Large tow carbon fibers and continuous production method of large tow carbon fibers

Abstract

The present application relates to the technical field of large-tow carbon fiber production, in particular to large-tow carbon fiber and a continuous production method of large-tow carbon fiber, and discloses a large-tow fiber, which comprises large-tow filaments and carbon fibers connected alternately, wherein the large-tow filaments and the carbon fibers are connected through self-tightening connection. By using this connection method, the end of the large-tow filaments in the box packaging can be connected with the end of the adjacent large-tow filaments in the box packaging, and the knot is firm, and the breaking strength of the knot reaches 156000 cN or more. By using the method that the large-tow filaments and the carbon fibers are connected through self-tightening connection, the continuous production of the large-tow carbon fiber can be realized, the number of times of winding around the roller is reduced, the production safety is high, the stable production time is improved, the amount of waste silk is reduced, the production cost is reduced, and the production efficiency is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of large-tow carbon fiber production, and particularly relates to a large-tow carbon fiber and a continuous production method of the large-tow carbon fiber. BACKGROUND

[0002] Carbon fiber (CF) is a new type of fiber material with a carbon content of more than 90%, high strength and high modulus. It not only has the inherent intrinsic properties of carbon materials, but also has the softness and processability of textile fibers. It is a new generation of reinforcing fiber, known as the "king of new materials" and "black gold". In the carbon fiber industry, carbon fibers with more than 48,000 roots per bundle (48K for short) are called large-tow carbon fibers. Although the performance of large-tow carbon fibers is not better than that of small-tow carbon fibers, the cost is lower. With the development of science and technology, large-tow carbon fibers are more widely used. They can be mainly applied to the fields of electromechanical, transportation, civil construction, energy, and textile industries, and are therefore also called industrial-grade carbon fibers. The main purpose of the oxidation of the precursor is to make the cyclization and intermolecular crosslinking of the linear polyacrylonitrile (PAN) macromolecular chain into a heat-resistant network ladder structure.

[0003] The pre-oxidation process of polyacrylonitrile (PAN) based precursor is very complex and contains complex physical and chemical changes. During the pre-oxidation process, the cyano group on the PAN molecular chain cyclizes and crosslinks, and the molecular chain changes from linear to ladder structure. The formation of a suitable cyclization structure in the precursor during the pre-oxidation process is the most basic factor for preparing ideal carbon fibers. The oxidation process is the key process that restricts the production efficiency of PAN-based carbon fibers, with the highest energy consumption and the longest time in the preparation process of carbon fibers.

[0004] CN115303892A introduces a splicing method of polyacrylonitrile-based carbon fiber precursor, which comprises the following steps: knotting the tail end of the first polyacrylonitrile-based carbon fiber precursor bundle and the head end of the second polyacrylonitrile-based carbon fiber precursor bundle to form a fixed knot, and leaving a thread end on one side of the fixed knot; the thread end of the first polyacrylonitrile-based carbon fiber precursor bundle is woven into the second polyacrylonitrile-based carbon fiber precursor bundle located on the other side of the fixed knot to form a first weaving part; the thread end of the second polyacrylonitrile-based carbon fiber precursor bundle is woven into the first polyacrylonitrile-based carbon fiber precursor bundle located on the other side of the fixed knot to form a second weaving part; the first weaving part, the fixed knot, and the second weaving part constitute a knot head; and an adhesive is coated on the knot head. The present application is mainly used to make the knot head have a certain strength, so that the knot head can directly pass through the pre-oxidation furnace, the low-carbon furnace, the high-carbon furnace, and the yarn collector from the yarn withdrawal rack, thereby reducing the downtime and improving the production efficiency. However, since a large amount of heat is released during the pre-oxidation process, the knotting of the precursor can cause the internal heat accumulation of the knot head to be overheated, and the bundle can be burnt off. In the production of large-tow carbon fibers, the pre-oxidation draft tension is greater, the pre-oxidation reaction is more intense, the knot head is more prone to fire, and there is a safety hazard.

[0005] The utility model discloses a carbon fiber continuous production is worn and is connected silk's device relates to silk equipment technical field, concretely is a kind of carbon fiber continuous production is worn and is connected silk's device, including mounting seat, the one side of mounting seat is fixedly connected with silk connecting box, the both sides of silk connecting box are fixedly connected with control sleeve, the upper surface of silk connecting box is equipped with connecting groove, the inner side wall of connecting groove is equipped with sliding slot, and the inside sliding connection of sliding slot has down-pressing silk subassembly.This carbon fiber continuous production is worn and is connected silk's device, when old silk and new silk position coincide to the below of down-pressing block, personnel can be lifted up control lever from the both sides of the equipment to make the pressing rod push down-pressing block downward, to reach the effect that old silk and new silk are pressed at high temperature by anti-adhesion pressing block.But through the way of fast pressing, it can lead to the strength of knot head not enough or unstable, cannot guarantee continuous production, in addition, this patent uses oxidizing furnace temperature to carry out high-temperature pressing, leading to the temperature of operating equipment is high, and there is operation safety risk. SUMMARY

[0006] The purpose of the present application is to overcome the problems of the prior art, such as the direct laying of raw filaments in the box for production, the excessive knot head at the connection between the end heads of adjacent two boxes of raw filaments, the delayed release of reaction heat at the knot head, the excessive heat accumulation causing the fire at the connection between the end heads of adjacent two boxes of raw filaments, the shutdown of the oxidizing furnace, and the inability to realize the continuous production of large-tow carbon fibers. The present application provides a large-tow carbon fiber and a method for the continuous production of large-tow carbon fibers. The large-tow carbon fiber includes alternately connected large-tow raw filaments, and the connection end heads of adjacent large-tow raw filaments are connected by a self-tightening knot method. The present application realizes the continuous production of large-tow carbon fibers, reduces the number of roll winding, improves the safety of production, increases the stable production time, reduces the amount of waste filaments, reduces the production cost, and improves the production efficiency.

[0007] To achieve the above-mentioned purpose, the present application provides a large-tow carbon fiber, which is characterized in that: the large-tow carbon fiber includes alternately connected large-tow raw filaments, and the connection end heads of adjacent large-tow raw filaments are connected by a self-tightening knot method. The self-tightening knot method includes: winding the pre-oxidized one end of an A segment of large-tow raw filament around the pre-oxidized one end of a B segment of large-tow raw filament to form a loop, and threading the filament head through the loop to tighten the knot head; winding the pre-oxidized other end of the B segment of large-tow raw filament around the pre-oxidized other end of the A segment of large-tow raw filament to form a loop, and threading the filament head through the loop to tighten the knot head; and after completing the knot, tightening the two ends of the two knot heads.

[0008] The second aspect of the present application provides a continuous production method of large tow carbon fibers, which comprises the following steps: (1) winding the pre-oxidized one end of the A section large tow precursor around the pre-oxidized one end of the B section large tow precursor to form a loop, and passing the thread end through the loop to tighten the knot; (2) winding the pre-oxidized other end of the B section large tow precursor around the pre-oxidized other end of the A section large tow precursor to form a loop, and passing the thread end through the loop to tighten the knot; (3) after completing the knotting, tightening the two knot ends; repeating the steps (1)-(3) of self-tightening connection according to the needs of continuous production; (4) after completing the connection, performing oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, washing, sizing, drying, and winding to collect the fibers.

[0009] The third aspect of the present application provides large tow carbon fibers prepared by the continuous production method of large tow carbon fibers described in the present application.

[0010] Through the above technical solution, the present application has the following beneficial effects:

[0011] The present application first proposes a large tow carbon fiber, which comprises large tow precursors connected alternately, and the end heads of adjacent large tow precursors are connected by a self-tightening knot method. Through the connection method described in the present application, the end heads of large tow precursors packed in boxes can be connected together with the end heads of adjacent large tow precursors packed in boxes. The knot is not only firm, but also has a breaking strength of more than 156000 cN.

[0012] After the end heads of adjacent large tow precursors are connected by the self-tightening knot method, the knot does not loosen or fall off during oxidation, and the connection does not produce smoke and fire due to heat accumulation and overheating, which ensures that the end heads of adjacent two boxes of precursors can be connected tightly and smoothly pass through the oxidation furnace, low-temperature carbonization furnace, high-temperature carbonization furnace, surface treatment, washing, sizing, drying, and winding production processes in sequence.

[0013] In the preferred embodiment of the present application, the self-tightening knot method is used to connect the end heads of adjacent large tow precursors, which can realize the continuous production of large tow carbon fibers, reduce the number of winding rollers, improve the stability of production time, reduce the amount of waste silk, reduce production costs, and improve production efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a schematic diagram of the connection of the end heads of adjacent large tow precursors by a self-tightening knot method. DETAILED DESCRIPTION

[0015] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not to be understood as being crucial in light of the functions to be fulfilled by the dimensions. The disclosed ranges are therefore to be understood to include values approximating these ranges. In respect of ranges of values, these ranges can be combined with one another either between the extreme values of the ranges, between an extreme value of a range and an isolated value, and between isolated values, to give one or more new ranges of values which should be considered as being specifically disclosed herein.

[0016] The present application first proposes a large-tow carbon fiber, comprising large-tow filaments connected alternately, adjacent large-tow filaments being connected through self-tight knotting, wherein the self-tight knotting comprises: winding an oxidized end of an A-section large-tow filament around an oxidized end of a B-section large-tow filament to form a loop, and threading the end of the filament through the loop to tighten the knot; winding the other oxidized end of the B-section large-tow filament around the other oxidized end of the A-section large-tow filament to form a loop, and threading the end of the filament through the loop to tighten the knot; and after the knotting is completed, tightening the two ends of the knots. Through the connecting method, in continuous production, the end-to-end heads of large-tow filaments packed in boxes can be connected with the end-to-end heads of adjacent large-tow filaments packed in boxes, the knots are firm, and the breaking strength of the knots reaches 156,000 cN or above. After the end-to-end heads of adjacent large-tow filaments are knotted, the knots do not come off or fall off in the oxidation process, and the connection does not produce smoke and fire due to heat accumulation and overheating, so that the end-to-end heads of two adjacent boxes of filaments can be connected firmly, and can smoothly pass through the production processes of an oxidation furnace, a low-temperature carbonization furnace, a high-temperature carbonization furnace, surface treatment, water washing, sizing, drying, and winding and collecting of filaments in sequence from a yarn placing rack.

[0017] In the present application, the K number of the large-tow filaments can be a conventional selection in the art, according to a preferred embodiment of the present application, the K number of each of the A-section large-tow filaments and the B-section large-tow filaments is 260-350K, preferably 290-320K. By adopting the foregoing preferred embodiment, the firmness of the connection between the filaments and the carbon fiber can be further improved, and the connection does not produce loosening and breaking.

[0018] In the present application, the length of the knot tail left after the end heads of the connection of the adjacent large-tow filaments are connected through self-tight knotting has no special requirement, according to a preferred embodiment of the present application, the end heads of the connection of the adjacent large-tow filaments are connected through self-tight knotting, and the length of the knot tail left after the self-tight knotting is 10-28cm, preferably 16-22cm. By adopting the foregoing preferred embodiment, the safety production stability of the knot passing through the oxidation furnace, the low-temperature carbonization furnace, and the high-temperature carbonization furnace can be further improved.

[0019] The application provides a continuous production method of large-tow carbon fibers, which comprises the following steps: (1) winding one end of a pre-oxidized A large-tow precursor around the pre-oxidized end of a B large-tow precursor to form a loop, and passing the thread end through the loop to tighten the knot; (2) winding the other end of the B large-tow precursor around the other end of the A large-tow precursor to form a loop, and passing the thread end through the loop to tighten the knot; (3) after the knotting is completed, the two knot ends are pulled tight; repeating the knot connection steps (1)-(3) according to the needs of continuous production; (4) after the connection is completed, performing oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, washing, sizing, drying and winding to collect the fibers. Through the continuous production method, the continuous production of large-tow carbon fibers can be realized, the number of roll winding is reduced, the production safety is high, the stable production time is improved, the amount of waste silk is reduced, the production cost is reduced, the production efficiency is improved, and the risk of fire caused by excessive heat accumulation at the connection of the precursor ends is avoided, thereby effectively realizing the continuous production of large-tow carbon fibers.

[0020] In the application, after step (1) and before step (2), the two ends of the large-tow precursor are respectively laid on the tension frame, the precursor is pulled tight and fixed, the tension frame is put into the pre-oxidation furnace, and the ends of the precursor are pre-oxidized. This step has no special requirements and can be performed according to the prior art, and the application will not be described here.

[0021] In the application, after the ends of the large-tow precursor are pre-oxidized in step (1), a cooling step is needed, and the cooling time and method have no special requirements and can be performed according to the prior art, and only cooling to room temperature is needed.

[0022] In the application, after the knot connection is completed in step (4), oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, washing, sizing, drying and winding are performed, and the specific steps and operating conditions have no special requirements and can be performed according to the prior art, and the application will not be described here.

[0023] In the application, the number of times of alternate connection of adjacent large-tow precursors is not limited and can be selected as needed.

[0024] The large-tow carbon fibers with the features of the application can achieve the purpose of the application, and the specific preparation steps and processes can be selected and adjusted as needed.

[0025] By using the preferred embodiment described above, the knot fracture strength at the connection of the precursor and the carbon fiber can be further improved, the stress in each direction of the knot is uniform, and the knot is stable and does not come off.

[0026] In the present application, the number of pre-oxidation of the large tow filaments has no special requirements, according to one preferred embodiment of the present application, the pre-oxidation of the large tow filaments is completed in two stages, including first pre-oxidation and second pre-oxidation; the temperature of the second pre-oxidation is 10-25℃ higher than that of the first pre-oxidation.

[0027] In the present application, the conditions of the first pre-oxidation of the large tow filaments can be the conventional selection in the art.

[0028] According to one preferred embodiment of the present application, the temperature of the first pre-oxidation of the large tow filaments is 215-270℃, preferably 235-260℃.

[0029] According to one preferred embodiment of the present application, the time of the first pre-oxidation of the large tow filaments is 10-70min, preferably 35-60min.

[0030] By adopting the foregoing preferred embodiment, the oxidation reaction of the filaments can be further effectively and rapidly carried out.

[0031] In the present application, the conditions of the second pre-oxidation of the large tow filaments can be the conventional selection in the art.

[0032] According to one preferred embodiment of the present application, the temperature of the second pre-oxidation of the large tow filaments is 240-280℃, preferably 250-270℃.

[0033] According to one preferred embodiment of the present application, the time of the second pre-oxidation of the large tow filaments is 10-70min, preferably 35-60min.

[0034] By adopting the foregoing preferred embodiment, the completion of the cyclization and dehydrogenation reaction of the filaments can be further ensured, and the linear macromolecular chain of the PAN-based filaments is converted into a ladder-shaped macromolecular structure through intramolecular cyclization and intermolecular crosslinking.

[0035] In the present application, the length of the tail left after knotting the connection end of the pre-oxidized large tow filaments and the connection end of the pre-oxidized adjacent large tow filaments has no special requirements, according to one preferred embodiment of the present application, the length of the tail left after knotting the connection end of the pre-oxidized large tow filaments and the connection end of the pre-oxidized adjacent large tow filaments is 10-28cm, preferably 16-22cm. By adopting the foregoing preferred embodiment, the safety production stability of the knot head in passing through the oxidation furnace, the low-temperature carbonization furnace and the high-temperature carbonization furnace can be further improved.

[0036] 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 100-210 cm, preferably 150-190 cm. By adopting the aforementioned preferred embodiment, it is possible to further improve the ability to ensure that the length of the pre-oxidized filament meets the length requirements for connection with carbon fibers.

[0037] This invention provides large-tow carbon fibers prepared by the continuous production method of large-tow carbon fibers described in this invention.

[0038] like Figure 1 The diagram shown illustrates how adjacent large filament bundles of the present invention are connected by a self-tightening method; wherein, Figure 1 In the diagram, 1 represents the pre-oxidized end of a large bundle of raw filaments; 2 represents the pre-oxidized end of a large bundle of raw filaments in an adjacent box.

[0039] 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:

[0040] Oxidation furnace throughput = (Number of nodes that successfully pass through the oxidation furnace / Total number of nodes entering the oxidation furnace) * 100%

[0041] 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%

[0042] 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%

[0043] The raw material for the silk is a commercially available product of brand SF from Sinopec Shanghai Petrochemical Co., Ltd.

[0044] 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:)

[0045] 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.

[0046] Low-temperature carbonization furnace: the low-temperature carbonization production process is carried out in a low-temperature carbonization furnace divided into six heating temperature zones, the pre-oxidized yarns from the outlet of the oxidation furnace enter the low-temperature carbonization furnace through a traction device, low-temperature carbonization is carried out in a nitrogen medium, and low-temperature carbonized yarns are prepared, the temperatures of the six heating temperature zones are 470℃, 540℃, 610℃, 670℃, 740℃ and 790℃ respectively, the yarns run in the low-temperature carbonization furnace, the draft ratio is controlled to be 1.06, and the total residence time in the low-temperature carbonization furnace is 1.2 minutes;

[0047] High-temperature carbonization furnace: the high-temperature carbonization production process is carried out in a high-temperature carbonization furnace divided into five heating temperature zones, the yarns from the outlet of the low-temperature carbonization furnace enter the high-temperature carbonization furnace through a traction device, high-temperature carbonization is carried out in a nitrogen medium, and high-temperature carbonized yarns are prepared, the temperatures of the five heating temperature zones are 1100℃, 1390℃, 1470℃, 1490℃ and 1400℃ respectively, the yarns run in the high-temperature carbonization furnace, the draft ratio is controlled to be 0.76, and the total residence time in the high-temperature carbonization furnace is 1.2 minutes;

[0048] Surface treatment: the surface treatment production process is that the yarns from the outlet of the high-temperature carbonization furnace enter a surface treatment tank through a traction device, an aqueous ammonium bicarbonate solution is used as an electrolyte, the voltage is 18V, the electrolyte concentration is 10%, and the residence time of the yarns in the electrolyte is 60 seconds;

[0049] Water washing: the yarns from the outlet of the surface treatment tank enter a water washing tank, the yarns are subjected to water washing, the water washing flow rate is 2800L / hour, and the water washing temperature is 50℃;

[0050] Sizing: a commercially available K7 epoxy emulsion sizing agent is used to impregnate and size the unsized carbon fibers, the time is 20s, and the temperature is 25℃;

[0051] Drying: vertical hot air drying, and the drying temperature is 170℃;

[0052] Winding and collecting yarns: the carbon fibers after sizing and drying are wound and collected by using a carbon fiber winding machine, and finished carbon fibers are prepared.

[0053] In the following implementation, the yarn head and the yarn tail are the two end heads of the yarn, and the K number of the large tow raw yarns is the same in the same example. Other parameters are shown in Table 1.

[0054] Example 1

[0055] In this example, the K number of the large tow raw yarns is 290K.

[0056] S1. A certain length of the yarn head and the yarn tail of each box of raw yarns is reserved, and the length of the yarn head and the yarn tail is 150cm.

[0057] S2. The ends of each box of raw silk are laid on the tension frame, the raw silk is tightened and fixed, the tension frame is put into the pre-oxidation furnace, and the ends of the raw silk are pre-oxidized. The pre-oxidation is divided into two stages. The first stage of oxidation is at an oxidation temperature of 235°C for 35 minutes, and the second stage of oxidation is at an oxidation temperature of 250°C for 35 minutes.

[0058] S3. The pre-oxidized end of the first box of large tow raw silk is wound around the pre-oxidized end of the adjacent other box of large tow raw silk to form a loop, and the end of the raw silk is passed through the loop, the knot is tightened, the pre-oxidized end of the adjacent other box of large tow raw silk is wound around the pre-oxidized end of the first box of large tow raw silk to form a loop, and the end of the raw silk is passed through the loop, and the knot is tightened (as shown in Figure 1

[0059] S4. After the knot is completed, the two ends of the knot are tightened, the excess ends of the raw silk are cut off, the length of the tail of the knot is left at 16 cm, and the two raw silks are tightened to make the knot more secure.

[0060] S5. The remaining large tow raw silk repeats steps S3 and S4, and after the above knot connection is completed, it is sequentially subjected to oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, washing, sizing, drying, and winding.

[0061] The implementation effect of this embodiment is shown in Table 3.

[0062] Example 2

[0063] The K number of the large tow raw silk in this embodiment is 300K.

[0064] S1. The ends of each box of raw silk are left with a certain length, and the length of the ends is 184 cm.

[0065] S2. The ends of each box of raw silk are laid on the tension frame, the raw silk is tightened and fixed, the tension frame is put into the pre-oxidation furnace, and the ends of the raw silk are pre-oxidized. The pre-oxidation is divided into two stages. The first stage of oxidation is at an oxidation temperature of 255°C for 50 minutes, and the second stage of oxidation is at an oxidation temperature of 264°C for 50 minutes.

[0066] S3. The pre-oxidized end of the first box of large tow raw silk is wound around the pre-oxidized end of the adjacent other box of large tow raw silk to form a loop, and the end of the raw silk is passed through the loop, the knot is tightened, the pre-oxidized end of the adjacent other box of large tow raw silk is wound around the pre-oxidized end of the first box of large tow raw silk to form a loop, and the end of the raw silk is passed through the loop, and the knot is tightened (as shown in Figure 1

[0067] S4. After the knot is completed, the two ends of the knot are tightened, the excess ends of the raw silk are cut off, the length of the tail of the knot is left at 20 cm, and the two raw silks are tightened to make the knot more secure.​​

[0068] S5. The remaining large tow precursor filaments repeat steps S3 and S4, and after the above knot connection is completed, sequentially pass through oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, washing, sizing, drying, and winding to collect the filaments.

[0069] The implementation effect of this example is shown in Table 3.

[0070] Example 3

[0071] The K number of the large tow precursor filaments in this example is 320K.

[0072] S1. A certain length of the head and tail of each box of precursor filaments is reserved, and the length of the head and tail is 190 cm.

[0073] S2. The head and tail of each box of precursor filaments are respectively laid on a tension frame, the precursor filaments are pulled tight and fixed, the tension frame is placed into a pre-oxidation furnace, and the head and tail of the precursor filaments are pre-oxidized. The pre-oxidation is divided into two stages, the first stage of oxidation has an oxidation temperature of 260°C and a time of 60 min, and the second stage of oxidation has an oxidation temperature of 270°C and a time of 60 min.

[0074] S3. The pre-oxidized end of the first box of large tow precursor filaments is wound around the pre-oxidized end of the adjacent other box of large tow precursor filaments to form a loop, and the head is passed through the loop. The pre-oxidized other end of the adjacent other box of large tow precursor filaments is wound around the other end of the pre-oxidized first box of large tow precursor filaments to form a loop, and the head is passed through the loop (as shown in Figure 1 ).

[0075] S4. After the knot connection is completed, the two ends of the two knots are pulled tight, the excess head and tail of the filaments are cut off, the length of the tail of the knot is left as 22 cm, and the two precursor filaments are pulled tight to make the knot more secure.

[0076] S5. The remaining large tow precursor filaments repeat steps S3 and S4, and after the above knot connection is completed, sequentially pass through oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, washing, sizing, drying, and winding to collect the filaments.

[0077] The implementation effect of this example is shown in Table 3.

[0078] Example 4

[0079] The K number of the large tow precursor filaments in this example is 260K.

[0080] S1. A certain length of the head and tail of each box of precursor filaments is reserved, and the length of the head and tail is 100 cm.

[0081] S2. The first end of the first box of large tow precursor is wound around the first end of the second box of large tow precursor, and the first end of the second box of large tow precursor is wound around the second end of the first box of large tow precursor, and the two ends of the first box of large tow precursor are pulled tight, and the two ends of the second box of large tow precursor are pulled tight.

[0082] S3. The first end of the first box of large tow precursor is wound around the first end of the second box of large tow precursor, and the first end of the second box of large tow precursor is wound around the second end of the first box of large tow precursor, and the two ends of the first box of large tow precursor are pulled tight, and the two ends of the second box of large tow precursor are pulled tight. Figure 1

[0083] S4. After the knot is completed, the two ends of the knot are pulled tight, and the excess ends of the first and second boxes of large tow precursor are cut, and the length of the knot tail left is 10 cm, and the two ends of the knot are pulled tight to make the knot more secure.

[0084] S5. The remaining large tow precursors are repeated steps S3 and S4, and after the knot connection is completed, the above-mentioned is sequentially subjected to oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, washing, sizing, drying, and winding.

[0085] The implementation effect of this example is shown in Table 3.

[0086] Example 5

[0087] All operation steps are the same as Example 1, except that the K number of the large tow precursor, the two-stage pre-oxidation temperature and the two-stage pre-oxidation residence time, the length of the ends of the first and second boxes of large tow precursor, and the length of the knot tail left after the knot is completed are different from those of Example 1. The specific values are shown in Table 2.

[0088] The implementation effect of this example is shown in Table 3.

[0089] Example 6

[0090] All operation steps and conditions are the same as Example 1, except that the K number of the large tow precursor is 250K, which is not within the preferred range of the present application.

[0091] Example 7

[0092] All operation steps and conditions are the same as Example 1, except that the length of the knot tail left after the knot is completed is 25 cm, which is not within the preferred range of the present application.

[0093] Example 8

[0094] ​All the operation steps and conditions are the same as those in Example 1, except that the original 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 application, the first stage of oxidation has an oxidation temperature of 228°C and a time of 32 min, and the second stage of oxidation has an oxidation temperature of 243°C and a time of 32 min.

[0095] The implementation effect of this example is shown in Table 3.

[0096] Example 9

[0097] All the operation steps and conditions are the same as those in Example 1, except that the length of one end of the large tow original filament is 132 cm, which is not within the preferred range of the present application.

[0098] The implementation effect of this example is shown in Table 3.

[0099] Comparative Example 1

[0100] All the conditions are the same as those in Example 1, except that the connection method of adjacent 290K large tow original filaments is a barrel knot knotting method, the original filament head of one box and the original filament tail of the adjacent box are stacked together in parallel, the stacked tows are wound around a loop, the head and tail are pulled tight through the loop, and the excess knot tail is cut off.

[0101] Table 1

[0102]

[0103] Table 2

[0104]

[0105] Table 3

[0106]

[0107] From the results in Table 1, it can be seen that Examples 1-9 using the large tow carbon fiber and the continuous production method of large tow carbon fiber of the present application have a 260-350K carbon fiber production process, can achieve firm connection of the ends of adjacent original filaments, the breaking strength of the knot head reaches 156000CN or more, and the knot head can smoothly pass through the oxidation furnace, the low-temperature carbonization furnace, and the high-temperature carbonization furnace, with an oxidation furnace passing rate of 100%, a low-temperature carbonization furnace passing rate of 100%, and a high-temperature carbonization furnace passing rate of 100%, and the implementation effect is good.

[0108] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including that each technical feature is combined in any other suitable manner. These simple modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.

Claims

1. A large tow carbon fiber, characterized by: The large-tow carbon fiber comprises large-tow filaments connected alternately, and the connecting ends of adjacent large-tow filaments are connected by self-tightening knots; The self-tightening knot comprises: winding the pre-oxidized one end of the A segment large-tow filament around the pre-oxidized one end of the B segment large-tow filament to form a loop, and passing the filament head through the loop to tighten the knot; Winding the pre-oxidized other end of the B segment large-tow filament around the pre-oxidized other end of the A segment large-tow filament to form a loop, and passing the filament head through the loop to tighten the knot; After the knot is completed, the two knot ends are tightened; The connecting ends of the large-tow filaments are subjected to pre-oxidation treatment; the pre-oxidation is performed in two stages, first pre-oxidation and second pre-oxidation; the temperature of the second pre-oxidation is 10-25℃ higher than that of the first pre-oxidation; The K number of each of the A segment large-tow filament and the B segment large-tow filament is 260-350K; The connecting ends of adjacent large-tow filaments are connected by self-tightening knots, and the length of the knot tail left after the self-tightening knot connection of each end of the connecting position is 10-28cm.

2. The large-tow carbon fiber according to claim 1, wherein, The K number of each of the A segment large-tow filament and the B segment large-tow filament is 290-320K.

3. The large-tow carbon fiber according to claim 1 or 2, wherein, The connecting ends of adjacent large-tow filaments are connected by self-tightening knots, and the length of the knot tail left after the self-tightening knot connection of each end of the connecting position is 16-22cm.

4. A continuous production method of the large-tow carbon fiber according to any one of claims 1-3, the method comprising the following steps: (1) winding the pre-oxidized one end of the A segment large-tow filament around the pre-oxidized one end of the B segment large-tow filament to form a loop, and passing the filament head through the loop to tighten the knot; (2) winding the pre-oxidized other end of the B segment large-tow filament around the pre-oxidized other end of the A segment large-tow filament to form a loop, and passing the filament head through the loop to tighten the knot; (3) after the knot is completed, the two knot ends are tightened; and the steps (1)-(3) of the self-tightening knot connection are repeated according to the needs of continuous production; (4) after the connection is completed, the large-tow filaments are subjected to oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, washing, sizing, drying, and winding; and the length of the knot tail left after the knotting of each end of the connecting position of adjacent large-tow filaments after pre-oxidation is 10-28cm; The pre-oxidation is performed in two stages, including first pre-oxidation and second pre-oxidation; and the temperature of the second pre-oxidation is 10-25℃ higher than that of the first pre-oxidation.

5. The method according to claim 4, wherein, The conditions of the first pre-oxidation comprise: the temperature is 215-270℃; and / or the time is 10-70min.

6. The method according to claim 5, wherein, The conditions of the first pre-oxidation comprise: the temperature is 235-260℃; and / or the time is 35-60min.

7. The method according to claim 4, wherein, The conditions of the second pre-oxidation comprise: the temperature is 240-280℃; and / or the time is 10-70min.

8. The method according to claim 7, wherein, The conditions of the second pre-oxidation include: a temperature of 250-270°C; and / or a time of 35-60 minutes.

9. The method of claim 4, wherein, After the adjacent large-tow precursor filaments are knotted respectively after pre-oxidation, the length of the knot tail left at the end of the connection is 16-22 cm.

10. The method according to claim 4, wherein, Before the pre-oxidation, the length of the end of the large-tow precursor filaments reserved for pre-oxidation in step (1) is 100-210 cm.

11. The method according to claim 10, wherein, Before the pre-oxidation, the length of the end of the large-tow precursor filaments reserved for pre-oxidation in step (1) is 150-190 cm.

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