Large-tow carbon fiber and continuous production method of 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 continuous production method of 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 in twisted winding connection. The ends, connected with the carbon fibers, of the large-tow precursors are knotted, the ends, packaged in a box, of the large-tow precursors can be connected with the ends, packaged in an adjacent box, of the large-tow precursors through the connecting method, knots are firm, and the breaking strength of the knots reaches 80000 cN or above; by using the connection method of twisted winding of the large-tow precursor end head, continuous production of large-tow carbon fibers can be realized, the roller winding frequency is reduced, the production safety is high, the stable production time is prolonged, 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 continuous production method of large-tow carbon fiber. Background Art

[0002] Carbon fiber is a new type of inorganic fiber material, with a series of excellent properties such as high specific strength, high specific modulus, high temperature resistance, corrosion resistance, fatigue resistance, radiation resistance, electrical conductivity, heat transfer, shock absorption, noise reduction and low relative density, etc. It is a typical high-performance fiber. As a high-tech material, carbon fiber is not only related to national defense construction, but also has broad application prospects in the civilian market.

[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] In the production process of small-tow carbon fiber based on polyacrylonitrile, the precursor is wound into a cylindrical ingot by a winding and collecting machine and placed on a creel. The precursor drawn from the creel is then subjected to oxidation, carbonization, surface treatment, washing, sizing, drying, winding and collecting processes to finally obtain a carbon fiber product. However, in the production process of large-tow carbon fiber, the precursor is not wound in a cylindrical ingot, but the precursor filament is directly laid in a box for production. Each box has a wire head and a wire tail, and the length of the precursor is fixed. When a box of precursor is about to be used up, the tail of the precursor in the box must be connected to the head of the precursor in the adjacent wire box to ensure that the precursor enters the oxidation area uninterruptedly and realizes online continuous production. Therefore, the connection between the precursors in the front and rear boxes is crucial. If the connection between the wire head and the wire tail is loose or broken, it is easy to cause the oxidation area to roll around, and even cause the oxidation furnace to catch fire. Stopping the production line to heat up and wire again will not only increase the labor intensity of the staff, but also cause intermittent production, generate a large amount of waste silk, and make it difficult to achieve economic benefits.

[0005] CN114262956A discloses a carbonization and splicing method for large-tow carbon fiber precursors, including the following steps: S1: Oxidation of reserved silk heads and PAN precursor tubes: untwisting the tail of the precursor bundle and another precursor bundle head to obtain 300-400mm silk heads, sleeve the tail end of the precursor bundle with the PAN precursor tube, lay it on the oxidation rack, and the precursor is naturally tightened and fixed; S2: using an air splicer to connect the precursor bundle head and the middle section of the bundle tail oxidation section, straighten and stretch the knot, and move the PAN precursor tube to the connection point for wrapping. This patent uses the method of pre-oxidation of the precursor tube bundle head and tail, and uses the PAN precursor tube to buckle the tail of the first tube with the reserved silk head of the second tube to form a tow. However, the wrapping of the original silk reel and the connection of the wire heads and tails of the large wire bundle cause more original silk to be stacked together. When oxidized, it will cause excessive heat storage inside the knot and cause the knot to burn out. In addition, the twisting operation of the wire reel will also cause the wire surface of the wire bundle to flip, resulting in uneven oxidation of the wire bundle.

[0006] CN114314196A discloses an online wire splicing production process and device for manufacturing carbon fiber. The online wire splicing production process comprises the following steps: (1) separating a gap between the original wire bundle A to be spliced, so that the original wire bundle A to be spliced ​​is separated from the original wire bundle B running next to the original wire bundle A; (2) using a carbon fiber bundle C wound on a wire-releasing device, twisting the knot of the carbon fiber bundle C into the original wire bundle B; (3) using the wire-releasing device to allow the carbon fiber bundle C to be naturally released; (4) docking the carbon fiber bundle C with the original wire bundle A to be spliced, so that the carbon fiber bundle C and the original wire bundle A form an integral wire bundle D; (5) using a wire-guiding device to guide the wire until the integral wire bundle D is completely straightened, removing the wire-guiding device, and the integral wire bundle D runs normally, thereby achieving the effect of connecting the broken wires and stably running. This patent is mainly aimed at the splicing of wires that are broken during operation. When the original wires are spliced ​​in this way, it is difficult to ensure the connection strength between the original wire bundle B and the carbon fiber bundle C, which affects the passability of the knot oxidation furnace. Summary of the invention

[0007] The purpose of the present invention is to overcome the problem that in the production process of large-tow carbon fiber in the prior art, the raw yarn is wound in a tubular ingot and continuous and stable production 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 yarn, carbon fiber and large-tow carbon fiber, thereby realizing the continuous production of large-tow carbon fiber, having the advantages of reducing the number of winding times, high production safety, increasing stable production time, reducing the amount of waste yarn, reducing production costs, and improving production efficiency.

[0008] In order to achieve the above-mentioned purpose, the present invention provides a large-tow carbon fiber on the one hand, which includes alternatingly connected large-tow precursors and carbon fibers, the large-tow precursors and carbon fibers are connected in a twisted manner, and the ends of the connection between the large-tow precursors and the carbon fibers are knotted.

[0009] According to a second aspect of the present invention, there is provided a method for continuous production of large-tow carbon fibers, the method comprising the following steps: (1) pre-oxidizing one end of a large-tow precursor, tying the pre-oxidized end into a tight knot, and then tying one end of the carbon fiber into a tight knot and connecting it with the pre-oxidized end of the large-tow precursor by twisting it in a twisted manner, and repeating the aforementioned winding connection according to the needs of continuous production; and (2) after the winding connection is completed, the wire is subjected to oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, water washing, sizing, drying, and winding.

[0010] A third aspect of the present invention provides large-tow carbon fibers prepared by the large-tow carbon fiber continuous production method of the present invention.

[0011] Through the above technical solution, the present invention has the following beneficial effects:

[0012] The present invention proposes for the first time a large-tow carbon fiber, including alternatingly connected large-tow precursors and carbon fibers, the large-tow precursors and the carbon fibers are connected in a twisted manner, and the ends of the large-tow precursors and the carbon fibers are knotted. 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 knots are firm, but the breaking strength of the knots reaches more than 80,000 cN.

[0013] The knots of the adjacent large bundles of raw silk ends after being knotted in the present invention will not only 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, thereby ensuring that the ends of the 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.

[0014] The present invention uses a connection method for twisting the ends of large-tow raw fibers, which can achieve continuous production of large-tow carbon fibers, reduce the number of roller windings, increase production safety, increase stable production time, reduce waste fiber volume, reduce production costs, and improve production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of each raw silk being divided into three strands, the ends of which are knotted and connected to the carbon fiber in a twisted manner. DETAILED DESCRIPTION

[0016] 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.

[0017] The present invention proposes a large-tow carbon fiber for the first time, comprising alternatingly connected large-tow precursors and carbon fibers, the large-tow precursors and the carbon fibers are twisted and connected, and the ends of the large-tow precursors and the carbon fibers are knotted; in the present invention, in continuous production, the ends of the large-tow precursors packed in boxes can be connected 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 80,000 cN. The knots of the 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 ends of the two adjacent boxes of precursors 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 and collecting production processes from the silk-releasing creel in sequence.

[0018] In the present invention, there is no special requirement for the K number of the carbon fiber. According to a preferred embodiment of the present invention, the K number of the carbon fiber is 40-100K, preferably 48-98K. 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.

[0019] 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 ends of the large tow precursor and the carbon fiber are tied, the length of the knot tail is 4-15 cm, preferably 6-10 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.

[0020] According to a preferred embodiment of the present invention, the ends of the large-tow precursor and the carbon fiber are respectively divided into corresponding multiple strands, and the strands of the large-tow precursor and the carbon fiber are respectively connected by twisting.

[0021] In the present invention, there is no special requirement for the number of strands of the ends of the large tow precursor and carbon fiber. According to a preferred embodiment of the present invention, the ends of the large tow precursor and carbon fiber are each divided into corresponding 2-10 strands, preferably 3-5 strands, and more preferably 3 strands.

[0022] By adopting the aforementioned preferred embodiments, the breaking strength of the knot at the connection between the raw silk and the carbon fiber can be further improved, ensuring that the knot is evenly stressed in all directions and that the knot is stable and does not loosen.

[0023] 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.

[0024] The large tow carbon fiber with the characteristics of the present invention can achieve the purpose of the present invention. The specific preparation steps and processes can be selected and adjusted according to the 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: (1) pre-oxidizing one end of the large tow precursor, tying the pre-oxidized end into a tight knot, and then twisting and connecting the end of the carbon fiber into a tight knot with the pre-oxidized end of the large tow precursor, and repeating the above-mentioned winding connection according to the needs of continuous production; (2) after the winding 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 number of windings can be reduced, the production safety is high, the stable production time is improved, the amount of waste silk is reduced, and the risk of fire caused by excessive heat storage at the connection of the precursor end is avoided, the production cost is reduced, and the production efficiency is improved; thereby, the continuous production of large tow carbon fiber can be effectively realized.

[0025] 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.

[0026] 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.

[0027] In the present invention, in 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.

[0028] In the present invention, the step (2) is to complete the winding and connection of the above-mentioned knots and then carry out oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, 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.

[0029] According to a preferred embodiment of the present invention, step (1) comprises: dividing the pre-oxidized end into multiple strands, and tying the ends of the multiple strands into tight knots; dividing one end of the carbon fiber into corresponding multiple strands, and tying the ends of the multiple strands into tight knots, and correspondingly twisting and connecting the strands of the pre-oxidized end of the large tow precursor and the strands of the carbon fiber.

[0030] According to a preferred embodiment of the present invention, the pre-oxidized end of the large-tow precursor and one end of the carbon fiber are each divided into corresponding 2-10 strands, preferably 3-5 strands, and more preferably 3 strands.

[0031] By adopting the aforementioned preferred embodiments, the breaking strength of the knot at the connection between the raw silk and the carbon fiber can be further improved, ensuring that the knot is evenly stressed in all directions and that the knot is stable and does not loosen.

[0032] 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.

[0033] In the present invention, the conditions for the first pre-oxidation of the large tow precursor may be conventionally selected in the art.

[0034] 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.

[0035] According to a preferred embodiment of the present invention, the temperature of the first pre-oxidation of the large-tow precursor is 200-250°C, preferably 220-240°C.

[0036] According to a preferred embodiment of the present invention, the first pre-oxidation time of the large-tow precursor is 10-40 minutes, preferably 20-30 minutes.

[0037] By adopting the above-mentioned preferred embodiments, the oxidation reaction of the raw silk can be carried out more efficiently and quickly.

[0038] In the present invention, the conditions for the second pre-oxidation of the large tow precursor may be conventionally selected in the art.

[0039] According to a preferred embodiment of the present invention, the temperature of the second pre-oxidation of the large-tow precursor is 220-260°C, preferably 230-255°C.

[0040] According to a preferred embodiment of the present invention, the second pre-oxidation time of the large-tow precursor is 10-40 minutes, preferably 20-30 minutes.

[0041] By adopting the aforementioned preferred embodiments, 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.

[0042] 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 100-160cm, preferably 120-150cm. 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.

[0043] In the present invention, there is no special requirement for the length of the tail of the knot left after the connection ends of the large tow precursor and the carbon fiber are respectively tied after pre-oxidation. According to a preferred embodiment of the present invention, the length of the tail of the knot left after the connection ends of the large tow precursor and the carbon fiber are respectively tied after pre-oxidation is 4-15 cm, preferably 6-10 cm. By adopting the above preferred embodiment, the safety production stability of the knot can be further improved through oxidation, low-temperature carbonization, and high-temperature carbonization.

[0044] The present invention provides large-tow carbon fibers prepared by the large-tow carbon fiber continuous production method of the present invention.

[0045] like Figure 1 As shown, each precursor of the present invention is divided into three strands, one end of the carbon fiber is divided into a corresponding plurality of strands, and the ends of the plurality of strands are each tied into a tight knot, and the strands of the pre-oxidized end of the large tow precursor and the strands of the carbon fiber are respectively connected by twisting in a corresponding manner; wherein, Figure 1 In the figure, 1 is the end of a large tow of raw yarn after pre-oxidation treatment; 2, carbon fiber.

[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 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;

[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 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.

[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 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;

[0055] 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;

[0056] 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;

[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: Vertical hot air drying, drying temperature 170℃;

[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] (1) 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 120cm.

[0063] (2) 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 120 cm ends of the raw silk ends and tails. The pre-oxidation is divided into two stages. The oxidation temperature of the first stage is 220°C and the time is 20 minutes. The oxidation temperature of the second stage is 230°C and the time is 20 minutes.

[0064] (3) The pre-oxidized silk head is divided into three strands on average, and the pre-oxidized silk tail is divided into three strands on average. After the silk head and the silk tail are tied into a knot, the length of the knotted silk head and the silk tail left is 6 cm.

[0065] (4) Divide the two ends of a 68K carbon fiber into three strands, tie a tight knot on each strand, and then slowly twist the three strands at one end of the 68K carbon fiber with the three strands of pre-oxidized fiber head in turn by kneading to form a twisted connection (such as Figure 1 Similarly, take the other end of the 68K carbon fiber and slowly twist them together with the adjacent pre-oxidized silk tails that are evenly divided into 3 strands and packed in boxes, making 3 knots in total. Repeat the process of alternately connecting the subsequent original silk head with one end of the carbon fiber.

[0066] (5) After the knots are twisted together, they are sequentially passed through an oxidation furnace, a low-temperature carbonization furnace, a high-temperature carbonization furnace, surface treatment, water washing, sizing, drying, and winding.

[0067] The implementation effect of this embodiment is shown in Table 3.

[0068] Example 2

[0069] (1) 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 135cm.

[0070] (2) 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°C and the time is 25 minutes. The oxidation temperature of the second stage is 248°C and the time is 25 minutes.

[0071] (3) The pre-oxidized silk head is evenly divided into 4 strands, and the pre-oxidized silk tail is evenly divided into 4 strands. After the silk head and the silk tail are knotted, the length of the knotted silk head and the silk tail left is 8 cm.

[0072] (4) Divide the two ends of a strand of 80K carbon fiber into four strands, tie a tight knot on each strand, and then slowly twist the four strands at one end of the 80K carbon fiber with the four strands of pre-oxidized fiber ends by kneading to form a twisted connection (such as Figure 1 Similarly, take the other end of the 80K carbon fiber and slowly twist them together with the adjacent pre-oxidized silk tails that are evenly divided into 4 strands and packed in boxes, making 4 knots in total. Repeat the process of alternately connecting the subsequent original silk ends with one end of the carbon fiber.

[0073] (5) After the knots are twisted together, they are sequentially passed through an oxidation furnace, a low-temperature carbonization furnace, a high-temperature carbonization furnace, surface treatment, water washing, sizing, drying, and winding.

[0074] The implementation effect of this embodiment is shown in Table 3.

[0075] Example 3

[0076] (1) 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.

[0077] (2) 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 240°C and the time is 30 minutes. The oxidation temperature of the second stage is 255°C and the time is 30 minutes.

[0078] (3) The pre-oxidized silk head is divided into 5 strands on average, and the pre-oxidized silk tail is divided into 5 strands on average. After the silk head and the silk tail are knotted, the length of the knotted silk head and the silk tail left is 10 cm.

[0079] (4) Divide the two ends of a 90K carbon fiber into 5 strands, tie a tight knot on each strand, and then slowly twist the 5 strands at one end of the 90K carbon fiber with the 5 strands of pre-oxidized fiber head by kneading to form a twisted connection (such as Figure 1Similarly, take the other end of the 90K carbon fiber and slowly twist them together with the adjacent pre-oxidized silk tails that are evenly divided into 5 strands and packed in boxes, making a total of 5 knots. Repeat the process of alternately connecting the subsequent original silk ends with one end of the carbon fiber.

[0080] (5) After the knots are twisted together, they are sequentially passed through an oxidation furnace, a low-temperature carbonization furnace, a high-temperature carbonization furnace, surface treatment, water washing, sizing, drying, and winding.

[0081] The implementation effect of this embodiment is shown in Table 3.

[0082] Example 4

[0083] All operating steps are the same as those in Example 1, except that the K number of the carbon fiber and large tow precursor is 42K, and the process parameter values ​​of the pre-oxidation temperature and pre-oxidation residence time, the length of the wire head and tail, the length of the knot and tail, and the number of strands of the precursor and carbon fiber are different from those in Example 1, as shown in Table 2.

[0084] The implementation effect of this embodiment is shown in Table 3.

[0085] Example 5

[0086] All operating steps are the same as those in Example 1, except that the K number of the carbon fiber and large tow precursor is 45K, and the process parameter values ​​of the pre-oxidation temperature and pre-oxidation residence time, the length of the wire head and tail, the length of the knot and tail, and the number of strands of the precursor and carbon fiber are different from those in Example 1, as shown in Table 2.

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

[0088] Example 6

[0089] All conditions are the same as those in Example 1, except that the K number of the carbon fiber and the large tow precursor is 38K, which is not within the preferred range of the present invention.

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

[0091] Example 7

[0092] All conditions are the same as in Example 1, except that the length of the knotted end is 12 cm.

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

[0094] Example 8

[0095] All conditions are the same as in Example 1, except that the number of strands of the precursor and carbon fiber is 8.

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

[0097] Example 9

[0098] All 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 205°C and the time is 28 minutes. The oxidation temperature of the second oxidation is 235°C and the time is 28 minutes.

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

[0100] Example 10

[0101] All conditions are the same as those in Example 1, except that the reserved length at one end of the large tow raw yarn is 115 cm, which is not within the preferred range of the present invention.

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

[0103] Comparative Example 1

[0104] All conditions are the same as those in Example 1, except that the large-tow carbon fiber only includes 48K large-tow precursors connected alternately, and does not include 48K carbon fiber.

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

[0106] Comparative Example 2

[0107] All conditions are the same as those in Example 1, except that: the connection method of 48K large-tow raw silk and 48K 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.

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

[0109] Comparative Example 3

[0110] All conditions are the same as those in Example 1, except that the ends of the 48K large tow precursor and the 48K carbon fiber are not knotted.

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

[0112] Table 1

[0113]

[0114] Table 2

[0115]

[0116]

[0117] Table 3

[0118]

[0119] It can be seen from the results in Table 3 that in the carbon fiber production process of Examples 1-10 using 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 80,000 CN, 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.

[0120] 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 alternately connected. The large-tow precursors and the carbon fibers are connected in a twisted manner, and the ends of the large-tow precursors and the carbon fibers are knotted.

2. The large tow carbon fiber according to claim 1, wherein: The carbon fiber has a K number of 40-100K, preferably a K number of 48-98K; and / or The connecting ends of the large tow raw yarn are pre-oxidized.

3. The large tow carbon fiber according to claim 1 or 2, wherein: After the ends of the large tow precursor and the carbon fiber are tied, the length of the knot tail is 4-15 cm, preferably 6-10 cm.

4. The large tow carbon fiber according to any one of claims 1 to 3, wherein: The ends of the large tow precursor and the carbon fiber are respectively divided into corresponding multiple strands, and the strands of the large tow precursor and the carbon fiber are respectively connected by twisting in a twisted manner; Preferably, the ends of the large-tow precursor yarn and the carbon fiber are each divided into corresponding 2-10 strands, preferably 3-5 strands, and more preferably 3 strands.

5. A method for continuously producing large-tow carbon fiber according to any one of claims 1 to 4, the method comprising the following steps: (1) pre-oxidizing one end of the large tow precursor, tying the pre-oxidized end into a tight knot, and then tying one end of the carbon fiber into a tight knot and connecting it with the pre-oxidized end of the large tow precursor by twisting, and repeating the above-mentioned winding connection according to the needs of continuous production; (2) After the winding connection is completed, it undergoes oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, water washing, sizing, drying, and winding.

6. The method according to claim 5, wherein: Step (1) comprises: dividing the pre-oxidized end into a plurality of strands, and tying the ends of the plurality of strands into a tight knot; dividing one end of the carbon fiber into a corresponding plurality of strands, and tying the ends of the plurality of strands into a tight knot, and correspondingly twisting and connecting the strands of the pre-oxidized end of the large tow precursor and the strands of the carbon fiber; and / or The pre-oxidized end of the large tow precursor and one end of the carbon fiber are each divided into corresponding 2-10 strands, preferably 3-5 strands, and more preferably 3 strands.

7. The method according to claim 5 or 6, wherein: The pre-oxidation is carried out in two stages, including a first pre-oxidation and a second pre-oxidation, wherein: The temperature of the second pre-oxidation is 10-30°C higher than the temperature of the first pre-oxidation; and / or The first pre-oxidation conditions include: The temperature is 200-250°C, preferably 220-240°C; and / or Time 10-40min, preferably 20-30min; and / or The second pre-oxidation conditions include: The temperature is 220-260°C, preferably 230-255°C; and / or The time is 10-40 min, preferably 20-30 min.

8. The method according to any one of claims 5 to 7, wherein: Before the pre-oxidation, in step (1), the reserved length of one end of the large tow precursor to be pre-oxidized is 100-160 cm, preferably 120-150 cm.

9. The method according to any one of claims 5 to 8, wherein: After the pre-oxidized large tow precursor is connected to the carbon fiber and the ends thereof are respectively knotted, the length of the knotted ends remaining is 4-15 cm, preferably 6-10 cm.

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.

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