JP2018178344A - Polyacrylonitrile-based flameproof fiber bundle, method for producing the same, and method for producing carbon fiber bundle - Google Patents

Abstract

An object of the present invention is to provide a polyacrylonitrile-based flameproofed fiber bundle capable of obtaining a carbon fiber bundle in which high density and excellent tensile strength and tensile elastic modulus are well expressed, and a method for producing the same. .
A ratio (R _i / R _m ) of a maximum value R _i of luminance to a minimum value R _m of luminance from a fiber center of red fluorescence when a fiber cross section is observed with a fluorescence microscope is 1.4. The ratio (R _o / R _m ) of the maximum value R _o of luminance to the minimum value R _m of luminance from ̃1.7 and from the outermost layer to 1 μm is 1.13 to 1.23, and the green of the fiber cross section The ratio (G _m / R _m ) of the minimum value G _m of the fluorescence brightness to the minimum value R _m of the brightness of the red fluorescence is 0.6 to 0.9, and the outer layer area in the dual structure is 88 to It is 95 area%, It is a polyacrylonitrile-type flameproof fiber bundle characterized by the above-mentioned.
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Description

  The present invention is directed to a polyacrylonitrile-based flame-resistant fiber bundle having a high density and a large outer layer area in double structure, which is used for producing a carbon fiber bundle exhibiting tensile strength and tensile modulus in a well-balanced manner, and a method for producing the same The present invention relates to a method for producing a carbon fiber bundle obtained by using the above-described flameproofed fiber bundle.

  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, it is required to improve mechanical properties such as tensile strength (hereinafter simply referred to as tensile strength means resin-impregnated strand strength) and tensile elastic modulus in a well-balanced manner. ing. At the same time, it is necessary to reduce the environmental burden in the production of carbon fiber bundles. In general, a method for producing a polyacrylonitrile (hereinafter, also referred to as PAN) carbon fiber bundle is to heat a PAN precursor fiber bundle at 200 to 300 ° C. in an oxidizing gas atmosphere to obtain a flame-resistant fiber bundle, and then It is obtained by heating at 1200 ° C. or higher under an active gas atmosphere. At that time, carbon, nitrogen and hydrogen atoms contained in PAN are eliminated by thermal decomposition, so the carbon fiber bundle yield (hereinafter also referred to as carbonization yield) is about half. Therefore, to increase the yield of carbon fiber bundles with equivalent production energy is required from the viewpoint of reducing the production energy per production amount, that is, the environmental load. In addition, in order to obtain a carbon fiber bundle that expresses tensile strength and tensile modulus in a well-balanced manner, it is important to form a uniform structure in the cross-sectional direction of the fiber, that is, to form a flameproof fiber bundle having a large outer layer area in double structure. It is.

  A lot of optimization of the flameproofing conditions has been considered up to now. In patent document 1, by carrying out high temperature processing in a flameproofing process, examination which makes heat quantity (J * h / g) given as small as possible, and improves the tensile strength of a carbon fiber bundle is made. Further, in Patent Documents 2 and 3, after heating the precursor fiber bundle in an oxidizing atmosphere at the initial stage of flame resistance, the density of the flameproof fiber bundle is increased in a short time by bringing it into contact with a high temperature heating roller at 250 to 300 ° C. Attempts have been made to increase the carbonization yield.

  In addition, numerous studies have been made to improve the outer layer area in the double structure of the flame-resistant fiber bundle by optimizing the flame-proof conditions. In Patent Document 4, the outer layer area in the double structure of a single fiber is measured by image analysis of a fluorescence microscopic image of a cross section of a single fiber (sometimes simply abbreviated as a single flame resistant single fiber) of a PAN-based fiberization fiber bundle. It has been proposed that the heat treatment in a high oxygen concentration atmosphere improves the outer layer area in the dual structure formed by the heat treatment in air. Further, in Patent Documents 5 and 6, an attempt is made to control the oxidation depth at the time of flameproofing by changing the polymer composition. Further, Patent Document 7 proposes that a spinning polymer modified with an amine compound is spun, and carbonization is carried out under a specific flameproofing condition to form a carbon fiber having three or more phase layers different in crystal size. ing. In addition, as a result of measuring the functional group distribution of the cross section of the flameproofed single fiber, Non-Patent Document 1 proposes that the flameproofing reaction proceeds as compared with the outer layer part at the center of the flameproofed single fiber. In Non-Patent Document 2, as a result of measuring the functional group distribution of the cross section of the flameproofed single fiber which was flameproofed under the condition of constant temperature for flameproofing, when the double structure of the flameproofed single fiber is small, the carbonyl group of the outer layer ( It has been proposed that the oxygen functionality is low and the distribution is small.

JP 2012-82541 A JP-A-58-163729 JP 2014-74242 A Japanese Patent Application Laid-Open No. 10-251923 JP, 2015-71722, A JP, 2013-103992, A International Publication No. 2015/105019 Srinivas Nunna, 8 others, "The effect of thermally induced chemical transformation on the structure and properties of carbon fiber precursor", [online], March 13, 2017, "Journal of Materials Chemistry, A ( Journal of Materials Chemistry A) "(UK), Volume 5, No. 16, p. 7372-7382 [searched on March 20, 2017], DOI <10.1039 / C7TA01022B> Gelayol Golkarnarenji, 6 others, “Development of a predictive model for study of skin-core phenomenon in stabilization process of PAN precusor”, [online], January 3, 2017, “Journal of Industrial and Engineering Journal of Industrial and Engineering Chemistry (Korea), Volume 49, p. 46-60 [searched on March 30, 2017], DOI <10.1016 / j. jiec. 2016.12.027>

  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 tensile strength and a carbonization yield. Further, in the proposal of Patent Document 2, since the temperature for temperature stabilization is simply increased by shortening the temperature for flame stabilization time, temperature control for temperature stabilization that can satisfy the required tensile strength is not performed, and a double structure is realized. Stress concentration control to the surface layer by the small outer layer area in the sex was a subject. Further, in the proposal of Patent Document 3, heat treatment is performed at a high temperature using a heating roller having 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 tensile strength has not been obtained due to the formation of defects due to fusion between single fibers during passage. In the proposal of Patent Document 4, since the flameproofing is performed by the high oxygen concentration, the flameproofing can not be controlled and sufficient tensile strength is not obtained. Further, in the proposals of Patent Documents 5 and 6 and Non-patent Document 1, since the temperature and time for stabilization were kept constant, the double structure of the single fiber for stabilization was large and the oxygen functional group of the inner layer was large. Further, in the proposal of Non-Patent Document 2, the flame resistance temperature and time were not precisely controlled, and the cross section of the single fiber of the fiber bundle was not three layers, and the oxygen functional group in the outer layer was low. The density of the yarn was low. Moreover, in patent document 7, since a flameproofing occurs uniformly by performing a flameproofing by a liquid phase using an amine-type polymer, the cross section of the single fiber of a flameproofed fiber bundle does not become 3 layers.

  In order to solve the problems in the prior art described above, the present invention is a polyacrylonitrile having a high density and a large outer layer area in double structure, which is used for producing a carbon fiber bundle exhibiting tensile strength and tensile modulus in a well-balanced manner. It is an object of the present invention to provide a system for making a flameproofed fiber bundle and a method for producing the same, and a method for producing a carbon fiber bundle obtained by using the flameproofed fiber bundle.

The PAN-based fiber-stabilized fiber bundle of the present invention for achieving the above-mentioned purpose (hereinafter sometimes simply referred to simply as the fiber-stabilized fiber bundle) is red when the cross section of the flame-resistant monofilament is observed with a fluorescence microscope. The ratio (R _i / R _m ) of the maximum value R _i of the luminance to the minimum value R _m of the radius 1 μm from the fiber center of the fluorescence is 1.4 to 1.7 and the maximum value of the luminance from the outermost layer to 1 μm a ratio of R _o and luminance minimum value _{R m} of _(R o / _{R m)} is 1.13 to 1.23, the fiber cross section green fluorescence intensity minimum _{G m} and the red fluorescence intensity of a ratio of the minimum value _{R m (G m / R m} ) is 0.6 to 0.9, the outer layer area in the double structure resistance is stabilized fiber bundle is 88 to 95 area%.

In addition, when the G _m / R _m of the fiber bundle obtained by heat-treating the polyacrylonitrile-based precursor fiber bundle in the step of heat-treating the bundle in the oxidizing atmosphere for 15 to 35 minutes is 0.2 The fiber bundle having an R _i / R _m of 1.0 to 1.2 and then a G _m / R _m of 0.4 is obtained by heat treatment for 9 to 15 minutes.

  Further, a carbon fiber bundle for achieving the above object is obtained by heat-treating the flame-resistant fiber bundle in an inert atmosphere at 1200 to 3000 ° C. after obtaining the flame-resistant fiber bundle as described above. Be

  According to the present invention, the density used for producing a carbon fiber bundle exhibiting tensile strength and tensile elastic modulus in a well-balanced manner by controlling the flameproofing time to satisfy an appropriate flameproofing structure in the flameproofing step It is possible to obtain a flame-resistant fiber bundle which is high and has a large outer layer area in double structure.

It is a figure which shows the red fluorescence photograph of the cross section of a flame-resistant single fiber, and the line profile of a brightness | luminance. It is a figure which shows the line profile of the green fluorescence photography of the cross section of a flame-resistant single fiber, and a brightness | luminance. It is a figure which shows the blue fluorescence photograph of the cross section of a flame-resistant single fiber, and the line profile of a brightness | luminance.

  The present inventors are keen on the requirements for obtaining a flame-resistant fiber bundle having a high density and a large outer layer area in double structure, which can obtain a carbon fiber bundle in which tensile strength and tensile elastic modulus are well expressed. The present invention has been achieved as a result of repeated studies.

That is, when the cross section of the flameproofed single fiber is observed with a fluorescence microscope, the flameproofed fiber bundle of the present invention is viewed from the intersection of the major axis and the minor axis of the redified flameproofed single fiber (hereinafter abbreviated as center). The ratio (R _i / R _m ) of the maximum value R _i of the brightness of radius 1 μm to the minimum value R _m of the brightness of the cross section of the flameproof single fiber is 1.4 to 1.7, preferably 1.5 to 1. 7 When the cross section of the flameproofed single fiber is observed with a fluorescence microscope, red fluorescence and green fluorescence are observed as shown in FIGS. 1 and 2 reflecting the structural distribution of PAN and flameproofing. By observing the cross section of the flameproofed fiber that has been flameproofed under specific conditions by observing it with a fluorescence microscope, as shown in FIG. 1, the brightest outermost layer (the luminance of the outermost layer of single fiber is less than the minimum value of the luminance from the outermost layer to 1 μm) In the case of a large area, it is defined as the area of the luminance from the outermost layer to the area of the minimum luminance), the brightest inner layer (the minimum value of the luminance in the cross section of a single fiber and the area of the half width of the luminance profile And the darkest blackened area (the area including the minimum value of luminance in the cross section of a single fiber, and when it has the bright outermost layer, it is defined as the area between the outermost layer and the inner layer). If not, ie, if the outermost layer is included in the minimum value of luminance, a multilayer structure of “the region from the outermost layer to the boundary with the inner layer” is observed. In the prior art (for example, non-patent document 1), the outermost layer is included in the blackened portion because the outermost layer is the minimum value of the brightness of single fibers, and many examples observed as a two-layer structure have been reported. As in the present invention, it has been found that the flameproofing under specific flameproofing conditions results in a three-layer structure having a bright outermost layer. In order to obtain the flameproofed fiber bundle of the present invention, it is important to precisely control the three-layer structure of the flameproofed single fiber by precisely controlling the flameproofing conditions. In blue fluorescence as shown in FIG. 3, no light emission of a single fiber cross section is observed. The components observed in the green fluorescence and the red fluorescence are not necessarily clarified, but are considered as follows. For green fluorescence, we observe emission of 495-570 nm wavelength excited by excitation light around 490 nm, and with red fluorescence we observe emission of wavelength 620-750 nm emitted by excitation light around 546 nm Do. When observing the cross section of the red fluorescent and flameproofed single fiber, it tends to be brighter than the green fluorescent. From this, it is considered that red fluorescence means that a conjugated system such as a ring structure or a unsaturated structure is more advanced than green fluorescence. The fact that each fluorescent color is bright, that is, the luminance is large, means that a large amount of each substance remains, and in the case of being blackened, it means that each substance is consumed. The reason why it looks like a multilayer structure by observing a cross section of a flameproofed fiber which has been flameproofed under a specific condition with a fluorescence microscope is not necessarily clear, but is considered as follows. That is, it is considered that a difference in reaction rate is generated in the outermost layer, the blackened portion, and the inner layer because the gas hardly diffuses to the inside of the flameproofed single fiber as the flameproofing reaction progresses. Since R _i represents the luminance of the inner layer and R _m represents the luminance of the blackened portion, that R _i / R _m is large means that the structural difference between the inner layer and the blackened portion is large. If R _i / R _m is 1.4 or less, the carbonization yield often decreases because the amount of heat treatment for flameproofing is insufficient, and R _i / R _m needs to be 1.4 or more . If the R _i / R _m is 1.7 or more, the tensile strength of the carbon fiber bundle is often reduced due to the large structural difference between the inner layer and the blackened portion, so R _i / R _m is 1.7 It is necessary to be the following. R _i / R _m can be measured by embedding a flame-resistant fiber bundle in a resin, polishing the cross section perpendicular to the fiber axis direction, and observing the cross section with a fluorescence microscope (details will be described) Will be described later). In addition, about a fluorescence microscope, illumination-device positions, such as a transmission type and an incident type, and objective lens positions, such as erecting and inversion, do not ask | require. In order to control such R _i / R _m , this can be achieved by controlling the temperature and time for the stabilization of the flame.

Oxidized fiber bundle of the present invention, the ratio of the minimum value _{R m} of the maximum value _{R o} and the luminance of the luminance from the outermost layer to 1μm _(R o / R _m) is 1.13 to 1.23, preferably It is 1.14-1.20, More preferably, it is 1.14-1.18. As described above, by observing the cross section of the flameproofed fiber which has been flameproofed under specific conditions, a three-layered structure of the bright outermost layer, the blackened portion and the brightest inner layer can be observed by observing with a fluorescence microscope. Since R _o represents the maximum luminance of the outermost layer and R _m represents the luminance of the blackened portion, that R _o / R _m is large means that the structural difference between the outermost layer and the blackened portion is large. When the structural difference between the inner layer and the blackened portion is large, the reaction of the outermost layer and the blackened portion rapidly progresses in the initial stage of the flame resistance, so that R _o / R _m becomes smaller. For this reason, if R _o / R _m is 1.13 or more, the structural difference in the cross section of the flame-resistant single fiber is small, and the tensile strength of the carbon fiber bundle is improved. If R _o / R _m is 1.23 or less, the carbonization yield can be sufficiently increased. R _o / R _m can be measured by embedding a flame-resistant fiber bundle in a resin, polishing the cross section perpendicular to the fiber axis direction, and observing the cross section with a fluorescence microscope (the details will be described later) To do). In order to control such R _o / R _m , this can be achieved by controlling the temperature and temperature for stabilization.

In the flame-resistant fiber bundle of the present invention, the ratio (G _m / R _m ) of the minimum value G _m of green fluorescence brightness to the minimum value R _m of red fluorescence brightness of the fiber cross section is preferably 0.6 to 0. .9, more preferably 0.7 to 0.8. The minimum green fluorescence intensity G _m (see FIG. 2) and the minimum red fluorescence brightness R _m (see FIG. 1) of the cross-section of the flameproofed monofilament are respectively the green and red fluorescence in the black part Means the brightness of As described above, the green fluorescence is considered to have a structure closer to PAN than the red fluorescence, so the luminance decreases earlier. On the other hand, as the flameproofing progresses, the difference in brightness between the inner layer of green fluorescence and the blackened portion decreases, and the brightness of green fluorescence often increases. Although the reason for this is not necessarily clear, it is considered that the brightness of the black portion relatively increases because the difference in the brightness between the inner layer and the black portion is small. The red fluorescence is considered to be a structure in which the ring structure and the unsaturated structure are partially advanced as compared to the green fluorescence, and decreases as the ring structure and the unsaturated structure are further developed as the flameproof reaction proceeds. There are many things. For this reason, the fact that G _m / R _m is large means that the oxidation reaction proceeds, and G _m / R _m correlates with the carbonization yield, so the higher the better from the viewpoint of reduction of production energy. If G _m / R _m is 0.6 or more, the carbonization yield can be sufficiently increased, and if G _m / R _m is 0.9 or less, the effect of increasing the carbonization yield is not saturated, so productivity From the point of view of G _m / R _m can be measured by embedding a flame-resistant fiber bundle in a resin, polishing a cross section perpendicular to the fiber axis direction, and observing the cross section with a fluorescence microscope (the details will be described later) To do). It may be adjusted flame temperature and time in order to control such a G _{m /} R _m.

  In the flameproof fiber bundle of the present invention, the area ratio (hereinafter referred to as the outer layer area in the dual structure property) in the cross section of the blackened thickness of the outer peripheral portion of the cross section perpendicular to the fiber axial direction of the flameproof single fiber is 88 to It is a flame-resistant fiber bundle which is 95 area%, Preferably it is 89-94 area%, More preferably, it is 90-94 area%. Here, the outer layer area in the double structure is the thickness of the outermost layer and the blackened portion which are observed when the cross section perpendicular to the fiber axial direction of the flameproofed single fiber is observed by the red fluorescence of the fluorescence microscope (hereinafter referred to as The area ratio (%) is obtained by dividing the area occupied by the outer layer thickness) by the entire cross-sectional area perpendicular to the fiber axial direction of the flameproof single fiber. As the outer layer area in the double structure property is increased, high tensile strength can be developed because the stress load on the single fiber cross section becomes uniform. However, when the outer layer area in the dual structural property is small, the effect of developing high carbonization yield and high tensile strength may be small. When the outer layer area in the double structure is 88 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. If it exceeds 94 area%, the stress concentration suppressing effect on the surface layer is saturated, so that 94 area% or less is preferable in order to avoid excessive heat treatment in the flameproofing step. The outer layer area in the double structure can be measured by embedding the flame-resistant fiber bundle in a resin, polishing the cross section perpendicular to the fiber axis direction, and observing the cross section with a fluorescence microscope (details will be described) Will be described later). The outer layer area in the double structure property calculated by the known method and the outer layer area in the double structure property in the method of the present invention are substantially equal, and the error is 1 to 2 area%. In order to control the area of the outer layer in such dual structure, it is sufficient to adjust the temperature and time for the oxidation.

Oxidized fiber bundle of the present invention, 2930 cm ^-1 peak intensity to 3200 cm ^-1 peak intensity of the infrared spectrum of 1μm from the outermost layer _{(I 3200o)} of the fiber cross-section _{(I 2930o)} and 2855cm ^-1 peak intensity _{(I 2855o) 2930} cm ⁻¹ (I ₂₉₃₀ ) peak intensity and 2855 cm ^{−1 for} the maximum value (I _OHo ) of the sum ratio (I _{3200 o} / (I _{2930 o} + I _{2855 o} )) and ₃₂₀₀ cm ⁻¹ peak intensity (I ₃₂₀₀ ) of the entire fiber cross section It is preferable that the ratio (I _OHo / I _OHm ) of the minimum value (I _OHm ) of the sum ratio (I ₃₂₀₀ / (I ₂₉₃₀ + I ₂₈₅₅ )) of the peak intensities (I ₂₈₅₅ ) be 1.2 to 1.5. , More preferably 1.2 to 1.4, still more preferably 1.2 to 1.3 The 3200 cm ⁻¹ peak intensity of the infrared spectrum of the fiber cross section reflects the stretching vibration of the OH group, and the 2930 cm ⁻¹ peak intensity and the 2855 cm ⁻¹ peak intensity reflect the stretching vibration of the CH group. Therefore, the ratio _{(I OH)} of the sum of the 2930 cm ^-1 peak intensity and 2855cm ^-1 peak intensity to 3200 cm ^-1 peak intensity means of oxidation since the ratio of OH groups to CH groups. Since I _OHo indicates the degree of oxidation of the outermost layer and I _OHm respectively indicate the degree of oxidation of the blackened part, that I _OHo / I _OHm means that the degree of oxidation of the outermost layer is higher than that of the inner layer. Do. If the degree of oxidation of the outermost layer is higher than that of the inner layer, it means that flameproofing is in progress, and a flameproof yarn having a high density can be obtained, and the carbonization yield of the carbon fiber bundle can be improved. preferable. On the other hand, when the degree of oxidation of the outermost layer is too high in comparison with the inner layer, the tensile strength of the carbon fiber bundle tends to decrease because the structural difference of the fiber cross section is large. For this reason, if I _OHo / I _OHm is 1.2 or more, the structural difference in the cross section of the flame-resistant single fiber is small, and the tensile strength of the carbon fiber bundle is improved. If I _OHo / I _OHm is 2.0 or less, the carbonization yield can be sufficiently increased. I _OHo / I _OHm is _measured by embedding a flame-resistant fiber bundle in a resin, preparing a section with a microtome, and observing the cross section by atomic force microscopy-infrared spectroscopy (AFM-IR) Yes (details will be described later). In order to control such I _OHo / I _OHm , it can be achieved by controlling the temperature and time of the oxidation.

Oxidized fiber bundle of the present invention, 2930 cm ^-1 peak intensity from the fiber center of the fiber cross-section for the 3200 cm ^-1 peak intensity of the infrared spectrum of the radius _{1μm (I 3200i) (I 2930i} ) and 2855cm ^-1 peak intensity _{(I 2855i} preferably the maximum value of the ratio of the sum _{(I 3200i / (I 2930i +} I 2855i)) ( the ratio of _{I OHi)} and _{I OHm (I OHi / I OHm} ) is 1.0 to 1.3) of more Preferably it is 1.0-1.2, More preferably, it is 1.1-1.2. Since I _OHi represents the degree of oxidation of the inner layer, and I _OHm represents the degree of oxidation of the blackened portion, that I _OHi / I _OHm means that the structural difference between the inner layer and the blackened portion is large. For this reason, if I _OHi / I _OHm is 1.0, the diffusion of the gas becomes uniform, and the structural difference between the inner layer and the black portion becomes small, which is preferable because the tensile strength of the carbon fiber bundle is improved. If the I _OHi / I _OHm is 1.3 or more, the structural difference between the inner layer and the blackened part tends to be large, so the tensile strength of the carbon fiber bundle tends to decrease, so I _OHi / I _OHm is 1.3 It is preferable that it is the following. I _OHi / I _OHm can be measured by embedding a flame-resistant fiber bundle in a resin, preparing a section with a microtome, and observing the cross section with AFM-IR (details will be described later). In order to control such I _OHi / I _OHm , this can be achieved by controlling the temperature and time of the oxidation.

Appropriate for the problem of manufacturing a flame-resistant fiber bundle having a high density and a large outer layer area in a dual structure, which is used for the production of a carbon fiber bundle exhibiting well-balanced excellent tensile strength and tensile elastic modulus Fiber bundles obtained by heat-treating various PAN-based precursor fiber bundles for a specific time in an oxidizing atmosphere, the inner layer and black when the ratio of green and red luminance of the single fiber cross section observed with a fluorescence microscope is a specific value It has been found that the heat treatment is performed in multiple stages so that the ratio of the red brightness of the colored portions falls within a specific range. The preferred embodiments of the present invention will be described in detail below. In the method for producing a flame-resistant fiber bundle suitable in the present invention, in the step of heat-treating the PAN-based precursor fiber bundle in an oxidizing atmosphere, G _m / R _m of the fiber bundle obtained by heat treatment for 15 to 35 minutes is R _i / R _m at 0.2 is preferably 1.0 to 1.2, more preferably 1.1 to 1.2. When R _i / R _m is 1.2 or less, the tensile strength is often improved because the outer layer area in the dual structure does not decrease even if the heat treatment that follows is at a high temperature. How G m _/ R _m to measure the fiber bundle in the middle course of the oxidization is 0.2, it is possible to adopt a method of measuring by sampling the fiber bundle in the process of production. When G _m / R _m of the fiber bundle sampled in the middle of the process is not 0.2, an average value of R _i / R _m may be adopted when the average of two points before and after is 0.2. However, the heat treatment time under the oxidizing atmosphere is preferably 15 to 35 minutes, more preferably 20 to 35 minutes. If the heat treatment time is 15 minutes or more, the value of R _i / R _m can be easily controlled, and the tensile strength can be improved. If the heat treatment time is 35 minutes or less, the value of R _i / R _m does not increase, and the tensile strength can be improved. G _m / R _m and R _i / R _m can be measured by embedding a flame-resistant fiber bundle in a resin, polishing a cross section perpendicular to the fiber axis direction, and observing the cross section with a fluorescence microscope (Details will be described later). In order to control such G _m / R _m and R _i / R _m , this can be achieved by controlling the temperature and time for the stabilization. The control of the flameproofing time can be achieved by controlling the flameproofing time by changing the speed at which the fiber bundle passes through the flameproofing furnace, the length of the flameproofing furnace, and the like.

After the heat treatment, more time for heat treating the fiber bundle was 0.4 _G m / _{R m} is preferably 9-15 minutes, more preferably 11 to 15 minutes. If the heat treatment time is 9 minutes or more, the density of the flame-resistant fiber bundle can be sufficiently increased, which is preferable. If the heat treatment time is 15 minutes or less, the value of R _i / R _m does not increase because the heat treatment becomes excessive, and the tensile strength can be improved, which is preferable. The control of the flameproofing time can be achieved by controlling the flameproofing time by changing the speed at which the fiber bundle passes through the flameproofing furnace, the length of the flameproofing furnace, and the like. In addition, the fiber bundle is heat-treated in an oxidizing atmosphere for 20 to 35 minutes with G _m / R _{m set} to 0.2 by the above heat treatment, and R _i / R _m when G _m / R _m mentioned above is 0.4 is obtained. , Preferably 1.2 to 1.5, more preferably 1.2 to 1.4. If R _i / R _m is 1.2 or more, the heat treatment amount for flame resistance is sufficient, and in many cases, it is preferable that the tensile strength be improved. When R _i / R _m is 1.4 or less, the tensile strength is often improved because the double structure does not decrease even if the heat treatment that follows is at a high temperature. How G m _/ R _m to measure the fiber bundle in the middle course of the oxidization is 0.4, it is possible to adopt a method of measuring by sampling the fiber bundle in the process of production. When G _m / R _m of the fiber bundle sampled in the middle is not 0.4, an average value of R _i / R _m when the average of two points before and after becomes 0.4 may be adopted. However, the heat treatment time under an oxidizing atmosphere with a G _m / R _m of 0.2 to 0.4 is preferably 20 to 35 minutes, more preferably 22 to 35 minutes. If the heat treatment time is 20 minutes or more, the value of R _i / R _m can be easily controlled, and the tensile strength can be improved. If the heat treatment time is 35 minutes or less, the tensile strength can be improved without the heat treatment becoming excessive. G _m / R _m and R _i / R _m can be measured by embedding a flame-resistant fiber bundle in a resin, polishing a cross section perpendicular to the fiber axis direction, and observing the cross section with a fluorescence microscope (Details will be described later). In order to control such G _m / R _m and R _i / R _m , this can be achieved by controlling the temperature and time for the stabilization. Control of the stabilization time can be achieved by changing the speed at which the fiber bundle passes through the inside of the stabilization furnace, the length of the stabilization furnace, or the like.

In order to switch the heat treatment conditions of flameproofing at the prescribed G _m / R _m and R _i / R _m , sample the fiber bundle during production to measure G _m / R _m and R _i / R _m and adjust The method of measuring G _m / R _m and R _i / R _m will be described later. For example, when G _m / R _m of the flame-resistant fiber bundle is lower than a specified value, G _m / R _m can be adjusted by increasing the temperature or prolonging the flame resistance time. In addition, when R _i / R _m is lower than a specified value, adjustment can be performed by lowering the temperature. 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.

  By precisely controlling these flameproofing, the flameproofed fiber bundle suitable for obtaining a carbon fiber bundle in which high carbonization yield and tensile strength and tensile elasticity are well-balancedly expressed is impaired in productivity and processability. In order to achieve this specifically, in order to achieve this specifically, the temperature and time for flameproofing may be controlled in accordance with the copolymerization component and the degree of orientation of the PAN-based precursor fiber bundle. For example, from the viewpoint of efficiently performing a flameproofing treatment, the use of a copolymer component such as itaconic acid, acrylamide or methacrylic acid facilitates the flameproofing reaction, or the lower the degree of orientation, the more the flameproofing reaction progresses. In order to facilitate the process, it is possible to precisely control the state of the three-layer structure of the flameproof structure by lowering the flameproof temperature or shortening the flameproof time.

The PAN-based precursor fiber bundle is preferably heat-treated in an oxidizing atmosphere to a density of preferably 1.32-1.35 g / cm ³ , more preferably 1.33-1.35 g / cm ³ , preferably 1 density The temperature at which the heat treatment is performed under an oxidizing atmosphere to a temperature of from 46.15 to 1.50 g / cm ³ , more preferably 1.47 to 1.50 g / cm ³ is preferably 275 to 295 ° C., and more preferably It is 280-290 ° C. 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 tensile strength of the carbon fiber bundle is improved. Moreover, since the heat processing time in high temperature can be ensured long in the subsequent oxidization process as it is 1.35 g / cm < ³ > or less, the tensile strength of a carbon fiber bundle can be improved. In order to switch the temperature at the specified density, the fiber bundle in the middle of the oxidization process may be collected, the density may be measured, and the density may be adjusted (the method of measuring the density will be described later). For example, when the density of the flameproofed fiber bundle is lower than a specified value, the density can be adjusted by increasing the temperature or prolonging the flameproofing time. 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.

In the present invention, the final density of the fiber bundle is preferably 1.46 to 1.50 g / cm ³ , more preferably 1.46 to 1.49 g / cm ³ , still more preferably 1. It is 47-1.49 g / cm < ³ >. Since the density and the carbonization yield are correlated, the higher the production energy, the better. When the density is 1.46 g / cm ³ or more, the carbonization yield can be sufficiently increased, and when the density is 1.50 g / cm ³ or less, the effect of enhancing the carbonization yield is not saturated, so from the viewpoint of productivity. It is effective. In order to complete the heat treatment at the specified density, it is sufficient to adjust the temperature and time for stabilization.

  If the heat treatment temperature is 275 ° C. or higher, the amount of heat applied when increasing the density can be reduced, and the tensile strength is improved. If the heat treatment temperature is 295 ° C. or less, the flameproof reaction can be advanced without decomposing the structure. It can often 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 flameproofing tension applied to the flameproofed fiber bundle at the time of heat treatment at 275 to 295 ° C. in an oxidizing atmosphere to a density of 1.46 to 1.50 g / cm ³ is preferably 1.6 to 4. It is 0 mN / dtex, more preferably 2.5 to 4.0 mN / dtex, still more preferably 3.0 to 4.0 mN / dtex. The tension in the flameproofing step (flameproofing tension) is the tension (mN) measured on the flameproof furnace outlet side divided by the denier (dtex) of the PAN-based precursor fiber bundle at the time of drying. When the tension is 1.6 mN / dtex or more, the orientation of the carbon fiber bundle is often sufficiently enhanced to improve the tensile strength, and when the tension is 4.0 mN / dtex or less, the deterioration by fluff tends to be small. There is.

In the present invention, the PAN-based precursor fiber bundle for carbon fiber bundle preferably has a density of 1 in an oxidizing atmosphere before the heat treatment to be performed until the density reaches 1.31 to 1.35 g / cm ^3. .22~1.24g / cm ^3, more preferably up density is 1.23~1.24g / cm ^3, preferably two hundred ten to two hundred and forty-five ° C., more preferably two hundred twenty to two hundred and forty-five ° C., more preferably from 225 to 240 Heat treated at ° C. When the density of the flameproofed fiber bundle is 1.22 g / cm ³ or more, the heat treatment stabilizes the chemical structure in the flameproofing process, and the tensile strength does not deteriorate even if the temperature of the subsequent heat treatment is high. Often improve. In addition, if 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 tensile strength and productivity. With respect to the temperature, the outer layer area in the double structure can be made sufficiently large at 210 ° C. or higher, and the outer layer area in the double structure with respect to the single fiber diameter of the PAN-based precursor fiber bundle of the present invention at 245 ° C. or lower. In many cases, the tensile strength is high because the temperature is low enough to prevent deterioration of the initial temperature.

After the heat treatment preferably performed until the density reaches 1.22 to 1.24 g / cm ³ , the density of the flame-resistant fiber bundle is preferably 1.32 to 1.35 g / cm ³ , more preferably 1.33. Heat treatment is preferably performed at 245 to 275 ° C., more preferably 250 to 270 ° C. in an oxidizing atmosphere until it reaches ̃1.34 g / cm ³ . When the density is 1.32 g / cm ³ or more, the heat treatment further stabilizes the chemical structure in the flameproofing process, and the outer layer area in the double structure does not decrease even if the subsequent heat treatment is at a higher temperature. It is often improved. In addition, the total heat treatment amount and time including the heat treatment that follows is reduced as 1.35 g / cm ³ or less, which is superior in terms of tensile strength. When the heat treatment temperature is 245 ° C. or more, the total heat treatment amount and time are reduced, and in many cases, it is superior in terms of tensile strength. Even if the heat treatment temperature is 275 ° C. or less, the outer layer area in the dual structure does not decrease even when heat treatment is performed on the flameproof fiber bundle having a density of 1.22 to 1.24 g / cm ³ , and tensile strength is developed. There are many.

  An outline of a method for producing a PAN-based precursor fiber bundle suitable for obtaining the carbon fiber bundle of the present invention will be described.

  It is preferable to use a PAN-based polymer as a raw material to be used for producing a PAN-based precursor fiber bundle. In the present invention, the PAN-based polymer refers to a polymer in which at least acrylonitrile is a main component of the polymer skeleton, and the main component usually accounts for 90 to 100% by mass of the polymer skeleton. It refers to the ingredients. In the production of the PAN-based precursor fiber bundle, the PAN-based polymer preferably contains a copolymerization component such as itaconic acid, acrylamide, methacrylic acid or the like, from the viewpoint of efficiently performing a flameproofing treatment. In the production of the carbon fiber precursor fiber bundle, the production method of the PAN-based polymer can be selected from among known polymerization methods. In the production of a PAN-based precursor fiber bundle suitable for obtaining the carbon fiber bundle of the present invention, the spinning solution comprises the above-mentioned PAN-based polymer in the form of dimethylsulfoxide, dimethylformamide, dimethylacetamide or a nitric acid / zinc chloride / rhodane sodium hydroxide aqueous solution Etc. are dissolved in a soluble solvent. In producing a PAN-based precursor fiber bundle, it is preferable to use a dry-wet spinning method to obtain a precursor fiber having a small average surface roughness on the surface of a single fiber. The spinning step includes a coagulation step of discharging and spinning the spinning solution from a spinneret by a dry-wet spinning method, a water washing step of washing the fiber bundle obtained in the coagulation step in a water bath, and a fiber obtained in the water washing step. It comprises a water bath drawing process of drawing the bundle in a water bath, and a drying heat treatment process of subjecting the fiber bundle obtained in the water bath drawing process to dry heat treatment, and if necessary, the fiber bundle obtained in the dry heat treatment process is steam drawn. May include a steam drawing process.

  In the production of the PAN-based precursor fiber bundle, the coagulation bath preferably contains a solvent such as dimethylsulfoxide, dimethylformamide and dimethylacetamide used as a solvent for the spinning solution, and a so-called coagulation promoting component. As the coagulation accelerating component, those which do not dissolve the PAN-based polymer described later 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 PAN-based precursor fiber bundle, it is preferable to use the water washing bath consisting of a plurality of stages of 30 to 98 ° C. in the water washing step to wash with water.

  Moreover, it is preferable that the draw ratio in a water-bath extending process is 2 to 6 times. The orientation of the PAN-based precursor fiber bundle can be enhanced when the draw ratio in the water-bath drawing step is 2 or more. When the draw ratio in the water bath drawing step is 6 or less, the effect of enhancing the orientation of the PAN-based precursor fiber bundle is not saturated, and the tensile strength often becomes high.

  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 exemplified by 100 to 200 ° C.

  A PAN-based precursor fiber bundle suitably used in the production of a carbon fiber bundle is obtained by performing steam drawing after the above-mentioned water washing step, water bath drawing step, oiling step, and drying heat treatment step performed by a known method. can get. In the present invention, the steam drawing is preferably carried out 2 to 6 times in pressurized steam. The orientation of the PAN-based precursor fiber bundle can be enhanced when the draw ratio in steam drawing is 2 or more. When the draw ratio in the steam drawing is 6 or less, the effect of enhancing the orientation of the PAN-based precursor fiber bundle is not saturated, and the tensile strength of the carbon fiber bundle is often high.

The orientation degree of the PAN-based precursor fiber bundle in the present invention is preferably 89 to 94%, and more preferably 90 to 93%. The degree of orientation is the degree of alignment of the PAN crystal part in the fiber axial direction, and the lower the degree of orientation, the easier G _m / R _m increases, and the larger R _i / R _{m and the} smaller R _O / R _m. Often. If the degree of orientation is 89% or more, it is preferable because the flameproofing reaction does not proceed excessively and it becomes easy to control with the flameproofing temperature and time. If the degree of orientation is 94% or less, the tensile strength of the carbon fiber bundle is often improved, which is preferable. The degree of orientation can be measured by a known method using wide-angle X-ray diffraction. The degree of orientation of the PAN-based precursor fiber bundle can be controlled by changing the draw ratio of the water bath drawing process or the steam drawing.

In the production of the carbon fiber bundle of the present invention, it is preferable to carry out pre-carbonization following the production step and the flameproofing step of the PAN-based precursor fiber bundle. In the pre-carbonization step, it is preferable to heat-process the obtained flameproofed fiber bundle at a maximum temperature of 500 to 1000 ° C. in an inert atmosphere until the density becomes 1.5 to 1.8 g / cm ³ .

  Subsequent to the pre-carbonization, carbonization is performed. In the present invention, in the carbonization step, the obtained pre-carbonized fiber bundle is produced in an inert atmosphere at a maximum temperature of 1200 to 3000 ° C., preferably 1200 to 1800 ° C., more preferably 1200 to 1600 ° C. If the maximum temperature is 1200 ° C. or higher, the nitrogen content in the carbon fiber bundle decreases and tensile strength is stably developed. If the maximum temperature is 3000 ° C. or less, a satisfactory carbonization yield can be obtained.

  The carbon fiber bundle obtained as described above is 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 and liquid phase electrolytic oxidation are used, but liquid phase electrolytic oxidation is preferably used from the viewpoint of high productivity and uniform treatment. 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 agent can also be applied to give the obtained carbon fiber bundle a bundling 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.

  In the method for producing a carbon fiber bundle of the present invention, the average single fiber diameter of the carbon fiber bundle is preferably 6.5 to 8.0 μm, more preferably 6.7 to 8.0 μm, still more preferably 7.0. It shall be -8.0 μm. The smaller the average single fiber diameter, the smaller the double structure tends to decrease, but when preparing a composite material, the high matrix resin viscosity may cause insufficient impregnation, 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 high carbonization yield and the development of the tensile strength of the composite material become stable. The average single fiber diameter can be calculated from the mass and density per unit length of the carbon fiber bundle and the number of filaments.

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

<Tensile strength and modulus of elasticity of carbon fiber bundle>
The tensile strength and the tensile modulus of elasticity of the carbon fiber bundle are determined according to the following procedure in accordance with the resin-impregnated strand test method of JIS-R-7608 (2004). As resin formulation, “Celoxide®” 2021 P (made by Daicel Chemical Industries, Ltd.) / 3 boron fluoride monoethylamine (made by Tokyo Chemical Industry Co., Ltd.) / Acetone = 100/3/4 (parts by mass) is used. As curing conditions, normal pressure, temperature 125 ° C., and time 30 minutes are used. Ten resin-impregnated strands of carbon fiber bundle are measured, and the average value is taken as the tensile strength. Strain is assessed using an extensometer. The strain range is 0.1 to 0.6%.

<Density of flameproofed fiber bundle>
1 to 3 g of a flame-resistant fiber bundle (including a fiber bundle obtained by sampling the flame-resistant fiber bundle during production) is collected and completely dried at 120 ° C. for 2 hours. Next, after measuring the absolute dry mass A (g), after impregnating with ethanol and sufficiently degassing, the mass B (g) of fiber bundle in the ethanol solvent bath is measured, density = (A x)) The density is determined by / (A−B). ρ is the ethanol density at the measurement temperature.

<R _i , R _m , R _o and G _m >
Embed a flame-resistant fiber bundle to be measured in epoxy resin, polish the cross section perpendicular to the fiber axial direction, and use the objective lens of at least 40 times the fluorescence microscope to make the cross section at least 80 times in total Observe. When blue fluorescence observation is performed, the absorption wavelength around 460 nm emitted by being excited by excitation light of excitation wavelength of 360 nm is emitted, and when green fluorescence observation is performed, 525 nm emitted by being excited by excitation light of 470 nm excitation wavelength In the case of red fluorescence, the absorption wavelength in the vicinity is observed by the absorption wavelength in the vicinity of 605 nm which is emitted by being excited by the excitation light of the excitation wavelength of 545 nm. Since the brightness of the fluorescence microscope changes in proportion to the exposure time, the exposure time is 2 seconds for green fluorescence observation, 1 s for red fluorescence observation, and an exposure time that does not reach saturated pixels in blue fluorescence observation I assume. Although the manufacturer of the fluorescence microscope and the fluorescence filter is not particularly limited, it is required to be a fluorescence filter satisfying the above-mentioned excitation wavelength and absorption wavelength, for example, BZ-X filter (DAPI, GFP, TRITC) from Keyence Corporation. The observed image is analyzed using image analysis software such as free software Image J. The boundary of the outer periphery of the flameproofed single fiber (including the intermediate process) can be accurately determined by using the blue fluorescence line profile shown in FIG. That is, since the single fiber cross section is black and the embedded resin emits blue light, it is possible to uniquely determine the boundary of the outer periphery of the fiber by taking the center from the maximum value to the minimum value of the blue brightness. R _i is the maximum value of luminance with a radius of 1 μm from the intersection of the major axis and minor axis of the fiber cross section in the image observed with red fluorescence. Among the images observed with R _m and red fluorescence, this is taken as the minimum value of the brightness of the fiber cross section. R _o is the maximum value of luminance from the outermost layer to 1 μm in the image observed with red fluorescence. G _m is taken as the minimum value of the luminance of the fiber cross-section among the images observed with green fluorescence. Two points of measurement are made per at least one fiber cross section and the average value of 30 fibers is used.

<Outer layer area in double structure>
The red, green and blue fluorescence images of the monofilament cross section are acquired by the method described in <R _i , R _m , R _o and G _m > above. The observed image is analyzed using image analysis software such as free software Image J. As in the known method, the ratio of the outer layer thickness to the single fiber cross-sectional area can be calculated by binarization to obtain the outer layer area in the double structure, but the end of the single fiber cross section as shown in FIG. A measurement profile can be suppressed by acquiring the line profile from the end to the end, and setting the length from the half width of the peak corresponding to the black portion to the inner layer to the outer layer thickness to suppress the measurement variation. The single fiber diameter defines the outer periphery from the blue fluorescence profile as described above, and is the average of the two longest points in the single fiber cross section. The outer layer area is calculated from the single fiber diameter and outer layer thickness from the boundary to the boundary of the outer periphery of the single fiber cross section, and this is taken as the outer layer area in double structure. Two points of measurement are made per at least one monofilament cross section and the mean value of 30 monofilaments is used.

<I _OHo , I _OHm and I _OHi >
The flame-resistant fiber bundle to be measured is embedded in an epoxy resin, and the cross section of a section prepared by a microtome is measured by AFM-IR. Since the AFM-IR utilizes the thermal expansion of the sample, the spatial resolution depends on the film thickness, and the smaller the film thickness, the higher the spatial resolution. On the other hand, when the film thickness is thin, the signal strength is weak and the S / N ratio is lowered, so that the film thickness is made 300 to 700 nm. The light source is a 1 kHz Tunable Pulsed Laser, and the AFM mode is a contact mode. The line analysis is performed in steps of 0.5 μm from 2600 to 3800 cm ⁻¹ from the center of the flame resistant yarn to the surface. The outermost layer is the boundary between epoxy resin and flame resistant yarn. That is, since the epoxy resin is non-oriented, no difference is seen in the IR spectrum in s-polarization and p-polarization, while the flame resistant yarn has a larger peak at 1368 cm ⁻¹ in s-polarization compared to p-polarization, Line analysis from the resin to the flame resistant yarn is performed, and the point where the ratio of the 1368 cm ^-1 peak intensity of s deflection and the 1368 cm ^-1 peak intensity of p deflection corrected baseline is over 1.05 as the outermost layer . The ratio of the sum of ₂₉₃₀ cm- ¹ peak intensity (I _{2930 o} ) and 2855 cm ^-1 peak intensity (I _{2855 o} ) to 3200 cm ^-1 peak intensity (I _{3200 o} ) to 1 μm from the outermost layer (I _{3200 o} / (I 2 _{930 o} + I _{2855 o} )) The maximum value is I _OHo , the ratio of the sum of ₂₉₃₀ cm ⁻¹ peak intensity (I ₂₉₃₀ ) and ₂₈₅₅ cm ⁻¹ peak intensity (I ₂₈₅₅ ) to ₃₂₀₀ cm ⁻¹ peak intensity (I ₃₂₀₀ ) of the entire fiber cross section (I ₃₂₀₀ / (I ₂₉₃₀₎ + _{I 2855))} minimum value _{I OHM} of fiber center (2930 cm ^-1 peak intensity to 3200 cm ^-1 peak intensity of radius 1μm from the fiber long axis and the intersection of the minor axis of the _{cross-section) (I 3200i) (I 2930i} ) and 2855cm ^-1 peak intensity (I ₂₈₅ The maximum value of the ratio of the sum of _5i ) (I _3200i / (I _2930i + I _2855i )) is I _{O Hi} . The peak intensities at 3200 cm ⁻¹ , 2930 cm ⁻¹ and 2855 cm ⁻¹ are the peak heights with baseline correction using the peak intensity of s-polarization. For AFM-IR, in addition to AFM-IR, total reflection measurement-infrared spectroscopy, atomic force microscope-Raman spectroscopy, etc. can be used as long as the device can identify the chemical structure from the excitation spectrum having resolution of nanometer order or more. There is no limitation on the form of

<Orientation degree of PAN-based precursor fiber bundle>
The degree of orientation in the fiber axial direction is measured as follows. The fiber bundle is cut into 40 mm long, and 20 mg is precisely weighed and collected, and after aligning the sample fiber axes so as to be exactly parallel, the thickness of 1 mm in width is uniform using a sample adjustment jig Prepare the sample fiber bundle. A thin collodion solution is impregnated and fixed so as not to lose its shape, and then fixed to a wide-angle X-ray diffraction measurement sample stage. From the half value width (H °) of the meridional profile spread including the highest intensity of diffraction observed around 2θ = 17 °, using the Kα ray of Cu monochromatized with Ni filter as the X-ray source, The degree of orientation (%) is determined using the following equation. The n number is 3 and the average value is obtained.

  Degree of orientation (%) = [(180−H) / 180] × 100.

<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 >.

(Examples 1 to 3 and Comparative Examples 1 to 13)
A copolymer comprising acrylonitrile and itaconic acid was polymerized by a solution polymerization method using dimethyl sulfoxide as a solvent to produce a PAN-based copolymer to obtain a spinning solution. The obtained spinning solution was discharged once from the spinneret into air, and was introduced into a coagulation bath consisting of an aqueous solution of 35% dimethyl sulfoxide controlled to 3 ° C. to form a fiber bundle coagulated by a dry-wet spinning method. The fiber bundle was washed with water at 30 to 98 ° C. by a conventional method, and stretched at that time. Subsequently, an amino-modified silicone-based silicone oil agent is applied to the fiber bundle after the water-bath drawing, and a drying and densification treatment is performed using a heating roller at 160 ° C. By drawing at a magnification shown in Table 1 under steam, the total draw ratio for fiber production was 12 times to obtain a carbon fiber precursor fiber bundle of 12000 single fibers. Next, for Examples 1 to 3 and Comparative Examples 1 to 13, using the conditions of the flameproof temperature and flameproof time shown in Table 2 with a flameproof furnace of 3 furnaces, the flameproof tension shown in Table 2 The carbon fiber precursor fiber bundle was heat-treated in an air atmosphere oven so as to adjust the draw ratio to obtain a flame-resistant fiber bundle.

  The obtained flame-resistant fiber bundle was subjected to pre-carbonization treatment 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.

R _i / R _m and G _m / R _m of the fiber bundle obtained by sampling the flame-resistant fiber bundle and the flame-resistant fiber bundle obtained in Table 1, R _o / R _m of the flame-resistant fiber bundle, outer layer in double structure property The area, tensile strength of carbon fiber bundle, and tensile modulus of elasticity are shown. Table 2 also shows R _i / R _m of the fiber bundle obtained by sampling the flame-resistant fiber bundle during production, the flame resistance time, the flame resistance temperature, and the flame resistance tension at the time of heat treatment at 275 to 295 ° C.

In Comparative Example _{1,7,8, G m / R m =} 0.4 for which a flame-resistant time since shortening a 6, 4, 3 min, _G m / _{R m} of oxidized fiber bundles respectively 0.5, It was as low as 0.5 and 0.4.

In Comparative Example 2, since the flame stabilization time after G _m / R _m = 0.4 was extended to 25 minutes, R _i / R _m of the flame resistant fiber bundle is 1.8, and I _OHi / I _OHm is 1.4. And the tensile strength decreased.

In Comparative Examples 3 and 4, the heat treatment temperatures until the fiber bundle having a density of 1.32 to 1.35 g / cm ³ reaches 1.46 to 1.50 g / cm ³ were as low as 265 ° C. and 274 ° C., respectively. The total amount of heat applied when raising the was large, and the tensile strength decreased.

In Comparative Example 5, since R _i / R _m at G _m / R _m = 0.4 was as high as 1.6 and I _OHo / I _OHm was as high as 1.7, the tensile strength decreased.

In Comparative Example 6, since R _i / R _m at G _m / R _m = 0.4 was lowered to 1.1, fiber bundle breakage occurred during the subsequent heat treatment at high temperature, and the process was not passed.

In Comparative Example 9, since the heat treatment temperature until the fiber bundle having a density of 1.32 to 1.35 g / cm ³ reaches 1.46 to 1.50 g / cm ³ is as high as 305 ° C., I _OHo / I _OHm is 1 .9, I _OHi / I _OHm increased to 1.5, fiber bundle breakage occurred, and the process was not passed.

In Comparative Example 10, since the heat treatment temperature until the fiber bundle having a density of 1.32 to 1.35 g / cm ³ reaches 1.46 to 1.50 g / cm ³ is as high as 300 ° C., I _OHo / I _OHm is 1 .8, I _OHi / I _OHm increased to 1.5, and the tensile strength decreased.

In Comparative Example 11, since the heat treatment temperature to reach a density of 1.22 to 1.24 g / cm ³ was as high as 250 ° C., I _OHo / I _OHm was as low as 1.1, and I _OHi / I _OHm was 1 The tensile strength was lowered.

In Comparative Example 12, a copolymer consisting of 96.5% by mass of acrylonitrile, 2.7% by mass of acrylamide and 0.8% by mass of methacrylic acid was used, but R _i when G _m / R _m = 0.4 As / R _m increased to 1.5, I _OHo / I _OHm decreased to 1.1, and the tensile strength decreased.

In Comparative Example 13, as a result of processing in the same manner as in Example 1 except that stretching was performed twice in pressurized steam in the spinning process, the degree of orientation decreased, and R _O / R _m was 1.10, I _OHo / I _The tensile strength decreased because the _OHm became as low as 1.1.

In Comparative Example 14, as a result of processing in the same manner as in Example 1 except that two furnaces were used for the flameproofing furnace, the density of the final flameproofed fiber bundle was as low as 1.38 g / cm ³ .

In Comparative Example 15, as a result of processing in the same manner as in Example 1 except that two furnaces were used as the flameproofing furnace, heat treatment was performed at a high initial stage of flameproofing at 260 ° C., and R _O / R _m became 1.00 and two layers. Since the I _OHo / I _OHm was as low as 1.0 and the I _OHi / I _OHm was as high as 1.6, the tensile strength was lowered.

  The present invention is suitable for the flameproofing process for the problem of producing a flameproofed fiber bundle suitable for simultaneously satisfying high density and excellent tensile strength without impairing productivity and processability. The second half high temperature heat treatment with the temperature profile develops high carbonization yield and excellent tensile strength. Taking advantage of this feature, the carbon fiber bundle produced from the flame-resistant fiber bundle obtained by the present invention is suitable for general industrial applications such as aircraft, automobiles, ship members, sports applications such as golf shafts and fishing rods, and pressure vessels. Used.

Claims (9)

The ratio (R _i / R _m ) of the maximum value R _i of the brightness of a radius 1 μm from the fiber center of red fluorescence to the minimum value R _m of the brightness of the fiber cross section when the fiber cross section is observed by a fluorescence microscope 1.7 and a ratio of the minimum value _{R m} of the maximum value _{R o} and the luminance of the luminance from the outermost layer to 1μm _(R o / R _m) is 1.13 to 1.23, the green fluorescence of the fiber cross section The ratio (G _m / R _m ) of the minimum value G _m of brightness to the minimum value R _m of brightness of red fluorescence is 0.6 to 0.9, and the outer layer area in double structure is 88 to 95 Polyacrylonitrile-based flameproofed fiber bundle having area%. The ratio of the sum of 2930 cm ^-1 peak intensity to 3200 cm ^-1 peak intensity of the infrared spectrum of 1μm from the outermost layer _{(I 3200o)} of the fiber cross-section _{(I 2930o)} and 2855cm ^-1 peak intensity _{(I 2855o) (I 3200o /} ( _I 2930o + I 2855o) maximum value) _{(I OHO)} and fiber cross section overall 3200 cm ^-1 peak intensity _(2930cm -1 _{(I ²⁹³⁰} for _{I 3200))} peak intensity and 2855cm ^-1 peak intensity of the sum of _{(I 2855)} 2. The polyacrylonitrile-based stabilization as claimed in claim 1, wherein the ratio (I _OHo / I _OHm ) of the minimum value (I _OHm ) of the ratio (I ₃₂₀₀ / (I ₂₉₃₀ + I ₂₈₅₅ )) is 1.2 to 1.5. Fiber bundle. The ratio of the sum of 2930 cm ^-1 peak intensity from the fiber center of the fiber cross-section for the 3200 cm ^-1 peak intensity of the infrared spectrum of the radius _{1μm (I 3200i) (I 2930i} ) and 2855cm ^-1 peak intensity _{(I 2855i) (I 3200i} / The polyacrylonitrile-based stabilization according to claim 1 or 2, _wherein the ratio (I _OHi / I _OHm ) of the maximum value (I _OHi ) to I _OHm of (I _2930i + I _2855i )) is 1.0 to 1.3. Fiber bundle. In the step of heat-treating polyacrylonitrile-based precursor fiber bundle in an oxidizing atmosphere, R _i / R _m when G _m / R _m of the fiber bundle obtained by heat-treating for 15 to 35 minutes is 0.2 is 1. and 0 to 1.2, heat treatment then _G m / _{R m} of fiber bundle was 0.4 9-15 minutes, the production method of the polyacrylonitrile-based flame-resistant fiber bundle according to any one of claims 1 to 3 . The fiber bundle with G _m / R _m of 0.2 is heat-treated in an oxidizing atmosphere for 20 to 35 minutes, and R _i / R _m is 1.2 to 1.2 when the G _m / R _m is 0.4. The manufacturing method of the polyacrylonitrile type | system | group flameproofed fiber bundle of Claim 4 set to 1.5. After heat treatment of polyacrylonitrile-based precursor fiber bundle to a density 1.32~1.35g / cm ³ in an oxidizing atmosphere, under an oxidizing atmosphere to a density 1.46~1.50g / cm ³ 275 The manufacturing method of the polyacrylonitrile type | system | group flameproofed fiber bundle of Claim 4 or 5 which heat-processes at -295 degreeC. The tension of a flame-resistant fiber bundle at the time of heat treatment at 275 to 295 ° C. in an oxidizing atmosphere to a density of 1.46 to 1.50 g / cm ³ is 1.6 to 4.0 mN / dtex, The manufacturing method of the polyacrylonitrile type | system | group flameproofed fiber bundle of description. After heat treatment at 210 ° C. to 245 ° C. to a density 1.22~1.24g / cm ³ in an oxidizing atmosphere, 245 ° C. The heat treatment carried out until the density of 1.32~1.35g / cm ³ The manufacturing method of the polyacrylonitrile type | system | group flameproofed fiber bundle of Claim 6 or 7 performed at -275 degreeC. After obtaining a polyacrylonitrile-based flame-resistant fiber bundle by the method according to any one of claims 4 to 8, the polyacrylonitrile-based flame-resistant fiber bundle is heat-treated at 1200 to 3000 ° C in an inert atmosphere to carbon fiber A method of producing a carbon fiber bundle, obtaining a bundle.