JP2021080607A - Production method of carbon fiber - Google Patents

Abstract

To provide an efficient production method of carbon fiber excellent in fiber openability, from which a prepreg or fabric excellent in appearance quality can be obtained, with reduced problems in a step of firing a fiber bundle of carbon fiber precursor to make carbon fiber.SOLUTION: A production method of carbon fiber includes production steps of a fiber bundle of carbon fiber precursor including recording data of continuous evaluation on a running fiber bundle of carbon fiber precursor, determining a problematic part based on the recorded data, and firing the fiber bundle of carbon fiber precursor with the problematic part removed.SELECTED DRAWING: Figure 1

Description

The present invention reduces defects in the process of firing carbon fiber precursor fiber bundles into carbon fibers, and efficiently produces carbon fibers having excellent fiber opening properties, which can obtain prepregs and woven fabrics having excellent appearance quality. Regarding the method.

Carbon fibers are obtained in the form of carbon fiber bundles by firing polyacrylonitrile fiber bundles or pitch fiber bundles. Polyacrylonitrile fiber bundles and pitch fiber bundles that are fired into carbon fiber bundles are called carbon fiber precursor fiber bundles, or simply precursor fiber bundles. In the present specification, the step of producing the precursor fiber bundle is called a spinning step, and the step of manufacturing the carbon fiber bundle and the carbon fiber from the precursor fiber bundle is called a firing step.

In addition, carbon fiber is known as a high-performance fiber used in fields such as sports, automobiles, ships, and civil engineering and construction.

While carbon fiber is required to have high performance, in order to meet the demand from users, the cost is reduced by increasing the size of production equipment in the spinning process and firing process, improving production speed, and increasing the total number of fibers per unit production machine. The field of application is greatly expanded.

However, it is known that increasing the size of production equipment and improving the production speed make uniform processing of fiber bundles more difficult, and minor defects in fiber bundles become a serious problem. For example, in the middle of the manufacturing process of the precursor fiber bundle, fluff and pills due to single yarn breakage, foreign matter adhesion, thickness unevenness, unexpected fiber skewing and fiber bundle cracking may occur. If the precursor fiber bundle has fluff, pills, foreign matter adhered, thickness unevenness, etc., when the precursor fiber bundle is fired to produce a carbon fiber bundle, it may be wrapped around a roll and the process passability deteriorates. It may lead to abnormal cutting in a flameproof oven or carbonization furnace. In addition, if there are unexpected oblique fibers in the precursor fiber bundle, oblique carbon fibers are also generated in the carbon fiber bundle produced from the precursor fiber bundle, and the prepreg is opened when the prepreg is made from the carbon fiber bundle. In some cases, the prepreg may have a gap, which may lead to a deterioration in the appearance quality. Similarly, with regard to cracking of the precursor fiber bundle, cracking of the carbon fiber bundle is likely to occur, which may lead to deterioration of the appearance quality of the prepreg, the woven fabric, etc., and such a defect of the fiber bundle is a defect of the precursor fiber. It is an important item to be managed in the bundle manufacturing process.

As a method for finding defects in fiber bundles continuously produced at high speed, a method for detecting defects in fiber bundles by measuring light exceeding the width of the fiber bundles and light receiving means has been proposed (Patent Document 1). However, the measuring method described in Patent Document 1 can detect large defects such as foreign matter adhesion over a wide range of fiber bundles and entanglement of single yarn fluff and growth, but single yarn fluff and fiber obliqueness. Small defects such as rows are difficult to detect.

On the other hand, a method has been proposed in which a fiber bundle is illuminated, the fiber bundle is imaged by a camera, and the obtained image is binarized and thinned to detect a defect in the fiber bundle (Patent Document 2). ). However, in the measuring method described in Patent Document 2, fluff and pills that seem to protrude from the fiber bundle when viewed from the camera can be detected, but the inside of the fluff and the fiber bundle that seems to fit within the width of the fiber bundle. Defects such as skew in are difficult to detect.

Japanese Unexamined Patent Publication No. 2008-203251 Japanese Unexamined Patent Publication No. 2011-053173

An object of the present invention is to quickly detect an abnormality occurring in a process of manufacturing a precursor fiber bundle (spinning process) and record information in view of the problems of the prior art, and to record a defect in the firing process based on the recorded information. The carbon fiber bundle is efficiently produced by identifying the portion that may cause a problem and calcining the body fiber bundle consisting of only the precursor fiber bundle from which the specified portion is removed to reduce the defects in the firing process. The purpose is to provide a method for producing a carbon fiber bundle which can be used.

The present invention provides the methods for producing carbon fibers according to the following (1) to (3) in order to solve the above problems.

(1) In the manufacturing process of the carbon fiber precursor fiber bundle, the running carbon fiber precursor fiber bundle is continuously evaluated and information is recorded, and the defect concern portion is determined based on the recorded information, and the defect concern portion is determined. A method for producing carbon fibers by firing a carbon fiber precursor fiber bundle from which the above has been removed.
(2) The method for producing carbon fiber according to claim 1, wherein the traveling carbon fiber precursor fiber bundle is continuously evaluated and information is recorded by the evaluation method having the following steps [A] to [D]. .. ..
[A] Step of irradiating the traveling fiber bundle with measurement light [B] Step of imaging the transmitted light from the fiber bundle [C] Data processing step (a) having the means of the following (a) to (c) A data processing means for determining a region in which a fiber bundle exists as a target region from an image obtained in an imaging step.
(B) A data processing means for detecting defects based on pixel information from an image obtained in the imaging step.
(C) Data processing means for classifying defect types according to the detected feature amounts of defects [E] Recording means for recording information on the defects.

According to the present invention, it is possible to avoid deterioration of process passability in the firing process, improve the production efficiency of carbon fibers, and prevent the outflow of carbon fiber bundles including defects such as skewing and cracking to the outside. This makes it possible to carry out quality control of carbon fiber bundles and carbon fibers at a high level.

It is a schematic side view which showed the 1st form of the apparatus which detects and records the defect of the precursor fiber bundle used in the method of manufacturing a carbon fiber of this invention. It is a schematic side view which showed the 2nd form of the apparatus which detects and records the defect of the precursor fiber bundle used in the method of manufacturing a carbon fiber of this invention. It is a schematic diagram which shows an example of the defect of the precursor fiber bundle in the 1st form to be detected in this invention. It is a schematic diagram which shows an example of the defect of the precursor fiber bundle in the 2nd form which is the detection target in this invention.

Hereinafter, embodiments of the present invention will be described in detail.
In the present invention, the carbon fiber precursor fiber bundle to be continuously evaluated is a fiber bundle composed of a plurality of filaments. The type of precursor fiber bundle is not particularly limited. Specific examples include acrylic fiber bundles, viscose fiber bundles, lignin fiber bundles, petroleum or coal pitch fiber bundles, and mesophase pitch fiber bundles derived from petroleum or coal pitch, which have high light transmission. , Acrylic fiber bundle and viscose fiber bundle can be preferably mentioned. The present invention can be particularly preferably applied to acrylic fiber bundles.

The precursor fiber bundle to be evaluated can satisfactorily detect defects by running on a predetermined thread path. Therefore, it is preferable to apply a tension of 0.01 cN / dtex or more to the evaluated traveling fiber bundle, and more preferably 0.05 cN / dtex or more. By applying a tension of 0.01 cN / dtex or more, it is possible to prevent the meandering of the single yarn and the single yarn bundle composed of several monofilaments from being separated from the precursor fiber bundle to be evaluated.

The illumination means is not limited in both the intensity and wavelength of the illumination light as long as sufficient transmitted light from the precursor fiber bundle can be obtained. In particular, when simultaneously inspecting defects in a plurality of fiber bundles in a place where a plurality of precursor fiber bundles are running in parallel, each fiber is in the direction across a row of parallel fiber bundles, that is, in the width direction. Anything that can uniformly illuminate the bundle will do. The lighting means at this time is preferably one that can illuminate each fiber bundle with a light amount difference of 20% or less in the width direction.

As the lighting means for illuminating the precursor fiber bundle, a fluorescent lamp for high-frequency lighting, a metal hararoid lamp, LED lighting, X-rays, infrared light, ultraviolet light, or the like can be used. Further, the light from a light source such as a halogen or an LED may be guided by an optical fiber to illuminate the lamp. In particular, when simultaneously inspecting defects in a plurality of fiber bundles in a place where a plurality of fiber bundles are running in parallel, it is preferable to use a high-frequency fluorescent lamp or LED lighting long in the width direction from the viewpoint of cost and maintainability.

Regarding the positional relationship between the illumination and the precursor fiber bundle, it is preferable to illuminate only the fiber bundle and increase the brightness difference from the background. For example, as shown in FIG. 1, the fiber bundle is illuminated perpendicularly. There is a method of performing imaging from an angle. In this positional relationship, the background is black as shown in the upper part of FIG. 3, and the fiber bundle is imaged brighter than the background. In this case, nothing is arranged in the field of view of the imaging means on the opposite side of the imaging means across the fiber bundle in order to prevent the background from being illuminated by the reflection of the lighting means.
It is preferable not to do so, but when some kind of equipment is arranged due to the convenience of installation space or the like, a light absorbing plate or the like may be placed between the equipment and the fiber bundle to prevent reflection of the illumination light from the equipment. As the light absorbing plate, for example, a black acrylic plate whose surface is not a mirror surface can be used. Further, as shown in FIG. 2, the imaging means may be arranged at a position facing the illumination with the fiber bundle sandwiched between them. In this case, the background is white as shown in the lower part of FIG. 3, and the fiber bundle is imaged darker than the background. With the configuration shown in FIG. 2, if the illumination intensity is too strong, the information of the transmitted light of the fiber bundle may be crushed due to halation during imaging, or the light from the background may wrap around on the fiber bundle due to diffraction. If the fiber bundle has high transparency, it is better to illuminate the fiber bundle perpendicularly and perform imaging at an angle because the information may be lost. It is preferable because it is easy.

As an imaging means for imaging a fiber bundle together with a background, a sensor in which light receiving elements (pixels) such as a CCD that receives light are arranged linearly or two-dimensionally to obtain data on brightness can be adopted. .. In particular, when simultaneously inspecting defects in a large number of fiber bundles running in parallel over a wide range, a line in which light receiving elements are linearly arranged, which has excellent width direction resolution and enables a wide range of inspections. A sensor camera is preferred.

In order to detect defects with high accuracy, it is preferable to take an image with a resolution of 5 times or more the defect size to be detected. For example, when detecting a defect having a size of 1 mm in both the width direction and the longitudinal direction, the imaging resolution is preferably finer than 0.2 mm. However, if the imaging resolution is made too fine, the amount of data becomes too large, and the data processing speed becomes slow.

Therefore, the measurement frequency needs to be adjusted according to the line speed of the manufacturing process. When the size of the defect to be detected in the longitudinal direction is 1 mm, it is possible to detect it accurately if the imaging resolution is finer than 0.2 mm. Therefore, for example, if the line speed is 500 m / min, the flow direction is measured. The frequency is set to about 40 kHz.

The image captured by the imaging means is determined by the data processing means with the region where the fiber bundle exists as the target region. The method of determining the target area is not particularly limited, but if the traveling position and edge of the fiber bundle are stable, the coordinates may be directly specified on the image, the fiber bundle may meander, or the fiber bundle may be determined. If the width of the image changes and the edge position changes, set a threshold value for the brightness value between the background and the fiber bundle, and target the area above or below the threshold value for each image as the area where the fiber bundle exists. The region may be determined. For example, when the image is taken in the first mode shown in FIG. 1, the area where the fiber bundle is present is imaged brighter than the background as shown in FIG. 3, so a threshold value is set between the background and the brightness value of the fiber bundle. However, the region exceeding the threshold value is determined as the region where the fiber bundle exists.

Next, defects are detected based on the pixel information from the image obtained in the imaging step. As a method for detecting a defect, for example, a threshold value of a pixel value is set, and a region exceeding or falling below the threshold value is detected as a defect. For example, if the target region is determined first, the average or median of the brightness values in the target region is set as the threshold value, and the portion below the threshold value is detected as a defect. Other methods include a method of detecting a difference as a defect while comparing with the shading level of the surroundings, and a method of detecting a defect having a specific shape by pattern matching. At that time, the area and length (distance in the long side direction), width (distance in the short side direction), angle with respect to the flow direction of the fiber, roundness, straightness, average brightness value, etc. occupied in the image of the detected defect. Is obtained as a feature quantity.

Next, the types of defects are classified based on the detected feature quantities of the defects. For example, defects with a large length and a small width, a straight line and a high straightness, and an angle different from the fiber flow direction are skewed, those with a large length and width are pills, and the average brightness value is the background brightness. Those close to the value are classified as cracks.
.. Either the step of determining the region where the fiber bundle exists as the target region or the step of detecting defects from the image may come first.

If the defect information obtained by these data processing means is detected at a level exceeding a predetermined judgment standard value, some abnormality has occurred during the process, and an alarm device for issuing an alarm is provided. It is preferable to have. By issuing an alarm, the wound product can be classified in units of packages, which prevents leakage to users and is preferable in quality control. For example, as a judgment reference value, there is a method of issuing an immediate alarm when the number of detected defects, the size, or even one specific defect type occurs.

As the alarm device, an alarm sound, an alarm light that blinks a light, or a means for transmitting an alarm signal to an operator by using a communication device such as a wire or a wireless device can be preferably used.

In addition, by combining these processing devices with an automatic cutter, suction device, etc., when the threshold value is continuously exceeded, the running thread is immediately cut to prevent abnormal thread outflow to the user at an early stage. You can also.

The detected defect information is recorded for each running thread and each running time. By recording the detected defect information for each traveling thread and each traveling time, it is possible to accurately grasp the defects existing in the package of the precursor fiber bundle. Here, the package of the precursor fiber bundle means a wound body in which the spun precursor fiber bundle is wound around a core such as a bobbin, or a package in which the spun precursor fiber bundle is transferred into a container.

In the present invention, based on the information on the type, size, frequency, and location of defects recorded by continuously evaluating and recording the traveling precursor fibers, the process may be wound around the roll in the firing process and the process passability may be deteriorated. , The part that may lead to abnormal cutting in a flame-resistant oven or carbonization furnace, and the part that may cause skewing or poor fiber opening in the manufactured carbon fiber bundle (hereinafter referred to as "defect concern part"). ) Is specified and removed.

A method for removing the defective portion from the carbon fiber precursor fiber bundle is not specified, but for example, in the step of sequentially feeding out the fiber bundle from the package of the precursor fiber bundle and repackaging it, the normal portion of the precursor fiber bundle (defect). If a defect is reached in the process of repackaging (the part that is not the part of concern), the repackaging of the downstream side is temporarily stopped and the extension of the upstream side is continued until the next normal part is reached, in the meantime. This can be done by cutting out the part that is concerned about the defect that has been drawn out, connecting the end of the normal part that has been drawn out earlier and the start end of the newly drawn out normal part, and restarting the repackaging on the downstream side. In this operation, in response to the operation of removing the defect concern portion, the defect information continuously evaluated and recorded is edited, and the evaluation information of the carbon fiber precursor fiber bundle from which the defect concern portion is removed is created. Is preferable.
It is also possible to remove the defect-concerned portion by removing the package having a defect exceeding the judgment standard from the information of the defect existing in each package obtained in the spinning process.

The present invention will be described below with reference to Examples.

A KDPL2-LK1000W manufactured by Kyoto Electric Equipment Co., Ltd. is used as the lighting means, and an image sensor XG-8700L manufactured by KEYENCE Co., Ltd. is used as the imaging means. Specifically, an 8192 pixel line camera XG-HL08M is connected, and all captured images are saved in the storage.

When a polyacrylonitrile fiber bundle (single fiber fineness 1.0 dtex) consisting of 60,000 fibers is used as the fiber bundle to be evaluated, the illumination is installed at a distance of 200 mm from the light-flooded portion with respect to the traveling fiber bundle for imaging. It is preferable that the means is installed so as to be tilted 70 ° with respect to the fiber bundle and is installed at a distance of 1200 mm from the tip of the lens.

Shooting is performed by running 12 fiber bundles in parallel at 65 m / min, and the imaging resolution in the longitudinal direction and the width direction can be about 0.1 mm. By recording the information that the defect was detected for each fiber bundle in the data processing means for 3 days, it is possible to obtain the information that evaluated the precursor fiber bundle of 3.37 million meters.

By firing the obtained precursor fiber bundle and comparing the occurrence status of defects in the firing process with the record of evaluating the precursor fiber bundle, the type, size, and the type and size of defects that may cause defects in the firing process. The frequency can be estimated and used as a criterion for the part of concern about defects.

The openness and cracking of the carbon fiber bundle obtained by firing are evaluated, and the record of evaluating the precursor fiber bundle is collated, and the type and size of defects that may cause a defect in the carbon fiber bundle, The frequency can be estimated and used as a criterion for the part of concern about defects.

Precursor fiber bundles manufactured under the same conditions as the precursor fiber bundle for which the criteria for determining the defect concern part were obtained are continuously evaluated under the same conditions and information is recorded. By firing the precursor fiber bundle removed from the body fiber bundle, it is possible to avoid defects in the firing step and obtain carbon fiber bundles and carbon fibers with reduced defects.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to avoid deterioration of process passability in the firing process, improve the production efficiency of the carbon fiber bundle, and prevent the carbon fiber bundle from flowing out to the outside including defects such as skewing and cracking. Therefore, the quality control of carbon fiber fiber bundles and carbon fibers can be carried out at a high level.

1: Fiber bundle 2: Illumination means 3: Measurement light 4: Transmitted light 5: Imaging means 6: Data processing means 7: Recording means

Claims (2)

In the process of manufacturing the carbon fiber precursor fiber bundle, the running carbon fiber precursor fiber bundle was continuously evaluated and information was recorded, the defect concern part was determined based on the recorded information, and the defect concern part was removed. A method for producing carbon fibers by firing a carbon fiber precursor fiber bundle. The method for producing carbon fiber according to claim 1, wherein the traveling carbon fiber precursor fiber bundle is continuously evaluated and information is recorded by the evaluation method having the following steps [A] to [D].
[A] Step of irradiating the traveling carbon fiber precursor fiber bundle with measurement light [B] Step of imaging the transmitted light from the carbon fiber precursor fiber bundle [C] The means of the following (a) to (c) Data processing step (a) A data processing means for determining a region in which a fiber bundle exists from an image obtained in the imaging step as a target region.
(B) A data processing means for detecting defects based on pixel information from an image obtained in the imaging step.
(C) A data processing means for classifying defect types according to the detected feature amount of the defect.
[D] Recording means for recording information on the defect.

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