Large-tow carbon fiber and its continuous production method

Abstract

This invention relates to the field of large-tow carbon fiber production technology, specifically to large-tow carbon fiber and its continuous production method. It discloses a large-tow fiber comprising alternating large-tow precursor fibers and carbon fibers. The precursor fibers and carbon fibers are connected by a flat knot. This connection method allows the end of a packaged large-tow precursor fiber to be connected to the end of an adjacent packaged large-tow precursor fiber, resulting in a strong knot with a tensile strength exceeding 120,000 cN. Using this flat knot connection method allows for continuous production of large-tow carbon fiber, reducing the number of times the fibers are wound around the roller, improving production safety, increasing stable production time, reducing waste fiber, lowering production costs, and increasing production efficiency.

Description

Technical Field

[0001] This invention relates to the field of large-tow carbon fiber production technology, specifically to large-tow carbon fiber and its continuous production method. Background Technology

[0002] Large-tow carbon fiber is mainly composed of carbon elements and possesses properties such as high temperature resistance, low density, high specific strength and specific modulus, friction resistance, thermal conductivity, and corrosion resistance. It has a fibrous, flexible appearance and can be processed into various fabrics. It can also be used as a reinforcing material in composites with resins, metals, ceramics, and carbon to manufacture advanced composite materials. Carbon fiber reinforced epoxy resin composites have the highest specific strength and specific modulus among existing engineering materials. The oxidation of the precursor fiber mainly aims to induce cyclization within the linear polyacrylonitrile (PAN) macromolecular chains and intermolecular crosslinking to generate a heat-resistant network ladder structure. Oxidation is usually carried out in an air atmosphere, with the temperature controlled between 180℃ and 280℃, and appropriate tension is applied during the process to prevent relaxation of the polymer molecular structure and maintain fiber orientation. To ensure that the polyacrylonitrile fibers do not melt or burn during high-temperature carbonization activation and to maintain their fiber morphology, pre-oxidation treatment is usually performed on the polyacrylonitrile fibers to convert their linear molecular chains into a heat-resistant cyclized structure, thereby improving their thermal stability. The oxidation reaction of polyacrylonitrile fibers is accompanied by a large amount of exothermic reaction.

[0003] A shorter pre-oxidation time results in a thinner sheath structure; a longer pre-oxidation time results in a thicker sheath structure in the carbon fiber. Pre-oxidation processes using low parameters (such as traction force and temperature) and with long processing times are less likely to form a distinct core-sheath structure, but also have relatively lower production efficiency.

[0004] In the production process of polyacrylonitrile-based small-tow carbon fiber, the precursor fiber is wound into a cylindrical spool using a winding and winding machine and placed on a yarn rack. The precursor fiber drawn from the yarn rack then undergoes oxidation, carbonization, surface treatment, washing, sizing, drying, and winding to finally obtain the carbon fiber product. However, in the production process of large-tow carbon fiber, the precursor fiber is not wound into a cylindrical spool; instead, the precursor fiber filaments are directly laid in boxes for production. Each box contains a filament head and a filament tail, and the length of the precursor fiber is fixed. When a box of precursor fiber is about to run out, the filament tail of that box must be connected to the filament head of the precursor fiber in the adjacent box to ensure that the precursor fiber enters the oxidation zone uninterruptedly, achieving continuous online production. Therefore, the connection between the precursor fibers in the two boxes is crucial. If the connection between the filament head and tail is loose or broken, it can easily cause the precursor fiber to wrap around the rollers in the oxidation zone, or even cause the oxidation furnace to catch fire. Stopping the production line to reheat and re-feed the fiber increases the labor intensity of the workers, leads to intermittent production, generates a large amount of waste fiber, and makes it difficult to achieve economic benefits.

[0005] CN211546739U describes a polyacrylonitrile pre-oxidized fiber splicing device. It includes an air connector and a splicing operating table. The air connector includes a fiber end holder with a slit forming a fiber splicing groove. Air injection holes are provided on the sidewall of the fiber splicing groove. The fiber end holder has an air inlet and an air inlet trigger. Two raw pre-oxidized fiber ends are placed on the splicing operating table, stacked together. The splicing operating table has multiple splicing grooves and also includes multiple fiber fixing rods. These rods are placed in different splicing grooves to press the raw pre-oxidized fiber ends together. At least one air connector for splicing the fiber ends is placed in a splicing groove. The fiber fixing rods and air connectors are placed in different splicing grooves. The raw pre-oxidized fiber ends pass through the fiber splicing groove and are spliced ​​within it. However, during the pre-oxidation process, a certain stretching tension is applied to the fiber bundle to maintain the axial orientation of the macromolecular chains to the fiber axis. Using this patented method will result in insufficient knot strength in the raw fiber, and the knot may break during the production process.

[0006] CN115303892A describes a method for splicing polyacrylonitrile-based carbon fiber precursors, comprising the following steps: knotting the tail end of a first polyacrylonitrile-based carbon fiber precursor bundle and the head end of a second polyacrylonitrile-based carbon fiber precursor bundle to form a fixed knot, leaving a filament end on one side of the fixed knot; weaving the filament end of the first polyacrylonitrile-based carbon fiber precursor bundle into the second polyacrylonitrile-based carbon fiber precursor bundle located on the other side of the fixed knot to form a first braided section; weaving the filament end of the second polyacrylonitrile-based carbon fiber precursor bundle into the first polyacrylonitrile-based carbon fiber precursor bundle located on the other side of the fixed knot to form a second braided section; the first braided section, the fixed knot, and the second braided section constitute a knot; and applying an adhesive to the knot. This invention is mainly used to give the knot a certain strength, so that the knot can directly pass from the unwinding frame through the pre-oxidation furnace, low-carbon furnace, high-carbon furnace, and finally to the winding machine, reducing downtime and improving production efficiency. However, because the pre-oxidation process releases a large amount of heat, knotting the precursor fibers can cause overheating inside the knot, leading to the burning off of the precursor bundle. In the production of large-tow carbon fiber, the pre-oxidation stretching tension is greater, the pre-oxidation reaction is more intense, and the knots are more prone to ignition, posing a safety hazard.

[0007] To address the aforementioned issues, a method for connecting large tow filaments is needed to solve the problem of continuous production of large tow carbon fibers, reduce downtime, and improve production efficiency. Summary of the Invention

[0008] The purpose of this invention is to overcome the problem in the existing technology that the raw filament produced by winding the tubular filament into a coil cannot be connected online during the production of large-tow carbon fiber, thus failing to achieve continuous production of large-tow carbon fiber. This invention provides a continuous production method for large-tow carbon fiber, which includes alternating large-tow raw filaments, carbon fibers, and a continuous splicing method for large-tow carbon fiber production. This method achieves continuous production of large-tow carbon fiber, offering advantages such as reduced number of roller windings, high production safety, increased stable production time, reduced waste filament, lower production costs, and increased production efficiency.

[0009] To achieve the above objectives, the present invention provides a large-tow carbon fiber, which includes alternating large-tow precursor fibers and carbon fibers, wherein the large-tow precursor fibers and carbon fibers are connected by a flat knot.

[0010] Preferably, the ends of the large tow filament and the carbon fiber are each divided into corresponding strands, and each strand of the large tow filament and the carbon fiber is connected by a flat knot.

[0011] Preferably, the ends of the large tow filament and the carbon fiber are each divided into 2-10 strands, more preferably 3-5 strands, and even more preferably 3 strands.

[0012] Preferably, the carbon fiber is 100-180K carbon fiber, and more preferably 125-150K.

[0013] Preferably, the connecting ends of the large bundle of raw filaments undergo pre-oxidation treatment.

[0014] Preferably, after the ends of the large tow filament and the carbon fiber are connected by a flat knot, the length of the knot tail is 5-20cm, preferably 8-15cm.

[0015] The second aspect of the present invention provides a continuous production method for large tow carbon fiber, the method comprising the following steps: (1) pre-oxidizing one end of the large tow raw filament, and connecting the pre-oxidized end to one end of the carbon fiber by means of flat knotting, and repeating the aforementioned flat knotting connection according to the needs of continuous production; (2) after the knotting connection is completed, the fiber undergoes oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, water washing, sizing, drying, and winding.

[0016] Preferably, step (1) includes: dividing the pre-oxidized end of the large tow filament into multiple strands, and dividing one end of the carbon fiber into corresponding multiple strands, which are then tied into tight knots with each strand of the pre-oxidized end of the large tow filament using a flat knot method; and / or

[0017] Preferably, the pre-oxidized end of the large tow filament and one end of the carbon fiber are each divided into 2-10 strands, more preferably 3-5 strands, and even more preferably 3 strands.

[0018] Preferably, before the pre-oxidation, in step (1), the length of the end of the large filament bundle that is pre-oxidized is 100-170cm, preferably 130-160cm.

[0019] Preferably, the pre-oxidation is carried out in two stages, including a first pre-oxidation and a second pre-oxidation. The conditions for the first pre-oxidation include: a temperature of 205-255℃, preferably 225-245℃; and / or a time of 10-55 min, preferably 25-40 min. The conditions for the second pre-oxidation include: a temperature of 230-265℃, preferably 235-260℃; and / or a time of 10-55 min, preferably 25-40 min; and / or a temperature 10-25℃ higher than the temperature of the first pre-oxidation.

[0020] Preferably, after the large tow filament is pre-oxidized, the length of the knot left at the connection end with the carbon fiber after knotting is 5-20cm, preferably 8-15cm.

[0021] The third aspect of the present invention provides large-tow carbon fibers prepared by the continuous production method of large-tow carbon fibers described in the present invention.

[0022] Through the above technical solution, the present invention has the following beneficial effects:

[0023] This invention proposes for the first time a large-tow carbon fiber, which includes alternating large-tow precursor fibers and carbon fibers. The large-tow precursor fibers and carbon fibers are connected by a flat knot. Using the connection method described in this invention, the end of the large-tow precursor fibers in a box can be connected to the end of the large-tow precursor fibers in an adjacent box. Not only is the knot strong, but the breaking strength of the knot reaches more than 120,000 cN.

[0024] The adjacent large filament bundle ends of the present invention are connected by a flat knot. Not only will the knot not loosen or fall off during the oxidation process, but the knot connection will also not produce smoke or fire due to overheating. This ensures that the ends of the adjacent two boxes of filaments can be connected firmly and can smoothly pass through the production processes of oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, washing, sizing, drying, and winding from the yarn feeding frame.

[0025] In a preferred embodiment of the present invention, the method of connecting adjacent large tow carbon fibers by flat knotting the ends can realize continuous production of large tow carbon fibers, reduce the number of times the fibers are wound around the roller, improve production safety, increase stable production time, reduce waste fiber, lower production costs, and improve production efficiency. Attached Figure Description

[0026] Figure 1This is a schematic diagram showing that each raw filament is divided into three strands, and the pre-oxidized end is connected to one end of the carbon fiber by a flat knot. Detailed Implementation

[0027] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0028] This invention, for the first time, proposes a large-tow carbon fiber comprising alternating large-tow precursor fibers and carbon fibers. The precursor fibers and carbon fibers are connected by a flat knot. In continuous production, this invention allows the ends of packaged large-tow precursor fibers to be connected to the ends of adjacent packaged large-tow precursor fibers via carbon fibers. This not only results in a strong knot with a tensile strength exceeding 120,000 cN, but also ensures that the knots do not loosen or fall off during oxidation, and prevent smoke and fire due to overheating at the connection point. This guarantees a tight connection between the ends of adjacent packages of precursor fibers, allowing them to smoothly pass through the production processes of oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, washing, sizing, drying, and winding from the yarn feeding frame.

[0029] In this invention, the operation steps for tying a square knot are as follows (after tying the knot, as shown in the image). Figure 1 As shown):

[0030] Step 1: Wrap the pre-oxidized end of the large tow filament around one end of the carbon fiber.

[0031] Step 2: Fold the pre-oxidized end of the large tow filament and one end of the carbon fiber together and cross them, with the pre-oxidized end of the large tow filament at the bottom.

[0032] Step 3: Pass the pre-oxidized end of the large tow filament around one end of the carbon fiber and insert it into the loop, then tie it together with the pre-oxidized end of the large tow filament and tighten it to form a flat knot. After tying the flat knot according to production needs, leave a certain length of filament end.

[0033] Step 4: Following the above knotting steps, tie the pre-oxidized end of the remaining large tow of raw filament after splitting to one end of the remaining carbon fiber after splitting in the same way.

[0034] In this invention, there are no special requirements on the number of strands at the ends of the large tow filament and the carbon fiber. According to a preferred embodiment of this invention, the ends of the large tow filament and the carbon fiber are each divided into 2-10 strands, preferably 3-5 strands, and more preferably 3 strands.

[0035] According to a preferred embodiment of the present invention, the ends of the large tow filament and the carbon fiber are each divided into corresponding strands, and each strand of the large tow filament and the carbon fiber is connected by a flat knot.

[0036] By adopting the aforementioned preferred embodiments, the fracture strength of the knot at the connection between the precursor filament and carbon fiber can be further improved, ensuring that the knot is subjected to uniform force in all directions and that the knot is stable and does not loosen.

[0037] In this invention, the number of times the large tow filaments and carbon fibers are alternately connected is not limited and can be selected as needed.

[0038] In this invention, the K number of the carbon fiber can be a conventional choice in the art. According to a preferred embodiment of the invention, the K number of the carbon fiber is 100-180K, preferably 125-150K. By adopting the aforementioned preferred embodiment, the strength of the connection between the precursor fiber and the carbon fiber can be further improved, and no loosening or breakage occurs at the connection point.

[0039] In this invention, after the ends of the large tow filaments and carbon fibers are knotted, the length of the knot tail is not particularly required. According to a preferred embodiment of the invention, after the ends of the large tow filaments and carbon fibers are knotted, the length of the knot tail is 5-20 cm, preferably 8-15 cm. By adopting the aforementioned preferred embodiment, the safe production stability of the knots in oxidation furnaces, low-temperature carbonization furnaces, and high-temperature carbonization furnaces can be further improved.

[0040] All large-tow carbon fibers with the features of this invention can achieve the purpose of this invention. The specific preparation steps and processes can be selected and adjusted as needed. According to the preferred embodiment of this invention, this invention provides a continuous production method for large-tow carbon fibers. The method includes the following steps: (1) pre-oxidizing one end of the large-tow precursor fiber, and connecting the pre-oxidized end to one end of the carbon fiber by a flat knot. The flat knot connection is repeated as needed for continuous production; (2) after the knot connection is completed, oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, water washing, sizing, drying, and winding are performed. Through this continuous production method, continuous production of large-tow carbon fibers can be realized, reducing the number of times the rollers are wound, improving production safety, increasing stable production time, reducing waste fiber, reducing production costs, improving production efficiency, and avoiding the risk of fire caused by excessive heat accumulation at the end connection of the precursor fiber, thus reducing production costs and improving production efficiency. Therefore, continuous production of large-tow carbon fibers can be effectively realized.

[0041] In this invention, the winding connection can be performed continuously, and the specific number of windings is determined according to the needs and the actual working conditions.

[0042] In this invention, after the pre-oxidation of the ends of the large filament bundle in step (1), a cooling step is required. There are no special requirements for the cooling time and method. It can be carried out with reference to the existing technology. It is only necessary to cool to room temperature.

[0043] In this invention, after step (1) and before step (2), the two ends of the large filament bundle are laid on the tension frame, the filament is tightened and fixed, the tension frame is placed in the pre-oxidation furnace, and the ends of the filament are pre-oxidized. This step has no special requirements and can be carried out with reference to the prior art. This invention will not elaborate on this step.

[0044] In this invention, after the above knots are wound and connected in step (4), the process involves oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, water washing, sizing, drying, and winding. There are no special requirements for the specific steps and operating conditions, and they can be carried out according to the existing technology. This invention will not elaborate on these steps here.

[0045] According to a preferred embodiment of the present invention, step (1) includes: dividing the pre-oxidized end of the large tow filament into multiple strands, and dividing one end of the carbon fiber into corresponding multiple strands, which are then tied into tight knots with each strand of the pre-oxidized end of the large tow filament using a flat knot method.

[0046] According to a preferred embodiment of the present invention, the step of knotting each strand in a flat knot is as follows: fold the end of the pre-oxidized large tow filament in half to form the first loop, and combine the remaining filaments at both ends of the loop together. After inserting one end of the carbon fiber from below the first loop, fold it downwards below the combined filaments to form the second loop, and then insert it from above into the first loop and tighten it. Preferably, the pre-oxidized end of the large tow filament and one end of the carbon fiber are each divided into 2-10 strands, preferably 3-5 strands, and more preferably 3 strands.

[0047] By adopting the aforementioned preferred embodiments, the fracture strength of the knot at the connection between the precursor filament and carbon fiber can be further improved, ensuring that the knot is subjected to uniform force in all directions and that the knot is stable and does not loosen.

[0048] In this invention, before the pre-oxidation treatment of the large tow filament in step (1), a length needs to be reserved at the pre-oxidation end of the large tow filament. There are no special requirements for the reserved length. According to a preferred embodiment of this invention, the reserved length at the pre-oxidation end before the pre-oxidation treatment of the large tow filament is 100-170 cm, preferably 130-160 cm. By adopting the aforementioned preferred embodiment, it can be further ensured that the length of the pre-oxidized filament meets the length requirements for connection with carbon fibers.

[0049] In this invention, there are no special requirements for the number of pre-oxidation times of the large filament precursor. According to a preferred embodiment of this invention, the pre-oxidation of the large filament precursor is completed in two stages, including a first pre-oxidation and a second pre-oxidation.

[0050] In this invention, the conditions for the first pre-oxidation of the large tow filament can be conventional choices in the art.

[0051] According to a preferred embodiment of the present invention, the temperature of the first pre-oxidation of the large tow filament is 205-255°C, preferably 225-245°C.

[0052] According to a preferred embodiment of the present invention, the first pre-oxidation time of the large tow filament is 10-55 min, preferably 25-40 min.

[0053] By adopting the aforementioned preferred embodiments, the oxidation reaction of the precursor fiber can be carried out more effectively and rapidly.

[0054] In this invention, the conditions for the second pre-oxidation of the large tow filament can be conventional choices in the art.

[0055] According to a preferred embodiment of the present invention, the temperature of the second pre-oxidation of the large tow filament is 230-265°C, preferably 235-260°C.

[0056] According to a preferred embodiment of the present invention, the second pre-oxidation time of the large tow filament is 10-55 min, preferably 25-40 min.

[0057] By adopting the aforementioned preferred embodiments, it is possible to further ensure that the precursor fiber completes the cyclization and dehydrogenation reaction. Through intramolecular cyclization and intermolecular crosslinking, the linear macromolecular chain of the PAN-based precursor fiber is transformed into a heat-resistant ladder-shaped macromolecular structure.

[0058] In this invention, there are no special requirements for the length of the knot tails left after the pre-oxidation of the large tow filaments and the connection ends with the carbon fibers are tied. According to a preferred embodiment of this invention, the length of the knot tails left after the pre-oxidation of the large tow filaments and the connection ends with the carbon fibers is 5-20 cm, preferably 8-15 cm. By adopting the aforementioned preferred embodiment, the safety and production stability of the knots during passage through oxidation furnaces, low-temperature carbonization furnaces, and high-temperature carbonization furnaces can be further improved.

[0059] This invention provides large-tow carbon fibers prepared by the continuous production method of large-tow carbon fibers described in this invention.

[0060] like Figure 1 As shown, in this invention, each raw filament is divided into three strands, and one end of the carbon fiber is divided into corresponding multiple strands, with each end of the multiple strands tied into a tight knot. A schematic diagram illustrates how each strand of the pre-oxidized end of the large tow raw filament and each strand of the carbon fiber are tied into a tight knot using a flat knot method; (See attached diagram). Figure 1 In the diagram, 1 represents the pre-oxidized end of a large bundle of raw filaments; 2 represents carbon fiber.

[0061] The present invention will be described in detail below through embodiments. In the following embodiments, the knot breaking strength parameter was measured using the GB / T19975-2005 test method for tensile properties of high-strength fiber filaments. In the present invention, the knot breaking strength data is the average value of three knot tests conducted in actual operation; the oxidation furnace pass rate, low-temperature carbonization furnace pass rate, and high-temperature carbonization furnace pass rate were calculated using the following methods:

[0062] Oxidation furnace throughput = (Number of nodes that successfully pass through the oxidation furnace / Total number of nodes entering the oxidation furnace) * 100%

[0063] Low-temperature carbonization furnace throughput = (Number of nodes that successfully pass through the low-temperature carbonization furnace / Total number of nodes entering the low-temperature carbonization furnace) * 100%

[0064] High-temperature carbonization furnace throughput = (Number of nodes that successfully pass through the high-temperature carbonization furnace / Total number of nodes entering the high-temperature carbonization furnace) * 100%

[0065] The raw material for the silk is a commercially available product of brand SF from Sinopec Shanghai Petrochemical Co., Ltd.

[0066] In the following examples and comparative examples, the oxidation furnace, low-temperature carbonization furnace, high-temperature carbonization furnace, surface treatment, washing, sizing, drying, and winding / dewinding processes all operate under the same conditions: (Details are as follows:)

[0067] Oxidation furnace: The oxidation process is carried out in four temperature zones for a total time of 60 minutes. The draw ratios between the four heating temperature zones are 1.26, 0.99, 0.98, and 0.96, respectively. The temperatures of the four temperature zones in the embodiments and comparative examples of this invention are shown in Table 1.

[0068] Low-temperature carbonization furnace: The low-temperature carbonization production process is carried out in a low-temperature carbonization furnace divided into 6 heating zones. The pre-oxidized filaments from the outlet of the oxidation furnace enter the low-temperature carbonization furnace through a traction device. Using nitrogen as the medium, low-temperature carbonization is carried out to produce low-temperature carbonized filaments. The temperatures of the 6 heating zones are 470℃, 540℃, 610℃, 670℃, 740℃, and 790℃, respectively. The filament bundle runs in the low-temperature carbonization furnace, with the draw ratio controlled at 1.06, and the total residence time in the low-temperature carbonization furnace is 1.2 minutes.

[0069] High-temperature carbonization furnace: The high-temperature carbonization production process is carried out in a high-temperature carbonization furnace divided into five heating zones. The filament bundle exiting the low-temperature carbonization furnace is drawn into the high-temperature carbonization furnace via a traction device, where nitrogen is used as the medium for high-temperature carbonization to produce high-temperature carbonized filaments. The temperatures of the five heating zones are 1100℃, 1390℃, 1470℃, 1490℃, and 1400℃, respectively. The filament bundle runs in the high-temperature carbonization furnace with a controlled draw ratio of 0.76, and the total residence time in the high-temperature carbonization furnace is 1.2 minutes.

[0070] Surface treatment: The surface treatment production process involves the filament bundles from the outlet of the high-temperature carbonization furnace being drawn into the surface treatment tank by a traction device, with ammonium bicarbonate aqueous solution as the electrolyte, a voltage of 18V, an electrolyte concentration of 10%, and the filament bundles staying in the electrolyte for 60 seconds.

[0071] Water washing: In the water washing production process, the filament bundles from the surface treatment tank outlet enter the water washing tank and are washed with water at a flow rate of 2800L / hour and a temperature of 50℃.

[0072] Sizing: Commercially available K7 epoxy emulsion sizing agent is used to impregnate and sizing the unsized carbon fiber for 20 seconds at a temperature of 25°C.

[0073] Drying: Horizontal hot air drying, drying temperature 100℃.

[0074] Winding and winding: After sizing and drying, the carbon fiber is wound and wound using a carbon fiber winding machine to obtain the finished carbon fiber.

[0075] In the following embodiments, the filament head and filament tail are the two ends of the filament, respectively. In the same embodiment, the large filament bundle and the carbon fiber have the same K number. Other parameters are shown in Table 2.

[0076] Example 1

[0077] (1) Each box of raw silk retains a certain length of the silk head and tail, with the silk head and tail length being 130cm.

[0078] (2) Place the filament head and tail of each box of raw filaments on the tension frame, tighten and fix the raw filaments, put the tension frame into the pre-oxidation furnace, and pre-oxidize the 130cm ends of the filament head and tail. The pre-oxidation is divided into two stages. The oxidation temperature of the first stage is 225℃ and the time is 25min. The oxidation temperature of the second stage is 235℃ and the time is 25min.

[0079] (3) The pre-oxidized filament head is divided into 3 strands on average, and the pre-oxidized filament tail is divided into 3 strands on average. After the filament head and tail are tied, the length of the knot and tail is 8cm.

[0080] (4) Divide each end of a 125K carbon fiber into three equal strands. Then, connect the three strands at one end of the 125K carbon fiber to the pre-oxidized fiber ends that have been divided into three equal strands using a flat knot method (e.g., Figure 1 As shown), there are a total of 3 knots. Similarly, take the other end of the 125K carbon fiber and connect it to the pre-oxidized yarn tails that are divided into 3 equal strands in the adjacent boxed packaging in a flat knot manner. There are a total of 3 knots. Repeat the alternating connection of the subsequent original yarn head and one end of the carbon fiber in sequence.

[0081] (5) After the above knotting and connection is completed, the process is carried out in sequence through oxidation, low temperature carbonization, high temperature carbonization, surface treatment, water washing, sizing, drying, and winding.

[0082] The implementation effect of this embodiment is shown in Table 3.

[0083] Example 2

[0084] (1) Each box of raw silk retains a certain length of the silk head and tail, with the silk head and tail length being 150cm.

[0085] (2) Place the filament head and tail of each box of raw filaments on the tension frame, tighten and fix the raw filaments, put the tension frame into the pre-oxidation furnace, and pre-oxidize the filament head and tail of the raw filaments. The pre-oxidation is divided into two stages. The oxidation temperature of the first stage is 232℃ and the time is 36min. The oxidation temperature of the second stage is 252℃ and the time is 36min.

[0086] (3) The pre-oxidized filament head is divided into 4 strands on average, and the pre-oxidized filament tail is divided into 4 strands on average. After the filament head and tail are tied, the length of the knot and tail is 12cm.

[0087] (4) Divide each end of a 135K carbon fiber into four equal strands. Then, connect each of the four strands at one end of the 135K carbon fiber to the pre-oxidized fiber ends that have been divided into four equal strands using a flat knot method (e.g., Figure 1 As shown), there are a total of 4 knots. Similarly, the other end of the 135K carbon fiber is connected to the pre-oxidized filament tails that are divided into 4 equal strands in turn by a flat knot. There are a total of 4 knots. The subsequent raw filament tails and carbon fiber ends are connected alternately in turn.

[0088] (5) After the above knotting and connection is completed, the process is carried out in sequence through oxidation, low temperature carbonization, high temperature carbonization, surface treatment, water washing, sizing, drying, and winding.

[0089] The implementation effect of this embodiment is shown in Table 3.

[0090] Example 3

[0091] (1) Each box of raw silk retains a certain length of the silk head and tail, with the silk head and tail length being 160cm.

[0092] (2) Place the filament head and tail of each box of raw filaments on the tension frame, tighten and fix the raw filaments, put the tension frame into the pre-oxidation furnace, and pre-oxidize the filament head and tail of the raw filaments. The pre-oxidation is divided into two stages. The oxidation temperature of the first stage is 245℃ and the time is 40min. The oxidation temperature of the second stage is 260℃ and the time is 40min.

[0093] (3) The pre-oxidized filament head is divided into 5 strands on average, and the pre-oxidized filament tail is divided into 5 strands on average. After the filament head and tail are tied together, the length of the knot and tail is 15cm.

[0094] (4) Divide each end of a 150K carbon fiber into 5 equal strands. Then, connect each of the 5 strands at one end of the 150K carbon fiber to the pre-oxidized fiber ends that have been divided into 5 equal strands using a flat knot method (e.g., Figure 1 As shown), there are a total of 5 knots. Similarly, take the other end of the 150K carbon fiber and connect it to the pre-oxidized filament tails that are divided into 5 strands in an even manner using a flat knot. There are a total of 5 knots. Repeat the alternating connection between the subsequent raw filament head and one end of the carbon fiber.

[0095] (5) After the above knotting and connection is completed, the process is carried out in sequence through oxidation, low temperature carbonization, high temperature carbonization, surface treatment, water washing, sizing, drying, and winding.

[0096] The implementation effect of this embodiment is shown in Table 3.

[0097] Example 4

[0098] All operating steps are the same as in Example 1, except that the process parameters for the K number of carbon fiber and large tow filament, the two-stage pre-oxidation temperature and the two-stage pre-oxidation residence time, the length of the filament head and tail, the number of strands of the filament and carbon fiber, and the length of the knotted head and tail after knotting are not within the preferred range of this invention. See Table 2 for details.

[0099] The implementation effect of this embodiment is shown in Table 3.

[0100] Example 5

[0101] All operating steps are the same as in Example 1, except that the process parameters for the K number of carbon fiber and large tow filament, the two-stage pre-oxidation temperature and the two-stage pre-oxidation residence time, the length of the filament head and tail, the number of strands of the filament and carbon fiber, and the length of the knotted head and tail after knotting are not within the preferred range of this invention. See Table 2 for details.

[0102] The implementation effect of this embodiment is shown in Table 3.

[0103] Example 6

[0104] All operating steps and conditions are the same as in Example 1, except that the K number of the carbon fiber and the large tow filament is 98K, which is not within the preferred range of this invention.

[0105] The implementation effect of this embodiment is shown in Table 3.

[0106] Example 7

[0107] All operating steps and conditions are the same as in Example 1, except that the length of the knotted end after tying the silk head and tail is 17cm, which is not within the preferred range of this invention.

[0108] The implementation effect of this embodiment is shown in Table 3.

[0109] Example 8

[0110] All operating steps and conditions are the same as in Example 1, except that the number of strands of the precursor filament and carbon fiber is 6, which is not within the preferred range of this invention.

[0111] The implementation effect of this embodiment is shown in Table 3.

[0112] Example 9

[0113] All operating steps and conditions are the same as in Example 1, except that the raw filament head and tail are pre-oxidized. The pre-oxidation is divided into two stages. The temperature and time of the second stage of oxidation are not within the preferred range of the present invention. The oxidation temperature of the first stage of oxidation is 213°C and the time is 232 min. The oxidation temperature of the second stage of oxidation is 39°C and the time is 39 min.

[0114] The implementation effect of this embodiment is shown in Table 3.

[0115] Example 10

[0116] All operating steps and conditions are the same as in Example 1, except that the length of the large filament bundle raw filament is 125cm, which is not within the preferred range of this invention.

[0117] The implementation effect of this embodiment is shown in Table 3.

[0118] Comparative Example 1

[0119] All conditions are the same as in Example 1, except that the large tow carbon fiber only includes alternating 125K large tow precursor fibers, excluding 125K carbon fibers.

[0120] The implementation effect of this embodiment is shown in Table 3.

[0121] Comparative Example 2

[0122] All conditions are the same as in Example 1, except that the 125K large tow filaments and 125K carbon fibers are connected by a tube knot. The filament heads of one box and the filament tails of the adjacent box are stacked together in parallel. The stacked filaments are wrapped in a loop, and the filament heads and tails are passed through the loop and tightened. The excess knots and tails are cut off.

[0123] The implementation effect of this embodiment is shown in Table 3.

[0124] Table 1

[0125]

[0126] Table 2

[0127]

[0128]

[0129] Table 3

[0130]

[0131] As can be seen from the results in Table 3, in the carbon fiber production process of Examples 1-10 of the present invention, which employ large-tow carbon fiber and continuous production method of large-tow carbon fiber, the ends of adjacent precursor fibers can be firmly connected together, the breaking strength of the knot reaches more than 120,000 CN, and the knot can pass smoothly through the oxidation furnace, low-temperature carbonization furnace, and high-temperature carbonization furnace. The pass rate of the oxidation furnace is 100%, the pass rate of the low-temperature carbonization furnace is 100%, and the pass rate of the high-temperature carbonization furnace is 100%, indicating good implementation effect.

[0132] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A large-tow carbon fiber, characterized in that: The large-tow carbon fiber comprises alternating large-tow precursor fibers and carbon fibers. The large-tow precursor fibers and carbon fibers are connected by a flat knot. The ends of the large-tow precursor fibers and carbon fibers are each divided into multiple strands, and each strand of the large-tow precursor fibers and carbon fibers is connected by a flat knot. The carbon fiber is 100-180K carbon fiber. After the ends of the large-tow precursor fibers and carbon fibers are connected by flat knots, the length of the knot tail is 5-20cm. The connected ends of the large-tow precursor fibers undergo pre-oxidation treatment. The pre-oxidation is carried out in two stages, including a first pre-oxidation and a second pre-oxidation. The temperature of the second pre-oxidation is 10-25℃ higher than that of the first pre-oxidation.

2. The large-tow carbon fiber according to claim 1, wherein, The ends of the large tow filaments and carbon fibers are each divided into 2-10 strands.

3. The large-tow carbon fiber according to claim 2, wherein, The ends of the large tow filaments and carbon fibers are each divided into 3-5 strands.

4. The large-tow carbon fiber according to claim 3, wherein, The ends of the large tow filaments and carbon fibers are each divided into three corresponding strands.

5. The large-tow carbon fiber according to claim 1, wherein, The carbon fiber is 125-150K.

6. The large-tow carbon fiber according to claim 1, wherein, After the ends of the large tow filament and the carbon fiber are connected by a flat knot, the length of the knot tail is 8-15cm.

7. A continuous production method for large-tow carbon fiber according to any one of claims 1-6, the method comprising the following steps: (1) Pre-oxidize one end of the large tow filament, and connect the pre-oxidized end to one end of the carbon fiber by a flat knot. Repeat the flat knot connection as needed for continuous production. (2) After the knotting and connection are completed, the process involves oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, water washing, sizing, drying, and winding and taking out the yarn. The pre-oxidation is carried out in two stages, including a first pre-oxidation and a second pre-oxidation. The temperature of the second pre-oxidation is 10-25°C higher than that of the first pre-oxidation.

8. The method according to claim 7, wherein, Step (1) includes: dividing the pre-oxidized end of the large tow filament into multiple strands, and dividing one end of the carbon fiber into corresponding multiple strands, which are then tied into tight knots with each strand of the pre-oxidized end of the large tow filament using a flat knot method.

9. The method according to claim 8, wherein, The pre-oxidized end of the large tow filament and one end of the carbon fiber are each divided into 2-10 strands.

10. The method according to claim 9, wherein, The pre-oxidized end of the large tow filament and one end of the carbon fiber are each divided into three corresponding strands.

11. The method according to claim 7, wherein, Before the pre-oxidation, in step (1), the length of the end of the large filament bundle that is pre-oxidized is reserved to be 100-170cm.

12. The method according to claim 11, wherein, Before the pre-oxidation, in step (1), the length of the end of the large filament bundle that is pre-oxidized is reserved to be 130-160cm.

13. The method according to claim 7, wherein, The conditions for the first pre-oxidation include: Temperature is 205-255℃; and / or Time: 10-55 minutes; and / or The conditions for the second pre-oxidation include: Temperature is 230-265℃; and / or The time is 10-55 minutes.

14. The method according to claim 13, wherein, The conditions for the first pre-oxidation include: Temperature is 225-245℃; and / or The time is 25-40 minutes; and / or The conditions for the second pre-oxidation include: Temperature is 235-260℃; and / or The time is 25-40 minutes.

15. The method according to claim 7, wherein, After the large tow filament is pre-oxidized, the connection ends of the filaments and carbon fibers are tied, and the length of the knot ends is 5-20cm.

16. The method according to claim 15, wherein, After the large tow filament is pre-oxidized, the connection ends of the filaments and carbon fibers are tied, and the length of the knot ends is 8-15cm.

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