Large-tow carbon fiber and large-tow carbon fiber continuous production method

Abstract

The invention relates to the technical field of large-tow carbon fiber production, in particular to a large-tow carbon fiber and a continuous production method of the large-tow carbon fiber, and discloses a large-tow fiber, the large-tow carbon fiber comprises a large-tow precursor and a carbon fiber which are alternately connected, and the large-tow precursor and the carbon fiber are connected in a self-tightening mode. The end socket of the large-tow precursor end packaged in a box can be connected with the end socket of the adjacent large-tow precursor end packaged in the box, so that knots are firm, and the breaking strength of the knots reaches 156000 cN or above; the large-tow precursor and the carbon fiber are connected in a self-tightening mode, continuous production of the large-tow carbon fiber can be achieved, the roller winding frequency is reduced, the production safety is high, the stable production time is prolonged, the waste yarn amount is reduced, the production cost is reduced, and the production efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of large-tow carbon fiber production, and in particular to large-tow carbon fiber and a large-tow carbon fiber continuous production method. Background Art

[0002] Carbon fiber (CF) is a new type of fiber material with high strength and high modulus fiber with a carbon content of more than 90%. 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 and is known as the "king of new materials" and "black gold". In the carbon fiber industry, carbon fibers with more than 48,000 strands per bundle (48K for short) are usually called large tow carbon fibers. Although the performance of large tows of carbon fiber is not as good as that of small tows, its cost is lower. With the development of science and technology, the application of large tows is also more extensive. It can be mainly used in industrial fields such as electromechanical, transportation, civil engineering, energy, and textiles, so it is also called industrial-grade carbon fiber. The main purpose of oxidation of the precursor is to cause cyclization and intermolecular cross-linking within the linear polyacrylonitrile (PAN) macromolecular chain to generate a heat-resistant mesh ladder structure.

[0003] The pre-oxidation process of polyacrylonitrile (PAN)-based precursors is very complex and involves complex physical and chemical changes. During the pre-oxidation process, the cyano groups on the PAN molecular chain undergo cyclization and cross-linking, and the molecular chain changes from a linear structure to a trapezoidal structure. The formation of a suitable cyclization structure of the precursor during the pre-oxidation process is the most basic factor in the preparation of ideal carbon fibers. The oxidation process is the most energy-intensive and time-consuming process in the preparation of carbon fibers, and is the key process that restricts the production efficiency of PAN-based carbon fibers.

[0004] CN115303892A introduces a method for connecting polyacrylonitrile-based carbon fiber precursors, which includes the following steps: knotting the tail end of a first polyacrylonitrile-based carbon fiber precursor strand and the head end of a second polyacrylonitrile-based carbon fiber precursor strand to form a fixed knot, and leaving a thread head on one side of the fixed knot; weaving the thread head of the first polyacrylonitrile-based carbon fiber precursor strand into the second polyacrylonitrile-based carbon fiber precursor strand located on the other side of the fixed knot to form a first braided wire section; weaving the thread head of the second polyacrylonitrile-based carbon fiber precursor strand into the first polyacrylonitrile-based carbon fiber precursor strand located on the other side of the fixed knot to form a second braided wire section; the first braided wire section, the fixed knot, and the second braided wire section constitute a knot; and applying an adhesive on the knot. The present invention is mainly used to make the knot have a certain strength, so that the knot can directly pass through the pre-oxidation furnace, the low-carbon furnace, the high-carbon furnace and the wire collecting machine from the withdrawal yarn rack, thereby reducing parking time and improving production efficiency. However, since a large amount of heat is released during the pre-oxidation process, the knotting of the precursor strands will cause the internal heat storage of the knot to overheat, causing the strand to burn out. In the production of large-tow carbon fiber, the pre-oxidation drafting tension is greater, the pre-oxidation reaction is more intense, the knots are more likely to catch fire, and there are safety hazards.

[0005] CN217968442U The utility model discloses a device for continuous production of carbon fiber through furnace wire connection, relates to the technical field of wire connection equipment, and is specifically a device for continuous production of carbon fiber through furnace wire connection, including a mounting seat, one side of the mounting seat is fixedly connected with a wire connection box, both sides of the wire connection box are fixedly connected with a control sleeve, the upper surface of the wire connection box is provided with a connection groove, the inner side wall of the connection groove is provided with a slide groove, and the inner side of the slide groove is slidably connected with a lower pressing wire assembly. The device for continuous production of carbon fiber through furnace wire connection, when the old wire and the new wire are overlapped below the lower pressing block, the personnel can lift the control rod upward from both sides of the device to make the pressing rod push the lower pressing block downward, so as to achieve the effect of pressing the old wire and the new wire at high temperature by the anti-adhesion pressing block. However, the knot connection is carried out by the fast pressing method, which will cause the knot strength to be insufficient or unstable, and continuous production cannot be guaranteed. In addition, this patent uses the oxidation furnace temperature for high-temperature pressing, which leads to high temperature of the operating equipment and there is an operational safety risk. Summary of the invention

[0006] The purpose of the present invention is to overcome the problem in the prior art that raw silk filaments are directly laid in boxes for production, the knots at the end connections of two adjacent boxes of raw silk are too large, the reaction heat at the knots cannot be released in time, and excessive heat storage causes the end connections of two adjacent boxes of raw silk to catch fire, the oxidation furnace stops, and the continuous production of large-tow carbon fibers cannot be achieved. A large-tow carbon fiber and a continuous production method of large-tow carbon fiber are provided. The large-tow carbon fiber includes alternatingly connected large-tow raw silks, and the connecting ends of adjacent large-tow raw silks are connected by self-tightening knots, thereby achieving continuous production of large-tow carbon fibers, which has the advantages of reducing the number of roller windings, high production safety, increasing stable production time, reducing the amount of waste silk, reducing production costs, and improving production efficiency.

[0007] In order to achieve the above-mentioned purpose, the present invention provides a large-tow carbon fiber, characterized in that: the large-tow carbon fiber includes alternating large-tow precursors, and the connecting ends of adjacent large-tow precursors are connected by a self-tightening knot; the self-tightening knot includes: wrapping one end of the pre-oxidized large-tow precursor of section A around one end of the pre-oxidized large-tow precursor of section B to form a loop, and passing the wire head through the loop to tighten the knot; winding the other end of the pre-oxidized large-tow precursor of section B with the other end of the pre-oxidized large-tow precursor of section A to form a loop, and passing the wire head through the loop to tighten the knot; after knotting is completed, tightening the two ends of the knot.

[0008] According to a second aspect of the present invention, there is provided a method for continuous production of large-tow carbon fiber, which comprises the following steps: (1) winding one end of the pre-oxidized large-tow precursor of segment A around one end of the pre-oxidized large-tow precursor of segment B to form a loop, and passing the wire head through the loop to tighten the knot; (2) winding the other end of the pre-oxidized large-tow precursor of segment B around the other end of the pre-oxidized large-tow precursor of segment A to form a loop, and passing the wire head through the loop to tighten the knot; (3) after knotting, tightening both ends of the two knots; repeating the self-tightening knot connection steps (1) to (3) according to the needs of continuous production; (4) after the connection is completed, the wire is oxidized, carbonized at low temperature, carbonized at high temperature, surface treated, washed, sizing, dried, and wound.

[0009] A third aspect of the present invention provides large-tow carbon fibers prepared by the method for continuous production of large-tow carbon fibers according to the present invention.

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

[0011] The present invention proposes for the first time a large-tow carbon fiber, comprising alternatingly connected large-tow precursors, wherein the connecting ends of adjacent large-tow precursors are connected by a self-tightening knot. Through the connection method described in the present invention, the ends of the large-tow precursors packaged in a box can be connected together with the ends of the large-tow precursors packaged in an adjacent box, and not only the knot is firm, but the breaking strength of the knot reaches more than 156,000 cN.

[0012] After the adjacent large bundles of raw silk ends of the present invention are connected by a self-tightening knot, not only will the knot not loosen or fall off during the oxidation process, but the connection will not produce smoke or fire due to overheating due to heat storage, ensuring that the two adjacent boxes of raw silk ends can be connected tightly and can smoothly pass through the oxidation furnace, low-temperature carbonization furnace, high-temperature carbonization furnace, surface treatment, washing, sizing, drying, and winding production processes from the silk unwinding frame.

[0013] In a preferred embodiment of the present invention, the present invention uses a method for connecting adjacent large-tow raw fibers by a self-tightening method, which can achieve continuous production of large-tow carbon fibers, reduce the number of roller windings, increase production safety, increase stable production time, reduce the amount of waste fibers, reduce production costs, and improve production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of connecting the ends of adjacent large bundles of raw fibers through a self-tightening knot. DETAILED DESCRIPTION

[0015] The endpoints and any values ​​of the ranges disclosed in this article 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0016] The present invention proposes a large-tow carbon fiber for the first time, including alternating large-tow precursors, and adjacent large-tow precursors are connected by a self-tightening knot method, wherein the self-tightening knot method includes: wrapping one end of the pre-oxidized large-tow precursor of segment A around one end of the pre-oxidized large-tow precursor of segment B to form a loop, and passing the wire head through the loop to tighten the knot; wrapping the other end of the pre-oxidized large-tow precursor of segment B around the other end of the pre-oxidized large-tow precursor of segment A to form a loop, and passing the wire head through the loop to tighten the knot; after knotting, tighten the two ends of the knots. Through the connection method of the present invention, in continuous production, the end of the large-tow precursor packaged in a box can be connected with the end of the large-tow precursor packaged in an adjacent box, and not only the knot is firm, but also the breaking strength of the knot reaches more than 156000cN. After the ends of adjacent large bundles of raw silk described in the present invention are knotted, not only will the knots not loosen or fall off during the oxidation process, but the connection will not produce smoke or fire due to overheating due to heat storage, ensuring that the ends of two adjacent boxes of raw silk can be connected tightly and can smoothly pass through the oxidation furnace, low-temperature carbonization furnace, high-temperature carbonization furnace, surface treatment, washing, sizing, drying, and winding production processes from the silk unwinding frame.

[0017] In the present invention, the K number of the large tow precursor can be a conventional choice in the art. According to a preferred embodiment of the present invention, the K number of the large tow precursor of segment A and the large tow precursor of segment B is 260-350 K, preferably 290-320 K. By adopting the aforementioned preferred embodiment, the firmness of the connection between the precursor and the carbon fiber can be further improved, and the connection will not loosen or break.

[0018] In the present invention, after the adjacent large tow strands are connected by a self-tightening knot, there is no special requirement for the length of the knot tails left at the respective ends of the connection. According to a preferred embodiment of the present invention, the adjacent large tow strands are connected by a self-tightening knot, and after the respective ends of the connection are connected by a self-tightening knot, the length of the knot tail left by the self-tightening knot is 10-28cm, preferably 16-22cm. By adopting the aforementioned 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 present invention provides a continuous production method of large-tow carbon fiber, which comprises the following steps: (1) winding one end of a pre-oxidized large-tow precursor of segment A around one end of a pre-oxidized large-tow precursor of segment B to form a loop, passing the wire head through the loop, and tightening the knot; (2) winding the other end of the pre-oxidized large-tow precursor of segment B around the other end of the pre-oxidized large-tow precursor of segment A to form a loop, passing the wire head through the loop, and tightening the knot; (3) after knotting, tightening the two ends of the two knots; repeating the self-tightening knot connection steps (1) to (3) according to the continuous production needs; (4) after the connection is completed, the wire is oxidized, low-temperature carbonized, high-temperature carbonized, surface treated, washed, sizing, dried, and wound. Through this continuous production method, the continuous production of large-tow carbon fiber can be achieved, the number of roller windings can be reduced, the production safety is high, the stable production time is increased, 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 storage at the connection of the original silk ends is avoided, the production cost is reduced, and the production efficiency is improved, thereby effectively realizing the continuous production of large-tow carbon fiber.

[0020] In the present invention, after step (1) and before step (2), the two ends of the large tow raw silk need to be laid on the tension frame respectively, the raw silk is tightened and fixed, the tension frame is placed in the pre-oxidation furnace, and the two ends of the raw silk are pre-oxidized. There are no special requirements for this step, and it can be carried out with reference to the prior art, and the present invention will not be elaborated here.

[0021] In the present invention, in the step (1), after the end of the large tow raw yarn is pre-oxidized, a cooling step is required. There is no special requirement for the cooling time and method, and it can be carried out in accordance with the existing technology, and it only needs to be cooled to room temperature.

[0022] In the present invention, the step (4) is to complete the above-mentioned knot connection through 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, which can be carried out according to the existing technology, and the present invention will not elaborate on them here.

[0023] In the present invention, the number of times the adjacent large tows of raw filaments are alternately connected is not limited and can be selected according to needs.

[0024] The large-tow carbon fibers having the characteristics of the present invention can achieve the purpose of the present invention, and their specific preparation steps and processes can be selected and adjusted as needed.

[0025] By adopting the aforementioned preferred implementation, the breaking strength of the knot at the connection between the original silk and the carbon fiber can be further improved, ensuring that the knot is subjected to uniform force in all directions and the knot is stable and does not loosen.

[0026] In the present invention, there is no special requirement for the number of pre-oxidation of the large-tow precursor. According to a preferred embodiment of the present invention, the pre-oxidation of the large-tow precursor is completed 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 the temperature of the first pre-oxidation.

[0027] In the present invention, the conditions for the first pre-oxidation of the large tow precursor may be conventionally selected in the art.

[0028] According to a preferred embodiment of the present invention, the temperature of the first pre-oxidation of the large-tow precursor is 215-270°C, preferably 235-260°C.

[0029] According to a preferred embodiment of the present invention, the first pre-oxidation time of the large-tow precursor is 10-70 minutes, preferably 35-60 minutes.

[0030] By adopting the above-mentioned preferred embodiment, the oxidation reaction of the raw silk can be carried out more efficiently and quickly.

[0031] In the present invention, the conditions for the second pre-oxidation of the large tow precursor may be conventionally selected in the art.

[0032] According to a preferred embodiment of the present invention, the temperature of the second pre-oxidation of the large-tow precursor is 240-280°C, preferably 250-270°C.

[0033] According to a preferred embodiment of the present invention, the second pre-oxidation time of the large-tow precursor is 10-70 minutes, preferably 35-60 minutes.

[0034] By adopting the aforementioned preferred implementation, it is possible to further improve the guarantee of the precursor to complete the cyclization and dehydrogenation reactions, and transform the linear macromolecular chain of the PAN-based precursor into a heat-resistant ladder-shaped macromolecular structure through intramolecular cyclization and intermolecular cross-linking.

[0035] In the present invention, there is no special requirement for the length of the knot tail left after the connection ends of the pre-oxidized large tow strands and the adjacent pre-oxidized large tow strands are tied. According to a preferred embodiment of the present invention, the length of the knot tail left after the connection ends of the pre-oxidized adjacent large tow strands are tied is 10-28 cm, preferably 16-22 cm. By adopting the aforementioned preferred embodiment, the safety production stability of the knot can be further improved when passing through the oxidation furnace, the low-temperature carbonization furnace, and the high-temperature carbonization furnace.

[0036] In the present invention, before the pre-oxidation treatment of the large tow precursor in step (1), it is also necessary to reserve a length of the pre-oxidation end of the large tow precursor, and there is no special requirement for the reserved length. According to a preferred embodiment of the present invention, before the pre-oxidation treatment of the large tow precursor, the reserved length of the pre-oxidation end is 100-210cm, preferably 150-190cm. By adopting the aforementioned preferred embodiment, it is possible to further improve the length of the pre-oxidized precursor to ensure that it meets the length requirement for connection with the carbon fiber.

[0037] The present invention provides large-tow carbon fibers prepared by the large-tow carbon fiber continuous production method of the present invention.

[0038] like Figure 1 As shown, it is a schematic diagram of the adjacent large tows of raw yarns of the present invention being connected by a self-tightening method; wherein, Figure 1 Among them, 1 is the end of a large tow raw silk that has been pre-oxidized; 2 is the end of a large tow raw silk that has been pre-oxidized in an adjacent box.

[0039] The present invention will be described in detail below through examples. In the following examples, the knot breaking strength parameter is measured by adopting the GB / T19975-2005 high-strength fiber tensile performance test method. In the present invention, the knot breaking strength data is the average value of three knot tests in actual operation; the oxidation furnace pass rate, low temperature carbonization furnace pass rate, and high temperature carbonization furnace pass rate are calculated by the following method:

[0040] Oxidation furnace pass rate = the number of knots that actually pass through the oxidation furnace / the total number of knots that enter the oxidation furnace * 100%

[0041] Low temperature carbonization furnace pass rate = the number of knots that actually pass through the low carbon furnace / the total number of knots that enter the low carbon furnace * 100%

[0042] High temperature carbonization furnace pass rate = the number of knots that actually pass through the high carbon furnace / the total number of knots that enter the high carbon furnace * 100%

[0043] The raw material of the raw silk is a commercial product with the brand name SF produced by 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 and collecting adopt the same operating conditions: specifically as follows:

[0045] Oxidation furnace: divided into four temperature zones, the total time is 60 min, the draft ratios between the oxidation furnaces in the four heating temperature zones are 1.26, 0.99, 0.98, and 0.96, respectively. The temperatures of the four temperature zones of the embodiment of the present invention and the comparative example 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 6 heating temperature zones. The pre-oxidized wire from the oxidation furnace outlet enters the low-temperature carbonization furnace through a traction device, and is low-temperature carbonized with nitrogen as the medium to obtain low-temperature carbonized wire. The temperatures of the 6 heating temperature zones are 470°C, 540°C, 610°C, 670°C, 740°C, and 790°C, respectively. The wire bundle runs in the low-temperature carbonization furnace, and the draft ratio is controlled to be 1.06. The total residence time in the low-temperature carbonization furnace is 1.2 min.

[0047] High temperature carbonization furnace: The high temperature carbonization production process is carried out in a high temperature carbonization furnace divided into 5 heating temperature zones. The tow at the outlet of the low temperature carbonization furnace enters the high temperature carbonization furnace through a traction device, and is carbonized at high temperature with nitrogen as the medium to obtain high temperature carbonized wire. The temperatures of the 5 heating temperature zones are 1100°C, 1390°C, 1470°C, 1490°C, and 1400°C, respectively. The tow runs in the high temperature carbonization furnace, and the draft ratio is controlled to be 0.76. 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 tow at the outlet of the high-temperature carbonization furnace enters the surface treatment tank through a traction device, with an ammonium bicarbonate aqueous solution as the electrolyte, a voltage of 18V, an electrolyte concentration of 10%, and the tow stays in the electrolyte for 60 seconds;

[0049] Water washing: In the water washing production process, the tow at the outlet of the surface treatment tank enters the water washing tank, where the tow is washed with water, with a water washing flow rate of 2800L / hour and a water washing temperature of 50°C;

[0050] Sizing: The unsized carbon fiber was impregnated and sized with commercially available K7 epoxy emulsion sizing agent for 20 seconds at a temperature of 25°C.

[0051] Drying: Vertical hot air drying, drying temperature 170℃;

[0052] Winding and collecting: The carbon fiber after sizing and drying is wound and collected using a carbon fiber winder to produce finished carbon fiber.

[0053] In the following implementation, the wire head and the wire tail are the two ends of the wire respectively, and the K number of the large wire bundle original wire and in the same embodiment is the same. Other parameters are shown in Table 1.

[0054] Example 1

[0055] The K number of the large tow raw yarn in this embodiment is 290K.

[0056] S1. The silk ends and tails of each box of raw silk are kept at a certain length, and the length of the silk ends and tails is 150cm.

[0057] S2. Lay the silk ends and tails of each box of raw silk on the tension frame respectively, tighten the raw silk and fix it, put the tension frame into the pre-oxidation furnace, and pre-oxidize the silk ends and tails of the raw silk. The pre-oxidation is divided into two stages. The oxidation temperature of the first stage is 235℃ and the time is 35min. The oxidation temperature of the second stage is 250℃ and the time is 35min.

[0058] S3. Wrap one end of the pre-oxidized bulk tow raw silk in the first box around one end of the pre-oxidized bulk tow raw silk in another box to form a loop, pass the wire head through the loop, and tighten the knot; wrap the other end of the pre-oxidized bulk tow raw silk in another box around the other end of the pre-oxidized bulk tow raw silk in the first box to form a loop, pass the wire head through the loop, and tighten the knot (such as Figure 1 shown).

[0059] S4. After finishing the knot, tighten the two ends of the knot, cut off the excess silk ends, leaving a length of 16cm at the knot ends, and tighten the two original silk threads to make the knot tighter.

[0060] S5. Repeat steps S3 and S4 for the remaining large bundles of raw silk, and after the knotting and connection are completed, the raw silk is successively 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 yarn in this embodiment is 300K.

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

[0065] S2. Lay the silk ends and tails of each box of raw silk on the tension frame respectively, tighten the raw silk and fix it, put the tension frame into the pre-oxidation furnace, and pre-oxidize the silk ends and tails of the raw silk. The pre-oxidation is divided into two stages. The oxidation temperature of the first stage is 255℃ and the time is 50min. The oxidation temperature of the second stage is 264℃ and the time is 50min.

[0066] S3. Wrap one end of the pre-oxidized bulk tow raw silk in the first box around one end of the pre-oxidized bulk tow raw silk in another box to form a loop, pass the wire head through the loop, and tighten the knot; wrap the other end of the pre-oxidized bulk tow raw silk in another box around the other end of the pre-oxidized bulk tow raw silk in the first box to form a loop, pass the wire head through the loop, and tighten the knot (such as Figure 1 shown).

[0067] S4. After finishing the knot, tighten the two ends of the knot, cut off the excess wire ends, leaving a length of 20cm at the knot ends, and tighten the two original wires to make the knot tighter.

[0068] S5. Repeat steps S3 and S4 for the remaining large bundles of raw silk, and after the knotting and connection are completed, the raw silk is successively subjected to oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, washing, sizing, drying, and winding.

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

[0070] Example 3

[0071] The K number of the large tow raw yarn in this embodiment is 320K.

[0072] S1. The silk ends and tails of each box of raw silk retain a certain length, and the length of the silk ends and tails is 190cm.

[0073] S2. Lay the silk ends and tails of each box of raw silk on the tension frame respectively, tighten the raw silk and fix it, put the tension frame into the pre-oxidation furnace, and pre-oxidize the silk ends and tails of the raw silk. The pre-oxidation is divided into two stages. The oxidation temperature of the first stage is 260℃ and the time is 60min. The oxidation temperature of the second stage is 270℃ and the time is 60min.

[0074] S3. Wrap one end of the pre-oxidized bulk tow raw silk in the first box around one end of the pre-oxidized bulk tow raw silk in another box to form a loop, pass the wire head through the loop, and tighten the knot; wrap the other end of the pre-oxidized bulk tow raw silk in another box around the other end of the pre-oxidized bulk tow raw silk in the first box to form a loop, pass the wire head through the loop, and tighten the knot (such as Figure 1 shown).

[0075] S4. After finishing the knot, tighten the two ends of the knot, cut off the excess silk ends, leaving a length of 22cm at the knot end, and tighten the two original silk threads to make the knot tighter.

[0076] S5. Repeat steps S3 and S4 for the remaining large bundles of raw silk, and after the knotting and connection are completed, the raw silk is successively subjected to oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, washing, sizing, drying, and winding.

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

[0078] Example 4

[0079] The K number of the large tow raw yarn in this embodiment is 260K.

[0080] S1. The silk ends and tails of each box of raw silk are kept at a certain length, and the length of the silk ends and tails is 100cm.

[0081] S2. Lay the silk ends and tails of each box of raw silk on the tension frame respectively, tighten the raw silk and fix it, put the tension frame into the pre-oxidation furnace, and pre-oxidize the silk ends and tails of the raw silk. The pre-oxidation is divided into two stages. The first stage has an oxidation temperature of 215°C and a time of 10 minutes. The second stage has an oxidation temperature of 240°C and a time of 10 minutes.

[0082] S3. Wrap one end of the pre-oxidized bulk tow raw silk in the first box around one end of the pre-oxidized bulk tow raw silk in another box to form a loop, pass the wire head through the loop, and tighten the knot; wrap the other end of the pre-oxidized bulk tow raw silk in another box around the other end of the pre-oxidized bulk tow raw silk in the first box to form a loop, pass the wire head through the loop, and tighten the knot (such as Figure 1 shown).

[0083] S4. After finishing the knot, tighten the two ends of the knot, cut off the excess silk ends, leaving a length of 10cm at the knot ends, and tighten the two original silk threads to make the knot tighter.

[0084] S5. Repeat steps S3 and S4 for the remaining large bundles of raw silk, and after the knotting and connection are completed, the raw silk is successively subjected to oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, washing, sizing, drying, and winding.

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

[0086] Example 5

[0087] All the operation steps are the same as those in Example 1, except that the process parameter values ​​of 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 wire head and tail, and the length of the wire head and tail after the wire head and tail are knotted are different from those in Example 1. The details are shown in Table 2.

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

[0089] Example 6

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

[0091] Example 7

[0092] All the operation steps and conditions are the same as those in Example 1, except that the length of the knotted silk head and tail is 25 cm, which is not within the preferred range of the present invention.

[0093] Example 8

[0094] All operating steps and conditions are the same as those in Example 1, except that the raw silk heads and tails are pre-oxidized, and the pre-oxidation is divided into two stages. The temperature and time of the second oxidation are not within the preferred range of the present invention. The oxidation temperature of the first oxidation is 228°C and the time is 32 minutes. The oxidation temperature of the second oxidation is 243°C and the time is 32 minutes.

[0095] The implementation effect of this embodiment 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 reserved length at one end of the large tow raw yarn is 132 cm, which is not within the preferred range of the present invention.

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

[0099] Comparative Example 1

[0100] All conditions are the same as those in Example 1, except that adjacent 290K large tows of raw silk are connected by a tube knotting method. The heads of the raw silk in one box and the tails of the raw silk in an adjacent box are stacked in parallel, the stacked tows are wound in a circle, the heads and tails are passed through the circle to be tightened, and the excess knot heads and tails are cut off.

[0101] Table 1

[0102]

[0103] Table 2

[0104]

[0105] Table 3

[0106]

[0107] It can be seen from the results in Table 1 that the embodiments 1-9 of the large tow carbon fiber and the continuous production method of large tow carbon fiber of the present invention. In the production process of 260-350K carbon fiber, the ends of adjacent raw fibers can be firmly connected together, the breaking strength of the knot reaches more than 156000CN, and the knot can smoothly pass through the oxidation furnace, low-temperature carbonization furnace, and high-temperature carbonization furnace, with a pass rate of 100% in the oxidation furnace, 100% in the low-temperature carbonization furnace, and 100% in the high-temperature carbonization furnace, and the implementation effect is good.

[0108] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A large tow carbon fiber, characterized in that: The large-tow carbon fiber comprises large-tow precursors connected alternately, and the connecting ends of adjacent large-tow precursors are connected by a self-tightening knot; The self-tightening knot method includes: wrapping one end of the pre-oxidized large-tow raw silk of section A around one end of the pre-oxidized large-tow raw silk of section B to form a loop, passing the wire head through the loop, and tightening the knot; The other end of the pre-oxidized large tow precursor of segment B is wound with the other end of the pre-oxidized large tow precursor of segment A to form a loop, and the wire head is passed through the loop to tighten the knot; After finishing the knot, tighten both ends of the knot; The connecting ends of the large tow raw yarn are pre-oxidized.

2. The large tow carbon fiber according to claim 1, wherein: The K number of each of the A-section large-tow precursor yarn and the B-section large-tow precursor yarn is 260-350K, preferably 290-320K.

3. The large tow carbon fiber according to claim 1 or 2, wherein: The connecting ends of adjacent large bundles of raw silk are connected by a self-tightening knot. After the respective ends of the connection are connected by a self-tightening knot, the length of the knot tail left by the self-tightening knot is 10-28 cm, preferably 16-22 cm.

4. A method for continuously producing large-tow carbon fiber according to any one of claims 1 to 3, the method comprising the following steps: (1) Wrapping one end of the pre-oxidized large tow precursor of section A around one end of the pre-oxidized large tow precursor of section B to form a loop, and passing the wire end through the loop to tighten the knot; (2) winding the other end of the pre-oxidized large tow precursor of section B with the other end of the pre-oxidized large tow precursor of section A to form a loop, passing the wire end through the loop, and tightening the knot; (3) After the knot is tied, tighten the two ends of the knot; repeat the steps (1) to (3) of the self-tightening knot connection according to the needs of continuous production; (4) After the connection is completed, the wire is oxidized, carbonized at low temperature, carbonized at high temperature, surface treated, washed, sizing, dried, and wound.

5. The method according to claim 4, wherein: The pre-oxidation is carried out in two stages, a first pre-oxidation and a second pre-oxidation; the temperature of the second pre-oxidation is 10-25° C. higher than the temperature of the first pre-oxidation.

6. The method according to claim 4 or 5, wherein: The first pre-oxidation conditions include: The temperature is 215-270°C, preferably 235-260°C; and / or Time is 10-70 min, preferably 35-60 min.

7. The method according to any one of claims 4 to 6, wherein: The second pre-oxidation conditions include: The temperature is 240-280°C, preferably 250-270°C; and / or The time is 10-70 min, preferably 35-60 min.

8. The method according to any one of claims 4 to 7, wherein: After the adjacent large bundles of raw silk are pre-oxidized and knotted, the length of the knot tails at the ends of the connections is 10-28 cm, preferably 16-22 cm.

9. The method according to any one of claims 4 to 8, wherein: Before the pre-oxidation, in step (1), the reserved length of one end of the large tow precursor to be pre-oxidized is 100-210 cm, preferably 150-190 cm.

10. The large-tow carbon fiber prepared by the method for continuous production of large-tow carbon fiber according to any one of claims 5 to 9.

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