Large-tow carbon fiber and continuous production method thereof

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 thereof, 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 flat knot tying 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 the knot is firm, and the breaking strength of the knot reaches 120000 cN or above; the method that adjacent large-tow precursor ends are connected in a flat knotting mode is used, continuous production of large-tow carbon fibers can be achieved, the number of times of roller winding is reduced, production safety is high, stable production time is prolonged, the amount of waste filaments is reduced, production cost is reduced, and 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 thereof. Background Art

[0002] Large tow carbon fiber is mainly composed of carbon elements, with high temperature resistance, low density, high specific strength and specific modulus, anti-friction, thermal conductivity and corrosion resistance. It is fibrous, soft, and can be processed into various fabrics. It can also be used as a reinforcing material and composited with resin, metal, ceramic and carbon to manufacture advanced composite materials. Carbon fiber reinforced epoxy resin composite materials have the highest specific strength and specific modulus among existing engineering materials. The main purpose of oxidation of the precursor is to cyclize and cross-link the linear polyacrylonitrile (PAN) macromolecular chain to generate a heat-resistant mesh ladder structure. Oxidation is usually carried out in an air atmosphere, the temperature is controlled at 180℃-280℃, and appropriate tension is applied during the process to avoid relaxation of the polymer molecular structure and maintain the fiber orientation. In order to make polyacrylonitrile fiber non-melting and non-flammable during high-temperature carbonization activation and keep its fiber morphology unchanged, polyacrylonitrile fiber is usually pre-oxidized to convert its linear molecular chain into a cyclized structure with heat resistance to improve its thermal stability. The oxidation reaction of polyacrylonitrile fiber is accompanied by a large amount of heat release.

[0003] If the fiber pre-oxidation time is short, the cortex structure is thin; if the pre-oxidation time is long, the cortex structure of the generated carbon fiber is thicker. If the relevant parameters used in the pre-oxidation production process are low (such as traction, temperature, etc.) and the processing time is long, it is not easy to form an obvious skin-core structure, but the relative production efficiency is low.

[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] CN211546739U introduces a polyacrylonitrile preoxidized wire head connecting device. It includes an air coupler and a connecting operation table; the air coupler includes a wire head clamp, the wire head clamp has a gap, the gap forms a fiber connecting groove, the side wall of the fiber connecting groove is provided with an air injection hole, and the wire head clamp is provided with an air inlet and an air inlet trigger; the wire heads of two raw silk preoxidized wires are placed on the connecting operation table, the two raw silk preoxidized wire heads are stacked together, the connecting operation table is provided with a plurality of connecting grooves, the connecting operation table also includes a plurality of fiber fixing rods, the plurality of fiber fixing rods are placed on different connecting grooves to press the wire heads of the raw silk preoxidized wires, at least one air coupler for connecting the wire heads is placed in the connecting groove, the fiber fixing rod and the air coupler are placed in different connecting grooves, the wire heads of the raw silk preoxidized wires pass through the fiber connecting groove and are connected in the fiber connecting groove. However, during the pre-oxidation process of the raw silk, a certain stretching tension is applied to the yarn bundle in order to maintain the axial orientation of the macromolecular chain to the fiber axis. The use of this patented method will result in insufficient knot strength of the raw silk, and the knot may be broken during the production process.

[0006] 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 drawing tension is greater, the pre-oxidation reaction is more intense, the knots are more likely to catch fire, and there is a safety hazard.

[0007] In order to solve the above problems, a method for connecting large tow raw fibers is needed to solve the problem of continuous production of large tow carbon fibers, reduce downtime, and improve production efficiency. Summary of the invention

[0008] The purpose of the present invention is to overcome the problem in the prior art that the raw silk produced by the winding method of the tubular silk ingot cannot be connected online during the production process of large-tow carbon fiber to realize the continuous production of large-tow carbon fiber, and provide large-tow carbon fiber and a continuous production method of large-tow carbon fiber. The large-tow carbon fiber includes a continuous production and splicing method of alternatingly connected large-tow raw silk, carbon fiber and large-tow carbon fiber, which realizes the continuous production of large-tow carbon fiber, has the advantages of reducing the number of winding times, high production safety, increasing stable production time, reducing the amount of waste silk, reducing production costs, and improving production efficiency.

[0009] In order to achieve the above objectives, 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 flat knotting.

[0010] Preferably, 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 flat knotting.

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

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

[0013] Preferably, the connecting ends of the large-tow precursor yarns are pre-oxidized.

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

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

[0016] Preferably, step (1) comprises: dividing the pre-oxidized end of the large tow precursor into multiple strands, dividing one end of the carbon fiber into corresponding multiple strands, and tying each strand of the pre-oxidized end of the large tow precursor into a fastened knot by a flat knot; and / or

[0017] Preferably, 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.

[0018] Preferably, before the pre-oxidation, in step (1), the reserved length of one end of the large tow precursor to be pre-oxidized is 100-170 cm, preferably 130-160 cm.

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

[0020] Preferably, after the connection ends of the pre-oxidized large tow precursor and the carbon fibers are respectively knotted, the length of the knotted ends remaining is 5-20 cm, preferably 8-15 cm.

[0021] 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.

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

[0023] The present invention proposes for the first time a large-tow carbon fiber, which includes alternatingly connected large-tow precursors and carbon fibers. The large-tow precursors and carbon fibers are connected by flat knotting. 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. Not only is the knot firm, but the breaking strength of the knot reaches more than 120,000 cN.

[0024] After the adjacent large bundles of raw silk ends of the present invention are connected by flat knotting, not only will the knot not loosen or fall off during the oxidation process, but the knot connection will not produce smoke and 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, low-temperature carbonization, high-temperature carbonization, surface treatment, washing, sizing, drying, and winding production processes from the silk unwinding frame.

[0025] In a preferred embodiment of the present invention, the present invention uses a method of connecting the ends of adjacent large tow raw fibers by flat knotting, 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 silk, reduce production costs, and improve production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1It is a schematic diagram that each raw silk is divided into three strands, and the pre-oxidized end ends are respectively connected to one end of the carbon fiber by flat knotting; DETAILED DESCRIPTION

[0027] 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.

[0028] The present invention proposes a large-tow carbon fiber for the first time, including alternating large-tow precursors and carbon fibers, the large-tow precursors and the carbon fibers are connected by flat knots. 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 by carbon fibers, and not only the knots are firm, but also the breaking strength of the knots reaches more than 120,000 cN. After the ends of the large-tow precursors of the present invention are connected by flat knots, not only the knots will not loosen or fall off during the oxidation process, but also the 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, low-temperature carbonization, high-temperature carbonization, surface treatment, washing, sizing, drying, winding and collecting production processes from the silk-releasing creel in sequence.

[0029] In the present invention, the steps of tying a square knot are as follows (the knot is completed as follows Figure 1 shown):

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

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

[0032] Step 3: Pass the pre-oxidized end of the large tow raw silk around one end of the carbon fiber and pass it through the loop, put it together with the pre-oxidized end of the large tow raw silk, tighten it to form a flat knot, and leave a certain length of the silk end after tying the flat knot according to production needs.

[0033] Step 4: According to the above knotting steps, the pre-oxidized end of the remaining large tow raw silk after the splitting and one end of the remaining carbon fiber after the splitting are knotted in the same way.

[0034] In the present invention, there is no special requirement for the number of strands into which the ends of the large-tow precursor and carbon fiber are divided. According to a preferred embodiment of the present invention, the ends of the large-tow precursor and carbon fiber are divided into corresponding 2-10 strands, preferably 3-5 strands, and more preferably 3 strands.

[0035] According to a preferred embodiment of the present invention, the ends of the large-tow 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 flat knotting.

[0036] 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.

[0037] 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.

[0038] 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 100-180 K, preferably 125-150 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.

[0039] 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 5-20 cm, preferably 8-15 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.

[0040] 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, connecting the pre-oxidized end with one end of the carbon fiber by flat knotting, and repeating the flat knotting connection method according to the continuous production needs; (2) after the knotting 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] In the present invention, the step (4) is to complete the winding 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.

[0045] According to a preferred embodiment of the present invention, the step (1) comprises: dividing the pre-oxidized end of the large tow precursor into multiple strands, dividing one end of the carbon fiber into corresponding multiple strands and tying each strand of the pre-oxidized end of the large tow precursor into a tight knot by a flat knot.

[0046] According to a preferred embodiment of the present invention, the steps of knotting the corresponding flat knots of each strand are: folding the end of the pre-oxidized large-tow precursor in half to form a first loop, and combining the remaining precursors at both ends of the loop together, allowing the end of one end of the carbon fiber to pass through the bottom of the first loop, and then folding it downward under the combined precursor to form a second loop, and then passing it into the first loop from the top to tighten; preferably, 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.

[0047] 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.

[0048] 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 100-170cm, preferably 130-160cm. 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.

[0049] 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.

[0050] In the present invention, the conditions for the first pre-oxidation of the large tow precursor may be conventionally selected in the art.

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

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

[0053] By adopting the above-mentioned preferred embodiment, the oxidation reaction of the raw silk can be carried out more efficiently and quickly.

[0054] In the present invention, the conditions for the second pre-oxidation of the large tow precursor may be conventionally selected in the art.

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

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

[0057] 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.

[0058] 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 5-20 cm, preferably 8-15 cm. By adopting the above preferred embodiment, the safety production stability of the knot can be further improved when passing through the oxidation furnace, low-temperature carbonization furnace, and high-temperature carbonization furnace.

[0059] The present invention provides large-tow carbon fibers prepared by the large-tow carbon fiber continuous production method of the present invention.

[0060] 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 corresponding multiple strands, and the ends of the multiple strands are each tied into a tight knot, and each strand of the pre-oxidized end of the large tow precursor and each strand of the carbon fiber are respectively tied into a tight knot by a flat knot; wherein, the attached Figure 1 In the figure, 1 is the end of a large tow of raw yarn after pre-oxidation treatment; 2, carbon fiber.

[0061] 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:

[0062] 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%

[0063] 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%

[0064] 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%

[0065] The raw material of the raw silk is a commercial product with the brand name SF produced by Sinopec Shanghai Petrochemical Co., Ltd.

[0066] In the following examples and comparative examples, the oxidation furnace, low-temperature carbonization furnace, high-temperature carbonization furnace, surface treatment, washing, sizing, drying, and winding and collecting adopt the same operating conditions: specifically as follows:

[0067] 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.

[0068] 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 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.

[0069] 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 passes through a traction device and enters the high temperature carbonization furnace. With nitrogen as the medium, high temperature carbonization is carried out 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, the draft ratio is controlled to be 0.76, and the total residence time in the high temperature carbonization furnace is 1.2 minutes.

[0070] Surface treatment: The surface treatment production process is that the filament bundle at the outlet of the high-temperature carbonization furnace enters the surface treatment tank through a traction device, using an 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 60s.

[0071] 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.

[0072] 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.

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

[0074] Winding and collecting: The carbon fiber after sizing and drying is wound and collected using a carbon fiber winder to produce finished carbon fiber.

[0075] 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.

[0076] Example 1

[0077] (1) The ends and tails of each box of raw silk are kept at a certain length, and the length of the ends and tails is 130cm.

[0078] (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 130 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 225°C and the time is 25 minutes. The oxidation temperature of the second stage is 235°C and the time is 25 minutes.

[0079] (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, the length of the knotted silk head and the silk tail is 8 cm.

[0080] (4) A strand of 125K carbon fiber is evenly divided into three strands at each end, and then the three strands at one end of the 125K carbon fiber are connected to the three strands of pre-oxidized fiber ends by flat knots (such as Figure 1 Similarly, the other end of the 125K carbon fiber is connected with the adjacent packaged silk tails which are evenly divided into 3 strands and have been pre-oxidized by flat knots, with a total of 3 knots. The subsequent original silk ends are alternately connected with one end of the carbon fiber.

[0081] (5) After the knotting and connection is completed, the wire is successively subjected to oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, water washing, sizing, drying, and winding.

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

[0083] Example 2

[0084] (1) 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.

[0085] (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 232°C and the time is 36 minutes. The oxidation temperature of the second stage is 252°C and the time is 36 minutes.

[0086] (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 12 cm.

[0087] (4) The two ends of a strand of 135K carbon fiber are equally divided into four strands, and then the four strands at one end of the 135K carbon fiber are connected to the four strands of pre-oxidized fiber ends by flat knots (such as Figure 1 Similarly, the other end of the 135K carbon fiber is connected with the 4 strands of pre-oxidized silk tails in turn by flat knots, with a total of 4 knots. The subsequent original silk ends are alternately connected with one end of the carbon fiber.

[0088] (5) After the knotting and connection is completed, the wire is successively subjected to oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, water washing, sizing, drying, and winding.

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

[0090] Example 3

[0091] (1) The ends and tails of each box of raw silk are kept at a certain length, and the length of the ends and tails is 160cm.

[0092] (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 245°C and the time is 40 minutes. The oxidation temperature of the second stage is 260°C and the time is 40 minutes.

[0093] (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 tied, the length of the knotted silk head and the silk tail is 15 cm.

[0094] (4) A strand of 150K carbon fiber is divided equally into 5 strands at each end, and then the 5 strands at one end of the 150K carbon fiber are connected to the 5 strands of pre-oxidized fiber ends respectively by a flat knot (such as Figure 1 Similarly, the other end of the 150K carbon fiber is connected with the 5 equally divided strands of pre-oxidized silk tails in turn through a flat knot, for a total of 5 knots, and the subsequent original silk ends are alternately connected with one end of the carbon fiber.

[0095] (5) After the knotting and connection is completed, the wire is successively subjected to oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, water washing, sizing, drying, and winding.

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

[0097] Example 4

[0098] All 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 invention. The details are shown in Table 2.

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

[0100] Example 5

[0101] 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 invention. The details are shown in Table 2.

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

[0103] Example 6

[0104] 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 98K, which is not within the preferred range of the present invention.

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

[0106] Example 7

[0107] 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 17 cm, which is not within the preferred range of the present invention.

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

[0109] Example 8

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

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

[0112] Example 9

[0113] All operating steps and conditions are the same as 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 213°C and the time is 232 minutes. The oxidation temperature of the second oxidation is 39°C and the time is 39 minutes.

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

[0115] Example 10

[0116] 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 125 cm, which is not within the preferred range of the present invention.

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

[0118] Comparative Example 1

[0119] All conditions are the same as those in Example 1, except that the large-tow carbon fiber only includes 125K large-tow precursors that are alternately connected, and does not include 125K carbon fiber.

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

[0121] Comparative Example 2

[0122] All conditions are the same as those in Example 1, except that: the connection method of 125K large tow raw silk and 125K 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.

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

[0124] Table 1

[0125]

[0126] Table 2

[0127]

[0128]

[0129] Table 3

[0130]

[0131] 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 120,000 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.

[0132] 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 flat knotting method.

2. The large tow carbon fiber according to claim 1, 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 flat knotting; 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.

3. The large tow carbon fiber according to claim 1 or 2, wherein: The carbon fiber is 100-180K carbon fiber, preferably 125-150K; and / or The connecting ends of the large tow raw yarn are pre-oxidized.

4. The large tow carbon fiber according to any one of claims 1 to 3, wherein: After the respective ends of the large tow precursor and the carbon fiber are connected by flat knotting, the length of the flat knot tail is 5-20 cm, preferably 8-15 cm.

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, connecting the pre-oxidized end to one end of the carbon fiber by a flat knot, and repeating the flat knot connection as required for continuous production; (2) After the knotting is completed, the wire is oxidized, carbonized at low temperature, carbonized at high temperature, surface treated, washed, sizing, dried, and wound.

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

7. The method according to claim 5 or 6, wherein: Before the pre-oxidation, in step (1), the reserved length of one end of the large tow precursor to be pre-oxidized is 100-170 cm, preferably 130-160 cm.

8. The method according to any one of claims 5 to 7, 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 205-255°C, preferably 225-245°C; and / or Time 10-55min, preferably 25-40min; and / or The second pre-oxidation conditions include: The temperature is 230-265°C, preferably 235-260°C; and / or The time is 10-55 min, preferably 25-40 min; and / or The temperature of the second pre-oxidation is 10-25°C higher than the temperature of the first pre-oxidation.

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 5-20 cm, preferably 8-15 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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