WO2019012999A1

WO2019012999A1 - Carbon fiber bundle and method for manufacturing same

Info

Publication number: WO2019012999A1
Application number: PCT/JP2018/024513
Authority: WO
Inventors: 松本直浩; 奥田治己; 田中文彦
Original assignee: 東レ株式会社
Priority date: 2017-07-10
Filing date: 2018-06-28
Publication date: 2019-01-17
Also published as: CN110832127B; KR20200028334A; JP6460284B1; US20200190705A1; KR102603178B1; JPWO2019012999A1; EP3653768A4; EP3653768A1; TW201908553A; CN110832127A

Abstract

The present invention is a carbon fiber bundle that satisfies a prescribed strand modulus of elasticity, a prescribed strand strength, a prescribed node strength, and a prescribed average single fiber diameter and has a prescribed probability of the presence of defects with a size of 50 nm or greater in recovered rupture cross-sections when single fiber tension tests are carried out for test lengths of 10 mm, wherein the carbon fiber bundle is suitably obtained by using a filter medium having a prescribed filtration precision and filter medium mesh to filter, under a prescribed filtration rate, a spinning solution in which a polyacrylonitrile copolymer is dissolved in a solvent, then spinning the filtered spinning solution to obtain a carbon fiber precursor fiber bundle, heat treating the carbon fiber precursor fiber bundle obtained to a prescribed density using a suitable temperature profile in an oxidizing atmosphere to obtain a fire resistant fiber bundle, and subsequently heat treating the fire resistant fiber bundle at a prescribed temperature in an inert atmosphere. The purpose of the present invention is to provide a carbon fiber bundle that exhibits superior strand strength and strand modulus of elasticity with excellent balance and which has superior node strength and a method for manufacturing the same.

Description

Carbon fiber bundle and method for producing the same

The present invention relates to a carbon fiber bundle and a method for producing the same.

Carbon fiber bundles are widely used as reinforcing fibers for composite materials, and there is a strong demand for higher performance. In particular, in order to reduce the weight of members such as pressure vessels, to improve mechanical properties such as resin impregnated strand strength of carbon fiber bundle and resin impregnated strand elastic modulus (hereinafter simply referred to as strand strength and strand elastic modulus) in a well-balanced manner Is required. At the same time, it is necessary to reduce the environmental burden in the production of carbon fiber bundles. In general, the polyacrylonitrile carbon fiber bundle is a process of heat treating a carbon fiber precursor fiber bundle in an oxidizing atmosphere at 200 to 300 ° C. (flameproofing step) and then heat treating it in an inert atmosphere of 1000 ° C. or more It can be obtained through the (carbonization step). At that time, carbon, nitrogen and hydrogen atoms contained in polyacrylonitrile are eliminated by thermal decomposition, so the carbon fiber bundle yield (hereinafter also referred to as carbonization yield) is about half. It is necessary to increase the yield of carbon fiber bundles with equivalent production energy from the viewpoint of reducing the production energy per production amount, that is, the environmental load.

Therefore, many techniques have been proposed for the purpose of improving the strand strength or carbonization yield of carbon fiber bundles by optimizing flame resistance conditions (Patent Documents 1-5).

In patent document 1, examination which makes heat quantity (J * h / g) given by carrying out high temperature processing in a flame-proof process as small as possible, and improves the strand intensity | strength of a carbon fiber bundle is made | formed. In Patent Document 2, setting the temperature for oxidation to a high temperature according to the amount of oxygen added in the middle of the process for flame-proofing, in Patent 3, heat and cool the carbon fiber precursor fiber bundle so as to prevent thermal runaway. In order to shorten the flameproofing process, it has been proposed that the flameproofing be made as high temperature as possible by repeating. Further, in Patent Documents 4 and 5, the carbon fiber precursor fiber bundle is heated in an oxidizing atmosphere at the initial stage of flame resistance, and then brought into contact with a high temperature heating roller at 250 to 300 ° C. An attempt was made to raise the carbonization yield by raising the

Patent Documents 6 and 7 propose carbon fiber bundles with high knot strength, which reflect mechanical properties other than in the fiber axial direction and exhibit sufficient mechanical properties in quasi-isotropic materials.

In Patent Document 8, when obtaining a flameproofed fiber bundle of a specific density in order to satisfy a high carbonization yield, a flameproofed fiber bundle of a specific density by heat treatment at a high temperature in the latter half with an appropriate temperature profile in the flameproofing step. A carbon fiber bundle has been proposed which has a well-balanced expression of high carbonization yield and excellent strand strength and strand modulus, and simultaneously satisfies excellent knot strength.

On the other hand, since carbon fiber is a brittle material and slight surface defects and internal defects cause strand strength reduction, delicate attention has been paid to the generation of defects. For example, in Patent Document 9, defects in the surface of a carbon fiber are reduced to obtain a carbon fiber bundle of high strand strength by densifying a carbon fiber precursor fiber bundle, reducing dust in the manufacturing process and removing defects by electrolytic treatment. It has been proposed.

JP 2012-82541 A JP-A-58-163729 Japanese Patent Application Laid-Open No. 6-294020 JP 2013-23778 A JP 2014-74242 A International Publication No. 2013/157613 JP, 2015-096664, A JP 2017-66580 A Japanese Examined Patent Publication 8-6210

However, in the proposal of patent document 1, since it is going to make small the integral value of the calorie | heat amount given at a flameproofing process, it was not enough for coexistence of strand strength and a carbonization yield. Further, in the proposals of Patent Documents 2 and 3, since the temperature for making the temperature is increased to shorten the time for making the temperature shorter, the temperature control for making the temperature sufficient to satisfy the required strand strength is not performed. Stress concentration control to the surface layer by the difference was a subject. In the proposals of Patent Documents 4 and 5, heat treatment is performed at a high temperature using a heating roller having a high heat transfer efficiency in order to perform heat treatment at a high temperature in a short time in the second half of the flameproofing process. Sufficient strand strength has not been obtained due to the formation of defects due to fusion between single fibers when passing through rollers and rollers. Although the proposal of Patent Document 6 states that the knot strength can be enhanced even by a large single fiber diameter mainly by adjusting the step of making the flame resistant, the effect is limited due to the structural distribution within the single fiber at the time of making it hard. And the level of knot strength was insufficient. Although the proposal of Patent Document 7 states that the knot strength can be enhanced by mainly adjusting the surface treatment of the carbon fiber bundle and the sizing agent, the single fiber diameter is limited and the single fiber diameter is limited. If it is low, the breaking tension of the single fiber in the manufacturing process is reduced, so there is a problem that the quality of the manufacturing process is reduced due to the fiber breakage. In the proposal of Patent Document 8, although the strand strength and the knot strength are enhanced by performing the second half high-temperature heat treatment with an appropriate temperature profile in the flameproofing process, the control of defects affecting these characteristics is not sufficient and improvement is There was room. In Patent Document 9, although defects on the surface of the carbon fiber can be effectively removed by electrolytic treatment, strong electrolytic treatment is required to remove the defects, and a long electrolytic treatment tank is required. There was a problem that it was difficult to carry out industrially. In addition, there is also a problem that a fragile layer which may lead to a decrease in composite physical properties due to strong electrolytic treatment is formed on the surface of the carbon fiber. Furthermore, as defects, the characteristics of defects in the fractured surface recovered when the single fiber tensile test is performed with a test length of 50 mm are specified, but the test length that affects the strand strength and the tensile strength of the composite material is 10 mm Because of their shortness, there is also an essential problem that merely specifying the characteristics of defects found in the test length of 50 mm does not necessarily result in carbon fiber bundles that enhance the tensile strength of the composite material.

In order to solve the problems in the prior art described above, the present invention provides a method for producing a carbon fiber bundle having well-balanced strand strength and strand elasticity and excellent knot strength without losing productivity. The purpose is

In order to achieve the above object, the method for producing a carbon fiber bundle of the present invention comprises a spinning solution in which a polyacrylonitrile copolymer is dissolved in a solvent, filtration accuracy B (μm) and filter medium weight D (g / m) ² ) using the filter medium having the above ² ) and filtering the spinning solution under the condition that the filtration rate A (cm / hour) satisfies the following formulas (1) to (3), and spinning the filtered spinning solution Obtain a carbon fiber precursor fiber bundle,
D-600 / (α x β) 0 0 (1)
α = 1-1 / (1 + exp (7-A)) (2)
β = 1−1 / (1 + exp (−0.23 × B)) (3)
The obtained carbon fiber precursor fiber bundle was heat treated to a density 1.32 ~ 1.35g / cm ³ in an oxidizing atmosphere, an oxidizing atmosphere to a density 1.46 ~ 1.50g / cm ³ This is a method for producing a carbon fiber bundle, wherein heat treatment is carried out at 275 ° C. or more and 295 ° C. or less to obtain a flame-resistant fiber bundle, and then the flame-resistant fiber bundle is heat-treated at 1200 to 1800 ° C. in an inert atmosphere.

The carbon fiber bundle of the present invention has a strand elastic modulus of 240 to 280 GPa, a strand strength of 5.8 GPa or more, a knot strength K [MPa] of -88d + 1390 ≦ K (d: average single fiber diameter [μm]), When a single fiber tensile test is performed with an average single fiber diameter in the range of 6.5 to 8.0 μm and a test length of 10 mm, the probability that a defect with a size of 50 nm or more exists on the recovered fractured surface is 35 % Or less of carbon fiber bundles.

According to the method of the present invention, when obtaining a flameproofed fiber bundle, it is possible to obtain a flameproofed fiber bundle of a specific density by heat treatment with an appropriate temperature profile in the flameproofing step, whereby strand strength and knots are obtained. Since the defects governing strength are controlled to a very low degree, it is possible to produce a carbon fiber bundle having well-balanced strength of strands and strand elasticity and excellent knot strength without losing productivity. Moreover, according to the carbon fiber bundle of the present invention, the carbon fiber bundle satisfies the productivity at the time of producing the composite material.

FIG. 1 is a scanning electron microscope (SEM) image of a fractured surface of carbon fiber. Radial streaks that converge to one point are identified. FIG. 2 is an enlarged image of the vicinity of the break starting point of FIG. Deposit-like defects are identified. FIG. 3 is an enlarged image of another fracture surface near the fracture origin. A dent-like defect is identified. FIG. 4 is an enlarged image of another fracture surface near the fracture origin. No noticeable morphological features above 50 nm are identified.

The carbon fiber bundle of the present invention has a strand strength of 5.8 GPa or more, preferably 6.0 GPa or more. When the strand strength is 5.8 GPa or more, the composite material exhibits good tensile strength when the composite material is manufactured using the carbon fiber bundle. The strand strength of the carbon fiber bundle is preferably as high as possible, but even if the strand strength is 7.0 GPa or less, sufficient tensile strength of the composite material can be obtained. The strand strength can be determined by the method described in the strand tension test of the carbon fiber bundle described later. The strand strength can be controlled by using the method for producing a carbon fiber bundle of the present invention described later.

The carbon fiber bundle of the present invention has a strand elastic modulus of 240 to 280 GPa, preferably 245 to 275 GPa, and more preferably 250 to 270 GPa. If the strand elastic modulus is 240 to 280 GPa, it is preferable because the balance between the strand elastic modulus and the strand strength is excellent. In particular, by controlling the strand elastic modulus to 250 to 270 GPa, it is easy to obtain a carbon fiber bundle with excellent strand strength. The strand elastic modulus can be determined by the method described in the strand tension test of the carbon fiber bundle described later. At this time, the strain range is set to 0.1 to 0.6%. The strand elastic modulus of the carbon fiber bundle mainly applies tension to the fiber bundle in any heat treatment process in the manufacturing process of the carbon fiber bundle, improves the internal / external structural difference which is the structural distribution in the single fiber, or It can control by changing carbonization temperature.

Further, in the carbon fiber bundle of the present invention, a knot strength is preferably 700 MPa or more, preferably 740 MPa or more, obtained by forming a knot portion at the midpoint of the carbon fiber bundle and conducting a bundle tension test. More preferably, the pressure is 770 MPa or more. The knot strength can be determined by the method described in the knot strength of the carbon fiber bundle described later. The knot strength is an index reflecting the mechanical properties of the fiber bundle other than the fiber axial direction. When producing the composite material, the carbon fiber bundle is loaded with a force in the bending direction. If the number of filaments is increased to efficiently produce the composite material, it is difficult to increase the running speed of the fiber bundle at the time of producing the composite material because fluff is generated, but if the knot strength is 700 MPa or more, the condition that the running speed of the fiber bundle is high However, composite materials can be obtained with high quality. In order to increase the knot strength of the carbon fiber bundle, in the method for producing a carbon fiber bundle of the present invention described later, in particular, it is preferable to control the structural parameters in the flameproofing step and the precarbonization step within a preferable range. Furthermore, reducing the defects on the surface of the carbon fiber can also increase the knot strength.

The carbon fiber bundle preferably has a number of filaments of 10,000 to 60,000. If the number of filaments is 10,000 or more, a composite material can be produced with high productivity. If the number of filaments is 60,000 or less, it is possible to suppress the generation of fluff during the production of the composite material, and the traveling speed of the fiber bundle can be increased, so that the productivity is likely to be increased.

The carbon fiber bundle has a knot strength K [MPa] (= N / mm ² ) satisfying -88d + 1390 390 K (where d is an average single fiber diameter [μm]). It is preferable that the relational expression of −88d + 1410 ≦ K be satisfied. This relational expression indicates that the knot strength is high relative to the average single fiber diameter. When the knot strength K satisfies -88d + 1390 、 K, even in the case of a carbon fiber bundle having a large average single fiber diameter which is likely to be fuzzed by rubbing with a guide or a roller during the filament winding forming process, fuzz generation is suppressed It is possible to increase the traveling speed of the bundle for shaping. In order to satisfy such a relational expression, it is preferable to set flameproofing conditions appropriately according to the average single fiber diameter by the manufacturing method of the present invention described later.

The carbon fiber bundle preferably has a probability that a defect of 50 nm or more exists on the recovered fractured surface when the single fiber tensile test is performed with a test length of 10 mm, preferably 35% or less, more preferably 30% or less More preferably, it is 25% or less. It is known that tensile failure of carbon fibers starts from defects. Various types of defects such as voids, scratches on the fiber surface, dents, deposits, or adhesion marks left after single fibers are adhered and separated by heat of heat treatment exist as defects that become the fracture starting point of carbon fibers In the present invention, all of these are not particularly distinguished, but the morphological features that become the fracture origin observable by scanning electron microscope (SEM) observation are collectively referred to as "defect". As a result of investigations by the present inventors, when a single fiber tensile test is performed with a test length of 10 mm, the carbon fiber bundle can be obtained if the probability that a defect with a size of 50 nm or more exists in the recovered fractured surface is 35% or less. It was found that the strand strength of the The important thing here is to set the trial length to 10 mm. When a single fiber tensile test is performed with a longer test length, for example, a test length of 50 mm, the probability, the strand strength, and the composite material can be examined also by examining the probability of the presence of a defect of a certain size or more. The inventors of the present invention have found that they do not necessarily correlate with tensile strength. The reason why it is effective to set the test length to 10 mm is considered to be that the test length governing the strand strength and the tensile strength of the composite material (generally referred to as the effective test length) is shorter than 10 mm. When the single fiber tensile test is performed with a test length of 10 mm, the strand strength of the carbon fiber bundle and the composite material can be obtained by setting the probability that a defect with a size of 50 nm or more is 35% or less on the recovered fractured surface. Defects affecting tensile strength are effectively reduced, resulting in high levels of strand strength, and tensile strength of the composite. “Probability that a defect with a size of 50 nm or more exists in the recovered fractured surface when the single fiber tensile test is performed with a test length of 10 mm” is the filtration speed and the filtration accuracy, which are the filtration conditions of the spinning solution, The filter material basis weight is controlled in accordance with the method described later, and is reduced by effectively removing foreign substances in the spinning solution.

In the carbon fiber bundle of the present invention, the average single fiber diameter is 6.5 to 8.0 μm, preferably 6.7 to 8.0 μm, more preferably 7.0 to 8.0 μm, and 7.3 to 8. 0 μm is more preferable, and 7.5 to 8.0 μm is the most preferable. The smaller the average single fiber diameter, the smaller the internal / external structural difference tends to decrease. However, when preparing a composite material, insufficient impregnation may occur due to the high matrix resin viscosity, which may lower the tensile strength of the composite material. When the average single fiber diameter is 6.5 to 8.0 μm, it is preferable because the insufficient impregnation of the matrix resin hardly occurs and the expression of high carbonization yield and strand strength becomes stable. The average single fiber diameter can be calculated from the mass and density per unit length of carbon fiber bundle and the number of filaments. The average single fiber diameter of the carbon fiber bundle is to increase the carbonization yield in the carbonization step by increasing the average single fiber diameter of the carbon fiber precursor fiber bundle, or by controlling the flameproof conditions, and the draw ratio of precarbonization. Can be enhanced by lowering

The carbon fiber bundle preferably has an average surface roughness Ra of 1.8 nm or less on the surface of a single fiber measured by an atomic force microscope (AFM). Details of the measurement method will be described later. The average surface roughness of the carbon fiber precursor fiber bundle is substantially maintained in the carbon fiber bundle. The average surface roughness is preferably 1.0 to 1.8 nm, and more preferably 1.6 nm or less. When the average surface roughness exceeds 1.8 nm, the stress concentration point at tension may easily occur, and the strand strength may decrease. The average surface roughness is preferably as low as possible, but when it is less than 1.0 nm, the effect is often saturated. The average surface roughness of the carbon fiber bundle can be controlled by appropriately controlling the spinning conditions of the carbon fiber precursor fiber bundle (spinning method or coagulation bath condition) or reducing the surface defect of the carbon fiber bundle.

The carbon fiber bundle preferably has an area ratio (hereinafter referred to as an outer layer ratio) within the cross section of the blackened thickness of the outer peripheral portion of the cross section perpendicular to the fiber axial direction of the carbon fiber single fiber is preferably 90 area% or more It is preferably 90 to 95 area%, more preferably 90 to 93 area%. Here, the outer layer ratio is an area ratio obtained by dividing the area occupied by the blackened thickness seen in the outer peripheral part when the cross section perpendicular to the fiber axial direction of the carbon fiber single fiber is observed with an optical microscope %). Since the orientation of the crystal part is lower in the interior than the blackened thickness of the carbon fiber single fiber and the strand elastic modulus is low, the surface layer stress concentration can be suppressed as the outer layer ratio becomes higher, so high strand strength can be expressed. When the outer layer ratio is low, it is difficult to develop high carbonization yield and high strand strength. When the outer layer ratio is 90 area% or more, the ratio of the stress bearing portion in the outer peripheral portion is sufficiently large, so that the stress concentration in the surface layer is suppressed. When the outer layer ratio exceeds 95% by area, the stress concentration suppressing effect on the surface layer is saturated, but the stranding strength may be lowered due to the temperature for temperature stabilization being deviated from the optimum temperature. The blackening thickness can be measured by embedding a carbon fiber bundle in a resin, polishing a cross section perpendicular to the fiber axis direction, and observing the cross section with an optical microscope. Details will be described later.

In order to solve the problems of the present invention, the method for producing a carbon fiber bundle of the present invention is a strand by subjecting the latter half to a high temperature heat treatment with an appropriate temperature profile in a flameproofing step to make the flameproofed fiber bundle a specific density. It has been found that carbon fiber bundles are obtained in which the defects governing strength and knot strength are controlled very little and high carbonization yield and excellent strand strength and knot strength are obtained. The preferred embodiments of the present invention will be described in detail below.

The carbon fiber precursor fiber bundle can be obtained by spinning a spinning solution in which a polyacrylonitrile copolymer is dissolved in a solvent. At this time, by filtering the spinning solution under specific conditions, foreign substances in the spinning solution are effectively removed, and then the filtered spinning solution is spun to obtain a carbon fiber precursor fiber bundle, which is obtained. The carbon fiber precursor fiber bundle can be subjected to at least a flameproofing step, a precarbonization step and a carbonization step to obtain a carbon fiber bundle of high strand strength with few defects. As a polyacrylonitrile copolymer, it is preferable to use the polyacrylonitrile copolymer which used the other monomer in addition to the acrylonitrile which is a main component. Specifically, the polyacrylonitrile copolymer preferably contains 90 to 100% by mass of acrylonitrile and less than 10% by mass of a copolymerizable monomer.

The polyacrylonitrile copolymer preferably contains a copolymer component such as itaconic acid, acrylamide, or methacrylic acid, from the viewpoint of improving the spinning process stability and efficiently performing the flame resistance treatment.

The method for producing the polyacrylonitrile copolymer can be selected from among known polymerization methods. In the production of a carbon fiber precursor fiber bundle, the spinning solution dissolves the polyacrylonitrile copolymer described above in a solvent in which polyacrylonitrile is soluble such as dimethylsulfoxide, dimethylformamide, dimethylacetamide or an aqueous solution of nitric acid, zinc chloride and sodium rhodanate It is

Prior to spinning the spinning solution as described above, it is preferable to pass the spinning solution through a filter device to remove the polymer raw material and impurities mixed in each step. Here, the filter device means a facility for filtering out foreign matter present in the spinning solution, an inflow path for introducing the spinning solution into the filter device, and a filter medium for filtering the spinning solution. And an outlet for guiding the filtered spinning solution out of the filter device, and a container for containing them. Here, the filter medium is a means for filtering the spinning solution contained in the filter device.

As a form of a filter medium, a leaf disc type filter, a candle type filter, a pleated candle type filter, etc. are used. In contrast to candle filters and pleated candle filters whose filter media have a certain curvature, leaf disc filters can be used almost flatly, so that the pore size distribution is less likely to spread and the washability is easily maintained. Is preferred.

The filter medium is a member having a direct role in removing foreign matter present in the spinning solution. The filter medium is required to have a defined open pore diameter with narrow variation, and additionally, chemical stability, heat resistance and pressure resistance to the substance to be treated are required. As such a filter material, a wire mesh produced by weaving metal fibers, a glass non-woven fabric, a filter material made of a sintered metal fiber structure, and the like are preferably used. The material of the filter medium is not particularly limited as long as it is inert in the spinning solution and there is no eluted component in the solvent, but metal is more preferable from the viewpoint of durability and cost. As specific metals, in addition to stainless steel (SUS304, SUS304L, SUS316, SUS316L, etc.), Inconel (registered trademark), Hastelloy (registered trademark), various alloys based on nickel, titanium, and cobalt are selected. The metal fiber manufacturing method is a so-called convergent fiber manufacturing method in which a large number of wire rods are put together as a bundle and wire diameter is reduced, and then each wire is separated to reduce the wire diameter, coil cutting method, chatter vibration cutting method, etc. Can be mentioned. When the filter medium is a wire mesh, the metal fibers need to be single fibers instead of fiber bundles, and therefore, they are manufactured by a method such as repeated drawing and heat treatment.

In the filtration of the spinning solution, the smaller the opening of the filter medium is, the easier it is to remove foreign substances in the spinning solution, but the clogging of the filter medium tends to occur. In the present invention, the foreign matter removal performance uses “filtration accuracy”. Here, the filtration accuracy (μm) is the particle diameter (diameter) of spherical particles capable of collecting 95% or more while passing through the filter medium. The filtration accuracy can be measured by the method of JIS standard (JIS-B 8356-8: 2002). The fact that the filtration accuracy is low is synonymous with the fact that the filtration accuracy is high. Further, as the thickness of the filter increases, foreign substances in the spinning solution can be more easily removed, but the pressure loss in the filter medium increases, and the stability of the production process decreases. So far, although the tendency as described above has been known, optimum filtration conditions are different for each filter medium, and a knowledge that can be generalized for filtration of a spinning solution has not been obtained. Therefore, at the time of the change of the filter medium, a great deal of time and cost are required to optimize the filtration conditions.

In the method for producing a carbon fiber bundle of the present invention, when the filtration accuracy of the filter medium used for the filtration of the spinning solution is B (μm) and the basis weight of the filter medium is D (g / m ² ), the filtration rate A (cm) The filtered spinning solution is filtered after the spinning solution is filtered under the condition that the relation between the filtration accuracy B (μm) and the filter material surface weight D (g / m ² ) satisfies the following formulas (1) to (3) The solution is spun to obtain carbon fiber precursor fiber bundles.
D-600 / (α x β) 0 0 (1)
α = 1-1 / (1 + exp (7-A)) (2)
β = 1-1 / (1 + exp (−0.23 × B)) (3).

Here, the filter basis weight D (g / m ² ) refers to the total basis weight of the filter medium excluding the mesh layer which may be laminated for the purpose of protecting the filter medium. The filter material basis weight D can be calculated by measuring the mass of the filter material cut into an arbitrary area and dividing the mass by the area.

The larger the filter material basis weight D, the higher the foreign matter trapping rate, and the smaller the size, the easier it is for foreign matter to slip through without passing through. Therefore, when the effect of the filter material basis weight D on the improvement of the quality of the carbon fiber precursor fiber bundle and the clogging suppression of the filter is measured while changing the filtration rate A and the filtration accuracy B, in any filtration rate and filtration accuracy It was confirmed that there is a minimum basis weight of the filter material (hereinafter referred to as the minimum basis weight of the filter material) capable of achieving both the improvement of the quality of the carbon fiber precursor fiber bundle and the suppression of clogging of the filter. According to the present experimental results, the lowest filter material weight can be expressed using the product α × β of mutually independent parameters α and β as shown in the second term on the left side of Formula (1). Here, α is defined as a function of the filtration rate A represented by the equation (2), and β is defined as a function of the filtration accuracy B represented by the equation (3). As the value of α × β is larger, the minimum filter material weight is smaller, and as α × β is smaller, the minimum filter material weight is larger. As the influence of individual variables, the larger the filtration rate A, the smaller α, and the lower the basis weight of the filter medium. As the filtration rate A decreases, α increases and the minimum filter material basis weight decreases. Similarly, as the filtration accuracy B is larger, β is smaller and the minimum filter material weight is larger. As the filtration accuracy B is smaller, β is larger and the minimum coating weight is smaller. By performing the filtration under the conditions satisfying the formulas (1) to (3), it is possible to simultaneously improve the quality of the carbon fiber precursor fiber bundle and suppress the clogging of the filter. Although this mechanism is not necessarily clear, it is considered as follows. That is, as the filtration accuracy is smaller, the foreign matter is more likely to be caught in the flow path in the filter medium, and the foreign matter can be effectively captured, but the filter tends to be clogged. However, when the filtration rate is low, deformation and spreading of foreign matter in the filter medium due to pressure loss are suppressed, so it is considered that the flow path in the filter medium is less likely to be clogged.

Moreover, it is preferable to use the filter medium which filtration accuracy B (micrometer) satisfy | fills following formula (4) as an example of the manufacturing method which obtains a carbon fiber bundle.
B ≧ 3 (4).

When the filtration accuracy B is 3 or more, clogging of the filter can be suppressed more effectively. The reason for this phenomenon is not necessarily clear, but as the value of the filtration accuracy B is large, the filtration pressure tends to be low, and the degree of deformation of the foreign matter is small, so it is considered that the filter clogging suppression effect tends to appear.

Next, a method of producing a carbon fiber precursor fiber bundle suitable for obtaining a carbon fiber bundle will be described. In producing a carbon fiber precursor fiber bundle, it is preferable to obtain a carbon fiber precursor fiber having a small average surface roughness on a single fiber surface by using a dry-wet spinning method. The method for producing a carbon fiber precursor fiber bundle comprises a spinning step of discharging a spinning solution from a spinneret into a coagulating bath and spinning by a wet-wet spinning method, and a water washing step of washing the fibers obtained in the spinning step in a water bath A water bath drawing process of drawing the fibers obtained in the water washing process in a water bath, and a drying heat treatment process of subjecting the fibers obtained in the water bath drawing process to dry heat treatment; It may include a steam drawing step of steam drawing the fibers.

In the production of the carbon fiber precursor fiber bundle, the coagulation bath preferably contains a coagulation promoting component and a solvent used as a solvent for the spinning solution. As the coagulation promoting component, those which do not dissolve the polyacrylonitrile copolymer and are compatible with the solvent used for the spinning solution can be used. Specifically, it is preferable to use water as a coagulation promoting component.

In the production of the carbon fiber precursor fiber bundle, the water bath temperature in the water washing step is preferably 30 to 98 ° C., and water washing is preferably performed using a water washing bath comprising a plurality of stages.

Further, the draw ratio in the water-bath drawing step is preferably 2 to 6 times.

After the water-bath drawing process, it is preferable to apply an oil agent made of silicone or the like to the fiber bundle for the purpose of preventing adhesion between single fibers. As such a silicone oil, it is preferable to use a modified silicone, and it is preferable to use one containing an amino-modified silicone having high heat resistance.

A well-known method can be utilized for a drying heat treatment process. For example, the drying temperature is 100 to 200 ° C., for example.

After the above-described water washing step, water bath drawing step, oiling step, and drying heat treatment step, the steam drawing step is further carried out to obtain a carbon fiber precursor fiber bundle more suitably used for the production of a carbon fiber bundle. In the steam drawing step, it is preferable to draw 2 to 6 times in pressurized steam.

The average fineness of single fibers contained in the carbon fiber precursor fiber bundle thus obtained is preferably 0.7 to 1.5 dtex, and more preferably 0.9 to 1.2 dtex. By setting the single fiber fineness to 0.7 dtex or more, the occurrence of fiber bundle breakage due to accumulation of single fiber breakage due to contact with a roller or a guide is suppressed, and the spinning process, flameproofing process, pre-carbonizing process and carbonization process Process stability of each process can be maintained. Further, by setting the single fiber fineness to 1.5 dtex or less, the outer layer ratio in each single fiber after the instabilization step is reduced, and the process stability in the subsequent carbonization step, the strand strength and the strand of the obtained carbon fiber bundle Elastic modulus can be improved. In order to adjust the single fiber fineness of the obtained carbon fiber precursor fiber bundle, the discharge amount of the spinning solution may be adjusted in the spinning process of discharging the spinning solution from the spinneret and spinning.

The resulting carbon fiber precursor fiber bundle is usually a continuous fiber. The number of filaments per fiber bundle is preferably 10,000 to 60,000.

In the method for producing a carbon fiber bundle of the present invention, the carbon fiber precursor fiber bundle is heat-treated in an oxidizing atmosphere to a density of 1.32 to 1.35 g / cm ^3, and then the density is 1.46 to 1.50 g / cm. Heat treatment is performed at 275 ° C. or more and 295 ° C. or less in an oxidizing atmosphere until it reaches cm ³ . That is, after the carbon fiber precursor fiber bundle is heat-treated to a predetermined density in the first half of the flameproofing process, heat treatment is performed at a high temperature of 275 ° C or more and 295 ° C or less in the second half of the flameproofing process.

Here, the oxidizing atmosphere is an atmosphere containing 10% by mass or more of known oxidizing substances such as oxygen and nitrogen dioxide, and an air atmosphere is preferable in terms of simplicity.

The density of the flameproofed fiber bundle is generally used as an index indicating the progress of the flameproofing reaction. Since the heat resistance is high when the density is 1.32 g / cm ³ or more, it is difficult to be decomposed when heat-treated at a high temperature, and the strand strength of the obtained carbon fiber bundle is improved. Moreover, since the heat processing time in high temperature can be ensured long in the following process as it is 1.35 g / cm < ³ > or less, the strand strength of a carbon fiber bundle can be improved. In the flameproofing process, in order to make it possible to switch the process temperature as described above when the density of the flameproofed fiber bundle is defined, the fiber bundle between the first half and the second half of the flameproofing process is collected and the density Should be measured. The method of measuring the density will be described later. For example, when the measured density of the flameproofed fiber bundle is lower than the specified value, the density of the flameproofed fiber bundle can be adjusted by raising the temperature or prolonging the flameproofing time in the first half of the flameproofing step.

In the flameproofing process, first, the carbon fiber precursor fiber bundle is heat-treated under an oxidizing atmosphere, preferably at 210 ° C. or more and less than 245 ° C., more preferably 220 ° C. or more and less than 245 ° C., still more preferably 225 ° C. or more and less than 240 ° C. As a result, a flame-resistant fiber bundle having a density of preferably 1.22 to 1.24 g / cm ³ , more preferably a density of 1.23 to 1.24 g / cm ³ is obtained. If the density of the flameproofed fiber bundle is 1.22 g / cm ³ or more, the heat treatment stabilizes the chemical structure of the single fiber in the process of flameproofing, and the difference in internal and external structure of the single fiber deteriorates even if the subsequent heat treatment is at high temperature. The strand strength is often improved because it disappears. In addition, when the density is 1.24 g / cm ³ or less, the total amount and time of heat treatment including the subsequent heat treatment are reduced, which often becomes superior in terms of strand strength and productivity. With regard to the temperature, it is preferable that the temperature is 210 ° C. or more because the difference between the internal and external structures can be sufficiently suppressed. When the temperature is less than 245 ° C., the single fiber diameter of the carbon fiber precursor fiber bundle is preferably a flameproof initial temperature sufficiently low to suppress the difference between internal and external structures, which is often preferred because the strand strength is high.

The heat treatment is performed until the density of the above-described fiber bundle is 1.22 to 1.24 g / cm ³ , and the heat treatment is performed in an oxidizing atmosphere to obtain a density of 1.32 to 1.35 g / cm ³ , Preferably, a flameproofed fiber bundle of 1.33 to 1.34 g / cm ³ is obtained. The heat treatment step is preferably performed at 245 ° C. or more and less than 275 ° C., more preferably 250 ° C. or more and less than 270 ° C. in an oxidizing atmosphere. When the density is 1.32 g / cm ³ or more, the heat treatment further stabilizes the chemical structure of single fibers in the process of flameproofing, and the difference in internal and external structure does not deteriorate even if the temperature of the subsequent heat treatment is higher. Often improve. In addition, if the density is 1.35 g / cm ³ or less, the total amount and time of heat treatment including the subsequent heat treatment decrease, and the strand strength and productivity become superior. When the heat treatment temperature is 245 ° C. or more, the total heat treatment amount and time decrease, and the strand strength and productivity often become superior. If the heat treatment temperature is less than 275 ° C., the difference in internal and external structure can be suppressed even if heat treatment is performed on the flameproof fiber bundle having a density of 1.22 to 1.24 g / cm ³ , and high strand strength is often expressed.

Subsequently, heat treatment is performed at a temperature of 275 ° C. or more and 295 ° C. or less, preferably 280 ° C. or more and 290 ° C. or less under an oxidizing atmosphere to obtain a flame-resistant fiber bundle with a density of 1.46 to 1.50 g / cm ³ . When the heat treatment temperature is 275 ° C. or higher, the amount of heat applied when increasing the density can be reduced, whereby the strand strength is improved. When the heat treatment temperature is 295 ° C. or less, the flameproofing reaction can be advanced without decomposing the structure of the single fiber, and the strand strength can be maintained. In order to measure the heat treatment temperature, a thermometer such as a thermocouple may be inserted into the heat treatment furnace of the flameproofing step to measure the temperature in the furnace. When the temperature in the furnace is measured at several points, if there is temperature unevenness or temperature distribution, the simple average temperature is calculated.

In the present invention, the final density of the fiber bundle is 1.46 to 1.50 g / cm ³ , preferably 1.46 to 1.49 g / cm ³ , and more preferably 1.47 to 1 It is .49 g / cm ³ . Since the density of the flame-stabilized fiber bundle correlates with the carbonization yield, the higher the density, the better from the viewpoint of reducing the production energy. When the density is 1.46 g / cm ³ or more, the carbonization yield can be sufficiently increased. When the density is 1.50 g / cm ³ or less, the effect of enhancing the carbonization yield is not saturated, which is effective from the viewpoint of productivity. In order to complete the heat treatment at the specified density, it is sufficient to adjust the temperature and time for stabilization.

In the step of heat treatment at 275 ° C. or more and 295 ° C. or less in an oxidizing atmosphere until the density of the above-mentioned fiber bundle for stabilization is 1.46 to 1.50 g / cm ³ , the tension (flame-resistant tension) applied to the fiber bundle for fiberization is It is preferably 1.6 to 4.0 mN / dtex, more preferably 2.5 to 4.0 mN / dtex, and still more preferably 3.0 to 4.0 mN / dtex. The flameproofing tension is a value obtained by dividing the tension (mN) measured on the flameproofing furnace outlet side by the as-dried fineness (dtex) of the carbon fiber precursor fiber bundle. When the tension is 1.6 mN / dtex or more, the orientation of the carbon fiber bundle is sufficiently enhanced, and the strand strength is often improved. If the tension is 4.0 mN / dtex or less, the grade deterioration due to fluff tends to be small.

Generally, when the density of the flame-resistant fiber bundle is increased to obtain a high carbonization yield, the strand strength of the carbon fiber bundle tends to decrease. In the method for producing a carbon fiber bundle of the present invention, even if the density of the flameproofed fiber bundle is increased by performing the second half high temperature heat treatment with an appropriate temperature profile in the flameproofing step, the internal / external structural difference of single fiber is largely suppressed. And, since the structure is stabilized, both high carbonization yield and high strand strength can be achieved.

Basically, a method for producing a carbon fiber bundle may be basically followed except for the above-mentioned flameproofing step, but in the method for producing a carbon fiber bundle of the present invention, pre-carbonization is carried out following the above-mentioned spinning process and flameproofing step. It is preferred to carry out the process. In the pre-carbonization step, the flame-resistant fiber obtained by the above-mentioned flame-resistance step is heat-treated in an inert atmosphere at a maximum temperature of 500 to 1000 ° C. to a density of 1.5 to 1.8 g / cm ³ It is preferable to obtain a pre-carbonized fiber bundle.

Following the pre-carbonization, a carbonization step is performed. In the carbonization step, it is preferable to obtain a carbon fiber bundle by heat-treating the pre-carbonized fiber bundle in an inert atmosphere at a maximum temperature of 1200 to 1800 ° C., preferably 1200 to 1600 ° C. If the maximum temperature is 1200 ° C. or higher, the nitrogen content in the carbon fiber bundle decreases and strand strength is stably developed. If the maximum temperature is at most 1800 ° C., a satisfactory carbonization yield can be obtained.

The carbon fiber bundle obtained as described above is preferably subjected to an oxidation treatment to introduce an oxygen-containing functional group in order to improve the adhesion to the matrix resin. As the oxidation treatment method, gas phase oxidation, liquid phase oxidation, liquid phase electrolytic oxidation and the like are used. From the viewpoint of high productivity and uniform processing, liquid-phase electrolytic oxidation is preferably used. The method of liquid phase electrolytic oxidation is not particularly specified, and may be carried out by a known method.

After the electrolytic treatment, a sizing treatment can also be performed to give the obtained carbon fiber bundle a focusing property. As the sizing agent, a sizing agent having good compatibility with the matrix resin can be appropriately selected according to the type of matrix resin used for the composite material.

The measuring methods of various physical property values described in the present specification are as follows.

<Strand Strength and Elastic Modulus of Carbon Fiber Bundle>
The strand strength and strand elastic modulus of the carbon fiber bundle are determined according to the following procedure according to the resin impregnated strand test method of JIS-R-7608 (2004). Ten resin-impregnated strands of the carbon fiber bundle are measured, and the average value is taken as the strand strength. Strain is assessed using an extensometer. The strain range is evaluated at 0.1 to 0.6%. In addition, as resin prescription, "CELLOXIDE (registered trademark)" 2021 P (made by Daicel Chemical Industries, Ltd.) / 3 / boron fluoride mono ethylamine (made by Tokyo Chemical Industry Co., Ltd.) / acetone = 100/3/4 (mass part) The curing conditions were as follows: normal pressure, temperature 125 ° C., time 30 minutes.

<Density measurement>
Collect 1.0 to 3.0 g of the flameproofed fiber bundle, and dry at 120 ° C. for 2 hours. Next, after measuring the absolute dry mass A (g), after impregnating with ethanol and sufficiently degassing, measure the fiber mass B (g) in the ethanol solvent bath, density = (A x rho) / (A Find the density by -B). ρ is the specific gravity of ethanol at the measurement temperature.

<Outer layer ratio of carbon fiber single fiber>
A carbon fiber bundle to be measured is embedded in a resin, a cross section perpendicular to the fiber axial direction is polished, and the cross section is observed at a total magnification of 1000 times with a 100 × objective lens of an optical microscope. The blackening thickness of the outer peripheral portion is measured from the cross-sectional microscope image of the polished surface. Analysis is performed using image analysis software Image J. First, black and white area division is performed by binarization in a single fiber cross-sectional image. For the luminance distribution in a single fiber cross section, the average value of the distribution is set as a threshold to perform binarization. In the obtained binarized image, the shortest distance from one point of the surface layer to the black-to-white lined area is measured in the fiber diameter direction. This is measured with respect to five points in the circumference of the same single fiber, and the average value is calculated as the blackened thickness at that level. Also, the outer layer ratio is calculated from the area ratio (%) of the blackened thickness portion to the entire cross section perpendicular to the fiber axial direction of the carbon fiber single fiber. The same evaluation is performed on 30 single fibers in the carbon fiber bundle, and the average value is used.

<Average single fiber diameter of carbon fiber bundle>
The mass A _f (g / m) and the density B _f (g / cm ³ ) per unit length are determined for a carbon fiber bundle consisting of a large number of carbon filaments to be measured. Assuming that the number of filaments of the carbon fiber bundle to be measured is C _f , the average single fiber diameter (μm) of the carbon fiber is calculated by the following equation.
Average single fiber diameter (μm) of carbon fiber
= (( _Af / _Bf / _Cf ) /?) ^(1/2) x 2 x 10 < ³ >.

<Nodular strength of carbon fiber bundle>
A 25 mm long grip is attached to each end of a 150 mm long carbon fiber bundle to make a test body. At the time of preparing the test body, a load of 9.0 × 10 ⁻⁵ N / dtex is applied to align the carbon fiber bundles. A knot is made at the midpoint of the test body, and a bundle tension test is performed with a crosshead speed at tension of 100 mm / min. The measurement is performed on a total of 12 fiber bundles, and the average value of 10 fibers obtained by dividing the two values of the maximum value and the minimum value is used as a measurement value. As the knot strength, a value obtained by dividing the maximum load value obtained in the bundle tension test by the average cross-sectional value of the carbon fiber bundle is used.

<Probability that a defect with a size of 50 nm or more exists>
A single fiber tensile test of carbon fiber single fiber is carried out according to JIS R7606 (2000), and a sample of carbon fiber single fiber after fracture including a fractured surface (hereinafter simply referred to as "fractured surface") is recovered. The number of single fibers used in the test is one set of 50. If 30 or more sets of fracture surfaces on both sides can not be recovered, one more set of 50 single fiber single-filament tensile tests is carried out to break both sides. Collect 30 or more cross sections. The strain rate in the tensile test is 0.4 mm / min.

From the set of fractured surfaces collected as described above, 30 sets are randomly selected to perform scanning electron microscope (SEM) observation. Before the observation, a deposition process for conductivity is not performed, and the acceleration voltage is 1 keV and the magnification is 25,000 to 50,000. In addition, in order to make it easy to determine the presence or absence of a minute defect, rotate the stage so that the fracture start point faces you and tilt the stage by 30 °, and observe the fracture start from diagonally above (see Figs. 1 to 4). ).

In the primary fractured surface of carbon fiber due to tensile fracture, the trace of fracture progressed radially from the fracture origin (i) remains as a radial streak, so that the streaks present in the SEM observation image are traced and converged to a single point The specified part is identified as the break origin (i). If the streaks can not be recognized, or the streaks can be recognized but dirt is attached near the fracture origin (i) and it is difficult to observe them, even if they are present on either of the fracture surfaces on both sides, the fracture Cross sections are excluded from the group evaluation. The fracture surface reduced by exclusion is replenished as appropriate, and finally 30 sets of fracture surfaces are observed.

If the fracture origin (i) can be identified, it is examined whether there are any morphological features. There are various types of morphological features, such as dents and deposits, marks that the fiber surface is partially peeled off, scratches, and adhesion marks. The morphological features that become the fracture origin observable by SEM are collectively called "defect". The length measured along the circumferential direction of the fiber, that is, the one having a size of 50 nm or more, is uniformly classified into "a fracture surface where a defect having a size of 50 nm or more exists" in the present invention regardless of the difference in appearance. If this is performed on the fracture surfaces on both sides and one of them is classified as "fracture surface with defects of 50 nm or more in size", the set is "fracture surface with defects of 50 nm or more in size" I assume. This is performed on all the 30 sets of SEM-observed fractured surfaces, and the total number of “fractured surfaces where defects of 50 nm or more exist” is divided by 30 which is the total number of fractured-surfaces observed in SEM. By multiplying, "probability (%) that a defect with a size of 50 nm or more exists" is calculated.

The test length in the single fiber tensile test is 10 mm, and a special test jig designed to be able to be carried out in water is used using a commercially available cyanoacrylate-based instant adhesive for fixing carbon fibers to a test strip backing. It carried out by A & D Tensilon "RTC-1210A". In addition, a scanning electron microscope (SEM) "S-4800" manufactured by Hitachi High-Technologies Corporation was used to observe the recovered fractured surface.

<Average surface roughness>
Ten carbon fiber single fibers to be evaluated are placed on a sample base, fixed with an epoxy resin as a sample, and evaluated using an atomic force microscope (in the example, NanoScope V Dimension Icon manufactured by Bruker AXS). In the embodiment, a three-dimensional surface shape image is obtained under the following conditions.
Probe: Silicon cantilever (OLYMPUS, OMCL-AC160TS-W2)
Measurement mode: Tapping mode scanning speed: 1.0 Hz
Scanning range: 600 nm x 600 nm
Resolution: 512 pixels x 512 pixels Measurement environment: Room temperature, in the atmosphere.

A three-dimensional surface shape image is measured under the above conditions for one single fiber, and the obtained measurement image takes into consideration the curvature of the fiber cross section, and the attached software (NanoScope Analysis) causes the data of device origin to swell. “Flat processing” to eliminate the “Fan processing”, “Median 8 processing” which is a filter processing to replace the value at the center of the matrix from the median value of Z data in a 3 × 3 matrix, and a cubic surface by the least squares method from all image data After performing image processing using “three-dimensional inclination correction” to obtain, fit, and correct in-plane inclination, surface roughness analysis is performed using attached software to calculate an average surface roughness. Here, the average surface roughness (Ra) is a three-dimensional extension of center line roughness Ra defined in JIS B 0601 (2001) so that it can be applied to surface measurement, from the reference surface to the designated surface It is defined as the value obtained by averaging the absolute value of the deviation of. In the measurement, ten different single fibers are randomly sampled, and one measurement is carried out ten times in total for one single fiber, and the average value is taken as a measurement value.

<Number of fluffs of carbon fiber bundle>
The grade of the carbon fiber bundle which affects the productivity at the time of manufacture of a composite material is evaluated by the method of counting the number of fluff directly by the following method. According to visual observation of the carbon fiber bundle during traveling at a traveling speed of 1.5 m / min and a draw ratio of 1 time, the number of broken single fibers protruding 5 mm or more from the surface of the carbon fiber bundle is counted at a length of 20 m of the carbon fiber bundle And evaluate the number of feathers per 1 m (lines / m).

Example 1
A copolymer consisting of 99% by mass of acrylonitrile and 1% by mass of itaconic acid was polymerized by a solution polymerization method using dimethyl sulfoxide as a solvent to produce a polyacrylonitrile copolymer to obtain a spinning solution. The spinning solution was flowed into the filter device and filtered. The filter medium used was a metal sintered filter with a filtration accuracy B of 1 μm, a filter medium thickness C of 800 μm, and a filter basis weight D of 2500 g / m ² , and filtration was performed under the filtering conditions of a filtration rate A of 3 cm / hour. The filtered spinning solution was once discharged from the spinneret into air and spun by a dry-wet spinning method introduced into a coagulation bath consisting of an aqueous solution of 35% dimethyl sulfoxide controlled to 3 ° C. The spun fiber bundle was washed with water at 30 to 98 ° C., and subjected to a water bath draw of 3.5 times. Subsequently, an amino-modified silicone-based silicone oil was applied to the fiber bundle after the water-bath drawing, and drying was performed using a roller heated to a temperature of 160 ° C. to obtain a fiber bundle of 12000 single fibers. The fiber bundle was stretched 3.7 times in pressurized steam to make the total draw ratio of yarn production 13 times. Thereafter, while applying a tension of 2 mN / dtex to the fiber bundle, the fluid discharge pressure is subjected to an entangling process with air at 0.35 MPa to obtain a carbon fiber precursor fiber bundle having a single fiber fineness of 1.1 dtex and 12000 single fibers. I got Next, using the flameproofing conditions described in condition 1 in Table 1, the carbon fiber precursor fiber bundle was heat-treated in an air atmosphere oven at a draw ratio of 1.0 to obtain a flameproofed fiber bundle.

The obtained flame-resistant fiber bundle was subjected to pre-carbonization treatment at a draw ratio of 0.95 times in a nitrogen atmosphere at a temperature of 300 to 800 ° C. to obtain a pre-carbonized fiber bundle. The obtained pre-carbonized fiber bundle was carbonized at a maximum temperature of 1350 ° C. in a nitrogen atmosphere. The obtained carbon fiber bundle was subjected to surface treatment and sizing agent application treatment to obtain a final carbon fiber bundle. At this time, the number of fluffs of the carbon fiber bundle was less than 0.1 / m, almost no fluff was observed, and the grade was good.

The strand strength, strand elasticity modulus, outer layer ratio of carbon fiber single fiber, and average single fiber diameter of the carbon fiber bundle obtained in Table 2 are shown.

(Example 2)
Carbon fiber precursor fiber bundles and carbon fibers and carbon fibers are similar to Example 1 except that the filter medium is changed to a metal sintered filter with a filtration accuracy B of 9 μm, a filter medium thickness C of 3200 μm, and a filter medium weight D of 6400 g / m ^2. I got a fiber bundle.

(Example 3)
In the filtration conditions, a carbon fiber precursor fiber bundle and a carbon fiber bundle were obtained in the same manner as in Example 1 except that the filtration rate A was changed to 6 cm / hour.

(Examples 4 and 5)
A carbon fiber precursor fiber and a carbon fiber bundle were obtained in the same manner as in Example 3 except that the draw ratio during preliminary carbonization was 1.05 in Example 4 and 1.10 in Example 5.

(Comparative example 1)
A carbon fiber precursor fiber bundle and a carbon fiber bundle were obtained in the same manner as in Example 2 except that the filter medium was changed to a metal sintered filter having a filter medium thickness C of 1600 μm and a filter medium basis weight D of 3200 g / m ² . The number of fluffs of the carbon fiber bundle was 0.2 / m, and the quality was deteriorated.

(Comparative example 2)
A carbon fiber precursor fiber bundle and a carbon fiber bundle were obtained in the same manner as in Comparative Example 1 except that the filtration rate A was changed to 6 cm / hour under the filtration conditions.

(Comparative example 3)
In the filtration conditions, carbon fiber precursor fiber bundles and carbon fiber bundles were obtained in the same manner as in Example 2 except that the filtration rate A was changed to 6 cm / hour.

(Comparative example 4)
In the filtration conditions, a carbon fiber precursor fiber bundle and a carbon fiber bundle were obtained in the same manner as in Example 3 except that the filtration rate A was changed to 8 cm / hour.

(Comparative example 5)
In the filtration conditions, carbon fiber precursor fiber bundles and carbon fiber bundles were obtained in the same manner as in Example 3 except that the filtration rate A was changed to 12 cm / hour.

(Example 6)
A carbon fiber bundle was obtained in the same manner as in Example 1 except that condition 2 in Table 1 was used as the flameproofing condition. The outer layer ratio of carbon fiber was 97%, and the strand strength was reduced as compared with Example 1.

(Example 7)
A carbon fiber bundle was obtained in the same manner as in Example 1 except that condition 3 in Table 1 was used as the flameproofing condition. The outer layer ratio of carbon fiber was 85%, and the strand strength was reduced as compared with Example 1.

The present invention can obtain a flame-resistant fiber bundle of a specific density by heat treatment with an appropriate temperature profile in the flame-proofing step, and thereby the number of defects governing strand strength and knot strength is controlled very little. A carbon fiber bundle can be produced without loss of productivity, while exhibiting well-balanced expression of strand strength and strand elastic modulus and high knot strength. Moreover, according to the carbon fiber bundle of the present invention, the carbon fiber bundle satisfies the productivity at the time of producing the composite material. Taking advantage of such characteristics, the carbon fiber bundle obtained in the present invention is suitably used for general industrial applications such as aircraft, automobiles, marine members, sports applications such as golf shafts and fishing rods, and pressure vessels.

(I) Fracture origin

Claims

Using a filter medium having a filtration accuracy B (μm) and a filter basis weight D (g / m 2 ), a spinning solution in which a polyacrylonitrile copolymer is dissolved in a solvent, the filtration rate A (cm / hour) After filtering under conditions satisfying (1) to (3), the filtered spinning solution is spun to obtain a carbon fiber precursor fiber bundle,
D-600 / (α x β) 0 0 (1)
α = 1-1 / (1 + exp (7-A)) (2)
β = 1−1 / (1 + exp (−0.23 × B)) (3)
The obtained carbon fiber precursor fiber bundle was heat treated to a density 1.32 ~ 1.35g / cm 3 in an oxidizing atmosphere, an oxidizing atmosphere to a density 1.46 ~ 1.50g / cm 3 A method for producing a carbon fiber bundle, wherein heat treatment is performed at 275 ° C. or more and 295 ° C. or less to obtain a flame-resistant fiber bundle, and then the flame-resistant fiber bundle is heat-treated at 1200 to 1800 ° C. in an inert atmosphere.
The tension of the flame-resistant fiber bundle is 1.6 to 4.0 mN / dtex when heat-treated at 275 ° C. or more and 295 ° C. or less in an oxidizing atmosphere until the density reaches 1.46 to 1.50 g / cm 3. The manufacturing method of the carbon fiber bundle of claim 1.
The carbon fiber precursor fiber bundle is heat-treated at a temperature of 210 ° C. or more and less than 245 ° C. to reach a density of 1.22 to 1.24 g / cm 3 in an oxidizing atmosphere, and then a density of 1.32 to subjected to heat treating to a 1.35 g / cm 3, and the density performs 1.32 ~ 1.35 g / cm to until 3 a heat treatment step performed at less than 275 ° C. 245 ° C. or higher, according to claim 1 or The manufacturing method of the carbon fiber bundle as described in 2.
Strand elastic modulus is 240 to 280 GPa, strand strength is 5.8 GPa or more, knot strength K [MPa] is -88d + 1390 390 K (d: average single fiber diameter [μm]), average single fiber diameter is 6.5 to 8. A carbon fiber bundle having a probability that a defect with a size of 50 nm or more is present in the recovered fractured surface at 35% or less when a single fiber tensile test is performed with a sample length of 10 mm while satisfying 0 μm.
The carbon fiber bundle according to claim 4, wherein the knot strength K is 770 MPa or more.
The carbon fiber bundle according to claim 4 or 5, wherein the average surface roughness Ra is 1.0 to 1.8 nm.
The carbon fiber bundle according to any one of claims 4 to 6, wherein an outer layer ratio of carbon fiber single fiber is 90 area% or more.