Method for continuously producing large-tow carbon fiber and large-tow carbon fiber

Abstract

The invention relates to the technical field of large-tow carbon fiber production, in particular to a large-tow carbon fiber and a method for continuously producing the large-tow carbon fiber, and discloses a large-tow fiber, the large-tow carbon fiber comprises large-tow precursors and carbon fibers which are alternately connected, and the large-tow precursors and the carbon fibers are connected in a spinning knot mode. The end socket of the large tow protofilament end packaged in a box can be connected with the end socket of the adjacent large tow protofilament end packaged in the box, the knot is firm, and the breaking strength of the knot reaches 140000 cN or above; the large-tow precursor end heads are connected in a spinning knot mode, continuous production of large-tow carbon fibers can be achieved, the roller winding frequency is reduced, the production safety is high, the stable production time is shortened, the waste silk 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 method for continuously producing large-tow carbon fiber. Background Art

[0002] Carbon fiber is an inorganic fiber with a carbon main chain structure with a carbon content of more than 90% formed by the cracking and carbonization of polyacrylonitrile under high temperature. Carbon fiber has many excellent properties, the main advantages of which are high strength and modulus, low density, good fatigue resistance, etc. Among them, large tow carbon fiber generally refers to the number of tows greater than or equal to 48K. Compared with small tow carbon fiber, large tow carbon fiber can use low-cost PAN fiber, and under the same production conditions, it can greatly increase the single-line production capacity of carbon fiber and achieve low-cost production, which largely breaks the application limitations caused by the high price of carbon fiber and is suitable for large-scale industrial applications. The main purpose of the oxidation of the raw silk is to cause the cyclization and intermolecular cross-linking within the linear polyacrylonitrile (PAN) macromolecular chain to generate a heat-resistant mesh ladder structure.

[0003] 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.

[0004] CN217263957U relates to the technical field of multi-point wire connection of tows, specifically a novel multi-point air connection device for tows. It comprises a multi-point air coupler, a connection device frame and a connection operation table; the multi-point air coupler comprises a plurality of tow clamps, air injection holes are arranged on the upper and lower sides of the fiber connection slot, each tow clamp is provided with an air intake switch, and the multi-point air coupler is provided with a compressed air distributor; a storage rack is arranged on the connection device frame, and a plurality of limit fixing rods are stored, and a linear guide rail, a slider and a cylinder are arranged on the frame, which are used to control the forward and backward movement of the connection operation table; two original silk tows are placed on the connection operation table, and the two silk tows are stacked together, and the connection operation table is pneumatically or manually moved into the tow clamp of the multi-point air coupler with the linear guide rail, and the original silk tow passes through a plurality of fiber connection slots at the same time and the tows are continuously connected at multiple points during the movement of the operation table. However, this patent requires multiple air connectors to work simultaneously, which makes it difficult to ensure that the air source pressure of each air connector is stable and consistent, resulting in some connection points failing to meet the connection requirements, which in turn leads to insufficient strength of the entire joint. Summary of the invention

[0005] 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 end connection method of two adjacent boxes of raw silk is not firm, which causes the end connection of the two adjacent boxes of raw silk to loosen or break, easily causing oxidation area winding rollers, 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 a continuous production method of alternating large-tow raw silk, carbon fiber and large-tow carbon fiber, which realizes the continuous production of large-tow carbon fiber, reduces the number of winding rollers, has high production safety, and increases stable production time, reduces the amount of waste silk, reduces production costs, and improves production efficiency.

[0006] In order to achieve the above-mentioned purpose, the present invention provides a large-tow carbon fiber, which includes alternating large-tow precursors and carbon fibers, and the large-tow precursors and carbon fibers are connected by a textile knot. The knots of the adjacent large-tow precursors of the present invention will not loosen or fall off during the oxidation process, and the knot connection will not produce smoke and fire due to overheating due to heat storage, ensuring that the wire heads and wire tails of the two adjacent boxes of precursors can be connected and tightened. It can smoothly pass through the oxidation furnace, low-temperature carbonization furnace, high-temperature carbonization furnace, surface treatment, washing, sizing, drying, and winding and collecting production processes from the wire-releasing creel in sequence.

[0007] In the present invention, the steps of tying a knot are as follows (tying is completed as follows: Figure 1 As shown, the specific step-by-step demonstration is as follows Figure 2 On the left is pre-oxidized large tow precursor, and on the right is carbon fiber):

[0008] Step 1: Cross the end of the pre-oxidized large tow precursor with one end of the carbon fiber at 75 degrees and leave 7 cm for each of the two ends at the two intersections, and then press the end of the pre-oxidized large tow precursor onto one end of the carbon fiber.

[0009] Step 2: Wrap one end of the carbon fiber around the end of the pre-oxidized large tow precursor yarn and press the end from the intersection of the above ends, so that one end of the carbon fiber is wrapped around to form a circle, and insert the end of the pre-oxidized large tow precursor yarn into the above circle, and at the same time tighten the end of the pre-oxidized large tow precursor yarn and one end of the carbon fiber.

[0010] In the present invention, after the ends of the large tow precursor and the carbon fiber are tied, there is no special requirement for the length of the knot tail. According to a preferred embodiment of the present invention, after the large tow precursor and the carbon fiber are connected by a textile knot, the length of the textile knot is 8-25 cm, preferably 13-20 cm. By adopting the above 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.

[0011] In the present invention, the K number of the carbon fiber can be a conventional choice in the art. According to a preferred embodiment of the present invention, the K number of the carbon fiber is 180-250 K, preferably 200-230 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.

[0012] According to a preferred embodiment of the present invention, the respective ends of the large-tow precursor and the carbon fiber are connected by a weaving knot.

[0013] According to a preferred embodiment of the present invention, the connecting ends of the large-tow precursor yarns are subjected to oxidation treatment.

[0014] In the present invention, the number of times the large tow precursor fibers and carbon fibers are alternately connected is not limited and can be selected according to needs.

[0015] The large tow carbon fiber with the characteristics of the present invention can achieve the purpose of the present invention, and its specific preparation steps and processes can be selected and adjusted according to needs. According to the preferred embodiment of the present invention, the present invention provides a continuous production method of large tow carbon fiber, which includes the following steps: S1. Pre-oxidize one end of the large tow precursor, connect the end of the pre-oxidized large tow precursor with one end of the carbon fiber by a textile knot, and repeat the aforementioned textile knotting method according to the needs of continuous production; S2. After the textile knot connection is completed, it is oxidized, carbonized at low temperature, carbonized at high temperature, 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 winding times can be reduced, the production safety is high, and the stable production time can be improved, the amount of waste silk can be reduced, the production cost can be reduced, the production efficiency can be improved, and the risk of fire caused by excessive heat storage at the connection of the precursor end can be avoided, the production cost can be reduced, and the production efficiency can be improved; thereby, the continuous production of large tow carbon fiber can be effectively achieved.

[0016] In the present invention, after step S1 and before step S2, 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.

[0017] In the present invention, in step S1, after the end of the large tow raw silk 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 with reference to the existing technology, and it only needs to be cooled to room temperature.

[0018] In the present invention, the step S2 completes the winding connection of the above-mentioned knots and then undergoes oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, water washing, sizing, drying, and winding to collect the wire. There are no special requirements for the specific steps and operating conditions, which can be carried out according to the existing technology and will not be elaborated in the present invention.

[0019] According to a preferred embodiment of the present invention, the weaving knotting method in step S1 includes: cross-folding the ends of the pre-oxidized large tow precursor yarns to form a first loop, inserting the end of one end of the carbon fiber from below the first loop, winding downward at the intersection of the precursor yarn ends to form a second loop, and then inserting the end of the carbon fiber from above to tighten.

[0020] In the present invention, in the step S1, after the ends of the large tow raw yarns are crossed, the crossing angle needs to be controlled to be 70-80 degrees, and the two yarn ends are exposed by 7 cm each.

[0021] In the present invention, the winding connection can be performed continuously, and the specific number of windings is determined according to needs and actual working conditions.

[0022] 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.

[0023] In the present invention, before the pre-oxidation treatment of the large tow precursor in step S1, 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 100-180cm, preferably 140-170cm. By adopting the aforementioned preferred embodiment, it can be further ensured that the length of the pre-oxidized precursor meets the length requirement for connection with the carbon fiber.

[0024] In the present invention, there is no special requirement for the length of the knot tail left after the connection ends of the large tow precursor and the carbon fiber are respectively knotted after pre-oxidation. According to a preferred embodiment of the present invention, after the large tow precursor and the carbon fiber are connected by a textile knot, the length of the knot tail left by the textile knot is 8-25 cm, preferably 13-20 cm. By adopting the above 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.

[0025] In the present invention, there is no special requirement for the number of pre-oxidation of the large-tow precursor.

[0026] 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.

[0027] According to a preferred embodiment of the present invention, the temperature of the second pre-oxidation is 10-30° C. higher than the temperature of the first pre-oxidation.

[0028] In the present invention, the conditions for the first pre-oxidation of the large tow precursor may be conventionally selected in the art.

[0029] According to a preferred embodiment of the present invention, the temperature of the first pre-oxidation of the large-tow precursor is 210-260°C, preferably 230-250°C.

[0030] According to a preferred embodiment of the present invention, the first pre-oxidation time of the large-tow precursor is 10-60 minutes, preferably 30-45 minutes.

[0031] By adopting the above-mentioned preferred embodiment, the oxidation reaction of the raw silk can be carried out more efficiently and quickly.

[0032] In the present invention, the conditions for the second pre-oxidation of the large tow precursor may be conventionally selected in the art.

[0033] According to a preferred embodiment of the present invention, the temperature of the second pre-oxidation of the large-tow precursor is 238-270°C, preferably 245-265°C.

[0034] According to a preferred embodiment of the present invention, the second pre-oxidation time of the large-tow precursor is 10-60 minutes, preferably 30-45 minutes.

[0035] By adopting the aforementioned preferred implementation, it is possible to further ensure that the precursor completes the cyclization and dehydrogenation reactions, and the linear macromolecular chains of the PAN-based precursor are converted into heat-resistant ladder-shaped macromolecular structures through intramolecular cyclization and intermolecular crosslinking.

[0036] The present invention provides large-tow carbon fibers prepared by the large-tow carbon fiber continuous production method of the present invention.

[0037] like Figure 1 As shown, it is a schematic diagram of the ends of the large tow precursor and carbon fiber of the present invention being connected by a weaving knot; wherein, Figure 1 In the figure, 1 is the end of a large tow of raw yarn after pre-oxidation treatment; 2, carbon fiber.

[0038] Through the above technical solution, the present invention has the following beneficial effects:

[0039] The present invention proposes for the first time a large-tow carbon fiber, including alternatingly connected large-tow precursors and carbon fibers, wherein the large-tow precursors and carbon fibers are connected by a textile knot. Through the connection method of the present invention, the ends of the large-tow precursors packaged in a box can be connected 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 140,000 cN.

[0040] The knots of the adjacent large bundles of raw silk ends after being knotted in the present invention not only do not loosen or fall off during the oxidation process, but also the knot connection will not produce smoke and fire due to overheating due to heat storage, ensuring that the wire ends and wire tails of the two adjacent boxes of raw silk can be connected and tightened. It can smoothly pass through the oxidation furnace, low-temperature carbonization furnace, high-temperature carbonization furnace, surface treatment, washing, sizing, drying, winding and wire collection production processes from the wire-releasing creel in sequence.

[0041] In a preferred embodiment of the present invention, the large-tow precursor used in the present invention is connected with the carbon fiber through a textile knot method, which can realize the continuous production of large-tow carbon fiber, reduce the number of roller windings, have high production safety, increase stable production time, reduce the amount of waste silk, reduce production costs, and improve production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic diagram of the connection between the raw silk and the carbon fiber textile knot;

[0043] Figure 2 It is a step-by-step diagram showing how to tie a knot between raw silk and carbon fiber textiles. DETAILED DESCRIPTION

[0044] 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.

[0045] The present invention proposes for the first time a large-tow carbon fiber, including alternatingly connected large-tow precursors and carbon fibers, wherein the large-tow precursors and the carbon fibers are connected by a textile knot. Through the connection method of the present invention, in continuous production, the ends of the large-tow precursors packed in boxes can be connected together with the ends of the large-tow precursors packed in adjacent boxes through carbon fibers, and not only the knots are firm, but also the breaking strength of the knots reaches more than 140,000 cN.

[0046] 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:

[0047] 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%

[0048] 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%

[0049] 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%

[0050] The raw material of the raw silk is a commercial product with the brand name SF produced by Sinopec Shanghai Petrochemical Co., Ltd.

[0051] 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:

[0052] Oxidation furnace: divided into four temperature zones, the total time is 60 minutes, the draft ratios between the four heating temperature zones of the oxidation furnace 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.

[0053] 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 at the outlet of the oxidation furnace 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 tow runs 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.

[0054] 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 filament bundle at the outlet of the low-temperature carbonization furnace passes through a traction device and enters the high-temperature carbonization furnace. High-temperature carbonization is carried out 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 filament bundle 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.

[0055] Surface treatment: The surface treatment production process is that the filament bundle at the outlet of the high-temperature carbonization furnace enters the surface treatment tank through a traction device, using ammonium bicarbonate aqueous solution as the electrolyte, the voltage is 18V, the electrolyte concentration is 10%, and the filament bundle stays in the electrolyte for 60 seconds.

[0056] Water washing: In the water washing production process, the tow at the outlet of the surface treatment tank enters the water washing tank and is washed with water. The water washing flow rate is 2800L / hour and the water washing temperature is 50°C.

[0057] 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.

[0058] Drying: Horizontal hot air drying, drying temperature 100℃.

[0059] Winding and collecting: The carbon fiber after sizing and drying is wound and collected using a carbon fiber winder to produce finished carbon fiber.

[0060] 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 tow precursor and the carbon fiber in the same embodiment is the same. Other parameters are shown in Table 2.

[0061] Example 1

[0062] The K number of the carbon fiber and the large tow precursor in this embodiment is 200K.

[0063] S1. Pre-oxidation of silk ends:

[0064] The ends and tails of the raw silk in each box are kept at a certain length, which is 140 cm. The ends and tails of the raw silk in each box are laid on the tension rack respectively, the raw silk is tightened and fixed, and the tension rack is placed in the pre-oxidation furnace to pre-oxidize the 140 cm ends of the raw silk heads and tails. The pre-oxidation is divided into two stages. The first stage has an oxidation temperature of 230°C and a time of 30 minutes. The second stage has an oxidation temperature of 245°C and a time of 30 minutes.

[0065] S2. The steps for tying the wire head and tail are as follows (the knot is completed as follows Figure 1 As shown, the specific step-by-step demonstration is as follows Figure 2 On the left is pre-oxidized large tow precursor, and on the right is carbon fiber):

[0066] Step 1: Cross the end of the pre-oxidized large tow precursor with one end of the carbon fiber at 75 degrees and leave 7 cm for each of the two ends at the two intersections, and then press the end of the pre-oxidized large tow precursor onto one end of the carbon fiber.

[0067] Step 2: Wrap one end of the carbon fiber around the end of the pre-oxidized large tow precursor yarn and press the end from the intersection of the above ends, so that one end of the carbon fiber is wrapped around to form a circle, and insert the end of the pre-oxidized large tow precursor yarn into the above circle, and at the same time tighten the end of the pre-oxidized large tow precursor yarn and one end of the carbon fiber to complete the knot; after the knot is completed, tighten both ends of the knot, cut off the excess wire ends, and leave a length of 13 cm for the knot tail, and repeat the alternating connection of the subsequent pre-oxidized end of the large tow precursor yarn and one end of the carbon fiber.

[0068] S3. After the above knots are twisted together, the yarn 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 2

[0071] The K number of the carbon fiber and the large tow precursor in this embodiment is 220K.

[0072] S1. Pre-oxidation of silk ends:

[0073] The ends and tails of the raw silk in each box are kept at a certain length, which is 155 cm. The ends and tails of the raw silk in each box are laid on the tension rack respectively, the raw silk is tightened and fixed, and the tension rack is placed in the pre-oxidation furnace to pre-oxidize the ends and tails of the raw silk. The pre-oxidation is divided into two stages. The first stage has an oxidation temperature of 243°C and a time of 40 minutes. The second stage has an oxidation temperature of 260°C and a time of 40 minutes.

[0074] S2. The steps for tying the wire head and tail are as follows (the knot is completed as follows Figure 1 As shown, the specific step-by-step demonstration is as follows Figure 2 On the left is pre-oxidized large tow precursor, and on the right is carbon fiber):

[0075] Step 1: Cross the end of the pre-oxidized large tow precursor with one end of the carbon fiber at 75 degrees and leave 7 cm for each of the two ends at the two intersections, and then press the end of the pre-oxidized large tow precursor onto one end of the carbon fiber.

[0076] Step 2: Wrap one end of the carbon fiber around the end of the pre-oxidized large tow precursor yarn and press the end from the intersection of the above ends, so that one end of the carbon fiber is wrapped around to form a circle, and insert the end of the pre-oxidized large tow precursor yarn into the above circle, and at the same time tighten the end of the pre-oxidized large tow precursor yarn and one end of the carbon fiber to complete the knot; after the knot is completed, tighten both ends of the knot, cut off the excess wire ends, and leave a length of 18 cm for the knot tail, and repeat the alternating connection of the subsequent pre-oxidized end of the large tow precursor yarn and one end of the carbon fiber.

[0077] S3. After the above knots are twisted together, the yarn is successively subjected to oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, washing, sizing, drying, and winding.

[0078] The implementation effect of this embodiment is shown in Table 3.

[0079] Example 3

[0080] The K number of the carbon fiber and the large tow precursor in this embodiment is 230K.

[0081] S1. Pre-oxidation of silk ends:

[0082] The ends and tails of the raw silk in each box are kept at a certain length, which is 170 cm. The ends and tails of the raw silk in each box are laid on the tension rack respectively, the raw silk is tightened and fixed, and the tension rack is placed in the pre-oxidation furnace to pre-oxidize the ends and tails of the raw silk. The pre-oxidation is divided into two stages. The first stage has an oxidation temperature of 250°C and a time of 45 minutes. The second stage has an oxidation temperature of 265°C and a time of 45 minutes.

[0083] S2. The steps for tying the wire head and tail are as follows (the knot is completed as follows Figure 1 As shown, the specific step-by-step demonstration is as follows Figure 2 On the left is pre-oxidized large tow precursor, and on the right is carbon fiber):

[0084] Step 1: Cross the end of the pre-oxidized large tow precursor with one end of the carbon fiber at 75 degrees and leave 7 cm for each of the two ends at the two intersections, and then press the end of the pre-oxidized large tow precursor onto one end of the carbon fiber.

[0085] Step 2: Wrap one end of the carbon fiber around the end of the pre-oxidized large tow precursor yarn and press the end from the intersection of the above ends, so that one end of the carbon fiber is wrapped around to form a circle, and insert the end of the pre-oxidized large tow precursor yarn into the above circle, and at the same time tighten the end of the pre-oxidized large tow precursor yarn and one end of the carbon fiber to complete the knot; after the knot is completed, tighten both ends of the knot, cut off the excess wire ends, and leave a length of 20 cm for the knot tail, and repeat the connection alternately between the subsequent pre-oxidized end of the large tow precursor yarn and one end of the carbon fiber.

[0086] S3. After the above knots are twisted together, the yarn is successively subjected to oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, washing, sizing, drying, and winding.

[0087] The implementation effect of this embodiment is shown in Table 3.

[0088] Example 4

[0089] All the operation steps are the same as those in Example 1, except that the process parameter values ​​of the carbon fiber and large tow precursor K number, the two-stage pre-oxidation temperature and the two-stage pre-oxidation residence time, the length of the silk head and tail, the number of strands of the precursor and carbon fiber, and the length of the knotted head and tail after the silk head and tail are tied are not within the preferred range of the present application. The details are shown in Table 2.

[0090] The implementation effect of this embodiment is shown in Table 3.

[0091] Example 5

[0092] All the operation steps are the same as those in Example 1, except that the process parameter values ​​of the carbon fiber and large tow precursor K number, the two-stage pre-oxidation temperature and the two-stage pre-oxidation residence time, the length of the silk head and tail, the number of strands of the precursor and carbon fiber, and the length of the knotted head and tail after the silk head and tail are tied are not within the preferred range of the present application. The details are shown in Table 2.

[0093] The implementation effect of this embodiment is shown in Table 3.

[0094] Example 6

[0095] All the operation steps and conditions are the same as those in Example 1, except that the K number of the carbon fiber and the large tow precursor is 170K, which is not within the preferred range of the present application.

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

[0097] Example 7

[0098] 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 23 cm, which is not within the preferred range of this application.

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

[0100] Example 8

[0101] 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 application. The oxidation temperature of the first oxidation is 223°C and the time is 28 minutes. The oxidation temperature of the second oxidation is 240°C and the time is 28 minutes.

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

[0103] Example 9

[0104] 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 128 cm, which is not within the preferred range of the present application.

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

[0106] Comparative Example 1

[0107] All conditions are the same as those in Example 1, except that the large-tow carbon fiber only includes alternately connected 200K large-tow precursor fibers, and does not include 200K carbon fibers.

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

[0109] Comparative Example 2

[0110] All conditions are the same as those in Example 1, except that: the connection method of the 200K large-tow raw silk and the 200K carbon fiber is a tube knotting method, the raw silk heads in one box and the raw silk tails in an adjacent box are stacked in parallel, the stacked tows are wound in a circle, the wire heads and tails are passed through the circle to be tightened, and the excess knot heads and tails are cut off.

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

[0112] Table 1

[0113]

[0114] Table 2

[0115]

[0116] Table 3

[0117]

[0118] It can be seen from the results in Table 3 that in the carbon fiber production process using the embodiment of the large-tow carbon fiber and the continuous production method of large-tow carbon fiber of the present invention, the ends of adjacent raw fibers can be firmly connected together, the breaking strength of the knots reaches more than 140000CN, and the knots can smoothly pass through the oxidation furnace, the low-temperature carbonization furnace, and the 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.

[0119] 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 and carbon fibers which are connected alternately, and the large-tow precursors and the carbon fibers are connected by a weaving knot.

2. The large tow carbon fiber according to claim 1, wherein: After the large tow precursor is connected with the carbon fiber by a weaving knot, the length of the knot head and tail left at the weaving knot is 8-25 cm, preferably 13-20 cm.

3. The large tow carbon fiber according to claim 1 or 2, wherein: The carbon fiber has a K number of 180-250K, preferably a K number of 200-230K.

4. The large tow carbon fiber according to any one of claims 1 to 3, wherein: The connecting ends of the large-tow precursor yarns are subjected to oxidation treatment.

5. A method for continuously producing large-tow carbon fiber according to any one of claims 1 to 4, characterized in that: The method comprises the following steps: S1. Pre-oxidizing one end of the large tow precursor, pre-oxidizing the end of the large tow precursor and one end of the carbon fiber by a textile knot, and repeating the aforementioned textile knotting method according to the needs of continuous production; S2. After the textile knot connection is completed, it undergoes oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, washing, sizing, drying, and winding.

6. The method according to claim 5, wherein: The weaving knotting method in step S1 includes: cross-folding the ends of the pre-oxidized large tow raw yarns in half to form a first loop, inserting the end of one end of the carbon fiber from below the first loop, winding downward at the intersection of the raw yarn ends to form a second loop, and then inserting it into the first loop from above and tightening it.

7. The method according to claim 5 or 6, wherein: Before the pre-oxidation, in step S1, the reserved length of one end of the large tow precursor to be pre-oxidized is 100-180 cm, preferably 140-170 cm.

8. The method according to any one of claims 5 to 7, wherein: After the large tow precursor is connected with the carbon fiber by means of a weaving knot, the length left at the weaving knot is 8-25 cm, preferably 13-20 cm.

9. The method according to any one of claims 5 to 8, wherein: The pre-oxidation is carried out in two stages, including a first pre-oxidation and a second pre-oxidation, wherein: The first pre-oxidation conditions include: The temperature is 210-260°C, preferably 230-250°C; and / or Time 10-60min, preferably 30-45min; and / or The second pre-oxidation conditions include: The temperature is 238-270°C, preferably 245-265°C; and / or The time is 10-60 min, preferably 30-45 min; and / or The temperature of the second pre-oxidation is 10-30°C higher than the temperature of the first pre-oxidation.

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

Images