Large tow carbon fibers and continuous process for producing large tow carbon fibers

Abstract

The present application relates to the technical field of large-tow carbon fiber production, in particular to large-tow carbon fiber and a continuous production method of large-tow carbon fiber, and discloses a large-tow fiber, which comprises large-tow filaments and carbon fibers connected alternately, the large-tow filaments and the carbon fibers are connected in a twisted manner, and the ends of the large-tow filaments and the carbon fibers are knotted. By using the connection method, the ends of the large-tow filaments in the packing box can be connected with the ends of the adjacent large-tow filaments in the packing box, the knot is firm, and the breaking strength of the knot is more than 80000 cN. By using the connection method of the twisted ends of the large-tow filaments, the continuous production of the large-tow carbon fiber can be realized, the number of winding rollers is reduced, the production safety is high, the stable production time is improved, the amount of waste silk is reduced, the production cost is reduced, and the production efficiency is improved.

Description

TECHNICAL FIELD

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

[0002] Carbon fiber is a new type of inorganic fiber material, which has 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 conduction, shock absorption, noise reduction and small relative density, and belongs to 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 civil market.

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

[0004] In the production process of polyacrylonitrile-based small-tow carbon fiber, the precursor is wound into a cylindrical spool by a winding yarn collector and placed on a creel. The precursor drawn from the creel is subjected to processes such as oxidation, carbonization, surface treatment, washing, sizing, drying, and winding yarn collection, and finally obtains carbon fiber products. However, in the production process of large-tow carbon fiber, the precursor is not wound in a cylindrical spool, but is directly laid in a box for running production. Each box has a head and a tail, and the length of the precursor is fixed. When a box of precursor is about to run out, the tail of the precursor in the box is connected to the head of the precursor in the adjacent box to ensure that the precursor enters the oxidation area continuously and realizes online continuous production. Therefore, the connection of the precursors in the front and rear boxes is crucial. If the connection between the head and the tail is loose or broken, it is easy to cause the oxidation area to wind around the roller, or even cause the oxidation furnace to catch fire. Stopping the production line and re-warming the yarn not only increases the labor intensity of the workers, but also causes the production to be intermittent, resulting in a large amount of waste yarn and difficulty in achieving economic benefits.

[0005] CN114262956A discloses a large tow carbon fiber precursor carbonization wire connecting method, comprising the following steps: S1: pre-reserve the wire head and PAN precursor wire drum oxidation: the precursor wire bundle tail and the other precursor wire bundle head are arranged out of 300-400mm wire head, the precursor wire bundle tail end is sleeved with the PAN precursor wire drum, and is laid on the oxidation rack, the precursor is naturally tensioned and fixed; S2: using air twisting connector to connect the middle section of the precursor wire bundle head and the tail oxidation section, after straightening the extension knot head, the PAN precursor wire drum is moved to the connection place for wrapping. This patent uses the method of pre-oxidizing the wire bundle head and tail of the precursor drum, and connects the tail wire of the first drum with the reserved wire head of the second drum by using the PAN precursor wire drum. However, the wrapping of the precursor drum and the connection of the wire head and tail of the large wire bundle together cause a large amount of precursor to be stacked together, which will cause excessive heat accumulation in the knot head during oxidation, resulting in knot head burning out, and the twisting operation of the drum will also cause the wire bundle surface to turn over, causing uneven oxidation of the wire bundle.

[0006] CN114314196A is an online wire connecting production process and device for carbon fiber manufacturing, which comprises the following steps: (1) separating the precursor wire bundle A to be connected by a gap, so that the precursor wire bundle A to be connected is separated from the precursor wire bundle B running beside it, (2) using a carbon fiber wire bundle C wound on a wire releasing device to twist the knot of the carbon fiber wire bundle C into the precursor wire bundle B, (3) using the wire releasing device to naturally release the carbon fiber wire bundle C, (4) butting the carbon fiber wire bundle C with the precursor wire bundle A to be connected, so that the carbon fiber wire bundle C and the precursor wire bundle A form an integral wire bundle D, (5) using a wire guide device to guide the wire until the integral wire bundle D is straightened, and then removing the wire guide device, so that the integral wire bundle D runs normally, achieving the effect of stable operation after connecting the broken wire. This patent mainly aims at connecting the broken wire during operation. It is difficult to ensure the connection strength of the precursor wire bundle B and the carbon fiber wire bundle C when connecting the precursor wire by this method, which affects the passability of the knot oxidation furnace. SUMMARY

[0007] The purpose of the present application is to overcome the problem that the precursor wire is wound in the form of a cylindrical spool in the production process of large tow carbon fiber, which cannot realize continuous and stable production. The present application provides a large tow carbon fiber and a continuous production method of large tow carbon fiber. The continuous production method of large tow carbon fiber using the large tow carbon fiber comprising alternately connected large tow precursor wire, carbon fiber and large tow carbon fiber realizes the continuous production of large tow carbon fiber, reduces the number of winding rollers, improves the safety of production, prolongs the stable production time, reduces the amount of waste wire, reduces the production cost, improves the production efficiency and other advantages.

[0008] In order to achieve the above-mentioned purpose, the present application provides a kind of large tow carbon fiber in one aspect, which includes large tow filaments and carbon fibers connected alternately, and the large tow filaments and carbon fibers are connected in a twisted manner, and the ends of the large tow filaments and carbon fibers are knotted.

[0009] The present application provides a continuous production method of large tow carbon fiber in a second aspect, which includes the following steps: (1) pre-oxidizing one end of the large tow filaments, knotting the pre-oxidized end, and then twisting and connecting the carbon fiber end knotted tightly with the pre-oxidized end of the large tow filaments, and repeating the above-mentioned connection according to the needs of continuous production; (2) after the connection, carrying out oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, washing, sizing, drying and winding.

[0010] The present application provides a large tow carbon fiber prepared by the continuous production method of large tow carbon fiber in a third aspect.

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

[0012] The present application first proposes a kind of large tow carbon fiber, which includes large tow filaments and carbon fibers connected alternately, and the large tow filaments and carbon fibers are connected in a twisted manner, and the ends of the large tow filaments and carbon fibers are knotted, and through the connection method, the ends of the large tow filaments packed in a box can be connected with the ends of the adjacent large tow filaments packed in a box, and the knot is firm, and the breaking strength of the knot is more than 80000 cN.

[0013] The knot of the adjacent large tow filament ends knotted in the present application not only does not loosen or fall off during oxidation, but also does not smoke or catch fire due to heat accumulation, which ensures that the two adjacent large tow filament ends can be connected tightly and smoothly pass through the oxidation furnace, low-temperature carbonization furnace, high-temperature carbonization furnace, surface treatment, washing, sizing, drying and winding production processes.

[0014] The connection method of the large tow filament ends twisted in the present application can realize the continuous production of large tow carbon fiber, reduce the number of winding rollers, improve the stability of production time, reduce the amount of waste silk, reduce production cost, and improve production efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a schematic diagram of each filament being divided into three strands, and the ends being knotted and twisted and connected with carbon fibers. DETAILED DESCRIPTION

[0016] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not critical to the invention. Any numeric range recited is intended to include all values from the lower value to the upper value, inclusive of both values, and to sub-ranges falling within the specified range. In this context, individual points within a range should be considered as being included within that range, and individual points can be combined to form new ranges, which are also considered to be disclosed herein.

[0017] The present application first proposes a large tow carbon fiber, comprising large tow filaments and carbon fibers connected alternately, the large tow filaments and the carbon fibers are connected in a twisted manner, and the ends of the large tow filaments and the carbon fibers are knotted; in the continuous production, the ends of the large tow filaments in the box packaging are connected together through the carbon fibers and the ends of the adjacent large tow filaments in the box packaging, the knot is firm, and the breaking strength of the knot is more than 80000 cN. After the ends of the large tow filaments are knotted, the knot does not loosen and fall off in the oxidation process, and the knot connection does not smoke and catch fire due to heat accumulation overheating, so that the ends of the adjacent two boxes of filaments can be connected tightly, and can smoothly pass through the oxidation furnace, the low-temperature carbonization furnace, the high-temperature carbonization furnace, the surface treatment, the washing, the sizing, the drying and the winding production processes in sequence.

[0018] In the present application, the K number of the carbon fiber has no special requirement. According to a preferred embodiment of the present application, the K number of the carbon fiber is 40-100K, and preferably the K number is 48-98K. By adopting the foregoing preferred embodiment, the firmness of the connection between the filaments and the carbon fiber can be further improved, and the connection does not loosen and break.

[0019] In the present application, after the ends of the large tow filaments and the carbon fibers are knotted, the length of the knot tail left has no special requirement. According to a preferred embodiment of the present application, after the ends of the large tow filaments and the carbon fibers are knotted, the length of the knot tail left is 4-15cm, and preferably 6-10cm. By adopting the foregoing preferred embodiment, the safety production stability of the knot 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 application, the ends of the large tow filaments and the carbon fibers are each divided into corresponding strands, and each strand of the large tow filaments and the carbon fibers is twisted and connected in a twisted manner.

[0021] In the present application, the number of strands of the ends of the large tow filaments and the carbon fibers has no special requirement. According to a preferred embodiment of the present application, the ends of the large tow filaments and the carbon fibers are each divided into corresponding 2-10 strands, preferably 3-5 strands, and more preferably 3 strands.

[0022] By adopting the foregoing preferred respective embodiments, the breaking strength of the joint at the connection between the precursor and the carbon fiber can be further improved, and the joint is stable and not loose.

[0023] In the present application, the number of times of the alternate connection between the large-tow precursor and the carbon fiber is not limited and can be selected as required.

[0024] The large-tow carbon fiber having the features of the present application can achieve the object of the present application, and the specific preparation steps and processes thereof can be selected and adjusted as required. According to the preferred embodiment of the present application, a continuous production method of a large-tow carbon fiber is provided, which comprises the following steps: (1) pre-oxidizing one end of a large-tow precursor, and twisting the pre-oxidized end into a tight joint, and twisting the end of a carbon fiber into a tight joint and then connecting the pre-oxidized end of the large-tow precursor in a spiral manner, and repeating the foregoing twisting connection as required for continuous production; (2) after the twisting connection is completed, performing oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, washing, sizing, drying, and winding and collecting the yarn. By the continuous production method, the number of times of winding around the roller can be reduced, the production safety is high, the stable production time is improved, the amount of waste yarn is reduced, and the risk of fire at the connection between the ends of the precursor due to excessive heat accumulation is avoided, the production cost is reduced, and the production efficiency is improved. Thus, the continuous production of the large-tow carbon fiber can be effectively achieved.

[0025] In the present application, the twisting connection can be continuously performed, and the number of twists is determined as required and according to the actual working conditions.

[0026] In the present application, after step (1) and before step (2), the two ends of the large-tow precursor are laid on a tension frame, the precursor is tensioned and fixed, the tension frame is placed in a pre-oxidation furnace, and the ends of the precursor are pre-oxidized. This step has no special requirements and can be performed according to the prior art, and the present application will not be described in detail here.

[0027] In the present application, after the ends of the large-tow precursor are pre-oxidized in step (1), a cooling step is required, and the cooling time and method have no special requirements and can be performed according to the prior art, and only cooling to room temperature is required.

[0028] In the present application, after the twisting connection of the joint is completed in step (2), oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, washing, sizing, drying, and winding and collecting the yarn are performed, and the specific steps and operating conditions have no special requirements and can be performed according to the prior art, and the present application will not be described in detail here.

[0029] According to a preferred embodiment of the present application, the step (1) comprises: dividing the pre-oxidized end into a plurality of strands, and tying a fast knot on the end of each strand; dividing the end of the carbon fiber into a corresponding plurality of strands, and tying a fast knot on the end of each strand, and connecting each of the plurality of strands of the pre-oxidized end of the large-tow precursor and the plurality of strands of the carbon fiber by twisting.

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

[0031] By using the foregoing preferred embodiments, the knot breaking strength at the connection between the precursor and the carbon fiber can be further improved, and the knot is stable and not loose.

[0032] In the present application, the pre-oxidation of the large-tow precursor is not particularly limited, and according to a preferred embodiment of the present application, the pre-oxidation of the large-tow precursor is completed in two stages, including first pre-oxidation and second pre-oxidation.

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

[0034] According to a preferred embodiment of the present application, the temperature for the second pre-oxidation is 10-30°C higher than that for the first pre-oxidation.

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

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

[0037] By using the foregoing preferred embodiments, the oxidation reaction of the precursor can be further effectively and rapidly carried out.

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

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

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

[0041] By adopting the foregoing preferred respective embodiments, the precursory fiber can be further ensured to complete the cyclization and dehydrogenation reactions, to be intramolecularly cyclized and intermolecularly crosslinked, and to convert the linear macromolecular chains of the PAN-based precursory fiber into the heat-resistant ladder macromolecular structure.

[0042] In the present application, before the step (1) of the pre-oxidation treatment of the large-tow precursory fiber, the pre-oxidation end of the large-tow precursory fiber needs to be reserved with a length. The reserved length has no special requirement. According to one preferred embodiment of the present application, the pre-oxidation end of the large-tow precursory fiber is reserved with a length of 100-160 cm, preferably 120-150 cm. By adopting the foregoing preferred embodiment, the length of the pre-oxidized precursory fiber can be further ensured to meet the length requirement for connection with the carbon fiber.

[0043] In the present application, the length reserved after the knotting of the connection end of the pre-oxidized large-tow precursory fiber with the carbon fiber has no special requirement. According to one preferred embodiment of the present application, the length reserved after the knotting of the connection end of the pre-oxidized large-tow precursory fiber with the carbon fiber is 4-15 cm, preferably 6-10 cm. By adopting the foregoing preferred embodiment, the safety production stability of the knot head in the processes of oxidation, low-temperature carbonization and high-temperature carbonization can be further improved.

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

[0045] As shown in Figure 1 Fig. 1, each precursory fiber is divided into three strands, one end of the carbon fiber is divided into corresponding multiple strands, and the end of each of the multiple strands is knotted into a tight knot head. Fig. 1 is a schematic diagram of the hemp flower type winding connection of each strand of the pre-oxidized end of the large-tow precursory fiber and each strand of the carbon fiber; wherein, Figure 1 In Fig. 1, 1 is the end end of the pre-oxidized large-tow precursory fiber; and 2 is the carbon fiber.

[0046] The present application will be described in detail through the following examples. In the following examples, the knot head breaking strength parameter is measured by adopting the GB / T19975-2005 high-strength fiber filament tensile property test method. In the present application, the knot head breaking strength data is the average value of three knot heads tested in actual operation. The oxidation furnace passing rate, the low-temperature carbonization furnace passing rate and the high-temperature carbonization furnace passing rate are calculated by the following methods.

[0047] Oxidation furnace passing rate = actual number of knot heads successfully passing through the oxidation furnace / total number of knot heads entering the oxidation furnace * 100%

[0048] Low-temperature carbonization furnace passing rate = actual number of knot heads successfully passing through the low-temperature carbonization furnace / total number of knot heads entering the low-temperature carbonization furnace * 100%

[0049] High temperature carbonization furnace passing rate = actual number of successfully passing through high carbon furnace / total number of entering high carbon furnace * 100%

[0050] The raw material of the original wire is a commercially available product with the brand SF from Shanghai Petrochemical Co., Ltd.

[0051] In the following examples and comparative examples, the same operating conditions are used for the oxidation furnace, low temperature carbonization furnace, high temperature carbonization furnace, surface treatment, water washing, sizing, drying, and winding and collecting the wire:

[0052] Oxidation furnace: four temperature zones are used, with a total time of 60 minutes, and the draw ratio between the four heating temperature zones of the oxidation furnace is 1.26, 0.99, 0.98, and 0.96. The temperatures of the four temperature zones in the examples and comparative examples of the present application 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 six heating temperature zones. The pre-oxidized wire from the outlet of the oxidation furnace enters the low temperature carbonization furnace through a traction device, and low temperature carbonization is carried out using nitrogen as the medium to produce low temperature carbonized wire. The temperatures of the six heating temperature zones are 470℃, 540℃, 610℃, 670℃, 740℃, and 790℃, respectively. The yarn runs in the low temperature carbonization furnace, with a controlled draw ratio of 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 five heating temperature zones. The yarn from the outlet of the low temperature carbonization furnace enters the high temperature carbonization furnace through a traction device, and high temperature carbonization is carried out using nitrogen as the medium to produce high temperature carbonized wire. The temperatures of the five heating temperature zones are 1100℃, 1390℃, 1470℃, 1490℃, and 1400℃, respectively. The yarn runs in the high temperature carbonization furnace, with a controlled draw ratio of 0.76, and the total residence time in the high temperature carbonization furnace is 1.2 minutes.

[0055] Surface treatment: the surface treatment production process is carried out by passing the yarn from the outlet of the high temperature carbonization furnace through a traction device into a surface treatment tank, using an aqueous ammonium bicarbonate solution as the electrolyte, with a voltage of 18V and an electrolyte concentration of 10%. The yarn stays in the electrolyte for 60 seconds.

[0056] Water washing: the water washing production process is carried out by passing the yarn from the outlet of the surface treatment tank into a water washing tank to wash the yarn. The water washing flow rate is 2800L / hour, and the water washing temperature is 50℃.

[0057] Sizing: the unsized carbon fiber is impregnated with a commercially available K7 epoxy emulsion sizing agent, with a time of 20s and a temperature of 25℃.

[0058] Drying: vertical hot air drying is used, with a drying temperature of 170℃.

[0059] Winding: after drying the carbon fiber, the carbon fiber is wound by using a carbon fiber winding machine to obtain the finished product.

[0060] In the following implementation, the head and tail of the fiber are the two ends of the fiber, and the K number of the large tow precursor and the carbon fiber is the same in the same embodiment. Other parameters are shown in Table 2.

[0061] Example 1

[0062] (1) A certain length of the head and tail of the precursor fiber in each box is reserved, and the length of the head and tail of the fiber is 120 cm.

[0063] (2) The head and tail of the precursor fiber in each box are respectively laid on the tension frame, the precursor fiber is tensioned and fixed, the tension frame is put into the pre-oxidation furnace, and the 120 cm end of the head and tail of the precursor fiber is pre-oxidized. The pre-oxidation is divided into two stages, the first stage of oxidation is at an oxidation temperature of 220°C for 20 minutes, and the second stage of oxidation is at an oxidation temperature of 230°C for 20 minutes.

[0064] (3) The head of the pre-oxidized fiber is evenly divided into 3 strands, the tail of the pre-oxidized fiber is evenly divided into 3 strands, and the length of the knot tail left after the head and tail are knotted is 6 cm.

[0065] (4) The two ends of a strand of 68K carbon fiber are evenly divided into 3 strands, and each strand is knotted with a tight knot. Then, the 3 strands at one end of the 68K carbon fiber are slowly twisted together with the pre-oxidized head divided into 3 strands in a rubbing manner to form a twisted connection (as shown in Figure 1 ), and there are 3 knots. Similarly, the other end of the 68K carbon fiber is slowly twisted together with the pre-oxidized tail divided into 3 strands in a rubbing manner, and there are 3 knots. The subsequent head of the precursor fiber and the end of the carbon fiber are alternately connected in sequence.

[0066] (5) The above knot joint is sequentially passed through the oxidation furnace, the low-temperature carbonization furnace, the high-temperature carbonization furnace, the surface treatment, the washing, the sizing, the drying, and the winding.

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

[0068] Example 2

[0069] (1) A certain length of the head and tail of the precursor fiber in each box is reserved, and the length of the head and tail of the fiber is 135 cm.

[0070] (2) The original silk head and tail of each box are respectively laid on the tension frame, the original silk is pulled tight and fixed, the tension frame is put into the pre-oxidation furnace, and the original silk head and tail are pre-oxidized. The pre-oxidation is divided into two stages. The first stage of oxidation is at an oxidation temperature of 235°C for 25 minutes, and the second stage of oxidation is at an oxidation temperature of 248°C for 25 minutes.

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

[0072] (4) One strand of 80K carbon fiber is evenly divided into 4 strands at both ends, and each strand is knotted with a tight knot. Then, the 4 strands at one end of the 80K carbon fiber are slowly twisted together with the pre-oxidized silk head divided into 4 strands in turn by rubbing to form a twisted connection (as shown in Figure 1 ), and there are 4 knots. Similarly, the other end of the 80K carbon fiber is slowly twisted together with the pre-oxidized silk tail divided into 4 strands in turn by rubbing, and there are 4 knots. The subsequent original silk head and the end of the carbon fiber are alternately connected in turn.

[0073] (5) The above knot joint is sequentially passed through the oxidation furnace, the low-temperature carbonization furnace, the high-temperature carbonization furnace, the surface treatment, the washing, the sizing, the drying, and the winding.

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

[0075] Example 3

[0076] (1) The length of the original silk head and tail of each box is reserved, and the length of the silk head and tail is 150 cm.

[0077] (2) The original silk head and tail of each box are respectively laid on the tension frame, the original silk is pulled tight and fixed, the tension frame is put into the pre-oxidation furnace, and the original silk head and tail are pre-oxidized. The pre-oxidation is divided into two stages. The first stage of oxidation is at an oxidation temperature of 240°C for 30 minutes, and the second stage of oxidation is at an oxidation temperature of 255°C for 30 minutes.

[0078] (3) The pre-oxidized silk head is evenly divided into 5 strands, the pre-oxidized silk tail is evenly divided into 5 strands, and the length of the knot tail left after the knotting of the silk head and tail is 10 cm.

[0079] (4) One strand of 80K carbon fiber is evenly divided into 5 strands at both ends, and each strand is knotted with a tight knot. Then, the 5 strands at one end of the 80K carbon fiber are slowly twisted together with the pre-oxidized silk head divided into 5 strands in turn by rubbing to form a twisted connection (as shown in Figure 1As shown), there are a total of 5 knots. Similarly, take the other end of the 90K carbon fiber and twist it slowly together with the pre-oxidized yarn tails that are divided into 5 equal strands in the adjacent box packaging. There are a total of 5 knots. Repeat this process to connect the end of the subsequent original yarn to one end of the carbon fiber.

[0080] (5) After twisting the above knots together, the yarn is 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 in Example 1, except that the K number of carbon fiber and large tow filament is 42K, and the process parameter values ​​of pre-oxidation temperature and pre-oxidation residence time, filament head and tail length, knot head and tail length, and the number of strands of filament 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 in Example 1, except that the K number of carbon fiber and large tow filament is 45K, and the process parameter values ​​of pre-oxidation temperature and pre-oxidation residence time, filament head and tail length, knot head and tail length, and the number of strands of filament 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 in Example 1, except that the K number of the carbon fiber and the large tow filament is 38K, which is not within the preferred range of this 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 after the silk head and tail are tied is 12cm.

[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 fiber 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 Example 1, except that the original filament head and tail are pre-oxidized, the pre-oxidation is divided into two stages, the temperature and time of the second stage of oxidation are not within the preferred range of the present application, the first stage of oxidation is at an oxidation temperature of 205°C for 28 minutes, and the second stage of oxidation is at an oxidation temperature of 235°C for 28 minutes.

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

[0100] Example 10

[0101] All conditions are the same as Example 1, except that the length of the large tow original filament at one end is 115 cm, which is not within the preferred range of the present application.

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

[0103] Comparative Example 1

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

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

[0106] Comparative Example 2

[0107] All conditions are the same as Example 1, except that the connection method of the 48K large tow original filament and the 48K carbon fiber is a barrel knot tying method, the original filament head of one box and the original filament tail of the adjacent box are stacked together in parallel, the tow stacked together is wound around a loop, the head and tail are pulled tight through the loop, and the excess knot tail is cut off.

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

[0109] Comparative Example 3

[0110] All conditions are the same as Example 1, except that the respective ends of the connection of the 48K large tow original filament and the 48K carbon fiber are not knotted.

[0111] The implementation effect of this example 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 application, the end of the adjacent precursor can be firmly connected together, the breaking strength of the joint reaches 80000 CN or more, and the joint can smoothly pass through the oxidation furnace, the low-temperature carbonization furnace and the high-temperature carbonization furnace, with the oxidation furnace passing rate of 100%, the low-temperature carbonization furnace passing rate of 100% and the high-temperature carbonization furnace passing rate of 100%, and the implementation effect is good.

[0120] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application and belong to the protection scope of the present application.

Claims

1. A large tow carbon fiber, characterized by: The large-tow carbon fiber comprises large-tow filaments and carbon fibers connected alternately, the large-tow filaments and the carbon fibers are connected in a twisted manner, and the ends of the connection of the large-tow filaments and the carbon fibers are knotted, the K number of the carbon fiber is 40-100K, the length of the knot tail left after the ends of the connection of the large-tow filaments and the carbon fibers are knotted is 4-15cm, the ends of the large-tow filaments and the carbon fibers are each divided into corresponding strands, the strands of the large-tow filaments and the carbon fibers are each connected in a twisted manner, the connecting ends of the large-tow filaments are subjected to pre-oxidation treatment, the pre-oxidation is divided into two stages, including first pre-oxidation and second pre-oxidation, and the temperature of the second pre-oxidation is 10-30℃ higher than that of the first pre-oxidation.

2. The large-tow carbon fiber according to claim 1, wherein the K number of the carbon fiber is 48-98K.

3. The large-tow carbon fiber according to claim 1, wherein the length of the knot tail left after the ends of the connection of the large-tow filaments and the carbon fibers are knotted is 6-10cm.

4. The large-tow carbon fiber according to claim 1, wherein the ends of the large-tow filaments and the carbon fibers are each divided into corresponding 2-10 strands.

5. The large-tow carbon fiber according to claim 4, wherein the ends of the large-tow filaments and the carbon fibers are each divided into corresponding 3-5 strands.

6. The large-tow carbon fiber according to claim 5, wherein the ends of the large-tow filaments and the carbon fibers are each divided into corresponding 3 strands.

7. A continuous production method of the large-tow carbon fiber according to any one of claims 1-6, the method comprising the following steps: (1) pre-oxidizing one end of the large-tow filaments, knotting the pre-oxidized end into a tight knot, and connecting the end of the carbon fiber knotted into a tight knot with the pre-oxidized end of the large-tow filaments in a twisted manner, and repeating the above-mentioned connection according to the needs of continuous production; (2) after the connection is completed, performing oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, washing, sizing, drying, and winding and collecting the filaments; the K number of the carbon fiber is 40-100K, and the length of the knot tail left after the ends of the connection of the pre-oxidized large-tow filaments and the carbon fibers are knotted is 4-15cm; the pre-oxidation is divided into two stages, including first pre-oxidation and second pre-oxidation, and the temperature of the second pre-oxidation is 10-30℃ higher than that of the first pre-oxidation. Step (1) comprises: dividing the pre-oxidized end into strands, knotting the ends of the strands into tight knots, dividing one end of the carbon fiber into corresponding strands, and knotting the ends of the strands into tight knots, and connecting the strands of the pre-oxidized large-tow filaments and the strands of the carbon fiber in a twisted manner; and / or the pre-oxidized end of the large-tow filaments and one end of the carbon fiber are each divided into corresponding 2-10 strands.

9. The method according to claim 8, wherein the pre-oxidized end of the large-tow filaments and one end of the carbon fiber are each divided into corresponding 3-5 strands.

10. The method according to claim 9, wherein the pre-oxidized end of the large-tow filaments and one end of the carbon fiber are each divided into corresponding 3 strands. ​ 8. The method of claim 7, wherein, ​ ​ ​ ​ ​ ​ 11. The method according to claim 7, wherein, the conditions of the first pre-oxidation include: a temperature of 200-250°C; and / or a time of 10-40 min; and / or the conditions of the second pre-oxidation include: a temperature of 220-260°C; and / or a time of 10-40 min.

12. The method according to claim 11, wherein, the conditions of the first pre-oxidation include: a temperature of 220-240°C; and / or a time of 20-30 min; and / or the conditions of the second pre-oxidation include: a temperature of 230-255°C; and / or a time of 20-30 min.

13. The method of claim 7, wherein, Before the pre-oxidation, in step (1), the length of the reserved end of the large-tow precursor which is pre-oxidized is 100-160 cm.

14. The method of claim 13, wherein, Before the pre-oxidation, in step (1), the length of the reserved end of the large-tow precursor which is pre-oxidized is 120-150 cm.

15. The method according to claim 7, wherein, the length of the reserved end of the large-tow precursor which is pre-oxidized and connected with the carbon fiber after the knotting is 4-15 cm.

16. The method according to claim 15, wherein, the length of the reserved end of the large-tow precursor which is pre-oxidized and connected with the carbon fiber after the knotting is 6-10 cm.

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