Method for detecting and judging section of carbon fiber precursor

Abstract

The invention belongs to the technical field of carbon fiber material testing, and discloses a method for detecting and judging the section of a carbon fiber precursor, which comprises the following steps: (1) preparing a precursor section slice sample: fixing a carbon fiber precursor bundle in a sampler, and cutting off the part, exposed out of the sampler, of the bundle to obtain the precursor section slice sample with the thickness of 0.8-1.2 mm; and (2) observing the cross section: placing the protofilament cross section slice sample prepared in the step (1) under an optical microscope, imaging by utilizing a transmission light source to penetrate through the protofilament cross section slice sample, and observing. According to the invention, the principle that the carbon fiber precursor has certain light transmission is utilized, a very thin section slice is cut from the precursor, the transmission light source can be directly utilized under an optical microscope for imaging, the section shape can be observed, the sample preparation process is simple, the detection time of a single sample is shortened, and the working efficiency is improved.

Description

Technical Field

[0001] This invention belongs to the field of carbon fiber material testing technology, specifically, it relates to a method for detecting and determining the cross-section of carbon fiber precursor. Background Technology

[0002] In the production of carbon fiber precursor, the uniformity of fineness is an important indicator for evaluating product quality. High-quality precursor products typically have a fineness CV value (coefficient of variation) of 2% to 8%. When used to manufacture carbon fibers, these low fineness CV values ​​can improve the stability of the mechanical properties of the carbon fibers.

[0003] The initial method for testing the fineness CV value of raw yarn products was to use a tensile strength integrated testing machine. However, each machine required approximately 30 minutes to test each sample, and could only test about 20 samples per machine. For a production scale with 400 to 500 raw yarn spindles, the testing efficiency of the integrated tensile strength machine could not match the production efficiency. Therefore, there is an urgent need for a testing method that can improve the efficiency of fineness CV value testing.

[0004] For carbon fiber precursor, the fineness of a single filament is directly related to the cross-sectional size of the fiber. Therefore, the fineness CV value of the precursor product can be determined by statistically analyzing the differences in cross-sectional size among the individual filaments in the fiber bundle. Current sample preparation methods for observing fiber cross-sections typically involve embedding the fiber bundle in an adhesive, followed by grinding and polishing the embedded sample to expose the fiber cross-section on the sample surface for observation. This sample preparation process is complex, time-consuming, and inefficient. Simplifying the sample preparation steps and shortening the preparation time are crucial for improving the efficiency of carbon fiber precursor cross-section testing.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for detecting and judging the cross-section of carbon fiber precursor that can quickly prepare samples and thus improve detection efficiency.

[0007] To solve the above-mentioned technical problems, the basic concept of the technical solution adopted by the present invention is as follows: A method for detecting and determining the cross-section of carbon fiber precursor fibers, comprising the following steps: (1) Making a cross-sectional slice sample of the original fiber: Fix the carbon fiber original fiber bundle in the sampler, cut off the part of the bundle exposed outside the sampler, and obtain a cross-sectional slice sample of the original fiber with a thickness of 0.8~1.2mm; (2) Observe the cross section: Place the original fiber cross section sample obtained in step (1) under an optical microscope and use a transmitted light source to image the original fiber cross section sample for observation.

[0008] In the above scheme, the raw fiber cross-section sample refers to a cross-section cut perpendicular to the length direction of the raw fiber, and the thickness direction of the sample is the same as the length direction of the raw fiber. When observed under an optical microscope, the raw fiber cross-section faces the objective lens of the optical microscope, that is, the raw fiber cross-section is basically parallel to the horizontal plane.

[0009] In this invention, a carbon fiber precursor bundle is fixed using a sampler, and the carbon fiber precursor is cut to obtain cross-sectional slices with a thickness of 0.8~1.2mm. Utilizing the principle that carbon fiber precursor has a certain degree of light transmittance, the thinned cross-sectional slices are placed under an optical microscope, allowing direct observation of the cross-sectional shape using a transmitted light source. This allows for qualitative or quantitative judgment of the fineness uniformity of the carbon fiber precursor through the observed cross-section. The aforementioned detection and judgment method features a simple sample preparation process, rapid imaging, shortened single-sample detection time, and improved work efficiency.

[0010] Meanwhile, compared to traditional detection methods that use reflected light sources to observe the cross-section, the present invention cuts the fiber into thin samples and then transmits light to observe the cross-section. This significantly improves resolution compared to reflected light sources, allowing for a clearer presentation of fine structures and enhancing the accuracy of edge detection. Furthermore, the imaging clarity of reflected light sources is greatly affected by the flatness of the sample cross-section; even slight differences in sample height can lead to variations in clarity across different areas of the image. In contrast, utilizing the planarity of transmitted light imaging ensures highly consistent clarity across different areas of the image, with no significant differences in depth of field.

[0011] In a preferred embodiment of the present invention, in step (1), the thickness of the original fiber cross-section slice sample is 0.9~1.1mm, more preferably 1mm.

[0012] In a further embodiment, the sampler includes a metal plate with through holes, the thickness of which is 0.8~1.2mm; In step (1), the filament bundle is inserted into the through hole on the metal plate, and the exposed part of the filament bundle is cut off with a blade close to both sides of the metal plate to obtain a cross-sectional slice sample of the original filament located in the through hole. In step (2), the metal plate with the original wire cross-section slice sample is placed under an optical microscope for observation; Preferably, the metal plate is made of stainless steel; Preferably, the thickness of the metal plate is 0.9~1.1mm, and more preferably 1.0mm.

[0013] In the above scheme, the blade cuts the filament bundle close to both sides of the metal plate. The thickness of the resulting raw filament cross-section slice sample can be controlled by utilizing the thickness of the metal plate. The operation is simple and easy to perform, and the thickness control of the raw filament cross-section slice is precise. During observation, the raw filament cross-section slice sample does not need to be removed; the metal plate can be placed directly under an optical microscope, making the operation convenient.

[0014] In a further embodiment, the through hole is a circular hole; Preferably, the diameter of the circular hole is 1.0~1.5mm.

[0015] In the above scheme, the through hole is a circular hole, which matches the overall cross-sectional shape of the wire bundle. This makes it easier to fill the circular hole after the wire bundle is inserted, which is beneficial for cutting the cross-section flat when cutting the wire bundle later. At the same time, the circular hole is easier to process, and it is easier to process the hole's peripheral wall into a smooth surface with low roughness, avoiding damage to the wire bundle from the rough surface of the hole's peripheral wall.

[0016] A further solution is to plug the circular hole in the metal plate when inserting the filament bundle into it, so that the carbon fiber filament bundle is fixed in the circular hole and will not move easily.

[0017] In one specific implementation, for a 1K carbon fiber precursor bundle, eight bundles are combined and then inserted into the circular hole.

[0018] As one specific implementation, for a 3K carbon fiber precursor bundle, the three bundles are combined and then inserted into the circular hole.

[0019] As one specific implementation, for a 6K carbon fiber precursor bundle, two bundles are combined and then inserted into the circular hole.

[0020] As one specific implementation, for carbon fiber precursor bundles of 12~48K, a bundle of fibers is directly inserted into the circular hole, or a portion of the fibers is separated from a bundle of fibers and inserted into the circular hole.

[0021] Using the above method, for raw yarn bundles with a lower K number, multiple bundles are combined before being inserted into the through-holes in the metal plate. In this way, raw yarns with different K numbers can be sampled using samplers of the same specifications (i.e., the circular holes in the metal plate have the same diameter), which is more convenient for operation.

[0022] In a further step, in step (1), the ends of the filament bundle are first trimmed with scissors to make them sharp, and then the sharpened end is inserted into and passes through the through hole on the metal plate.

[0023] Trimming the ends of the filament bundle into pointed structures makes it easier to insert the bundle into small circular holes, preventing some individual filaments from failing to enter the circular holes and affecting the sample preparation effect.

[0024] In a further embodiment, the optical microscope has an upper light source that illuminates the sample surface from above, and a lower light source that transmits light through the sample from below. In step (2), the upper light source is turned on first so that the light shines on the sample surface from the top. The observation field is adjusted so that the original silk cross-section slice sample is within the field of view that can be observed. Then the lower light source is turned on to transmit light through the sample. Finally, the observation is carried out with the upper light source off and the lower light source on.

[0025] In a further step (2), after adjusting the field of view, the upper light source is turned off first, then the lower light source is turned on, and then the focal length and / or the light source brightness are adjusted to make the image clear.

[0026] In a further step, in step (1), carbon fiber precursor bundles with a moisture regain of no more than 2% are used to make precursor cross-section slice samples. Preferably, step (A) is included before step (1): the carbon fiber precursor bundle is left to stand at standard temperature and humidity until the moisture regain reaches less than 2%, and then step (1) is performed.

[0027] In the above scheme, the standard temperature and humidity refer to a temperature of 20±2℃ and a relative humidity of 65±5%.

[0028] In a further embodiment, the optical microscope is connected to a digital image acquisition device; Step (2) is followed by step (3): using the digital image acquisition device to take a picture of the cross-sectional slice sample of the original silk under an optical microscope to obtain a cross-sectional image.

[0029] By setting up digital image acquisition equipment, on the one hand, the images in the optical microscope can be observed directly on the digital image acquisition equipment, resulting in a clearer field of view. On the other hand, cross-sectional images can be photographed and saved, facilitating archiving and subsequent research.

[0030] In a further step, after obtaining the cross-sectional image in step (3), the cross-sectional image is analyzed to determine the fineness CV value of the carbon fiber precursor bundle. Preferably, in step (3), a scale consistent with the magnification of the objective lens currently used in the optical microscope is selected, and a cross-sectional image is taken. Several different cross-sectional dimensions of the monofilaments are measured from the cross-sectional image, and the fineness CV value of the carbon fiber precursor bundle is calculated. Herein, the cross-sectional dimension refers to the length of the cross-section measured in a specific direction, and then the coefficient of variation of the multiple measured cross-sectional dimensions is calculated as the fineness CV value.

[0031] In the above scheme, a scale that matches the magnification of the objective lens currently used by the optical microscope is first selected, and then a cross-sectional image is taken. The cross-sectional dimensions of the single filament can be directly measured in the cross-sectional image, so that the measured readings are consistent with the actual dimensions.

[0032] In this invention, the obtained cross-sectional images show significant color differences between the cross-sectional locations of individual filaments and the gaps between different filament cross-sections. As one specific implementation, existing image analysis techniques can be used to analyze the cross-sectional images, identify the cross-sections of each filament, and measure the cross-sectional dimensions of the filaments to calculate the fineness CV value. As another specific implementation, the inspector can also directly measure the cross-sectional dimensions of the filaments from the obtained cross-sectional images and calculate the fineness CV value.

[0033] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art.

[0034] The present invention offers a simple sample preparation process and rapid imaging, reducing the single-sample testing time to 3 minutes. It can process at least 400 samples per day, significantly improving work efficiency. Using this method, the uniformity of the fiber fineness of the raw yarn can be determined quickly and promptly, facilitating adjustments by production personnel before the raw yarn is packaged into bobbins to ensure uniformity. For manufacturers with a production scale of 50,000 tons, this can reduce adjustment time by approximately 810 minutes daily, reduce defective products by 118 kg, and reduce defective products by approximately 43 tons annually, resulting in savings and efficiency gains of 860,000 yuan per year.

[0035] The specific embodiments of the present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0036] The accompanying drawings, as part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention, but do not constitute an undue limitation of the invention. Obviously, the drawings described below are merely some embodiments, and those skilled in the art can obtain other drawings based on these drawings without creative effort. In the drawings: Figure 1 This is a schematic diagram of the sampler in an embodiment of the present invention; Figure 2 This is a cross-sectional image obtained by taking a photograph in an embodiment of the present invention.

[0037] In the diagram: 1. Metal plate; 2. Through hole.

[0038] It should be noted that these accompanying drawings and textual descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art by referring to specific embodiments. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0040] Embodiments of the present invention provide a method for detecting and determining the cross-section of carbon fiber precursor, comprising the following steps: (1) Making a cross-sectional slice sample of the original fiber: Fix the carbon fiber original fiber bundle in the sampler, cut off the part of the bundle exposed outside the sampler, and obtain a cross-sectional slice sample of the original fiber with a thickness of 0.8~1.2mm; (2) Observe the cross section: Place the original fiber cross section sample obtained in step (1) under an optical microscope and use a transmitted light source to image the original fiber cross section sample for observation.

[0041] In the above scheme, cross-sectional samples of the precursor fibers with a thickness of 0.8~1.2mm are prepared. Utilizing the principle that carbon fiber precursor fibers have a certain degree of light transmittance, the cross-sectional shape can be directly observed under an optical microscope using a transmitted light source. The sample preparation process is simple, efficient, and rapid, with the carbon fiber precursor fiber bundle being directly cut after being fixed by a sampler. This reduces the detection time for a single sample and improves work efficiency. Furthermore, the transmitted light source provides no significant difference in depth of field between the front and back of the sample cross-section. Compared to traditional detection methods that use reflected light sources, this method yields cross-sectional images with highly consistent clarity across different regions and more clearly reveals fine structures, facilitating accurate determination of the edge positions of the single-fiber cross-section.

[0042] The thickness of the raw fiber cross-section slice sample is controlled between 0.8 and 1.2 mm. This ensures that the light source can pass through the sample to achieve clear imaging, while also preventing the fiber from being easily damaged during the sample preparation process if the thickness is too thin, thus ensuring the integrity of the raw fiber cross-section in the prepared sample.

[0043] As a preferred embodiment, the thickness of the raw fiber cross-section slice sample is controlled between 0.9 and 1.1 mm to obtain a clearer cross-sectional image. In the optimal embodiment, the thickness of the raw fiber cross-section slice sample is controlled at 1.0 mm.

[0044] Furthermore, the sampler used in the embodiments of the present invention is as follows: Figure 1 As shown, it includes a metal plate 1 with through holes 2. The thickness of the metal plate 1 determines the thickness of the final sample, that is, the thickness of the metal plate 1 is selected to be 0.8~1.2mm, preferably 0.9~1.1mm, and more preferably 1.0mm.

[0045] In step (1), the filament bundle is inserted into the through hole 2 on the metal plate 1, and then the exposed part of the filament bundle is cut off by using a blade close to both sides of the metal plate 1, thereby obtaining a raw filament cross-section slice sample with a thickness of 0.8~1.2mm located in the through hole 2. In step (2), no additional fixing treatment is required for the cut filament bundle. The metal plate 1 is directly placed under an optical microscope, and the raw filament cross-section slice sample can be transferred to the optical microscope for observation along with the sampler, simplifying the operation steps.

[0046] In the embodiments of the present invention, the metal plate 1 is preferably a stainless steel plate, which avoids the problem of rust.

[0047] In a specific embodiment of the present invention, the metal plate 1 is a smooth stainless steel plate.

[0048] A metal plate 1 of specific thickness is used as a sampler. During sample preparation, the exposed portion of the filament is cut off by placing a blade close to both sides of the metal plate 1. The thickness of the resulting filament cross-section slice is basically the same as the thickness of the metal plate 1. The operation is simple and easy, and precise control over the thickness of the filament cross-section slice can be achieved, resulting in good imaging effects. During observation, the sample does not need to be separated from the metal plate 1; instead, it can be directly transferred to the optical microscope using the metal plate 1. This operation is convenient and ensures that the filament cross-section to be observed faces the objective lens of the optical microscope, guaranteeing imaging quality.

[0049] In practice, the blade should be used slowly and gradually to cut the fiber bundle, ensuring the resulting cross-section is roughly flush with the surface of the metal plate 1. Specifically, the inspector holds the blade close to the surface of the metal plate 1 and performs multiple cutting motions, each cutting only a portion of the fibers in the bundle, rather than severing the bundle completely in one go. Maintaining a slow cutting speed prevents excessive speed from causing fiber cracking, altering the fiber cross-sectional shape, and affecting the test results. A smooth surface on the metal plate 1 reduces friction between the blade and the surface, preventing the blade from jamming during cutting and avoiding uneven cross-sections.

[0050] In embodiments of the present invention, when inserting the carbon fiber filament bundle into the through hole 2 on the metal plate 1, the through hole 2 must be tightly sealed to fix the filament bundle in place and prevent it from easily moving during the cutting process. Specifically, in actual operation, after the filament bundle is inserted into the through hole 2, the exposed part of the filament bundle can be gently pulled; the filament bundle should not move when pulled.

[0051] In one specific implementation, the through hole 2 on the metal plate 1 is a circular hole with a diameter of 1.0~1.5mm. Using a circular hole as the through hole 2 for fixing the wire bundle, its shape matches the overall cross-sectional shape of the wire bundle, making it easier to fill the through hole 2 after the wire bundle is inserted, resulting in a better fixing effect on the wire bundle, and making it easier to ensure that the cross-section is cut flat when cutting the wire bundle later.

[0052] In a preferred embodiment, the diameter of the circular hole is 1.0 mm.

[0053] In the above scheme, if the diameter of the circular hole is too small, it will be difficult to insert the wire bundle completely into the circular hole during actual operation, which will affect the sample preparation efficiency. On the other hand, if the diameter of the circular hole is too large, it will be difficult to seal the circular hole tightly, and the wire bundle will easily move during the cutting process, affecting the sample preparation effect.

[0054] For carbon fiber precursor products with different K numbers, the size of a single filament bundle usually varies considerably. In order to enable carbon fiber precursor products with different K numbers to use the same sampler, that is, to use a metal plate 1 with the same diameter of through hole 2 for sample preparation, the embodiments of the present invention further adopt the following scheme.

[0055] In one specific implementation, for a 1K carbon fiber precursor bundle, eight bundles are combined and then inserted into the through hole 2 on the metal plate 1. For a 3K carbon fiber precursor bundle, three bundles are combined and then inserted into the through hole 2. For a 6K carbon fiber precursor bundle, two bundles are combined and then inserted into the through hole 2. For 12~48K carbon fiber precursor bundles, one bundle of fibers can be directly inserted into the through hole 2, or a portion of the fibers can be separated from one bundle to form the bundle to be tested and inserted into the through hole 2.

[0056] In the above scheme, for raw filament products with a small K-number, two or more bundles of filaments can be combined and then inserted into the through hole 2 on the metal plate 1 to ensure that the raw filament bundle inserted into the through hole 2 can tightly fill the through hole 2. For raw filament products with a large K-number, if a single bundle of fibers cannot be inserted into the through hole 2, some fibers can be separated from a single bundle of fibers to form a smaller overall bundle, which can then be inserted into the through hole 2.

[0057] Using the above method, there is no need for complex processing such as pre-embedding the fibers. The original fiber bundle can be fixed relatively stably in the through hole 2, and the cross section can be easily cut with a blade. Compared with the sample preparation process in the prior art, which requires pre-embedding and then grinding and polishing, the sample preparation efficiency is greatly improved.

[0058] In one specific embodiment of the present invention, in actual operation, when it is necessary to merge two or more bundles of filaments, a single filament bundle can be taken, and then formed into two or more bundles by folding it in half, and then inserted into the through hole 2. The operation is simple and easy.

[0059] It should be noted that, in the above scheme, the definition of a single filament bundle refers to a single filament bundle produced during the carbon fiber precursor process.

[0060] In a further scheme, in step (1), the ends of the filament bundle are first trimmed with scissors to make the ends of the filament bundle sharp, and then the sharpened end is inserted into and passes through the through hole 2 on the metal plate 1.

[0061] In one specific implementation, the inspector holds the filament bundle near its end with one hand and uses scissors in the other to trim the end of the filament bundle into a pointed shape. Since the diameter of the through hole 2 is very small and close to the outer diameter of the filament bundle, trimming the end of the filament bundle in advance makes it easier to insert the filament bundle completely into the through hole 2, avoiding the situation where some individual filaments fail to enter the through hole 2 and thus affect the sample preparation effect.

[0062] In a further embodiment of the invention, the optical microscope used has an upper light source and a lower light source. When observing a sample using the optical microscope, the upper light source illuminates the sample surface from above, and the lower light source is a transmission light source that transmits light through the sample from below to form an image. In step (2), the sample is placed under the optical microscope. First, the upper light source is turned on so that light illuminates the sample surface from above. The field of view is adjusted so that the cross-sectional slice of the protofilament is within the observable field of view. Then, the lower light source is turned on to transmit light through the sample. Finally, observation is performed with the upper light source off and the lower light source on.

[0063] Furthermore, in step (2), after completing the operation of adjusting the field of view, the upper light source is turned off first, and then the lower light source is turned on. After that, the focal length and / or the light source brightness are adjusted to make the image display clear.

[0064] As a specific implementation method, after placing the metal plate 1 with the sample under an optical microscope, first turn on the upper light source to illuminate the sample, adjust the field of view so that the target observation area (that is, the area where the original wire cross-section slice sample is located) falls into the field of view, then turn off the upper light source and turn on the lower light source, and then adjust the focus and light source brightness to make the image clear.

[0065] In the above scheme, the sample is first illuminated by an upper light source, which facilitates quick location of the target observation area and avoids the tedious sample finding problem under pure transmission light, thus improving operational efficiency. Then, switching to a lower light source for separate transmission imaging, combined with adjustments to the focus and light source brightness, ensures clear imaging and improves observation efficiency.

[0066] In a further embodiment of the present invention, in step (1), carbon fiber precursor bundles with a moisture regain of no more than 2% are used to make precursor cross-section slice samples.

[0067] As one specific implementation, step (A) is included before step (1): the carbon fiber precursor bundle is left to stand under standard temperature and humidity until the moisture regain reaches below 2%, and then step (1) is performed. The standard temperature and humidity refer to: temperature of 20℃±2℃ and relative humidity of 65%±5%.

[0068] As another specific implementation method, if the moisture regain of the carbon fiber precursor bundle to be tested is below 2%, then the above step (A) is not required, and the sample preparation process in step (1) can be carried out directly.

[0069] Moisture regain refers to the percentage of water weight in a material relative to its dry weight. For fiber materials, the moisture regain at which the absorption and release of moisture reach equilibrium under certain atmospheric conditions is called the equilibrium moisture regain. The equilibrium moisture regain of carbon fiber precursor is typically between 1% and 2%. However, due to environmental conditions, the moisture regain of the carbon fiber precursor sample may exceed 2% when taken for testing.

[0070] When the moisture regain of carbon fiber precursor is too high, it can cause internal expansion of the fiber, resulting in unstable cross-sectional shape and even irregular changes in cross-sectional shape compared to the actual shape. Because of this difference between the fiber cross-section and the actual cross-section, the accuracy of the test results will be affected.

[0071] In the above scheme, for carbon fiber precursor bundles with a moisture regain of more than 2%, they are first allowed to stand at standard temperature and humidity to reach equilibrium, so that the moisture regain approaches the equilibrium level. When the moisture regain decreases to 2% or lower, samples are prepared, and the cross-section of the carbon fiber precursor is observed after sample preparation, which enables more accurate testing.

[0072] For carbon fiber precursor bundles with an initial moisture regain of no more than 2%, although their current moisture regain may not have reached the equilibrium moisture regain, experiments have shown that cross-sectional testing at the current moisture regain level has little impact on the test results. To ensure testing efficiency, carbon fiber precursor bundles with a moisture regain below 2% can be directly sampled without equilibration.

[0073] On the other hand, excessive moisture regain can also lead to changes in the internal structure of carbon fiber precursor, thereby affecting its mechanical properties. Sample preparation under excessive moisture regain conditions may increase the difficulty of cutting the fiber cross-section flat, and the fiber may be prone to cracking when cut, affecting the test results.

[0074] In a further embodiment of the present invention, the optical microscope used in step (2) is connected to a digital image acquisition device.

[0075] Step (2) is followed by step (3): using the digital image acquisition device to take a picture of the cross-sectional slice sample of the original silk under an optical microscope to obtain a cross-sectional image.

[0076] In one specific implementation, an embodiment of the present invention employs a metallurgical microscope system that combines optical microscopy, photoelectric conversion, and computer image processing technologies to observe and photograph the prepared samples.

[0077] More specifically, the metallurgical microscope system organically combines an optical microscope with a computer or digital camera through photoelectric conversion. In other words, the digital image acquisition device described in the above scheme can be a computer or a digital camera.

[0078] In one specific embodiment, a metallurgical microscope 9XB-PC is used. This metallurgical microscope has a transmission observation function, which meets the requirement of the present invention to observe the cross-sectional slice sample of the original wire by irradiating it with a transmission light source.

[0079] The metallurgical microscope system is used during the testing process. The testers can not only observe the sample through the eyepiece of the microscope, but also directly display the magnified image of the microscope on the screen of a computer or similar electronic device. The field of view is clearer and it is also convenient to take pictures and save them.

[0080] Furthermore, after obtaining a cross-sectional image by taking a photograph, the obtained cross-sectional image can be analyzed to determine the fineness CV value of the carbon fiber precursor, or other parameters related to the fiber cross-section.

[0081] The aforementioned fineness CV value, or other parameters related to fiber cross-section, can be obtained by using image analysis methods to identify and extract the cross-sectional edge of the monofilament from the obtained cross-sectional image, automatically measuring and calculating the cross-sectional dimensions. The data processing is rapid, allowing production personnel to make timely adjustments based on the results before the raw yarn is formed into a bobbin, effectively ensuring the uniformity of the fineness of the raw yarn product, significantly reducing the production of defective products, and achieving the goal of saving costs and increasing efficiency.

[0082] Alternatively, the inspector can visually identify the cross-sectional edge of the monofilament in the cross-sectional image, mark the edge position, and then measure the cross-sectional dimensions using software, or manually measure and combine with a scale to determine the cross-sectional dimensions, and then calculate the fineness CV value, or other parameters related to the fiber cross-section.

[0083] As a preferred embodiment, in step (3), a scale that is consistent with the magnification of the objective lens currently used by the optical microscope is selected, and a cross-sectional image is taken. The cross-sectional dimensions of several different monofilaments are measured from the cross-sectional image, and the fineness CV value of the carbon fiber precursor bundle is calculated.

[0084] The above method is suitable for inspectors to independently calibrate the cross-sectional edges and measure the cross-sectional dimensions. Specifically, first, a scale matching the magnification of the objective lens currently used by the optical microscope is selected, then a cross-sectional image is taken. The operator can then directly mark the positions of the two ends of the dimension to be measured in the cross-sectional image based on the cross-sectional edges, and the measured cross-sectional dimensions can be directly output.

[0085] Figure 2 The image shown is a cross-sectional image obtained using the detection and judgment method provided in this embodiment of the invention. The light-colored area represents the cross-section of each filament, and the dark-colored area represents the gap between different filament cross-sections. It can be seen that there is a clear color difference between the two areas, and the boundary line between each filament cross-section is also clearly visible.

[0086] To calculate the fineness CV value, as a specific implementation method, existing image analysis techniques are used to process and analyze the aforementioned cross-sectional image. This allows for the extraction of the cross-section of each filament from the image based on color differences, and then the cross-sectional dimensions of each filament can be calculated based on the image magnification. By statistically calculating the cross-sectional dimensions of different filaments in the cross-sectional image, the fineness CV value can be obtained.

[0087] Alternatively, inspectors can clearly identify the edges of each monofilament cross-section by comparing the color depth of different areas in the cross-sectional image, thereby manually marking the position of the cross-sectional edges and obtaining data on the dimensions of different monofilament cross-sections, which can then be used to calculate the fineness CV value.

[0088] It should be noted that, in the embodiments of the present invention, the fineness CV value refers to the coefficient of variation calculated from multiple length sample data after measuring the length of the monofilament cross section in a specific direction, which is used as the fineness CV value.

[0089] In other words, in the above scheme, the cross-sectional dimension of a monofilament refers to the length of the cross-section in a specific direction. For example, if the cross-section is basically circular, the cross-sectional dimension is the diameter of the circular cross-section. If the cross-section is elliptical, the cross-sectional dimensions of each monofilament need to be measured in the same specific direction. That is, either the major axis length can be measured as the cross-sectional dimension for calculating the fineness CV value, or the minor axis length can be measured as the cross-sectional dimension for calculating the fineness CV value.

[0090] As one specific implementation method, such as Figure 2 In the cross-sectional image shown, the shape of the monofilament cross-section resembles a broad bean. In actual testing, it is preferable to measure the distance between the two ends along the length of the cross-section as the cross-sectional dimension.

[0091] In embodiments of the present invention, the formula for calculating the fineness CV value is as follows: in, S This represents the sample standard deviation of the cross-sectional dimensions of each individual filament section measured. This is the sample mean of the cross-sectional dimensions of each measured monofilament section.

[0092] Specifically, sample mean and sample standard deviation S The calculation formula is as follows: in, n This refers to the sample size, which is the number of monofilament cross-sections measured. This refers to the cross-sectional dimensions of a single sample.

[0093] As one specific implementation method, a qualified standard for the fineness CV value is predetermined, that is, a preset qualified threshold. If the calculated fineness CV value is not higher than the qualified threshold, it means that the fineness uniformity of the raw yarn product obtained under the current production conditions meets the requirements. However, if the calculated fineness CV value is higher than the qualified threshold, the production conditions need to be adjusted in time, such as replacing the spinneret.

[0094] In a further embodiment of the present invention, after obtaining the cross-sectional image, the shape and size information of each filament cross-section in the cross-sectional image can be used to determine whether the sample being tested has any non-conforming issues. These non-conforming issues include thin filaments, stiff filaments, and fused filaments.

[0095] In one specific implementation, if the obtained cross-sectional image contains a single filament cross-section with a cross-sectional size smaller than 1 / 2 of the normal cross-sectional size, then the single filament is a thin filament.

[0096] It should be noted that the "normal cross-sectional size" mentioned in the embodiments of the present invention is related to the specifications of the carbon fiber precursor product. Specifically, when producing the precursor product, the target fineness is determined according to actual needs, and the actual fineness of the produced precursor product is made as close as possible to the target fineness by controlling the production process. After the carbon fiber precursor is produced, samples are taken to determine whether the fineness meets the requirements. If the fineness meets the requirements, further samples are prepared to observe the cross-section of the precursor. Through sampling statistics, when the cross-sectional dimensions of most samples show significant consistency (i.e., the cross-sectional dimensions are basically equal), the consistent cross-sectional dimensions are the "normal cross-sectional size".

[0097] In one specific implementation, if the obtained cross-sectional image contains a single filament cross-section whose cross-sectional size is more than 1.5 times that of a normal cross-section, and the single filament cross-section is brighter than other cross-sections, then the single filament is a stiff filament.

[0098] As a specific implementation, if there are two or more monofilament cross sections stuck together in the obtained cross-sectional image, that is, there is no dividing line between adjacent monofilament cross sections, then there is a problem of filament merging.

[0099] It should be noted that, in the embodiments of the present invention, when measuring the cross-sectional dimensions of monofilaments to calculate the fineness CV value, for monofilament cross-sections that are obviously too large or too small to be observed by the naked eye (such as the aforementioned fine filaments, stiff filaments, etc.), if their proportion in the cross-sectional image is very small (for example, 200 to 400 monofilament cross-sections are captured in the cross-sectional image, while the number of monofilament cross-sections that are obviously too large or too small to be observed by the naked eye does not exceed 3), they are not counted. Instead, a certain number of monofilament cross-sections are randomly selected from multiple cross-sections with relatively similar cross-sectional sizes, and the cross-sectional dimensions are measured respectively before calculating the fineness CV value.

[0100] In the preferred scheme, to ensure that the calculated fineness CV value is closer to the true level, when selecting the monofilament cross-sections to be measured, after excluding abnormal cross-sections such as thin filaments, stiff filaments, and fused filaments in the cross-sectional image, it is necessary to uniformly select several monofilament cross-sections with slightly different cross-sectional sizes for measurement. For example, under visual observation, several monofilament cross-sections of slightly larger size are randomly selected, several from medium-sized monofilament cross-sections are randomly selected, and several from slightly smaller monofilament cross-sections are randomly selected. In the final selected sample, the number of large, medium, and small-sized monofilament cross-sections is basically the same. The fineness CV value calculated in this way can better reflect the true level of uniformity of the fiber bundle fineness.

[0101] In one detailed embodiment of the present invention, the method for detecting and determining the cross-section of carbon fiber precursor includes the following steps: A) The carbon fiber precursor to be tested is left to stand at standard temperature and humidity until the moisture regain reaches below 2%; if the moisture regain in the initial state is not higher than 2%, then no standing operation is performed. 1) Prepare a cross-sectional sample of the raw yarn: Take an appropriate amount of fiber according to the specifications of the raw yarn. For 1K, take a bundle of raw yarn and fold it in half to make eight bundles. For 3K, take a bundle of raw yarn and fold it in half to make three bundles. For 6K, take a bundle of fiber and fold it in half to make two bundles. For 12-48K, take a bundle of raw yarn directly, or separate some fibers from a bundle of fibers. The sampled raw filament bundle is inserted into the through hole on the metal plate. A blade is used to cut off the part of the filament bundle exposed on both sides of the metal plate while keeping it close to the surface of the metal plate. During the cutting process, the blade is required to cut the filament bundle slowly, so that the cross-section formed by the cutting is basically flush with the surface of the metal plate, and a raw filament cross-section slice sample with a thickness of 0.8~1.2mm is obtained. 2) Observe the cross section: Place the original wire cross section sample obtained in step (1) together with the metal plate under the metallographic microscope, turn on the upper light source to irradiate the sample, adjust the observation field of view until the target observation area falls into the observation field of view, then turn off the upper light source and turn on the lower light source, adjust the focus and the brightness of the light source to make the image clear; wherein, the metallographic microscope is a 9XB-PC metallographic microscope. 3) Photographing and analysis: Select a scale that matches the magnification of the objective lens currently used in the metallurgical microscope, and take a photograph to obtain a cross-sectional image; analyze the cross-sectional image to determine the cross-sectional condition of the sample.

[0102] In one specific implementation, in step (3), the cross-sectional condition of the sample includes the fineness CV value of the carbon fiber precursor bundle, and / or whether there are problems with fine filaments, stiff filaments or fused filaments.

[0103] Example 1 This embodiment performs cross-sectional testing on 3K carbon fiber precursor. The testing method specifically includes the following steps: A) Take the 3K carbon fiber precursor to be tested and test its moisture regain to meet the level of less than 2%; 1) Prepare a cross-sectional sample of the raw wire: Use a 1.0mm thick stainless steel plate with a 1.0mm diameter circular through hole as a sampler; Take a bundle of raw wire and fold it into three bundles. Insert the sampled raw wire bundle into the circular through hole. Use a blade to cut off the part of the wire bundle exposed on both sides of the stainless steel plate, keeping it close to the surface of the stainless steel plate. During the cutting process, the blade should be used slowly to cut the wire bundle little by little, so that the cross section formed by the cutting is basically flush with the surface of the stainless steel plate, and a raw wire cross section sample with a thickness of about 1.0 mm is obtained. 2) Observe the cross section: Place the original wire cross section sample obtained in step (1) together with the stainless steel plate under the metallographic microscope, turn on the upper light source to irradiate the sample, adjust the observation field of view until the target observation area falls into the observation field of view, then turn off the upper light source and turn on the lower light source, and then adjust the focus and light source brightness to make the image clear; wherein, the metallographic microscope is a 9XB-PC metallographic microscope. 3) Photography and Analysis: Select a scale that matches the magnification of the objective lens currently used on the metallurgical microscope, and take a photograph to obtain a cross-sectional image, such as... Figure 2 As shown; After excluding abnormal cross sections such as thin filaments, stiff filaments, and fused filaments in the cross section images, 20 monofilament cross sections were randomly selected from the remaining monofilament cross sections (the number of cross sections with slightly larger, moderate, and slightly smaller dimensions should be as even as possible among the selected monofilament cross sections). The distance between the two ends of the cross section in the length direction was measured as the cross section size, and the coefficient of variation of the sample was calculated as the fineness CV value. The results are shown in Table 1 below.

[0104] Table 1 In the above embodiment, the qualified standard for the fineness CV value is set to ≤13%. The actual fineness CV value obtained by sampling and calculation is 2.93%, which meets the above qualified standard. This means that the fineness uniformity of the raw yarn product obtained under the current production conditions meets the requirements.

[0105] The detection and judgment method provided in this invention can achieve rapid sample preparation of the raw fiber cross-section, significantly shortening the sample preparation time and improving detection efficiency. After sample preparation, taking advantage of the raw fiber's certain light transmittance, an optical microscope can be used with a transmitted light source to quickly obtain an image of the raw fiber cross-section, further improving detection efficiency and shortening the detection time for a single sample.

[0106] Using the above-described detection and judgment methods, the cross-sectional shape of the tested carbon fiber precursor can be quickly and directly observed. Combined with image analysis technology, the cross-sectional dimensions of a single filament can be directly output for calculating the filament's fineness CV value. Alternatively, inspectors can use computer assistance to measure the cross-sectional dimensions from the image and calculate the filament's fineness CV value. This allows production personnel to make adjustments before the precursor is packaged into bobbins, ensuring the uniformity of the precursor's fineness. Simultaneously, it allows for analysis and judgment of issues such as the presence of thin filaments, stiff filaments, or tangled filaments, enabling timely adjustments and reducing the production of defective products.

[0107] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method of detecting and determining a cross section of a carbon fiber precursor, characterized by, The method comprises the following steps: (1) preparing a cross-section slice sample of the raw fiber: fixing a carbon fiber raw fiber bundle in a sampler, cutting off the part of the bundle exposed to the sampler, and obtaining a cross-section slice sample of the raw fiber with a thickness of 0.8-1.2 mm; (2) observing the cross-section: placing the cross-section slice sample of the raw fiber prepared in step (1) under an optical microscope, imaging the sample by using a transmission light source, and observing the sample.

2. The method of claim 1, wherein the method is characterized by: The sampler comprises a metal plate with a through hole, and the thickness of the metal plate is 0.8-1.2 mm; In step (1), the bundle is inserted into the through hole on the metal plate, and the exposed part of the bundle is cut off by a blade close to the two side surfaces of the metal plate to obtain a cross-section slice sample of the raw fiber in the through hole; In step (2), the metal plate with the cross-section slice sample of the raw fiber is placed under the optical microscope for observation; Preferably, the material of the metal plate is stainless steel; Preferably, the thickness of the metal plate is 0.9-1.1 mm, and more preferably, the thickness is 1.0 mm.

3. The method of claim 2, wherein the step of determining the cross-sectional area of the carbon fiber precursor filament is performed by the following steps of: The through hole is a circular hole; ​ Preferably, the diameter of the circular hole is 1.0-1.5 mm; More preferably, the diameter of the circular hole is 1.0 mm.

4. The method for detecting and determining the cross-section of carbon fiber precursor according to claim 3, characterized in that, For a 1K carbon fiber raw fiber bundle, eight bundles are combined and then inserted into the circular hole; And / or, for a 3K carbon fiber raw fiber bundle, three bundles are combined and then inserted into the circular hole; And / or, for a 6K carbon fiber raw fiber bundle, two bundles are combined and then inserted into the circular hole; And / or, for a 12-48K carbon fiber raw fiber bundle, one bundle is inserted into the circular hole, or part of the fibers in one bundle is separated and inserted into the circular hole.

5. The method of detecting and determining the cross section of a carbon fiber precursor filament according to any one of claims 2 to 4, characterized in that, In step (1), the end of the bundle is first trimmed with scissors, the end of the bundle is sharpened, and then the sharpened end is inserted through the through hole on the metal plate.

6. The method of detecting and determining the cross section of a carbon fiber precursor filament according to any one of claims 1 to 5, characterized in that, The optical microscope has an upper light source that irradiates the sample surface from the upper side, and a lower light source that transmits the sample from the lower side; In step (2), first turn on the upper light source to irradiate the sample surface from the upper side, adjust the observation field of view so that the cross-section slice sample of the raw fiber is in the range of the observation field of view, then turn on the lower light source to transmit the sample, and finally observe the sample under the condition that the upper light source is turned off and the lower light source is turned on.

7. The method for detecting and determining the cross-section of carbon fiber precursor according to claim 6, characterized in that, In step (2), after the operation of adjusting the observation field of view is completed, first turn off the upper light source, then turn on the lower light source, and then adjust the focal length and / or the brightness of the light source to make the image clear.

8. The method of claim 1 to 7, wherein In step (1), a carbon fiber raw fiber bundle with a moisture regain of not more than 2% is used to prepare the cross-section slice sample of the raw fiber; Preferably, before step (1), a step (A) is included: placing the carbon fiber raw fiber bundle under standard temperature and humidity until the moisture regain is below 2%, and then performing step (1).

9. The method of claim 1 to 8, wherein The optical microscope is connected with a digital image acquisition device; After step (2), a step (3) is further included: taking a photo of the imaging of the cross-section slice sample of the raw fiber under the optical microscope by using the digital image acquisition device to obtain a cross-section image.

10. The method of detecting and determining the cross section of a carbon fiber precursor according to claim 9, characterized by, In step (3), after the cross-section image is obtained, the cross-section image is analyzed to determine the fineness CV value of the carbon fiber raw fiber bundle; Preferably, in step (3), a scale consistent with the objective magnification currently used by the optical microscope is selected, and a cross-section image is taken again, and the cross-sectional dimensions of several different filaments are measured from the cross-section image, and the CV value of the carbon fiber precursor filament bundle is calculated.

Images