 12 to 50, more preferably in the range of 20 to 40. is there.

Here, the spinning draft refers to the surface speed (rolling speed of the coagulated yarn) of a roller having a driving source with which the spun yarn (filament) first leaves the spinneret and comes into contact with the PAN-based weight in the spinneret hole. The value divided by the linear velocity (discharge linear velocity) of the combined solution. The discharge linear velocity is a value obtained by dividing the volume of the polymer solution discharged per unit time by the die hole area. Accordingly, the discharge linear velocity is determined by the relationship between the discharge amount of the polymer solution and the hole diameter of the spinneret. The polymer solution containing the PAN-based polymer exits the spinneret hole, contacts the coagulation bath, and gradually solidifies to become a coagulated yarn (filament). At this time, the filament is pulled by the first roller, but the uncoagulated spinning solution is more easily stretched than the filament. Therefore, the spinning draft indicates the magnification at which the spinning solution is stretched until it is solidified. That is, the spinning draft is expressed by the following formula.
Spinning draft = (coagulated yarn winding speed) / (discharge line speed)
Increasing the spinning draft also greatly contributes to fiber diameter reduction. If the spinning draft is less than 12, it is difficult to achieve the necessary precursor fiber fineness without stretching unless a method such as reducing the diameter of the die hole is taken. In addition, when the spinning draft exceeds 50, the degree of crystal orientation tends to increase, and the tensile elastic modulus of the carbon fiber increases. Since the PAN-based polymer solution used in the present invention has a low elongation viscosity before a specific strain is applied, the spinning tension is low, the degree of crystal orientation is easily suppressed, and a strain that causes breakage is applied. It is presumed that the elongational viscosity is increased by strain hardening, and this is a mechanism for suppressing breakage.

  In the present invention, the discharge linear velocity is preferably 1 to 10 m / min. When the discharge linear velocity is less than 1 m / min, productivity tends to decrease, but the effect of reducing the tensile elastic modulus of the carbon fiber tends to be small. On the other hand, when the discharge linear velocity exceeds 10 m / min, a high shear stress is generated in the spinneret hole, the molecular orientation is likely to proceed due to the shear stress, and the tensile elastic modulus of the carbon fiber tends to deviate from the upper limit. The discharge linear velocity can be controlled by the average hole diameter and the number of holes of the spinneret and the discharge amount of the polymer solution.

  The average pore diameter of the spinneret used in the present invention is preferably 0.10 mm to 0.26 mm, more preferably 0.15 to 0.2 mm. When the spinneret average pore size is smaller than 0.10 mm, a high shear stress is applied to the polymer solution, which is the spinning solution, and molecular orientation proceeds. For example, in the production of clothing and industrial ultrafine PAN fibers, a wet spinning method using ultrafine spinneret holes is often employed, but this is disadvantageous from the viewpoint of productivity and molecular orientation. On the other hand, if the average pore diameter of the spinneret exceeds 0.26 mm, it is difficult to obtain a precursor fiber fineness of 1.8 dtex or less without increasing the spinning draft.

  The number of holes in the spinneret is preferably 1000 to 12000. When the number of holes is less than 1000, productivity decreases. On the other hand, when the number of holes exceeds 12,000, the total yarn fineness becomes too large, and it may not be suitable as a textile use in which a small crimp is preferable.

  The take-up speed of the coagulated yarn is preferably 20 to 200 m / min. When the take-up speed of the coagulated yarn is less than 20 m / min, the productivity tends to decrease, but the effect of lowering the tensile elastic modulus of the carbon fiber tends to be small, and when the take-up speed of the coagulated yarn exceeds 200 m / min, The tension expression due to the bath liquid resistance in the coagulation process and the water washing process due to the yarn running at high speed in the liquid becomes too large, and molecular orientation may proceed in this process.

  In the present invention, the single fiber fineness of the dried coagulated yarn is determined by the polymer concentration of the polymer solution containing the polyacrylonitrile polymer, the spinning draft, and the pore diameter of the spinneret used. The single fiber fineness (dtex) of this dried coagulated yarn of the present invention is preferably 1.4 to 2.3 dtex, more preferably 1.4 to 2 dtex. The single fiber fineness of the dried coagulated yarn corresponds to the fiber diameter of the single fiber constituting the coagulated yarn at the time of coagulation. When the single fiber fineness of the dried coagulated yarn exceeds 5 dtex, There is a need to increase the stretching ratio of the process, and molecular orientation occurs. In particular, from the viewpoint of suppressing molecular orientation, it is preferable that the single fiber fineness of the dried coagulated yarn is 2.3 dtex or less. On the other hand, when the single fiber fineness of the dried coagulated yarn is less than 1.4 dtex, the effect of lowering the tensile modulus of carbon fiber is saturated and there is no cost advantage.

  In the present invention, the dried coagulated yarn coagulated yarn having a single fiber fineness of 1.4 to 2.3 dtex has a PAN-based polymer solution having a polymer concentration of 6 to 25% by weight and an average pore diameter of 0.10. It can be obtained by discharging and spinning from a spinneret of ˜0.26 mm while controlling the spinning draft to 12-50.

  The single fiber fineness (dtex) of the dried coagulated yarn in the present invention means that the coagulated yarn taken up by a roller having a drive source that first contacts after leaving the spinneret is washed with running water for 1 hour or more, and single fiber The dry weight (g) per 10,000 m.

  In the present invention, the degree of crystal orientation of the single fiber constituting the dried coagulated yarn is preferably 60 to 80%. When the degree of crystal orientation exceeds 80%, the resulting carbon fiber precursor fiber has a high degree of crystal orientation, and the tensile elasticity modulus of the carbon fiber may be too high even when fired without tension.

  In the coagulation bath used in the present invention, it is preferable to use a mixture of a solvent of an acrylonitrile polymer such as dimethyl sulfoxide, dimethylformamide and dimethylacetamide used as a solvent in the PAN polymer solution and a so-called coagulation promoting component. As the coagulation accelerating component, a component that does not dissolve the PAN-based polymer and is compatible with the solvent used in the PAN-based polymer solution is preferable. Specifically, it is preferable to use water. The coagulation bath used in dry and wet spinning is preferably set within a known range so as to control the shape of the cross section of the single fiber constituting the coagulated yarn and the roughness of the side surface of the fiber. When it is desired to roughen the unevenness of the fiber side surface, it is preferable to raise the coagulation bath temperature, and the coagulation bath concentration is preferably set to 50 to 80% by weight. Moreover, when making fiber cross-sectional shape into elliptical shape or (beta) cross-sectional shape, it is preferable to set coagulation bath concentration to 45 to 75 weight%.

  In the present invention, after a PAN polymer solution is introduced into a coagulation bath and coagulated to form a coagulated yarn, a precursor fiber bundle is obtained through a water washing step, a bath drawing step, an oil agent application step, and a drying step. . Moreover, you may add a dry heat extending process to said process. The coagulated yarn after coagulation may be directly stretched in the bath without the water washing step, or may be stretched in the bath after removing the solvent by the water washing step. The stretching in the bath can be usually performed in a single or a plurality of stretching baths adjusted to a temperature of 30 to 98 ° C. At that time, the draw ratio in the bath is preferably 1 to 1.9 times, more preferably 1 to 1.5 times.

  After the stretching process in the bath, it is preferable to apply an oil agent made of silicone or the like to the stretched yarn for the purpose of preventing adhesion between the single fibers. As the silicone oil, it is preferable to use a silicone oil containing a modified silicone such as amino-modified silicone having high heat resistance.

  A known method can be used for the next drying step. For example, a drying condition in which the drying temperature is 70 to 200 ° C. and the drying time is 10 seconds to 200 seconds gives preferable results. Although it may be stretched after the drying step for the purpose of improving productivity and improving the degree of crystal orientation, there is a risk of degrading the quality due to fluffing. What is important is that the degree of crystal orientation of the polyacrylonitrile fiber is reduced moderately, and the single fiber fineness of the precursor fiber is made thin. For this purpose, the spinning draft is increased as much as possible, and the drawing after the coagulation step is performed. The magnification is to be lowered. Therefore, the magnification (= final yarn speed / coagulated yarn take-up speed) combining the drawing step in the bath and the dry heat drawing step is preferably 1 to 1.9 times, more preferably 1 to 3 times, More preferably, it is 1 to 1.5 times. In particular, it is preferable to take relaxation as it shrinks in the drying process, and after pulling the coagulated yarn, obtaining a low-orientation precursor fiber without drawing as much as possible is the point to obtain a low elastic modulus carbon fiber. .

  In this way, polyacrylonitrile fiber that is a precursor fiber having a single fiber fineness of 1.2 to 1.8 dtex is obtained. The single fiber fineness of the polyacrylonitrile fiber is preferably 1.4 to 1.8 dtex. If the single fiber fineness is less than 1.2 dtex, the tensile elastic modulus of the carbon fiber will increase. On the other hand, if the single fiber fineness exceeds 1.8 dtex, the difference between the inner and outer structures of each single fiber constituting the fiber bundle after flame resistance becomes large, and yarn breakage occurs in the subsequent carbonization process, and carbon fibers cannot be obtained. The single fiber fineness (dtex) in the present invention is a weight (g) per 10,000 m of single yarn.

  In the present invention, the crystal orientation degree of the obtained precursor fiber bundle for PAN-based carbon fibers is preferably 70 to 83%. If the degree of crystal orientation exceeds 83%, the resulting carbon fiber may have a high tensile modulus.

  The precursor fiber obtained as described above is usually in the form of a continuous fiber bundle (filament). The number of filaments per continuous fiber bundle (multifilament) is preferably 1,000 to 24,000, and more preferably 1,000 to 6,000. The number of filaments per yarn is preferably larger for the purpose of improving productivity. However, if the number of filaments is large, the crimp becomes large when made into a woven fabric or the damaged area as a woven composite material when subjected to an impact. Since it may become large, the smaller one is preferable, and it is preferable to make it within the above range, particularly within 6000.

  Next, the manufacturing method of the PAN system continuous carbon fiber bundle of this invention is demonstrated.

  In the following flame resistance, preliminary carbonization and carbonization steps, the most important point is the maximum tension per single fiber, and it is preferable to control the tension to 10 to 100 mg. The control is most easily performed by the stretch ratio. When the tension is less than 10 mg, the suspension between the rollers is large, and it is difficult to design the furnace so as not to rub the furnace wall. When it exceeds, orientation may advance too much and a desired elastic modulus may not be obtained.

  Each step will be described.

  The precursor fiber bundle for a PAN-based carbon fiber produced by the above-described method is preferably tensioned or stretched under an oxidizing atmosphere at a temperature of 200 to 300 ° C., more preferably a stretch ratio of 0.8 to 1. After flameproofing while stretching at 0, pre-carbonization treatment is preferably performed while stretching at a stretch ratio of 0.9 to 1.0 in an inert atmosphere at a temperature of 300 to 800 ° C. A PAN-based continuous carbon fiber bundle is produced by carbonization in an inert atmosphere having a maximum temperature of 000 ° C., preferably while stretching at a stretch ratio of 0.9 to 0.97. Since the degree of orientation of the precursor fiber is lower than usual, even in such a draw ratio range, there is little expression of tension, and a preferable tension range is obtained.

Air is preferably employed as the oxidizing atmosphere in the flameproofing treatment. The density of the flameproof fiber obtained in this flameproofing step is preferably 1.3 to 1.5 g / cm ³ . That is, when the flame resistance is insufficient and the density of the flame resistant fiber is less than 1.3 g / cm ³ , adhesion between single yarns is likely to occur during carbonization, and a large amount of decomposition gas is generated. Therefore, it is difficult to obtain carbon fibers having high compression elongation. On the other hand, if the flame resistance is excessively advanced, the main chain of the polymer is broken, and the tensile strength of the carbon fiber finally obtained is lowered, so that the flame resistance density may not exceed 1.5 g / cm ^3. preferable.

  In the present invention, the preliminary carbonization treatment or carbonization treatment is performed in an inert atmosphere. Examples of the gas used in the inert atmosphere include nitrogen, argon, and xenon. Preferably used. In the preliminary carbonization treatment, it is preferable to set the heating rate in the temperature range to 500 ° C./min or less. Further, the maximum temperature in the carbonization treatment can be appropriately set according to the desired tensile modulus of the carbon fiber, but in general, the higher the maximum temperature of the carbonization treatment, the higher the tensile elasticity modulus of the obtained carbon fiber. When a precursor fiber having a low crystal orientation is used, the crystal orientation of the graphite structure is difficult to increase. Further, the higher the maximum temperature of carbonization treatment, the lower the saturated water absorption rate, and depending on the state of the precursor fiber, the saturated water absorption rate should be 0.4% by weight or less by setting the temperature to 1100 to 1250 ° C. or higher. Can do. The saturated water absorption rate is satisfied within a predetermined range, and the lower the maximum temperature of carbonization, the higher the carbonization yield and the smaller the basic unit of acrylonitrile as a raw material, which is a preferable embodiment. From the above viewpoint, the maximum temperature for carbonization is preferably 1,100 to 3,000 ° C, more preferably 1,200 to 1,900 ° C.

  By the method as described above, the PAN-based continuous carbon fiber bundle of the present invention is obtained. The PAN-based continuous carbon fiber bundle of the present invention has a strand tensile elastic modulus of 70 to 140 GPa. In a structural material in which a PAN-based continuous carbon fiber bundle is used, the elastic modulus is often the main design value. Even if the PAN-based continuous carbon fiber bundle of the present invention is used as a part of the structural material, the elastic modulus is a little. Therefore, it is necessary to reduce the weight of the material, and the required requirement is satisfied if the elastic modulus is 70 GPa or more. In addition, since the elastic modulus strongly depends on the orientation degree and the interplanar spacing of the graphite crystallites, it is necessary to have a high orientation degree in order to increase the elastic modulus. In order to decrease, the elastic modulus needs to be 140 GPa or less.

  The PAN-based continuous carbon fiber bundle of the present invention has a breaking elongation of 1.3 to 3% in a strand tensile test. When structural materials are combined with carbon fibers with a high modulus of elasticity, the stress load of carbon fibers with a high modulus of elasticity is large. Propagates to the entire structure material and lowers the overall breaking elongation. Therefore, a breaking elongation of 1.3% or more is required, and when the breaking elongation exceeds 3%, it is often over-specification. .

Further, the PAN-based continuous carbon fiber bundle of the present invention has a saturated water absorption rate of 0 to 0.4% by weight. The moisture contained in the carbon fiber is preferably as small as possible in order to lower the composite material properties, and the saturated water absorption is practically 0.4% by weight or less. The saturated water absorption depends on the structure of the carbon fiber, and the PAN-based carbon fiber has an unclear crystal structure. In terms of the carbonization temperature, the saturated water absorption is about 10% by weight up to about 1100 ° C. When the structure becomes clear, the saturated water absorption rate suddenly becomes zero. Since the PAN-based continuous carbon fiber bundle of the present invention has a low degree of precursor fiber orientation, a low elastic modulus can be maintained even when the carbonization temperature exceeds 1100 ° C. The saturated water absorption was measured according to the following method. After washing 10 g of the fiber with acetone, it is dried for 2 hours at a temperature of 110 ° C., returned to room temperature in a desiccator, weighed in an absolutely dry state, and this weight is designated as A. Next, this sample is allowed to stand for 24 hours in a humidity controller at 30 ° C. and 100% humidity, and then weighed to obtain B as the weight. The saturated water absorption C (%) is expressed by the following formula.
・ Saturated water absorption C (%) = (B−A) / C × 100
In the PAN-based continuous carbon fiber bundle of the present invention, the ratio of nitrogen element obtained from elemental analysis is 1 to 7%. If there is too much nitrogen element, the physical properties of the carbon fiber will be reduced due to the disorder of the graphite crystal structure. However, if it is 7% or less, the deterioration of the physical properties will be suppressed, and the composite material will have at least 1% nitrogen element derived from the PAN structure. As a result, the adhesion with the resin used as the resin is improved. The nitrogen element content is more preferably 4-7%.

  The PAN-based continuous carbon fiber bundle of the present invention has a crystallite size (hereinafter sometimes referred to as Lc) in the C-axis direction of the graphite crystal determined from 002 diffraction lines by X-ray diffraction measurement of 1.3 to 2. 0, and the crystal orientation degree of the 002 plane is 75 to 80%. When Lc is 1.3 or more, the graphite crystallinity contributes sufficiently to the expression of an effective elastic modulus, and when Lc exceeds 2.0, the a-axis direction of the crystallite increases and buckling easily occurs, and the compressive strength is increased. descend. The Lc of the carbon fiber can be controlled by the carbonization temperature, and the Lc increases as the carbonization temperature is increased. Further, if the degree of crystal orientation is less than 75%, the elastic modulus is not effectively expressed, so that the cost performance is bad. If the degree of crystal orientation exceeds 80%, the anisotropy becomes too strong and the compressive strength is lowered. Since the degree of crystal orientation is linked to the increase in crystallinity, it can be controlled even at the carbonization temperature, but there is a limit because there is a restriction that does not increase the saturated water absorption, and it is most controlled by the degree of orientation of the precursor fiber. preferable.

  The PAN-based continuous carbon fiber bundle of the present invention preferably has a single fiber surface area ratio of 1.02 to 1.2 as measured by a method described later using an atomic force microscope, more preferably 1. 03 to 1.09. The surface area ratio is represented by the ratio between the actual surface area of the carbon fiber surface and the projected area, and indicates the degree of surface roughness. A surface area ratio closer to 1 means smoother and more advantageous for improving the tensile strength of the carbon fiber. However, the adhesiveness with the resin tends to be lowered, and is controlled according to the desired performance balance. When the surface area ratio is less than 1.01, the adhesiveness with the resin is significantly lowered. When the surface area ratio is more than 1.2, a variation in strength may be induced due to a variation in the shape of the surface. The above surface area ratio is controlled by the spinning method and the coagulation method, and there is a tendency for dry and wet spinning to have a smooth surface. However, in coagulation, the coagulation rate is slowed, for example, the solvent concentration in the coagulation bath is set high. By performing the above, the skin layer becomes thin and fibrils are brought out on the surface, and the fibrils can be enlarged by increasing the solidification unit, for example, by increasing the solidification temperature, so that an uneven surface can be obtained. It is difficult for pitch-based carbon fibers to have irregularities reflecting such fibrils.

  In the PAN-based continuous carbon fiber bundle of the present invention, the ratio of the major axis to the minor axis of the fiber cross section of the single fiber measured by the method described later is preferably 1.05 to 1.6. As the shape collapses from the perfect circle, the secondary moment of the cross section increases, the compressive strength increases, and the area of the interface with the resin increases, so that the adhesiveness increases. When the major axis / minor axis is less than 1.05, it is difficult to obtain the above-described effect. When the major axis / minor axis exceeds 1.6, strength reduction and fluff generation may occur.

  The PAN-based continuous carbon fiber bundle of the present invention preferably has an average single fiber diameter of 7 to 11 μm. The smaller the average single fiber diameter is, the higher the potential of average tensile strength is. However, if the average single fiber diameter is smaller than 7 μm, it tends to buckle against compressive stress, and if the average single fiber diameter is larger than 11 μm, flameproofing treatment inside the single fiber is performed. Since it becomes insufficient, the tensile strength may be difficult to improve. The average single fiber diameter is obtained by calculating the diameter assuming that the cross-sectional area per single fiber obtained from the fiber weight, specific gravity and the number of filaments is circular.

  The PAN-based continuous carbon fiber bundle of the present invention preferably has 1000 to 6000 filaments. When the number of filaments is less than 6,000, there is a merit that the crimp is small when made into a woven fabric, and peeling at the time of drilling as a composite material is reduced. Further, if the number of filaments is less than 1000, handling becomes complicated.

  The PAN-based continuous carbon fiber bundle of the present invention preferably has a Weibull shape factor m ″ of a single fiber tensile strength measured by a method described later of 7 to 10, more preferably 8 or more. Single fiber tensile strength When the Weibull shape factor m ″ is less than 7, not only the fluff increases when used as a composite material, but the woven fabric using such a carbon fiber as a woven yarn crimps the woven fabric. CFRP using, the tensile properties are lowered, and the composite material properties may be greatly lowered particularly when combined with a resin having a high elastic modulus for aircraft. The higher the Weibull shape factor of the single fiber tensile strength, the better. However, it is often difficult to make it 10 or more. The Weibull shape factor m ″ of the single fiber tensile strength is important to make the precursor fiber used homogeneous and to reduce the variation between the single fibers. Further, each step of the firing step when producing the carbon fiber It is possible to control by setting the draw ratio so that the Weibull shape factor of the fiber having undergone the process does not expand.

  Single fiber tensile strength is calculated | required as follows based on JISR7606 (2000). First, a continuous carbon fiber bundle having a length of about 20 cm is roughly divided into four equal parts, and single fibers are sampled sequentially from the four bundles. At this time, the entire bundle is sampled as evenly as possible. The sampled single fiber is fixed to the perforated mount using an adhesive. A mount on which a single fiber is fixed is attached to a tensile tester, and a tensile test is performed with a test length of 25 mm, a tensile speed of 1 mm / min, and 50 single fiber samples. In all processes such as sampling, fixing to mount and attaching to testing machine, the single fiber may be broken before the tensile test, so it was broken to avoid selective removal of the weak yarn If so, repeat the batch.

  For the cross-sectional area of the fiber, the average cross-sectional area was calculated from the fineness and density measured by the method described later. The single fiber tensile strength obtained in this way is Weibull plotted by the ln strength and the double logarithm of the function 1 / (1-F) of the fracture probability F, and is obtained by the least square approximation when F is 0.3 to 1. A Weibull shape factor is calculated from the obtained slope. Although the Weibull shape factor m is obtained by approximating one straight line from the Weibull plot, the Weibull plot of carbon fiber is often bent. The low strength side from the bending point contains many defects and the Weibull shape factor is often large, and the high strength side from the bending point is often small. Observing the fracture condition as a composite material, although stress concentration occurs near the break point due to the breakage of single fibers, it is easy to cause breakage of adjacent single fibers, but the breakage of single fibers leads to the breakage of the entire composite material However, depending on the properties of the matrix resin, the composite material often breaks when single fiber breakage occurs in the number of about 10 to 30% of all single fibers. For this reason, the Weibull shape factor on the lower strength side than the bending point may hardly affect the strength of the composite material, and the Weibull shape factor on the higher strength side than the bending point is often important. The inflection point fluctuates when the fracture probability F is about 0.1 to 0.6, but even if the Weibull shape factor is determined in the range of 0.3 to 1 with a fixed value of 0.3, there is no significant difference in the value. There is no mistake in technical significance.

In the PAN-based continuous carbon fiber bundle of the present invention, the square R ² of the correlation coefficient of the Weibull plot approximated by one straight line in the single fiber tensile test is 0.92-1, preferably 0.94-1. . This Weibull plot often bends and is often expressed as a mixed mode Weibull plot. However, the degree of bending is large when converted assuming a short test length. Regardless of the length of the unidirectional composite material, the carbon fiber single fiber length is said to be 1 mm or less. At that time, the 1-fracture probability F, that is, the ratio of the remaining single fiber and the product S of the applied stress and the applied stress is plotted, and the maximum value of S is highly correlated with the tensile strength of the unidirectional CFRP. It is ideal that the inflection point with an upwardly convex S curve is a single curve. However, when the degree of bending is strong, the curve has a plurality of inflection points, and the maximum of S for the average single fiber tensile strength. In many cases, the value is small and the mechanical properties cannot be exhibited effectively. This S assumes that the other single fibers uniformly bear the stress of the broken single fiber, and stress concentration around the broken single fiber occurs, so it does not directly indicate the composite material characteristics. However, S is effective as an index that indirectly indicates the characteristics of the composite material.

The square R ^{2 of the} correlation coefficient indicates the degree of bending of the Weibull plot. The smaller the correlation function is, the more the curve is bent. This parameter contributes in particular to the properties of the unidirectional composite material. Reinforced fabrics with large crimps are often used in combination with unidirectional composite materials, and it is preferable to maximize the mechanical properties of both. If the square R ^{2 of the} correlation coefficient is less than 0.92, it is necessary to improve the average value of the mechanical properties of the carbon fiber in order to satisfy the mechanical properties of the unidirectional composite material.

The square R ^{2 of the} correlation coefficient can approach 1 by reducing large defects added separately from the defects distributed in the carbon fiber. Large defects are formed by fusion during the production of the precursor fiber, foreign matters contained in the raw polymer solution, dirt during the process, etc., and it is preferable to reduce them. Note that the micro- and macro-defects determined from the size of the fracture surface of the fracture surface in the single-fiber tensile test observed with an electron microscope cannot be classified into high and low single-fiber tensile strength. The relationship with the square of the correlation coefficient R ² is low.

  The PAN-based continuous carbon fiber bundle of the present invention obtained as described above can be subjected to electrolytic treatment for surface modification. The electrolytic solution used for the electrolytic treatment includes an acidic solution such as sulfuric acid, nitric acid and hydrochloric acid, an alkali solution such as sodium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, ammonium carbonate and ammonium bicarbonate, or a salt thereof as an aqueous solution. Can be used as Here, the amount of electricity required for the electrolytic treatment can be appropriately selected according to the carbonization degree of the carbon fiber to be applied.

  Electrolytic treatment can optimize the adhesion to the carbon fiber matrix in the resulting fiber reinforced composite material, causing brittle fracture of the composite material due to too strong adhesion and lowering the tensile strength in the fiber direction In addition, although the tensile strength in the fiber direction is high, the adhesive property with the resin is poor, and the problem that the strength characteristics in the non-fiber direction are not expressed is solved, and in the obtained fiber reinforced composite material, in both the fiber direction and the non-fiber direction A balanced strength characteristic is developed.

  After the electrolytic treatment, a sizing treatment can also be performed in order to impart convergence to the PAN-based continuous carbon fiber bundle. As the sizing agent, a sizing agent having good compatibility with the matrix resin or the like can be appropriately selected according to the type of resin used.

  The PAN-based continuous carbon fiber bundle obtained by the present invention is an aircraft member, a pressure vessel member, an autoclave molding as a prepreg, a resin transfer molding as a preform such as a woven fabric, and a filament winding. It is suitably used as sports members such as automobile members, fishing rods and golf shafts.

  Hereinafter, the manufacturing method of the precursor fiber bundle for PAN-based carbon fibers and the manufacturing method of the PAN-based continuous carbon fiber bundle of the present invention will be described more specifically with reference to examples. Next, a method for measuring each characteristic used in the examples will be described.

<Single fiber fineness (dtex) of precursor fiber bundle>
A fiber bundle having a filament number of 6,000 was wound 10 times on a 1 m metal frame, and then its weight was measured to calculate the weight per 10,000 m.

<Single fiber fineness (dtex) of dried coagulated yarn>
Coagulated yarn with 6,000 filaments was wound 10 times on a 1m metal frame, then washed with running water for 1 hour and dried at 120 ° C for 2 hours, and the weight was measured per 10,000m. It calculated | required by calculating a weight.

<Crystal orientation degree of precursor fiber bundle (%)>
The degree of orientation in the fiber axis direction was measured as follows. The precursor fiber bundle is cut to a length of 40 mm, 20 mg is precisely weighed, a sample is collected, and the sample fiber axes are aligned so as to be exactly parallel, and then a thickness of 1 mm is used using a sample adjustment jig. Prepare a uniform sample fiber bundle. After impregnating with a thin collodion solution and fixing the shape so as not to collapse, it is fixed to a sample table for wide-angle X-ray diffraction measurement. From the half width (H °) of the spread of the profile in the meridian direction including the highest intensity of diffraction observed near 2θ = 17 °, using Cu Kα ray monochromated with a Ni filter as the X-ray source. The degree of crystal orientation (%) was determined using the following formula.
Crystallinity degree (%) = [(180−H) / 180] × 100
<Various molecular weights: Mz, Mw and Mn>
A sample solution is prepared in which the polymer to be measured is dissolved in dimethylformamide (added with 0.01 N lithium bromide) at a concentration of 0.1% by weight. When measuring the precursor fiber, it is necessary to dissolve the precursor fiber in a solvent to form the specimen solution. However, the precursor fiber is highly oriented, and the more dense the substance, the less soluble and the longer the dissolution time. In addition, since the higher the dissolution temperature, the lower the molecular weight tends to be measured, the precursor fiber is pulverized and dissolved in a solvent controlled at a temperature of 40 ° C. with stirring with a stirrer for one day. About the obtained sample solution, a molecular weight distribution curve is calculated | required from the GPC curve measured on condition of the following using GPC apparatus, and Mz, Mw, and Mn are calculated.
・ Column: Column for polar organic solvent GPC ・ Flow rate: 0.5 ml / min
・ Temperature: 75 ℃
・ Sample filtration: Membrane filter (0.45μm cut)
・ Injection volume: 200 μl
・ Detector: Differential refractive index detector Mw uses at least six types of monodispersed polystyrenes with different molecular weights and known molecular weights to create an elution time-molecular weight calibration curve, and corresponds to the corresponding elution time on the calibration curve. It is obtained by reading the molecular weight in terms of polystyrene.

  In an example of the present invention, CLASS-LC2010 manufactured by Shimadzu Corporation as a GPC apparatus and TSK-GEL-α-M (× 2) manufactured by Tosoh Corporation as a column and TSK-guard Column α manufactured by Tosoh Corporation. , Dimethylformamide and lithium bromide manufactured by Wako Pure Chemical Industries, Ltd., 0.45 μm-FHLP FILTER manufactured by Millipore Corporation as a membrane filter, and RID-10AV manufactured by Shimadzu Corporation as a differential refractive index detector, Monodispersed polystyrenes for preparing a calibration curve were those having molecular weights of 184,000, 427,000, 791,000 and 1,300,000, 1,810,000, 4210,000.

<Tensile strength and elastic modulus of carbon fiber bundle>
It is determined according to JIS R7608 (2007) “Resin-impregnated strand test method”. The resin-impregnated strand of the carbon fiber bundle to be measured was 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylate (100 parts by weight) / 3 boron fluoride monoethylamine (3 parts by weight) / acetone (4 parts by weight) ) Is impregnated into carbon fiber or graphitized fiber and cured at a temperature of 130 ° C. for 30 minutes. The number of carbon fiber strands to be measured is 6, and the average value of each measurement result is the tensile strength. In Examples of the present invention, “Bakelite” (registered trademark) ERL4221 manufactured by Union Carbide Co., Ltd. was used as 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylate.

<Weibull shape factor m ″ of single fiber tensile strength of carbon fiber bundle, square R ^{2 of} correlation coefficient>
The single fiber tensile strength of the carbon fiber bundle is determined as follows based on JIS R7606 (2000). First, a carbon fiber bundle having a length of about 20 cm is roughly divided into four equal parts, and 100 single fibers are sampled sequentially from the four bundles. At this time, the entire bundle is sampled as evenly as possible. The sampled single fiber is fixed to the perforated mount using an adhesive. A mount on which a single fiber is fixed is attached to a tensile tester, and a tensile test is performed with a test length of 25 mm, a strain rate of 1 mm / min, and a single fiber sample number of 100. The Weibull shape factor is defined by the following equation.
lnln {1 / (1-F)} = mlnσ + C
In the above formula, F is the fracture probability, determined by the symmetric sample cumulative distribution method, σ is the single fiber tensile strength (MPa), m is the Weibull shape factor in the range F is 0 to 1, and C is It is a constant. If Weibull plotting is performed with lnln {1 / (1-F)} and lnσ, m can be obtained from the linear approximation slope. The correlation function at that time is R. Further, m ″ can be obtained from the slope obtained by linear approximation with F being 0.3 to 1.

The cross-sectional area of the single fiber is determined by dividing the weight per unit length (g / m) by the density (g / m ³ ) for the carbon fiber bundle to be measured based on JIS R7607 (2000), and further filament Divide by the number to obtain the single fiber cross-sectional area.

<Crystallite size of carbon fiber bundle>
By aligning the carbon fiber bundles used for measurement and solidifying them with a collodion / alcohol solution, a square column measurement sample having a length of 4 cm and a side length of 1 mm is prepared. About the prepared measurement sample, it measured on the following conditions using the wide angle X-ray-diffraction apparatus.
-X-ray source: CuKα ray (tube voltage 40 kV, tube current 30 mA)
-Detector: Goniometer + Monochromator + Scintillation counter-Scanning range: 2θ = 10-40 °
Scan mode: Step scan, step unit 0.02 °, counting time 2 seconds In the obtained diffraction pattern, the half-value width is obtained for a peak appearing in the vicinity of 2θ = 25 to 26 °, and the next Scherrer ( The crystal size was calculated according to the Scherrer equation.
Crystallite size (nm) = Kλ / β ₀ cos θ _B
However,
・ K: 1.0, λ: 0.15418 nm (X-ray wavelength)
・ Β ₀ : (β _E ² −β ₁ ² ) ^1/2
Β _E : Apparent half width (measured value) rad, β ₁ : 1.046 × 10 ⁻² rad
・ Θ _B : Bragg diffraction angle 2θ = crystal orientation degree from the half width (H °) of the spread of the profile in the meridian direction including the maximum intensity of diffraction observed around 25 to 26 °, using the following formula (%) Was calculated.
Crystallinity degree (%) = [(180−H) / 180] × 100
As the wide-angle X-ray diffractometer, XRD-6100 manufactured by Shimadzu Corporation was used.

<Average single fiber diameter of carbon fiber bundle>
A weight Af (g / m) and a specific gravity Bf (g / cm ³ ) per unit length are determined for a carbon fiber bundle composed of a large number of carbon filaments to be measured. The number of filaments of the carbon fiber bundle to be measured was Cf, and the average single fiber diameter (μm) of the carbon fiber was calculated by the following formula.
-Average single fiber diameter (μm) of carbon fiber = ((Af / Bf / Cf) / π) ^(1/2) × 2 × 10 ³ .

<Nitrogen content>
Organic elemental analysis was performed using Yanagimoto Seisakusho CHN Corder Model MT-3, the nitrogen content was determined, and the nitrogen content relative to the sample weight was calculated. The moisture content in the sample was measured, and the sample weight was corrected.

<Surface area ratio of single fiber of carbon fiber bundle>
An atomic force microscope (SPI3800N / SPA-400, manufactured by Seiko Instruments Inc.) was prepared by placing several precursor single fibers to be evaluated on a sample stage and fixing both ends with an adhesive solution (for example, a stationery correction solution). ) To obtain an image of a three-dimensional surface shape under the following conditions.
Probe: Silicon cantilever (Seiko Instruments, DF-20)
Measurement mode: Dynamic force mode (DFM)
・ Scanning speed: 1.5Hz
・ Scanning range: 3μm × 3μm
・ Resolution: 256 pixels x 256 pixels The obtained measurement image is fitted with a first-order plane obtained from the entire data of the image by the least square method using the attached software in consideration of the curvature of the fiber cross section. After performing the primary inclination correction for correcting the inclination and subsequently performing the secondary inclination correction for correcting the quadratic curve in the same manner, the surface roughness analysis was performed with the attached software, and the surface area ratio was calculated. The measurement was performed by sampling three different single fibers at random, one time for each single fiber, three times in total, and taking the average value as the value.

<Ratio of major axis and minor axis of fiber cross section of single fiber (major axis / minor axis)>
After passing a carbon fiber bundle for measurement through a tube made of vinyl chloride resin having an inner diameter of 1 mm, the sample is prepared by cutting it with a knife. Next, the sample was adhered to the SEM sample stage with the fiber cross-section facing upward, and Au was further sputtered to a thickness of about 10 nm, and then accelerated voltage 7.00 kV using a PHILIPS XL20 scanning electron microscope. The fiber cross section is observed under the condition of a working distance of 31 mm, the major axis and minor axis of the fiber section of the single fiber are measured, and the ratio of major axis / minor axis is determined by major axis / minor axis.

<Interfacial shear strength>
Interfacial shear strength, which is evaluation of adhesive strength with resin, was performed by a single fiber embedding (fragmentation) method. Specifically, it was carried out by the method described in Realize, “Development and Evaluation Method of Carbon Fiber”, pages 157 to 160. That is, a test piece in which one single fiber was embedded in a resin was produced, and an elongation greater than the breaking elongation of the fiber was imparted to the test piece. Interfacial shear strength was calculated from the following equation by reading the length of each fiber broken in the resin.
・ Critical fiber length (mm) = 4 × average fiber length (mm) / 3
Interfacial shear strength (MPa) = fiber strength (MPa) × fiber diameter (mm) / 2 × critical fiber length (mm)
The resin used for preparing the test piece was 100 parts of “Araldide CY230” manufactured by CIBA-GEIGY and 35 parts of “Hardener HY2967”, which was poured into a dedicated mold, and heated at a temperature of 20 ° C. The composition was cured at a temperature of 60 ° C. for 6 hours under a temperature condition of 6 hours. The tensile test was performed at room temperature of 20-25 ° C. After imparting elongation within a range where the test piece did not break (elongation 7%), the length of the fiber broken in the resin was read with a polarizing microscope, and the average fiber length was calculated.

[Example 1]
100 parts by weight of AN, 1 part by weight of itaconic acid, and 360 parts by weight of dimethyl sulfoxide were mixed and placed in a reaction vessel equipped with a reflux tube and a stirring blade. After replacing the space in the reaction vessel with nitrogen to an oxygen concentration of 100 ppm, 0.003 part by weight of 2,2′-azobisisobutyronitrile (hereinafter sometimes abbreviated as AIBN) as a polymerization initiator. The heat treatment was performed under the following conditions with stirring.
(1) Hold at a temperature of 60 ° C. for 3.5 hours Next, in the reaction vessel, 10 parts by weight of dimethyl sulfoxide, 0.4 part by weight of AIBN as a polymerization initiator, and 0.1 part by weight of octyl mercaptan as a chain transfer agent After the parts were metered in, heat treatment under the following conditions (referred to as heat treatment condition A) was performed with further stirring, and the remaining unreacted monomer was polymerized by a solution polymerization method to obtain a PAN polymer solution.
(2) Hold for 4 hours at a temperature of 60 ° C. (3) Increase the temperature from 60 ° C. to 80 ° C. (Temperature increase rate: 10 ° C./hour)
(4) Hold for 6 hours at a temperature of 80 ° C. Use the obtained PAN-based polymer solution to prepare a polymer concentration of 20% by weight, and then blow ammonia gas until the pH reaches 8.5. Thus, an ammonium group was introduced into the PAN polymer while neutralizing itaconic acid to obtain a spinning solution. The PAN-based polymer had Mw of 400,000, Mz / Mw of 5.2, and M _{Z + 1} / Mw of 10.

The obtained spinning solution was discharged into the air once at a temperature of 40 ° C. at a temperature of 40 ° C. and having a hole number of 3,000 and a nozzle diameter of 0.15 mm, and passed through a space of about 2 mm. Spinning was carried out by a dry-wet spinning method introduced into a coagulation bath composed of an aqueous solution of 20% by weight dimethyl sulfoxide controlled to a temperature to obtain a coagulated yarn. When the spinning draft at this time was dried under the conditions of 28, a coagulated yarn having a coagulated yarn single fiber fineness of 1.5 dtex was obtained, washed with water, further provided with an amino-modified silicone-based silicone oil, and a temperature of 165 ° C. Was dried for 30 seconds using a roller heated to obtain a carbon fiber precursor fiber bundle having a total draw ratio of 1 ×, a final spinning speed of 30 m / min, and 3000 filaments. The obtained carbon fiber precursor fiber bundle had a crystal orientation degree of 76%, excellent quality, and stable yarn passing through. The obtained carbon fiber precursor fiber bundle was subjected to flame resistance treatment in air having a temperature distribution of 250 to 270 ° C. with a tension per single fiber of 20 mg for 30 minutes to obtain a flame resistant fiber bundle. The obtained flame-resistant fiber bundle had a specific gravity of 1.45 g / cm ³ . Subsequently, the obtained flame-resistant fiber bundle was subjected to preliminary carbonization treatment so that the tension per single fiber was 30 mg in a nitrogen atmosphere having a temperature distribution of 300 to 700 ° C., and the maximum temperature was 1350 ° C. In a nitrogen atmosphere, carbonization was performed so that the tension per single fiber was 20 mg, and a continuous carbon fiber bundle was obtained. In this case, the baking process passability was good. Table 1 summarizes data such as strand properties of the obtained carbon fiber bundle.

[Example 2]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the maximum carbonization temperature was changed to 1250 ° C. The results are shown in Table 1.

[Example 3]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the coagulation bath concentration was changed to a 60% by weight dimethyl sulfoxide aqueous solution. The results are shown in Table 1.

[Example 4]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the coagulation bath concentration was 79% by weight dimethyl sulfoxide aqueous solution and the temperature was changed to 20 ° C. The results are shown in Table 1.

[Comparative Example 1]
100 parts by weight of AN, 1 part by weight of itaconic acid, 0.4 part by weight of AIBN as a radical initiator, and 0.1 part by weight of octyl mercaptan as a chain transfer agent are uniformly dissolved in 370 parts by weight of dimethyl sulfoxide, which is stirred with a reflux tube. Placed in a reaction vessel with wings. After replacing the space in the reaction vessel with nitrogen, heat treatment was performed under polymerization condition A while stirring, and polymerization was performed by a solution polymerization method to obtain a PAN polymer solution. The obtained PAN-based polymer solution was prepared so that the polymer concentration was 20% by weight, and then ammonia gas was blown until the pH reached 8.5 to neutralize itaconic acid, while the ammonium group was neutralized. Was introduced into the polymer to prepare a spinning solution. The PAN-based polymer had Mw of 350,000, Mz of 620,000, Mz / Mw of 1.8, M _{Z + 1} / Mw of 3, and the spinning solution had a viscosity of 55 Pa · s. . A coagulated yarn was obtained in the same manner as in Example 1 except that the spinning solution was changed to the spinning solution obtained as described above, but the yarn was broken and could not be spun. The results are shown in Table 1.

[Comparative Example 2]
In order to cover the low spinnability using the same spinning solution as in Comparative Example 1, the average pore diameter of the spinneret was set to 0.05 mm, and the spinning draft was set to 3, so that the carbon was the same as in Example 1. Fiber was obtained. At this time, the stretch ratio in the firing step was the same as in Example 1. Probably because the discharge linear velocity from the spinneret increased, the degree of orientation of the precursor fibers increased, and the elastic modulus of the carbon fiber bundles increased too much. The results are shown in Table 1.

[Comparative Example 3]
Except for changing the single fiber fineness of the precursor fiber bundle to 2.0 dtex by adjusting the discharge amount from the spinneret, carbon fiber was obtained in the same manner as in Example 1, but the flame resistance was insufficient. Probably because of this, yarn breakage occurred in the carbonization process, and a carbon fiber bundle could not be obtained. The results are shown in Table 1.

[Comparative Example 4]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the spinning draft was 14 and the dry heat draw ratio after drying was doubled. At this time, the stretch ratio in the firing step was the same as in Example 1. The degree of orientation of the precursor fiber bundle was increased, and the elastic modulus of the carbon fiber bundle was too high. The results are shown in Table 1.

[Reference example]
Table 1 shows related characteristic values of commercially available pitch-based low elastic modulus carbon fibers (XN-05 manufactured by Nippon Graphite Fiber Co., Ltd.).

Claims (8)

  A polyacrylonitrile-based continuous carbon fiber bundle having a strand tensile modulus of 70 to 140 GPa, a breaking elongation of 1.3 to 3%, and a saturated water absorption of 0 to 0.4% by weight, and elemental analysis The nitrogen content determined from 1 to 5%, the C-axis crystallite size determined from the 002 diffraction line by X-ray diffraction measurement is 1.3 to 2.0 nm, and the degree of crystal orientation of the 002 plane is Polyacrylonitrile-based continuous carbon fiber bundle that is 75-80%.   The polyacrylonitrile-based continuous carbon fiber bundle according to claim 1, wherein the surface area ratio of single fibers constituting the continuous carbon fiber bundle is 1.02 to 1.2.   The polyacrylonitrile-based continuous carbon fiber bundle according to claim 1 or 2, wherein the ratio of the major axis to the minor axis (major axis / minor axis) of the fiber cross section of the single fiber constituting the continuous carbon fiber bundle is 1.05 to 1.6. .   The polyacrylonitrile-based continuous carbon fiber bundle according to any one of claims 1 to 3, wherein the continuous carbon fiber bundle has 1000 to 6000 filaments and a single fiber diameter of 7 to 11 µm. 5. The Weibull shape factor m ″ of the single fiber tensile strength is 7 to 10, and the square R ² of the correlation coefficient of the Weibull plot approximated by one line is 0.92 to 1. 5. Polyacrylonitrile-based continuous carbon fiber bundle.   A polyacrylonitrile polymer having a weight average molecular weight Mw of 100,000 to 1,000,000 and a polydispersity Mz / Mw (Mz represents a Z average molecular weight) of 2.7 to 6 is dissolved in a solvent to form a heavy polymer. Setting control of a polymer solution having a coalescence concentration of 6 to 25% by weight from a spinneret having an average pore diameter of 0.10 to 0.26 mm so that the spinning draft of the polymer solution is in the range of 12 to 50 Thus, a coagulated yarn having a single fiber fineness of 1.4 to 2.3 dtex obtained by spinning, spinning, dry-wet spinning, and drying is obtained, and then the coagulated yarn is drawn at a draw ratio of 1 to 1.9. A method for producing a precursor fiber bundle for a polyacrylonitrile-based carbon fiber, characterized in that a drawn fiber having a single fiber fineness of 1.2 to 1.8 dtex is drawn at a double.   The method for producing a precursor fiber bundle for polyacrylonitrile-based carbon fibers according to claim 6, wherein the take-up speed of the coagulated yarn is 20 to 200 m / min.   A precursor fiber for polyacrylonitrile-based carbon fiber obtained by the production method according to claim 6 or 7 is subjected to flameproofing treatment in air at a temperature of 200 to 300 ° C, and then an inert atmosphere at a temperature of 300 to 800 ° C. Process for producing a polyacrylonitrile-based continuous carbon fiber bundle having a maximum tension of 10 to 100 mg per single fiber when carbonized in an inert atmosphere at a temperature of 1,100 to 3,000 ° C. .