JP4821330B2 - Method for producing flame-resistant fiber bundle and method for producing carbon fiber bundle - Google Patents

Description

The present invention relates to a method for producing a flame-resistant fiber bundle from which a polyacrylonitrile-based carbon fiber bundle having a small fineness variation rate is obtained, and a method for producing the carbon fiber bundle .

  Carbon fiber has a high specific strength and specific modulus compared to other reinforcing fibers, so it is industrially widely used as a reinforcing fiber for composite materials in general industrial applications such as aerospace, sports and automobiles, ships, and civil engineering. It's being used. The demand for high-performance carbon fiber as a reinforcing fiber for composite materials is increasing year by year. In particular, for carbon fiber composite materials for aircraft use, strict quality control is required and quality stabilization is essential, and the quality of the composite material using carbon fiber is also the quality of the carbon fiber itself, so the quality level of the carbon fiber itself In addition, there is a demand for a reduction in carbon fiber quality variation, in other words, quality stability.

  In order to meet the demands from these users, carbon fiber manufacturers are increasing production capacity by increasing the size of production facilities and increasing the thickness of carbon fibers while maintaining high quality. In addition, as a precursor fiber for carbon fiber, a polyacrylonitrile fiber having excellent quality and production stability is generally used. As such a polyacrylonitrile fiber, tensile property which is one of the main characteristics of the carbon fiber is used. In order to increase the strength, it is often obtained by applying a dry and wet spinning method.

  In general, it is known that the fineness of the carbon fiber bundle is proportional to the amount of heat treatment that the traveling precursor fiber undergoes in the flameproofing process. However, when the production equipment is enlarged due to the above-mentioned persistent demands for cost reduction from each user, the heat treatment amount varies due to the treatment temperature fluctuation in the flameproofing process, and as a result, the carbon fiber bundle fineness also varies. growing. For this reason, the quality of the high-order processing is also adversely affected, and the carbon fiber bundle content of the carbon fiber sheet (hereinafter referred to as prepreg) manufactured by the unidirectional prepreg method or the filament winding method is not stable and high. Instability of the quality of the next processed product has been invited.

  Several proposals have been made in the past to solve this carbon fiber bundle fineness variation problem. First, there is a method of reducing the fineness variation, that is, the fluctuation rate of the precursor fiber bundle itself (see Patent Document 1). Here, when the acrylonitrile-based precursor fiber bundle that is the raw material of the carbon fiber bundle is produced by a wet spinning method, in the pressurized steam stretching process, the stretching ratio by the heating roller installed immediately before the stretching apparatus and the stretching ratio by the pressurized steam Varies with time, but since it is not possible to perform both stretchings at exactly the same time, the fact that the distribution of these two stretchings intermittently causes the fineness variation in the longitudinal direction of the precursor fiber. Pointed out. In order to suppress the fineness fluctuation of the precursor fiber, it is described that it is important to suppress the draw ratio by the heating roller and reduce the fluctuation of the yarn tension at the time of pressurized steam drawing. It is described that the precursor fiber bundle obtained by such a drawing method has less unevenness in the longitudinal direction of the carbon fiber bundle obtained by firing. However, there is no description about the specific fineness variation rate of the carbon fiber bundle, and the effect is unknown. Further, in this known example, a polyacrylonitrile-based precursor fiber by wet spinning is assumed, and the strength level of the carbon fiber bundle cannot be said to be sufficiently high from 4750 MPa to 5000 MPa. Further, the present inventors have examined that precursor fibers produced by wet spinning have low scratch resistance, cause fluffing in the firing process, and cause deterioration in quality of high-order workability. When twisting is intentionally added to suppress fuzzing, the spreadability of the fiber bundle is lowered, and there is a problem that yarn breakage occurs during high-order processing with a prepreg sheet.

  As another method for solving the problem of variation in the carbon fiber bundle fineness, there are several methods relating to a technique for reducing variation in heat resistance for heat resistance, that is, suppressing temperature unevenness. For example, there has been proposed a flameproofing furnace that controls the temperature of hot air supplied based on an average value of temperatures detected by a plurality of temperature sensors installed in a flameproofing treatment chamber (see Patent Document 2). It is described that the use of this apparatus has the effect of reducing the variation in the fineness of the carbon fiber by making the temperature in the flameproofing treatment chamber uniform. However, this method cannot be expected to suppress the carbon fineness variation in the machine width direction due to the increase in equipment size. Also, when the outside air temperature during daytime and nighttime changes suddenly, the temperature fluctuation at the furnace end occurs due to the influence of the outside air temperature, and the fluctuation of the fineness of the carbon fiber bundle running through that part increases, resulting in an increase in fineness variation. .

  There has also been proposed a method in which heat treatment is uniformly applied to a flameproof yarn that travels in a furnace by changing the output of a flameproof heating means depending on the location (see Patent Document 3). However, in this publication, the heating means is installed in the circulation part different from the flameproofing treatment chamber where the flameproofing yarn is actually traveling, along the fiber traveling direction and below the traveling yarn, A sufficiently uniform heat treatment resulting in a decrease in thermal efficiency cannot be imparted to the flameproof intermediate yarn running through the flameproofing chamber.

  There is also a technology that focuses on improving the sealing performance at the slit, which is the only opening in the flameproofing furnace (see Patent Document 4). This is an air curtain that blows air outside the furnace as an air curtain to the traveling fiber bundle, but the distance between the nozzle that blows air directly on the fiber bundle and the fiber bundle is as short as 4 cm or less, and the air wind speed is 15 to 20 m. Because of the high speed of / sec, the inherent fluff is exposed to the outside of the running yarn, that is, fluffing occurs, and the process passability is significantly reduced.

As described above, in the conventional technique, in the dry and wet spinning method in which strength is easily developed, a carbon fiber bundle with small fineness variation and excellent quality cannot be obtained.
International Publication No. 00-005440 Pamphlet JP 2004-124310 A JP 2004-115983 A JP 2004-143647 A

The object of the present invention is to produce a flame-resistant fiber bundle using polyacrylonitrile-based precursor fiber as a raw material by a dry and wet spinning method that expresses high strength, and particularly excellent in quality stability with a small variation in fineness, that is, a small variation rate. and to provide a manufacturing method of a preferred carbon fiber bundle in aircraft applications.

Moreover, in order to solve the said subject, the manufacturing method of the flame-resistant fiber bundle of this invention has either of the following structures. That is,
(I) A plurality of polyacrylonitrile-based precursor fiber bundles for carbon fibers are run in parallel, and have a flameproofing treatment chamber in which hot air at a constant temperature is provided and a circulating portion for circulating the hot air, and the running of the fiber bundles Using a flameproofing furnace in which a plurality of slits for turning in and out the flameproofing yarn at both ends in the direction and a folding roller are installed, the flameproofing chamber is passed multiple times to obtain a flameproofed fiber bundle. A method for producing a flameproof fiber bundle, wherein the flameproofing furnace comprises a heating means installed on a flameproofing chamber wall parallel to the running direction of the flameproofing yarn, and the position where the heating means is installed The end of the machine width direction that is above the flameproofing intermediate thread and the direction in which the heating means is installed is parallel to the traveling direction of the flameproofing intermediate thread, and the temperature fluctuation range for the day in the flameproofing treatment chamber The temperature is 3 ° C. or less. A method of manufacturing a Honooka fiber bundle,
(Ii) A plurality of polyacrylonitrile-based precursor fiber bundles for carbon fiber are run in parallel, and have a flameproofing treatment chamber in which hot air at a constant temperature is provided and a circulating portion for circulating the hot air, and the fiber bundle runs. Using a flameproofing furnace in which a plurality of slits for turning in and out the flameproofing yarn at both ends in the direction and a folding roller are installed, the flameproofing chamber is passed multiple times to obtain a flameproofed fiber bundle. A method of manufacturing a flame-resistant fiber bundle, wherein a fiber bundle passing through a central part in the machine width direction having a width of 30% to 70% of the entire machine width of the flameproofing treatment chamber is a fiber bundle passing through other than the central part The method for producing a flame-resistant fiber bundle characterized by reducing the number of times of passing through the flame-resistant treatment chamber as compared to
(Iii) A plurality of polyacrylonitrile-based precursor fiber bundles for carbon fibers are run in parallel, and have a flameproofing treatment chamber in which hot air at a constant temperature is provided and a circulating portion for circulating the hot air, and the running of the fiber bundles Using a flameproofing furnace in which a plurality of slits for turning in and out the flameproofing yarn at both ends in the direction and a folding roller are installed, the flameproofing chamber is passed multiple times to obtain a flameproofed fiber bundle. A method for producing a flame-resistant fiber bundle, in which a gas of 0 ° C. or more and 50 ° C. or less is applied independently from the circulation portion to the flame-resistant intermediate yarn running in the center in the machine width direction from the uppermost portion of the flame-resistant treatment chamber A method of manufacturing a flame-resistant fiber bundle characterized by spraying
It is .

  According to the present invention, as described below, the fineness variation rate of the carbon fiber bundle in the longitudinal direction and the machine width direction is reduced, the strength is easily developed, and the quality stability is improved. As a result, higher order including prepreg Stabilization of the quality of processed products can be achieved.

  As the form of the fiber yarn of the carbon fiber bundle in the present invention, the twisted yarn obtained by twisting and firing the precursor fiber, the untwisted yarn obtained by untwisting the twisted yarn, and substantially the precursor fiber Although untwisted yarns that are heat-treated without twisting can be used, non-twisted yarns or untwisted yarns are preferable in view of higher-order processability, and from the viewpoint of spreadability during higher-order processing, untwisted yarns are preferable.

  Furthermore, the carbon fiber bundle of the present invention is preferably made of carbon fibers having a surface area ratio measured by an atomic force microscope of 1.00 to 1.10, more preferably 1.00 to 1.05. 0.000 to 1.03 is more preferable. If the surface area ratio is within this range, the surface of the carbon fiber bundle is smoother, which is preferable from the viewpoint of the spreadability of the yarn, and at the same time, is easy to express the strength and is preferable from the aspect of quality. In addition, the preferable strength range of the carbon fiber bundle is 5200 MPa or more, more preferably 5500 MPa or more.

  The surface area ratio of the carbon fiber bundle referred to here represents the degree of roughness of the surface of the carbon fiber bundle, and indicates that the surface area ratio becomes smoother as the surface area ratio approaches 1. In the examples of the present application, the surface area ratio of the carbon fiber bundle can be measured using an atomic force microscope by the following method (however, the measuring method is not limited to the one described here). That is, a carbon fiber bundle to be measured is cut to a length of about several mm, fixed on a substrate (silicon wafer) using a silver paste, and a Dimension 3000 stage system is used in a NanoScope IIIa atomic force microscope (AFM) manufactured by Digital Instruments. The three-dimensional surface shape image is obtained for the central portion of the single yarn in the cross-sectional direction under the following conditions.

-Scanning mode: Tapping mode-Probe: Olympus Optical Co., Ltd. Si cantilever integrated probe OMCL-AC120TS
・ Scanning range: 2.5μm × 2.5μm
・ Scanning speed: 0.4Hz
・ Number of pixels: 512 × 512
Measurement environment: For each sample at room temperature and in the air, the image obtained by observing one single thread at a time is processed by the software (Nano Scope III version 4.22r2) attached to the device, Filtering is performed using a first-order Flatten filter, a Lowpass filter, and a third-order Plane Fit filter, and an actual surface area and a projected area are calculated for the entire obtained image. The actual surface area is an area obtained from an average radius obtained based on an image of the cross-sectional shape along the circumferential direction in the cross-sectional direction of one single yarn to be evaluated. . On the other hand, the circle area obtained from the inscribed circle of the image is the projected area, and the ratio of the actual surface area to the projected area corresponds to the surface area ratio mentioned here. Specifically, the surface area ratio used in the present invention is obtained from the following equation. The above measurement is carried out once for each of five single yarns arbitrarily selected for each sample, and the arithmetic average value of three places excluding the maximum value and the minimum value is taken as the final surface area ratio.

Surface area ratio = actual surface area / projected area Further, both the longitudinal direction fineness variation rate and the machine width direction fineness variation rate of the carbon fiber bundle are preferably 1.5% or less, more preferably 1.3% or less. 1.0% or less is more preferable.

  If the longitudinal fineness variation rate of the carbon fiber bundle exceeds 1.5%, the content of the carbon fiber bundle is not stable in prepreg production or the like, so that the quality of the high-order processed product formed from the prepreg itself varies. In particular, in a unidirectional prepreg that performs high-order processing using a large number of carbon fiber bundles as raw materials, if the variation in the longitudinal fineness of the carbon fiber bundle increases, the carbon fiber bundle bobbin is adjusted so that the desired carbon fiber bundle content in the prepreg sheet is obtained. Even if set, the weight per unit area of the carbon fiber bundles contained in the prepreg is not stable, so that non-standard or variation in composite quality occurs, and the prepreg quality and production yield are lowered.

  The longitudinal fineness variation rate of the carbon fiber bundle here is determined as follows.

  In an atmosphere with a temperature of 23 ± 5 ° C and a relative humidity of 60 ± 20%, the carbon fiber bundle, which is a sample for evaluating the longitudinal fineness variation rate, is accurately rectangular in shape so that no 1m twist is inserted in the longitudinal direction from the carbon fiber bobbin Disconnect. Next, a 20 m carbon fiber bundle is peeled from the bobbin in the longitudinal direction from the cut surface of the bobbin carbon fiber bundle. Thereafter, the carbon fiber bundle is again accurately cut from the bobbin so that 1 m twist does not enter in the longitudinal direction to obtain a second sample, and then the carbon fiber bundle of 20 m in the longitudinal direction is peeled off from the bobbin as in the previous period. . Sampling is performed according to the above method until 50 samples of rectangular carbon fiber bundles are obtained. The collected carbon fiber bundle sample is measured by electronic weighing, and the fineness variation rate is obtained based on the following formula.

Longitudinal fineness fluctuation rate (%) = (σ1 / A) × 100
Here, σ1 is a standard deviation of all measured fineness data, and A is an average value of all measured fineness data. Here, the total data refers to the carbon fiber bundle fineness data of 50 samples collected from each bobbin.

  The carbon fiber bundle of the present invention is in the form of a bundle in which a plurality of single fibers are gathered, but the carbon fiber bundle in which the plurality of single fibers are gathered is preferably substantially untwisted. Here, “substantially untwisted” means that the number of turns is 0.5 turn or less per 1 m of the carbon fiber bundle, even if twist is present.

  Moreover, since the variation in the machine width direction is also considered as a factor of the fineness variation of the carbon fiber bundle, it is important to reduce this. Usually, in order to produce efficiently, a plurality of fiber bundles made of polyacrylonitrile or the like, which are precursor fiber bundles of carbon fiber bundles, are placed in parallel and made flame resistant in the flameproofing process at the same time. A fiber bundle is obtained at the same time. The flame resistant yarn fiber bundle is pre-carbonized and then carbonized to simultaneously fire a plurality of carbon fiber bundles. At this time, the fineness variation rate between the carbon fiber bundles in the machine width direction is obtained as follows.

A carbon fiber bundle bobbin for obtaining a sample for evaluating the fineness variation rate in the machine width direction is selected according to the following method for the carbon fiber bundle co-fired in the same machine. That is, the carbon fiber bundle bobbin obtained by winding the carbon fiber bundle fired at the same time is wound from one endmost yarn in the machine to the other endmost yarn wound every 10 lines. Choose until. Further, two carbon fiber bundle bobbins around which the yarn running on both ends is wound are added.
Carbon fiber in an atmosphere of 23 ± 5 ° C and relative humidity of 60 ± 20% so that no twist is entered from the bobbin surface layer of each carbon fiber bundle bobbin selected by the above method exactly 1 m in the longitudinal direction. Cut the bundle precisely into a rectangular shape. The cut carbon fiber bundle is measured by electronic weighing, and the fineness variation rate between the carbon fiber bundles is obtained from the following equation.

Flux variation rate between bundles (%) = (σ2 / B) × 100
Σ2 used in the equation is a standard deviation of all measured fineness data, and B is an average value of all measured fineness data.

  In the carbon fiber bundle, the preferable range of the number of single fibers is 3000 or more, the more preferable range is 6000 or more, and the more preferable range is 12000 or more. When the number of single fibers is less than 3,000, the handleability is poor, and in addition, the fluff is liable to occur due to rubbing with a roller in the firing step, and the quality is lowered.

  The upper limit of the number of single fibers is not particularly limited, but if they are too thick, there will be no uniformity in the resin-impregnated prepreg when processed into a prepreg, and as a result, voids will be created when molding carbon fiber reinforced plastic, resulting in physical properties. Since it falls, it is preferable that the number of single fibers is 48000 or less.

  The above-described carbon fiber bundle of the present invention can be produced as follows. First, a polyacrylonitrile fiber bundle having a constitution in which acrylonitrile is 90% by weight or more and a monomer copolymerizable with acrylonitrile is less than 10% by weight is used as a carbon fiber precursor. Examples of the copolymerizable monomer include acrylic acid, methacrylic acid, itaconic acid or their methyl ester, propyl ester, butyl ester, alkali metal salt, ammonium salt, allyl sulfonic acid, methallyl sulfonic acid, and styrene sulfonic acid. And at least one selected from the group consisting of these alkali metal salts. The polyacrylonitrile-based precursor fiber bundle is heated and flame-resistant using a specific condition described later in a temperature range of 200 ° C. to 300 ° C. in an oxidizing atmosphere such as air to produce a flame-resistant fiber bundle. . The obtained flame-resistant fiber bundle is then subjected to a preliminary carbonization treatment within a temperature range of 300 ° C. to 1000 ° C. in an inert atmosphere such as nitrogen before the carbonization treatment. A carbon fiber bundle can be produced by carbonizing at a maximum temperature of 1000 ° C. to 2500 ° C. in an inert atmosphere such as nitrogen after the preliminary carbonization treatment. As the surface treatment to be applied after the carbonization treatment, there is an electrolytic oxidation surface treatment for the purpose of enhancing the adhesion with a resin by generating a functional group on the surface of the carbon fiber bundle. The methods include liquid phase oxidation using a chemical solution, electrolytic oxidation in which a carbon fiber bundle is treated as an anode in an electrolyte solution, and gas phase oxidation by plasma treatment in a phase state. As the surface treatment method, an electrolytic oxidation treatment method that is relatively easy to handle and is advantageous in terms of cost is preferably employed. As the electrolytic solution, either an acidic aqueous solution or an alkaline aqueous solution can be used. As the acidic aqueous solution, sulfuric acid or nitric acid exhibiting strong acidity is preferable, and as the alkaline aqueous solution, ammonium carbonate, ammonium bicarbonate, ammonium bicarbonate, or the like is preferable. An aqueous solution of an inorganic alkali is preferably used. After performing the electrolytic oxidation treatment, a sizing agent can be applied to the carbon fiber bundle and used for a molded product. The kind of the sizing agent here is not particularly limited, but a bisphenol A type epoxy resin mainly composed of an epoxy resin or an aliphatic compound having two or more epoxy groups at both ends having a linear structure is preferable. Used. The epoxy group is preferably a highly reactive glycidyl group. Specific examples of the aliphatic compound having an epoxy group in the present invention include glycerin polyglycidyl ethers for glycidyl ether compounds and polyethylene glycol diglycidyl ethers for diglycidyl ether compounds.

  Here, the following conditions are adopted in order to produce a flameproof fiber bundle suitable for obtaining the carbon fiber bundle of the present invention. The first is as follows. Usually, it is known that the fineness of the carbon fiber bundle largely depends on the amount of heat treatment applied in the flameproofing process. The variation rate of the fineness of the carbon fiber bundle directly affects the fineness variation rate of the flameproof fiber bundle corresponding to the intermediate yarn, so uniformizing the amount of flameproofing heat treatment is extremely effective in suppressing the fineness variation rate of the carbon fiber bundle. is important. There are roughly two types of flameproofing furnace structures depending on the installation positions of the rollers that allow the flameproofing intermediate yarn to enter and exit at both ends in the strand running direction in the flameproofing treatment chamber. One is an in-furnace roller installation type in which the roller is in the flameproofing treatment chamber, and although there is an advantage that the temperature can be made uniform, the occurrence of rolling of the flameproof fiber bundle including the fiber bundle in the process of flameproofing during production is rolled Since it is impossible to deal with time, there is a disadvantage that once winding occurs, an emergency stop is forced for disaster prevention reasons, and productivity is greatly reduced. The other is an out-of-furnace roller installation type in which the roller is installed outside the flameproofing treatment chamber. While the temperature fluctuation is large, the roller can be wound and the production loss due to winding is minimized. This is a structure with excellent cost performance. Although any flameproof furnace structure may be used, an outside-roller installation type is preferable from the viewpoint of cost performance and reduction of production loss during disaster prevention. FIG. 1 is a schematic side view showing an example of an outside-roller installation type flameproof furnace. A plurality of polyacrylonitrile-based precursor fiber bundles for carbon fibers are run in parallel and guided to the flameproofing treatment chamber 1. The structure of the flameproofing furnace is fixed to a so-called flameproofing intermediate yarn 2 which is a fiber bundle before a polyacrylonitrile-based precursor fiber bundle for carbon fiber is made into a flameproof fiber bundle, in which a plurality of flameproof furnaces are running in parallel. There are a flameproofing treatment chamber 1 to which hot air of temperature is provided, and a circulation part 3 that circulates the hot air, and a plurality of flameproofing yarns that enter and exit the flameproofing treatment chamber 1 at both ends in the fiber bundle traveling direction. The slit 5 and the folding roller 4 are installed. The fiber bundle enters and exits from the slit 5, is folded back by the folding roller 4, and passes through the flameproofing treatment chamber 1 in a zigzag manner. A plurality of precursor fiber bundles and flameproofing intermediate yarns 2 are aligned in the machine width direction of the flameproofing treatment chamber (from the front to the back in FIG. 1).

  In the flameproofing process, the flameproofing yarn running inside the flameproofing chamber causes an exothermic reaction, so it is necessary to suppress and control the excessive heat generation of the running yarn from the disaster prevention side. It is common to remove heat by blowing hot air whose temperature is controlled through the circulation section to the running yarn. Specifically, the hot air supply direction includes a direction in which a plurality of flameproof yarns travel in parallel in the flameproofing chamber, a direct flow that supplies hot air from the vertical direction, and a hot air from the side of the flameproof yarn. There are two types of parallel flow. In the present invention, the hot air supply direction may be any direction, but in the case of parallel flow, the hot air temperature must be divided and controlled, and in order to add equipment such as a heater, the cost performance is inferior. Although there is a problem, in the direct flow, it is possible to collectively control the temperature in the hot air circulation portion, which is superior in cost performance than the parallel flow, and is a more preferable form as a device. In addition, the flameproofing furnace shown in FIG. 1 is an orthogonal flow.

  As the shape of the folding roller, a grooved shape is preferable so that the yarn vibration caused by hot air of the running yarn in the flameproofing chamber can be suppressed and a certain degree of form retention can be maintained in the flameproofing chamber. When there is no groove on the roller, adjacent yarns are entangled in the flameproofing chamber and heat is easily stored, which is not preferable for disaster prevention, and an oil agent such as silicone is transferred from the precursor fiber bundle to the roller (so-called gum-up) ) And thread winding due to adhesion may occur.

  The temperature in the flameproofing treatment chamber that affects the fineness of the carbon fiber bundle is usually controlled by heating means such as a gas heater 6 in the circulation section 3 and a circulation fan 7. Day and night fluctuations may occur. Seasonal fluctuations can be suppressed by changing the supply hot air temperature in a timely manner, but it is extremely difficult to suppress daytime and nighttime temperature fluctuations because fluctuations in outside air temperature cannot be predicted. In particular, when there is a manufacturing process in a place with an inland climate, the influence on the change in the fineness of the carbon fiber bundle becomes serious in spring and autumn when the temperature fluctuation range is large. In order to minimize the longitudinal fineness variation rate of the carbon fiber bundle in consideration of the influence of the outside air temperature, the average temperature fluctuation in the flameproofing treatment chamber is 3 ° C. or less, more preferably 2 ° C. or less, more preferably Must be controlled to be 1 ° C. or lower. If the temperature fluctuation range exceeds 3 ° C, the flameproofing temperature, that is, the amount of heat treatment in the flameproofing process, changes over time, and the longitudinal flameproof yarn fiber bundle, and hence the carbon fiber bundle longitudinal fineness fluctuation. Invite.

  The fluctuation range of the average temperature in the flameproofing treatment chamber here can be obtained as follows. Since a plurality of flameproofing yarns that are exothermic are running in the flameproofing treatment chamber, the upper part of the room is usually hotter than the lower part due to the chimney effect. As a matter of course, the outer wall portion of the flameproofing treatment chamber has a lower temperature due to heat radiation to the outside than the central portion. In order to accurately measure the average temperature in the flameproofing chamber, the temperature difference must be taken into consideration and both the high temperature portion and the low temperature portion in the flameproofing chamber must be included. That is, the average temperature of the flameproofing chamber is obtained as follows. For the horizontal direction, five thermocouples including the four corners and the center of the flameproofing treatment chamber are installed as measurement locations. For the height direction, when processing is performed in a plurality of stages in the height direction, an equal number is measured for each stage. However, it is possible to replace only the three steps of the top, middle and bottom as measurement locations (however, the average value for each floor and the average value for only three steps were measured, and the values were different) When you take the average value for each floor.) The measurement point on each floor is a place 5 to 15 cm away from the plane parallel to the ground surface including the flameproof yarn running in parallel in the furnace. The temperature at the plurality of measurement locations is simultaneously measured every hour to obtain an average value, which is defined as the average temperature in the flameproofing treatment chamber at that time. The measurement is performed continuously for 24 hours, and the difference between the highest average temperature and the lowest average temperature is calculated and set as the temperature fluctuation range in the flameproofing treatment room (day and night).

  As a means suitable for suppressing the temperature fluctuation in the flameproofing chamber day and night, first, as a normal means, a heating means is provided on the wall of the flameproofing chamber that is most easily affected by the outside air temperature. More specifically, a heating means is provided in the flameproofing treatment chamber in parallel to the flameproofing yarn traveling direction. Although the installation location is not limited, the side wall of the flameproofing treatment chamber is preferable in consideration of heat radiation to the outside. Moreover, although it does not limit about a heating means and its number, A heater is preferable as a heating means when a control precision is considered. FIG. 3 shows an example in which the heater 9 as a heating means is installed on the side wall of the flameproofing treatment chamber 1.

  Also, the position where the heating means is installed is above the traveling flameproof intermediate yarn and the end in the machine width direction, and the direction of installing the heating means is parallel to the traveling direction of the flameproof intermediate yarn. More preferably. This is because if the heating means is provided at the end in the machine width direction where the temperature decreases due to heat radiation from the flameproofing treatment chamber to the outside, the temperature before being supplied to the flameproofing yarn becomes uniform. FIG. 4 shows a case where the heater 9 as the heating means is installed on the wall of the flameproofing treatment chamber 1 so as to satisfy such a condition (illustration of the circulation portion and the like is omitted).

  On the other hand, the fineness variation rate with respect to the machine width direction depends on the fineness of the acrylonitrile precursor fiber bundle, which is the raw material, but at the same time, due to the amount of heat treatment in the flameproofing process, thus improving cost performance, that is, production capacity If the flameproofing furnace is increased in size to increase the heat treatment amount, unevenness of the heat treatment amount occurs for each fiber bundle in the machine width direction, and as a result, the fineness variation rate in the machine width direction increases. In order to suppress this variation in fineness in the firing process, it is important to make the heat treatment amount in the flameproofing process that the yarn receives in the machine width direction as uniform as possible. As another means for producing a flame-resistant fiber bundle suitable for achieving this object and obtaining the carbon fiber bundle of the present invention, there is a method called a pass yarn path. This is a method of minimizing the overall unevenness of the heat treatment amount by intentionally changing the number of stages of flameproofing treatment in the machine width direction. More specifically, it is possible to use either a method of reducing the number of processing stages at the central portion where the heat treatment amount in the flameproofing step is large or increasing the number of processing steps at the end portion where the heat treatment amount is small. When increasing the number of processing steps, a roller must be newly installed, which is disadvantageous in terms of cost. Therefore, means for reducing the number of processing steps is preferable. The range in which this pass yarn path is applied is in the range of 30 to 70%, preferably 40 to 60% of the entire machine width centering on the machine width center. If it is less than 30%, the number of yarns to which the pass yarn path is applied is small, and it is impossible to sufficiently reduce the fineness variation because the uniform heat-resistant heat treatment cannot be achieved. On the other hand, if it exceeds 70%, the number of yarns to which the pass yarn path is applied increases, and the fineness of most of the carbon fiber bundle itself decreases, and the fineness variation does not become small. FIG. 2 shows an example in which the number of processing stages in the central portion where the amount of heat treatment in the flameproofing process is large is reduced. The yarn at the end portion passes through the yarn path 8 passed through the yarn at the central portion, but the yarn at the central portion passes through the yarn path without passing through the yarn path. In addition, you may use together the technique which installs a heating means in the wall of the flameproofing processing chamber as mentioned above to the technique of such a pass yarn path. Furthermore, as another means for producing a flame-resistant fiber bundle suitable for obtaining the carbon fiber bundle of the present invention, a gas having a temperature lower than the furnace temperature is applied to a plurality of flame-resistant intermediate yarns running in the flame-resistant treatment chamber. It is supplied independently from the circulation part. Generally, due to the heat generated in the flame-proofing yarn running in the flame-proofing chamber, the upper part of the furnace becomes a flame-resistant high temperature from the lower part due to the chimney effect, and the central part also generates heat from the adjacent yarns. It is hard to be heated and becomes hotter than the furnace end. In other words, the upper part and the central part of the flameproofing treatment chamber form a maximum temperature region, which causes variations in the machine width direction fineness of the flameproofed fiber bundle, that is, the carbon fiber bundle in the machine width direction. Only with the hot air supplied from the circulation part, the hot air diffuses throughout the flameproofing chamber, so it may be difficult to efficiently remove the heat at the center of the furnace upper part, which is the highest temperature region. . In such a case, as shown in FIG. 5, apart from the hot air supplied from the circulation unit 3, flame resistance is achieved by using a nozzle 10 disposed at the tip of the gas supply pipe 11 from the top of the flameproofing treatment chamber. By blowing a gas at a temperature lower than the temperature of the heat treatment chamber locally onto the flame-proofing yarn running in the center of the heat treatment chamber, the temperature of that portion is lowered and the temperature inside the flame treatment chamber is leveled. Can bring. In addition, since a gas lower than the temperature of the flameproofing treatment chamber is supplied to the gas supply pipe 11, it is preferable to attach a heat insulating material around the pipe in order to prevent tar adhesion and tar falling to the flameproofing middle yarn. Further, the degree of gas blowing from the nozzle 10 can be controlled by attaching the valve 13 and the flow meter 12. The gas here is not particularly limited, but it is preferable to use air in consideration of cost. In this case, it is important that the temperature of the gas to be blown is 0 ° C. or higher and 50 ° C. or lower, preferably 5 ° C. or higher and 45 ° C. or lower, more preferably 10 ° C. or higher and 40 ° C. or lower. If a gas whose temperature is too low is blown, the temperature difference between the flameproofing treatment room temperature and the gas to be blown is too large, and the heat removal effect of the flameproofing yarn running in the center in the machine width direction is too great, making the part flameproof. Since the fiber bundle fineness decreases, the fineness variation in the machine width direction of the flameproof fiber bundle, and consequently the fineness variation in the machine width direction of the obtained carbon fiber bundle increases. On the other hand, if a gas whose temperature is too high is blown, the difference in temperature between the flameproofing treatment room temperature and the blown gas is small, and a sufficient heat removal effect cannot be obtained, and the fineness of the flameproof fiber bundle that has traveled in the center in the machine width direction The fineness variation in the machine width direction remains large without decreasing. As the gas blowing means, it is preferable to use a nozzle as shown in FIG. 5 from the viewpoint of equipment cost and flow rate control accuracy, but flame resistance that travels in the machine width direction center from the top of the flameproofing treatment chamber. Other means may be used as long as it is a means capable of spraying a gas on the intermediate yarns independently of the circulating portion. Furthermore, the distance between the gas blowing means such as a nozzle and the flameproof intermediate yarn is 0.5 m or more and 5 m or less, preferably 1 m or more and 4 m or less, more preferably 1 m or more and 3 m or less. If the interval is too small, not only the local flameproofing yarn can be removed, but the gas flow rate is too high to induce fluffing, which may lead to a decrease in process passability. On the other hand, if the interval is too large, the gas to be blown is diffused before reaching the flame-proofing yarn that travels, and a local cooling effect cannot be obtained, and the flame-proofing furnace becomes large and economically disadvantageous. . The flow rate of the blowing gas is 0.05% or more and 5% or less, preferably 0.05% or more and 3% or less, more preferably 0.05% with respect to the flow rate circulating in the heat treatment chamber in a standard state of 0 ° C. and 1 atm. It is good to make it 1% or less. If the flow rate is too high, the running flameproof yarn may fluff due to gas blowing or vibrate vigorously and entangle with adjacent running yarns, which may cause heat storage. Further, if the flow rate is too small, a sufficient heat removal effect cannot be obtained, and the fineness variation in the machine width direction remains large without decreasing the fineness of the flame-resistant fiber bundle that has traveled in the center in the machine width direction. Sufficient heat removal gas blowing means is not limited to one place, and may be provided over two or more places as necessary. It should be noted that such a gas blowing technique can be appropriately combined with a technique for installing a heating means on the wall of the flameproofing treatment chamber as described above and a technique for pass yarn path. Thus, according to the present invention, the quality stability is improved by reducing the fineness variation rate of the carbon fiber bundle in the longitudinal direction and the machine width direction, and as a result, the unidirectional prepreg method, the filament winding method, etc. Stabilization of the quality of high-order processed products such as manufactured prepregs can be achieved.

Hereinafter, the present invention will be specifically described by way of examples.
Example 1
An acrylic polymer solution prepared by polymerizing 99% by weight of acrylonitrile and 1% by weight of itaconic acid is prepared, and an acrylonitrile-based precursor fiber bundle having a single fiber fineness of 0.74 dtex and a filament number of 24,000 by a dry and wet spinning method. Got. A plurality of obtained precursor fiber bundles were run in parallel, introduced into a flameproofing furnace, and subjected to a flameproofing treatment to obtain a flameproofed fiber bundle. In the flameproofing treatment, in the flameproofing furnace in which a plurality of flameproofing yarns run in parallel and flameproof the precursor fibers in the air, the temperature in the flameproofing treatment chamber is 200 ° C. with respect to the running yarns. There are a flameproofing chamber in which hot air at a constant temperature set to be within a range of ˜270 ° C. is supplied from the vertical direction, and a circulation part for circulating the hot air from below to above, and in the flameproofing chamber In the flameproofing furnace shown in FIG. 5, a plurality of slits and groove-turning rollers are installed at both ends of the strand running direction to enter and exit the flameproofed yarn, and in a direction parallel to the flameproofing yarn running direction. By installing a heater on the side wall of the flameproofing chamber as shown in FIG. 3, the temperature fluctuation range in the flameproofing chamber during the day and night was set to 1 ° C. Furthermore, in order to reduce the number of processing stages in the machine width central part, which is the part where the heat treatment amount in the flame resistance treatment is high and the fineness of the carbon fiber bundle is large, which accounts for 50% of the total machine width, The pass yarn path was applied so that the distance would be 95% of the total travel distance of the flameproofing treatment chamber obtained when traveling on the roller. In addition, a nozzle 10 is installed as shown in FIG. 5 in the center portion in the machine width direction 1 m above the flameproofing yarn running on the uppermost stage of the flameproofing treatment chamber, and a standard state of 0 ° C. and 1 atm from this nozzle. The air at 25 ° C. was sprayed onto the flame resistant yarn in a form independent of the circulating part at a flow rate of 1% with respect to the flow rate circulating in the heat treatment chamber. The obtained flame-resistant fiber bundle was then pre-carbonized in a temperature range of 400 ° C. to 800 ° C. in a nitrogen atmosphere, and further carbonized in a temperature range of 900 ° C. to 1900 ° C. in a nitrogen atmosphere, followed by the sulfuric acid aqueous solution. As an electrolytic solution, surface treatment was performed with an electric quantity of 10 coulomb per gram of carbon fiber bundle, washing and washing with water, and then a sizing agent mainly composed of bisphenol A type epoxy resin was adhered to 1% by weight to obtain carbon fiber. Got a bunch. The obtained carbon fiber bundle has a surface area ratio measured by an atomic force microscope of 1.02 and is substantially untwisted (0.1 turns / m or less), and the carbon fiber bundle fineness variation rate is in the longitudinal direction. The variation rate was 1.0%, the variation rate between the carbon fiber bundles was 0.7%, and the quality was excellent with little variation in fineness.
(Example 2)
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the pass yarn path was not applied and all the yarns had the same number of treatment stages. The obtained carbon fiber bundle has a surface area ratio measured by an atomic force microscope of 1.02 and is substantially untwisted (0.1 turns / m or less), and the carbon fiber bundle fineness variation rate is in the longitudinal direction. The variation rate was 1.0% and the variation rate between the carbon fiber bundles was 1.0%, which was excellent in quality with little variation in fineness.
(Example 3)
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the heater installed on the side wall of the flameproofing treatment chamber in the direction parallel to the flameproofing middle yarn was removed. At this time, the temperature fluctuation difference in the flameproofing chamber was 3 ° C. The obtained carbon fiber bundle has a surface area ratio measured by an atomic force microscope of 1.02 and is substantially untwisted (0.1 turns / m or less), and the carbon fiber bundle fineness variation rate is in the longitudinal direction. The variation rate was 1.3%, and the variation rate between carbon fiber bundles was 1.0%, which was excellent in quality with little variation in fineness.
Example 4
A carbon fiber bundle was obtained in the same manner as in Example 1 except that air was not blown from the nozzle. The obtained carbon fiber bundle has a surface area ratio measured by an atomic force microscope of 1.02 and is substantially untwisted (0.1 turns / m or less), and the carbon fiber bundle fineness variation rate is in the longitudinal direction. The variation rate was 1.0% and the variation rate between the carbon fiber bundles was 1.0%, which was excellent in quality with little variation in fineness.
(Comparative Example 1)
Without applying the pass yarn path, remove the heater installed on the side wall of the flameproofing treatment chamber in the direction parallel to the flameproofing yarn, and remove the air from the nozzle. A carbon fiber bundle was obtained in the same manner as in Example 1 except that. At this time, the temperature fluctuation difference in the flameproofing chamber was 5 ° C. The obtained carbon fiber bundle has a surface area ratio measured by an atomic force microscope of 1.03 and is substantially untwisted (0.3 turns / m or less), and the carbon fiber bundle fineness variation rate is in the longitudinal direction. The variation rate increased to 3.0%, the variation rate between the carbon fiber bundles increased to 3.0%, and the quality potential was low.
(Comparative Example 2)
An acrylic polymer solution prepared by polymerizing 99% by weight of acrylonitrile and 1% by weight of itaconic acid from an acrylonitrile-based precursor fiber bundle, and a single fiber fineness of 1.1 dtex obtained by a dry and wet spinning method, filaments A carbon fiber bundle was obtained in the same manner as in Comparative Example 1 except that the number was changed to several thousand. However, fluffing occurred by rubbing with a roller in the firing process, the quality deteriorated, and the process passability was reduced. Due to the decrease, a carbon fiber bundle could not be obtained. At this time, the temperature fluctuation difference in the flameproofing chamber was 5 ° C.

  The carbon fiber bundle of the present invention can be widely applied to aerospace, sports and general industrial applications since its fineness variation rate is small and quality stabilization with high-order processability can be expected. Suitable for aircraft use. The carbon fiber bundle of the present invention is widely used industrially as a reinforcing fiber for composite materials and is industrially useful.

It is a see-through | perspective schematic side view of the flameproofing furnace used by this invention. It is a see-through | perspective schematic side view of the flameproofing furnace explaining 1 aspect of this invention. 1 is a partially transparent schematic front view of a flameproofing furnace illustrating one embodiment of the present invention. It is a see-through | perspective schematic side view of the flameproofing furnace explaining 1 aspect of this invention. It is a see-through | perspective schematic side view of the flameproofing furnace explaining 1 aspect of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Flameproofing process chamber 2 Flameproofing middle thread 3 Circulation part 4 Folding roller 5 Slit 6 Gas heater 7 Circulating fan 8 Passed yarn path 9 Heater 10 Nozzle 11 Gas supply pipe 12 Flow meter 13 Valve

Claims (5)

A plurality of polyacrylonitrile-based precursor fiber bundles for carbon fiber are run in parallel, and have a flameproofing treatment chamber in which hot air at a constant temperature is provided and a circulation part for circulating the hot air, and both ends in the running direction of the fiber bundle. Using a flameproofing furnace in which a plurality of slits for turning in and out the flameproofing yarn and a folding roller are installed, the flameproofing fiber is obtained by passing through the flameproofing treatment chamber multiple times to obtain a flameproofed fiber bundle. A method of manufacturing a bundle, wherein the flameproofing furnace is provided with a heating means on a flameproofing chamber wall parallel to the traveling direction of the flameproofing intermediate yarn, and the position where the heating means is installed is flameproofing to travel. The end of the machine width direction is above the intermediate yarn and the direction in which the heating means is installed is parallel to the running direction of the flameproof intermediate yarn, and the temperature fluctuation range for the day in the flameproofing treatment chamber is 3 ° C. Flame resistance characterized by: Method of manufacturing a 維束. A plurality of polyacrylonitrile-based precursor fiber bundles for carbon fiber are run in parallel, and have a flameproofing treatment chamber in which hot air at a constant temperature is provided and a circulation part for circulating the hot air, and both ends in the running direction of the fiber bundle. Using a flameproofing furnace in which a plurality of slits for turning in and out the flameproofing yarn and a folding roller are installed, the flameproofing fiber is obtained by passing through the flameproofing treatment chamber multiple times to obtain a flameproofed fiber bundle. A method for manufacturing a bundle, in which a fiber bundle passing through a central portion in the machine width direction having a width of 30% to 70% of the entire machine width of the flameproofing treatment chamber is compared with a fiber bundle passing through other than the central portion. And reducing the number of times of passing through the flameproofing treatment chamber. A plurality of polyacrylonitrile-based precursor fiber bundles for carbon fiber are run in parallel, and have a flameproofing treatment chamber in which hot air at a constant temperature is provided and a circulation part for circulating the hot air, and both ends in the running direction of the fiber bundle. Using a flameproofing furnace in which a plurality of slits for turning in and out the flameproofing yarn and a folding roller are installed, the flameproofing fiber is obtained by passing through the flameproofing treatment chamber multiple times to obtain a flameproofed fiber bundle. A method for manufacturing a bundle, in which a gas of 0 ° C. or more and 50 ° C. or less is blown independently from the circulating portion to the flame-resistant intermediate yarn traveling in the center in the machine width direction from the uppermost portion of the flameproofing treatment chamber. A method for producing a flameproof fiber bundle characterized by the above. The said flameproofing furnace is a manufacturing method of the flameproofing fiber bundle of Claim 2 or 3 which installs a heating means in the flameproofing chamber wall parallel to the running direction of the flameproofing middle yarn. A flame-resistant fiber bundle obtained by the method according to any one of claims 1 to 4, wherein the carbon fiber bundle is carbonized at 1000 ° C to 2500 ° C after preliminary carbonization at 300 ° C to 1000 ° C. Manufacturing method .

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